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  • Articles  (192)
  • 82.50  (192)
  • Springer  (192)
  • Physics  (192)
  • Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics  (75)
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  • Articles  (192)
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  • Springer  (192)
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  • Physics  (192)
  • Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics  (75)
  • Energy, Environment Protection, Nuclear Power Engineering
  • 1
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    Applied physics 45 (1988), S. 279-284 
    ISSN: 1432-0649
    Keywords: 07.65 ; 33 ; 42.55 ; 82.50
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The photophysical properties such as singlet absorption and fluorescence spectra, the fluorescence quantum yield and fluorescence decay time as well as the laser performance data such as the tuning range, the conversion efficiency, and the photochemical stability of 12 sterically hinderedp-quaterphenyls have been measured in ethanol and/or dioxane at room temperature. The sterically hinderedp-quaterphenyls exhibit shorter laser dye emissions in the 330–380 nm range than the parent compoundp-quaterphenyl. The conversion efficiencies of the sterically hinderedp-quaterphenyls range between 1 and 21%. The photochemical stability of the sterically hinderedp-quaterphenyls is by a factor of 10 to 20 better in dioxane than in ethanol. 2-Methyl-5-tert. butyl-p-quaterphenyl and 2,5,2‴,5‴-tetramethyl-p-quaterphenyl are among the most stable UV laser dyes known today.
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  • 2
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    Applied physics 48 (1989), S. 489-493 
    ISSN: 1432-0649
    Keywords: 82.50 ; 42.60
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Films of polyethylene terephthalate (PET) can be successfully etched with 9 μm radiation from a pulsed TEA CO2 laser. The relationship between etch depth and fluence is broadly similar to that observed for excimer laser etching but with a less well-defined threshold. Time-resolved photoacoustic measurements of stress waves generated in the interaction show that at a fluence of 1.8 J cm−2 ablation occurs 100–200 ns after the start of the laser pulse, a time which is consistent with the rate of thermal decomposition of PET. The volatile products of ablation are carbon monoxide, carbon dioxide, methane, ethyne, ethene, benzene, ethanal, and small quantities of other products. For fluences close to and appreciably above the threshold the ablated material consists predominantly of involatile species of relatively high molecular weight, whereas at higher fluences substantial fragmentation of the polymer to small molecules occurs.
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  • 3
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    Applied physics 51 (1990), S. 103-107 
    ISSN: 1432-0649
    Keywords: 82.50 ; 33
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The CO2 TEA laser irradiation of CBr2F2 in the presence of Cl2 yielded 13C-enriched CBrClF2 and 13C-enriched CCl2F2 under selected experimental conditions. As the photolysis proceeded, the 13C concentration of CBrClF2 decreased gradually and that of CCl2F2 increased up to 90% or higher. These results can be explained by the mechanism involving the secondary 13C-selective IRMPD of the primary product CBrClF2. On the other hand, the carbon-containing product for a CCl2F2/Br2 system was only CBrClF2; the further IRMPD of which probably regenerated CBrClF2 in the presence of Br2. The decomposition probabilities of 12C- and 13C-containing molecules in both systems were measured as functions of laser line, laser fluence, and reactant pressures.
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  • 4
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    Applied physics 37 (1985), S. 151-157 
    ISSN: 1432-0649
    Keywords: 78,60 ; 61.8 ; 82.50
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract 1,4-Diazabicyclo[2.2.2]octane (DABCO) was tested as a flashlamp-pumped laser lifetime-extender with a variety of coumarin dyes and solvents under both air and argon. In a few cases, DABCO could be considered to have extended the lifetime as much as threefold; however, the selection of the appropriate cover gas and/or solvent could often yield a much greater improvement in the absence of DABCO. In general, DABCO was not found to be very valuable as a lifetime-extender. Furthermore, under some conditions DABCO was found to markedly reduce the laser lifetime and output.
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  • 5
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    Applied physics 37 (1985), S. 189-195 
    ISSN: 1432-0649
    Keywords: 82.50 ; 42.60
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract O2/O3 mixtures are ignited by absorption of laser pulses of a TEA CO2 laser along the axis of a cylindrical cell. The dependence of the radial propagation of the O3 decomposition, detected by uv absorption of the ozone, on laser fluence and on O3 concentration is investigated. Oscillations of the signals are identified to be the first radial acoustic mode of the cell. For mixtures of 0.35 bar and 0.70 bar total pressure and O3 percentages within 20–50%, the ignition limit is in the order of 0.1–0.2 J/cm3 (absorbed energy density). These values are in reasonable agreement with the results of the corresponding numerical simulations.
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  • 6
    ISSN: 1432-0649
    Keywords: 33 ; 82.50 ; 42.55
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We measured the photoionization cross-sections of anthracene, 1,2-benzanthracene,p-terphenyl, and 2,5-diphenylfuran molecules excited to the singlet and triplet electronic states intermediate in the stepwise two-photon ionization process at 266 nm (all compounds) and at 355, 391 and 417 nm (anthracene).
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  • 7
    ISSN: 1432-0649
    Keywords: 33 ; 82.50
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The multiple-photon absorption of pulsed TEA CO2 laser radiation by SF6 molecules cooled toT R≃40K andT v≃160K in the free jet expansion from a pulsed supersonic nozzle has been investigated at energy fluences of 0.1 to 3.0 J·cm−2. For practically all laser lines which coincide with the linear absorption spectrum of thev 3 vibrational mode of SF6 [P(12)...P(28), 10,6 m], the dependence of the absorbed energyE ab on the exciting energy fluence was found to be steeper than linearE ab∼Φn, wheren=(1.1 to 1.8). Considerable increases of the absorption cross sections with increasing energy fluence were observed. The fraction of the molecules interacting with the laser radiation is estimated.
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  • 8
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    Applied physics 30 (1983), S. 79-81 
    ISSN: 1432-0649
    Keywords: 82.50 ; 82.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract CF2ClCF2Cl and ethyl acetate have absorption bands of similar width centered at the same frequency. Kinetics of the decompositions of these compounds by a cw CO2 laser have been studied over a range of laser frequencies extending to 25 cm−1 below band center. At constant translational temperature and pressure, the CF2ClCF2Cl rate constant changes by more than 200 with frequency, while the corresponding change for ethyl acetate is at most 3. The effect of laser frequency increases with increasing CF2ClCF2Cl pressure, while the reverse is true in ethyl acetate. Arrhenius plots show activation energies independent of both frequency and pressure.
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  • 9
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    Applied physics 33 (1984), S. 57-61 
    ISSN: 1432-0649
    Keywords: 33 ; 42.60 ; 82.50
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A laser photodesorption microscope has been applied to obtain 4×103-fold images of rhodamine crystals on a tip with a diameter of 66μm. Peculiarities of the formation of these images have been studied with different values of electric field strength on the tip and laser pulse intensities.
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  • 10
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    Applied physics 36 (1985), S. 111-113 
    ISSN: 1432-0649
    Keywords: 82.50
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    Topics: Physics
    Notes: Abstract Carbon-13 isotope selectivities and specific decomposition yields in the infrared multiple-photon decomposition of CHF3 and CDF3 were examined as a function of wave number using a CO2 TEA laser. The observed maximum selectivities were 30 for CHF3 and 55 for CDF3. The specific decomposition yields in CDF3 were considerably larger than those in CHF3.
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  • 11
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    Applied physics 36 (1985), S. 203-206 
    ISSN: 1432-0649
    Keywords: 82.30 ; 82.50
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The OH rotational polarization produced by the reaction of fast H atoms from the polarized 193 nm photolysis of HBr with O2 (2.6 eV collision energy) has been measured by laser-induced fluorescence using polarized analysis light. A strong rotational polarization parallel to the electric vector of the dissociation laser and perpendicular to the flight direction of the H atoms is observed. Implications for the H+O2 reaction dynamics at high collision energies are discussed.
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  • 12
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    Applied physics 37 (1985), S. 79-86 
    ISSN: 1432-0649
    Keywords: 82.50
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An experimental study has been performed of the carbon-14 enrichment achievable in the ultraviolet laser dissociation of mixtures of14CH2O and12CH2O. The14C:12C enrichment factor in the CO product has been measured at 352.2 nm as a function of laser linewidth, formaldehyde temperature and pressure, and degree of carbon-14 depletion. The enrichment decreases with an increase in each of these parameters; the highest enrichment, 1190, was measured at 0.02 cm−1, 303 K, 1 Torr and a14C depletion of 10%. The results are assessed in terms of their application to radiocarbon dating, in particular for groundwater dating required for nuclear waste disposal, and to the enrichment of14C operating wastes extracted from nuclear reactors to a level suitable for commercial sale.
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  • 13
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    Applied physics 39 (1986), S. 187-190 
    ISSN: 1432-0649
    Keywords: 82.50 ; 33
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Selective decomposition of CDF3 at natural abundance level (≈150ppm) in fluoroform has been achieved by infra-red multiple-photon excitation at moderate substrate pressure using 100 ns FWHM CO2 laser pulses. Effects of energy fluence, number of laser pulses, buffer gas pressure and substrate pressure on decomposition yield and bulk selectivity are reported and discussed.
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  • 14
    ISSN: 1432-0649
    Keywords: 82.50 ; 82.80
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Usingone standard commercial dye laser, tellurium dimers Te2 — formed by excimer laser induced photoelimination from CH3TeTeCH3 at room temperature — are ionized isotope selectively.
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  • 15
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    Applied physics 42 (1987), S. 167-172 
    ISSN: 1432-0649
    Keywords: 82.50 ; 82.40 ; 42.60.Kg
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A new working molecule 1,1,1,3,3,3-hexafluoro-2-(trifluoromethyl)-propane-2-t (CF3)3CT, is reported for the isotope separation of tritium by TEA CO2-laser-induced multiphoton dissociation (MPD). Selective and efficient dissociation of (CF3)3CT was observed by irradiation at about 980 cm−1 where (CF3)3CH was nearly transparent. The critical fluence for dissociation of (CF3)3CT at 10R(28) 980.9 cm−1 was estimated to be as low as 4.6 J/cm2, which is the lowest of the tritiated halocarbons that we have ever reported. A detailed study was made of the pressure dependence of the dissociation rate constants for (CF3)3CT and (CF3)3CH to clarify the collisional effects in their MPD. The hydrogen isotope exchange between (CF3)3CH and HTO was found to be extremely rapid, which is advantageous in the practical laser separation cycle for tritium removal from water.
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  • 16
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    Applied physics 47 (1988), S. 233-237 
    ISSN: 1432-0649
    Keywords: 82.50 ; 33 ; 35
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Energy absorption by CDF3 for different energy fluences from an intense TEA CO2 laser is reported as function of the pressure of CDF3 and various bath gases (He, Ne, Ar, Xe, and CHF3). Collisional behavior at different conditions is discussed.
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  • 17
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    Applied physics 47 (1988), S. 243-245 
    ISSN: 1432-0649
    Keywords: 82.50 ; 82.65
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The IRMPD of Si2F6 by a CO2 TEA laser was applied to isotopically selective CVD of silicon. A white film, probably consisting of polymers of SiF2, was deposited on a metal foil during the irradiation of natural Si2F6 with the laser radiation at 951.19 cm−1 and about 1.5 J cm−2. Upon heating, the film became dark brown, evolving SiF4. The30Si content was found to be as high as about 20%.
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  • 18
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    Applied physics 48 (1989), S. 249-252 
    ISSN: 1432-0649
    Keywords: 33.00 ; 39.00 ; 82.50
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The V-T/R relaxation time of CDF3 was measured studying the laser-induced infrared fluorescence emitted by vibrationally excited CDF3. Following excitation by the 10R(12) line of a TEA CO2 laser infrared fluorescence has been detected without spectral resolution in the 1100–700 cm−1 range. A decay rate of 28.8 ms−1 Torr−1 was obtained for pure CDF3 when it is excited with a fluence of 390 mJ/cm2. Measurements have also been made in the presence of different bath gases (He, Ne, Ar, Xe, and CHF3).
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  • 19
    ISSN: 1432-0649
    Keywords: 82.50 ; 33
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have been studying the practical CO2-laser-induced13C separation by a two-stage IRMPD process. The IRMPD of natural CHClF2 in the presence of Br2 mainly produced CBr2F2, which was found to be highly enriched with13C. The yield and13C-atom fraction of CBr2F2 were examined as functions of pulse number, laser line, laser fluence, total pressure, and Br2 pressure using a CO2 TEA laser with an output less than 1 J pulse−1 in order to optimize experimental conditions for13C separation. For example, we obtained CBr2F2 at a13C concentration of 55% in the irradiation of the mixture of 100-Torr CHClF2 and 10-Torr Br2 with the laser radiation at a wavenumber of 1045.02 cm−1 and at a fluence of 3.4 J cm−2. The mechanism for the IRMPD is discussed on the basis of observed results. Using 8-J pulses, we were able to obtain 1.9×10−4 g of13C-enriched CBr2F2 (13C-atom fraction, 47%) per pulse under selected conditions. It is possible to produce 90% or higher13C by the second-stage IRMPD of the CBr2F2 in the presence of oxygen.
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  • 20
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    Applied physics 48 (1989), S. 449-452 
    ISSN: 1432-0649
    Keywords: 42.55M ; 82.50 ; 33.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The laser performance and related photophysical properties of two very soluble perylene dyes with long chain secondary alkyl groups were investigated in cyclohexane solution. With a dye laser as pump source a tuning range of 555–580 nm was obtained at an optimum concentration of 3×10−4 M. The quantum efficiencies (η=0.29 and 0.21) were better than 1/2 that of rhodamine 6G. No photodegradation was observed over an excitation period of several hours.
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  • 21
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    Applied physics 49 (1989), S. 301-305 
    ISSN: 1432-0649
    Keywords: 82.50 ; 81.15
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have studied the photolysis of molybdenum hexacarbonyl by focused excimer laser radiation. It was found that electronically excited Mo atoms detected in the focus region of a KrF laser are due to a direct two photon absorption transition. The upper limit of the energy for complete dissociation of Mo(CO)6 has been derived from these results. Two photon dissociation in the gas phase should be the dominant process at metal film deposition on substrates positioned perpendicularly and near to the focus. Adding buffer gases to the organometallic vapor particle formation was observed in the whole irradiated gas volume. The analysis of scattered He-Ne laser light yields information about the density and size of these particles. Some conclusions are drawn with respect to structured metal film deposition with high spatial selectivity.
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  • 22
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    Applied physics 51 (1990), S. 314-316 
    ISSN: 1432-0649
    Keywords: 82.50 ; 42.60
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Ablation of polyetheretherketone (PEEK), a high temperature thermoplastic, by XeCl laser radiation occurs at fluences in excess of 0.07±0.01 J cm−2. The volatile products of ablation are CO and C2H2 with smaller quantities of CH4, C4H2, C6H6 and other C3 and C4 hydrocarbons. At fluences close to the threshold ablation produces involatile material of relatively high molecular weight but at high fluences extensive disruption of the PEEK structure occurs with conversion of all of the oxygen in the polymer to carbon monoxide.
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  • 23
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    Applied physics 51 (1990), S. 443-450 
    ISSN: 1432-0649
    Keywords: 82.50 ; 82.65NZ
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The photodesorption and photodecomposition pathways of dimethylgold hexafluoroacetylacetonate, DMG (hfac), adsorbed on a cooled quartz substrate is reported for 222-nm KrCl excimer laser radiation. The time-of-flight (TOF) of neutral photoproducts, desorbed from the surface of the gold film formed during the experiment, were analyzed under collisionless conditions by a differentially-pumped mass spectrometer. Extensive dissociation of adsorbed DMG (hfac) into DMG and the hfac ligand was observed. The ligand was found to recombine with a CH3 radical on the surface. Translational energy distributions for the detected species were obtained by deconvoluting the TOF curves into a self-consistent set of Maxwell-Boltzmann distributions for the desorbed parent molecule, laser-induced decomposition products, and surface recombination reaction products. The implications of these results for the mechanistic details of the low-pressure, laser-assisted organometallic deposition of DMG(hfac) are discussed.
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  • 24
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    Applied physics 51 (1990), S. 454-457 
    ISSN: 1432-0649
    Keywords: 82.50 ; 33.00 ; 35.00
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The 18O-selective IR MPD of perfluorodimethyl ether (CF3)2O has been studied. The dissociation yields of (CF3)2 18O (β18) and (CF3)2 16O (β16) and the isotope selectivity α(18/16) have been measured as functions of TEA CO2-laser frequency, laser fluence and ether parent pressure. The (CF3)2O molecule has been found to provide highly efficient 18O separation. The MPD yield of the desired isotope 18O varies in the range 3–13%; the selectivity α(18/16) achieves a value of 95 at the laser line 10P22, at moderate fluence Ø=4 J/cm2 and at P (CF 3)2 O=0.5 Torr.
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  • 25
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    Applied physics 52 (1991), S. 14-21 
    ISSN: 1432-0649
    Keywords: 52.80 ; 33.00 ; 82.50
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Dielectric barrier discharges (silent discharges) are used to excite a large number of excimers radiating in the VUV, UV or visible spectral range. The excited species include rare-gas dimers, halogen dimers as well as rare-gas halogen excimers and mercury halogen excimers. In many cases narrow-band UV radiation of typically 1–17 nm halfwidth and remarkable efficiency (1–10%) could be generated. Thus, dielectric barrier discharges provide a simple, versatile arrangement to study the basic reaction kinetics of excimer formation and also bear a substantial potential for large-scale industrial UV processes.
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  • 26
    ISSN: 1432-0649
    Keywords: 82.50
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    Topics: Physics
    Notes: Abstract The decomposition of ethylene by pulsed, unfocussed CO2-laser radiation has been studied at pressures from 500 to 3000 Torr, using the P(14) line of the 10.6μm band (v=949.48cm−1) at incident fluences from about 0.1 to 1.0J/cm2. Major products in order of decreasing importance were 1,3-butadiene, acetylene, ethane, propane, 1-butene and methane. These are known products of the thermal free-radical chain decomposition, and it is concluded that the laser-induced decomposition under our conditions is a transient bulk thermal reaction occurring in a thin disc of heated gas close to the entrance window of the reaction vessel at temperatures ranging from about 1000 to 1500K. As in the thermal decomposition, cyclobutane was observed to be a minor product, which in a sequence of laser pulses approached a final constant concentration. The possibility that this corresponded to an equilibrium concentration at some “effective” reaction temperature was explored. Computer simulation was used to model the accumulation of cyclobutane in the system, both in a single pulse and in a sequence of pulses, and predictions of this model were compared with experiment. It was concluded that cyclobutane could be used in this way as an approximate internal thermometer, within certain limits. Mechanisms of formation of the free-radical chain products are discussed. It is concluded that the chains are initiated by the bimolecular disproportionation reaction, 2C2H4 → C2H3+C2H5, and that secondary initiation by dissociation of the product, 1-butene, becomes increasingly important as the reaction proceeds, leading to autocatalysis. It is further concluded that the radical chain decomposition in this system is a transient process occurring in a brief time interval following the short laser pulse (FWHM=110ns), and is far from steady-state conditions.
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  • 27
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    Applied physics 52 (1991), S. 266-272 
    ISSN: 1432-0649
    Keywords: 82.50
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    Topics: Physics
    Notes: Abstract The CO2-laser-induced infrared multiple photon decomposition of natural CBr2F2 in the presence of oxygen has been examined as a function of pulse number (30–1500), reactant pressures (CBr2F2, 10–150 Torr and O2, 5–90 Torr), laser line [9P(8)–9P(32)], and laser fluence (1–3 J cm−2) to optimize irradiation conditions for 13C-enrichment. CF2O was the main carbon containing product and afterwards was converted into CO2 via hydrolysis. A small amount of C2Br2F4 was detected only under extreme conditions, for example, at high laser fluences or wavenumbers close to an absorption band. The 13C-atom fraction of the final product CO2 was found to be 20–80%, depending on experimental conditions. The two-stage IRMPD process proposed previously has been examined in further detail in the present study. First, CBr2F2 containing about 30% of 13C was prepared in the 13C-selective IRMPD of natural CHClF2 in the presence of Br2. The second-stage IRMPD of the CBr2F2 in the presence of oxygen under selected conditions resulted in the high enrichment of 13C beyond 90%.
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  • 28
    ISSN: 1432-0649
    Keywords: 42.70 ; 82.80 ; 82.50
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    Topics: Physics
    Notes: Abstract Photobleaching of three different xanthene dyes namely, Erythrosin B (ERB), Eosin Y (EOY) and Rose Bengal (ROB) in Poly(Vinyl Alcohol) (PVA) matrix has been studied. Quantum yield values of photobleaching using an argon-ion laser (514.5 nm) were determined in presence of an electron donor (TriEthAnolamine, TEA) and/or Cr(VI). Evaluated quantum yield values suggest that erythrosin B undergoes faster photobleaching than eosin Y or rose bengal in presence of TEA. Presence of Cr(VI) in addition to TEA drastically decreases the quantum yield. Possible reaction pathways of photobleaching are discussed.
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  • 29
    ISSN: 1432-0649
    Keywords: 82.50 ; 33
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    Topics: Physics
    Notes: Abstract The multiple photon dissociation of ppm level CTCl3 in CDCl3 and the selectivity of T/D separation were investigated using a pulsed ammonia laser. The effect of laser frequency, fluence and buffer gas pressure on the dissociation rate and isotopic selectivity were studied. The depletion of CDCl3 was not observed within experimental errors. A lower limit of single step selectivity factor was found to be 〉5000 at 133 Pa substrate pressure.
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  • 30
    ISSN: 1432-0649
    Keywords: 82.50 ; 33.00
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    Topics: Physics
    Notes: Abstract Measurements of multiphoton absorption of 16 µm Raman-laser radiation in supercooled238UF6 at 90 K were performed by using a pulsed Laval nozzle with an optical path length of 50 cm. The laser fluence was varied between 50 and 500 mJ/cm2 for four frequencies in the range from 625 to 629 cm−1. The energy absorbed by238UF6 molecules was investigated as a function of laser frequency or fluence, and highly accurate results were obtained with the use of the nozzle whose optical path length is much greater than that of nozzles used before. The results indicated that the absorption cross section at the peak absorption frequency (627.8cm−1) was proportional to the −1/3 power of the fluence.
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  • 31
    ISSN: 1432-0649
    Keywords: 07.75 ; 33.00 ; 82.50
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    Topics: Physics
    Notes: Abstract A MultiPhoton-Ionization Time-Of-Flight Mass Spectrometry (MPI/TOFMS) apparatus was developed for real-time measurement of the uranium isotopic ratio in nascent UF5 formed by the 266 nm photolysis of effusive UF6 ( 〈 300 K, ≈ 1.3 × 10−4 Pa). The UF5 was selectively and efficiently multiphoton ionized by 532 nm radiation at appreciably low fluences ( 〈 10 J/cm2). The main ions observed, U+ and U2+, were subsequently analyzed with a TOFMS with mass resolution of 1190 to separate235U n+ and238U n+ completely. The isotopic ratio measurements showed good precision resulting from the excellent agreement which was observed between the isotopic ratios in UF5 products and those in a parent UF6 sample. These results suggested that the MPI/TOFMS method can be applied to the real-time analysis of separation factors in the molecular laser isotope separation of uranium by ionization of UF5 following the infrared photodissociation of UF6.
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  • 32
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    Applied physics 55 (1992), S. 488-493 
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    Keywords: 42.55.Gp ; 78.65 ; 81.60.Jw ; 82.50
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    Topics: Physics
    Notes: Abstract Clean ablation of poly(tetrafluoroethylene) (PTFE) at etch rates in excess of 7µm/pulse has been achieved with an excimer laser using 308nm radiation and a 25 ns pulse width. This was accomplished by doping the ultraviolet-transparent PTFE polymer with polyimide. Ablation rates were investigated as a function of fluence in the range from 1 to 12J/cm2 and dopant levels up to 15% (wt/wt). Results show that at a given fluence there exists an optimum absorption coefficient ⇌max, for which maximum ablation rates are achieved. The value of ⇌max was found to decrease with increasing fluence. The relationship between ⇌max and fluence was determined from existing ablation rate models and found to compare favorably with empirical results.
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  • 33
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    Notes: Abstract IR laser chemistry of CHF3 is investigated in both neat form and in the presence of Cl2 for carbon-13 enrichment. Infrared multiple-photon dissociation of CHF3 is an order of magnitude more efficient in the scavenged system compared to the neat case. The photolysis of CHF3/Cl2 mixture results in two products, viz., CF2Cl2 and C2F4Cl2 but with different enrichment factors. The parametric studies show that C2F4Cl2 arises due to MPD of CF2Cl2 in secondary photolysis.
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  • 34
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    Notes: Abstract Chemical reactions induced by CO2-laser radiation in mixtures of silane and hexafluoroacetone afford various gaseous silicon- and carbon-containing compounds and result in deposition of microstructures of carbon, C/F/O and Si/C/O/F materials. These products are suggested to be formed by a variety of exothermic reactions initiated through SiH4-photosensitized decomposition of hexafluoroacetone. Silane is shown to be a very potent reagent for the reduction of C-F bonds.
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  • 35
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    Applied physics 56 (1993), S. 363-366 
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    Keywords: 78.55 ; 82.50
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    Topics: Physics
    Notes: Abstract The temperature dependence of the luminescence quantum yield of powdered titaniumdioxide in vacuum, nitrogen, and water vapor, respectively, was measured in the temperature range 300 K to 800 K. The observed luminescence is attributed to luminescence from surface states. We find that the luminescence is thermally quenched, as predicted by a simple model. Furthermore, the luminescence is shifted towards shorter wavelengths with increasing temperature. We also observed that the luminescence in vacuum is weakly quenched in the presence of nitrogen or water vapor.
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  • 36
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    Notes: Abstract Infrared multiphoton dissociation experiments with two wavelengths in different mixtures of chlorodifluoromethane and ammonia have been carried out. It is shown that the presence of ammonia in the sample induces a decrease in the chlorodifluoromethane dissociation yield. It has been observed that the distinct chemical reaction channels are differently activated as the time delay between the two laser pulses is varied. The ratio of the obtained products in the infrared multiphoton dissociation changes with the composition of the initial mixture and are not compatible with the mechanism suggested by Sugita and Arai for this reaction in single IR wavelength excitation if it is assumed to be the only contributing mechanism other than that for direct CF2HCl dissociation and subsequent C2F4 formation from the resulting CF2 radicals. It appears that, although for simultaneous two-wavelength irradiation the presence of an accumulated solid NH4Cl deposit does not significantly influence the reaction, this is no longer the case when time delays are introduced between the two beams.
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  • 37
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    Applied physics 59 (1994), S. 25-36 
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    Keywords: 82.50 ; 33.80.Gj ; 81.15.- z
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    Topics: Physics
    Notes: Abstract The laser-induced decomposition of WCl6 in the gas-phase is investigated by means of absorption, Raman and laser-induced fluorescence spectroscopy. With visible Ar+-laser radiation dissociation of WCl6 into WCl4 and Cl2 has been observed. Further decomposition can be achieved in the presence of H2 employing ultraviolet Ar+-laser radiation at 360 nm. A complete reduction to W requires even shorter wavelengths. The experimental results are analyzed on the basis of model calculations. Implications on the Laser-induced Chemical Vapor Deposition (LCVD) of W are discussed.
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  • 38
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    Keywords: 33.00 ; 82.50
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    Notes: Abstract The time-dependent change in the concentration of UF6 monomers populated in the ground state was monitored in a supersonic Laval nozzle flow with an infrared diode-laser spectrometer in which the frequency of the laser beam was fixed at theυ = 1 ← 0 transition (627.7 cm−1) of theν 3 vibrational mode of the238UF6 monomer. The concentration of UF6 monomers in the ground state increased immediately after a single shot from a Raman laser tuned to a vibrational mode of UF6 clusters (614.8 cm−1) was applied to the gas in the nozzle. Subsequently, this concentration leveled off and slowly returned to the previous level. These results indicate that the population of UF6 monomers in the ground state increased as a result of the predissociation of UF6 clusters vibrationally excited with Raman laser radiation. It is demonstrated that one can utilize this procedure for vibrational predissociation of UF6 clusters as a technique to increase the concentration of UF6 monomers in an irradiation zone for molecular laser isotope separation of uranium.
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  • 39
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    Applied physics 9 (1976), S. 335-337 
    ISSN: 1432-0630
    Keywords: 32 ; 82.50
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract A new method of photoionization cross-section measurement based on the observation of saturation in the ion yield as a function of radiation intensity has been proposed. The photoionization cross-sections for the 62P1/2 and 62P3/2 levels of Rb atoms of the fundamental and second harmonics of ruby laser radiation are measured, with a tunable pulsed dye laser used for excitation. The following values of cross-sections are obtained: (1.7±0.4)·10−17 cm2 and (1.5±0.4)·10−17 cm2 for the levels 62P3/2 and 62P1/2, respectively, ionized by radiation of v2=14403 cm−1, and (1.9±0.5)·10−17 cm2 for the 62P3/2 level ionized by v2=28806 cm−1 radiation.
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  • 40
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    Notes: Abstract Time-resolved infrared emission spectra in the wavelength region of 2–5 μm were measured for the CO2-laser-induced photolysis of trifluoromethane-d (CDF3) and its mixtures with trifluoromethane-h (CHF3). The reactant pressures were 0.1–20 Torr at room temperature; some collisions were expected to occur within the laser-pulse duration. The emissions due to vibrationally excited CDF 3 * (C-D stretching mode and probably combination mode) and DF* were observed at the same time for the irradiation of pure CDF3. DF* should be produced in the unimolecular decomposition of CDF 3 * . The dependences of the DF* emission on the experimental condition are explicable on the assumption that the collisional energy transfer followed by the decomposition of CDF3 plays an important role in the present IRMPD, besides its direct multiple-photon decomposition. The mixture of CDF3 and CHF3 showed the emissions due to HF* and CHF 3 * in addition to DF* and CDF 3 * . The ratio between the DF* and HF* emission intensities,I DF/I HF, was examined as a function of pressure. The pressure dependences were similar to those of the selectivity determined previously from the concentration changes of CDF3 and CHF3. The irradiation of mixtures with a long furation pulse (80 ns fwhm with a 2μs) resulted in a marked decrease inI DF/I HF.
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  • 41
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    Applied physics 32 (1983), S. 193-198 
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    Keywords: 42.55 ; 33 ; 82.50
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    Topics: Physics
    Notes: Abstract The vibrational relaxation time constant for theB v=0 vibrational level of XeCl* has been investigated by observing the coupling between theB v=1 andB v=0 vibrational levels under saturated lasing conditions. Based on this observation, estimates of the expected extraction efficiency from theB-state have been made.
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  • 42
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    Applied physics 33 (1984), S. 43-49 
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    Topics: Physics
    Notes: Abstract A frequency-doubled carbon dioxide laser of modest output energy (1 mJ) has been used to study, for the first time, the infrared multiphoton absorption by, and dissociation of, the unsubstituted carbonyls of vanadium, chromium, iron, nickel, molybdenum, and tungsten. The multiphoton absorption cross-sections measured for Ni(CO)4, Fe(CO)5, Cr(CO)6, Mo(CO)6, and V(CO)6 are high (σ∼2×10−17) and ensure facile multiphoton dissociation. In focussed beams a pressure independent reaction yield proportional to the 1.5 power of the beam energy is observed for Fe(CO)5, Cr(CO)6, and Mo(CO)6 implying threshold fluences of only 32, 25, and 26 mJ cm−2, respectively. The stoichiometry of the reaction, observed by a pressure measurement technique, is consistent with production of metal atoms and carbon monoxide as final products for Ni(CO)4, Fe(CO)5, Cr(CO)6, and Mo(CO)6. This extensive decarbonylation along the ground state surface is consistent with recent studies of the photochemistry of these molecules from excited electronic states.
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  • 43
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    Applied physics 37 (1985), S. 63-65 
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    Topics: Physics
    Notes: Abstract The deposition of lead film on quartz substrates by photolysing tetraethyl lead vapor with a laser is reported. The dependence of the deposition rate on the pressure of tetraethyl lead, on the light intensity and on the pressure of the buffer gas is measured. Deposition phenomena at low light intensity are discussed.
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  • 44
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    Applied physics 33 (1984), S. 83-90 
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    Keywords: 82.50 ; 82.40 ; 42.60
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    Topics: Physics
    Notes: Abstract Tritium isotope separation by CO2-laser induced multiphoton dissociation of CTF3 is investigated. For the optimization of the performance of this working substance, trifluoromethane, the conditions to yield high-selectivity at high-operating pressure and low-critical fluence for complete dissociation are studied using our deconvolution procedure. The irradiation conditions are varied over the following ranges; wavenumber: 1052–1087 cm−1, gas temperature: 25°C to −78°C, CHF3 pressure: 5–205 Torr. The selectivities exceeding 104 are observed for 85–205 Torr CHF3 at −78°C by the irradiation at 1057 cm−1.
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  • 45
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    Applied physics 34 (1984), S. 97-106 
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    Keywords: 82.50 ; 33
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    Notes: Abstract C2F3Cl is photolyzed with a TEA-CO2 laser at 1050.44 cm−1 with focussed fluences up to 280 J/cm2. The stable products in the IRMPD of C2F3Cl are determined for up to 10 Torr of C2F3Cl being photolyzed both neat and with added O2. C2F4 and trans-C2F2Cl2 are found to occur in the greatest yield though C3F5Cl, C3F4Cl2, C4F7Cl, and C2F3Cl3 also appear to be primary products. When O2 is present F2CO, FClCO, and CF2ClCOF are the exclusive products. The formation of these products are for the most part consistent with a carbene formation dissociation mechanism for C2F3Cl IRMPD. C2F3Cl3 may best be explained by another mechanism competitive with carbene formation. Many products attributed to secondary photolysis mechanisms are observed for long photolysis times.
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  • 46
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    Applied physics 37 (1985), S. 31-34 
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    Keywords: 78.60 ; 61.8 ; 82.50
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    Topics: Physics
    Notes: Abstract Reducing the diameter of the flashlamp was found to increase the percent improvement in output of a solid-state laser caused by using luminescent coolants. However, this change in diameter also reduced the effectiveness of the flashlamp in producing long (150 μs) laser pulses so that an overall decrease in laser output was observed. In the formation of short (40 μs) laser pulses, on the other hand, larger absolute values were obtained using the smaller diameter flashlamp.
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  • 47
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    Applied physics 39 (1986), S. 61-63 
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    Keywords: 82.30 ; 82.50
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    Notes: Abstract 1-Nitroadamantane was produced by irradiating a solution of adamantane and NO2 in CCl4 with the visible lines (457.9–514.5 nm) of an argon-ion laser. At these wavelengths NO2 does not photodissociate to form O atoms, and thus the nitration reaction must be initiated by another species, probably vibronically excited NO2 (NO 2 *† ). The intensity of the laser enables the reaction to be carried out in a reasonable length of time, despite the strong quenching of NO 2 *† by CCl4.
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  • 48
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    Applied physics 43 (1987), S. 123-126 
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    Notes: Abstract It is shown that, in the case of some halomethanes for which an Arrhenius-type relation can be fitted to the IRMPD probabilities as a function of CO2-laser pulse energy, the pre-exponential factor is about equal to the ratio of the reaction volume to the total gas volume.
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  • 49
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    Applied physics 46 (1988), S. 271-282 
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    Keywords: 82.80 ; 87.00 ; 82.50
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    Topics: Physics
    Notes: Abstract Through the development of powerful laser spectroscopy techniques new means for advanced diagnostics and sample analysis have emerged. Applications of laser spectroscopy in the fields of energy, environmental and medical research are discussed. Emphasis is placed on non-intrusive diagnostic techniques for studying combustion processes, for remote monitoring of atmospheric pollutants and for industrial and medical applications of laser-induced fluorescence. Selected examples from work performed at the Lund Institute of Technology are used as illustrations, and references to books, reviews and selected papers are given.
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  • 50
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    Applied physics 41 (1986), S. 109-117 
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    Keywords: 82.50 ; 82.30 ; 42.60
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    Topics: Physics
    Notes: Abstract Several monoatomic and homonuclear diatomic gases absorb energy from a focused CO2-laser photon field. It has been established that the pressure threshold for the energy absorption correlates qualitatively with the known ionization potentials of those gases. The simplified phenomenological theory of the CO2-laser-induced dielectric breakdown of gases is invoked to explain this phenomenon. In the H2−D2 system, the formation of HD is observed under these conditions. The examination of the reaction yields for HD formation demonstrates that the system studied does not reach equilibrium under our experimental conditions. Considerations regarding kinetics of primary processes reveal that ionic species, created originally via an inverse bremsstrahlung mechanism, are converted into atomic transients in fast ionic association processes. The latter species initiate chain reactions with surrounding molecules of substrates leading to the formation of HD. Simple kinetic analysis based on a non-steady-state assumption permitted the derivation of an expression for the yield of HD formation. This equation was fitted to the experimental data assuming that the temperature of the reaction rises with an increase of the amount of D2 in the mixture. Some other aspects regarding the behavior of this system in a focused CO2 laser beam are also discussed.
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  • 51
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  • 52
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  • 53
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    Applied physics 30 (1983), S. 195-202 
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    Keywords: 78.60 ; 61.8 ; 82.50
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    Notes: Abstract Solutions of 13 fluorescent dyes have been used as energy transfer agents in place of the normal coolant of a Nd-YAG laser. Dye mixtures were used in a few cases where incomplete absorption of flashlamp pump energy was observed. Improvements of over 100% in laser output were observed for some dyes having a long Stokes shift when tested at both a low-input energy and a low-pulse rate. However, the absolute improvement in laser output for these dye solutions was small, and the improvement could be obtained almost as well by merely increasing the pulse rate. Various factors associated with the effectiveness of transfer-dye solutions are discussed.
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    Applied physics 26 (1981), S. 111-116 
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    Notes: Abstract The effect of focusing a laser beam on the intensity (I) dependence of multiphoton processes was examined. A general method is given to deduce a genuine intensity dependence from the focused-beam experiment. In addition, some typical examples were examined in detail. For the dependence of the type ofI n, an apparent relation ofI 3/2 appears only when there is a change of dependence asI n→Im, withn〉3/2 andm〈3/2. A genuine intensity dependence can be obtained directly from the focused beam experiment ifn does not change throughout the irradiated volume, or if the conditionn〉3/2〉m does not hold. The case of gradually decreasingn, as is common for the infrared multiphoton reaction probability (P), was also analyzed taking the Arrhenius-type dependence,P ∝ exp(−Θ/I), as an example. A simple method is proposed to obtain a genuine relation betweenP andI for this type of intensity dependence.
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  • 55
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  • 56
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    Notes: Abstract A pyroelectric detector with a time resolution of 3–5 μs and a TEA CO2 laser have been used in diagnostics of a pulsed molecular beam (a free jet). The kinetic energy distribution of molecules was determined by using time-of-flight measurements both with a laser and without it. A combination of the laser with the pyroelectric detector makes it possible to determine the kinetic energy distribution of molecules in a selected internal state and to measure the energy absorted by the molecules of the beam from a laser pulse. The results obtained for pure SF6 and the SF6 seeded in He have been presented and analyzed. The advantages and the disadvantages of the method are being discussed in comparison with other available methods of diagnostics of molecular beams and free jets.
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  • 57
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    Notes: Abstract An ir multiphoton dissociation (MPD) process in multiple-frequency ir-laser fields has been experimentally realized. A selectivity ofS=104 was obtained in separating13C/12C isotopes upon multiple-frequency ir multiphoton dissociation (MFMPD) of the CF2HCl molecule, the dissociation yield13β for the13CF2HCl molecule amounting to around 1%. A yield of13β was reached at a selectivity ofS=102, and the total laser fluence required for the process was reduced. A new mechanism—“sticking” of molecules on the lower discrete vibrational levels—responsible for the low MPD yields observed for some molecules is discussed and a technique to eliminate it and thus maximize the dissociation yields is proposed. Ways to improve the selectivity by MFMPD are analyzed and a simple method for obtaining from a single TEA CO2 laser a multiple-frequency radiation suitable for experimental realization of MFMPD is suggested.
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    Applied physics 39 (1986), S. 55-59 
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    Notes: Abstract The 488 nm laser-induced reaction of NO2 with CO has been investigated and the results computer-modeled. Two reaction mechanisms were considered:1) the direct reaction of vibronically excited NO2 (NO 2 * † ) with CO to form CO2, and 2), the reaction of an intermediate NO3 radical formed by the reaction of NO 2 * † with NO2 followed by NO3+CO→NO2+CO2. The modeling results strongly support the former as the dominant mechanism.
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  • 59
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    Notes: Abstract There is a general agreement that efficient infrafed laser induced separation of carbon isotopes requires a two-stage process. An efficient first stage 1%→50%13C enrichment was shown by Gauthier et al. [1] to be feasible and competitive with conventional technology. In this work, second-stage CO2 laser enrichment of equimolar mixtures of12CHClF2 and13CHClF2 has been demonstrated yielding tetrafluoroethylene containing 95% or 99%13C. Forward enrichment by selective decomposition of the13CHClF2 fraction was very efficient, absorbing only 6 and 16 eV, respectively, per carbon atom produced at 95% and 99%13C content.
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    Applied physics 43 (1987), S. 247-251 
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    Notes: Abstract The enhancement of the Li+H2→LiH+H reaction due to laser excitation of the Li atom to the2p state has been investigated using absorption techniques. Using a rate equation model we obtain from our data a reaction cross-section σ[Li(2p)+H2→LiH+H]=(0.10±0.03)Å2 at 515°C. By selectively exciting one Li isotope the reaction is made isotope selective, suggesting an efficient means of isotope separation.
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    Applied physics 42 (1987), S. 181-184 
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    Notes: Abstract Excimer laser (248 nm, 15 ns) photoablation products from the polymers PMMA and polystyrene are directly observed using picosecond uv laser (290 nm, 1 ps) ionization time-of-flight mass spectroscopy. Species heavier than the monomer masses are detected, which cannot be attributed to simple direct fragments of the polymer chains, but rather show the importance of fast chemistry and/or photochemistry during the ablation process.
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    Applied physics 42 (1987), S. 221-223 
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    Notes: Abstract The maskless photoassisted etching of n-type Ga0.47In0.53As is examined for basic KOH solutions in comparison with GaAs and InP material. The etch rate increases with laser intensity and with carrier concentration up to a saturation value. The best etch rate is obtained with molar KOH in ethyl alcohol (7 μms−1 for laser intensity 104 W cm−2). Selective etching have been realized on heterojunction in order to isolate p-n junctions without the help of masks.
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    Applied physics 26 (1981), S. 57-60 
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    Notes: Abstract We report on the “laser snow” effect observed in CS2 vapour illuminated by uv lines of a krypton laser. We discuss the effect of diffusion and convection processes on the threshold value of the CS2 vapour pressure. We discuss also the kinetics of the formation process related to the proposed model of chemical reactions induced by laser light.
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  • 64
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    Notes: Abstract The initial stage of thermochemical instability induced by an absorbing inclusion within a transparent matrix, which irradiated by a laser beam, is studied. The instability results in a low threshold (formally non-threshold) optical breakdown of the matrix. It is brought about by the additional absorption of the laser light by the products of the chemical reactions in the matrix. The instability is characterized by a certain induction time when the rate of the chemical reactions is almost steady. When the induction is over, their rate rapidly increases. Theoretical estimate of the induction time are offered. The experimental study of the induction time dependence on the laser-beam intensity confirmed the theoretical estimation.
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    Notes: Abstract Isotope separation of tritium from deuterium in heavy water was attempted by CO2-laser-induced, highly-selective multiphoton dissociation of C2TF5 present in C2DF5. Single-step T/D separation factors exceeding 3000, 1000, and 500 were attained, respectively, for the first time with CO2 laser 10P(34) 931.0 cm−1 at 10, 20, and 30 Torr pentafluoroethane pressures at −78 °C (i.e., equivalent to 15, 30, and 45 Torr at room temperature).
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  • 66
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    Applied physics 28 (1982), S. 341-348 
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    Keywords: 82.50 ; 82.40 ; 42.60
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    Notes: Abstract Isotope separation of tritium by CO2 laser-induced multiphoton dissociation (MPD) of C2TF5 is reported for the first time. The MPD spectrum obtained for C2TF5 comprised a broad peak at about 940 cm−1 where C2HF5 was nearly transparent. The unimolecular dissociation of C2TF5 was induced with much lower laser fluence than that for CTF3, another working molecule we proposed for laser isotope separation of tritium. The mechanisms and kinetics of the dissociation of C2TF5 and C2HF5 were investigated under various experimental conditions: laser frequency, pulse energy, pulse duration, tritium concentration, sample pressure, buffer gas pressure and irradiation geometry. Single-step separation factors exceeding 500 were achieved with the most efficientP(20) line in 00o–10o0 transition at 944.2 cm−1.
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  • 67
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    Applied physics 38 (1985), S. 219-224 
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    Keywords: 82.30 ; 82.50
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    Notes: Abstract The reaction of NO2 with isobutane, induced by 488 nm laser radiation, to form 2-nitro-2-methylpropane has been investigated and the results computer-modeled according to two possible reaction mechanisms. The first scheme involves the direct abstraction of H from isobutane by vibronically excited NO2 (NO 2 *Δ ), and the second, abstraction by an intermediate NO3 radial produced by NO 2 *Δ +NO2. The modeling results strongly support the NO 2 *Δ scheme as the dominant reaction mechanism.
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  • 68
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    Applied physics 40 (1986), S. 35-38 
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    Keywords: 42.55 ; 82.50
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    Notes: Abstract An experimental investigation on shortening of travelling-wave ASE employing a transversal pumping is presented. A N2 laser with λ=337.1 nm, pulsewidth: 700 ps is used as a pump source. An ASE pulse with duration of 45, 55 and 45 ps from dye solution of Rh 6G, Rh B and C311, respectively, is obtained. Pulse shapes of output signals generated from these solutions in three different pumping schemes are compared.
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  • 69
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    Applied physics 41 (1986), S. 61-68 
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    Keywords: 82.50 ; 33.80
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    Notes: Abstract Selective infrared multiphoton dissociation of13CF3Cl induced by CO2 laser pulses adjusted on $$\bar v$$ = 1071.9 cm−1 has been studied in the energy rangeE between 0.5 and 2 J per laser pulse or fluence range between 5 and 25 J per cm2, and in the pressure range between 0.10 and 60 Torr. The effect of these parameters on the isotopic selectivity of the dissociation gives information on the rotational relaxation constants. As for the dissociation probabilities, they vary exponentially withE −1. The applicability of such an Arrhenius-type relation is discussed and semi-quantitatively justified.
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  • 70
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    Applied physics 45 (1988), S. 83-86 
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    Notes: Abstract The successful synthesis of ethylamine with a cw tunable CO2 laser is reported. This action occurs at normal pressure (∼5.32×104 Pa) and temperature (〈100° C). No catalyst is used. The experiment shows a high directionality of this reaction. No other product except ethylamine is yielded. A possible mechanism for this reaction is discussed.
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  • 71
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    Keywords: 33.80 K ; 82.50
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    Notes: Abstract The yield of the multiphoton dissociation of CF3Cl and CF3Br induced by TEA-CO2 laser pulses has been studied in the pressure range between 0.25 and 8 Torr, the laser wavelength being chosen so as to excite preferentially the minor isotopic components13CF3Cl and13CF3Br. For both compounds the dissociation probability is found either to increase almost linearly or to decrease monotonously with gas pressure, according as the laser beam is focused or unfocused, respectively. This behaviour is explained by rotational relaxation effects, and a value of 22ns·Torr for the rotational self-relaxation time of CF3Cl is obtained.
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  • 72
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    Applied physics 29 (1982), S. 139-142 
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    Keywords: 78.60 ; 61.80 ; 82.50
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    Notes: Abstract A 3-parameter dye laser degradation equation is introduced that has been based upon a theoretical analysis of a laser oscillator. The new equation and the 4-parameter empirical laser degradation equation used previously in this series are further developed to allow calculation of the lifetime of a dye solution for any fraction of laser output degradation. These lifetime equations are shown to be dependent upon the input energy per pulse and the threshold of lasing. The new 3-parameter equation allows the degradation constants to be determined with less change in laser output than did the original 4-parameter empirical expression.
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  • 73
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    Keywords: 33 ; 82.50
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    Notes: Abstract The role of played by the intensity of the exciting TEA CO2 laser pulses in the processes of ir multiphoton absorption (MPA) of SF6 molecules cooled toT R≃40 K andT v≃160 K in a pulsed supersonic jet and the dissociation of SF6 in a bulk atT≃300 K under essentially collisionless conditions have been investigated. A strong dependence of MPA and the dissociation yield on pulse intensity were observed. The frequency dependences of the intensity effects were studied.
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  • 74
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    Applied physics 45 (1988), S. 145-149 
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    Keywords: 82.50 ; 85.60 ; 42.55M
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    Notes: Abstract TICT states, accessible in twisted multichromophoric systems, are nonradiative funnels to the ground state in many dyes. By controlling these funnels, faster saturable absorbers for subpicosecond laser pulses can be developed. Oriented assemblies of TICT molecules, as in liquid crystalline polymers, are expected to exhibit light-induced macroscopic charge separation. Chemical approaches to supramolecular bistable species are also shown.
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  • 75
    ISSN: 1432-0649
    Keywords: 33.00 ; 82.50
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    Notes: Abstract Using a photodissociation technique, we have measured the IR spectrum of thev 21 mode of the (CF3)3 CI molecule with a vibrational energy ofE 2=42500±3500 cm−1 which is more than two times the dissociation energy. The experimental spectrum of a Lorenzian shape with a halfwidth of γ2=10.8±1.5 cm-1 has been analyzed simultaneously with the results of the preceding work (γ1=8.6±0.6 cm-1) that were obtained at a lower vibrational energy (E 1=36500±2500 cm−1).
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  • 76
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    Applied physics 48 (1989), S. 453-462 
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    Keywords: 82.50 ; 82.65
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    Notes: Abstract Model calculations on laser-induced photolytic gas-phase processing have shown that the concentrations of photogenerated species and the reaction rates depend not only on the electronic properties of precursor molecules and on the wavelength and intensity of the laser excitation, but also on the size of the laser focus, the type of the substrate material and, significantly, on the material and geometry of the reaction chamber. In particular, it has been demonstrated that a dependence of the reaction rate,W, on the radius of the laser beam on the substrate surface,w o, according toW∝w 0 −n cannot be employed, in general, in a simple way to separate adsorbed-phase and gas-phase contributions to the reaction rate as claimed in previous investigations. Even in pure photolytic gas-phase processing, the exponentn can vary within the range 0〈n〈=2, depending on the various different parameters and material properties.
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  • 77
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    Applied physics 35 (1984), S. 1-5 
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    Keywords: 82.50 ; 33 ; 35
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    Notes: Abstract Increase of the emission bandwidth of a high-pressure CO2 laser up to 1.5 cm−1 increases the multiphoton absorption cross-section of SF6. Comparison with the previously found [9] increased absorption for shorter pulses suggests that this is also a bandwidth effect. Spectral structures as narrow as 1 cm−1 above the 10th absorption step are invoked to explain the observations. The temperature effect, which disappears in the broad-band case, confirms this view.
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  • 78
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    Applied physics 50 (1990), S. 385-392 
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    Notes: Abstract The 13C-selective infrared multiple-photon decomposition (IRMPD) of mixtures of CHClF2 and HI was examined in collimated and focused beam geometries using a CO2TEA laser. The carbon-containing products were CH2F2 and CHF2I. The former product showed remarkably high 13C atom concentrations beyond 95% under selected experimental conditions, while the latter contained 25% or less. The observed results can be explained satisfactorily in terms of the consecutive two-stage IRMPD process occurring in a single irradiation procedure, where the first-stage IRMPD of natural CHClF2 produces 13C-enriched CHF2I via the insertion of the initial decomposition fragment CF2 into HI, and the second stage is the subsequent 13C-selective IRMPD of the CHF2I to form a CHF2 radical and an I atom. The CHF2 radical reacts with HI to form CH2F2. Decomposition probabilities of 12CHClF2 and 13CHClF2 were measured as a function of laser fluence to optimize enrichment conditions. Furthermore, partial decomposition probabilities or relative production yields were measured as functions of laser line, pressure of HI, and pressure of CHClF2. Both stages showed high 13C selectivities in the irradiation with the laser radiation around 1040 cm−1 and at fluences below 4 J cm−2. This mixture is one of the most promising chemical systems for the production of highly enriched 13C.
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  • 79
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    Applied physics 51 (1990), S. 137-140 
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    Keywords: 06 ; 81.40 ; 82.50
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    Notes: Abstract Optothermal methods for the study of UV laser ablation are discussed. Pyroelectric and photoacoustic measurements for PMMA and Al irradiated at 193 nm are reported. Ablation thresholds are estimated. The different mechanisms contributing to the signal generation are discussed.
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  • 80
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    Keywords: 82.50 ; 33 ; 35
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    Notes: Abstract The dissociation probabilities of32SF6 and some of34SF6 have been measured at a large number of CO2 laser lines both at room temperature and at 140 K. The longwavelength wing of this dissociation spectrum is exponential in the wavenumber. Its logarithmic slope is proportional to the inverse temperature. Selectivities are high enough at 140 K, that the photons are consumed only for the rare isotope in the case of34SF6 and nearly so for36SF6. For33SF6 further improvement of the selectivity would be desirable.
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  • 81
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    Keywords: 42.55E ; 42.65J ; 42.60H ; 82.50
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    Notes: Abstract We observed self-focusing and self-defocusing of a TEA CO2 laser pulse in CDF3 vapor under different conditions. The experimental parameters we varied are the pressure inside the interaction cell, the frequency of the laser, the energy and the temporal length of the pulse. We have shown that it is possible to pass from self-focusing to self-defocusing by only increasing the intensity of the laser pulse. We propose a physical model that can explain these experimental results. This model is different from that used to explain the selffocusing of a CO2 laser in SF6.
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  • 82
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    Applied physics 47 (1988), S. 195-199 
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    Keywords: 42.55.M ; 82.50 ; 33.20
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    Notes: Abstract The potential of rubrene as a laser dye was investigated in deaerated solutions with a XeCl excimer laser as pump source. Laser tuning range, quantum efficiency and photostability as well as excited singlet state absorption (ESA) spectra were measured. The (S1-S2) absorption band strongly overlaps with the fluorescence spectrum and thus ESA constitutes an important loss factor in the lasing process while triplet absorption can be neglected in the wavelength region of interest. Laser performance of rubrene is superior compared to other polycyclic aromatic hydrocarbons which can be considered as model compounds of the lasing process in organic dyes.
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  • 83
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    Applied physics 47 (1988), S. 239-242 
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    Notes: Abstract Infrared multiple-photon dissociation (IRMPD) of CDCl3 was studied using a tunable TEA CO2 laser. Effects of number of irradiation pulses, wavelength and energy fluence as well as of sample pressure on the reaction yield are reported.
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  • 84
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    Notes: Abstract The single-photon effect of the self-induced optical activity (SIOA) has been investigated experimentally for the first time in the vicinity of potassiumD 1,2 lines. Experimental data on self-induced gyrotrophy and dichroism are presented and compared with the theoretical model proposed earlier. The limiting action of SIOA on the efficiency of resonance parametric generators and polarization spectroscopy is outlined.
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  • 85
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    Applied physics 49 (1989), S. 77-83 
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    Keywords: 82.50 ; 33.00 ; 35.00
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    Notes: Abstract Isotopically selective (with respect to 18O) one- and two-frequency multiphoton dissociation of dimethyl ether (CH3)2O by pulsed TEA CO2 laser radiation has been studied. The maximum primary selectivity, α℞16, is attained with the dissociation yields of the desired component (CH3) 2 18 O β18=5×10−4 and 1.7×10−2 for one- and two-frequency excitation, respectively. The dependences of MPD yields and selectivity on laser radiation frequency, (CH3)2O pressure, buffer gas (N2) pressure and temperature have been measured. Multiphoton absorption coefficients have been measured and the average number of absorbed quanta calculated. The laser photon energy consumed for separating one 18O atom has been estimated: 11 and ∼4 keV/18O atom for one- and two-frequency excitation, respectively.
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  • 86
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    Notes: Abstract Isotope-selective multiphoton dissociation of CTF3 in the presence of CDF3 by TEA CO2 laser is studied. The highest T/D selectivity of 58 was observed at a sample pressure of 2 Torr in the presence of 20 Torr of argon on excitation by the 9P(24) CO2 laser line. The effect of multiple-frequency irradiation on selectivity is studied in the P and Q branches of the v 2 absorption band of CTF3. No improvement in the selectivity is noticed on going from single- to multiple-frequency irradiation. These results are compared with previous multiple-frequency work on the CTF3/CHF3 system, and explained in terms of strong spectroscopic interference from 13CDF3 in the present case.
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  • 87
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    Notes: Abstract Isotope separation of tritium by multiple photon dissociation process in multiple frequency fields of a TEA-CO2 laser is reported for the first time. A ten-fold improvement in the bulk selectivity was obtained in 8.5 Torr CTF3/CHF3 in the presence of buffer gas at room temperature using 9R(8) to 9R(14) CO2 laser lines compared to single frequency excitation. Investigations of various process parameters such as exciting laser frequencies, pulse energy, sample and buffer gas pressure indicate that this is a promising technique for the separation of tritium.
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  • 88
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    Notes: Abstract The dissociation of UF6 sensitized by multiple photon excitation of a series of halomethanes: CF4, CF3Cl, and CF2Cl2 has been investigated. The roles of various experimental parameters like exciting frequency, fluence and pressures of sensitizer/UF6 on the dissociation yield were studied to examine (1) the characteristics of the sensitizer/UF6 system and (2) the coupling of vibrational energy between two molecular systems. The efficiency of the energy transfer process was estimated on the basis of long range dipole-dipole interaction to gain an understanding of the dissociation process.
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  • 89
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    Applied physics 58 (1994), S. 79-81 
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    Keywords: 42.55. Mv ; 82.50
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    Notes: Abstract The laser characteristics of a new dye, 7-Diethyl-amino-3-Styryl Benz31 yimidazo (1,2-a) Quinoline (DSBQ) have been investigated in two solvents: DiMethylSulfOxide (DMSO) and DiMethylFormamide (DMF) by excitation with a pulsed nitrogen laser and compared with that of the standard dye rhodamine B. The lasing range of the dye is nearly 40 nm with maxima at 635 nm and 625 nm in DMSO and DMF, respectively. The efficiency of this dye (DSBQ) has been found to be better than half that of rhodamine B.
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  • 90
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    Applied physics 60 (1995), S. 61-65 
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    Keywords: 32.00 ; 42.65 ; 82.50
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    Notes: Abstract A novel method for exciting the two-photon 2p 3 3p 3 P ←2p 4 3 P atomic oxygen transition is reported. The transition energy is provided by the combined photon energies of the second and third Stokes orders of a deuterium-filled Raman shifter pumped by an ArF-excimer laser. The ArF-excimer-pumped Raman shifter performance is characterized and the approach is demonstrated in an atomic oxygen population created by molecular oxygen absorption and predissociation in room air.
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  • 91
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    Notes: Abstract In infrared multiphoton dissociation of supercooled UF6 irradiated with multifrequency para-H2 Raman laser beams, separation factors and contrast ratios were measured by selective multiphoton ionization of the photoproduct UF5 at 532 nm followed by time-of-flight mass spectrometric analysis. The relationship between separation factor and contrast ratio is discussed theoretically and quantitatively investigated in the experiments. From this relationship, we obtain the irradiation conditions of the laser-beam fluences for attaining a high separation factor and estimate the value of the intrinsic separation factor in multifrequency dissociation of UF6.
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  • 92
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    Applied physics 62 (1996), S. 169-171 
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    Keywords: 82.50 ; 32.20 ; 33.80
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    Notes: Abstract Mn2(CO)10 was photolysed in the gas phase by the XeCl-excimer laser with fluence in the range 25–300 mJ/cm2 and a dye laser. The UV/VIS emission of the products was probed on a nanosecond time scale. The emission from excited states of metal atoms was detected only. The Mn atoms are predominantly formed in their ground statea 6 S 2 1/2. The absorption of one photon and the subsequent relaxation process leads to the formation ofz 6 P J 0 (J = 11/2, 21/2, 31/2) states and emission of photons at a wavelength of 403 nm. The formation of the excited statese 8 D 5 1/2,z 6 F 4 1/2 0 ande 6 D 4 1/2 and the subsequent emission observed at wavelengths of 357, 383 and 446 nm requires the absorption of two photons by the ground-state Mn atoms. In addition, transition from thea 6 D j (J = 11/2, 21/2) lower states were observed in the wavelength-resolved Laser-Induced Fluorescence (LIF) spectra.
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  • 93
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    Notes: Abstract The isotope-selective multiphoton dissociation of CHClF2 in a multipass refocusing Herriott cell was used to enrich more than 4 moles of chlorodifluoromethane to 99.99% of12C isotopic purity. It is the largest isotope quantity ever separated by a laser process. A cw excited mechanically Q-switched CO2 laser, which delivers 16 mJ pulses at 5 kHz was used. The enrichment controlled by a mass-spectrometer and guided by a PC was run with a rate of 25 g12C per 24 h.
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  • 94
    ISSN: 1432-0649
    Keywords: 82.20 ; 82.50
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    Notes: Abstract The product branching ratio was studied in relation to the radical scrambling mechanism of laser isotope separation of uranium. A mixture of UF6/CH4/Ar was irradiated either using a low-intensity cw-UV source (high-pressure Hg lamp, 250 nm ∼ 400 nm) or using high-intensity pulsed UV lasers (4th-harmonic YAG laser at 266 nm or KrF laser at 248 nm) in a supersonic nozzle reactor. While the latter gave a higher C2H6/CH3F ratio in the photoproduct than the former, the C2H6/CH3F branching ratio was found to disagree with the results reported in a static cell experiment. This anomaly in the results obtained using a supersonic nozzle reactor was well represented by a model proposed in this study which assumed no mixing before a shock wave zone and sufficient mixing after it, leading to complete suppression of radical recombination.
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    Applied physics 47 (1988), S. 223-228 
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    Notes: Abstract A TEA CO2 laser was used to study the infrared multiple-photon absorption (IRMPA) and dissociation (IRMPD) spectra of CDCl3 in the fluence ranges 0.01–1.4 and 7–45 J/cm2, respectively, for different sample pressures. Experimental results were modeled with a master equation formulation which includes rotational and anharmonic bottlenecks and collisional effects. Experimental and calculated results show that CDCl3 has great rotational and anharmonic restrictions at the first stages of excitation. The IRMPD spectrum falls more slowly than the linear absorption spectrum at the blue wing due to intramolecular vibrational relaxation at the quasi-continuum level of excitation.
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  • 96
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    Applied physics 30 (1983), S. 153-156 
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    Keywords: 07.62 ; 82.50
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    Notes: Abstract A crow-bar technique employing a light-activated silicon switch is described to overcome stray electron effects in streak cameras. The technique is applied in picosecond fluorescence studies of intramolecular charge tranfer processes in a compound of the type A-(CH2)3-D (A: anthracene, D: dimethylaniline) where the locally excited state and the exciplex state are shown to be formed sequentially.
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  • 97
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    Notes: Abstract Difluoromethane CH2F2 containing 90–98% 13C was obtained in the selective IRMPD of mixtures of CBr2F2/HI, CCl2F2/HI, and CBrClF2/HI. In CBr2F2/HI mixtures, the intermediate product CHBrF2 resulting from the reaction between the initial decomposition fragment CBrF2 and HI underwent secondary selective IRMPD to form highly 13C-enriched CH2F2 in continuous laser irradiation. The intermediate product in the mixtures of CCl2F2/HI and CBrClF2/HI was found to be CHClF2, but no significant secondary photodecomposition in CBrClF2/HI mixtures occurred owing to the low absorption cross section of CHClF2 at the adopted laser frequencies and fluences. The observed decomposition probabilities and selectivities under different conditions with respect to laser frequency, fluence, and partial pressures of halogenated difluoromethanes and HI suggest that CBr2F2 is one of the better candidates for practical 13C separation by IRMPD.
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  • 98
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    Applied physics 49 (1989), S. 145-148 
    ISSN: 1432-0649
    Keywords: 81.15 ; 82.50
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    Topics: Physics
    Notes: Abstract We use tunable UV laser light in the region 200–320 nm, produced by frequency doubling the output of a dye laser, for the decomposition of organometallic compounds. This method has been applied to TMA, trimethylaluminum Al(CH3)3. Only the TMA monomer absorbs UV light for λ 〉220 nm. TMA decomposes by one-photon absorption mainly into two channels: aluminum atoms Al plus organic fragments, and aluminummonomethyl AlCH3 molecules plus organic fragments. The ratio [Al]/[AlCH3] is wavelength dependent. We present a mechanism to explain the photolysis of trimethyl compounds of group III elements (Al, Ga, In).
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  • 99
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The photophysical properties of a new dye, 7-Diethyl AminoCoumarin with a Rigid substitution in the 3-position (referred to as DARC) have been studied in three solvents: dioxane, DMF and DMSO. The dye has been found to have a fluorescence quantum efficiency (ϕfl) between 0.40 and 0.80 in these solvents. The dye-laser performance of this dye has also been investigated in dioxane, DMF and DMSO, under nitrogen-laser pumping and compared with that of the commercially available standard laser dye, Coumarin 515 (C-515). A tuning range of nearly 70 nm was obtained in the blue-green region with an efficiency up to 80% of that of the standard dye. The observed characteristics of the dye are explained in terms of the sructural rigidization of the dye in the 3-position which inhibits the formation of the Twisted Intramolecular Charge Transfer (TICT) conformation in the excited state leading to an enhancement of theϕ fl and a considerable improvement in the laser performance.
    Type of Medium: Electronic Resource
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  • 100
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 54 (1992), S. 109-112 
    ISSN: 1432-0649
    Keywords: 82.50
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Three schemes for imaging OH with tunable excimer lasers are compared: Excitation and detection at 308 nm (0–0 band, XeCl laser), excitation with a KrF laser at 248 nm (3–0 band) and a new scheme using excitation at 308 nm and detection at 343 nm (0–1 band). Each scheme has certain advantages: The first scheme gives by far the highest signal, the second is less sensitive to collisional quenching and the third is suited to dirty environments because of the long excitation wavelength and off-resonance detection.
    Type of Medium: Electronic Resource
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