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  • 1
    Electronic Resource
    Electronic Resource
    Temperature dependence of the photorefractive effect in undoped Bi12GeO20 (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 783-789 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The low-temperature four-wave mixing (FWM) photorefractive response was investigated in undoped Bi12GeO20 (BGO) crystals. The FWM diffraction efficiency increases as the temperature is lowered until a local maximum is reached after which it decreases. The temperature where the maximum intensity FWM signal occurs depends on the write conditions. A model assuming both electron and hole gratings was used to describe the observations. Two shallow trap levels of 0.015 and 0.08 eV were identified as being responsible for the fast decay (〈1 s) components of the FWM signal in undoped BGO.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354866
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  • 2
    Electronic Resource
    Electronic Resource
    Effects of the structure and composition of lead glasses on the thermal lensing of pulsed laser radiation (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 3693-3700 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The thermal lensing characteristics of several silicate, germanate, phosphate, and borate glasses were studied using a laser with a 7 ns pulse at 457 nm in a tight focus geometry. A geometric model was developed to describe the quadratic radial profile of the refractive index resulting from the laser-induced temperature profile. This model was utilized to interpret the effects of some of the relevant experimental parameters on the fluence transmission experiments. The influence of material properties such as different types of network former and modifier ions on the nonlinear optical properties of these materials were also studied. It was found that: (i) the greatest influence of the network modifier ions was due to their effect on the absorption coefficient of the glasses; (ii) in lead glasses, the thermo-optic coefficients dn/dT of the germanates and silicates with random network structures were greater than those of the borate and phosphate glasses with ring and chain structures; and (iii) the main contribution to the thermo-optic coefficient comes from the thermally induced changes in the electronic polarizability of the glass components. In these glasses, the oxygen polarizability provides the dominant contribution and is affected by the variations in the polarizing power (charge to radius-squared ratio) of the network former ions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350879
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  • 3
    Electronic Resource
    Electronic Resource
    Origin of picosecond-pulse-induced, degenerate four-wave-mixing signals in KTa1−xNbxO3 crystals (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 20-28 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Transient gratings have been produced in KTa1−xNbxO3 by picosecond-pulse, two-photon excitation using degenerate four-wave-mixing techniques. The excitation process has been characterized through fluorescence studies, and the fluorescence is attributed to the transition between an excited state and the ground state of B4+ ions that are produced in ABO3 perovskite crystals. Strong electron-phonon coupling gives rise to the luminescence quenching. The observed degenerate four-wave-mixing signal is shown to be due predominantly to a phase grating caused by a change in the susceptibility associated with the formation of Nb4+ or Ta4+ ions in the peak region of the grating. The grating signal intensity was found to be dependent on the concentration of niobium ions and the crossing angle of the two laser write beams.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350312
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  • 4
    Electronic Resource
    Electronic Resource
    Refractive index gratings in rare-earth-doped alkaline earth glasses (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 913-917 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Four-wave-mixing techniques were used to produce permanent laser-induced refractive index gratings in Eu3+ -doped silicate glasses. These gratings are associated with a thermally induced change in the local glass structure at the site of the Eu3+ ions, leading to a double-minimum potential well for the electronic energy levels of the Eu3+ ions. The effects on the characteristics of the permanent laser-induced gratings produced by changing the divalent modifier ions of the glass host are reported and a theoretical model is presented to explain the physical origin of the change in the refractive index of the material.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347333
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  • 5
    Electronic Resource
    Electronic Resource
    Investigation of the photorefractive effect in Bi2TeO5 (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 5465-5473 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Single crystals of Bi2TeO5, both undoped and doped with transition-metal-ion dopants, were grown with high optical quality. Continuous-wave four-wave-mixing experiments on these crystals show a strong photorefractive signal with a multicomponent decay. The photorefractive efficiency was studied as a function of the wavelength, intensity, polarization direction, and crossing angle of the laser write beams, and the sample orientation. Both absorption and phase gratings were observed with their relative strengths dependent on the laser wavelength and sample dopants. The signal evolves in time from a defect population grating, to trapped charge gratings involving two different types of traps, to fixed gratings produced by oxygen ion displacements. The photorefractive effect in this material is found to be of the photoconductive type and it produces a larger diffraction efficiency than that observed in sillenite materials under the same experimental conditions. A mechanism is proposed for the various physical processes leading to the different decay components of the signal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350518
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  • 6
    Electronic Resource
    Electronic Resource
    Site-selection spectroscopy, energy transfer, and laser emission in Nd3+-doped Ba2MgGe2O7 (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 6372-6379 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A detailed spectroscopic and pump wavelength dependent laser study has been performed on Nd3+ ions in Ba2MgGe2O7. Site-selection spectroscopy experiments reveal fifteen distinct crystal field sites for the Nd3+ ions. At room temperature, excitation of ions in any one of these sites is followed by efficient, thermally activated energy transfer to ions in a site having a laser emission transition at 1054 nm. Laser-pumped laser experiments were performed to determine the pumping threshold and slope efficiency of laser action in this material for different monochromatic pump wavelengths. The measured slope efficiencies were found to be pump wavelength dependent and ranged from 6% to 22%. Excited-state absorption of pump photons was shown to be responsible for this variation in the slope efficiency.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346884
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  • 7
    Electronic Resource
    Electronic Resource
    Nonradiative energy-transfer processes in Cd1−xMnxF2 crystals (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 28-36 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The absorption and fluorescence spectra and fluorescence decay kinetics of Cd1−x MnxF2 crystals with x=0.018, 0.063, 0.084, 0.26 were measured as a function of temperature under argon-ion and nitrogen laser excitation. In addition, laser-induced grating measurements were made as a function of write beam crossing angle for various temperatures between 15 and 50 K. It was found that a characteristic intrashell luminescence comes from two Mn subsystems, one composed of single Mn2+ ions and the second of Mn ion aggregates. Based upon the four-wave-mixing experiment, a relatively strong energy migration was found in each of these subsystems, but with a weak, if any, communication between them. The diffusion coefficients for both subsystems increase as the temperature is raised, and above 50 K strong diffusion erases the light-induced gratings beyond the possibility of detection. The long-lived components of the four-wave-mixing transient signals are associated with the other point defects, either created or photoexcited by the strong laser beams.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350703
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  • 8
    Electronic Resource
    Electronic Resource
    The dependence of laser-induced refractive index changes in glass on the chemical composition (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 6083-6091 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The properties of permanent, laser induced refractive index gratings in rare-earth doped glasses have been characterized in a variety of materials including lithium borates, lead and magnesium silicates, lead borate-germanates and lead germanates. This work is combined with the previous results obtained on phosphate and silicate glasses to develop an understanding of the effects of glass composition (both network former and modifier ions) on the ability of a material to produce gratings with high scattering efficiencies. The grating efficiencies and the writing/erasing dynamics were studied, and the two-level-system-model developed previously was employed to explain the results. The results show the importance of having flexible glass networks with low polarizing power of the network former ions, and a high content of nonbridging oxygen ions. In addition, it is important to have light, highly polarizable modifier ions with weak chemical bond strengths to the oxygen ions. This type of glass combined with rare-earth ions that like to exist in more than one local coordination environment and that couple strongly to high energy vibrational modes of the host, are found to be very effective in producing local structural changes that lead to room-temperature-stable refractive index gratings.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464847
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  • 9
    Electronic Resource
    Electronic Resource
    Determination of nonlinear susceptibilities by transforming random variables (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6735-6740 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-peak-power lasers are typically used as pump sources in nonlinear optical measurements. Intrinsic to these sources are pulse-to-pulse output energy instabilities. We report on how pump instabilities affect the measurement of nonlinear susceptabilites and develop theory which relates statistical parameters of a general, arbitrary pump energy probability distribution to those of its corresponding mth harmonic output. The relation leads to a simple method of data analysis whereby pump instabilities can be used as a tool in determining the nonlinear susceptibility of a material. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361494
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  • 10
    Electronic Resource
    Electronic Resource
    Contribution of second-harmonic generation to the creation of free carriers in CdTe single crystals (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 1632-1634 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is shown that cadmium telluride exhibits second-harmonic generation under 1064 nm ps pulse excitation despite strong absorption of the green light which is generated. The process of second-harmonic generation contributes to the creation of an electron-hole plasma in CdTe which affects the measured value of the two-photon absorption coefficient and other nonlinear properties of the material.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.103148
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