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1

Digitale Medien

Proton spin-lattice relaxation dispersion of liquid crystal polymers: Characterization of local and collective motions (1992)

Zeuner, U. ; Dippel, T. ; Noack, F. ; [weitere]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 97 (1992), S. 3794-3802

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: This paper reports on studies of the longitudinal proton spin relaxation dispersion T1Z(ω) of a nematic main chain liquid crystal polymer (M¯n=30 000) over a very broad Larmor frequency range (1 kHz≤ω/2π≤120 MHz). Analysis of the experiments is achieved in terms of a density operator treatment employing the Redfield approximation. The results show that collective motions contribute to the proton spin relaxation process in the kilohertz regime, as found for low molar mass liquid crystals, whereas the conventional megahertz range is dominated by reorientation of individual molecules. The intramolecular motions consist of trans–gauche isomerization and phenyl ring flips. These motions are the fastest in the hierarchy of time with correlation times of 10−10 s in the nematic melt of the polymer at T≈460 K. The intermolecular (whole molecule) motions are interpreted as rotational diffusion in an orienting potential. They exhibit a T1Z(ω)∼ω0.65 dispersion in the megahertz range and have correlation times ranging from 10−9 to 10−7 s at this temperature. The slowest motions affecting longitudinal spin relaxation can be assigned to nematic order director fluctuations characterized by a broad distribution of thermally activated modes. Analysis of the dispersion profiles in the kilohertz regime provides the viscoelastic parameters of the main chain liquid crystal polymer. At T=460 K, an average elastic constant of K=8×10−11 N and an effective viscosity of η=1×103 Pa s have been determined. Using the experimentally accessible value for the short wavelength cutoff of the elastic modes, one obtains the mean-square amplitude of the director fluctuations 〈θ02(approximately-greater-than)=0.02, corresponding to a director order parameter of SOF=0.98. Thus, the contributions of the collective chain motions to the measured order parameters are negligible.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.462960

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2

Digitale Medien

Extension of the tuning range of a femtosecond Ti:sapphire laser amplifier through cascaded second-order nonlinear frequency conversion processes (1994)

Petrov, V. ; Seifert, F. ; Kittelmann, O. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 76 (1994), S. 7704-7712

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: The article presents single step and cascade methods for converting the femtosecond radiation from a 1 kHz repetition rate Ti:sapphire regenerative amplifier to the near-infrared (1.2–1.5 μm and 1.6–2.2 μm), visible (554–593 nm), and for the first time to our knowledge to the vacuum ultraviolet spectral region well below 190 nm. Using only solid state materials (nonlinear optical crystals) femtosecond pulses are generated through phase-matched mixing processes down to 172.7 nm. The developed scheme for femtosecond parametric conversion provides nearly bandwidth limited femtosecond pulses, whose duration is comparable or even shorter than that of the pump pulses. The temporal gain narrowing in the optical parametric amplifier is identified as a pulse compression mechanism on the femtosecond time scale leading to generation of infrared light pulses as short as ≈50 fs. As a whole our all-solid state laser complex provides independently tunable and synchronized sub-200 fs light pulses simultaneously at several wavelengths and practically without relative jitter. © 1994 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.357944

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3

Digitale Medien

Vacuum ultraviolet application of Li2B4O7 crystals: Generation of 100 fs pulses down to 170 nm (1998)

Petrov, V. ; Rotermund, F. ; Noack, F.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 84 (1998), S. 5887-5892

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: We investigate and characterize the newly grown crystal Li2B4O7 which is transparent down to 160 nm for nonlinear optical conversion into the vacuum ultraviolet using sum frequency mixing with femtosecond pulses. This material exhibits excellent properties below 180 nm and makes possible the generation of wavelengths down to 170 nm with an all solid state laser system. The most important advantage of Li2B4O7 in this spectral range turns out to be the possibility of utilizing noncritical phase matching with maximized effective nonlinearity. We demonstrate generation of nearly transform limited 100 fs pulses between 170 and 185 nm with conversion efficiency of 4%. Their peak powers range from 200 kW at 170 nm to 〉2 MW at 185 nm. © 1998 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.368904

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4

Digitale Medien

High repetition rate traveling wave optical parametric generator producing nearly bandwidth limited 50 fs infrared light pulses (1994)

Petrov, V. ; Seifert, F. ; Noack, F.

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 65 (1994), S. 268-270

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ISSN: 1077-3118

Quelle: AIP Digital Archive

Thema: Physik

Notizen: A 1 kHz Ti:sapphire femtosecond regenerative amplifier system is used to pump a lithium triborate optical parametric generator in a type II noncritical phase matching configuration and a β-barium borate parametric amplifier. Infrared pulses near 1460 nm as short as 50 fs are achieved with a pulse duration/bandwidth product of only 0.44.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.112367

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5

Digitale Medien

A New Freezing Mixture (1929)

Noack, F.

s.l. : American Chemical Society

Industrial & engineering chemistry 21 (1929), S. 1001-1001

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ISSN: 1520-5045

Quelle: ACS Legacy Archives

Thema: Chemie und Pharmazie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1021/ie50239a003

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6

Digitale Medien

Optical parametric generation of femtosecond pulses up to 9 μm with LiInS2 pumped at 800 nm (2001)

Rotermund, F. ; Petrov, V. ; Noack, F.

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 78 (2001), S. 2623-2625

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ISSN: 1077-3118

Quelle: AIP Digital Archive

Thema: Physik

Notizen: We demonstrate direct access to the 4.8–9 μm spectral region with 800 nm, 1 kHz pumping of a femtosecond optical parametric amplifier based on the wide-gap wurtzite-type LiInS2. LiInS2 did not exhibit two-photon absorption at 800 nm and seems applicable at this pump wavelength with intensities of the order of 100 GW/cm2 for down-conversion of high energy ultrashort pulses up to its mid-IR edge at (approximate)12 μm. © 2001 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1369386

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7

Digitale Medien

Nuclear magnetic resonance field-cycling proton relaxation study of polymer dispersed liquid crystals (1996)

Schwarze-Haller, D. ; Noack, F. ; Vilfan, M. ; [weitere]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 105 (1996), S. 4823-4832

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: The frequency and temperature dependence of the longitudinal proton relaxation time T1 has been studied in liquid crystal droplets embedded in a solid polymer matrix in the nematic and isotropic phase over a broad Larmor frequency range (500 Hz≤νL≤84 MHz) employing the fast-field-cycling technique. The comparison of the droplet data, bulk 5CB data, and the pure polymer data show that T1 is dominated by the cross relaxation at the liquid crystal–polymer interface in the entire frequency range. In the low frequency range (νL≤1 MHz), an additional relaxation process determines T1 in both phases, namely reorientations mediated by translational replacements in the nematic phase and the exchange relaxation in the isotropic phase. The analysis of the cross relaxation rate k reveals that the simplified model of Vilfan is only applicable in the nematic phase and leads to an anchoring time τAS of the molecules at the surface which is ≈1.3×10−4 s. This model, however, cannot be applied in the isotropic phase, but must be extended by the spin diffusion time τP, which in this case determines the cross relaxation rate. The anchoring time τAS, which in the isotropic phase corresponds to the correlation time of the additional process, is much shorter than in the nematic phase, namely τAS≈10−6 s. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.472319

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8

Digitale Medien

NMR relaxation investigation of water mobility in aqueous bovine serum albumin solutions

Grosch, L. ; Noack, F.

Amsterdam : Elsevier

BBA - Protein Structure 453 (1976), S. 218-232

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ISSN: 0005-2795

Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Thema: Biologie

Materialart: Digitale Medien

URL: http://linkinghub.elsevier.com/retrieve/pii/0005-2795(76)90267-1

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9

Digitale Medien

A high-field air-cored magnet coil design for fast-field-cycling NMR

Schweikert, K.H. ; Krieg, R. ; Noack, F.

Amsterdam : Elsevier

Journal of Magnetic Resonance (1969) 78 (1988), S. 77-96

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ISSN: 0022-2364

Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Thema: Physik

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1016/0022-2364(88)90158-8

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10

Digitale Medien

A powerful NMR field-cycling device using GTOs and MOSFETs for relaxation dispersion and zero-field studies

Rommel, E. ; Mischker, K. ; Osswald, G. ; [weitere]

Amsterdam : Elsevier

Journal of Magnetic Resonance (1969) 70 (1986), S. 219-234

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ISSN: 0022-2364

Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Thema: Physik

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1016/0022-2364(86)90004-1

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