CaltechAUTHORS: Article
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A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenFri, 06 Sep 2024 18:57:09 -0700Self-trapping of optical beams in photorefractive media
https://resolver.caltech.edu/CaltechAUTHORS:CROjosab93
Year: 1993
We study the possibility of self-trapping of an optical beam in a photorefractive medium under the combined influence of diffraction and self-scattering (two-wave mixing) of its spatial frequency components. We investigate the spectrum of solutions for the resulting photorefractive spatial solitons and discuss their unique properties. Design considerations and material requirements for experimental realization of these solitons, together with specific examples, are given.https://resolver.caltech.edu/CaltechAUTHORS:CROjosab93Temporal evolution of fanning in photorefractive materials
https://resolver.caltech.edu/CaltechAUTHORS:SEGol93a
Year: 1993
We present detailed calculations of the temporal and spatial evolution of beam fanning in photorefractive crystals that is initiated by scattering from noise. We show that fanning starts from beam coupling between the incident radiation and part of the incident radiation scattered by noise at or near the input plane. We show that scattering within the volume of the crystal has negligible effect on fanning, that absorption affects the time response but not the spatial pattern of the fanning, and that the difference between calculations including only phase-matched terms and those including non-phase-matched terms is negligible.https://resolver.caltech.edu/CaltechAUTHORS:SEGol93aTemporal evolution of photorefractive double phase-conjugate mirrors
https://resolver.caltech.edu/CaltechAUTHORS:SEGol93b
Year: 1993
We present wave-optics calculations of the temporal and spatial evolution from random noise of a double phase-conjugate mirror in photorefractive media that show its image exchange and phase-reversal properties. The calculations show that for values of coupling coefficient times length greater than two the process exhibits excellent conjugation fidelity, behaves as an oscillator, and continues to operate even when the noise required for starting it is set to zero. For values less than two, the double phase-conjugation process exhibits poor fidelity and disappears when the noise is set to zero.https://resolver.caltech.edu/CaltechAUTHORS:SEGol93bDouble phase conjugation
https://resolver.caltech.edu/CaltechAUTHORS:ENGjosab94
Year: 1994
We model the double phase-conjugate mirror (DPCM) as a function of time, the average direction of propagation of the two beams forming the DPCM, and one transverse coordinate. Calculations show that the conjugation fidelity and reflectivity have different dependencies on the photorefractive coupling coefficient times length; the fidelity turns on abruptly with a threshold, whereas the reflectivity increases smoothly. The DPCM behaves as an oscillator at and above threshold: the time required for the reflectivity to reach the steady state dramatically slows down near threshold (like critical slowing down in lasers); above threshold the DPCM is self-sustaining even if the random noise terms used to start the process are set to zero. A decrease in the noise level improves the fidelity but increases the response time. The use of unbalanced input beam ratios results in asymmetric conjugation such that the fidelity obtained on the side of the weaker input beam is significantly reduced. The slowing down diminishes with increasing noise level or unbalanced input intensities.https://resolver.caltech.edu/CaltechAUTHORS:ENGjosab94Fixing of photorefractive volume holograms in K1-yLiyTa1-xO3
https://resolver.caltech.edu/CaltechAUTHORS:LEYol95
Year: 1995
We report the f ixing of photorefractive holographic gratings with high eff iciency in a sample of K1-yLiyTa1-xNbxO3 doped with Cu, V, and Ti. Holograms are thermally fixed through the screening of a photorefractive space-charge field by a nonphotoactive species at elevated temperatures. Fixed holograms are revealed by illumination at lower temperatures. Diffraction efficiencies of 25% in a 0.54-cm-thick sample are measured. Holograms undergo thermal decay with a 0.67-eV activation energy.https://resolver.caltech.edu/CaltechAUTHORS:LEYol95Amplitude-equation formalism for four-wave-mixing geometry with transmission gratings
https://resolver.caltech.edu/CaltechAUTHORS:ENGjosab97
Year: 1997
An amplitude equation is derived for a four-wave-mixing geometry with nearly counterpropagating, mutually incoherent, nondiffracting pump beams, spatially overlapping in a photorefractive material with a nonlocal response. This equation extends the earlier linear two-dimensional theory to the weakly nonlinear regime. The analysis also starts from a more complete equation for the photorefractive effect, which leads to the prediction of novel effects especially apparent in the nonlinear regime. Precise predictions for the spatiotemporal behavior of the grating amplitude in the nonlinear regime are presented. The range of validity of the amplitude equation is studied. The characteristics of the instability in the nonlinear regime are analyzed through a front-selection analysis.https://resolver.caltech.edu/CaltechAUTHORS:ENGjosab97Holographic characterization of chain photopolymerization
https://resolver.caltech.edu/CaltechAUTHORS:ENGjosab99
Year: 1999
A holographic characterization technique is developed in accordance with a general photopolymerization model. The technique allows detailed quantification of the chemical parameters, including their variation from the Trommsdorff effect. The holographic procedure is especially suited for studying the diffusion of the chemical reactants.https://resolver.caltech.edu/CaltechAUTHORS:ENGjosab99Chirped Laser Seeding for SBS Suppression in a 100-W Pulsed Erbium Fiber Amplifier
https://resolver.caltech.edu/CaltechAUTHORS:20150602-134628255
Year: 2015
DOI: 10.1109/JQE.2015.2425963
A pulsed Er/Yb fiber amplifier is seeded with a frequency-chirped diode laser for the purpose of suppressing stimulated Brillouin scattering (SBS), as an alternative to the conventional broadband seed. SBS in the final stage of the amplifier limits the output power. A chirp of 5 ยท10^(15) Hz/s is seen to increase the SBS threshold by nine times, compared with the case with no chirp. The final stage of the amplifier is modeled with a system of equations that are solved for the laser field, Stokes field, acoustic field, pump power, amplified spontaneous emission power, Yb inversion, and Er inversion, as a function of z and t. The experimental and theoretical results are in good agreement. The SBS threshold scales linearly with chirp, when the effective seed linewidth (the product of chirp and fiber transit time) is much greater than the Brillouin linewidth.https://resolver.caltech.edu/CaltechAUTHORS:20150602-134628255