Dimensionality and size of photorefractive spatial solitons

We study experimentally self-trapping of optical beams in photorefractive media and show that the trapping is inherently asymmetric with respect to the two (transverse) trapping dimensions. We also present experimental results that show how the sizes of the resultant photorefractive spatial solitons are independent (within their range of existence) of the amplitude of the externally applied electric field used to generate them

Photorefractive Dark and Vortex Solitons

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Photorefractive self-focusing and defocusing as an optical limiter

Focusing and defocusing of laser light has been observed for many years. Kerr type materials exhibit this effect but only for high intensities. We show experimental evidence that photorefractive materials can also produce dramatic focusing and defocusing. Whereas Kerr materials produce this effect for high intensities, photorefractive materials produce these effects independent of intensity indicating that this effect would be ideal for an optical limiter. We compare the characteristics of Kerr and photorefractive materials, discuss the physical models for both materials and present experimental evidence for photorefractive defocusing. Self-focusing and defocusing was observed for any incident polarization although the effect was more pronounced using extraordinary polarized light. In addition, self-focusing or defocusing could be observed depending on the direction of the applied electric field. When the applied field was in the same direction as the crystal spontaneous polarization, focusing was observed. When the applied field was opposite the material spontaneous polarization, the incident laser light was dramatically defocused

Laser-Induced Photon-Branched Chain Reaction in a Chemically-Active Gas-Dispersed Medium

A promising avenue in the development of high-energy pulsed chemical HF/DF lasers and amplifiers is the utilization of a photon-branched chain reaction initiated in a two-phase active medium, that is, a medium containing a laser working gas and ultradispersed passivated metal particles. These particles are evaporated under the action of IR laser radiation which results in the appearance of free atoms, their diffusion into the gas, and the development of a photon-branching chain process, which involves photons as both reactants and products. The key obstacle here is the formation of a relatively large volume (in excess of 10^3 cm^3) of the stable active medium and filling this volume homogeneously for a short time with a submicron monodisperse metal aerosol, which has specified properties. In this paper, results are presented for an extensive study of laser initiation of a photon-branched chain reaction in a gas-dispersed H2- F2 medium

Ultrashort Laser Pulse Heating of Nanoparticles: Comparison of Theoretical Approaches

The interaction between nanoparticles and ultrashort laser pulses holds great interest in laser nanomedicine, introducing such possibilities as selective cell targeting to create highly localized cell damage. Two models are studied to describe the laser pulse interaction with nanoparticles in the femtosecond, picosecond, and nanosecond regimes. The first is a two-temperature model using two coupled diffusion equations: one describing the heat conduction of electrons, and the other that of the lattice. The second model is a one-temperature model utilizing a heat diffusion equation for the phonon subsystem and applying a uniform heating approximation throughout the particle volume. A comparison of the two modeling strategies shows that the two-temperature model gives a good approximation for the femtosecond mode, but fails to accurately describe the laser heating for longer pulses. On the contrary, the simpler one-temperature model provides an adequate description of the laser heating of nanoparticles in the femtosecond, picosecond, and nanosecond modes

Photorefractive spatial solitons—theory and experiments

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