We will show that, in three-mode approximation, an exact analytic solution of a steady-state parametric frequency
conversion problem can be obtained by analytic solution of independent nonlinear Schrodinger equations with
corresponding coupled boundary conditions.
We show the speed of response of a photorefractive self-pumped phase-conjugate mirror can be considerably (6 - 20 times) accelerated by special training procedures. Efficiency of some such procedures is compared and analyzed.
We show that experimental data, obtained by picosecond biharmonic pumping technique for high-temperature
superconductive (Y-Ba-Cu-O) films, can be interpreted in terms of non-equilibrium electronic states with a 'frozen'
(meta-stable) energy gap in the electronic spectrum.
It is shown that stability of Henyey-Greenstein phase function gives a possibility to solve quickly a multiple-scattering
light propagation problem with the same a priori information about interaction as in the primary problem definition.
In the paper we will show that formation of a phase-conjugated wave in a self-pumped phase-conjugate mirror can be
considerably (6 - 20 times faster) accelerated by a special training procedure. Efficiency of some static and dynamic
training procedures will be compared and analyzed.
It will be shown that stability of the Henyey-Greenstein phase function gives a possibility to solve quickly a multiple-scattering light propagation problem with the use of the same a priori information about the interaction processes as in the primary problem definition.
We show that both the spectral-temporal and temperature "anomalies" of experimental data, obtained by pump-probe spectroscopy of HTSC compounds, can be interpreted with taking into account inter-band electronic transitions and a "frozen" energy gap in the sample electronic spectrum.
Dynamics of self-pumping photorefractive double phase-conjugate mirrors is considered. It is shown that depending on experimental conditions as phase-conjugation with efficiency up to 60-80 % as formation of unstable structures of soliton-like filaments can be realized.
Accuracy of some approximate ultra-fast algorithms, specially developed for real-time solution of direct and inverse problems of diffusion optical tomography of extra-large (with size about 1000 scattering lengths and more) objects, will be considered.
A new ultra-fast (increasing the calculation rate about 9 orders and more) calculation scheme, enabling one to solve small-angle multi-scattering problems for large (size about 100 scattering lengths and more) objects is described.
It will be shown that experimental data, obtained by pump-probe measurements in HTSC compounds, can be interpreted in terms of long-living meta-stable non-equilibrium states with specific energy gap and rather high (up to 600 K) electronic temperature.
A new laser technology, based on spatiallyl non-uniform illumination of ultra-thin ferromagnetic films by short trains of ultra-short laser pulses and enabling to create the regular domain structures, is presented.
Fast approximate statistical nonlinear algorithm of the diffusion optical tomography inverse problem solution has been described. Results of this algorithm approbation by the example of reconstruction of a rather complicated internal structure of strongly scattering and weekly absorbing large- size model objects have been presented. CW radiation of low- power diode lasers of near IR region has been used in experimental realizations.
On the basis of experimental data of degenerate four-photon spectroscopy of Ni, Au and Pt ultra-thin (with the thickness approximately 10 divided by 20 nm) films, a conclusion about a predominant role of inter-band electronic transitions under formation of a nonlinear response of such films in the visible range has been made. It has been shown that, when a metal film thickness is smaller than the mean-free path, thermalization and cooling of optically excited electronic subsystem result from an ultra-fast inelastic scattering of excess free carriers on the film surface. Numerical estimations, performed for ultra-thin Ni films, have shown that, thanks to this scattering process, up to 10% of picosecond (duration approximately 20 ps) pump pulse energy can be transformed to the surface deformations. In case of spatially non-uniform optical excitation, an efficient direct generation of the surface acoustical waves can be realized.
To interpret the data of transient nonlinear spectroscopy of cooper-oxide high-temperature superconductors, a phenomenological model, describing magneto-dipole self- organization of holes in CuO2 planes and kinetics of the corresponding phase transition, has been developed. It has been shown that, for the exchange energy approximately 100 meV and the doping level <n> approximately 0.1 hole/cell, the temperature T decreases below the critical point T* approximately 150 K leads to formation of a spatially non-uniform distribution of holes (the stripe- structure) and to appearance of corresponding energy gap in the electronic structure. Calculated steady-state dependencies of T* on <n> and of the gap width on T agree with the known experimental data. The predicted phase transition kinetics depends on the initial temperature T. When T* < T < Tm approximately equals (1.4 divided by 1.5) T*, the stripe-structure decay is rather slow (approximately 10-9s and more) two-stage process. During the first stage, a large-scale fluctuation of an average dipole moment is formed and after that the spatial region, entrained in the fluctuation, broadens as the phase switching wave.
New class of stable multicomponent self-consistent light field distributions is presented by the example of a problem of nonlinear wave propagation through a photorefractive crystal with drift nonlinear response. Exact analytical expressions for light field distributions of the components of such periodical solutions, which include up to three mutually incoherent light field components, have been obtained. It has been shown that such cnoidal waves are stable and their spatial structure is robust to collisions with the same cnoidal waves and to stochastic perturbations of the intensity.
We propose new and promising technique for studying quantum- size structures. We tested this technique based on optical two-photon excitation and probing of renormalized electron spectrum in our investigation of monocrystalline PbTe films. We revealed sharp dependence of spectral position of two- photon resonances versus film thickness L equals 6, 18, and 30 nm. Our theoretical model explained this result by taking into account Pb Te band structure, electron-electron and electron-phonon interactions, and redistribution of charge carriers due to inter- and intraband processes. Estimation T2 >= 300 fs for decay time of interband polarization was obtained.
A new efficient numerical scheme for solution of problems simulating dynamics of nonlinear interaction in photorefractive crystals has been developed and tested. Using the criterion of maximal mitigation of dynamic phase distortions, the processes of two- and four-beam interaction in InP:Fe has been optimized.
We propose new and promising procedure for nonlinear spectroscopy of high-Tc superconductive thin films. It enables us to determine the phase transition temperature, superconducting energy gap width, interaction constants, etc. For Y-Ba-Cu-O thin films, we present our results in testing of this procedure including investigation of relaxation kinetics after picosecond optical excitation of the film.
An effective procedure for nonlinear spectroscopy of high-Tc superconductive thin films is proposed. It enables to determine as their phase, as critical temperature, superconducting energy gap width, constants of interaction, etc. Results of its testing for Y-Ba-Cu-O thin films are presented, including results of investigation of relaxation kinetics of preliminary picosecond optical excitation.
By picosecond spectrometer with two tunable dye lasers, high temperature superconducting (HTSC) (monocrystal Y-Ba-Cu-O with critical temperature Tc equals 87 K) and metal (Ni) thin films have been investigated. A self-diffraction process efficiency (eta) versus biharmonic pumping component detuning (Omega) has been measured at the temperature (Theta) equals 300 and 80 K. It is found that there is a well-defined dip on the dispersion curve (eta) ((Omega) ) for the HTSC films at (Theta) equals 80 K and -10 cm-1 (Omega) -50 cm-1. This region upper limit corresponds to a superconducting energy gap value 2(Delta) . At 10 cm-1 -1, any distinction of the same type is absent. In other respects all obtained dispersion curves are similar. They consist of the central peak ((eta) approximately equals 10-7, (Omega) -1) and wide wings ((eta) approximately equals 10-9, (Omega) 10 cm-1) with the interference structure. Y-Ba-Cu-O film resonances are coincided with the phonon mode frequencies (120, 335, and 580 cm equals -1). It is shown that photoexcitation kinetics (the sample ''darkening'') must consist of some components. A characteristic time of the most ''ultrafast'' component below 5 fs has been estimated and a complex subpicosecond quantum beats presence has been predicted.
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