V.Ya. Gayvoronsky

Impact of incorporated anatase nanoparticles on the second harmonic generation in KDP single crystals

The second harmonic generation efficiency was studied for the single crystalline potassium dihydrogen phosphate matrix with incorporated TiO2 nanocrystals in the field of the mode-locked Nd:YAG laser pulses. For the first time the frequency conversion efficiency gain was observed for KDP:TiO2 single crystal (SC) instead of KDP SC due to the internal self-focusing effect of the pump beam caused by the giant cubic nonlinear optical response of the embedded nanoparticles.

Optimization of Diffraction Efficiency and Gain for Two-Wave Mixing in Cubic (111)-Cut Photorefractive Piezocrystals

The dependence of the diffraction efficiency of holograms and the effective gain of the signal wave on the polarization and orientation angles is investigated for two-wave mixing in transmission geometry in cubic (111)-cut photorefractive piezocrystals (classes 23 and 43 m). It is shown theoretically and experimentally that in 2.1 mm thick BSO crystals (class 23) the piezoelectric effect leads to an increase of the diffraction efficiency by 70% and of the gain by 30% for certain values of the polarization and orientation angles. Without the piezoelectric effect the diffraction efficiency does not depend on polarization and orientation angles in both optically active (BSO) and optically inactive (GaAs) crystals, whereas the effective gain depends on polarization and orientation angles while its maximum value remains constant. It is found that for thickness of BSO crystal 8.2 mm the diffraction efficiency and the effective gain do not depend on polarization of reading light. For the first time the experimental dependence of maximum diffraction efficiency of hologram in (111)-cut BSO crystal on the orientation angle θ is found. The results of the experiment confirm correctness of chosen physical model of the diffraction.

Structure-sensitive changes in the terahertz absorption spectra of merocyanine dye derivatives

The low-frequency vibrational modes of the series of merocyanines (malononitrile derivative) have been investigated by pulsed terahertz spectroscopy. The terahertz absorption spectra are shown to contain both intermolecular and intramolecular vibrational modes in the range of 0.15–3.45 THz (5–115 cm−1). An unambiguous correlation is established between the purposeful modification of the molecular structure of merocyanine dyes and the change in their terahertz absorption spectra.

Attractors and auto-oscillations for feedback controlled photorefractive beam coupling

Abstract We investigate the physics of a novel nonlinear system, feedback controlled photorefractive beam coupling. Inertia of the electronic feedback is found to be an element crucial for permanent operation of this system. Theoretically and experimentally we have found a wealth of periodic and quasi-periodic regimes for observable characteristics of the feedback controlled wave coupling. A good qualitative agreement between theory and experiment is obtained for LiNbO 3 crystals.

Broadband second-harmonic and sum-frequency generation in KH2PO4 crystals doped with anatase nanocrystals

Broadband second-harmonic (SH) and sum-frequency generation was studied in KH2PO4 crystals with incorporated anatase modification of titania nanocrystals. A tiny amount (10−5 wt.%) of titania nanoparticles in the anatase phase exhibits a pronounced (up to 15%) increase of the SH efficiency in comparison with the nominally pure potassium dihydrogen phosphate (KDP) crystal. Higher anatase fraction (10−4 wt.%) results in a reduction of the SH conversion efficiency. The rise of the SH signal is attributed to resonant excitation of the defect states at the nanocrystal interface, and its subsequent decrease at higher concentration is likely to be related to a light scattering in the crystal bulk.

Diffusion recording in photorefractive sillenite crystals: an analytical approach for engineering purposes

Simple formulae for the two-wave mixing (TWM) gain and diffraction efficiency obtained in the approximation of weak coupling and strong optical activity allow us to tune the experimental setup for interferometric applications. We prove that two invariant parameters, trace and determinant of the coupling tensor, are sufficient to optimize the experimental setup. Both practically important crystal cuts, (110) and (111), can be treated in a unified manner. Fundamental TWM properties (90°-jumps of the optimum polarization, apparent doubling of the local maxima of the diffraction efficiency in comparison with the gain, drastic changes between regimes of small and large polarization rotation, the crucial role of elastooptic properties) are systematized. The guidelines for the design of an optimum experimental setup for interferometric applications including anisotropic self-diffraction using sillenite crystals are presented. Quantitative agreement with previous experimental data is demonstrated.

Optimization of diffraction efficiency and gain for two-wave mixing in cubic (111)-cut photorefractive piezocrystals

The dependence of the diffraction efficiency of holograms and the effective gain of the signal wave on the polarization and orientation angles is investigated for two-wave mixing in transmission geometry in cubic (1 1 1)-cut photorefractive piezocrystals (classes 23 and 43m). It is shown theoretically that maximum diffraction efficiency and gain in BSO and GaAs depend on the orientation angle. It is confirmed experimentally for BSO crystal (class 23). It is obtained theoretically and experimentally that in 2.1 mm thick BSO crystals the piezoelectric effect leads to an increase of the diffraction efficiency by 70% and of the gain by 30% for certain values of the polarization and orientation angles.

Nonlinear optical analysis of bulk oxidized carbonaceous materials response

In this study the nonlinear optical response of porous μm sized carbonaceous particles (cp) was studied within the self-action of 42 ps laser pulses at 1064 nm. Photoinduced absorption efficiency (PAE) of air-thin layer of cp was examined versus the total surface area of cp. The porous thin layer shows predictably discrete response, depending on the level of the surface oxidation. Surprisingly, the ratio between PAE and the surface area show a constant trend within the experimental error range. This observation makes NLO response a promising regulator could be used in metrology of related bulk porous materials.

Characterization of improved laser phosphate glasses

Improved laser phosphate glasses were obtained varying the glass formula with Ba²⁺ and Sr²⁺. The absorptive nonlinear optical (NLO) response at two regimes was used for monitoring the figure of merit of glass media. The NLO response efficiency is affected by Sr²⁺ addition. The equimolar ratio of Ba²⁺ to Sr²⁺ in the host glass matrix gives improved composition with the lowest value of Im(x⁽¹³⁾) and highest matrix rigidity. UV-Vis analysis confirms the observations obtained from an analysis of optical scattering. The mixed Sr/Ba laser glasses supposed to have a high potential in the field of laser optics.

Linear and Nonlinear Optical Properties of Merocyanines Derivatives of Malonodinytriles

A detailed complex study of the series of neutral merocyanine derivatives of malonodinytriles with variable donor terminal groups and with the same acceptor group is carried out. The absorption spectra and nonlinear optical (NLO) characteristics are measured. It is shown that the long-wavelength absorption band is highly sensitive to the donor strength of the variable residue terminal group. The distinct dependence of the state dipole moments and characteristics of the electron transitions on the chemical constitution of merocyanine molecules was confirmed by quantum-chemical calculations. An analysis of the obtained results shows that the change in the electron characteristics of the ground and excited states due to variations in the chemical constitution of merocyanine molecules is accompanied by sensible variations in the NLO response. With allowance for the calculation, the effect of molecular topology on the experimental linear and NLO characteristics could be correctly interpreted.