Stationary Energy Transfer Research Articles

Dynamic interferometer on the base of Sn2P2S6 photorefractive crystal modified by indiffusion of Cu

Introduction: The photorefractive parameters of the Sn 2 P 2 S 6 single crystals modified by different ways (doping, post-growth treatment) permit to realize the dynamic interferometers. A specific interest represent the samples with strong compensation process. Purpose: This article is devoted to consideration of usage of the Sn 2 P 2 S 6 crystal modi­fied by an indiffusion of the Cu atoms as an active element of the dynamic interfe­rometer, and analyzing of its frequency parameters. Results: The diffusion-modified Sn 2 P 2 S 6 sample demonstrates an increased com­pen­sation of the photorefractive gratings that manifests itself in the complex dyna­mics of the stationary energy transfer. This peculiarity is also observed in the frequency spectra mea­sured at the phase modulation of the interacting beams. These frequency spectra of the first and second harmonics, as well as the corresponding stationary component, are obtained and analysed. Conclusion: The dynamic interferometer on the basis of the Cu-doped Sn 2 P 2 S 6 with strong gain compensation allows to construct the band-pass frequency filters, and also to study the two-wave mixing gain spectrum using frequency-modulation technique.

Photorefractive properties of near-stoichiometric LiNbO3 grown from congruent melts containing K2O

The photorefractive properties of nominally pure near-stoichiometric LiNbO3 crystals grown from congruent melts containing 11 mol % K2O are studied, and some photorefractive properties which are very different from those in congruent LiNbO3 crystals are observed. Large stationary energy transfer (Γmax=25 cm−1) exists in near-stoichiometric crystals though the photovoltaic field is dominant. The light-induced scattering fanning is markedly asymmetric in the crystals, which is very different from the symmetric fanning observed in congruent ones. Our analysis shows that these differences are caused by the large photovoltaic field and the relatively small density of filled traps in as-grown near-stoichiometric LiNbO3.

The influence of light scattering on energy transfer in hologram recording in PLZT ceramics

A theoretical and experimental study of the influence of holographic noise gratings on the stationary energy transfer in hologram recording is made for the transparent ferroelectric ceramic PLZT 10/65/35. The effect of an isolated noise wave on the energy transfer is considered within the limits of the dynamic theory of hologram recording developed by Kukhtarev et al. The proposed model explains, qualitatively well, the observed gain factor decrease for thick samples. The significant role of noise gratings in PLZT is supported by the observations for the first time of photo-induced coherent light scattering.

Intensity dependence of stationary energy transfer in degenerate two-wave mixing in a reflection geometry with photorefractive crystals

Intensity dependence of stationary energy transfer in degenerate two-wave mixing in a reflection geometry with photorefractive crystals

Degenerate two-wave mixing in photorefractive crystals with multiple internal reflections

The effect of multiple internal reflections on the stationary energy transfer in degenerate two-wave mixing, in a reflection geometry, with photorefractive crystals is studied. Numerical results obtained by using the shooting method are presented graphically. Generally it is found that the presence of multiple internal reflections reduces the amount of energy transferred between the two interacting beams. However, under some special conditions the energy transfer can be enhanced.

Numerical study of energy transfer between a beam and its internal reflection component in a nonlinear medium

A theoretical study is presented of a special case of stationary energy transfer in degenerate two-wave mixing in a reflection geometry. The two interacting beams consist of a beam and its first-order internal reflection component created at the boundary of a nonlinear medium. Numerical results obtained from the computer calculations are presented as graphs. It is found that, under suitable conditions, this phenomenon can be used to eliminate the multiple internal reflections.

Energy transfer between two beams in writing a reflection volume hologram in a dynamic medium

A theoretical study is presented of the stationary energy transfer between two beams in the writing of a reflection hologram in a dynamic medium. The intensities of the two beams both inside the medium and at the surfaces are determined as a function of absorption coefficient, the effective coupling constant, the initial intensity ratio and the thickness of the medium. Numerical results obtained from the computer calculations are presented in graphical form.

Stationary energy transfer controlled by applied field at hologram formation in PLZT ceramics

The stationary energy transfer (SET) at holographic grating formation due to the quadratic electro-optic effect in PLZT—9.2 ceramics is studied theoretically by means of a model of bipolar conductance and experimentally. It is shown that the SET is controlled by the applied field, providing a rather high gain (120 cm-1) as compared with other ferroelectric crystals. The high gain in PLZT at strong fields has been caused by a high value of the effective linearized electro-optic coefficient.

Coherent light amplification and optical phase conjugation in photoconductive electro-optic materials

The electric field and fringe spacing dependence of the stationary energy transfer between two writing beams in volume phase-hologram formation with photoconductive electro-optic materials (KNbO3:Fe2+, Bi12(Si, Ge)O20) has been studied. Experimental results are compared with the theoretical expressions describing the influence of the different photoinduced space-charge fields in photorefractive media. A peak exponential gain of Γ = 15 cm-1 has been reached in KNbO3:Fe2+ for the proper choice of experimental parameters such as recording wavelength, fringe spacing, applied electric field etc.).Results of the electric field dependence of the wave front reflectivity ρ in degenerate four-wave mixing experiments are reported and discussed in terms of a similar theoretical treatment as the two-wave mixing experiments. It is shown, that peak reflectivities of ρ = 10 percent have been reached for KNbO3:Fe2+, that conjugate complex wave fronts can be generated and that distorted optical wave fronts can be effectivi...

Coherent light amplification and optical phase conjugation in photoconductive electro-optic materials

Abstract The electric field and fringe spacing dependence of the stationary energy transfer between two writing beams in volume phase-hologram formation with photoconductive electro-optic materials (KNbO3:Fe2+, Bi12(Si,Ge)O20,…) has been studied. Experimental results are compared with the theoretical expressions describing the influence of the different photoinduced space-charge fields in photorefractive media. A peak exponential gain of Γ = 15 cm−1 has been reached in KNbO3:Fe2+ for the proper choice of experimental parameters such as recording wavelength, fringe spacing, applied electric field etc.). Results of the electric field dependence of the wavefront reflectivity p in degenerate four-wave mixing experiments are reported and discussed in terms of a similar theoretical treatment as the two-wave mixing experiements. It is shown, that peak reflectivities of p = 10 percent have been reached for KNbO3:Fe2+, that conjugate complex wavefronts can be generated and that distorted optical wave fronts can be...

Energy transfer and sensitivity in phase Hologram recording with reduced KNb03

Abstract The transport length of photocarriers in reduced KNb03 is comparable with the holographic grating spacing. Hologram formation in this case is followed by a stationary energy transfer between recording beams which, in contrast to other ferroelectrics, can be controled by an applied electric field (Eo). The contribution of photovoltaic mechanism to photorefraction is shown to be small, and diffusion of free photogenerated electrons is responsible for photorefraction at Eo=0.

Dynamic self-diffraction of coherent light beams

A review is given of the present state of theoretical and experimental work on the interaction of two coherent light beams of equal frequency in a nonlinear medium. It is shown that dynamic self-diffraction is substantially different for media with different types of response. Stationary energy transfer between interacting beams is possible in the case of nonlocal nonsymmetric response, whereas this type of transfer is forbidden in the case of local response. Different mechanisms for self-induced changes in the refractive index are examined together with the corresponding processes of energy transfer between the writing beams. The more important applications of dynamic self-diffraction are discussed.

Diffraction efficiency and energy transfer during hologram formation in reduced KNbO3

Volume phase-hologram formation by the photorefractive effect in KNbO3 is accompanied by a stationary energy transfer between writing beams. The change in energy transfer by applying an electric field on the reduced crystals is shown to be due to an efficient increase in migration length which can reach values comparable or larger than the fringe spacing. It is demonstrated that photovoltaic contribution to the diffraction efficiency and energy transfer is rather small in reduced KNbO3 and that diffusion of photogenerated free holes is the dominant charge transport for the photorefractive effect in unbiased crystals. The experimental results for diffraction efficiency and energy transfer as a function of grating spacing, electric field, light intensity and temperature is well described by a recent theory of Kukhtarev and Vinetskii.