Photorefractive Semiconductors Research Articles

Nonlinear dispersion of backward-wave four-wave mixing in a photorefractive semiconductor and its effect on group velocity

Photorefractive backward-wave four-wave mixing may be configured for the amplification of the phase conjugate output and the attenuation of the transmitted output. The nondegenerate-in-frequency interaction is studied in such a configuration, realized in a semiconductor CdTe crystal. The spectra measured at different outputs show the gain and attenuation resonances. The preliminary study of optical pulse propagation demonstrates that, due to different nonlinear dispersions at different outputs of the selected wave mixing configuration, a slowing down of light is observed at the phase conjugate output, while an acceleration of light is detected at the transmitted output for the same input pulse at the same interaction.

Impact of nonlinear electron transport model on character of light propagation in photorefractive semiconductors

The paper presents an analysis of nonlinear light propagation in photorefractive gallium arsenide. Two methods of nonlinear electron transport modelling have been distinguished, differentiated by the curve representing the dependence of electron drift velocity on the electric field. It has been shown that the phenomena of self-trapping of optical beams and the effect of bending of beam trajectories are possible both within the model for which the electron drift curve does not pass a local minimum, as in the case when the existence of a local minimum is taken into account. Since the model without a local minimum allows the excitation of charge carrier domains oscillations, the impact of this phenomenon on light propagation has been analysed. It has been shown that the oscillations have a limiting effect on the time window in which effective self-trapping of light occurs, and that they can manifest themselves in the form of oscillations in the intensity of the optical beam.

Spatial modulation spectroscopy of semiconductors using dynamic gratings

Subject of study. Several characterization methods that utilize recording and reading out of dynamic gratings to analyze functional materials are proposed. Method. The methods are based on pulsed recording of thin and volume dynamic gratings followed by reconstruction using continuous laser emission to facilitate the detection of the formation and relaxation dynamics of the recorded diffraction grating. Nonlinear optical, thermo-optic, and kinetic properties of condensed media were obtained based on the measured kinetics of the diffracted signals. Main results. The performance characteristics of a dynamic grating method were analyzed for characterization and parameter measurements of functional materials. In particular, the efficacy of the measurement of the kinetic properties for pulsed recordings of thin and volume holographic gratings was demonstrated. The lifetimes of the short- and long-lived trap levels involved in recording of the dynamic grating were determined in a photorefractive bismuth silicate crystal and the dependence of the diffraction efficiency of the gratings on the intensity of the recording radiation was determined. The advantages of using an additional grating (homodyne) to enable the separation of the contributions of different simultaneously manifesting nonlinearity mechanisms were demonstrated. This method was applied to monocrystalline germanium. A method for assessing the thickness of a film on the surface of a sample based on the amplitude of an oscillating component related to a sound wave propagating in air in the vicinity of the film’s surface was also proposed. A silicon dioxide film was considered as an example. The application of the diffraction to different orders on volume dynamic gratings was proposed for the measurement of the nonlinear optical susceptibility of the fifth and higher orders. The proposed approach was evaluated on photorefractive crystals and semiconductor media. The kinetic and thermo-optic properties, including the time of the population of trap levels, thermo-optic coefficient, and thermal diffusivity, of the media were determined. Practical significance. The proposed characterization methods facilitate the isolation of different nonlinearity mechanisms involved in the formation of dynamic gratings and the measurement of nonlinear optical, thermo-optic, and kinetic properties (optical susceptibilities of different orders, thermo-optic coefficient, thermal diffusivity, and lifetimes of free-charge carriers and trap levels).

Four-wave mixing by phase-amplitude holographic gratings in the photorefractive piezocrystal of 43m symmetry class

A system of coupled-wave equations for calculating the vector amplitudes of linearly polarized light waves at four-wave mixing by phase-amplitude holographic gratings in a cubic photorefractive semiconductor of an arbitrary cut belonging to the 43m symmetry class is presented. The dependences of the intensities of the polarization components of the reversed light wave on the orientation angle for GaAs crystal of (110)-cut are calculated on the basis of the numerical solution of the system of coupled-wave equations. The obtained dependences are compared with the known theoretical and experimental data. It is shown that the best agreement between the results of theoretical modeling and experimental data at calculating the counterpropagating four-wave mixing in GaAs crystal of (110)-cut is achieved if formation of several phase-amplitude holographic gratings is allowed, and the contribution of the photoelastic and inverse piezoelectric effects are taken into account together with absorption of the crystal. Keywords: four-wave mixing, photorefractive semiconductor, light wave, holographic grating, coupled wave equations.

Четырехволновое взаимодействие на фазово-амплитудных голографических решетках в фоторефрактивном пьезокристалле класса симметрии 43m

A system of coupled-wave equations for calculating the vector amplitudes of linearly polarized light waves at four-wave mixing by phase-amplitude holographic gratings in a cubic photorefractive semiconductor of an arbitrary cut belonging to the 4 ̅3m symmetry class is presented. The dependences of the intensities of the polarization components of the reversed light wave on the orientation angle for GaAs crystal of (110)-cut are calculated on the basis of the numerical solution of the system of coupled-wave equations. The obtained dependences are compared with the known theoretical and experimental data. It is shown that the best agreement between the results of theoretical modeling and experimental data at calculating the counterpropagating four-wave mixing in GaAs crystal of (110)-cut is achieved if formation of several phase-amplitude holographic gratings is allowed, and the contribution of the photoelastic and inverse piezoelectric effects are taken into account together with absorption of the crystal.

Near-infrared image recovery based on modulation instability in CdZnTe:V.

We propose a near-infrared image recovery method based on modulation instability in the photorefractive semiconductor CdZnTe:V. The formation mechanism of modulation instability in CdZnTe:V is discussed, and the theoretical gain model is derived. Theoretical results of optical image recovery at 1 µm and 1.5 µm wavelengths demonstrate that the maximum cross-correlation gain is 2.6 with a signal to noise intensity ratio of 0.1. These results suggest that our method could be one of potential aids for near-infrared imaging.

Enhancement of two-wave mixing gain coefficient by resonant mechanism in photorefractive semiconductor

In this paper, two-wave mixing in photorefractive semiconductors at large modulation depth is theoretically analyzed and discussed. An analytic expression of space-charge field normalized to the weak externally applied dc electric field value is presented and a one center-two band model which includes both temperature and electron-hole is considered. The variations of space-charge field with dc field and Fe2+ concentration are investigated. Furthermore, the variations of the gain coefficient with temperature, intensity beam ratio, incident angle, and incident light intensity are analyzed. The results show that both the space-charge field and gain coefficient can increase with a stronger dc field. When the dc field is less than 10 kV/cm, applying a strong dc field can significantly improve the space charge filed and gain coefficient. As the incident intensity rises, under the influence of the intensity-dependent resonant effect, a maximum gain coefficient is achieved for an optimum incident intensity which increases with the temperature. Besides, an optimal angle of incidence is obtained at which the gain coefficient is maximum. It is demonstrated that the optimal incident intensity of 21 mW/cm2 and the optimal angle of 5° can be obtained under the temperature of 300 K and the dc field of 10 kV/cm conditions. The present work can provide theoretical guidance for the practical application of two-wave mixing in photorefractive crystals.

Oscillations of charge carrier domains in photorefractive bipolar semiconductors.

The article presents analysis of the formation of charge carrier domains generated by a localized optical beam and the phenomenon of their oscillations. The research was carried out for bipolar photorefractive semiconductors characterized by nonlinear transport of electrons. The analysis allowed us to determine a set of basic quantitative parameters that have an impact on the appearance of carrier oscillations and their character.

Fast self-trapping of light in photorefractive semiconductors

The paper presents an analysis of fast self-trapping of light as part of high-intensity pulse propagation in photorefractive gallium arsenide. Temporal evolution of picosecond pulses has been analysed for various material parameter values, using numerical techniques which take into consideration bipolar carrier transport and the hot-electron effect. A strong laser beam self-bending effect, which can be used for switching optical signals, has been demonstrated, and the conditions of its occurrence have been discussed.

Impact of proton implantation parameters on the photoconductivity of photorefractive multiple quantum wells

Semi-insulating GaAs/AlGaAs multiple quantum wells are photorefractive materials with high sensitivity and a short response time. Semi-insulation of these structures is commonly obtained by proton implantation. We present the measurements of photoconductivity in the samples with different proton doses. The results were compared to the theoretically predicted relationship between photoconductivity and the donor to acceptor concentration ratio. This allows to estimate the impact of proton dose on deep donor concentration. Full Text: PDF References D.D. Nolte, "Semi-insulating semiconductor heterostructures: Optoelectronic properties and applications", J. Appl. Phys. 85, 6259 (1999). CrossRef D.D. Nolte, M.R. Melloch, in Photorefractive effects and Materials, ed. D.D. Nolte (Kluwer, Dordrecht, 1995). CrossRef Q. Wang, R.M. Brubaker, D.D. Nolte, M.R. Meloch, "Photorefractive quantum wells: transverse Franz–Keldysh geometry", J. Opt. Soc. Am. B 9, 1626 (1992). CrossRef Q. Wang, RM. Brubaker, D.D. Nolte, "Photorefractive phase shift induced by hot-electron transport: multiple-quantum-well structures", J. Opt. Soc. Am. B 11, 1773 (1994). CrossRef M. Wichtowski, A. Ziolkowski, E. Weinert-Rączka, "A general approach to the space?charge field solution in photorefractive materials in a TWM geometry", J. Opt. 12, 065201 (2010). CrossRef A. Ziółkowski, "Self-bending of light in photorefractive semiconductors with hot-electron effect", Opt. Expr. 22, 4599 (2014). CrossRef K. Seeger, Semiconductors Physics, fifth ed., Chapter 1 (Springer-Verlag, Berlin, 1991). CrossRef S.M. Sze, Physics of Semiconductors Devices, Second ed., Chapter 1 (Wiley, New York, 1981). S. Balasubramanian, I. Lahiri, Y. Ding, M.R. Melloch, D.D. Nolte, "Two-wave-mixing dynamics and nonlinear hot-electron transport in transverse-geometry photorefractive quantum wells studied by moving gratings", Appl. Phys. B 68, 863 (1999). CrossRef P. Yeh in Introduction to Photorefractive Nonlinear Optics, (Wiley, New York, 1993). CrossRef

On the mobility-lifetime products in photorefractive GaAs-AlGaAs quantum wells structures determined by moving grating technique measurements

The method to determine mobility-lifetime products of photoexcited electrons and holes in semi-insulating GaAs-AlGaAs quantum wells structures is proposed. The method is based on measurements of a photoconductivity and optical investigations of a photorefractive material response in wave-mixing setup using the running grating technique. Full Text: PDF References L. Solymar, D.J. Webb, A. Grunnet-Jepsen, The physics and applications of photorefractive materials (Clarendon Press: Oxford 1996). D.D. Nolte, M.R. Melloch, Photorefractive effects and Materials, ed. by D.D.Nolte (Kluwer, Dordrecht, 1995). S. Balasubramanian, I. Lahiri, Y. Ding, M.R. Melloch, D.D. Nolte, "Two-wave-mixing dynamics and nonlinear hot-electron transport in transverse-geometry photorefractive quantum wells studied by moving gratings", Appl. Phys. B 68, 863 (1999). CrossRef M Wichtowski, "Wave mixing analysis in photorefractive quantum wells in the Franz–Keldysh geometry under a moving grating", Appl. Phys. B 115, 505 (2014). CrossRef Q. Wang, R.M. Brubaker, D.D. Nolte, "Photorefractive phase shift induced by hot-electron transport: multiple-quantum-well structures", J. Opt. Soc. Am. B 9, 1773 (1994). CrossRef M. Shur GaAs devices and circuits (Springer, New York, 1989). D.D. Nolte, "Semi-insulating semiconductor heterostructures: Optoelectronic properties and applications", J. Appl. Phys. 85, 6259 (1999). CrossRef G.C. Valley, H. Rajbenbach, H.J. von Bardeleben, "Mobility?lifetime product of photoexcited electrons in GaAs", Appl. Phys. Lett. 56, 364 (1989). CrossRef A. Ziółkowski, "Temporal analysis of solitons in photorefractive semiconductors", J. Opt. 14, 035202 (2012). CrossRef

Self-bending of light in photorefractive semiconductors with hot-electron effect

This article analyzes nonlinear light propagation in semiconductors with bipolar conductivity and nonlinear transport of electrons. We show how the competition between electron and hole conductivity can influence light propagation, leading to the self-bending effect of optical beam trajectory, which depending on the value of trap compensation coefficient may be stationary or transient.

A numerical approach to nonlinear propagation of light in photorefractive media

The article presents a new approach to the analysis of light propagation in photorefractive materials. The discussed numerical method can be used for an analysis of the dynamics of nonlinear effects taking place in those media in which an analytical approach requires the use of approximations or is impossible. As an example of how the method works, the results of simulation are shown, illustrating the process of spatial solitary wave formation in two materials: a photorefractive semiconductor and a ferroelectric crystal.

Interband photorefractive effect in semiconductors with hot-electron transport at arbitrary modulation depth

Hot-electron transport in photorefractive semiconductors strongly affects the recording of photorefractive grating. However, the theoretical description of this behavior has been always made under small signal approximation. In this paper rigorous numerical investigation of stationary and transient behavior of photorefractive grating induced in the semiconductor quantum wells structure is presented. The calculations were performed in the framework of the band transport model for the case of high modulation depth. The comparison between numerical and approximated analytical solutions is given as well as between linear and nonlinear transport model. Obtained results allow to verify some statement formulated in few earlier works concerning beneficial effects of electron transport nonlinearity.

Perturbative approach to space-charge field dynamics in photorefractive semiconductors

A general perturbative approach to solving photorefractive material equations for a two-wave mixing geometry is developed. The method allows the study of both stationary and transient states of the space-charge field. As an example, solutions were given for GaAs–AlGaAs photorefractive multiple quantum well structures working in the Franz–Keldysh geometry. Approximate explicit expressions describing the recording and erasure dynamics of photorefractive gratings have been derived. The results are compared with numerical solutions of a complete set of material equations.

Temporal analysis of solitons in photorefractive semiconductors

Temporal analysis of both the photorefractive mechanism and soliton propagation in a slab semiconductor waveguide is presented. As an example, a structure based on GaAs/AlGaAs MQWs was investigated. Both a numerical and simple analytical approach based on the bipolar band-transport model is used to derive a temporal photorefractive response on localized illumination. The corresponding propagation problem describing the evolution of screening soliton profiles in media with quadratic electro-optic effect was also discussed.

Infrared sensitive liquid crystal photorefractive hybrid cell with semiconductor substrates

Refractive index grating recording is achieved in the infrared in a nematic liquid crystal placed between semiconductor CdTe substrates. Light-induced space-charge field created in photorefractive semiconductor substrates varies an alignment of liquid crystal molecules inhomogeneously in space forming a spatial modulation of the refractive index in liquid crystal. Two-beam coupling is studied in the hybrid cell, in which a gain factor Γ=16 cm−1 is achieved in the layer of liquid crystal of the sandwich.

Coherent collisions of infrared self-trapped beams in photorefractive InP:Fe

In this paper, we experimentally demonstrate collisions between two copropagating parallel coherent beams inside the photorefractive semiconductor iron doped indium phosphide (InP:Fe) at λ=1064 nm.

A general theory of two-wave mixing in nonlinear media

A general theory of two-wave mixing (TWM) in nonlinear media is presented. Assuming a gain (or absorption) grating and a refractive index grating are generated because of the nonlinear process in a nonlinear medium, the coupled-wave equations of TWM are derived based on Maxwell's wave equation. The coupled-wave equations can be decoupled as coupled equations for the intensity and coupled equations for the phase of both beams, and these two sets of coupled equations can be solved analytically by using average total intensity in the medium instead of using the total intensity. Compared with the previous theory of TWM, the theory presented here is more general, and the applications of the theory to photorefractive materials, Kerr media, and semiconductor broad-area amplifiers are described.

Adaptive interferometers with no external field using reflection gratings in CdTe:Ge at 1550 nm

We demonstrate experimentally the operation of an adaptive two-wave mixing interferometer with no field applied to a photorefractive crystal in which the quadrature condition is introduced by an external π/2 phase step. To achieve high signal to noise ratio the counter-propagating geometry for grating recording is used with a CdTe:Ge crystal, ensuring effective recording of reflection holograms. It is demonstrated that the interferometer with a photorefractive semiconductor crystal provides good sensitivity without the adverse effects that are normally associated with an applied field.