Conjugate Wavefront Research Articles

Dynamics of self-initiation and oscillation threshold of a system of two coupled double phase-conjugating mirrors

The Born approximation is used to analyse the dynamics and to determine the self-oscillation threshold of a system of two coupled phase-conjugating mirrors made of photorefractive crystals. It is shown that the duration of the period before oscillation is governed by the formation of a mode with a conjugate wavefront in a resonator.

NON-LAGRANGIAN NONLINEARITY AND COHERENT OPTICAL WAVE MIXING PROCESSES

Interaction of optical beams in media with diagonal-bipolar nonlinearity is theoretically investigated. It is shown that the nonlinearity is not Lagrangian and allows processes violating energy flux conservation law. Conditions for energy exchange to take place are found. Probe beam amplification in the field of counterpropagating pumps and wavefront conjugation are investigated to exhibit some remarkable features. Coherent interaction of waves of different frequencies through recording static gratings is shown to lead also to energy exchange processes owing to non-Lagrangian character of nonlinearity.

Optical probing of amplitude obstacles by contrast inversion at wave-front conjugation

The contrast inversion of a DFWM-conjugate wave which is realised by a π-shift of its zeroth harmonic with respect to the remainders has been first investigated. The experimental results for a one-dimensional object and computer-calculated data for space-distributed amplitude obstacles are discussed.

Dynamics of self-initiation of lasing in a semilinear phase-conjugating mirror with a large number of transverse modes

It is shown theoretically and experimentally that the appearance of lasing in a semilinear phase-conjugating mirror is preceded by a silent zone due to the formation of a mode with the conjugate wavefront in a multimode resonator.

Image Retrieval by Holographically Generated Phase Conjugate Wavefronts

Holographically generated conjugate wavefronts have been used for realising optical associated memory elements which can reproduce complete stored information when addressed only by a partial information

Heterodyne Interferometer with Photorefractive BGO Crystals

Abstract In this paper we show that it is possible to make a heterodyne interferometer with a single photorefractive BGO crystal using the technique of moving gratings. The main problems of obtaining good fidelity of the phase conjugate wavefront with such a method are discussed theoretically within the framework of the well-known scalar approximation to the photorefractive four-wave mixing process (no absorption, no pump depletion). Experimental phase measurements for obtaining the phase distribution of the signal wave are also presented.

Simultaneous wave-front and polarization conjugation of picosecond optical pulses by stimulated Rayleigh-wing scattering

Using phase conjugation by stimulated Rayleigh-wing scattering (SRWS) in carbon disulfide, we have observed simultaneous correction of wave-front and polarization distortions. SRWS was excited by pulses of 20-psec duration containing as much as 15 microJ of energy at a wavelength of 0.53 microm and produced phase-conjugate reflectivities as large as 10%.

Wave-front conjugation by stimulated Brillouin scattering near the critical point

Problem of wave-front conjugation (WC) near the critical temperature of phase transition II (when substances change their structure). It was found experimentally that near the critical temperature T c , the conjugated wave disappeared. In these experiments the WC was observed in a methanol solution of critical concentration by the use of stimulated Brillouin scattering (SBS) where the temperature was changed from 10 to 21.5 o C (22 o C is the temperature of phase transition II for the methanol solution). The work reported here is a theoretical investigation of WC processes by SBS near the critical temperature of phase transition II

Nonlinear acoustic phenomena due to bubble drift in a gas–liquid mixture

Nonlinear acoustic effects associated with collective dynamics of bubbles in a liquid are considered in this article. The mechanism of nonlinearity is caused by the variation of the bubble concentration in space due to bubble drift under the effect of radiation pressure and hydrodynamic (Bjerknes) forces (the latter may result in bubble coalescence). First, the individual behavior of a bubble or a pair of bubbles in an acoustic field is considered. Second, kinetic equations for the bubble distribution function in an acoustic field are derived, and, third, different effects of sound propagation are discussed. They include some steady-state and transient ‘‘envelope waves’’ propagating together with ‘‘concentration waves.’’ A simple model of ‘‘nonlinear transparency’’ in acoustics, which is in qualitative agreement with experimental results, is touched upon. A harmonic wave in a medium with homogeneous bubble distribution is shown to be unstable, and may possibly result in such effects as wave front conjugation, self-focusing of sound, and, probably, the formation of bubble groups.

Wavefront conjugation and amplification for optical communication through distorting media: experiment

The laboratory performance of recently proposed new architectures for optical communication through distorting media is investigated. After phase-conjugating a weak beam with a mutually incoherent source a power amplification with a gain factor of 500 was demonstrated. The amplified beam can be employed for distortion-free optical communication by direct signal transmission. In a different configuration, wavefront matching applicable for coherent detection is proved to be feasible.

Atomic flame spectrometry based on polarization-modulated optical phase conjugation by resonant degenerate four-wave mixing

Doppler-free flame spectrometry based on polarization-modulated optical phase conjugation in an air-acetylene flame is reported as a sensitive analytical technique with high spectral resolution using a relatively weak continuous-wave dye laser. Optical signal detection is efficient since the signal is a coherent time-reversed replica of the probe beam. Utilizing polarization properties of the phase conjugate wavefront and the resonant degenerate four-wave mixing process, polarization-modulated detection is demonstrated to offer many advantages. Signal-to-noise ratio is enhanced by at least a factor of 20 as compared to amplitude-modulated detection. Detection limit of Doppler-free sodium spectrum is reported at 0.2 ng ml .

Wavefront conjugation and amplification for optical communication through distorting media

Combining double-phase conjugation with various coherent amplifiers leads to an amplified beam (forward or conjugated) derived from a local laser but bearing the transversal phase pattern of a received signal beam from a remote laser. We suggest several uses in optical communication through a distorting atmosphere.

Nonlinear optics and transformation of light in gases

A review of current theoretical and experimental research in the field of nonlinear optical frequency mixing in gaseous media: The authors examine fundamental physical principles and features of nonlinear optics of gases and vapors of chemical compounds. The experimental methods employed are described. Major advances in the fields of optical frequency conversion to infrared, vacuum-ultraviolet, and soft x-ray spectral ranges; improvement in the detection of weak IR signals by conversion to the visible and near ultraviolet ranges; and wavefront conjugation are described. Practical applications of discussed methods are emphasized.

Contribution of resonance medium amplitude and phase modulation to the effectiveness of phase conjugation by degenerate four-wave mixing

The contribution of amplitude and phase modulation to the energetic efficiency of wavefront conjugation (WFC) under degenerate four-wave mixing is studied in resonant media simulated by a two- or a three-level scheme. It is shown that a WFC-mirror of reflectivityR higher than unity may be achieved only in the presence of the medium phase modulation. Optimum conditions for obtaining high-efficiency (R>1) WFC are defined.

Polarization wavefront conjugation by means of transient holograms in rigid dye solutions

Polarization wavefront conjugation by means of four-wave mixing in rigid solutions of azo-dyes is investigated. The polarization characteristics of the holographic recording are studied. It is shown that due to the photoinduced anisotropy storage an exact reconstruction of the signal wave polarization is achieved. For such holographic recording the reversed wave generated in the four-wave mixing is conjugated in phase as well as in polarization. The polarization holographic recording of a wave with polarization spatially modulated by an anisotropic distorter is demonstrated and compensation of the polarization inhomogeneities is achieved by passing the phase conjugated wave back through the scatterer.

Wavefront reconstruction (conjugation) by stimulated scatterings: A review

In this paper, we give review of our work on the holographic image reconstruction of the volume object, illuminated by giant laser pulses of nano- and picosecond duration, and of its Fourier spectrum which has been observed experimentally in Raman, Brillouin, and Rayleigh stimulated scatterings. Image reconstruction laws have been investigated. Wavefront conjugation with transformation, obeying holography principles, has been shown to take place at the backward SRS. A physical model of the phenomenon is given. The diffraction efficiency of dynamic holograms in the stimulated scatterings has been measured. The possibility of the light beams spatial structure conversion at the stimulated scatterings has been experimentally shown.

Dynamic gratings and the associated self diffractions and wavefront conjugation processes in nematic liquid crystals

The origins and the dynamics of optical nonlinearities in nematic liquid crystal films, namely, laser-induced molecular reorientational and thermal refractive index changes, are analyzed in the context of optical wave mixings. Theoretical expressions for the basic non-linearities, the rise and decay time, diffraction efficiencies, and other pertinent parameters involved in the dynamic grating formation are derived. Experimental results obtained with visible and infrared laser pulses are analyzed. Some newly observed novel nonlinear processes are also reported.

Acoustic analogues of nonlinear-optics phenomena

This review discusses nonlinear acoustic phenomena which are analogous to corresponding phenomena in optics: self-interaction effects in acoustic beams, parametric effects, stimulated scattering of sound, wave-front (phase) conjugation of sound waves, and also techniques of active acoustic spectroscopy. The authors point out that these processes must evolve rather rapidly in space and time in order to avoid the formation of shock waves and the nonlinear dissipation of energy which accompanies them; this rapid evolution is provided by the interaction of sound with non-acoustic forms of fluid motion: convection, oscillating bubbles, and by thermal, hydrodynamic and concentration waves. Features which are peculiar to nonlinear acoustic phenomena are emphasized, i.e., the parametric mechanism for acoustic phase conjugation and the possibility of detecting stimulated acoustic scattering by single scatterers. The goal of the review is to draw additional attention to promising developments in nonlinear acoustics.

Nonlinear Optical Properties Of Liquid Crystals For Optical Imaging Processes

We present an account of two recently observed nonlinear optical imaging processes, wavefront conjugation and infrared-to-visible image conversion, in liquid crystal films. We include discussion of dynamics, efficiency, resolution, aberration correction, and noise removal in these two processes.

Orientational optical nonlinearity of liquid crystals

The orientational optical nonlinearity of the mesophases of liquid crystals (LCs) is attracting ever more attention, owing to the high values of the constants characterizing it, owing to the many interesting specific features that LCs introduce even into traditional nonlinear optical effects, and owing to the potentialities of studying the physical properties of LCs. This article presents the state of the theory and experiment of orientational interaction of light waves with LCs. Especial attention is paid to the physical mechanisms of interaction?the light-induced Freedericksz effect, recording of director gratings, and the action of surface light waves on the orientation of the director. Varied manifestations of the effects of orientational self-action and interaction of light waves are discussed: self-focusing of light, nonlinear optical activity, mutual focusing, stimulated light scattering, and wave-front conjugation. Optical nonlinearities specific for the mesophase of a liquid crystal and associated with absorption of light quanta are also discussed. They include photoconformational nonlinearity, thermal-orientational nonlinearity, and liquid-crystal light valves. Especial attention is paid to the methodological problem of deriving the Euler?Lagrange?Rayleigh variational equations and to the correct choice of the free energy for the system LC + electromagnetic field. Section 8 traces the history of the studies of orientational optical nonlinearity of LCs and reviews the studies whose results are not directly reflected in the main text, and also reviews the studies on practical applications of light-induced orientational effects.