Generation Of Phase Conjugate Waves Research Articles

Synthesis and properties of polyesters having cyanoazobenzene units in the side chain

Side chain liquid crystalline polyesters [COPh(O[CH 2 ] 6 OPhN=NPhCN)COO(CH 2 ) 6 OPh-X-PhO(CH 2 ) 6 O] n (X= -, O, CO, CH 2 ) are synthesized and their phase transitions and phase-conjugate wave generation properties are investigated

Photorefractive Response Characteristics and Generation of Phase-Conjugate Wave in Bi12GeO20 and Bi12SiO20 Crystals

The response time of the photorefractive effect in Bi12GeO20 was evaluated for the first time using nearly degenerate two-wave mixing. The result was analyzed in the context of the charge transport theory and the trap density was determined as NA=2.4×1021 m-3. It was also found that an optimum amplitude of the displacement of the piezomirror exists in the moving-grating method. By adopting this amplitude, the reflectivities of the phase-conjugate wave reached 490% and 430% for Bi12SiO20 and Bi12GeO20, respectively.

Optical phase conjugation in polycarbonate resin doped with Coumarin 314 dye

Optical phase conjugate wave generation in Coumarin 314-doped polycarbonate resin is investigated by using 488-nm light for writing the grating and 632.8-nm light for reading it. The observed oscillatory behavior of grating growth as a function of writing time is attributed to heating effects.

Localized-delocalized transition of the exciton and scaling description of phase-conjugated wave generation.

Under nearly resonant pumping of Frenkel excitons, the third-order optical process generating phase-conjugated waves is theoretically investigated by taking full account of the effect due to static on-site disorder and finite sample size. The scaling theory of the Anderson localization allows us to show that the phase-conjugated signal has the spectral anomaly for pump and probe frequencies around the exciton mobility edge. We systematically evaluate the dependence of the phase-conjugated signal on various physical quantities, namely, randomness, the detuning of the pump and probe frequencies from the exciton mobility edge, the misalignment of two pump beams, and the system size.

Nonlinear Equivalent Circuit Model Analysis of Acoustic Devices and Propagation of Surface Acoustic Wave

The generation of acoustic phase conjugate waves is demonstrated using our previously reported nonlinear equivalent circuit of thin bar with length-extensional vibration. Next, a new nonlinear equivalent circuit for propagating nonlinear surface acoustic wave (SAW) is proposed. Using this new circuit, it is shown that the metallic grating wave guide of SAW is equivalent to the nonlinear lattice in which the SAW soliton propagates. Finally, the experimental study about this waveguide is successfully performed.

Generation of Phase Conjugate Wave from a Visible InGaAlP Laser

This paper presents the first quantitatively measured results of detuning and spatial characteristics of the phase conjugate wave which is emitted from a Fabry-Perot cavity-type InGaAlP laser. Bandwidth of a nearly-degenerate four-wave mixing was confirmed to be due to the relaxation oscillation frequency of the laser. The reflectivity of the phase conjugate mirror and the amplification gain were larger than 10 and 100, respectively. By the off-axial injection of the probe beam to a broad stripe laser, the emitted phase conjugate wave was separated spatially from the pump beam. Non-degenerate four-wave mixing characteristics of an AlGaAs laser were also measured for the first time. Its 3-dB cutoff frequency was as large as 0.1 THz, which was determined by the reciprocal of the half-cycle time of the intracavity light-wave.

Localized-delocalized transition of an exciton studied by generation of phase-conjugated waves

Under nearly resonant pumping of Frenkel exciton, the disorder effect on third-order optical processes of generating phase-conjugated waves is theoretically investigated by use of the scaling theory of Anderson localization. The phase-conjugated signal is expected to have the spectral anomaly for pump- and probe-frequencies around the exciton mobility edge.

Singular enhancement of phase-conjugated wave generation near the mobility edge of an exciton

The generation of a phase-conjugated wave is shown to be enhanced when the pump and probe frequencies approach the mobility edge of excitons. This is derived theoretically by applying the scaling theory of the diffusion coefficient in transport phenomena to the third-order optical polarization. We will also discuss how to observe this singularity.

Generation of Phase Conjugate Wave Using LiNbO3:Fe and Application to Optical Associative Memory

Experimental results are presented for a phase conjugate wave generation using an iron-doped lithium niobate single crystal by the degenerate four-wave mixing method. More than 300% reflection efficiency is achieved, and it is almost independent of the total incident optical intensity. The generator is then applied as a phase conjugate mirror to an all-optical associative holographic memory to reflect and amplify the diffracted beams. The retrieved output image is formed by using partial input illumination.

Generation of phase conjugate waves in dichromated gelatin and related materials

Evidence is reported, we believe for the first time, on the generation of phase conjugate waves in dichromated gelatin, methylene blue doped gelatin, and methylene blue doped dichromated gelatin.

Phase conjugation via unequal amplitude multiple gratings in photorefractives: A simple shooting method for numerical solution

We present a simple shooting method to obtain numerical solutions of the nonlinear coupled-wave equations for degenerate four-wave mixing in photorefractive crystals when four different types of the index gratings of unequal amplitudes are responsible for phase-conjugation. Our analysis includes the effects of pump depletion and absorption in the medium. Intensities of the four beams, both inside and at the output surface, are obtained as a function of four unequal coupling strengths and absorption coefficient. Intensity of the generated phase-conjugate beam is shown as a function of both the small and wide ranges of signal beam intensity. It is found that the multigrating operation with a careful choice of coupling constants and their combinations may improve the phase-conjugate wave generation. Also the presence of absorption reduces the phase-conjugate intensity more significantly when all the gratings are operative than when a single grating is allowed. Numerical results obtained from the computer calculations are presented in graphical form.

Weak localization of polaritons and the generation of phase-conjugated light waves.

The microscopic mechanism of generation of phase-conjugated light waves is presented in terms of weak localization of polaritons. Phase-conjugated waves, which are the time-reversal propagation of probe light, are shown to be enhanced by constructive interference between elastic multiple scattering of polaritons at impurities and time-reversed processes. This is characteristic of the time-reversal invariance of the system. We list several characteristics of generation of phase-conjugated waves due to the weak localization of polaritons. These observations will be applied to check the present theory.

Generation of Optical Phase-Conjugate Wave from Bi12SiO20

In order to establish the optimum geometric condition for the generation of phase-conjugate wave(PCW) from photorefractive Bi12SiO20 crystal, dependences of the PCW intensity on incidence angle and probe-beam power were measured on two-types of crystal with different orientations. The maximum intensity was obtained when the pump-beam with polarization parallel to the [001] axis entered the (110) surface with the incidence angle of 45°. On the other hand, the PCW has a maximum when the pump-beam with polarization parallel to the [110] axis entered the (001) surface perpendicularly. The results can be explained by changes of optical indicatrix due to local electric fields duplicating interference patterns inside BSO crystal.

Weak localization of exciton polaritons and generation of phase-conjugated light wave

Microscopic mechanism of generation of phase-conjugated light wave is presented in terms of weak localization of polaritons. Phase-conjugated wave which is time-reversal propagation of probe light is shown to be enhanced by constructive interferences between elastic multiple-scatterings of polariton at impurities and its time-reversed processes. We list up several characteristics of generation of phase-conjugated wave due to the weak localization of polaritons. Observations of these will work to check the present theory.

Phase-conjugate amplification through transverse optical Zeeman pumping in resonant doppler-broadened degenerate four-wave mixing

Degenerate four-wave mixing in an inhomogeneously broadened folded three-level system is considered to analyse theoretically the generation of phase-conjugate signals in optically dense media. The counter-propagating pump waves and the copropagating probe and forward pump waves are taken to be orthogonally polarized and interact selectively with the coupled one-photon transitions such that ground-state Zeeman coherence plays the dominant role in phase-conjugate wave generation. It is shown that even in a purely absorptive resonant interaction, transverse optical pumping gives rise to amplified reflection and coupled-mode oscillation, being the required pump intensities very low compared to that needed for saturation of the optical transitions.

Generation of phase conjugate waves in a Bi12SiO20(BSO) crystal. Dependence on the spatial frequency of the written grating.

Generation of phase conjugate waves in a photorefractive Bi12SiO20 (BSO) crystal is studied with particular attention to the dependence of the efficiency on the spatial frequency of the written grating. The influence of mis-alignment between input beams is also investigated in detail. Since the diffracted output energy is particularly sensitive to the incident angle of the readout beam, alignning of the readout beam to meet Bragg conditionis of critical importance. It is found that diffraction efficiency is proportional to the square of the fringe spacing, ∧2, under the condition of relatively small spacing ∧while it is proportional to ∧-2 when the spacingexceeds a certain value. The result is consistent with “two-level charge transfer model ”proposed by Peltier etal. From the fringe spacing giving a maximum diffraction efficiency, the density of acceptor traps is determined to be 1.3 ×1015cm-3 in the BSO crystal used.

Time character of phase-conjugate reconstructed waves

The time dependence of phase-conjugate wave generation in liquids has been studied using four-wave mixing of picosecond laser pulses and different polarization configurations. Response and decay times of some possible physical processes contributing to the phase-conjugate wave generation have been measured.

Generation of Phase-Conjugate Waves by Optical Surface Waves

Generation of Phase-Conjugate Waves by Optical Surface Waves

Generation of a forward-traveling phase-conjugate wave in germanium

In this communication, we report the generation of a picosecond forward-traveling phase-conjugate wave at 1.06 μm in thin germanium samples by degenerate four-wave mixing. At this wavelength, the conjugate wave is produced by diffraction of the pump from an absorption grating produced by direct absorption of pump and signal pulses. We measure and discuss the transient effects caused by the finite duration of the nonlinear material response.