Self-Pumped Phase-Conjugated Waves Research Articles

Multiple Self-Pumped Phase-Conjugated Waves by Pulsed Laser

Multiple self-pumped phase-conjugated (SPPC) images with more different types of information than previously obtained SPPC images were obtained using a nanosecond-pulsed beam instead of continuous-wave beams. The minimum number of incident pulses, i.e., the minimum energy, required to generate one SPPC wave for one type of information strongly depended on the product of the number of incident pulses and the total power of incident beams. Both the time required for the generation (rise time) and the time required for the elimination (fall time) of SPPC images changed in the first-order exponential manner. These times due to the photorefractive effect were a sensitive function of beam intensity such that total energy transfer required long interaction length in BaTiO3 crystal.

Generation of Multi Self-Pumped Phase-Conjugated Waves by Pulsed Laser

Two self-pumped phase-conjugated (SPPC) images produced from two signal laser beams transporting different types of information were observed using a photorefractive barium titanate (BaTiO3) crystal. We have studied the smallest numbers of incident pulses required to generate one and two phase-conjugated images for one and two types of information, respectively, in order to transport much information. The lowest energy required for the generation of one phase-conjugated image depended strongly on the product of the numbers of incident pulses and the power of the incident pulsed beam.

Generation of Two Self-Pumped Phase-Conjugated Waves at 532 nm by Nanosecond Pulsed Laser

Self-pumped phase-conjugated (SPPC) images produced by two SPPC beams generated from a single nanosecond-pulsed laser beam are successfully obtained at beam power ratios of up to 4:1. The two SPPC beams are incident on opposite faces [(100) and (100)] of a photorefractive barium titanate (BaTiO3) crystal, and the SPPC images are reproduced on the respective crystal faces with high quality due to the reduced interference between the two SPPC beams owing to the delay between the nanosecond pulses of each beam. The quality of the images and the maximum power ratio at which both images are observable are superior to the continuous-wave configuration.

Generation of Two Self-Pumped Phase-Conjugated Waves at Different Wavelengths Using Single Photorefractive Crystal

Two self-pumped phase-conjugated waves at different wavelengths are successfully generated using an undoped barium titanate crystal. With one signal beam at a wavelength of 514.5 nm incident to the (100) face of the crystal and the other at a wavelength of 488.0 nm incident to the opposite (100) face with an offset of 2 mm, two phase-conjugated images are produced even at high power ratios between the signal beams. The use of two different wavelengths prevents interference between the two signal beams, resulting in the generation of phase-conjugated waves over a wide dynamic range.

Generation of Two Self-Pumped Phase-Conjugated Waves Transporting Different Information Using Single Photorefractive Crystal

Two optical configurations for generating two self-pumped phase-conjugated waves from two signal laser beams transporting different information were presented: one in which the two signal laser beams were directed at two opposite faces [(100) and (100)] of the crystal and the other in which both beams were directed at the same (100) face. Using a barium titanate (BaTiO3) single crystal as a self-pumped phase-conjugated mirror, the generation conditions of two discrete self-pumped phase-conjugated waves of high quality with reduced interference were investigated. Successfully self-pumped phase-conjugated images were observed to be more readily achievable by changing the incident beam power than by changing the incident position onto a single face.

Generation of Four Self-Pumped Phase-Conjugated Waves Using Single Photorefractive Crystal

A method of generating self-pumped phase-conjugated waves from four signal beams transporting different information using a single crystal of barium titanate is presented. With one pair of signal beams directed on the (100) face of the crystal and the other pair directed on the opposite (100) face, phase-conjugated images were produced according to the relative power of the two beam pairs. Images were produced even when the beams in each pair fully overlapped on the incident crystal face. At high power ratios (e.g., 1:5), no images of the lower-power beams were produced. The absence of fanning loops in the crystal for the lower-power beams indicates that the information was erased due to scattering of the higher-power beams and/or the interaction between the beams in the crystal. The generation of phase-conjugated waves could therefore be controlled selectively by adjusting the relative beam power of the input signal beams.

Response characteristics of a self-pumped phase-conjugate mirror to spatially nonuniform phase changes of an incident wave and their applications

The response of a self-pumped phase-conjugate mirror to spatially nonuniform phase change of incident wave is examined with a phase-conjugate Fizeau interferometer. The experimental results make it clear that the spatially nonuniform phase change of the incident wave is not reversed by the self-pumped phase-conjugate wave (SPPCW) immediately after the phase change, and the decrease of phase-conjugate reflectivity caused by the nonuniform phase change is proportional to the nonuniformity of the phase change. The phase characteristic of the SPPcw makes the phase-conjugate Fizeau interferometer for surface profile measurements insensitive to object vibrations. The reflectivity characteristics enable us to measure the nonuniform phase change by detecting the intensity of the SPPCW.

Emission Characteristics of Internally Self-Pumped Phase-Conjugate Wave in Photorefractive KNbO3:Fe and BaTiO3 Crystals

The reflectivity and the response time of the self-pumped phase conjugation in unreduced KNbO3:Fe and BaTiO3 were measured and compared as functions of incident beam intensity, incidence angle and incidence position of the crystal. The self-pumped phase conjugation of KNbO3:Fe was generated in narrow regions of the incidence angle and position, in comparison with that of BaTiO3. It was also observed that the response time of KNbO3:Fe was longer than that of BaTiO3 under the same experimental conditions.

Temperature Effect in (K0.5Na0.5)0.2(Sr0.75Ba0.25)0.9Nb2O6: Cu Crystal Self-Pumped Phase-Conjugator

A reflectivity of 45% of the self-pumped phase-conjugate wave in (K0.5-Na0.5)0.2(Sr0.75Ba0.25)0.9Nb2O6:Cu crystal at the environmental temperature T ∼ 70°C has been obtained. The temperature effect in this kind of self-pumped phase-conjugator is studied.

Induced self-pumping phase-conjugation with BaTiO3

We have found that when interacting with a crystal of BaTiO3 and under certain conditions, a beam which originally does not produce a self-pumped phase conjugate (SPPC) wave may shift to the self-pumping state due to the influence of another beam. The two beams are incident on the photorefractive crystal at neighboring sides and they may be coherent or incoherent to each other. The phenomenon has been observed even when the two beams are alternately shining on the crystal, or are derived from different kinds of lasers.

Observation of self-pumped phase-conjugate wave in Cu-KNSBN crystal

A self-pumped phase-conjugate wave was first observed by us in a Cu-doped (K 0.5Na 0.5) 0.2(Sr 0.61Ba 0.39) 0.9Nb 2O 6 crystal at Ar + laser wavelengths. The highest phase-conjugate reflectivity measured was 29.2% at 514.5 nm laser wavelength.