Showing papers on "Phase conjugation published in 1999"
TL;DR: In this paper, high fidelity, polarised, optical phase conjugation via stimulated Brillouin scattering of CW laser radiation in a multimode silica fiber was obtained in a 4.23 km length of fiber with a Nd:YAG laser.
39 citations
TL;DR: In this paper, phase conjugation in an inhomogeneously broadened rare-earth doped crystal using electromagnetically induced transparency was shown to achieve an energy efficiency of 10% with ;1/4 of maximal Raman coherence.
Abstract: We demonstrate efficient phase conjugation in an inhomogeneously broadened rare-earth doped crystal using electromagnetically induced transparency. The observed frequency conversion efficiency of the phase conjugate in energy over a backward pump beam is as high as 10% with ;1/4 of maximal Raman coherence. This efficient phase conjugation has potential applications of nonlinear optical processes such as frequency up-conversion and Raman excited spin-echo optical memory. @S1050-2947 ~99!50704-X#
37 citations
TL;DR: In this article, a trapped multicomponent atomic Bose-Einstein condensate is considered, where spin exchange collisions result in a transfer of population between different internal states.
Abstract: We consider a trapped multicomponent atomic Bose-Einstein condensate, concentrating specifically on condensates in the hyperfine ground state $F=1,$ where spin exchange collisions result in a transfer of population between $m=0$ and $m=\ifmmode\pm\else\textpm\fi{}1$ internal states. Drawing an analogy with the optical situation, we show that this system can be regarded as a matter-wave analog of optical multiwave mixing. This opens up the way to realize matter-wave phase conjugation, whereby an incident atomic beam can be ``time reversed.'' In addition, matter-wave phase conjugation also offers novel diagnostic tools to study the coherence properties of condensates, as well as to measure the relative scattering lengths of hyperfine sublevels.
32 citations
TL;DR: In this paper, the collisional properties of partially coherent solitons (PCSs) were investigated with a photorefractive crystal and it was shown that collisions in nonlinear media cause the PCS comprised of few mutually incoherent soliton components to change its shape.
Abstract: We present experimental results related to collisional properties of partially coherent solitons (PCSs). In experiments with a photorefractive crystal we show that collisions in nonlinear media cause the PCS comprised of few mutually incoherent soliton components to change its shape.
29 citations
13 Jun 1999
TL;DR: In this paper, a novel retrodirective array with intrinsic gain has been developed and demonstrated successfully for the first time, where each heterodyne scattering element employs a balanced FET mixer, which provides effective isolation between RF and IF signals with identical frequencies to realize phase conjugation.
Abstract: A novel retrodirective array with intrinsic gain has been developed and demonstrated successfully for the first time. Each heterodyne scattering element employs a balanced FET mixer, which provides effective isolation between RF and IF signals with identical frequencies to realize phase conjugation. A 4-element array has been fabricated, which demonstrated excellent retrodirectivity.
26 citations
TL;DR: In this article, the time-varying dispersion of ultrafast laser pulses can be self-adaptively stabilized using real-time dynamic spectral holography in semiconductor photorefractive quantum wells.
Abstract: The time-varying dispersion of ultrafast laser pulses can be self-adaptively stabilized using real-time dynamic spectral holography in semiconductor photorefractive quantum wells. Dispersion of all orders is compensated by forming a dynamic spectral-domain hologram of a signal pulse (that has a time-varying dispersion) referenced to a stable clock pulse. The hologram is read out using forward-scattering phase conjugation to remove phase distortion to all orders, including drift in the time of flight. We have achieved adaptive cancellation of time-of-flight excursions up to ±15 ps to an accuracy of ±15 fs with a compensation bandwidth of 1 kHz.
25 citations
TL;DR: In this paper, phase conjugate waves of ultrasound were generated in PZT ceramics through nonlinear piezoelectric interaction between an incident ultrasonic field at ω and an electric field at 2ω.
Abstract: Phase conjugate waves of ultrasound were generated in PZT ceramics through nonlinear piezoelectric interaction between an incident ultrasonic field at ω and an electric field at 2ω. The amplitude reflectivity of the phase conjugator was 23% at 10 MHz. The behavior of the incident waves and the phase conjugate waves were visualized by stroboscopic schlieren technique. Time-reversal property and the automatic correction of wavefront distortion in the phase conjugate process were confirmed. A scanning ultrasonic imaging system with a PZT phase conjugator has been built. This system was used to visualize test samples composed of solid plates and phase disturbers. Images by phase conjugate reflection yielded clear figures of the solid plates in spite of the existence of phase disturbers made of agarose gel with rough surfaces, whereas conventional images showed serious distortion.
23 citations
TL;DR: The wide holographic bandwidth of LiNbO(3) makes it possible to record submicrometer pixels and reconstruct them by phase conjugation in a holographic memory system that reduces the system cost and increases the system storage density.
Abstract: The bandwidth of holographic recording in LiNbO3 (Fe doped) in the 90° geometry is studied theoretically and experimentally. The wide holographic bandwidth of LiNbO3 makes it possible to record submicrometer pixels and reconstruct them by phase conjugation in a holographic memory system. This approach reduces the system cost and increases the system storage density. We demonstrate the recording and the phase-conjugate reconstruction of various pixel sizes down to 1 μm × 1 μm . The signal–noise ratio and the bit-error rate are examined.
22 citations
TL;DR: The characteristics of a new high-gain photorefractive polymer composite with a PNP chromophore with intensity dependence of TWC gain are investigated and higher diffraction order and forward phase conjugation in a TWC geometry are observed and explained.
Abstract: The characteristics of a new high-gain photorefractive polymer composite with a PNP chromophore are investigated. Competition between beam fanning and two-wave coupling (TWC) is predicted and verified experimentally. The intensity dependence of TWC gain is studied. Higher diffraction order and forward phase conjugation in a TWC geometry are observed and explained.
20 citations
TL;DR: Recently, a new class of laser resonators was introduced that utilizes diffractive mirrors and an additional intracavity diffractive phase element that achieved high modal discrimination and low fundamental-mode loss by use of sinusoidal and pseudorandom diffractivephase elements.
Abstract: Recently, a new class of laser resonators was introduced that utilizes diffractive mirrors and an additional intracavity diffractive phase element. High modal discrimination and low fundamental-mode loss were achieved simultaneously by use of sinusoidal and pseudorandom diffractive phase elements. An intracavity phase element consisting of a simple single-step phase modulation is approximated by a Gaussian with a small radius. Explicit expressions are obtained for the modal-discrimination factor as a function of resonator parameters with a Gaussian output mirror. Numerical simulations are performed for a phase element with a step singularity in the phase function, the fundamental mode of this cavity being super-Gaussian. The modal discrimination of the cavity is studied for different radii of the single-step phase modulation, the position of the phase plate, and the cavity Fresnel number. Optimum solutions are found for a plane output mirror with either a striped or a circular shape.
19 citations
TL;DR: The principle and basic experimental results of the acoustic phase conjugation by nonlinear piezoelectricity are described in this article, where an original explanation based on the modulation of sound velocity by the electric field together with the concept of time grating is given.
Abstract: The principle and the basic experimental results of the acoustic phase conjugation by nonlinear piezoelectricity are described. Acoustic phase conjugate waves at frequency ω are generated as a result of the interaction between incident acoustic waves at ω and pump electric fields at 2ω. An original explanation based on the modulation of sound velocity by the electric field together with the concept of time grating is given. Coupling equations for the PZT ceramics as a nonlinear material are derived. Experimental results of the sound velocity modulation and the phase conjugate generation in nonlinear piezoelectric PZT ceramics are shown. Amplitude reflectivity of the phase conjugation was 23% for the acoustic incidence at 10 MHz.
TL;DR: In this article, phase conjugation and dynamic holography were demonstrated by degenerate four-wave mixing in a continuous-wave diode-pumped Nd:YVO4 laser for the first time.
Abstract: We demonstrate phase conjugation and dynamic holography by degenerate four-wave mixing in a continuous-wave diode-pumped Nd:YVO4 laser for the first time. A phase-conjugate reflectivity of 1.4% is obtained with a 12 W diode power. The experimental results and the optimizing parameters, such as the cavity mirror reflectivities, are compared with results from a steady-state theoretical analysis.
23 May 1999
TL;DR: In this article, the authors demonstrate phase conjugation by degenerate four-wave mixing (DFWM) in a diode-pumped Nd:YVO/sub 4/gain medium.
Abstract: Summary form only given. In recent years, phase conjugation by degenerate four-wave mixing (DFWM) in saturable gain media has been the subject of intense investigation for applications to dynamic holography and laser architectures with intracavity phase distortion compensation. The authors demonstrate, for the first time to their knowledge, cw DFWM and dynamic holography in a compact, easy-to-handle diode-pumped Nd:YVO/sub 4/ gain medium. Since the laser itself is used as the nonlinear mirror, no additional gain medium is needed and the counterpropagating pump beams are automatically provided by laser oscillation.
TL;DR: In this article, optical-pumping-induced population-grating transfer between hyperfine levels of the cesium D2 line is observed through four-wave mixing in a sample of cold atoms.
Abstract: Optical-pumping-induced population-grating transfer between hyperfine levels of the cesium D2 line is observed through four-wave mixing in a sample of cold atoms. Diffraction efficiencies of order of 1% have been measured for a large range of angular apertures. We have studied the angular dependence of the diffracted signal in the limit of small atomic velocities and discussed its application for a nondestructive diagnostic of the trap dynamic. Image processing with nearly degenerate frequency conversion was also demonstrated using this specific mechanism. @S1050-2947 ~99!05302-0#
Patent•
10 Aug 1999
TL;DR: In this paper, a phase modulator encodes phase conjugation information and compensates the amt. aberrations, by which a desired output beam may be synthesized.
Abstract: PROBLEM TO BE SOLVED: To provide a relatively high average power fiber laser using optical fibers having relatively less complication than that of known systems. SOLUTION: A phased array 30 of parallel fiber amplifiers is coupled to a common master oscillator 22. The respective fiber amplifiers are provided with independently regulatable optical phase modulators 26. A wave front sensor 38 for leading out a feedback signal for phase control is used. Arbitrary phase profile information is impressed to this phase modulator, by which a desired output beam may be synthesized. Then, the fiber amplifier array subjected to the phase control functions as a synthetic aperture signal transmitter at an optical frequency. This fiber amplifier array is combined with a beacon phase surface sensor for the beam propagation in the amt. air. The phase modulator encodes phase conjugation information and compensates the amt. aberrations.
TL;DR: It is shown that phase-conjugate energy reflectivity of as much as 20,000% with a four-pass geometry in the longitudinally pumped polymer dye was obtained at 564 nm with degenerate four-wave mixing.
Abstract: We demonstrate the use of highly efficient degenerate four-wave mixing for phase conjugation with multipass geometries in a polymer laser dye saturable amplifier. Phase-conjugate energy reflectivity of as much as 20,000% with a four-pass geometry in the longitudinally pumped polymer dye was obtained at 564 nm.
TL;DR: In this article, beam combination characteristics were numerically and experimentally investigated in an array laser amplification using stimulated Brillouin scattering (SBS) phase conjugation, and the effect of piston errors due to imperfect phase locking was clarified.
TL;DR: A generalization of the theory of phase conjugation of partially coherent waves interacting with either deterministic or random weakly scattering nonabsorbing media is presented.
Abstract: The theory of distortion correction by phase conjugation, developed since the discovery of this phenomenon many years ago, applies to situations when the field that is conjugated is monochromatic and the medium with which it interacts is deterministic. In this Letter a generalization of the theory is presented that applies to phase conjugation of partially coherent waves interacting with either deterministic or random weakly scattering nonabsorbing media.
TL;DR: In this paper, the scattering properties of a Kerr layer near a phase conjugate mirror were investigated in both TE and TM polarization by an iterative method that applies to any periodic structure.
23 May 1999
TL;DR: In this article, a 5x microscope lens was used to launch the pump signal from single mode CW Nd:YAG laser into the fiber, the ends of which were cleaved.
Abstract: Summary form only given. It's known since the 1970's that stimulated Brillouin scattering (SBS), through its phase conjugation (PC) properties, provides an effective means for beam clean-up of moderate to high power pulsed lasers, and recently demonstrated for average power in the kW range for repetitive mode operation. We report the observation and characterisation of high fidelity PC via SBS of CW laser radiation in multimode silica fibre (core/ cladding diameters 50/125 mm, numerical aperture 0.1, attenuation of -1 dB/km). A 5x microscope lens was used to launch the pump signal from single mode CW Nd:YAG laser into the fibre, the ends of which were cleaved.
TL;DR: In this paper, the spatial and temporal dynamics arising in a photorefractive crystal (BaTiO3) during the process of double phase conjugation was studied experimentally. And, by the calculation of the correlation index, the spatial correlation decreased as the transverse interaction region was increased.
Abstract: Spatial and temporal dynamics arising in a photorefractive crystal(BaTiO3) during the process of double phase conjugation was studied experimentally. We studied the dynamical effects caused by the buildup of the diffraction grating and turn on of phase conjugated beams, as well as the spatial effects caused by the finite transverse coupling of beams and the propagation direction of beams. We observed conical emission in DPCM. We believe that various temporal and spatial instabilities are due to movement of the nonlinear grating. For a real beam coupling and constructive interaction of interference fringes in the crystal, we observed steady, periodic, irregular temporal behavior. And, by the calculation of the correlation index, we found that the spatial correlation decreased as the transverse interaction region was increased.
TL;DR: In this article, the authors investigate the properties of propagation and self-pumped phase conjugation (SPPC) of 90-fs laser pulses at 450 nm in BaTiO3.
Abstract: We investigate the properties of propagation and self-pumped phase conjugation (SPPC) of 90-fs laser pulses at 450 nm in BaTiO3. Femtosecond SPPC in BaTiO3, both in air and in immersion oil, is explored; it is demonstrated that femtosecond self-pumped phase-conjugate pulses are generated from all crystallographic faces of BaTiO3 in immersion oil. We measure the duration of the pulses after propagation and SPPC by using electric field cross correlation. The duration of SPPC increases as the incident angle increases. Because of the partial compensation of the negative angular dispersion, the self-pumped phase-conjugate pulse undergoes a total dispersion smaller than that of the transmitted pulse. By managing the angular dispersion of the femtosecond phase conjugator, we can control the total dispersion and thus the duration of the self-pumped phase-conjugate pulses. The experimental results agree with the theoretical simulations.
TL;DR: In this paper, the phase conjugation at steady-state stimulated Brillouin scattering (SBS) of an aberrated laser beam is numerically investigated in the case of a PC-mirror composed of an ordered phase plate, main focusing lens and SBS-cell.
TL;DR: In this paper, a degenerate four-wave mixing geometry with vertically polarized counter-propagating pump beams was used to achieve near-perfect vector phase conjugation at 488 nm in a methyl red dye impregnated polymethylmethacrylate film.
TL;DR: In this article, the possibility for realizing an optical memory using dynamic refreshment is discussed, where the information stored in a photorefractive crystal is incessantly read out, transmitted into an auxiliary memory and from this back into the crystal again and in this way refreshed.
Abstract: In this paper we discuss the possibility for realizing an optical memory using dynamic refreshment. Via phase-correct back-coupling by means of nonlinear optical phase-conjugation, the information stored in a photorefractive crystal is incessantly read out, transmitted into an auxiliary memory and from this back into the crystal again and in this way refreshed. Practical realizations and first results are presented.
28 Jun 1999
TL;DR: In this paper, different schemes of phase conjugation during formation of the self-organized hexagonal spot array in the photorefractive crystal KNbO 3 were described, and both forward and backward phase-conjugated beams are observed in the two-beam coupling geometry.
Abstract: In this paper, we describe different schemes of phase conjugation during formation of the self-organized hexagonal spot array in the photorefractive crystal KNbO 3 . Both forward and backward phase-conjugated beams are observed in the two-beam coupling geometry. We present also theoretical description of this multiplexed phase conjugation, introducing concept of the scattering wave-vector diagrams that visualize contributions from the transmission and reflection gratings.
TL;DR: In this article, the authors investigated the performance improvement in bandwidth by using a phase conjugate reflected beam for signal transmission in the presence of turbulent air, which may be caused by convection from a heated earth surface.
Abstract: An optical link over several kilometers between buildings or remote sites will have significantly reduced bandwidth in the presence of turbulent air, such as may be caused by convection from a heated earth surface. Bandwidth is decreased by amplitude and phase fluctuations due to the turbulence. This paper investigates the performance improvement in bandwidth by using a phase conjugate reflected beam for signal transmission. Weak fluctuations, consistent with the Rytov transformation, are assumed. A computer simulation is developed that uses a statistical model of the turbulent channel to assess the effectiveness of this approach.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
TL;DR: In this article, the reflection behavior of VO2 films for the 1.06 μm wavelength at the semiconductor-metal phase transition was investigated and the nonlinearity caused by photoinduced transition was used for phase conjugation of a pulsed Nd:YAG laser.
Abstract: The change in the reflection behavior of VO2 films for the 1.06 μm wavelength at the semiconductor–metal phase transition was investigated. The nonlinearity caused by photoinduced transition was used for phase conjugation of a pulsed Nd:YAG laser. At 60 Hz Q-switching rate and average intensities of the pump and probe waves at 1 and 0.3 W/cm2, respectively, the reflection coefficient of the conjugated wave was ∼1%, the threshold energy density was 8 mJ/cm2, the rise time of the signal was 30 ns. The response rate of the phase conjugation via the VO2 films is discussed.
TL;DR: In this article, a theoretical investigation of optical phase conjugation by use of nearly degenerate four-wave mixing in a two-level atomic system is presented, which is based on the semiclassical dressed state approach, which offers a very transparent picture of the physics involved in the nonlinear process.
Abstract: We present a theoretical investigation of optical phase conjugation by use of nearly degenerate four-wave mixing in a two-level atomic system. The description is based on the semiclassical dressed-state approach, which offers a very transparent picture of the physics involved in the nonlinear process. The theory provides an explanation in terms of a quantum interference between two channels for the strong reduction of the optical phase-conjugate yield when the pump fields are tuned to the atomic resonance. In addition, the model predicts an efficient generation of the optical phase conjugate if the system is prepared in a pure dressed state.