Showing papers on "Phase conjugation published in 1989"
03 Oct 1989
TL;DR: In this paper, the concept of optical phase-conjugate mirrors, valid for monochromatic signals, is extended to large-bandwidth pulses such as those used in ultrasound echography.
Abstract: Focusing on a reflective target in an inhomogenous medium is difficult. In order to obtain good focusing properties, the concept of optical phase-conjugate mirrors, valid for monochromatic signals, is extended to large-bandwidth pulses such as those used in ultrasound echography. The transducer's linear response to the acoustic pressure allows replacement of the phase conjugation by a time-reversal operation on the pulse echo signals. The time-reversal mirror is an array of transmit-receive transducers. A first incident wave is reflected by the target. The received signals are stored in shift registers, reversed in times and then reemitted. The major advantage of this process is that the waves distorted by the aberrating medium are corrected by the mirror operation and the back propagation through the medium. When the medium contains several reflectors, this time-reversal process can be iterated in order to focus on the most-reflective one. >
353 citations
TL;DR: Various nonlinear optical phenomena in photorefractive media and selected applications in optical computing, including optical phase conjugation, two- and four-wave mixing, and real-time holography are described.
Abstract: This paper describes various nonlinear optical phenomena in photorefractive media and selected applications in optical computing. These phenomena include optical phase conjugation, two- and four-wave mixing, and real-time holography. The applications include image amplification and subtraction, logic and matrix operations, and optical interconnection.
79 citations
TL;DR: The photorefractive performance of a special 45 degrees - cut crystal of BaTiO(3) and compared it with the conventional 0 degrees -cut material and the effects of an externally applied electric field parallel to the grating wave vector on the gain and response time were investigated.
Abstract: We have characterized the photorefractive performance of a special 45°-cut crystal of BaTiO3 and compared it with the conventional 0°-cut material. An increased peak gain coefficient of 26 cm−1 was measured using near normal beam incidence. Response times measured were ∼1 order of magnitude faster than similar 0° -cut crystals. The effects of an externally applied electric field parallel to the grating wave vector on the gain and response time were investigated. As an application example, the crystal was used to produce efficient and stable self-pumped image phase conjugation.
56 citations
TL;DR: In this paper, the nuclear and electronic contributions to the third-order susceptibility χ3 in a phase conjugation experiment were resolved by a method of resolving the nuclear contributions.
Abstract: We present a method of resolving the nuclear and electronic contributions to the third‐order susceptibility χ3 in a phase conjugation experiment. The technique is applied to octylmethylpolysilane yielding χ3 (electronic)=(1.8±0.5)×10−12 esu and χ3(nuclear)=(1.1±0.4)×10−12 esu at 532 nm.
54 citations
TL;DR: Fibers were prepared for second-harmonic generation by injecting a frequency-doubled (seed) signal with the fundamental light from a Nd:YAG laser with interferometric precision.
Abstract: Fibers were prepared for second-harmonic generation by injecting a frequency-doubled (seed) signal with the fundamental light from a Nd:YAG laser. The relative phase shift between the seed and the second-harmonic light generated by the fiber was measured to be close to 90° (≃99 ± 9.2°). A water cell was used to sweep the relative phase of the waves with interferometric precision. Some physical consequences of a π/2 phase shift are pointed out.
41 citations
TL;DR: In this article, an experimental investigation of enhanced backscattering (partial phase conjugation) for phase screens generated by a propane gas burner or a group of electric fan heaters is presented.
Abstract: We report an experimental investigation of enhanced backscattering (partial phase conjugation) for phase screens generated by a propane gas burner or a group of electric fan heaters. A 10-cm-diameter collimated laser beam is transmitted through the phase screen to a plane mirror and reflected back through the same screen. When the doubly scattered radiation is imaged at infinity, an intensity enhancement is observed in the backscattering direction. The backscattering peak can have a width close to the diffraction limit despite the large scattering that is due to the screens and to the relatively large astigmatism of the collimating mirror. The results are shown to be in good agreement with the theoretical predictions.
40 citations
TL;DR: The parameters which govern the effective interaction length at threshold for phase conjugation due to stimulated Brillouin scattering are investigated and the length is found to be the shorter of the following parameters: the cell length, 3 times the coherence length or 5 times the Rayleigh range of the input laser radiation.
Abstract: We have investigated experimentally the parameters which govern the effective interaction length at threshold for phase conjugation due to stimulated Brillouin scattering. We found the length to be the shorter of the following parameters: the cell length, 3 times the coherence length or 5 times the Rayleigh range of the input laser radiation. We have also found that the fidelity of the return depends strongly on the coherence length when this parameter is much shorter than the cell length. Results are also presented on fluctuations in fidelity at high power and long pulse lengths.
40 citations
TL;DR: In this article, the temporal behavior of optical phase conjugation by single-grating anisotropic four-wave mixing in photorefractive crystals is studied and numerical evidence for optical instabilities of the phase-conjugate wave amplitude is shown.
Abstract: The temporal behavior of optical phase conjugation by single-grating anisotropic four-wave mixing in photorefractive crystals is studied. Numerical evidence for optical instabilities of the phase-conjugate wave amplitude is shown.
35 citations
TL;DR: In this article, phase conjugation by Brillouin scattering in SF/sub 6/ gas has been implemented on a two-pass KrF amplifier to provide near-diffraction-limited output pulses having a very low background level of amplified spontaneous emission.
Abstract: Phase conjugation by Brillouin scattering in SF/sub 6/ gas has been implemented on a two-pass KrF amplifier to provide near-diffraction-limited output pulses having a very low background level of amplified spontaneous emission. The pulse duration is variable between 1 and 10 ns by simply attenuating the input pulse. These pulses have also been used for the generation of much shorter duration pulses by truncated Brillouin scattering at the surface of cyclohexane. >
34 citations
TL;DR: A phase-conjugate interferometer is described that is self-referencing, compact, and insensitive to environmental disturbances, provides twice the sensitivity of conventional interferometers, and produces a direct representation of an incident wave front.
Abstract: We describe a phase-conjugate interferometer that consists of a partially transmitting conventional mirror placed in front of and in close proximity to a phase-conjugate mirror. The interferometer is self-referencing, compact, and insensitive to environmental disturbances, provides twice the sensitivity of conventional (nonphase-conjugate) interferometers, and produces a direct representation of an incident wave front. We have constructed such a device using internally self-pumped phase conjugation in barium titanate and have used the device to characterize the wave front produced by an aberrated optical system.
34 citations
TL;DR: Nonlinear laser spectroscopy based on optical phase conjugation by degenerate four-wave mixing in an absorbing liquid analyte solution is reported as a sensitive analytical technique using a relatively low-power continuous-wave argon ion laser as the excitation source.
Abstract: Nonlinear laser spectroscopy based on optical phase conjugation by degenerate four-wave mixing in an absorbing liquid analyte solution is reported as a sensitive analytical technique using a relatively low-power continuous-wave argon ion laser as the excitation source. This novel laser method provides excellent detection sensitivity since the analytical signal is a wavefront-reversed replica of the probe beam. Optical signal detection is convenient and efficient since the signal is a visible coherent laser beam. Important characteristics of this nonlinear laser method include cubic dependence of signal on laser power and quadratic dependence of signal on concentration. Excellent sensitivity, small detection volume, and convenient sample introduction offer many potential applications in trace-level condensed-phase analysis of continuously flowing systems. A preliminary detection limit of 2.9 X 10(-18) mol of eosin B in a simple flow cell is reported.
TL;DR: It is shown that hologram fixing in Bi(12)TiO(20) using a technique involving thermal cycling and an external ac field is feasible and effective.
Abstract: We demonstrate hologram fixing in Bi12TiO20 using a technique involving thermal cycling and an external ac field.
TL;DR: It has been determined that the x((3)) value of colloid semiconductor glass OG530 at 532 nm is 7 x 10(-12) esu.
Abstract: We have constructed a new interferometer that uses two phase-conjugate mirrors. This device allows for the measurement of the relative phase shift and the ratio of the nonlinear susceptibilities of materials. We have been able to measure weak reflectivity signals not detectable by normal degenerate four-wave mixing methods. It has been determined that the χ(3) value of colloid semiconductor glass OG530 at 532 nm is 7 × 10−12 esu.
TL;DR: It is observed that the specular reflectivity from the input face of a phase-conjugate mirror decreases by over 600% relative to the standard Fresnel reflectivity value upon the onset of phase conjugation, or wave-front reversal.
Abstract: We observe that the specular reflectivity from the input face of a ${\mathrm{BaTiO}}_{3}$ phase-conjugate mirror decreases by over 600% relative to the standard Fresnel reflectivity value upon the onset of phase conjugation, or wave-front reversal. Reasonable agreement is obtained using a model involving the destructive interference of the Fresnel-reflected beam with a series of phase-conjugate wave generated internal to the crystal. The basic diminishing effect should be universal and hence observable in other classes of self-pumped and externally pumped phase conjugators.
TL;DR: The use of holography to achieve the phase conjugation of temporal signals is theoretically discussed and the reversal of a particular asymmetric pulse envelope is experimentally demonstrated.
Abstract: We theoretically discuss the use of holography to achieve the phase conjugation of temporal signals. The reversal of a particular asymmetric pulse envelope is experimentally demonstrated. The holographic material is a photorefractive crystal used in a four-wave mixing configuration.
TL;DR: Two-wave mixing and self-pumped phase-conjugation measurements for GaAlAs laser-diode radiation at 830 nm in BaTiO(3) are reported, representing significant improvements over corresponding values previously reported.
Abstract: We report two-wave mixing and self-pumped phase-conjugation measurements for GaAlAs laser-diode radiation at 830 nm in BaTiO3 At 11°C, two-wave mixing gain coefficients as large as 18 cm−1 and response times of the order of 1 min have been observed by using an optimized mixing geometry Phase-conjugate reflectivities as large as 56% with 10-sec response times have also been measured using BaTiO3 in a passive ring conjugator when the source laser is optically isolated from the conjugator These results represent significant improvements over corresponding values previously reported
TL;DR: In this article, the saturation properties of dye molecules that are rigidly held in a solid host are qualitatively different from those of free-rotating dye molecules, and these unique saturation characteristics can be exploited to achieve nearly perfect vector phase conjugation for field strengths near the saturation intensity.
Abstract: The saturation properties of dye molecules that are rigidly held in a solid host are qualitatively different from those of molecules that are free to rotate. We have found that these unique saturation characteristics can be exploited to achieve nearly perfect vector phase conjugation for field strengths near the saturation intensity. We have studied these properties experimentally by using fluorescein-doped boric acid glass as the nonlinear-optical material.
TL;DR: In this article, a 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.
TL;DR: A coupled-mode theory is developed for photorefractive hologram sharing in mutually pumped phase conjugators and shows that the spatial gain coefficients for the mutually conjugated beams are twice as large as those of other scattered beams.
Abstract: A coupled-mode theory is developed for photorefractive hologram sharing in mutually pumped phase conjugators. The theory shows that the spatial gain coefficients for the mutually conjugated beams are twice as large as those of other scattered beams.
TL;DR: In this article, the phase shift and cross talk of conjugate waves from a self-pumped phase-conjugate mirror are investigated by a phenomenological model based on the four-wave mixing process and measured as a function of a uniform phase change of a wave incident upon the mirror.
TL;DR: In this article, a dynamically reprogrammable optical interconnect is demonstrated using temporally multiplexed writing beams in photorefractive double phase conjugation to achieve arbitrary fanout and fan-in.
Abstract: A dynamically reprogrammable optical interconnect is demonstrated using temporally multiplexed writing beams in photorefractive double phase conjugation to achieve arbitrary fan‐out and fan‐in. Applications to neural networks and image transmission through thick distortions are discussed.
TL;DR: In this article, the authors demonstrate self-pumped phase conjugation in photorefractive semiconductors using 1.32 µm light and an ac field technique to enhance the gain coefficient in InP:Fe and a single input pump beam.
Abstract: We report here for the first time the demonstration of self‐pumped phase conjugation in photorefractive semiconductors using 1.32 μm light. Using an ac field technique to enhance the gain coefficient in InP:Fe and a single input pump beam, phase conjugate reflectivities of 11% were measured using an input beam intensity of less than 1 mW/mm2. These results open up many possibilities for using photorefractive semiconductors in applications with low‐power infrared diode lasers.
TL;DR: In this article, both real-time and double-exposure phase conjugate interferometries are demonstrated with an eosin-doped gelatin film, which can be generated by degenerate four-wave mixing (DFWM) and holographic processes.
TL;DR: In this paper, a new type of conical emission in atomic sodium was observed, and phase conjugation experiments were conducted to explain the changes in reflectivity as a function of probe angle, which are not explained by existing theory.
Abstract: Observations of a new type of conical emission in atomic sodium provide the motivation for a series of phase conjugation experiments. These experiments show large variations in the reflectivity as a function of probe angle, which are not explained by existing theory. Analysis which includes self-induced refractive index changes leads to numerical calculations, which agree well with the observations. >
TL;DR: In this paper, phase conjugation of extremely weak signals using a phase-conjugate mirror based on Mandelstam-Brillouin-enhanced four-wave mixing, coupled with an optical quantum amplifier, is considered.
Abstract: Phase conjugation (PC) of extremely weak signals using a phase-conjugate mirror based on Mandelstam-Brillouin-enhanced four-wave mixing, coupled with an optical quantum amplifier, is considered. PC of a pulse with energy 4*10/sup -17/ J is achieved. PC conditions for amplified superluminescence noise of the optical quantum amplifier are specified and the limiting parameters are estimated. It is shown experimentally that if the signal-to-noise ratio (S/N) is equal to unity, the energy of an input signal for which phase conjugation is possible corresponds to 30 photons per transverse mode. >
TL;DR: What is to the authors' knowledge the first demonstration of Brillouin-enhanced four-wave mixing over a long atmospheric path and the phase-conjugate return energy measured at the retroreflector increased by a factor of 10 over the initial weak beam.
Abstract: We report what is to our knowledge the first demonstration of Brillouin-enhanced four-wave mixing over a long atmospheric path. Weak laser light reflected from a remote retroreflector was input to a high-gain conjugate mirror. The resulting amplified output returns to the retroreflector owing to its phase-conjugate nature. Despite atmospheric effects the phase-conjugate return energy measured at the retroreflector increased by a factor of 10(4) over the initial weak beam.
TL;DR: In this paper, phase conjugate reflectivity was measured as a function of the incident pulse duration, showing agreement with the theory of nonlinear electroacoustic interaction in LiNbO3.
Abstract: Acoustic phase conjugate waves were generated at 60 MHz using nonlinear electroacoustic interaction in LiNbO3. The phase conjugate reflectivity was measured as a function of the incident pulse duration. The amplitude reflectivity was of the order of 10−3 for a 1.8×104 V m−1 pump electric field and was proportional to the incident pulse duration, showing agreement with the theory.
TL;DR: A method for achromatic volume holography is described using a combination of material and grating dispersion with barium titanate as the dispersive material and a bandwidth of 250 nm is realized.
Abstract: A method for achromatic volume holography is described using a combination of material and grating dispersion. With barium titanate as the dispersive material, a bandwidth of 250 nm is realized. The device may be used for broadband phase conjugation and image reconstruction.
TL;DR: In this article, the reflectivity of an external ring phase conjugate mirror is measured as a function of temperature for 515 nm radiation, and the maximum reflectivity is 26% at 124 °C.
Abstract: Self‐pumped phase conjugation is observed using a KNbO3 crystal. The reflectivity of an external ring phase conjugate mirror is measured as a function of temperature for 515 nm radiation. The maximum reflectivity is 26% at 124 °C. On cooling, the reflectivity decreases and vanishes completely below 62 °C. The phase conjugate nature of the retroreflected beam is illustrated. The temperature‐dependent response time is shown to be proportional to (T−56 °C)−1.