Showing papers on "Phase conjugation published in 1988"
TL;DR: In this paper, a review of the application of phase conjugation to solid-state lasers is presented, using demonstrated techniques for compensating static and thermally induced aberrations and depolarizations, as well as energy scaling by coherent coupling of multiple-gain media.
Abstract: Phase conjugation by stimulated Brillouin scattering represents a fundamentally promising approach for achieving power scaling of solid-state lasers. Following a summary of the power scaling problem and an overview of phase conjugation concepts, a review is presented of the application of phase conjugation to solid-state lasers. The author describes power scaling using demonstrated techniques for compensating static and thermally induced aberrations and depolarizations, as well as energy scaling by coherent coupling of multiple-gain media. Applications to diode-pumped lasers are discussed, as is a novel approach for power scaling of diode lasers themselves. Future research directions are indicated regarding conjugation fidelity at increasingly higher energies or with short-pulse and/or broadband lasers. >
183 citations
TL;DR: This new photorefractive interaction is characterized by reasonable Phi* reflectivities (~10-25%), good Phi* fidelity, and no image cross talk.
Abstract: Two mutually incoherent extraordinary laser beams, incident upon opposite a faces of a BaTiO3 crystal, generate a set of photorefractive holograms that channel both beams toward the +c face of the crystal, where they are internally reflected into the opposite channel. The resultant cross coupling of the two incident beams produces a pair of phase-conjugate (ϕ*) beams. This new photorefractive interaction is characterized by reasonable ϕ* reflectivities (~10–25%), good ϕ* fidelity, and no image cross talk. The variations in ϕ* reflectivity with crystal orientation, angles of incidence, and intensity ratio are presented. The formation times of the photorefractive gratings responsible for the phase conjugation are significantly shorter than those of other self-pumped phase conjugators.
154 citations
TL;DR: Computed Gaussian-beam results agree well with analytic plane-wave calculations that straddle Raman-Nath and Bragg regimes for counterpropagating waves in Kerr media for both focusing and defocusing nonlinearities.
Abstract: Continuous-wave and oscillatory transverse instabilities are predicted for counterpropagating waves in Kerr media for both focusing and defocusing nonlinearities. Neither a cavity nor a finite response time is required. Computed Gaussian-beam results agree well with analytic plane-wave calculations that straddle Raman-Nath and Bragg regimes.
128 citations
TL;DR: In this paper, the principles and design of optical arrays are discussed, and an augmented 4 × 4 matrix is derived to describe the optical behavior of a misaligned optical element, which accounts for imaging properties, phase conjugation properties, and some other new properties of arrays.
Abstract: Publisher Summary This chapter discuses the principles and design of optical arrays. Arrays of optical elements can be found in nature, such as the compound eyes of insects, and in everyday life, such as the corner-cube arrays on cars and bicycles or on road signs. The chapter describes the most unusual new phenomena associated with arrays—that is, the non-Gaussian imaging property of GRIN (gradient index) rod arrays and the pseudo phase conjugation phenomenon of corner-cube arrays. The chapter reviews the essential features of the 2 × 2 ray transfer matrix method. The augmented 4 × 4 matrix introduced to describe the optical behavior of a misaligned optical element is derived. The chapter examines how an array may be treated in terms of a 2 × 2 matrix, which accounts for imaging properties, phase conjugation properties, and some other new properties of arrays. Some examples of arrays that possess interesting properties are given. The problem of the quality of synthesized images is treated by analyzing the additional aberrations of the arrays, and interference fringe formation, with particular regard to the conditions under which they can be eliminated.
65 citations
TL;DR: In this paper, a model for mutually pumped phase conjugation was proposed and demonstrated for two mutually incoherent laser beams pump each other, producing a pair of phase-conjugate beams through a cross-readout process.
Abstract: A model is proposed and demonstrated for mutually pumped phase conjugation when two mutually incoherent laser beams pump each other, producing a pair of phase-conjugate beams through a cross-readout process. The model considers the buildup of two independent counterpropagating oscillations in a ring resonator containing two-beam-cbupling gain media. The experimental demonstration of the model using two photorefractive BaTiO3 crystals in a ring cavity gave simultaneous phase-conjugate images with good fidelity and no image cross talk. As expected, the counterpropagating oscillations were slightly detuned in frequency (∼1 Hz) from the corresponding pumping beams with frequency shifts related to the ring-cavity length. Frequency shifts were also observed in the phase-conjugate beams, with their magnitudes dictated by energy conservation for nondegenerate four-wave mixing.
61 citations
TL;DR: Calculations of the nonlinear optical behavior are developed for model composites consisting of nanospheres with a metallic core and a nonlinear shell suspended in a non linear medium, indicating that phase-conjugate reflectivity enhancements of 10(8) may be possible.
Abstract: Calculations of the nonlinear optical behavior are developed for model composites consisting of nanospheres with a metallic core and a nonlinear shell suspended in a nonlinear medium. The concept for the enhancement of optical phase conjugation from all these nonlinear regions is that the optical field can be concentrated both inside and in the neighborhood of the metallic core, aided by surface-mediated plasmon resonance. Calculations for gold cores and aluminum cores indicate that phase-conjugate reflectivity enhancements of 10(8) may be possible.
47 citations
TL;DR: It is shown by means of a quantum electrodynamic calculation that excess noise is inherent in the process of optical phase conjugation, both in that the state of the field leaving a phase-conjugate mirror can always be described classically and that the fluctuations in the generated field are always greater than those predicted by Poisson statistics.
Abstract: We show by means of a quantum electrodynamic calculation that excess noise is inherent in the process of optical phase conjugation, both in that the state of the field leaving a phase-conjugate mirror can always be described classically (i.e., its phase-space density is positive semidefinite) and in that the fluctuations in the generated field are always greater than those predicted by Poisson statistics. Except in special cases, quantum noise imposes a limitation on the ability of phase conjugation to remove the eff'ects of aberrations.
42 citations
TL;DR: In this article, a 20 kHz ac square-wave electric field was used to enhance the beam-coupling gain and the degenerate four-wave mixing reflectivity of photorefractive GaAs at 1.06 μm.
Abstract: We have used a 20-kHz ac square-wave electric field to enhance the beam-coupling gain and the degenerate four-wave mixing reflectivity of photorefractive GaAs at 1.06 μm. The largest measured four-wave mixing reflectivity in the steady state was 15% at a grating period of 9 μm and an applied voltage of 3.2 kV across 0.4 cm. Theoretical results predict substantially higher reflectivity values for a field of 8 kV/cm; the origin of this discrepancy is thought to be space-charge effects that prevent us from obtaining the full field inside the crystal. We have also measured a transient reflectivity of 510% during the switch on of the backward pump beam. Finally, we have determined the accuracy of wave-front reversal through measurements of piston-error correction and conjugation fidelity.
40 citations
TL;DR: A method of polarization (vector) wavefront reversal by four-wave mixing in a photoanisotropic material is described and the way to achieving these conditions by optically controlling the anisotropy of the nonlinear medium is demonstrated experimentally.
Abstract: A method of polarization (vector) wavefront reversal by four-wave mixing in a photoanisotropic material is described. Jones matrices, describing the dynamic holographic gratings recorded in the material at arbitrary polarization of the signal wave, are derived. They are employed to define the conditions for generating a wave that is fully conjugate (by polarization as well) to the signal wave. The way to achieving these conditions by optically controlling the anisotropy of the nonlinear medium is demonstrated experimentally.
38 citations
Proceedings Article•
25 Apr 1988
TL;DR: In this paper, a method of real-time optical image subtraction using holographic interference in photorefractive media is proposed, which is performed on a barium titanate (Ba-TiO3) crystal.
Abstract: We propose a new method of real-time optical image subtraction using holographic interference in photorefractive media. An experimental demonstration is performed on a barium titanate (Ba-TiO3) crystal.
37 citations
01 Jan 1988
TL;DR: In this article, a theoretical description of the interaction of optical waves due to the resonant nonlinear response of an atomic system is presented, which is explicitly applied to several examples of current interest, including single-beam saturation spectroscopy, pump-probe saturation, modulation and phase conjugation.
Abstract: We present a theoretical description of the interaction of optical waves due to the resonant nonlinear response of an atomic system. We emphasize how the resonant nature of the nonlinear coupling is modified by the shifting of the atomic energy levels as a consequence of the dynamic Stark effect and show the equivalent role played by population pulsations in determining the nature of the nonlinear coupling. A general formalism is developed to treat these effects and is explicitly applied to several examples of current interest, including single-beam saturation spectroscopy, pump–probe saturation spectroscopy, modulation spectroscopy, degenerate four-wave mixing for phase conjugation, and instabilities in the beam propagation through resonant media.
Patent•
09 Dec 1988TL;DR: In this paper, a method for iterative phase conjugation adaptive reduction of phase aberration effects upon the time delays necessary for formation of a beam of coherent energy focused within a non-homogeneous medium at a selected range R from, and at an angle ϑ with respect to the normal to, the surface of an array of a plurality N of transducers, each for providing a portion of the energy of the beam when excited and for converting energy reflected to a signal therefrom, first bounces from a large collection of scatter-ers, contained in a portion to be investigated
Abstract: A method for iterative phase conjugation adaptive reduction of phase aberration effects upon the time delays necessary for formation of a beam of coherent energy focused within non-homogeneous medium at a selected range R from, and at an angle ϑ with respect to the normal to, the surface of an array of a plurality N of transducers, each for providing a portion of the energy of the beam when excited and for converting energy reflected thereto to a signal therefrom, first bounces from a large collection of scatterers, contained in a portion of the medium to be investigated, a probe beam for that beam angle ϑ. The received signals from each of the (N-1) pairs of adjacent transducers are cross-correlated to derive a like number of phase conjugation correction signals, which are then arithmetically operated upon to provide a time correction for the time delay associated with each probe beam transducer, for that range R and angle ϑ. The time correction for each transducer then modifies each of at least one iteration of excitation to, and return signal received from, the media portion. A plurality of iterations, with each excitation made with the most recent corrected delays values, better focuses the interrogating beam, until, after a selected number of iterations, actual imaging data can be obtained with minimal phase aberrations.
TL;DR: The undepleted-pumps photorefractive four-wave mixing equations for the case of orthogonally polarized pump beams are solved and the phase-conjugate reflectivities are measured.
Abstract: We solve the undepleted-pumps photorefractive four-wave mixing equations for the case of orthogonally polarized pump beams. Advantages over the parallel-polarized-pumps case include the potential for reflectivity enhancement and easy isolation of the conjugator from the source. The phase-conjugate reflectivities for both the parallel and orthogonally polarized pump beam cases were measured with a BaTiO3 crystal, and the results support our theoretical predictions.
TL;DR: In this article, the response of a photorefractive phase conjugator to time-varying signals is examined, and the effects of various parameters on the fidelity and stability of the conjugation process are determined.
Abstract: The response of a photorefractive phase conjugator to time-varying signals is examined. Maxwell’s equations are coupled to the material equations followed by linearization using a strong undepleted pump approximation and simplification by the slowly varying envelope approximation. The resulting set of equations is solved by frequency-domain techniques. The solution is expressed in terms of a transfer function that relates the complex frequencies of the probe and the conjugate field. Limiting forms of the transfer function are derived, and a comparison with a Kerr material is made. The effects of various parameters on the fidelity and stability of the conjugation process are determined. Numerical results are presented showing the distortion of time-varying signals owing to the nonideal conjugation process.
Patent•
22 Aug 1988TL;DR: In this article, a spatial light modulator is used to transfer electrical data into an optical form and then employs the photorefractive effect in the bulk for processing the data, which can be used for optical information processing, matrix multiplication, and integrated semiconductor optical information processors.
Abstract: Optical processing using photorefractive GaAs and other compound semiconductor crystals (28) is achieved in a four-wave mixing configuration. Potential applications of optical processing include spatial light modulation, phase conjugation, correlation, convolution, edge enhancement, matrix multiplication, incoherent-to-coherent conversion, and many others. In particular embodiments, optical processing, matrix multiplication, and integrated semiconductor optical information processors are demonstrated. In the case of integration of semiconductors and optical information processors, a spatial light modulator (88) is fabricated on a surface of a compound semiconductor crystal to form an integrated device (86). The device uses the spatial light modulator to transfer electrical data into an optical form and then employs the photorefractive effect in the bulk for processing the data.
TL;DR: Qualitatively different polarization behavior is observed for pump intensities near or above the two-photon saturation intensity, as predicted by third-order theories.
Abstract: We have studied the polarization properties of phase conjugation by degenerate four-wave mixing resonantly enhanced by the sodium 3S1/2 → 6S1/2 two-photon-allowed transition. As predicted by third-order theories, this interaction leads to simultaneous conjugation of the optical wave front and state of polarization (vector phase conjugation) when the pump intensities are sufficiently weak. However, qualitatively different polarization behavior is observed for pump intensities near or above the two-photon saturation intensity.
TL;DR: Using a degenerate optical phase conjugation device, a new real-time coherent optical Wigner distribution and ambiguity function implementation method for both one-and two-dimensional complex signals is suggested in this paper.
TL;DR: In this paper, achromatic optical systems forming phase shifters and phase modulators are presented and shown to produce phase-angle shifts in incoming waves which are independent of wavelength over broad spectral ranges.
TL;DR: 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.
Abstract: 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.
TL;DR: In this paper, a double-phase conjugate mirror was used for image subtraction, addition, and intensity inversion by two orthogonally polarized image-bearing phase conjugates.
Abstract: We demonstrate, using a double‐phase conjugate mirror, image subtraction, addition, and intensity inversion by two orthogonally polarized image‐bearing phase conjugate waves.
TL;DR: In this paper, a general theory of polarization and spatial information recovery by modal dispersal and phase conjugation is presented by means of a coherency matrix formalism, applied to a system that consists of a multimode modal-scrambling fiber terminated by a conventional phase-conjugate mirror that reflects only one polarization component.
Abstract: A general theory of polarization and spatial information recovery by modal dispersal and phase conjugation is presented by means of a coherency matrix formalism. The theory is applied to a system that consists of a multimode modal-scrambling fiber terminated by a conventional phase-conjugate mirror that reflects only one polarization component. The degree of polarization and the signal-to-noise ratio of the reconstructed field are discussed as a function of input-beam launching conditions. Some experimental results are also shown for comparison with the theory.
TL;DR: The use of the optical phase conjugation (OPC) process for parallel digital and symbolic optical computing is described and an OPC-based ultrafast optical computing architecture is proposed.
Abstract: The use of the optical phase conjugation (OPC) process for parallel digital and symbolic optical computing is described. Using spatially encoded logic and symbolic variables, various OPC-based parallel ultrafast optical logic, symbolic as well as interconnect processors are detailed. The proposed devices are experimentally verified using picosecond pulses from a mode-locked Nd3+:YAG laser. Based on these processors, an OPC-based ultrafast optical computing architecture is proposed.
TL;DR: In this paper, an optimized configuration for phase conjugation and four-wave mixing in cubic photorefractive crystals (such as GaAs and Bi12SiO20) is presented.
Abstract: An analysis of an optimized configuration for phase conjugation and four‐wave mixing in cubic photorefractive crystals (such as GaAs and Bi12SiO20) is presented We obtain an exact solution of the four‐wave mixing configuration, and find a wide range of self‐oscillation regime
TL;DR: In this article, the storage and reconstruction of time and space-domain variations of light fields with arbitrarily variable polarization states and their full phase conjugation were accomplished using photochemically accumulated stimulated photon echo.
TL;DR: Experimental results obtained with a picosecond mode-locked Nd3+:YAG laser are presented to support the use of the optical phase-conjugation process for optical residue computation.
Abstract: The use of the optical phase-conjugation (OPC) process for optical residue computation is proposed. By using an OPC-based parallel switching array, various optical position-coded residue-mapping units for carry-free addition, subtraction, and multiplication operations are described. Experimental results obtained with a picosecond mode-locked Nd3+:YAG laser are presented to support the proposal.
02 Jun 1988
TL;DR: In this article, the authors proposed a technique which combines the larger bandwidth attainable with heterodyne-interferometry with a large light-gathering power necessary for optical detection of ultrasonic signals from rough surfaces.
Abstract: For the application of ultrasonic signals generated by short laser pulses via thermoelasticity and by ablation of surface material at solid surfaces, it is desirable to detect these signals in a contact-free manner at rough surfaces. If one could use optical interferometers as detectors this would constitute a new tool for the remote nondestructive testing of materials and components. Velocity interferometers are suitable instruments for this purpose /1/, however, their bandwidth is limited, in practice to about 10 MHz. We have developed a technique which allows one to combine the larger bandwidth attainable with heterodyne-interferometry with a large light-gathering power necessary for optical detection of ultrasonic signals from rough surfaces.
TL;DR: In this article, a theory of degenerate four-wave mixing (DFWM) of arbitrary polarized waves in an anisotropic optically active photorefractive crystal using the method of coupled waves, a system of differential equations is deduced describing the coupling process.
Abstract: A theory is presented of degenerate four-wave mixing (DFWM) of arbitrary polarized waves in an anisotropic optically active photorefractive crystal. Using the method of coupled waves, a system of differential equations is deduced describing the coupling process. This system is specified to DFWM in crystals of the Bi/sub 12/GeO/sub 20/-type and numerically solved based on the shooting method. Some peculiarities of phase conjugation in these crystal are discussed. >