Showing papers on "Phase conjugation published in 1990"

Saturable absorption, wave mixing, and phase conjugation with bacteriorhodopsin.

Abstract: Bacteriorhodopsin exhibits strong nonlinear and saturation behavior with very low light intensities (~10 mW/cm(2)). A model and an experimental study of the saturation are described. Four-wave mixing experiments are used for obtaining phase conjugation and information on the holographic resolution of the material. Two kinds of samples were prepared and used in the experiments: films of bacteriorhodopsin in a solid polyvinylalcohol (polymer) matrix and in water.

Double phase conjugation in tungsten bronze crystals

Abstract: In this paper we report a new method for double phase conjugation particularly suited to the tungsten bronze crystal strontium barium niobate. It has also been observed to produce conjugate waves in BaTiO(3) and BSKNN. This new arrangement is called the bridge conjugator because the two beams enter opposing [100] crystal faces and fan together to form a bridge without reflection off a crystal face. Our measurements indicate that the bridge conjugator is competitive with previously reported double phase conjugate mirrors in reflectivity, response time, ease of alignment, and fidelity.

Mutually pumped phase conjugation in photorefractive strontium barium niobate: theory and experiment

Abstract: Two mutually incoherent laser beams can generate each other’s phase-conjugate replica by sharing holograms in a photorefractive strontium barium niobate (SBN) crystal. The path of each beam inside the SBN crystal uses three internal reflections at the crystal faces. We discuss phase-conjugate imaging, moving gratings induced by an applied electric field, the time response of grating formation, and the dependence of the phase-conjugate reflectivity on the incident-beam ratio. Also, we derive the amplitude coupled-wave solutions for mutually pumped phase conjugators with two coupled gratings, and we compare the theoretical results with our experimental results.

High precision retardation measurement using phase detection of Young’s fringes

Abstract: Phase detection of Young’s fringes is applied to a highly precise retardation measurement. A simple common-path polarizing interferometer is used with a birefringent wedge and a polarizer. The birefringent wedge introduces a spatially linear phase difference between orthogonally polarized light and Young’s fringes are formed on an image sensor. The phase difference between the orthogonally polarized components of light is proportional to the phase of Young’s fringes. Thus, the retardation is equal to the Young’s fringes’ phase change before and after insertion of the retarder into the common-path interferometer. The phase of Young’s fringes is calculated from the Fourier cosine and sine integrals of the fringe profile. The experimental results for wave plates, a Soleil-Babinet compensator, and a Pockels cell are presented with error estimates. The accuracy of the retardation measurement is experimentally estimated to be greater than λ/2100.

Efficient self-pumped phase conjugation at near-infrared wavelengths using cobalt-doped BaTiO(3).

Abstract: Using BaTiO3 crystals doped with cobalt, we have measured the reflectivity of self-pumped phase-conjugate mirrors operating in the total-internal-reflection geometry as a function of wavelength in the range between 633 and 933 nm We find that for cobalt concentrations above 25 parts in 106, the reflectivity is higher than 50% for all the investigated wavelengths At a wavelength of 800 nm the reflectivity is independent of incident power over a range of 12 to 600 mW

Information erasing in the phenomenon of long-lived photon echo

Abstract: The possibility of erasing information in an arbitrary cell of an optical memory device based on the phenomenon of long-lived photon echo is theoretically considered. Optimal conditions for a maximal number of write-erase cycles in a given cell are obtained, and an experimental setup for observing this effect is proposed.

High-speed, low-power optical phase conjugation using a hybrid amorphous silicon/ferroelectric-liquid-crystal device

Abstract: Optical phase conjungation using an amorphous silicon/ferroelectric-liquid-crystal light modulator shows an optical response of 100 microsec with a diffraction efficiency of 8.5% for an incident optical intensity of 1 mW/cm(2).

Real-time holographic associative memory using doped LiNbO3 in a phase-conjugating resonator.

Abstract: A real-time holographic associative memory that combines holography with phase conjugation is proposed. In the memory a type of doped LiNbO3 is used as a holographic recording medium and as a phase-conjugate mirror that provides optical feedback, thresholding, and gain. The device can store information and recall a complete image when only a portion of the stored image is input to the system. An outline of the principles and the experimental results are given, and the system’s addressing ability and selectivity are demonstrated.

Self-pumped phase conjugation with nanosecond pulses in strontium barium niobate.

Abstract: We report the observation of self-pumped phase conjugation by means of internal reflection in a photorefractive medium produced by a series of intense nanosecond pulses. Nanosecond pulses from a YAG laser ranging in intensity from 9 × 104 to 9 × 105 W/cm2 were used. The crystal was rhodium-doped strontium barium niobate. The conjugate signal began with the first pulse, and the time to reach 63% of its equilibrium value scaled as I−2. The equilibrium reflectivity was 29%. A similar cw experiment with the 514-nm line of an argon laser produced a response time that scaled as I−1.1.

Coherent beam and image amplification by Brillouin two-beam coupling in CS 2

Abstract: We report an experimental study of Brillouin two-beam coupling in CS2 at 1.06 μm in the regime below the pump’s stimulated Brillouin scattering (SBS) threshold. Angular discrimination between the pump and signal beams is employed. No competitive self-SBS (phase conjugation) of the pump was observed despite operation near the SBS threshold. Image intensification by a factor of 300 is demonstrated with this configuration.

Power laser generator with control of the direction of emission of the output beam

Abstract: This invention relates to power laser generators in which it is possible to control the angular direction of output laser beams. The generator according to the present invention is characterized by the fact that it successively comprises on the same optical axis of propagation, a pilot laser beam generator to generate a laser beam wavelength, a controllable deflector, a beam separator, a laser amplifying medium with the wavelength of the pilot beam, and a phase conjugation nonlinear mirror. The laser generator is applicable, in particular, to missile guidance systems or in telemetry systems.

High‐reflectivity self‐pumped phase conjugator using total internal reflection in KNbNO3:Fe

Abstract: A self‐pumped phase conjugate reflectivity of 74.8% is obtained with a suitably cut KNbO3:Fe crystal in a polygonal shape. The design and operation of this self‐pumped phase conjugator is described. The build‐up time is observed to be dependent on the input power. The phase conjugate nature of the retroreflected beam has been further confirmed by a significant decrease in the specular reflectivity of the input surface of the crystal.

Phase Conjugation in Methyl-Orange-Doped PVA Films by Photoinduced Anisotropy

Abstract: The influence of photoinduced anisotropy (dichroism and birefringence) in methyl-orange-doped polyvinyl alcohol film upon optical phase conjugation is investigated. The reflectivity of the phase-conjugate (PC) beam due to degenerate four-wave mixing (DFWM) is measured under the condition that the polarization states of a probe and two pump beams are mutually orthogonal. The more efficient PC beam generates at 515 nm rather than at 488 nm. At 515 nm, the reflectivity of the PC beam exceeds 10 percent about 30 minutes after the initiation of DFWM. It was found that birefringence rather than dichroism contributes to the generation of the PC beam at 515 nm.

Simultaneous wave-front and polarization conjugation of picosecond optical pulses by stimulated Rayleigh-wing scattering.

Abstract: Using phase conjugation by stimulated Rayleigh-wing scattering (SRWS) in carbon disulfide, we have observed simultaneous correction of wave-front and polarization distortions. SRWS was excited by pulses of 20-psec duration containing as much as 15 μJ of energy at a wavelength of 0.53 μm and produced phase-conjugate reflectivities as large as 10%.

Time reversal of Berry's phase by optical phase conjugation

Abstract: We examine experimentally the time-reversal properties of Berry’s geometrical phase in one of its optical manifestations, Pancharatnam’s phase, through the use of optical phase conjugation. The time-reversal symmetry of the total optical system is broken by a nonreciprocal element, a Faraday rotator. Nevertheless, we find that the geometrical part of the phase acquired by an optical wave in passing through the system still respects time-reversal invariance.

Optical phase conjugation in dyes embedded in polymer films

Abstract: Studies on low power optical phase conjugation (OPC) in three saturable dyes, viz., eosin, erythrosin B, and rose bengal, embedded in two polymer films, viz., gelatin and polyvinyl alcohol, are presented. Experiments are performed using the 514.5 nm line of an argon-ion laser. Saturation intensities are determined from the transmission versus intensity plots, and triplet lifetimes are estimated from the phosphorescence decay curves. OPC experiments are performed, and the variation of OPC reflectivity with intensity and absorption length is studied. Experimental results are compared with the theory of degenerate four-wave mixing in absorbing media proposed by R. L. Abrams and R. C. Lind [Opt. Lett. 2(4), 94 (1 978)]. There is fair agreement between the theory and the experimental observations. The limitations in using these films for cw OPC applications are briefly discussed.

Signal enhancement in collinear four-wave mixing

Abstract: The solitary-wave solutions of the four-wave equations are studied, and their relevance to four-wave mixing in finite media is discussed. In general, the transfer of action from the pump waves to the probe and signal waves is limited by nonlinear phase shifts that detune the interaction. However, by controlling the linear phase mismatch judiciously, it is often possible to effect a complete transfer of action from the pump waves to the probe and signal waves.

Second-order polarizability holograms in few-mode fibers: phase conjugation and angular selectivity.

Abstract: Second-order polarizability holograms in optical fibers were recorded by picosecond radiation of a neodymium laser together with its second harmonic. High angular selectivity of holograms was observed for various input angles of the reading IR beam. We observed phase conjugation of the green signal by using an oppositely directly IR beam to read the holograms. Coherent erasure of a hologram was demonstrated by means of a second exposure by an interference pattern of opposite sign.

Self‐pumped and double phase conjugation in GaAs with applied dc electric field

Abstract: Self-pumped and double phase conjugation are first demonstrated in undoped GaAs with applied dc electric field at 1.06 micron wavelength. Phase-conjugate reflectivities of up to 3 percent and 0.5 percent, respectively, are obtained and other dependences are reported. Reported values of the self-pumped phase-conjugate reflectivity are compared with those of InP.

High-reflectivity phase conjugation using Brillouin preamplification

Abstract: We describe experiments in which a weak laser pulse is phase conjugated by using a high-gain Brillouin amplifier in front of a stimulated Brillouin scattering phase-conjugate mirror. We observe phase conjugation with signal energies as low as 3 × 10−13 J and with a maximum reflection coefficient of 2 × 108.

Low power optical phase conjugation in dyes embedded in polyvinyl alcohol films

Abstract: Low power optical phase conjugation in polyvinyl alcohol films embedded with saturable dyes is reported. Phase conjugate reflectivity achieved is higher than that obtained in the case of similar gelatin films.

A Semiconductor Laser as a Stable Phase Conjugate Mirror for Linewidth Reduction of Another Semiconductor Laser

Abstract: An AlGaAs laser was used as a phase conjugate mirror. Reflectivities as high as 103 and bandwidth as wide as 1.9 GHz were observed. The linewidth of a second AlGaAs laser was reduced to 1/5 times that of its free-running value by optical feedback of the phase conjugate wave generated by the first laser. The reduced linewidth was independent of the separation between the two lasers, and was maintained in a stable manner for over two hours.

Motion detection, novelty filtering, and target tracking using an interferometric technique with GaAs phase conjugate mirror

Abstract: A method and apparatus for detecting and tracking moving objects in a noise environment cluttered with fast- and slow-moving objects and other time-varying background. A pair of phase conjugate light beams carrying the same spatial information commonly cancel each other out through an image subtraction process in a phase conjugate interferometer, wherein gratings are formed in a fast photorefractive phase conjugate mirror material. In the steady state, there is no output. When the optical path of one of the two phase conjugate beams is suddenly changed, the return beam loses its phase conjugate nature and the interferometer is out of balance, resulting in an observable output. The observable output lasts until the phase conjugate nature of the beam has recovered. The observable time of the output signal is roughly equal to the formation time of the grating. If the optical path changing time is slower than the formation time, the change of optical path becomes unobservable, because the index grating can follow the change. Thus, objects traveling at speeds which result in a path changing time which is slower than the formation time are not observable and do not clutter the output image view.

Three-wave and four-wave forward phase-conjugate imaging in photorefractive bismuth silicon oxide.

Abstract: Phase-conjugate images in the forward direction are obtained by a new type of four-wave interaction and by the Heer-Griffin type of three-wave interaction. The nonlinear medium is bismuth silicon oxide in which the interaction is optimized by detuning the input beam(s). Measurements are made for several test objects and interbeam angles.