Phase Conjugate Image Research Articles

Time response of Brillouin-induced four-wave mixing with short signal pulse: Application to time-gated imaging

We investigate the time response of a phase conjugate mirror based on Brillouin-induced four-wave mixing, with a signal pulse that is shorter than the pump pulse. We show that, with suitable tailoring of the temporal profiles of signal and pump pulses, Brillouin-induced four-wave mixing can be used for time-gated phase conjugate imaging with a depth resolution on the order of 1 metre.

High-resolution phase-conjugate imaging in double-pumped phase conjugators

Phase-conjugate images with a resolution greater than 250 lines/mm are obtained through the use of a bridge, double-pumped phase conjugator. We demonstrate that this conjugator can carry out imageprocessing tasks, such as the addition and subtraction of complex spatial distributions, with a spatial resolution of >100 lines/mm. These results represent a significant improvement over previously reported resolutions obtained from photorefractive mutually pumped phase conjugators and approach the theoretical limit imposed by the grating spacing and cross talk.

Location and profile of phase conjugate image with gaussian beam pumping

AbstractWhen applying phase conjugate waves to various types of image processing, the characteristics of the wavefront, generated by the nonlinear optical medium, are an important research problem. The characteristics of a phase conjugate mirror with plane wave pumping have been investigated in previous research. To perform more realistic analysis, we derive equations describing the image location of the phase conjugate mirror with fundamental mode Gaussian beams as the pumping light and calculate the phase conjugate images numerically. The relationship between the probe light and the phase conjugate image using the Fresnel diffraction formula will be formulated first. Then the image location and the image magnification factor in consideration of the wave‐front curvature of the pump light is derived. Then the characteristics of the image location are analyzed considering the change of the curvature radius of the Gaussian beam in the thickness direction of the nonlinear optical medium. The image profile of the phase conjugate mirror is found by numerical calculation. The results show for the first time the effects of wavefront curvature of the pump light on the image reconstruction capability, which is an important characteristic of the phase conjugate mirror.

Photon-echo amplification by an external-cavity amplifier

We demonstrate as much as 2.5 × 10(5) amplification of a photon-echo signal using a simple external-cavity amplifier. The method may be useful in regeneration of photon echo and memory refresh in a dynamic photon-echo optical memory system. We propose an image storage system that is capable of regeneration and amplification of phase-conjugate images in a feedback loop.

Phase-conjugate inlaging properties in high-efficiency KNSBN:Cu double phase-conjugate mirror

In this study, we investigate the performance of a high-efflciency KNSBN:Cu double phase-conjugate mirror (DPCM). A phase-conjugate transmissivity as high as 58% and a phase-conjugate reflectivity as high as fivefold are observed. Experimental results also show that the DPCM has a good fidelity of phase-conjugate image. Also, amplified phase-conjugate images are observed.

Picosecond optical correlation using dynamic holography in polyacetylene

An image-processing system based on four-wave mixing in a film of polyacetylene less than 100 nm thick is demonstrated with a 1-ps processing cycle time. Image phase conjugation and cross correlation are performed with a resolution space-bandwidth product of 0.68 x 10(5) (equivalent to 261 x 261 pixels) in the phase-conjugate image. The light source was amplified optical pulses from a colliding-pulse mode-locked dye laser at a wavelength of 625 nm.

Multiple forward phase conjugation in a photorefractive bismuth silicate crystal

The geometrical configuration in which two pump beams and one non coplanar signal beam are incident upon the same side of a bismuth silicate crystal is investigated. It is shown that a strong interaction giving rise to a multiplicity of output beams (three of them phase conjugate) may be obtained when the pump beams are detuned in the opposite directions by the same amount. The phase conjugate images obtained are analysed.

Forward phase conjugation by three-wave mixing with bacteriorhodopsin

Forward phase conjugate images are obtained by three-wave mixing in bacteriorhodospin. A possible use of the process for spatial filtering is discussed.

Two-dimensional mapping of temperature in a flame by degenerate four-wave mixing in OH

Phase conjugate images are produced by resonant degenerate four-wave mixing from rotationally excited OH molecules in a premixed, laminar methane/air flame. By comparing signal intensities in the images produced using transitions from different rotational levels, the temperature map of a planar section of the flame is derived.

Color imaging in photorefractive crystals

Color phase-conjugate imaging is demonstrated using a multi-colored laser beam. Speed of response, size of the image, clarity of the image, and the intensity of the image are investigated. Color images are stored and recalled without crosstalk between different colors.

Resonance fluorescence spectrum of an atom near a phase conjugator

Resonance fluorescence by an atom near the surface of a phase conjugator is studied. The atom is irradiated by a finite-linewidth laser beam, and the bandwidth is modelled by a randomly fluctuating phase. Expressions for the steady-state atomic density operator and the resonance fluorescence spectrum are obtained. For a small laser linewidth the spectrum contains two delta peaks: the usual peak at the laser frequency and its phase-conjugate image. In the limit of separated lines the spectrum consists of the Mollow triplet and its phase-conjugate replica. In the image triplet the positions of the fluorescence line and the three-photon line are reversed, as compared with the original triplet. Also, the intensity of the image spectrum is distributed differently over the three lines.

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

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.

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

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.

Two-dimensional imaging of OH in flames by degenerate four-wave mixing

Degenerate four-wave mixing is used to produce two-dimensional images of OH distributions in atmosphericpressure flames. The phase-conjugated images from single laser pulses exhibit excellent signal-to-noise ratios and illustrate that degenerate four-wave mixing has outstanding potential as a multidimensional diagnostic for combustion environments.

Two-dimensional phase-conjugate imaging of atomic distributions in flames by degenerate four-wave mixing

We report the demonstration of a technique using resonant degenerate four-wave mixing to produce high-resolution, background-free images of atomic distributions in flames. Comparison with laser-induced-fluorescence methods and applications of the method to species of interest in combustion are briefly discussed.

Model for mutually pumped phase conjugation

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.

Spatially multiplexed phase conjugate imaging and processing in photorefractive BSO

Theoretical considerations and experimental results are presented for simultaneous degenerate multi-wave mixing in photorefractive BSO. Using the same crystal volume and common pump beams, multiple imaging has been achirved in which each image shows no cross-talk. The mutual modification of the multiplexed gratings presents no problem in terms of destructive depletion effects. Simultaneous correlation of two images with the same test image has also been achieved, verifying the independent nature of each grating within the crystal.

New applications of ferroelectrics for optical devices

Abstract In recent years ferroelectric materials with their large electrooptic coefficients have found new optical applications in the field of phase conjugate optics, image processing and dynamic holography. Some of these applications are based on the photoinduced refractive index changes or photorefractive effect which are due to the linear electro-optic effect driven by photoinduced space-charge fields. In this paper we give a review of recent nonlinear optical experiments with photorefractive ferroelectrics.

A two-dimensional vectorial theory of degenerate four-wave mixing

Coupled vector differential equations are derived for the amplitudes of four arbitrarily polarised waves incident in the perpendicular overlap configuration. Analytic solutions for reflection coefficients relating the amplitudes of the object and image beams are presented for the cases of strong pump beams in either parallel or perpendicular polarisation. Conditions are derived for obtaining a phase-conjugate image beam with various polarisations of object beam and for maximising the power of the reflected beam.