Showing papers on "Phase conjugation published in 1987"
TL;DR: In this paper, the authors have observed a darkening effect and the formation of permanent volume gratings in CdSSe semiconductor-doped glasses, both phenomena being certainly due to the same photochemical mechanism.
Abstract: We have observed a darkening effect and the formation of permanent volume gratings in CdSSe semiconductor-doped glasses, both phenomena being certainly due to the same photochemical mechanism. This allowed us to reconcile contradictory results concerning the speed of their nonlinear response. We also studied the frequency dependence of χ(3) below the gap and the intensity dependence of the reflectivity of these phase-conjugate mirrors. Our results can be interpreted in terms of the band-filling model with Boltzmann statistics. Finally, frequency- and time-resolved luminescence measurements helped us to interpret various results.
335 citations
TL;DR: A theory of four-wave mixing in semiconductor laser media is developed by considering the contributions of both the gain and index gratings created by the carrier-density modulation occurring at the beat frequency of the pump and the probe waves, showing that the dominant contribution to the four- wave mixing process comes from the index grating.
Abstract: A theory of four-wave mixing in semiconductor laser media is developed by considering the contributions of both the gain and index gratings created by the carrier-density modulation occurring at the beat frequency of the pump and the probe waves. The general formalism can be applied to semiconductor lasers operating below or above threshold. As an illustration, we consider the case in which the semiconductor laser is operated as a traveling-wave amplifier. The results show that the dominant contribution to the four-wave mixing process comes from the index grating. Further, the index grating makes the probe transmission asymmetric with respect to the pump-probe detuning.
91 citations
TL;DR: A detailed analysis of phase conjugation at 1.06 μm, in the transparency region of soluble polydiacetylenes is presented in this article, where different grating contributions are isolated.
Abstract: A detailed analysis of picosecond time‐resolved phase conjugation at 1.06 μm, in the transparency region of soluble polydiacetylenes is presented. Different grating contributions are isolated. It is shown that in red and blue gel forms, phase conjugation at high pump energies is driven by two‐photon absorption degenerate six‐wave mixing, superimposed on degenerate four‐wave mixing. The third‐order nonlinear susceptibility of these polymers is reported: It reaches 10−11 esu (30 times CS2 value) for the pure blue amorphous polymer. Two‐photon excited species increase phase conjugation at 1‐GW cm−2 pump power by one order of magnitude.
71 citations
69 citations
TL;DR: In this article, optical detection of ultrasonic signals of 75 MHz center frequency has been carried out by heterodyne interferometry at the rough surface of an aluminum sample The distorted wave front was reconstructed by optical phase conjugation leading to an increase of the light gathering power of the interferometer.
Abstract: Optical detection of ultrasonic signals of 75 MHz center frequency has been carried out by heterodyne interferometry at the rough surface of an aluminum sample The distorted wave front was reconstructed by optical phase conjugation leading to an increase of the light‐gathering power of the interferometer
64 citations
Patent•
21 Sep 1987TL;DR: In this paper, a method for phase conjugation adaptive reduction of phase aberration effects upon the time delays necessary for information 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, is presented.
Abstract: A method for phase conjugation adaptive reduction of phase aberration effects upon the time delays necessary for information 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; cross-correlating, for each probe beam, the received signals from each of the (N-1) pairs of adjacent transducers to derive a like number of phase conjugation correction signals; arithmetically operates upon the plurality of phase conjugation correction signals to provide a time correction for the time delay associated with each probe beam transducer, for that range R and angle θ; and then modifies by the time correction for each transducer the time delay of both transducer excitations and return signals received from the media portion to be investigated to reduce phase aberration in the resulting image.
55 citations
TL;DR: In this article, an experimental study of the coupling of diode laser arrays to various photorefractive phase conjugate mirrors is presented, where frequency locking of arrays as well as the control of their emitted light patterns are demonstrated.
Abstract: An experimental study of the coupling of diode laser arrays to various photorefractive phase conjugate mirrors is presented. We demonstrate frequency locking of arrays as well as the control of their emitted light patterns.
52 citations
42 citations
Patent•
11 Dec 1987TL;DR: In this article, 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 scatterers, contained in a part of the medium
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 drive 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.
41 citations
01 Jul 1987
TL;DR: Experimental and theoretical results are presented demonstrating that recovery of the spatial and polarization modes of the incident light takes place only when a phase conjugator at the fiber output preserves polarization on reflection.
Abstract: When polarized light is incident upon a long multimode fiber, the emerging light is randomly distributed among the spatial and polarization modes. We present experimental and theoretical results demonstrating that recovery of the spatial and polarization modes of the incident light takes place only when a phase conjugator at the fiber output preserves polarization on reflection.
36 citations
TL;DR: Transient phase conjugation by degenerate four-wave mixing in saturable dyes is investigated theoretically and experimentally in this paper, where two pump waves and a probe wave are simultaneously turned on and the pump waves are turned on well before the incidence of the probe wave.
Abstract: Transient phase conjugation by degenerate four-wave mixing in saturable dyes is investigated theoretically and experimentally. Two special cases are examined: (1) the case in which two pump waves and a probe wave are simultaneously turned on and (2) the case in which the pump waves are turned on well before the incidence of the probe wave. For case (1) a peak appears in the transient reflectivity for high pump intensity, while for case (2) the reflectivity increases monotonically with time up to the steady-state value irrespective of the value of the pump intensity.
TL;DR: In this paper, the authors used a demountable hollow cathode discharge cell and a continuous-wave dye laser to detect optical phase conjugation in the de degnerate four-wave mixing.
Abstract: Optical phase conjugation in the hollow cathode lamp by degnerate four-wave mixing is a novel analytical laser spectroscopic method in which a laser beam is generated as the signal beam. With the use of a demountable hollow cathode discharge cell and a continuous-wave dye laser, the signal beam is clearly visible to the naked eye when 1 μg of sodium is placed inside the cathode cavity. Since the signal beam is a time-reversed replica of the probe laser beam, highly efficient optical signal detection can be performed with minimum optical background noise. Since the signal is Doppler-free with negligible Lorentzian broadening (30 Torr discharge pressure), it provides excellent spectral resolution. Sodium D2 hyperfine lines of 3s 2S1/2 (F' = 2) → 3p 2P3/2 (F = 3) and 3s 2S1/2 (F' = 1) → 3p 2P3/2 (F = 0) were resolved. In addition to excellent spectral resolution and ease of signal detection, the technique also offers unique properties of optical phase conjugation.
TL;DR: Measurements of the two-wave mixing gain as a function of frequency detuning in photorefractive crystals are presented, indicating that the phase shift of the photoreFractive inde grating with respect to the light interference pattern is not exactly 90 degrees, as is often assumed.
Abstract: We present measurements of the two-wave mixing gain as a function of frequency detuning in photorefractive crystals. In many cases, this function is asymmetric, indicating that the phase shift of the photorefractive inde grating with respect to the light interference pattern is not exactly 90 degrees , as is often assumed. In four-wave mixing, the phase of the phase-conjugate wave contains the phase of the pumping and probe waves and a phase shift determined by the interaction taking place in the nonlinear medium. This second term, the phase shift of the phase conjugator, is a function of the type of grating and the phase shift of this grating. The phase shift of the grating obtained from the two-wave mixing measurements compares well with that obtained from four-wave mixing measurements of the phase of the phase conjugator.
TL;DR: High reflectivities are obtained as a result of Brillouin resonance enhancement in this geometry, and the quality of the phase-conjugation process is not degraded even by the use of an aberrated pump wave.
Abstract: The results of an experimental investigation of a new geometry for producing phase conjugation by Brillouin-enhanced four-wave mixing are presented. In this geometry, the four-wave mixing medium is carbon disulfide, and the backward-going pump wave is created from the transmitted forward-going pump wave by stimulated Brillouin scattering (SBS) in glycerol. The two pump waves are hence phase conjugates of each other, and the quality of the phase-conjugation process is not degraded even by the use of an aberrated pump wave. The probe wave is created by SBS in carbon disulfide, which has a Brillouin frequency half that of glycerol, and the conjugate wave is therefore generated at the same frequency as the probe. Since the pump and signal waves differ in frequency by the Brillouin frequency of the carbon disulfide four-wave mixing medium, high reflectivities (approximately 2000%) are obtained as a result of Brillouin resonance enhancement.
TL;DR: Long-term storage and phase conjugation of multiple images by using a backward-stimulated echo scheme in the 3H4 -3Po transition of Pr3+:LaF3 crystal is observed.
Abstract: We have observed long-term storage and phase conjugation of multiple images by using a backward-stimulated echo scheme in the 3H4–3P0 transition of Pr3+:LaF3 crystal. The temporal order of the multiple-echo images is the reverse of that of the input images. Each of the echo images is a phase-conjugate replica of the input images and lasts as long as 15 sec. This constitutes, in principle, the first reported demonstration of an ultrafast holographic movie using a stimulated photon echo.
Patent•
19 Jun 1987
TL;DR: In this article, the phase conjugation reflector produces a phase-conjugated replica of a specularly reflected and thresholded portion of the input beam, which is retroreflected toward the source.
Abstract: Apparatus is disclosed for phase conjugation of an input beam with thresholding of spatially resolvable parts of the beam that have amplitudes greater than a predetermined threshold value. A phase conjugation reflector produces a phase conjugated replica of a specularly reflected and thresholded portion of the input beam, which is retroreflected toward the source of the input beam. All of the spatial components of the phase conjugated replica retain the same relative phase relationships with respect to each other as the incident complex beam. In a preferred embodiment the invention comprises a liquid crystal light valve (LCLV) system, input and output polarizers, and a phase conjugate mirror (PCM). This combination of elements forms a device that can function as a threshold retroreflector with ˜106 resolvable elements. Thresholding is accomplished by allowing part of each spatially resolvable component to reach the photoconductive layer on the opposite side of the LCLV dielectric mirror that reflects the component. The dielectric mirror can be made partially transmissive, or an optical feedback path can be provided to convey a portion of each spatially resolvable component to the photoconductive layer behind the point of reflection by the dielectric mirror. Various feedback methods are presented. The phase conjugate mirror can be implemented by means of any of the phenomena which give rise to phase conjugate retroreflection, such as stimulated scattering, stimulated photorefraction, three-wave mixing, or four-wave mixing.
TL;DR: Optical systems that retrieve phase information from intensity information are presented and are optical implementations of the Gerchberg-Saxton algorithm.
Abstract: Optical systems that retrieve phase information from intensity information are presented. They are optical implementations of the Gerchberg-Saxton algorithm. The solution is achieved as oscillations build up inside a resonator where a photorefractive crystal serves as an amplifier or phase conjugate mirror.
TL;DR: In this article, a backward-stimulated echo produced on the 3H4-3P0 transition of Pr3+:LaF3 is found to be a phase-conjugated spatial reproduction of the first excitation pulse.
Abstract: We have observed spatial-image storage and phase conjugation, using a backward-stimulated echo in a solid sample. The image storage and the delayed phase conjugation were observed to last for at least 15 sec, which is 3 × 105 times longer than the radiative lifetime of the excited state. The backward-stimulated echo produced on the 3H4–3P0 transition of Pr3+:LaF3 is found to be a phase-conjugated spatial reproduction of the first excitation pulse. The image storage time depends strongly on the sample temperature.
TL;DR: Image restoration after a double pass through a multimode fiber using a polarization-preserving phase conjugator is demonstrated and results indicate that the resolution of the restored image is limited by the number of guided modes.
Abstract: Image restoration after a double pass through a multimode fiber using a polarization-preserving phase conjugator is demonstrated. Results indicate that the resolution of the restored image is limited by the number of guided modes and that the contrast is restored only when the phase conjugator preserves polarization on reflection.
TL;DR: A real-time hologram generated in the liquid-crystal layer of a leaky-mirror silicon light valve is read by the same low-intensity beams used to record it, allowing correction of path-propagation aberrations.
Abstract: A real-time hologram generated in the liquid-crystal layer of a leaky-mirror silicon light valve is read by the same low-intensity beams used to record it. For a particular geometry, one of the diffracted beams propagating away from the device is the optical phase conjugate of one of the original beams, thus permitting correction of path-propagation aberrations. Experimental results show correction of tilt, focusing error, and random phase aberrations.
TL;DR: It is shown theoretically and experimentally that the positions of the fringes produced by interference between a wave incident upon a phase-conjugate mirror and the wave leaving the mirror depend on the phase associated with the incident wave.
Abstract: We show theoretically and experimentally that the positions of the fringes produced by interference between a wave incident upon a phase-conjugate mirror and the wave leaving the mirror depend on the phase associated with the incident wave. This result is in contrast to that obtained when an ordinary metal mirror is used, in which case the interference pattern is found to beindependent of the phase of the incident wave.
TL;DR: Experiments using photorefractive BaTiO(3) are in good agreement with theory and demonstrate the ability of the system to choose the combination of output mode and frequency that maximizes the mode gain.
Abstract: If the time-reversal symmetry of a ring phase conjugator is broken, the output of the device is no longer the phase conjugate of the input. For a TEM00 input wave, the output wave can be a higher-order resonator mode, although there is no resonator. Additionally, there will be a frequency shift between the input and output waves that varies discontinuously as the asymmetry in the ring is increased. Experiments using photorefractive BaTiO3 are in good agreement with theory and demonstrate the ability of the system to choose the combination of output mode and frequency that maximizes the mode gain.
TL;DR: In this article, the problem of steady-state degenerate holographic four-wave mixing in transmission geometry in nonlinear dynamic media is reduced to a Sturm-Liouville or a one-dimensional quantum-mechanical scattering problem, which is treated exactly.
Abstract: The problem of steady-state degenerate holographic four-wave mixing in transmission geometry in nonlinear dynamic media is reduced to a Sturm-Liouville or a one-dimensional quantum-mechanical scattering problem, which is treated exactly. Linear absorption in the medium is accounted for, and pump depletion is allowed. No restrictions are placed on the spatial phase mismatch between light-interference fringes and refractive-index gratings. Energy and phase transfer are considered simultaneously.
TL;DR: In this article, the degenerate four-wave mixing in photorefractive GaAs was performed by phase conjugation, edge enhancement, and autocorrelation, and the results showed that undoped, semi-insulating, liquid-encapsulated Czochralski-grown GaAs crystals can be used as effective optical processing media despite their small electro-optic coefficient.
Abstract: Three image processing experiments were performed by degenerate four‐wave mixing in photorefractive GaAs. The experiments were imaging by phase conjugation, edge enhancement, and autocorrelation. The results show that undoped, semi‐insulating, liquid‐encapsulated Czochralski‐grown GaAs crystals can be used as effective optical processing media despite their small electro‐optic coefficient.
TL;DR: A self-consistent formalism is developed for treating propagation of beams in situations which include phase conjugation and nonreciprocal elements.
Abstract: A self-consistent formalism is developed for treating propagation of beams in situations which include phase conjugation and nonreciprocal elements Two equivalent field representations, the rectangular polarization and the circular polarization representation, are considered, and the rules for transforming between them are derived An example involving a proposed new current fiber sensor is analyzed using the formalism
TL;DR: In this article, a phase conjugate mirror was used as a common end mirror for coherent operation of multiple pulsed dye oscillators in both a narrow-band and a broadband configuration.
Abstract: We have obtained coherent operation of multiple pulsed dye oscillators by using a single phase conjugate mirror as a common end mirror for up to three physically distinct cavities. The phase conjugate mirror operates via the photorefractive effect in a crystal of BaTiO3, through a four‐wave mixing process that requires no external pumping beams. The system has been operated in both a narrow‐band (0.05 nm) and a broadband (0.25 nm) configuration.
TL;DR: Using carbon disulfide as a scattering medium, the first observation to the authors' knowledge of self-pumped Brillouin-induced four-wave mixing in a manner analogous to self-Pumped four- wave mixing in BaTiO(3) is reported.
Abstract: We report the first observation to our knowledge of self-pumped Brillouin-induced four-wave mixing in a manner analogous to self-pumped four-wave mixing in BaTiO3. Using carbon disulfide as a scattering medium, we have observed both double and treble Brillouin-shifted conjugate beams.
TL;DR: In this paper, the authors measured phase conjugation by degenerate four wave mixing (PCD4MW) efficiency in ruby and GdAlO 3 :Cr +3 and its interpretation in terms of their previously measured value of the nonlinear index of refraction, n 2, which means that a dispersive grating generates the conjugated wave.
Patent•
13 Oct 1987TL;DR: In this article, a phase conjugate mirror using Brillouin enhanced four-wave mixing is presented, in which a forward going pump wave is created from the forward-going pump wave which is transmitted through the four wave mixing medium.
Abstract: Method and apparatus for optical phase conjugation, which apparatus is also known as a phase conjugate mirror, utilizes Brillouin enhanced four wave mixing in which a forward going pump wave and a backward going pump wave have frequencis which differ by twice the Brillouin frequency of the medium. The probe wave and the conjugate wave, which is obtained by Brillouin enhanced four wave mixing in the medium, have the same frequency, which differs from the pump wave frequencies by the Brillouin frequency of the four wave mixing medium. High reflectivity (gain) is obtained as a result of Brillouin resonance enhancement. The backward going pump wave is created from the forward going pump wave which is transmitted through the four wave mixing medium by stimulated Brillouin scattering in a Brillouin scattering medium having a Brillouin frequency twice that of the four wave mixing medium. The two pump waves are therefore phase conjugates of each other and the quality of the phase conjugation process is not degraded even by the use of an aberrated pump wave.