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Conference on Lasers and Electro-Optics

Observation of retromodulation/conjugation using a self-pumped atomic sodium PCM

Celestino J. Gaeta, David M. Pepper

Published Apr 24, 1989• 0 citations
OpenAlex

Abstract

We report on the observation of retromodulation/conjugation using a self-pumped conjugator employing atomic sodium as the nonlinear medi- um. Previous observations of retromodulation/ conjugation employed a crystal of BaTiO3 as the nonlinear medium.1 Although the latter approach is simple in its configuration and high temporal data rates are possible, photorefractive materials possess a relatively limited response time to spatial changes of the incoming wavefront. In the present set of experiments, we demonstrated a retromodulator which potentially has several desirable features Including (1) high spatial bandwidth, (2) fast response time to wavefront changes (projected gigahertz bandwidth), (3) high temporal data rates possible (projected gigahertz bandwidth), (4) low threshold powers required (50 mW demonstated), and (5) rapid buildup time. These features indicate that such classes of retromodulators may be useful in low power level free space and guided-wave communication links as well as in novel optical resonators and gyroscopes.

Related papers

Optical phase conjugation with a sodium Raman laser

Joanne DiFrancisco‐Donoghue, Jonathan S. Kane, Philip Hemmer

Recently, there has been increased interest in the use of resonant atomic systems for performing optical-wavefront conjugation. This interest has arisen because resonant systems are inherently fast, with response times in the nanosecond range. However, resonant systems tend to have lower efficiencies and greater optical power requirements than do photorefractive crystals, such as BaTiO3. In this paper, we explore the possibility of using a highly efficient Raman laser1 in a sodium-vapor cell to obtain efficient phase conjugation at greatly reduced optical power densities. In this demonstration we use a self-pumped (linear-cavity) conjugator for simplicity. With this setup, we have achieved phase- conjugate reflectivities of 2% with input powers of only 20 W/cm2. This is only 2% of the optical power density previously reported2 to obtain comparable reflectivity with a self-pumped scheme in sodium vapor.

Quantum Electronics and Laser Science Conference•May 12, 1991•0 citations

Retromodulation/conjugation using a self-pumped atomic sodium phase-conjugate mirror

Celestino J. Gaeta, David M. Pepper

A self-pumped atomic sodium phase-conjugate mirror was modified to include an amplitude modulator, which thus formed a device capable of encoding temporal information onto the phase-conjugate return beam. Modulation rates of as much as 4 MHz with modulation depths in the range of 70-90% (both limited by the electronics and the modulator) have been obtained by using an intracavity acousto-optic modulator.

Optics Letters•Jun 1, 1991•5 citations

Response of a self-pumped phase-conjugate mirror for two mutually coherent inputs

Tokuyuki Honda, Hirokazu Matsumoto

Photorefractive self-pumped phase conjugation is attractive for its simplicity and high reflectivity with low-power light sources. In order to realize its potential applications, it is important to study its response. So far the response of a phase-conjugate wave has been described with its rise time. It has not studied how the phase-conjugate wave responds when the spatial structure of an input probe wave is changed dynamically. We investigated the response of the phase conjugate wave by using two mutually coherent input beams, which can be regarded as components of a probe wave, and by introducing sinusoidal phase changes into one of them with varied frequencies. Each input beam has a power of 6 mW at the wavelength of 515 nm. A BaTiO3 crystal was employed as a self-pumped phase-conjugate mirror.1 By measuring relative phase between the two output beams, which can be regarded as components of a phase-conjugate wave, we found the response characteristic represented by a time-lag of first order, which is similar to RC circuit. The response time thus determined was 0.32 s, which was much shorter than the rise time of 30 s obtained with the same condition.

Annual Meeting Optical Society of America•Jan 1, 1990•0 citations

Self-pumped optical phase conjugation with a sodium Raman laser

J. Donoghue, J. S. Kane, Philip Hemmer +1 more

We report self-pumped optical phase conjugation in which the pumps are self-induced as standing waves in a linear Raman laser. Self-pumped reflectivities approaching 5% are obtained for input intensities of 20 W/cm(2). This low optical input intensity combined with predicted submicrosecond response times suggests that the resonant Raman interaction may provide the basis for a promising new class of nonlinear-optical material.

Optics Letters•Sep 1, 1991•11 citations

Observation of harmonic phase conjugation in a photorefractive medium

Tallis Y. Chang, Pochi Yeh

We demonstrate for the first time, to our knowledge, second harmonic optical phase conjugation, using the second spatial harmonics of a nonsinusoidal grating formed in a photorefractive material. The possibility of harmonic phase conjugation has been considered previously for artificial Kerr media.1 We have applied the same idea to barium titanate, since the existence of the higher-order gratings in this material has been known to us for some time. In our experiment, two 1.06-µm cw Nd:YAG laser beams wrote a grating in a poled photorefractive barium titanate crystal. Then a second harmonic of the YAG at 0.532 µm read out the grating in a counterpropagating direction to one of the writing beams. In this geometry, the usual Bragg condition is not satisfied. The reflectivity of the 0.532-µm signal was rather weak, ~0.01%, with ~0.1-mW reading beam power. The buildup time was around 3 s, with loosely focused writing beams with 50-mW power in each beam. The same experiment with a SBN crystal showed no significant harmonic phase conjugation. Finally, we stress that this effect is different from the previously published result.2

Annual Meeting Optical Society of America•Jan 1, 1986•0 citations

Applications of a semi-self-pumped phase conjugate mirror

Mark Cronin‐Golomb, Amnon Yariv

We introduce a semi-self-pumped phase conjugate mirror (PCM) in which one pump is externally injected into a ring resonator while the other is self-induced as in a unidirectional ring resonator. One application is in one-way imaging through optical distortions using a phase conjugate window.1 The original realization of the phase conjugate window was similar to an externally pumped PCM and had the disadvantage of requiring a clean pump beam coherent with the distorted probe. This meant that the clean beam had to bypass the distortion, thus limiting the practical utility of the device. By replacing the externally pumped PCM portion of the device with a semi-self-pumped PCM, the clean beam can be self-induced as an oscillation beam. The second application is as a thresholding phase conjugate mirror which would be useful, for example, in some optical associative memories.2 In the semi-self-pumped phase conjugator, the presence of the externally injected pumping beam suppresses buildup of the self-induced pumping beam until the signal reaches a certain threshold intensity.

Annual Meeting Optical Society of America•Jan 1, 1986•0 citations
We report on the observation of retromodulation/conjugation using a self-pumped conjugator employing atomic sodium as the nonlinear medi- um. Previous observations of retromodulation/ conjugation employed a crystal of BaTiO3 as the nonlinear medium.1 Although the latter approach is simple in its configuration and high temporal data rates are possible, photorefractive materials possess a relatively limited response time to spatial changes of the incoming wavefront. In the present set of experiments, we demonstrated a retromodulator which potentially has several desirable features Including (1) high spatial bandwidth, (2) fast response time to wavefront changes (projected gigahertz bandwidth), (3) high temporal data rates possible (projected gigahertz bandwidth), (4) low threshold powers required (50 mW demonstated), and (5) rapid buildup time. These features indicate that such classes of retromodulators may be useful in low power level free space and guided-wave communication links as well as in novel optical resonators and gyroscopes.
Recently, there has been increased interest in the use of resonant atomic systems for performing optical-wavefront conjugation. This interest has arisen because resonant systems are inherently fast, with response times in the nanosecond range. However, resonant systems tend to have lower efficiencies and greater optical power requirements than do photorefractive crystals, such as BaTiO3. In this paper, we explore the possibility of using a highly efficient Raman laser1 in a sodium-vapor cell to obtain efficient phase conjugation at greatly reduced optical power densities. In this demonstration we use a self-pumped (linear-cavity) conjugator for simplicity. With this setup, we have achieved phase- conjugate reflectivities of 2% with input powers of only 20 W/cm2. This is only 2% of the optical power density previously reported2 to obtain comparable reflectivity with a self-pumped scheme in sodium vapor.
Photorefractive self-pumped phase conjugation is attractive for its simplicity and high reflectivity with low-power light sources. In order to realize its potential applications, it is important to study its response. So far the response of a phase-conjugate wave has been described with its rise time. It has not studied how the phase-conjugate wave responds when the spatial structure of an input probe wave is changed dynamically. We investigated the response of the phase conjugate wave by using two mutually coherent input beams, which can be regarded as components of a probe wave, and by introducing sinusoidal phase changes into one of them with varied frequencies. Each input beam has a power of 6 mW at the wavelength of 515 nm. A BaTiO3 crystal was employed as a self-pumped phase-conjugate mirror.1 By measuring relative phase between the two output beams, which can be regarded as components of a phase-conjugate wave, we found the response characteristic represented by a time-lag of first order, which is similar to RC circuit. The response time thus determined was 0.32 s, which was much shorter than the rise time of 30 s obtained with the same condition.
We demonstrate for the first time, to our knowledge, second harmonic optical phase conjugation, using the second spatial harmonics of a nonsinusoidal grating formed in a photorefractive material. The possibility of harmonic phase conjugation has been considered previously for artificial Kerr media.1 We have applied the same idea to barium titanate, since the existence of the higher-order gratings in this material has been known to us for some time. In our experiment, two 1.06-µm cw Nd:YAG laser beams wrote a grating in a poled photorefractive barium titanate crystal. Then a second harmonic of the YAG at 0.532 µm read out the grating in a counterpropagating direction to one of the writing beams. In this geometry, the usual Bragg condition is not satisfied. The reflectivity of the 0.532-µm signal was rather weak, ~0.01%, with ~0.1-mW reading beam power. The buildup time was around 3 s, with loosely focused writing beams with 50-mW power in each beam. The same experiment with a SBN crystal showed no significant harmonic phase conjugation. Finally, we stress that this effect is different from the previously published result.2
We introduce a semi-self-pumped phase conjugate mirror (PCM) in which one pump is externally injected into a ring resonator while the other is self-induced as in a unidirectional ring resonator. One application is in one-way imaging through optical distortions using a phase conjugate window.1 The original realization of the phase conjugate window was similar to an externally pumped PCM and had the disadvantage of requiring a clean pump beam coherent with the distorted probe. This meant that the clean beam had to bypass the distortion, thus limiting the practical utility of the device. By replacing the externally pumped PCM portion of the device with a semi-self-pumped PCM, the clean beam can be self-induced as an oscillation beam. The second application is as a thresholding phase conjugate mirror which would be useful, for example, in some optical associative memories.2 In the semi-self-pumped phase conjugator, the presence of the externally injected pumping beam suppresses buildup of the self-induced pumping beam until the signal reaches a certain threshold intensity.