© 2026 Aqora Quantum S.A.S.

Terms Privacy Legal Notice

Final Report

Self-pumped phase conjugation in a supersonically flowing medium

Nicholas Djeu

Published Sep 1, 1987• 0 citations

Abstract

Abstract : This program investigated the feasibility of producing degenerate two wave mixing gain in a noninverted resonant medium with local response. According to theory, two wave mixing gain should be possible if the resulting index grating is shifted in space with respect to the intensity grating produced by the two crossed beams. A pulsed molecular beam valve operated at 100 C was used to produce the supersonically cooled I2 jet. To achieve the moving grating effect, the pump and probe beams were to be crossed in a plane containing the flow axis, with each beam nearly perpendicular to that axis. The pulsed beam valve produced a broad forward peaked distribution of molecules. The velocity distribution at any given point, however, was mainly along the direction of the line joining that point to the nozzle orifice. This was the evidenced by the fluorescence pattern along the laser beam path, which consisted of sharp filaments across the laser beam corresponding to various hyperfine components of a single rotational transition Doppler tuned into resonance with the laser beam at various angles of inclination. Gain in the planned experiment would be observable only within a narrow range of detuning (obtained by crossing the pump and probe beams), and therefore only a small solid angle of the I2 jet is useful. Various nozzles were tried with the pulsed valve device. Under the best circumstances, an integrated absorption of only about 10% was measured. With the required angular selection, the expected gain would be on the order of .01%. Since the stability of the laser was such that even after signal averaging a noise of the order of 0.1% remained, it precluded our attempt to demonstrate gain, self pumped, supersonic flow. Keywords: Iodine.

Related papers

Self-pumped phase conjugation in sodium vapor

Celestino J. Gaeta, Juan Francisco Lam, R. C. Lind

We have used a two-wave mixing gain process in sodium vapor to construct a self-pumped phase conjugator. This was done by forming a resonator around a quartz sodium cell equipped with Brewster angle windows. A pump beam is then directed into the sodium cell at a small angle to the longitudinal axis of the resonator. At sufficiently high cw pump intensities, the ac-Stark effect pro- vides sufficient gain to achieve oscillation. Although this gain is unidirectional it occurs on the wings of the sodium resonance so that the backward traveling optical field in the resonator does not experience loss due to sodium absorption. The counterpropagating optical fields in the resonator interact with the pump in an internal four- wave mixing process to produce a fourth optical field (phase conjugate to the pump field). Our experiment was conducted at the sodium D2 resonance. The pump laser was a 699 autoscan single frequency ring dye laser providing pump intensities up to several hundred watts per square centimeter.

Annual Meeting Optical Society of America•Jan 1, 1988•1 citation

Intensity dependence of two-wave mixing absorption in a resonant medium

Gang He, J. W. Mirick, R. S. F. Chang +1 more

Two-wave mixing absorption in a supersonic beam containing I2 has been studied. The results are in agreement with theory for probe intensities comparable with the pump intensity. However, at very low probe-beam intensities, the absorption deviates substantially from the predicted value and becomes the same as that for the pump beam alone. We believe that this behavior is caused by density variations in the molecular beam and suggest that this effect can be developed into a tool for probing optical inhomogeneities on a microscopic scale.

Optics Letters•Aug 1, 1987•0 citations

High-gain optical phase conjugation using degenerate four-wave mixing via coherent population trapping in moving atoms

X. Xia, D. S. Hsiung, M. S. Shahriar +2 more

Summary form only given. Previously, we have used four-wave mixing via coherent population trapping to achieve optical phase conjugation (OPC) with high gain, using two dye lasers and a sodium vapor cell. The /spl Lambda/ transition used involved the two hyperfine ground states and one excited state, so that two different optical frequencies were needed to satisfy the two-photon resonant condition between the probe and one of the pump beams. Later, we demonstrated in rubidium that a single hyperfine transition with Zeeman sublevels is enough to achieve OPC with equally high gain, thus eliminating the need for high-frequency sideband generation. However, in order to guarantee that the diffraction from the grating is primarily dispersive, the backward pump beam had to be detuned by about 60 MHz from the probe and the forward pump. One of the key disadvantages of such a nondegenerate scheme is that applications such as phase-conjugate mirrors are hard to implement. Here, we report the observation of optical phase conjugation in rubidium with equally high gain, but all the frequencies are degenerate.

Conference on Lasers and Electro-Optics•Jan 1, 1998•1 citation

Pulsed rotating supersonic source for merged molecular beams

Les Sheffield, Mark Hickey, V. B. Krasovitskiy +3 more

We describe a pulsed rotating supersonic beam source, evolved from an ancestral device [M. Gupta and D. Herschbach, J. Phys. Chem. A 105, 1626 (2001)]. The beam emerges from a nozzle near the tip of a hollow rotor which can be spun at high-speed to shift the molecular velocity distribution downward or upward over a wide range. Here we consider mostly the slowing mode. Introducing a pulsed gas inlet system, cryocooling, and a shutter gate eliminated the main handicap of the original device in which continuous gas flow imposed high background pressure. The new version provides intense pulses, of duration 0.1-0.6 ms (depending on rotor speed) and containing ∼10(12) molecules at lab speeds as low as 35 m/s and ∼10(15) molecules at 400 m∕s. Beams of any molecule available as a gas can be slowed (or speeded); e.g., we have produced slow and fast beams of rare gases, O(2), Cl(2), NO(2), NH(3), and SF(6). For collision experiments, the ability to scan the beam speed by merely adjusting the rotor is especially advantageous when using two merged beams. By closely matching the beam speeds, very low relative collision energies can be attained without making either beam very slow.

arXiv:1204.1029•Review of Scientific Instruments•Jun 1, 2012•9 citations

Degenerate four-wave mixing of c-w h-f laser beams in h-f absorption cell. Technical report

H. Mirels, John G. Coffer, Jay M. Bernard +1 more

Phase conjugation of a cw hydrogen fluoride (HF) laser beam has been investigated experimentally and theoretically using resonant degenerate four-wave mixing (DFWM) in an HF gas absorption cell. A single-line single-mode HF laser, operating on P1(8), P1(9),or P1(10) transitions, provided total (forward plus backward) pump beam intensities of 130, 600, and 400 W/sq. cm., respectively, in the HF absorption cell. A probe beam intensity of the order of 10 W/sq. cm. was also provided. Conjugate reflection of the probe beam was investigated as a function of gas cell pressure and as a function of frequency detuning from line center. The variation of reflectivity with gas cell pressure at fixed laser beam intensity indicated a peak reflectivity of the order of .0001 at pressures from 2 to 4 Torr. Measurement of conjugate beam intensity, as a function of frequency detuning from the line center,provided a signal with a full width at half maximum (FWHM) of about 30 MHz. The latter is of the order of the homogeneous width, for HF at the test pressure, and may be compared to the Doppler width delta nu sub d = 300 MHz for the medium. An Analytical model is presented which provides theoretical estimatesmore » for the variation of reflectivity with pressure. Effects of diffusion, thermal conduction, pump depletion, and a nonuniform (Gaussian) profile are considered. Theoretical estimates for peak reflectivity agree with experiments to within a factor of about 2.« less

•Aug 6, 1990•0 citations

Self-oscillation and self-pumped phase conjugation in Cr:YAlO/sub 3/

Ian C. McMichael, Tallis Y. Chang

Summary form only given. When two beams of different frequency interact in a medium with a local nonlinear optical response, one beam experiences gain at the expense of the other. We refer to this process as nondegenerate two-wave mixing. This paper shows measurements of the nondegenerate two-wave mixing gain for a weak probe beam interacting with a strong pump beam in a crystal of Cr:YAlO/sub 3/. The laser wavelength is 515 nm and the probe is down-shifted with respect to the pump by approximately 5 Hz. Gain in excess of 12 times is obtained.

Conference on Lasers and Electro-Optics•Jan 1, 1996•1 citation

Abstract : This program investigated the feasibility of producing degenerate two wave mixing gain in a noninverted resonant medium with local response. According to theory, two wave mixing gain should be possible if the resulting index grating is shifted in space with respect to the intensity grating produced by the two crossed beams. A pulsed molecular beam valve operated at 100 C was used to produce the supersonically cooled I2 jet. To achieve the moving grating effect, the pump and probe beams were to be crossed in a plane containing the flow axis, with each beam nearly perpendicular to that axis. The pulsed beam valve produced a broad forward peaked distribution of molecules. The velocity distribution at any given point, however, was mainly along the direction of the line joining that point to the nozzle orifice. This was the evidenced by the fluorescence pattern along the laser beam path, which consisted of sharp filaments across the laser beam corresponding to various hyperfine components of a single rotational transition Doppler tuned into resonance with the laser beam at various angles of inclination. Gain in the planned experiment would be observable only within a narrow range of detuning (obtained by crossing the pump and probe beams), and therefore only a small solid angle of the I2 jet is useful. Various nozzles were tried with the pulsed valve device. Under the best circumstances, an integrated absorption of only about 10% was measured. With the required angular selection, the expected gain would be on the order of .01%. Since the stability of the laser was such that even after signal averaging a noise of the order of 0.1% remained, it precluded our attempt to demonstrate gain, self pumped, supersonic flow. Keywords: Iodine.

We have used a two-wave mixing gain process in sodium vapor to construct a self-pumped phase conjugator. This was done by forming a resonator around a quartz sodium cell equipped with Brewster angle windows. A pump beam is then directed into the sodium cell at a small angle to the longitudinal axis of the resonator. At sufficiently high cw pump intensities, the ac-Stark effect pro- vides sufficient gain to achieve oscillation. Although this gain is unidirectional it occurs on the wings of the sodium resonance so that the backward traveling optical field in the resonator does not experience loss due to sodium absorption. The counterpropagating optical fields in the resonator interact with the pump in an internal four- wave mixing process to produce a fourth optical field (phase conjugate to the pump field). Our experiment was conducted at the sodium D2 resonance. The pump laser was a 699 autoscan single frequency ring dye laser providing pump intensities up to several hundred watts per square centimeter.

Two-wave mixing absorption in a supersonic beam containing I2 has been studied. The results are in agreement with theory for probe intensities comparable with the pump intensity. However, at very low probe-beam intensities, the absorption deviates substantially from the predicted value and becomes the same as that for the pump beam alone. We believe that this behavior is caused by density variations in the molecular beam and suggest that this effect can be developed into a tool for probing optical inhomogeneities on a microscopic scale.

Summary form only given. Previously, we have used four-wave mixing via coherent population trapping to achieve optical phase conjugation (OPC) with high gain, using two dye lasers and a sodium vapor cell. The /spl Lambda/ transition used involved the two hyperfine ground states and one excited state, so that two different optical frequencies were needed to satisfy the two-photon resonant condition between the probe and one of the pump beams. Later, we demonstrated in rubidium that a single hyperfine transition with Zeeman sublevels is enough to achieve OPC with equally high gain, thus eliminating the need for high-frequency sideband generation. However, in order to guarantee that the diffraction from the grating is primarily dispersive, the backward pump beam had to be detuned by about 60 MHz from the probe and the forward pump. One of the key disadvantages of such a nondegenerate scheme is that applications such as phase-conjugate mirrors are hard to implement. Here, we report the observation of optical phase conjugation in rubidium with equally high gain, but all the frequencies are degenerate.

We describe a pulsed rotating supersonic beam source, evolved from an ancestral device [M. Gupta and D. Herschbach, J. Phys. Chem. A 105, 1626 (2001)]. The beam emerges from a nozzle near the tip of a hollow rotor which can be spun at high-speed to shift the molecular velocity distribution downward or upward over a wide range. Here we consider mostly the slowing mode. Introducing a pulsed gas inlet system, cryocooling, and a shutter gate eliminated the main handicap of the original device in which continuous gas flow imposed high background pressure. The new version provides intense pulses, of duration 0.1-0.6 ms (depending on rotor speed) and containing ∼10(12) molecules at lab speeds as low as 35 m/s and ∼10(15) molecules at 400 m∕s. Beams of any molecule available as a gas can be slowed (or speeded); e.g., we have produced slow and fast beams of rare gases, O(2), Cl(2), NO(2), NH(3), and SF(6). For collision experiments, the ability to scan the beam speed by merely adjusting the rotor is especially advantageous when using two merged beams. By closely matching the beam speeds, very low relative collision energies can be attained without making either beam very slow.

Phase conjugation of a cw hydrogen fluoride (HF) laser beam has been investigated experimentally and theoretically using resonant degenerate four-wave mixing (DFWM) in an HF gas absorption cell. A single-line single-mode HF laser, operating on P1(8), P1(9),or P1(10) transitions, provided total (forward plus backward) pump beam intensities of 130, 600, and 400 W/sq. cm., respectively, in the HF absorption cell. A probe beam intensity of the order of 10 W/sq. cm. was also provided. Conjugate reflection of the probe beam was investigated as a function of gas cell pressure and as a function of frequency detuning from line center. The variation of reflectivity with gas cell pressure at fixed laser beam intensity indicated a peak reflectivity of the order of .0001 at pressures from 2 to 4 Torr. Measurement of conjugate beam intensity, as a function of frequency detuning from the line center,provided a signal with a full width at half maximum (FWHM) of about 30 MHz. The latter is of the order of the homogeneous width, for HF at the test pressure, and may be compared to the Doppler width delta nu sub d = 300 MHz for the medium. An Analytical model is presented which provides theoretical estimatesmore » for the variation of reflectivity with pressure. Effects of diffusion, thermal conduction, pump depletion, and a nonuniform (Gaussian) profile are considered. Theoretical estimates for peak reflectivity agree with experiments to within a factor of about 2.« less

Summary form only given. When two beams of different frequency interact in a medium with a local nonlinear optical response, one beam experiences gain at the expense of the other. We refer to this process as nondegenerate two-wave mixing. This paper shows measurements of the nondegenerate two-wave mixing gain for a weak probe beam interacting with a strong pump beam in a crystal of Cr:YAlO/sub 3/. The laser wavelength is 515 nm and the probe is down-shifted with respect to the pump by approximately 5 Hz. Gain in excess of 12 times is obtained.