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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Phase-conjugate characteristics of SF 6 by degenerate four-wave mixing at 10.6 μm

Bangwei Cai, Baida Lü, Xiang Sean Zhou, Shengbiao Tang

Published May 1, 1990• 0 citations
Publisher

Abstract

Degenerate-four-wave mixing (DFWM) is an important technique for the generation of phase-conjugate wave, to which much attention has been paid. In this paper. a tunalile CW CO2 1.aser is used as the pump sourse and gaseous SF6 as the nonlinear medium, the dependence of reflectivity of phase-conjugate wave generated by DFWM on the pump intensity, the pressure in SF6, the angle between the pump and probe beams as welt as the potarization of the optical fields etc, is investigated experimentatty and exptained theoretically. Peak reftectivity of 2.1x101 is abtained at P=4 Torr in the gaseous SF6. In the Doppler-free phase-conjugate spectrum of SF6 five absorption dips are observed and the spectral resolving power is measured to be about 3 MHz.

DOI
10.1117/12.18322

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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)•Jan 1, 1998•0 citations
Degenerate-four-wave mixing (DFWM) is an important technique for the generation of phase-conjugate wave, to which much attention has been paid. In this paper. a tunalile CW CO2 1.aser is used as the pump sourse and gaseous SF6 as the nonlinear medium, the dependence of reflectivity of phase-conjugate wave generated by DFWM on the pump intensity, the pressure in SF6, the angle between the pump and probe beams as welt as the potarization of the optical fields etc, is investigated experimentatty and exptained theoretically. Peak reftectivity of 2.1x101 is abtained at P=4 Torr in the gaseous SF6. In the Doppler-free phase-conjugate spectrum of SF6 five absorption dips are observed and the spectral resolving power is measured to be about 3 MHz.
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
CW phase conjugation on the ν3 vibrational bands of SF6 and OsO4 is demonstrated as a means of investigation in high resolution spectroscopy through resonant degenerate four-wave mixing at 10.6 µm by using a stable low power CO2 laser operating on the P(18), P(16), P(12) lines respectively. Peak reflectivities of 3.8 10-3 are measured in SF6. They only reach 0.34 10-3 in OsO4. Phase conjugate spectra with 2 MHz, namely sub-Doppler resolutions, are compared with simultaneous recordings of the saturated-absorption spectra over a 80 MHz bandwidth. The saturation splitting encountered on a one-photon transition in SF6 is also analysed in terms of pressure broadening and pump imbalance.
In this paper, frequency-doubled Nd:YAG laser's phase conjugation has been investigated experimentally using resonant degenerate four-wave mixing (DFWM). The iodine solution was used as resonant medium. In this way, the energy of the DFWM phase conjugation beam arrived at 43μJ/pulse while the total pump beam's energy reached 8mJ/pulse. The relation between the pulse energy of the DFWM phase conjugation beam and that of the pump beam was investigated. We also measured the optical field distributions of pump beam and DFWM phase conjugation beam, from which it can be noticed that the DFWM phase conjugation can improve the laser beam quality. At the same time, we observed the influence of the pump beam's disturbance on the DFWM signal.
Phase conjugation (PC) processes at degenerate four-wave mixing (DFWM) in the active medium of a pulsed e-beam controlled discharge CO2-laser were studied both experimentally and theoretically. The experiment was carried out with the following parameters: laser gas mixture CO2:N2:He=1:2:4, gas pressure 0.3 bar, active medium length 1.2 m, resonator length 12 m (17.7 m for single line laser), interaction angle ~10 mrad at DFWM without optical delay between probe wave and co-propagating pump one. Integral PC reflectivity (PCR) strongly depends on such parameters as: specific input energy (Fig. 1); intensity ratio for probe J3 and co-propagating pump J1 wave (Fig.2); coherency of the laser radiation, that varied by rotation of mutual polarization or with optical delay between probe wave and co-propagating pump one; geometry of DFWM; output mirror reflectance Rout (8-80%) (PCR was maximum with Rout of 8% but best quality of PC signal was observed with Rout =80%); gas mixture composition and pressure, being maximum for a mixture with a low fraction of helium and at higher pressure (up to 0.6 bar). A periodical dependence of PCR on optical delay between probe and co-propagating pump wave with periods 10−3 and 10−5 m was observed. The PCR did not depend on spectral content and a degree of linear polarization of the laser radiation.