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Optics Letters

On-resonant phase-conjugate reflection and amplification at 106 μm in inverted CO_2

Robert A. Fisher, B. J. Feldman

Published May 1, 1979• 55 citations
Publisher

Abstract

We have obtained phase-conjugate reflection and amplification with an effective reflectivity exceeding unity by redirecting the output of a TEA CO(2)-laser oscillator into its own gain medium. The intense counterpropagating waves within the laser were coupled through the saturated medium to provide the nonlinearity in a process analogous to degenerate four-wave mixing.

DOI
10.1364/ol.4.000140

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Relaxation time of phase-conjugate reflection via four-wave mixing of radiation in the active medium of a CO2laser

Valeri I. Kovalev

The experimental relaxation time of degenerate four-wave mixing based on the nonlinearity of saturation of the active media of TEA CO 2 lasers (~0.3 μs) is shown to be an order of magnitude less than the time calculated on the basis of the existing theories. A new mechanism is proposed to account for the relaxation of such mixing in the active media of TEA CO 2 lasers. This mechanism postulates erasure of gratings, formed in the course of the fourwave mixing, of the population inversion of the active levels of a laser due to a high rate of filling of the upper level by resonant energy transfer from nitrogen molecules.

Quantum Electronics•Sep 30, 1994•1 citation
We have obtained phase-conjugate reflection and amplification with an effective reflectivity exceeding unity by redirecting the output of a TEA CO(2)-laser oscillator into its own gain medium. The intense counterpropagating waves within the laser were coupled through the saturated medium to provide the nonlinearity in a process analogous to degenerate four-wave mixing.
We demonstrate experimentally that phase-conjugation (PC) by resonant degenerate four-wave mixing in Na vapour can reach large efficiencies in the c.w. regime (reflectivity up to 250%). With PC reflectivity exceeding unity, a c.w. phase-conjugate laser oscillation is obtained, for the first time on a resonant gas medium. We show that large Na densities are required, as well as large frequency detunings of the intense incident beams. The PC oscillation is characterized through threshold effect, pump depletion, and polarization characteristics.
An experimental investigation was made of the reflection by a nonlinearity from gain saturation in the active medium of a TEA CO 2 laser under degenerate four-wave mixing conditions. A new mechanism of relaxation of the response to such a nonlinearity was identified and processes with submicrosecond and subnanosecond relaxation times were found in CO 2 . The saturation intensities for these processes and the conditions for achieving high reflection intensities as a result of such a mixing were determined.
An investigation was made determining the parameters affecting the phase conjugate reflectivity in a four-wave mixing scheme using a pulsed TEA CO2 laser and gaseous sulfur hexafluoride (SF6) as the nonlinear medium. With a low energy CO2 laser (60 mJ pulse energy) an optimum energy reflectivity of 20 % was achieved at a pump-probe angle of 30 mrad, a SF6 pressure of 50 hPa at the lOiim P(1O) laser transition for exactly aligned counterpropagating pump waves. In addition, the reflectivity showed a substructure when enlarging the angular mismatch between the pump waves. A simulation of the phase conjugate intensity distribution was carried out solving the Kirchhoff- Fresnel integral equation.
The experimental relaxation time of degenerate four-wave mixing based on the nonlinearity of saturation of the active media of TEA CO 2 lasers (~0.3 μs) is shown to be an order of magnitude less than the time calculated on the basis of the existing theories. A new mechanism is proposed to account for the relaxation of such mixing in the active media of TEA CO 2 lasers. This mechanism postulates erasure of gratings, formed in the course of the fourwave mixing, of the population inversion of the active levels of a laser due to a high rate of filling of the upper level by resonant energy transfer from nitrogen molecules.