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

Degenerate four-wave mixing and phase conjugation of pulsed CO2 laser radiation on transient gratings inside its own inverted medium

L. A. Afanas’ev, А. А. Ионин, А. А. Котков, Leonid V. Seleznev, Michail G. Galushkin, Konstantin V. Mitin

Published Mar 29, 1996• 0 citations
Publisher

Abstract

Degenerate four-wave mixing (DFWM) and phase conjugation (PC) of pulsed CO2 laser radiation on transient gratings inside its own laser medium have been studied both experimentally and theoretically. The operational mode of the e-beam controlled discharge CO2 laser has been chosen in such a way (CO2:N2:He equals 1:2:4, p equals 0.28 atm, tin equals 30 microsecond(s) ) that the laser pulse length ((tau) out approximately 10 - 20 microsecond(s) ) is comparable with an effective relaxation time of the upper laser level ((tau) rel approximately 15 - 30 microsecond(s) ). The time-history of the CO2 laser and PC signal pulses, and PC reflectivity have been thoroughly investigated for different cavity Q factors and specific electrical energy inputs. It has been shown, that the formation of the PC signal under the intracavity DFWM on gain (amplitude) and thermal (phase) gratings is characterized by a complicated time history that reflects the main relaxation processes taking place inside the inverted medium. A feature of the transient PC process inside the laser active medium is the dependence of the effective relaxation time of the upper laser level on the intensity of pumping waves. PC reflectivity has been obtained by numerical calculations. A comparison of the theoretical and experimental data confirms the contribution of two different mechanisms of grating formation under DFWM inside the active medium of the CO2 laser.

DOI
10.1117/12.236898

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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)•Jan 1, 1996•0 citations
Degenerate four-wave mixing (DFWM) and phase conjugation (PC) of pulsed CO2 laser radiation on transient gratings inside its own laser medium have been studied both experimentally and theoretically. The operational mode of the e-beam controlled discharge CO2 laser has been chosen in such a way (CO2:N2:He equals 1:2:4, p equals 0.28 atm, tin equals 30 microsecond(s) ) that the laser pulse length ((tau) out approximately 10 - 20 microsecond(s) ) is comparable with an effective relaxation time of the upper laser level ((tau) rel approximately 15 - 30 microsecond(s) ). The time-history of the CO2 laser and PC signal pulses, and PC reflectivity have been thoroughly investigated for different cavity Q factors and specific electrical energy inputs. It has been shown, that the formation of the PC signal under the intracavity DFWM on gain (amplitude) and thermal (phase) gratings is characterized by a complicated time history that reflects the main relaxation processes taking place inside the inverted medium. A feature of the transient PC process inside the laser active medium is the dependence of the effective relaxation time of the upper laser level on the intensity of pumping waves. PC reflectivity has been obtained by numerical calculations. A comparison of the theoretical and experimental data confirms the contribution of two different mechanisms of grating formation under DFWM inside the active medium of the CO2 laser.
Degenerate four-wave mixing (DFWM) and phase conjugation (PC) of pulsed carbon-dioxide laser radiation on transient gratings inside its own laser medium have been studied both experimentally and theoretically. The operational mode of the e-beam controlled discharge carbon-dioxide laser has been chosen in such a way (CO2:N2:He equals 1:2:4, p equals 0.28 atm, tin equals 30 microseconds) that the laser pulse length ((tau) out approximately equals 10 - 20 microseconds) is comparable with an effective relaxation time of the upper laser level ((tau) rel approximately 15 - 30 microseconds). The time-history of the carbon-dioxide laser and PC signal pulses, and PC reflectivity have been thoroughly investigated for different cavity Q factors and specific electrical energy inputs. It has been shown, that the formation of the PC signal under the intracavity DFWM on gain (amplitude) and thermal (phase) gratings is characterized by a complicated time history that reflects the main relaxation processes taking place inside the inverted medium. A feature of the transient PC process inside the laser active medium is the dependence of the effective relaxation time of the upper laser level on the intensity of pumping waves. PC reflectivity has been obtained by numerical calculations. A comparison of the theoretical and experimental data confirms the contribution of two different mechanisms of grating formation under DFWM inside the active medium of the carbon-dioxide laser.
Degenerate four-wave mixing (DFWM) and phase conjugation (PC) of pulsed carbon-dioxide laser radiation on transient gratings inside its own laser medium have been studied both experimentally and theoretically. The operational mode of the e-beam controlled discharge carbon-dioxide laser has been chosen in such a way (CO2:N2:He equals 1:2:4, p equals 0.28 atm, tin equals 30 microseconds) that the laser pulse length (tauout approximately 10 - 20 microseconds) is comparable with an effective relaxation time of the upper laser level (taurel approximately 15 - 30 microseconds). The time-history of the carbon-dioxide laser and pc signal pulses, and pc reflectivity have been thoroughly investigated for different cavity Q factors and specific electrical energy inputs. It has been shown, that the formation of the PC signal under the intracavity DFWM on gain (amplitude) and thermal (phase) gratings is characterized by a complicated time history that reflects the main relaxation processes taking place inside the inverted medium. A feature of the transient pc process inside the laser active medium is the dependence of the effective relaxation time of the upper laser level on the intensity of pumping waves. Pc reflectivity has been obtained by numerical calculations. A comparison of the theoretical and experimental data confirms the contribution of two different mechanisms of grating formation under DFWM inside the active medium of the carbon-dioxide laser.
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.
Energetic, temporal and spectral characteristics of the process of phase conjugation (PC) at intracavity degenerate four wave mixing (DFWM) of frequency selective pulsed e-beam controlled discharge CO laser radiation have been studied both experimentally and theoretically. Maximum PC reflectivity (PCR) on energy comes up to 1.5% being independent of specific input energy. The dependencies of PCR on energy have quite different behavior for various selected spectral lines. An influence of lasing and PC process in adjacent vibrational bands on PCR for the selected spectral line has been experimentally demonstrated, PCR decreasing at switching on adjacent vibrational bands. The numerical model has been formulated to simulate the temporal behavior of PC process on large scale gain (amplitude) and refraction (phase) gratings formed in the active medium of CO laser. The trend in the calculated temporal behavior of PCR is the same as for the experimental result, the theoretical PCR being higher as compared to experimental one. The resonance (amplitude) mechanism of PC process seems to be a prevailing one for DFWM of CO laser radiation.
The phase conjugation (PC) reflectivity of the laser radiation inside its own laser medium reflects the non-linear properties of the medium. To study the properties of carbon monoxide (CO) laser medium the temporal and spectral characteristics of PC reflectivity of pulsed e-beam controlled discharge cryogenically cooled CO laser radiation under degenerate four-wave mixing (DFWM) inside its own laser medium were studied experimentally. The interaction length of DFWM was about 100 cm. The pulse length of the CO laser beam was 50 - 500 µs, the gas density was up to 0.5 Amagat, the gas temperature was about 120 K.