Interferometric measurement of refractive index and temperature profiles in a pulsed CO2laser amplifier

The spatial and temporal refractive-index changes produced by a pulsed discharge in a CO
2
-N
2
mixture, under conditions which produce gains in excess of 10 dB/m, have been measured experimentally using an interferometric technique. The spatial refractive-index variation can lead to a significant increase in the divergence of a beam propagating through a laser amplifier a few meters in length. From the measured refractive-index changes, the gas temperature profile after the cessation of the current pulse has been calculated. The peak temperature obtained is between 600 and 700 K. The addition of helium to the CO
2
-N
2
mixture did not significantly affect the peak temperature but did result in a decrease in the thermal relaxation time.