Rotational level competition in CO2lasers

Competition effects between rotational levels of the rotation-vibration band of CO
2
at 10.6 μ have been investigated in both traveling-wave and standing-wave CO
2
lasers operated in a single mode and single frequency. In a ring laser, Doppler shift and gain proportionality as a function of gas flow can be used to generate a gain anisotropy as a function of frequency so that the ring laser operates as a unidirectional oscillator. Over a narrow frequency interval, two rotational levels can be made to oscillate with oppositely directed traveling waves with an intensity crossover between the two Doppler centers. In this way, a discriminant can be derived that allows frequency stabilization to 5 parts in 10
¹²
in frequency. In standing-wave lasers of high-frequency stability, the rotational level competition can be observed by synchronous detection of a low-frequency variation of the heterodyne beat frequency signal of two lasers. The competition effects are due to intensity-dependent anomalous dispersion arising from saturation.