Single-frequency operation of gas

Wavelength selection in gas lasers. Many laser gas discharges create population inversions on several different atomic transitions, If tlie gain coefficients 

The resolution obtainable in laser spectroscopy experiments is limited ultimately by the bandwidth of the multimode laser output. This is not usually important in laser-induced fluorescence or Raman scattering experiments. However, for Brillouin scattering, for saturated absorption, and for two-photon absorption experiments, single-frequency lasers are essential. These are also necessary in interferometry and holography whenever the optical path difference exceeds 30 cm. Many different schemes for obtaining singlefrequency output from lasers have been reported. We shall consider only a few of the most commonly used techniques. We assume throughout that the laser has been constrained to 

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Saturation characteristics and single-frequency operation of gas lasers... 

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