Frequency stabilization of gas lasers

The state of the art in the field of frequency stabilization of gas lasers is surveyed. A brief discussion of the methods employed to determine the frequency stability of lasers is followed by a listing of the principle causes of frequency instability. The close relationship existing between the control system design and the laser environment is pointed out. Stabilization techniques based on the use of atomic resonance and on the use of interferometers are discussed in detail. Many of these techniques are capable of achieving long-term frequency stabilities of one part in 10⁹or better, which appears to be entirely adequate for most systems applications.