Frequency stability of a helium neon laser system with external cavity control

Many applications of gas lasers depend upon the extremely high spectral purity of their output signals. To fully exploit this remarkable spectral purity requires a high degree of frequency stabilization and laser mode control. In the past few years much effort has been expended in attempts to devise and test various methods of frequency stabilization. This investigation lists a number of these methods employed over the past few years. Further, it describes a state-of-the-art system employing two identical lasers and utilizing a combination of several of the known methods of frequency stabilization plus the use of an external cavity to passively control the frequency of the Fabry-Perot laser cavity. Data from this system has been analyzed and the state-of-the-art results of long term and short term relative frequency stability is presented.