Investigation of the stability and frequency shifts of a twomode He–Ne–CH4 laser

An investigation was made of the frequency stability and reproducibility of a two-mode He–Ne laser with a methane absorbing cell. Mode interaction with a small mode spaciang (ν₁₂<10 MHz) was utilized to obtain large-amplitude power resonances. A frequency stability of 2×10^–14 was achieved with an averaging time of 10 sec and the first measurements were made of the frequenccy shifts of a stabilized two-mode laser as a function of the main oscillator parameters. The frequency reproducibility of two identical oscillators was found to be 10^–12.