Investigation of the mode competition in an He–Ne/CH4 laser with independent variation of the mode spacing and spatial shift

An experimental and theoretical investigation was made of the competition between the two axial modes in a two-mode He–Ne/CH₄ laser with independent variation of the mode spacing and spatial shift. The conditions were determined for obtaining the maximum contrast of the power resonances in an oscillator of this type. It was shown that the sensitivity of spectrometers utilizing such a laser can reach 10^–9 cm^–1 for ~1 m lengths of absorbing medium.