Improvement of intermodal frequency stability of two-mode HeNe laser

A method of improving intermodal frequency stability of two-mode helium-neon laser has been developed. The approach is based on using in the stabilization circuit a signal processor for real-time analysis of data from an LF amplitude and an HF frequency detector. We propose to use the signal from the LF detector in the initial phase of the stabilization process and the signal from the HF detector afterwards. Experiments proved that with the suggested design it is possible to obtain frequency stability of the intermodal frequency better than 100 Hz or 2*10-10 for 1000s averaging. In the paper we also show the influence the intermodal frequency stability on the absolute stability of the laser frequency.