Mutual coherence of two coupled multiline continuous-wave HF lasers.

Two multiline cw HF lasers employing unstable resonators were coupled by injecting 20% of each laser output into the other laser. The mutual coherence of the two output beams was measured by recording the visibility V of the interference fringes generated when the beams are overlapped. Both single-line and multiline interference patterns were observed. The output from the two lasers in the present experiment (20% coupling) was completely coupled, indicating that the achievement of stable coupling is not dependent on careful adjustment of the length of each laser resonator.