FM eliminated CH4 locked frequency stabilization of 3.39-micron He-Ne laser in dual feedback control

The frequency of the 3.39-micron He-Ne laser was locked in the CH4 saturated absorption line by means of integral-proportional feedback control, i.e., dual feedback control. The frequency modulation was applied by a vibrating mirror placed outside a laser cavity, obtaining a modulation-free laser beam with a stabilized frequency. The long-term stability achieved under integral feedback control was about + or - 1.1 x 10 to the -11th, which was further improved to + or - 1.35 x 10 to the -12th under dual feedback control. The Allan variance measured by the photomixing technique was 1.77 x 10 to the -12th.