FM eliminated CH4locked frequency stabilization of 3.39 µm He-Ne laser in dual feedback control

The frequency of the 3.39 μm He-Ne laser was locked to the CH
4
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
\pm1.1 \times 10^{-11}
, which was further improved to
\pm 1.35 \times 10^{-12}
under dual feedback control. The Allan variance measured by the photomixing technique was
1.77 \times 10^{-12}
at an average time 100 s.