The frequency of the 3.39 μm He-Ne laser was locked to 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 ±1.1 X 10-11, which was further improved to ±1.35 X 10–12 under dual feedback control. The Allan variance measured by the photomixing technique was 1.77 X 10–12 at an average time 100 s.
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics
- Condensed Matter Physics
- Electrical and Electronic Engineering