Study of Offset Frequency Locking and Active Frequency Stabilization for Two RF-Excited Waveguide CO2 Laser With Common Ground Electrode

In this paper, we designed the offset frequency locking and active frequency stabilization system for the continuous-wave (CW) and electro-optical Q-switched RF-excited waveguide CO₂ lasers to provide an ideal light source for coherent radar. The CW laser is used as a local laser, and the pulsed laser is used as a main laser, which can produce Q-switched and cavity-dumped laser synchronously. A closed-loop laser frequency control system was used to stabilize the Q-switched laser at the gain curve center frequency and to lock the two lasers at a selected heterodyne frequency. The system includes two parts: 1) pulsed laser frequency stabilization and 2) offset frequency locking. The frequency stabilization part can keep the Q-switched laser oscillating at the peak of the gain curve by measuring the pulse build-up time continuously and controlling the cavity length. The offset frequency locking circuits keep the heterodyne frequency around the selected frequency by measuring the frequency of the beat signals and controlling the CW laser cavity length. In the experiment, the long-term frequency shift of the pulse laser was measured to be less than ±16 MHz and the offset frequency fluctuation was less than ±2 MHz when the frequency control system was in a closed-loop operation.