Laser Frequency Offset Locking with Dual-modulation

We report a laser frequency offset locking scheme for coherent population trapping (CPT) atomic clock. Based on a usual half-wave modulation in CPT atomic clocks, we add a radio frequency signal to the laser driving current to form dual-modulation to compensate the frequency shift of optical transition due to buffer gas in the clock cell. The Doppler-free absorption enhanced spectrum produced by dual-modulation is observed and successfully applied to the laser frequency offset locking. In our scheme, a frequency shift device is no longer necessary, thus the clock's size, weight, power, complexity, environmental sensitivity, and cost are reduced, this is suitable for implementing compact and high-performance CPT and POP atomic clocks.