Effects of the intensity difference of two laser fields on coherent population trapping clocks

We have studied the effects of the intensity difference of the two laser fields on the performance of the coherent population trapping (CPT) atomic clocks. Our experimental results show that there is a ratio range for the intensity of the two laser fields, between 1:2 and 2:1, in which the CPT resonance has larger amplitude and narrower line width. If we can adjust the ratio close to the center (1: 1), the signal quality (ratio of amplitude to line width) of CPT resonance will be efficiently improved. Our results also show that using full hyperfine frequency to modulate the laser has its advantages.