If the frequency of a laser is modulated sinusoidally, the first harmonic component of saturated absorption signal can be used as error signal to stabilize the frequency of the laser.

• 对激光器进行频率调制, 检测原子分子饱和吸收信号中的一次谐波成分得到频率误差信号, 反馈控制可以实现激光频率的稳定。