基于共焦法布里-珀罗腔的无调制激光频率锁定

将激光器锁定到合适的参考频率上,可以有效改善激光器的频率稳定性。对于共焦法布里-珀罗(CFP)腔,沿腔轴的光路与同腔轴有一小夹角的光路对应的光程不同,因此二者对应的腔共振透射峰的频率之间会发生相对频移。这一特性可用来产生以共焦法布里-珀罗腔作为频率标准稳定激光频率的类色散型鉴频曲线,而不需要对激光频率或者共焦法布里-珀罗腔长进行调制扰动,也无需采用相敏探测。实验中实现了自制的852 nm光栅反馈半导体激光器相对于共焦法布里-珀罗腔的无调制频率锁定,由闭环锁定后的误差信号分析,30 s内典型的频率起伏小于340 kHz,较相同时间段内激光器自由运转时的频率起伏(约10 MHz)有了显著的改善。还通过调节入射到共焦法布里-珀罗腔两光束之间的夹角来改变频移量,对不同频率间隔下的类色散型鉴频曲线的斜率以及对激光器锁频后的频率稳定性作了比较。

Modulation-Free Frequency Stabilization of a Laser Based on a Confocal Fabry-Perot Cavity

Locking laser to a proper reference frequency can obviously improve the laser′s frequency stability.The optical path and frequencies are different for axial and paraxial beams traveling through a confocal Fabry-Perot (CFP) cavity, thus the frequency difference between them which is a dispersion-like signal can be used to stabilize the laser frequency. Thus the phase-sensitive detection via lock-in and frequency dither on the laser or cavity are no longer required. With this modulation-free stabilization method, a homemade 852 nm grating-external-cavity diode laser is stabilized to a CFP cavity frequency, whose frequency jitter is less than ±340 kHz in 30 seconds estimated from locked error signal. The long-term frequency stability was greatly improved compared with the frequency fluctuation of about 10 MHz under free-running condition in the same time scale. Moreover, the frequency shift and the zero-crossing slope of the dispersion-like frequency-discriminating signal can be conveniently changed by adjusting the angle between the two incident beams. The laser frequency stability locking with different frequency interval is investigated.