将频率调制加在声光调制器上,用三次谐波探测法获得了铯原子D2线的三阶微分饱和光谱.采用这种激光器无调制扰动方案结合三次谐波锁频技术,实现了852 nm的分布布拉格反射器半导体激光器相对于6S1/2F=4-6P3/2F′=5超精细跃线的频率锁定.由锁定后的频率误差信号估算,10 s内激光频率起伏小于±350 kHz,相对频率稳定度约1×10-9.这种无调制扰动方案可以消除一般的饱和吸收稳频方法中由于直接对激光器进行频率调制而带来的额外频率噪声;三次谐波锁频技术的应用,还可有效地降低铯原子饱和吸收谱中剩余多普勒背景的影响.

Third derivative saturation absorption spectrum of cesium D 2 line is demonstrated via the third harmonic technique, under the condition that the frequency modulation is applied to a external acousto optical modulator. By using this undithering scheme combined with the technique of third harmonic locking, frequency of a 852 nm DBR diode laser is locked to the hyperfine component of cesium 6S 1/2 F=4→6P 3/2 F′=5. A frequency jitter of less than ±350 kHz in 10 s and the frequency stability of about 1×10 -9 are estimated based on the error signal after locking in the preliminary stabilization. This locking scheme without frequency dither can avoid the extra frequency noise resulted from direct frequency dither on diode laser in normal saturation absorption technique, and application of third harmonic technique can strongly reduce the residual Doppler background.