Modulation-free laser frequency locking by AOM shifted cesium sub-doppler spectra

Locking laser source to a proper frequency standard can obviously improve the laser's frequency stability. Using two acousto-optic modulators (AOMs) to shift the saturation absorption spectra of cesium D₂ line by tuning the DC voltage of the radio frequency voltage controlled oscillator's (RF VCO) V_f inputing port the AOM shifted sub-Doppler spectra were gotten, and dispersion-like frequency discriminating signal was obtained by subtracting the two relatively shifted sub-Doppler spectra. Modulation-free absolute frequency stabilization of an 852 nm grating-external-cavity diode laser was demonstrated with a frequency shifting of 80 MHz. Thanks to this modulation-free locking scheme, the typical frequency jitter of less than ±270 kHz in 50 s, relative to the cesium hyperfine transition of ⁶S_1/2F=4↔⁶P_3/2 F'=5, was estimated in preliminary stabilization. The long-term frequency stability was greatly improved comparing with the frequency fluctuation of about 14 MHz under free-running condition in the same time scale. This scheme can avoid the extra frequency noise as well as intensity noise duo to the direct frequency dither on laser source in the conventional saturation absorption technique.