Laser frequency locking based on the normal and abnormal saturated absorption spectroscopy of 87Rb

We present a practical method to avoid the mis-locking phenomenon in the saturated-absorption-spectrum laserfrequency-locking system and set up a simple theoretical model to explain the abnormal saturated absorption spectrum. The method uses the normal and abnormal saturated absorption spectra of the same transition 5~2S, F = 2–5~2P, F’= 3 saturated absorption of theRb Dresonance line. After subtracting these two signals with the help of electronics, we can obtain a spectrum with a single peak to lock the laser. In our experiment, we use the normal and inverse signals of the transitions 5~2S, F = 2–5~2P, F’= 3 saturated absorption of theRb Dresonance line to lock a 780-nm distributed feedback(DFB) diode laser. This method improves the long-term locking performance and is suitable for other kinds of diode lasers.