Recent progresss in frequency stabilization of diode laser

The frequencies of diode lasers have been highly stabilized by using Doppler‐free saturated absorption spectra of alkali‐metal atoms, and long term stability in terms of Allan variance σ better than 10−13 has been achieved. In this method, the diode laser frequency has been directly modulated to obtained the derivative of resonance, which is used as the error signal to control the diode current. New methods are studied to obtain nearly derivative of Doppler‐free resonance, without frequency modulation. The frequency stability of a diode laser locked at the center of a resonance is similar to above case of the saturated absorption.