Laser frequency stabilization by bichromatic saturation absorption spectroscopy

We present and analyze a bichromatic version of the well-known saturation absorption spectroscopy technique used to stabilize lasers to atomic resonances without Doppler broadening. We show that the spectroscopic properties can be transferred between two transitions at very different wavelengths by spectral hole burning in a Doppler-broadened atomic ensemble. Specifically, we demonstrate that this technique can be used to stabilize a laser to the D1 line of Rb87 by obtaining a saturation absorption spectrum with a strong pump laser stabilized to the D2 line. This allows for more freedom in the choice of the probe laser frequency offsets compared to conventional saturation absorption spectroscopy. We compare our experimental results to an analytical model and numerical results based on rate equations.