Laser frequency stabilization via bichromaticDoppler-free spectroscopy of 87Rb D1 line

We demonstrate a bichromatic Doppler-free spectroscopy of an 87RbD1 line by using a dual-frequency, counterpropagating laser field with orthogonal linear polarizations. A reversed Doppler-free resonance dip is observed in the dual-frequency scheme, and a significant improvement of frequency discrimination curve is acquired due to the coherent population trapping (CPT) effect. The influence of the static magnetic field and laser intensity on the spectroscopy is studied in both single- and dual-frequency schemes. After locking the laser frequency to the 87RbD1 line in the dual-frequency stabilization scheme, the beat note fractional frequency stability is at the level of 7×10−12 at 1 s integration time. This technique can be used in various applications, such as CPT atomic clocks, laser spectroscopy, quantum optics, and laser-cooling experiments.