Dispersion-like signals in velocity-selective saturated-absorption spectroscopy

We observed a dispersion-like signal from a caesium-vapour cell configured for saturated-absorption spectroscopy. Two parallel laser beams used as probes intersected a pump laser beam at a finite crossing angle. The dispersion-like signal was obtained from the difference in intensities of the two probe lasers passing through the vapour cell. The shape of the dispersion-like signal depended on the crossing angle and the crossing position of the intersecting beams. Using the dispersion-like signal as a frequency discriminator, we were able to stabilize the laser frequency without any frequency modulation. The frequency fluctuation was reduced to 22 kHz using a proportional amplifier and an integrator as a feedback circuit. (C) 2001 Elsevier Science B.V. All rights reserved.