A NOVEL METHOD TO COMPENSATE FOR THE EFFECT OF LIGHT SHIFT IN A RUBIDIUM ATOMIC CLOCK PUMPED BY A SEMICONDUCTOR-LASER

Light shift (i.e., microwave resonance frequency shift induced by the electric field of the pumping light) was precisely measured in a rubidium atomic clock pumped by a semiconductor laser. It was confirmed that the spectral lineshape of the microwave resonance, which was used as a frequency discriminator for the atomic clock in the optical microwave double resonance experiment, depends strongly on the spatial distribution of the laser beam intensity, laser frequency detuning, and modulation parameters of the microwave frequency. Based on measurements of the deformation of the resonance lineshape, a self-tuning system was built to compensate for the effect of light shift. As a result of controlling the laser frequency with this system, a long-term drift of the microwave frequency as low as 6.3 × 10−13/h was obtained. © 1990 IEEE