Theoretical and Experimental Study of Light Shift in a CPT-Based RB Vapor Cell Frequency Standard

Abstract

One of the important subjects in coherent-population- trapping-based (CPT-based) vapor cell frequency standards is the light shift (ac Stark shift). We calculate the light shift using a numerical method and perturbation approximation. Experimentally, we measure light shift using a pair of phase-locked diode lasers as well as a frequency-modulated diode laser. There is good agreement between theory and experiment. A method of controlling light shift in CPT-based frequency standards is proposed and implemented in Agilent Laboratories. The short-term stability of our CPT-based rubidium vapor cell frequency standard is measured as 1.3 x 10(-12) tau (-1/2), which is limited by the phase noise of the reference local oscillator used.