Relationship between coherent population trapping oscillation and Raman detuning

Abstract

Coherent population trapping (CPT) oscillation is a transient oscillation phenomenon based on the CPT effects, which is related to the Raman detuning of the coherent bichromatic laser fields from the hyperfine ground-states of three-level Λ system. In this work, sawtooth wave is adopted to modulate the frequency of microwave signal to make Raman detuning change uniformly and stepping. Meanwhile, by building the relationship between the microwave frequency modulation rate and the change rate of Raman detuning, the effects of the change rate and mode of Raman detuning on CPT oscillation are analyzed respectively. The results reveal that when the Raman detuning is changing uniformly, the CPT oscillation will occur in the condition that the change rate is highly enough, and the excited oscillations show non-harmonic oscillation behavior. When the Raman detuning is triggered by step change, the excited CPT oscillation is a damping oscillation, and the oscillation frequency is equal to the Raman detuning. The modulation of Raman detuning is realized by using sawtooth wave to modulate the microwave frequency, and then the complete establishment of CPT state and the complete attenuation of CPT oscillation process are achieved. This work presents a new modulation method to realize the CPT oscillation, which shows great application potential in the field of weak magnetic measurements and atomic clocks.