Two-Photon Optical Frequency Reference With Active AC Stark Shift Cancellation

摘要

In some embodiments, two light beams having different frequencies can be counter-propagated through an atomic absorber having an atomic transition frequency approximately equal to the sum of the frequencies of the two beams. When the beams are appropriately tuned, the atomic absorber absorbs significant amount of light of at least the lower power beam. The amount of light remaining after the absorber is an indication of how well the frequencies are tuned to the absorber. At least one of the beam frequencies has an FM modulation applied prior to the absorber. This means the phase of the remaining light compared to the FM modulation, along with the intensity of the remaining light, can be used to provide a first feedback signal to adjust the frequencies of the beams to match the absorber frequency. Finally, both beams have amplitude modulation applied before the absorber. Comparing the response of the first feedback signal to the AM modulation frequency generates an intensity ratio feedback signal used to adjust the power of at least one of the beams and realize the zero light shift condition.