Feedback-controlled and digitally processed coherent population trapping resonance conversion in87Rb vapour to high-contrast resonant peak

This work reports on the study of a new approach to achievement of high-contrast resonant signals from coherent population trapping (CPT) resonances in Rb vapour based on feedback control and real-time digital processing of severalmeasured parameters. Thismethod consists in stabilisation of the value of a function depending on several systemparametersmeasured as the frequency difference of the bichromatic pump radiation is scanned through adjustment of the pumping radiation power with a feedback loop. The present workmade use of two such parameters: the pumping radiation power incident on and exiting from the optical cell. Exploration of the proposedmethod has shown that stabilisation of a linear combination of these two parameters results in a resonant peakwhose contrast exceeds that of regular CPT resonance bymore than two orders ofmagnitude at relatively slowCPT resonance scan rates, (scanning frequency of the frequency difference of the bichromatic field∼1Hz).When dynamically exciting the CPT resonance (the scan frequency of the frequency difference of the bichromatic field equal to 2 kHz), the resonant peak contrast was enhanced by over an order ofmagnitude.