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

Abstract

This work reports on the study of a new approach to achievement of high-contrast resonant signals from coherent population trapping (CPT) resonances in 87 Rb vapour based on feedback control and real-time digital processing of several measured parameters. This method consists in stabilisation of the value of a function depending on several system parameters measured as the frequency difference of the bichromatic pump radiation is scanned through adjustment of the pumping radiation power with a feedback loop. The present work made use of two such parameters: the pumping radiation power incident on and exiting from the optical cell. Exploration of the proposed method has shown that stabilisation of a linear combination of these two parameters results in a resonant peak whose contrast exceeds that of regular CPT resonance by more than two orders of magnitude at relatively slow CPT resonance scan rates, (scanning frequency of the frequency difference of the bichromatic field ∼1 Hz). 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 of magnitude.

High-quality electromagnetically-induced absorption resonances in a buffer-gas-filled vapour cell

“…One of the most attractive features of the EIT resonances consists in their subnatural linewidth, which can be very narrow (from several hundreds of kHz and down to units of Hz) [14,15]. Also, a high EIT signal contrast of several to tens percent has been observed by many authors (e.g., see [16][17][18][19][20][21][22][23]).…”

“…However, in the majority of works the contrast implies just a ratio between the EIA amplitude and amplitude of a wide pedestal, which suffers Doppler and buffer-gas collisional broadening (see [22,23,40], for example). In this case we have:…”

Properties of Rb CPT Atomic Clock at Subharmonic Microwave Modulation Frequencies

“…Adjustment of the power of the microwave signal added to the laser injection current (Fig. 7) not only affects distribution of the radiation power among the sidebands, but also allows suppression of light shift of the CPT resonance [38], [39]. Shown in Fig.…”