Line-shape comparison of electromagnetically induced transparency and Raman Ramsey fringes in sodium vapor

Abstract

We have simultaneously studied electromagnetically induced transparency (EIT) and Raman Ramsey fringes (RRF) in sodium vapor, in the same theoretical framework and the same experimental scheme. RRF spectra and EIT spectra can be simply distinguished by whether the gate timing of the detection is set at the beginning (RRF) or at the end (EIT) of the excitation pulses. The EIT spectral peaks exhibited pronounced ac Stark shifts linearly depending upon the pumping power (8.8 kHz/mW), while in the RRF spectra such shifts were almost negligible (0.19 kHz/mW), provided that the pulse separation is sufficiently large. This fact promotes RRF as a strong candidate for next-generation compact atomic clocks. Transient spectra in between RRF and EIT have also been investigated by changing the gate timing within the excitation pulse, and the transition time from RRF to EIT was found to be of the order of a few microseconds.