Abstract
We report observation of query pulse length dependent Ramsey interference (QPLD-RI), using pulsed Raman excitation in rubidium vapor. This is observed when a long, attenuated query pulse is used during pulsed Raman excitation. We explain the physical mechanism behind the QPLD-RI using a Bloch vector model. We also use numerical solutions to time-dependent density matrix equations to simulate this interference effect, showing qualitative agreement with experimental results. Presence of such interference could create a potential source of error in a vapor cell Raman clock constructed using frequency-domain Ramsey interference (FDRI).
Highlights
Optical fields separated in space can interfere to produce Ramsey fringes via the coherence induced by the atomic polarization [1]
Our study shows that query pulse length dependent Ramsey interference (QPLD-RI) can produce pulse length dependent broadening as well as asymmetry in frequency-domain Ramsey interference (FDRI) fringes used for a vapor cell Raman clock, causing a potential source of error
We show that broadening affects the fractional frequency stability of a clock, and asymmetry changes the magnitude of the light-shift induced error due to optical detuning, which is unavoidable in a vapor cell based Raman clock because of the presence several hyperfine transitions in the excited state manifold, which all contribute to the clock signal because of Doppler broadening
Summary
Optical (or microwave) fields separated in space (or time) can interfere to produce Ramsey fringes via the coherence induced by the atomic polarization [1]. Several papers have reported Ramsey interference using different schemes such as the Doppler-free two-photon resonance, ground-state Zeeman coherence and polarization rotation, and suggested their applications in precision metrology [2,3,4,5,6] Some of these studies have shown interference resulting from atomic diffusion where a coherently prepared atom escapes and reenters the interaction region with a residual phase memory [5,6]. Frequency-domain Ramsey fringes are generated by changing the frequency of the oscillatory field away from the atomic resonance during interrogation This method was originally applied to separated field microwave interactions in an atomic beam to yield narrower atomic resonances [7]. The interference produced by this scheme is commonly referred to as Raman Ramsey interference (RRI)
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