Abstract

In this work, we address the issue of the suitability of blue fluorescent light as a frequency offset reference during the ladder-level excitation $5S_{1/2}\to 5P_{3/2}\to 5D_{3/2}$ of ${}^{85}\mathrm{Rb}$ atoms. A simple pump–probe spectroscopy experiment is performed to generate non-degenerate blue light emission produced by the spontaneous decay route $5D_{3/2}\to 6P_{3/2}\to 5S_{1/2}$. By varying the relative intensity of the pump–probe combination, we can hover between regimes dominated by mechanisms such as double resonance optical pumping (DROP) and Autler–Townes splitting. The efficacy of the blue fluorescence (420 nm) as a frequency offset reference is pronounced under the DROP regime due to its narrow (∼natural) linewidth. To provide further insight into the stability performance, the pump laser connecting the $5P_{3/2}\to 5D_{3/2}$ transition is stabilized to the peak of the blue light with the help of a probe stabilized to the saturation absorption signal of the $5S_{1/2}\to 5P_{3/2}$ transition. For this purpose, we used the coherence-induced modulation transfer technique. The error frequency noise power spectra and the subsequent Allan variance calculation clearly show that probe fluctuations are transferred to the pump laser because of an existing two-photon coherent coupling.

© 2018 Optical Society of America

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