Accessing the $\rm 5S_{1/2} \rightarrow 5D_{5/2}$ two-photon transition in Rb using a diode laser system

TL;DR

This paper demonstrates the observation of a two-photon transition in rubidium vapor at 778 nm using a diode laser, achieving Doppler-free spectra with high frequency precision, which can serve as a stable optical reference.

Contribution

The study reports the first detailed observation and spectral characterization of the $ m 5S_{1/2} ightarrow 5D_{5/2}$ two-photon transition in rubidium vapor using a diode laser system.

Findings

Doppler-free hyperfine spectra observed in rubidium isotopes.

Linewidth of 2.2 MHz, narrower than single-photon D2 transition.

Transition frequency measured with 8 kHz accuracy.

Abstract

We report observation of the $\rm 5S_{1/2} \rightarrow 5D_{5/2}$ two-photon transition in Rb vapor at 778 nm, using an external cavity diode laser system and a heated vapor cell. The spectra in the two isotopes show well-resolved hyperfine transitions. The peaks are Doppler free, and have a Lorentzian lineshape with a typical linewidth of 2.2 MHz. This linewidth is larger than the natural linewidth of 300 kHz, but is still 5--10 times smaller than the linewidth for single-photon transitions in the D$_2$ line. Since the absolute frequency of this transition is measured with 8 kHz precision, it can form a better secondary reference in the optical regime compared to the D$_2$ line.