Doppler-free two-photon resonances for atom detection and sum frequency stabilization

TL;DR

This paper demonstrates Doppler-free two-photon resonances in rubidium atoms for precise atom detection and introduces a novel sum frequency stabilization method for lasers based on these resonances.

Contribution

It presents a new approach for atom detection and laser stabilization using Doppler-free two-photon fluorescence in rubidium atoms.

Findings

Successful detection of two-photon excitation via blue fluorescence.

Quantitative analysis of fluorescence dependence on atomic density and laser detuning.

Effective sum frequency stabilization method demonstrated.

Abstract

We investigate the excitation of the 5D_{5/2} level in Rb atoms using counter-propagating laser beams, which are nearly resonant to the one-photon 5S_{1/2} - 5P_{3/2} and 5P_{3/2} - 5D_{5/2} transitions, ensuring that a sum of the optical frequencies corresponds to the 5S_{1/2} - 5D_{5/2} transition. The excitation produced by two-photon and step-wise processes is detected via spontaneously emitted fluorescence at 420 nm arising from the 6P_{3/2} - 5S_{1/2} transition. The dependences of blue fluorescence intensity on atomic density and laser detuning from the intermediate 5P_{3/2} level have been investigated. The sensitivity of the frequency detuned bi-chromatic scheme for atom detection has been estimated. A novel method for sum frequency stabilization of two free-running lasers has been suggested and implemented using two-photon Doppler-free fluorescence and polarization resonances.