Non-linear spectroscopy of rubidium: An undergraduate experiment

TL;DR

This paper presents undergraduate experiments on non-linear spectroscopy of rubidium, demonstrating Doppler-free techniques like saturated absorption and two-photon absorption, and exploring atomic structure, selection rules, and magnetic effects.

Contribution

It introduces a versatile experimental setup for high-resolution rubidium spectroscopy, combining multiple methods to study atomic structure and quantum rules.

Findings

Successful Doppler-free spectra of rubidium obtained

Hyperfine structure measured with two-photon absorption

Electric dipole selection rules demonstrated

Abstract

In this paper, we describe two complementary non-linear spectroscopy methods which both allow to achieve Doppler-free spectra of atomic gases. First, saturated absorption spectroscopy is used to investigate the structure of the $5{\rm S}_{1/2}\to 5{\rm P}_{3/2}$ transition in rubidium. Using a slightly modified experimental setup, Doppler-free two-photon absorption spectroscopy is then performed on the $5{\rm S}_{1/2}\to 5{\rm D}_{5/2}$ transition in rubidium, leading to accurate measurements of the hyperfine structure of the $5{\rm D}_{5/2}$ energy level. In addition, electric dipole selection rules of the two-photon transition are investigated, first by modifying the polarization of the excitation laser, and then by measuring two-photon absorption spectra when a magnetic field is applied close to the rubidium vapor. All experiments are performed with the same grating-feedback laser diode, providing an opportunity to compare different high resolution spectroscopy methods using a single experimental setup. Such experiments may acquaint students with quantum mechanics selection rules, atomic spectra and Zeeman effect.