Rubidium spectroscopy at high-pressure buffer gas conditions: detailed balance in the optical interaction of an absorber coupled to a reservoir

TL;DR

This paper investigates rubidium vapor absorption and emission under high-pressure buffer gas conditions, revealing detailed thermodynamic scaling and thermalization effects, with implications for laser cooling and optical thermometry.

Contribution

It provides the first detailed experimental analysis of Kennard Stepanov scaling and thermalization in high-pressure rubidium buffer gas environments.

Findings

Observation of Kennard Stepanov scaling in high-pressure conditions

Determination of pressure broadening and shift of rubidium D lines

Evidence of thermalization of atomic and molecular submanifolds

Abstract

Optical spectroscopy of atoms and molecules is a field where one usually operates very far from thermal equilibrium conditions. A prominent example is spectroscopy of thin vapors, where the pump irradiation leads to a non equilibrium distribution within the electronic structure that is well shielded from the environment. Here we describe experimental work investigating absorption and emission lines of rubidium vapor subject to a noble buffer gas environment with pressure 100 to 200 bar, a regime interpolating between usual gas phase and liquid solid state conditions. Frequent elastic collisions in the dense buffer gas sample cause a large coupling to the environment. We give a detailed account of recent observations of the Kennard Stepanov scaling, a Boltzmann like thermodynamic frequency scaling between absorption and emission profiles, for both atomic and molecular rubidium species in the gaseous environment. Our observations are interpreted as due to the thermalization of alkali noble gas submanifolds in both ground and electronically excited states respectively. Both pressure broadening and shift of the high pressure buffer gas D lines system are determined. We also discuss some prospects, including possible advances in collisional laser cooling and optical thermometry.