# Two-photon excitation of rubidium atoms inside porous glass

## TL;DR

This study investigates two-photon laser excitation of rubidium atoms within porous glass, revealing unique spectral lineshapes caused by wave-vector randomization and effects of radiation trapping, with implications for understanding light-matter interactions in disordered media.

## Contribution

It demonstrates how porous glass affects two-photon excitation spectra of rubidium, highlighting wave-vector randomization and radiation trapping effects in a novel experimental setup.

## Key findings

- Unusual flat-top lineshapes due to wave-vector randomization
- Spectral effects of radiation trapping at high atomic densities
- Minor influence of atomic response time limited by pore size

## Abstract

We study the two-photon laser excitation to the 5D$_{5/2}$ energy level of $^{85}$Rb atoms contained in the interstices of a porous material made from sintered ground glass with typical pore dimensions in the 10 - 100 $\mu$m range. The excitation spectra show unusual flat-top lineshapes which are shown to be the consequence of wave-vector randomization of the laser light in the porous material. For large atomic densities, the spectra are affected by radiation trapping around the D2 transitions. The effect of the transient atomic response limited by time of flight between pores walls appears to have a minor influence in the excitation spectra. It is however revealed by the shortening of the temporal evolution of the emitted blue light following a sudden switch-off of the laser excitation.