Absolute strong-field ionization probabilities of ultracold rubidium atoms

TL;DR

This paper presents precise measurements of absolute strong-field ionization probabilities of ultracold rubidium atoms exposed to ultrashort laser pulses, with results matching ab-initio theoretical predictions across a broad intensity range.

Contribution

It provides the first direct experimental validation of ab-initio calculations of ionization probabilities in ultracold rubidium atoms under strong laser fields.

Findings

Experimental data agree with theoretical predictions.

Ionization probabilities measured across a wide intensity range.

Study includes non-resonant and resonant regimes near the Keldysh parameter unity.

Abstract

We report on precise measurements of absolute nonlinear ionization probabilities obtained by exposing optically trapped ultracold rubidium atoms to the field of an ultrashort laser pulse in the intensity range of $1 \times 10^{11}$ to $4 \times 10^{13}$ W/cm$^2$. The experimental data are in perfect agreement with ab-initio theory, based on solving the time-dependent Schr\"odinger equation without any free parameters. Ultracold targets allow to retrieve absolute probabilities since ionized atoms become apparent as a local vacancy imprinted into the target density, which is recorded simultaneously. We study the strong-field response of $^{87}$Rb atoms at two different wavelengths representing non-resonant and resonant processes in the demanding regime where the Keldysh parameter is close to unity.