Positronium laser cooling via the $1^3S$-$2^3P$ transition with a broadband laser pulse

TL;DR

This paper demonstrates laser cooling of positronium atoms using a broadband laser pulse to saturate a specific transition, resulting in a significant increase in the cold fraction and reduction in temperature.

Contribution

It introduces a novel broadband laser cooling technique for positronium, achieving effective Doppler cooling in free-flight conditions.

Findings

Temperature reduced from 380 K to 170 K

58% increase in coldest fraction of positronium

Observation of two laser-induced effects

Abstract

We report on laser cooling of a large fraction of positronium (Ps) in free-flight by strongly saturating the $1^3S$-$2^3P$ transition with a broadband, long-pulsed 243 nm alexandrite laser. The ground state Ps cloud is produced in a magnetic and electric field-free environment. We observe two different laser-induced effects. The first effect is an increase in the number of atoms in the ground state after the time Ps has spent in the long-lived $3^3P$ states. The second effect is the one-dimensional Doppler cooling of Ps, reducing the cloud's temperature from 380(20) K to 170(20) K. We demonstrate a 58(9) % increase in the coldest fraction of the Ps ensemble.