Photoassociation and coherent transient dynamics in the interaction of ultracold rubidium atoms with shaped femtosecond pulses - I. Experiment

TL;DR

This paper experimentally explores how shaped femtosecond laser pulses induce photoassociation and coherent transient dynamics in ultracold rubidium atoms, revealing non-linear effects and phase control of molecular formation.

Contribution

It demonstrates spectrally shaped femtosecond pulses can coherently control rubidium molecule formation and transient dynamics, with experimental evidence of non-perturbative excitation and phase effects.

Findings

Observation of coherent oscillations in molecular formation rate

Non-linear dependence of photoassociation signal on pulse energy

Phase control of coherent transients via chirped pulses

Abstract

We experimentally investigate various processes present in the photoassociative interaction of an ultracold atomic sample with shaped femtosecond laser pulses. We demonstrate the photoassociation of pairs of rubidium atoms into electronically excited, bound molecular states using spectrally cut femtosecond laser pulses tuned below the rubidium D1 or D2 asymptote. Time-resolved pump-probe spectra reveal coherent oscillations of the molecular formation rate, which are due to coherent transient dynamics in the electronic excitation. The oscillation frequency corresponds to the detun-ing of the spectral cut position to the asymptotic transition frequency of the rubidium D1 or D2 lines, respectively. Measurements of the molecular photoassociation signal as a function of the pulse energy reveal a non-linear dependence and indicate a non-perturbative excitation process. Chirping the association laser pulse allowed us to change the phase of the coherent transients. Furthermore, a signature for molecules in the electronic ground state is found, which is attributed to molecule formation by femtosecond photoassociation followed by spontaneous decay. In a subsequent article [A. Merli et al., submitted] quantum mechanical calculations are presented, which compare well with the experimental data and reveal further details about the observed coherent transient dynamics.