Molecular vibrational cooling by Optical Pumping with shaped femtosecond pulses

TL;DR

This paper generalizes a laser-based optical pumping method using shaped femtosecond pulses to selectively cool molecules into arbitrary vibrational levels, enhancing control over molecular states.

Contribution

It introduces a novel pulse shaping technique to target specific vibrational levels, extending previous vibrational cooling methods to arbitrary levels.

Findings

Large fraction of molecules transferred into targeted vibrational levels

Method can be extended to rotational cooling

Limitations and potential improvements discussed

Abstract

Some of us have recently reported in Science 321 232 (2008) vibrational cooling of translationally cold Cs_2 molecules into the lowest vibrational level v=0 of the singlet X 1Sigma_g ground electronic state. Starting from a sample of cold molecules produced in a collection of vibrational levels of the ground state, our method was based on repeated optical pumping by laser light with a spectrum broad enough to excite all populated vibrational levels but frequency-limited in such a way to eliminate transitions from v=0 level, in which molecules accumulate. In this paper this method is generalized to accumulate molecules into an arbitrary selected "target" vibrational level. It is implemented by using ultrashort pulse shaping techniques based on Liquid Crystal spatial light modulator. In particular a large fraction of the initially present molecule is transferred into a selected vibrational level such as v=1, 2 and 7. Limitations of the method as well as the possible extension to rotational cooling are also discussed.