Rovibrational optical cooling of a molecular beam

TL;DR

This paper demonstrates rapid rovibrational cooling of a molecular beam of barium monofluoride within 440 microseconds using enhanced broadband light sources, significantly improving cooling speed and efficiency.

Contribution

It reports the first ultrafast rovibrational cooling of a molecular beam using optimized broadband light sources, achieving cooling in less than half a millisecond.

Findings

Vibrational cooling transferred all populations to the vibrational ground state.

Rotational temperature was reduced by nearly a factor of 10.

Population of lowest rotational levels increased by over tenfold.

Abstract

Cooling the rotation and the vibration of molecules by broadband light sources was possible for trapped molecular ions or ultracold molecules. Because of a low power spectral density, the cooling timescale has never fell below than a few milliseconds. Here we report on rotational and vibrational cooling of a supersonic beam of barium monofluoride molecules in less than 440 $\mu$s. Vibrational cooling was optimized by enhancing the spectral power density of a semiconductor light source at the underlying molecular transitions allowing us to transfer all the populations of $v''=1-3$ into the vibrational ground state ($v''=0$). Rotational cooling, that requires an efficient vibrational pumping, was then achieved. According to a Boltzmann fit, the rotation temperature was reduced by almost a factor of 10. In this fashion, the population of the lowest rotational levels increased by more than one order of magnitude.