Internal-state thermometry by depletion spectroscopy in a cold guided beam of formaldehyde

TL;DR

This paper introduces a method to measure the internal state distribution of guided formaldehyde molecules using depletion spectroscopy, revealing their thermal characteristics and state purity.

Contribution

The study demonstrates a novel spectroscopic technique to analyze internal states of cold molecules in a guided beam, aligning experimental results with theoretical temperature models.

Findings

Measured state populations match theoretical temperature predictions.

Guided beam purity corresponds to a thermal ensemble at ~30 K.

Depletion spectroscopy effectively probes internal molecular states.

Abstract

We present measurements of the internal state distribution of electrostatically guided formaldehyde. Upon excitation with continuous tunable ultraviolet laser light the molecules dissociate, leading to a decrease in the molecular flux. The population of individual guided states is measured by addressing transitions originating from them. The measured populations of selected states show good agreement with theoretical calculations for different temperatures of the molecule source. The purity of the guided beam as deduced from the entropy of the guided sample using a source temperature of 150K corresponds to that of a thermal ensemble with a temperature of about 30 K.