Precision Infrared Spectroscopy in a Molecular Beam Experiment

With frequency combs having become available for the infrared regime, a new generation of precision spectrometers has been made possible. Combining the high power, wide range tunability, and narrow line width of OPO systems with the possibility to accurately determine their frequency via a frequency comb, spectrometers with a sub MHz accuracy are built.1 By locking the OPOs to the frequency comb their frequencies can be stabilized to an even higher accuracy and their phases can be controlled, which opens the way to new possible experiments.

We are building a precision spectroscopy molecular beam setup, where two narrow linewidth OPOs are stabilized and phase-locked with an infrared frequency comb and used as light sources. The molecular beam is generated in a supersonic expansion of a pulsed nozzle and doped by e.g. laser evaporation. With this setup, several different experiments are feasible, for instance cavity ring-down spectroscopy or two-photon sub-Doppler spectroscopy. These experiments allow for a wide range of applications, for instance this setup is perfectly suited for accurate measurements of gas-phase molecules and molecular clusters. As a different application, we explore the interaction of light with chiral molecules. The phase control of all light sources will be used to differentiate between enantiomers and induce transitions between these. In an effort to push the limits of precision spectroscopy, this setup might reach an accuracy high enough to detect the energy difference between enantiomers caused by the parity violation.

1 Asvany, O., Krieg, J., and Schlemmer, S. “Frequency comb assisted mid-infrared spectroscopy of cold molecular ions”, Review of Scientific Instruments, (2012), 83, 093110.