Broadband UV/VIS cavity-enhanced ultrafast spectroscopy*

Conventional ultrafast spectroscopy requires optically dense samples such as solids or liquids. However, studying jet-cooled gas-phase molecules is more desirable for direct comparison to ab initio theory. In molecular beams, one can also study systems that do not exist in solution such as clusters and radicals. To this end, we have developed an ultrafast spectrometer based on the cavity-enhancement of frequency combs to enable transient absorption measurements in molecular beams, with a demonstrated detection limit of ΔOD = 1×10^-9/√Hz [1]. With probe pulses tunable between 450 and 700 nm, broadband ultrafast transient absorption spectra can be recorded. In this way, we can record the same observable routinely used in solution-phase studies, but now from jet-cooled molecules and clusters, enabling direct comparison of the molecular dynamics in different environments. We will discuss technical details of this novel spectrometer and ultrafast spectroscopy of chemical dynamics. For example, we will discuss proton transfer in 1-hydroxy 2-acetonaphthone and the internal conversion of salicylideneaniline in argon clusters of varying size.

[1] M. A. R. Reber, Y. Chen, and T. K. Allison, Optica 3, 311 (2016).