WIDELY TUNABLE UV/VIS CAVITY-ENHANCED ULTRAFAST SPECTROSCOPY AND EXCITED STATE PROTON TRANSFER IN JET-COOLED MOLECULES AND CLUSTERS

Ultrafast optical spectroscopy methods, such as transient absorption spectroscopy and 2D spectroscopy, are typically restricted to optically thick samples, such as solids and liquid solutions. We have developed a technique, Cavity-Enhanced Ultrafast Spectroscopy, to study dynamics in a molecular beam with femtosecond temporal resolution. By coupling frequency combs into optical cavities, we previously demonstrated ultrafast transient absorption measurements with a detection limit of $\Delta$OD $= 2 \times 10^{-10} (10^{-9} /\sqrt{\textrm{Hz}})$.\footnote{M. A. R. Reber, Y. Chen, and T. K. Allison, Optica \textbf{3}, 311 (2016)} In this talk, I will present a widely tunable version of this spectrometer operating at probe wavelengths between 450 and 700 nm (8000 \wn) using only one set of dispersion managed cavity mirrors. The tunable probe comb is generated using an intracavity doubled optical parametric oscillator. I will discuss the technical details of this spectrometer and its application to the dynamics of excited state intramolecular proton transfer (ESIPT) in jet-cooled molecules and clusters