Initially developed as a tool for metrology, frequency combs are widely used for precision spectroscopy. However, their utility for ultrafast spectroscopy is not yet realized. Exploiting the properties of frequency combs, we are improving the sensitivity, spectral resolution, and broadband detection of ultrafast spectroscopies. One such technique we are developing, called Cavity-Enhanced Transient Absorption Spectroscopy (CETAS), uses fiber-laser frequency combs coupled to external enhancement cavities to increase the sensitivity of ultrafast transient absorption spectroscopy. The home-built fiber-laser system provides an affordable and stable source of the ultrafast pulses. The external enhancement cavities increase both the laser power and effective absorption path length, thus improving the signal by several orders of magnitude over traditional transient absorption spectroscopy. Noise subtraction and reduction techniques further increase the absorption sensitivity. Altogether the sensitivity is more than four orders-of-magnitude better than the previous best techniques, which allows for the study dilute samples in molecular beams on the femtosecond timescale with transient absorption spectroscopy. Additionally, CETAS has sufficient spectral resolution to study ultrafast vibrational dynamics and the role of vibrational states in ultrafast electronic dynamics.

Ultrafast spectroscopy with frequency combs: Enabling new measurements in time-resolved vibrational spectroscopy

2019 Spring National Meeting

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