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Construction of a Cavity-Enhanced Transient Absorption Spectrometer for Ultrafast Molecular Beam Measurements

Portrait of Nicholas Cooper, speaker
Nicholas Cooper
Graduate Student, Department of Chemistry
University of Georgia
iSTEM Building 2, Room 1218
Physical Seminar

Ultrafast spectroscopy is a powerful tool in order to probe transient dynamics of a variety of chemically relevant systems. Traditional ultrafast spectroscopy is done in either a thin film or solution phase as the concentration of the samples can easily yield high signals at relatively low powers, however these measurements are subject to solvation effects and can have a difficult time agreeing with theoretical models and other experimental methods such as time-resolved photoelectron spectroscopy. To remedy this problem, a home-built transient absorption spectrometer is constructed in order to take ultrastfast gas phase measurements through the use of a cavity enhanced frequency comb and supersonic molecular beam expansion. Here a Yb:fiber laser has been coupled into an external enhancement cavity within a differentially pumped vacuum chamber in order to both increase the overall power of the laser, and to fully stabilize the resulting pulse train into a frequency comb. Cavity enhancement in combination with lock-in amplification and an auto-balanced reference detector allow for an increase in signal of 3 orders of magnitude as well as a 30dB reduction in noise. In order to test the system, transient absorption spectroscopy on the second excited singlet state of azulene will be discussed.

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