Graduate Thesis Or Dissertation


Bringing Two-Dimensional Fourier Transform Electronic Spectroscopy into the Short-Wave Infrared Public Deposited

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  • Two-dimensional Fourier Transform (2D FT) spectroscopy in the short-wave infrared (1-2 μ) enables high frequency and time resolution experiments of molecular dyes, third-generation photovoltaic systems, and carotenoids - all rich in electronic transitions in this spectral region. Such experiments require short pulses with broad spectra to probe fast dephasing or solvation dynamics as well as couplings between widely spaced electronic transitions. Stable, low-dispersion interferometers at Brewster's angle are introduced for multioctave-spanning nonlinear spectroscopies. We adapt a compact, phase-characterized Mach-Zehnder interferometer to the short-wave infrared; active stabilization produces accurate and evenly spaced time delays between the two excitation pulses in 2D FT spectroscopy. An intrinsically phase-stable Sagnac interferometer is introduced to enhance the interferometric signal detection with respect to the copropagating local oscillator in partially collinear 2D FT spectroscopy. These interferometers exploit the air-glass interface Brewster's angle of thin-film metallic beam splitters to preserve expected output phase shifts and to minimize secondary reflections over multiple octaves. A homebuilt short-wave IR noncollinear optical parametric amplifier with a periodically poled crystal provides broadband excitation and detection. The output pulses are compressed with a deformable mirror using second-harmonic generation feedback in a genetic algorithm to pulse durations as low as 10 fs. Together this light source and the interferometric 2D spectrometer have enabled the first 2D FT electronic spectroscopy in this wavelength range; we analyze the early time solvation dynamics of IR-26 dye. Agreement between experimental and simulated purely absorptive 2D spectra of this dye proves the feasibility of the spectrometer design. Accurate evolution time delays in the partially collinear geometry reduce ambiguities in the phasing of these 2D spectra. Finally, initial 2D spectra of lead chalcogenide quantum dots exhibit first exciton transition (bleach) peaks; weak negative peaks potentially reflect biexciton shifts. These spectra lay the groundwork for broadband 2D FT spectroscopy to find exciton couplings and dephasing rates to help establish the mechanism of carrier multiplication for high-efficiency photovoltaics.
Date Issued
  • 2012-01-01
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  • 2019-11-13
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