The push to study the atomic and molecular dynamics at ever smaller time scales has been the main driving force for developing laser systems with ever shorter pulse durations. Thus far, picosecond lasers and femtosecond lasers have been used with great success in femtochemistry to study molecular dynamics such as molecular rotation and vibration, which all occur in the tens to hundreds of femtosecond. To study electron dynamics however, which are on the order of attoseconds, one needs attosecond laser sources to be able to have the time resolution required to probe ultrafast electron dynamics such as AC Stark shifts, Rabi oscillations and other more complex dynamics such as charge migration. By using few-cycle Titanium:Sapphire femtosecond lasers focused tightly into a generating gas like argon and neon, extreme ultraviolet spectra could be produce through high harmonic generation (HHG). Initial attosecond light sources based on Titanium:Sapphire sources produced HHG spectra up to 150 eV. In order to be able to probe the inner valence shells of atoms and molecules, increasing the cutoff energy of the harmonic spectra becomes necessary. Since the harmonic cutoff energy scales with the square of λ2, longer wavelength driving lasers were developed to increase the harmonic cutoff energies. However, since the harmonic yield at constant laser intensity scales with ~λ-6, thus driving laser photon flux must also increase as the driving laser wavelength increases. It is for this reason that in our lab, a 3 mJ 1.7 µm optical parametric-chirp pulse amplification (OPCPA) laser system was developed and the spectra can reach as high as 450 eV using helium as the generating gas. A number of numerical simulations were done to make suggested improvements to the OPCPA and the DFG seed source. The Titanium:Sapphire amplifiers for the OPCPA were rebuilt from a three-stage system to a two-stage system while producing similar output pulse energies after compression. This laser system will thus be more stable and maintenance will be easier. In this work, an OPCPA system which delivers CEP stable 2 mJ 12-fs pulses centered at 1.7 µm was used to conduct experiments near the water window. This system was used to study below-threshold harmonics produced in Argon, to perform Attosecond Transient Absorption Spectroscopy (ATAS) of Argon at 249 eV and to develop the semi-infinite gas cell which is a high flux soft x-ray source.
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Doctor of Philosophy (Ph.D.)
College of Optics and Photonics
Optics and Photonics
Optics and Photonics
Length of Campus-only Access
Doctoral Dissertation (Open Access)
Chew, Andrew, "Attosecond Transient Absorption Spectroscopy in the Water Window" (2020). Electronic Theses and Dissertations, 2020-. 194.