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Title: Long and short wavelength optical sources for attosecond science
Author: Johnson, Allan Stewart
ISNI:       0000 0004 7427 7045
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2017
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In this thesis I describe work extending attosecond science into new regimes through the development of novel light sources. Thus far attosecond science has been driven primarily through two technologies: titanium-doped sapphire lasers capable of generating few-cycle femtosecond laser pulses in the near infrared (800 nm) wavelength range, and high harmonic generation driven by these pulses, which creates attosecond pulses in the extreme ultraviolet frequency range (10-150 eV). We attempt to move into new regimes for attosecond science through the development of light sources at new wavelengths. Through the use of an optical parametric amplifier and hollow-core fibre pulse compression, we have generated 1.3-cycle pulses at a central wavelength of 1750 nm (7.1 fs duration) with excellent spatio-temporal quality and high energies of 750 uJ per pulse at a repetition rate of 1 kHz. Three novel diagnostics were developed in order to characterize the temporal properties of these pulses: a SEA-F-SPIDER, a third harmonic single-shot FROG, and a third harmonic D-scan. Our short-wavelength infrared laser source has been applied to high harmonic spectroscopy of substituted benzenes. By careful control of macroscopic conditions, we obtain harmonic spectra comparable to theoretical calculations. We find a minimal effect of deuteration upon the few-femtosecond dynamics of benzene. Using the few-cycle 1750 nm pulses, high harmonic generation has been extended to the soft X-ray regime, and we have generated attosecond pulses at all photon energies across the water window (284-540 eV). Energies of tens of picojoules are generated, with estimated pulse durations of several hundred attoseconds. The spatial properties of the harmonic radiation were also examined, and found to be well described by Gaussian optics. Finally, the soft X-ray harmonic radiation was used to obtain X-ray absorption spectra from a variety of samples to demonstrate the utility of our source.
Supervisor: Marangos, Jon ; Tisch, John Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral