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Title: Few-femtosecond deep-UV pulses for transient-absorption experiments
Author: Brahms, Malte Christian
ISNI:       0000 0004 7655 400X
Awarding Body: University of London
Current Institution: Imperial College London
Date of Award: 2018
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In this thesis I describe the development, implementation and characterisation of a source of wavelength-tunable few-femtosecond laser pulses in the deep ultraviolet spectral region for use in time-resolved experiments. I also propose and model an extension of this source capable of simultaneously generating a single-cycle driving pulse for extreme nonlinear optics as well as a few-femtosecond ultraviolet pulse. Building on advances in the field of femtochemistry, ultrafast science is moving towards ever shorter timescales and more complex systems. One of the key building blocks for the next generation of experiments studying ultrafast dynamics in molecules will be the availability of few-femtosecond pulses to directly address electronic resonances whose corresponding photon energy lies in the vacuum and deep ultraviolet spectral regions. By harnessing the capabilities of soliton self-compression in novel micro-structured waveguides, we have generated pulses in the deep ultraviolet with energies of hundreds of nanojoules. The delivery of these pulses to an experiment as well as the measurement of their temporal profile pose significant challenges due to the dispersive properties of optical materials in the ultraviolet. We have developed an in-vacuum device for ultrafast pulse characterisation, and by directly coupling the waveguide to vacuum we were able to measure distortion-free pulses with durations below 10 fs at a range of different central wavelengths. Numerical modelling of a scaled-up version of the apparatus shows that the self-compressed driving pulse in the ultraviolet pulse generation process can maintain its shape when delivered directly to vacuum. The single-cycle pulse duration makes it an ideal driver for extreme nonlinear optics and the generation of isolated attosecond pulses in the soft X-ray spectral region.
Supervisor: Marangos, Jonathan ; Tisch, John Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral