High-order harmonic generation with self-compressed femtosecond pulses

Anderson, Patrick (2015) High-order harmonic generation with self-compressed femtosecond pulses. University of Southampton, Physical Sciences and Engineering, Doctoral Thesis, 136pp.

Record type: Thesis (Doctoral)

Abstract

Here, a state-of-the-art model is developed that can predict both the evolution of an intense laser pulse propagating through a gas-filled fibre, and the extreme ultraviolet field that it generates.

This model is first used to discover a new mechanism for compressing energetic laser pulses to few cycle durations within short gas-filled fibres at pressures where high-order harmonic generation is routinely performed. Next, the fibre design is optimised for enhanced phase-matching using the model. Once fabricated and integrated into the source characterisation apparatus, the conversion efficiency at 30-40 nm is found to be almost an order of magnitude higher than comparable sources. Preliminary simulations also predict that isolated attosecond pulses may emerge from the fibre if parameters are carefully tuned.

Additionally, a 13.5 nm source is developed in an extended gas cell geometry. Filters suitable for this wavelength are tested and a single harmonic is then selected and brought to a focus. This apparatus is now being used by the wider scientific community to image test objects and biological samples.

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