Experimental investigation of the emission of high-brightness extreme ultraviolet radiation from laser-plasma interactions

This thesis was previously held under moratorium from 4/11/2019 to 07/11/2023The laser wakefield accelerator is a novel particle accelerator that takes advantage of the large electric fields generated by separating oppositely charged particles in plasma. The ponderomotive force of an intense, ultra-short duration, laser pulse drives density waves in under-dense plasma to create an accelerating structure similar to that of a radio-frequency cavity, but with a longitudinal field strength more than a thousand times larger, and travelling at a velocity close to that of light. Electrons can gain a sufficiently high longitudinal velocity on reaching the back of the accelerating structure to become trapped inside it. These injected electrons then “surf” the plasma wave to reach energies that can exceed several GeV on the centimetre scale. This enables millimetre sized acceleration stages that act as ultra-compact table-top sources of both high energy particles and radiation beams. To date, theoretical and experimental work on radiation production from the laser wakefield accelerator has focussed on the emission of few keV to 1 MeV photons from electrons undergoing betatron oscillations inside the plasma structure. This thesis, in contrast, presents one of the first experimental investigations of radiation emitted at extreme ultraviolet wavelengths approaching the water window. The spectral, spatial and coherence properties of radiation beams produced by the laser plasma interaction are measured. In addition, a Kirkpatrick-Baez microscope focusing optic is developed for proof-of-principle application experiments to demonstrate the usefulness of the source. The spectra of hard x-ray betatron radiation is measured and first tests of the Kirkpatrick-Baez microscope undertaken to focus the radiation to a small spot size. Extreme ultraviolet (XUV) radiation has been observed between 3 and 31 nm with a large number of photons (7.6 × 1013 photons sr−1 at 20 nm) passing through the spectrometer slit. Measurements with a series of double slits show that the source has a high degree of longitudinal coherence with a source size diameter of 50 μm. The source size and spectral measurements give a calculated peak brightness of 6.4 × 1027 photons/s/mm2/mrad2/0.1% BW, occurring at 7.5 nm, assuming the duration of the radiation pulse is Fourier limited to 11 as.The laser wakefield accelerator is a novel particle accelerator that takes advantage of the large electric fields generated by separating oppositely charged particles in plasma. The ponderomotive force of an intense, ultra-short duration, laser pulse drives density waves in under-dense plasma to create an accelerating structure similar to that of a radio-frequency cavity, but with a longitudinal field strength more than a thousand times larger, and travelling at a velocity close to that of light. Electrons can gain a sufficiently high longitudinal velocity on reaching the back of the accelerating structure to become trapped inside it. These injected electrons then “surf” the plasma wave to reach energies that can exceed several GeV on the centimetre scale. This enables millimetre sized acceleration stages that act as ultra-compact table-top sources of both high energy particles and radiation beams. To date, theoretical and experimental work on radiation production from the laser wakefield accelerator has focussed on the emission of few keV to 1 MeV photons from electrons undergoing betatron oscillations inside the plasma structure. This thesis, in contrast, presents one of the first experimental investigations of radiation emitted at extreme ultraviolet wavelengths approaching the water window. The spectral, spatial and coherence properties of radiation beams produced by the laser plasma interaction are measured. In addition, a Kirkpatrick-Baez microscope focusing optic is developed for proof-of-principle application experiments to demonstrate the usefulness of the source. The spectra of hard x-ray betatron radiation is measured and first tests of the Kirkpatrick-Baez microscope undertaken to focus the radiation to a small spot size. Extreme ultraviolet (XUV) radiation has been observed between 3 and 31 nm with a large number of photons (7.6 × 1013 photons sr−1 at 20 nm) passing through the spectrometer slit. Measurements with a series of double slits show that the source has a high degree of longitudinal coherence with a source size diameter of 50 μm. The source size and spectral measurements give a calculated peak brightness of 6.4 × 1027 photons/s/mm2/mrad2/0.1% BW, occurring at 7.5 nm, assuming the duration of the radiation pulse is Fourier limited to 11 as