Radiation generation via a laser-driven oscillating plasma aperture

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Control of the spatial-temporal and polarisation properties of high power laser pulses are central to the development of compact laser-plasma-based particle accelerators and radiation sources, which have wide-ranging potential applications. Plasma can withstand extremely high energy densities and its optical properties can be varied on the ultra fast timescale of a high power laser pulse, enabling dynamic manipulation of intense light. The project builds upon our programme of work investigating relativistic photonic phenomena in intense laser-plasma interactions and specifically laser light diffraction and harmonic generation in a relativistic plasma aperture. Whereas our previous experiments with linearly polarised light generated bunches of high energy electrons at fixed points in the aperture, we now propose to investigate the use of circular polarisation to drive plasma oscillations around the rim of the plasma aperture, to generate high harmonics of the fundamental plasma frequency. It is predicted theoretically that when the driving laser is circularly polarised, the high-harmonic generation process facilitates a conversion of the spin angular momentum of the fundamental light into the intrinsic orbital angular momentum of the harmonics. An experimental verification of this will open up a new realm of possibilities for producing intense extreme ultraviolet vortices, and diffraction-based high harmonic generation at relativistic intensities.Central to the development of this novel and enabling particle and radiation source technology is the development of mechanisms to control radiation generation in plasma. The project will explore the physics of the generation of high harmonic radiation and optical vortices via the oscillating plasma aperture mechanism. The objectives are to:1. Investigate the spectrum of harmonics generated by linearly-polarised intense laser pulses interaction with an ultrathin foil target 2. Investigate changes to the spectrum of harmonics generated when changing from linear to circular polarisation3. Investigate the extent to which the spectral and spatial-intensity distribution of the harmonics generated can be controlled by variation of the degree of ellipticity in the polarisation of the laser light.