XUV lensless imaging with spatially shaped high-harmonic beams

Thesis

This thesis presents two novel advances in the field of high harmonic generation along with a demonstration of application to the lensless imaging technique known as Fourier Transform Holography. Also presented are images obtained with the technique of coherent diffractive imaging.

The first advance is that of an increase in harmonic brightness through the manipulation of the spatial phase of the driver laser. The transverse driver intensity in the focal plane of a fixed lens was shaped from Gaussian to supergaussian whilst the spot size was concomitantly increased. Within the range of experimental values, the increasing supergaussian order enabled the harmonic source size to increase at a faster rate than the driver spot size. This changed the scaling relationship between the detected harmonic flux and driver spot size from quadratic to a power of 2.3±1.72. Without changing the focussing optic, the brightness of the harmonic beam was increased by a factor of 5±0.65.

The second advance is that of the generation of multiple harmonic sources through the manipulation of the spatial phase of the driver laser. The intensity distribution of the driver beam was spatially shaped to form a user defined distribution of foci with programmable positions and relative energies. For two foci, experimental results are presented showing the generation of two independent but mutually coherent harmonic beams. Using these two harmonic beams, a Fourier Transform Holography target comprising two distinct features was illuminated. It is shown that under comparable conditions, distributing the illumination to match the shape of the target yielded an image with a superior signal to noise ratio.

Authors: Treacher, D

• DOI: 10.5287/ora-dag7pze6b
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: SLM; Femtosecond; HHG
• Subjects: Lensless imaging; Spatial shaping