Professor Simon Hooker

Abstract:

High harmonic generation (HHG) is a promising tabletop source of coherent short wavelength radiation, with applications spanning science and engineering [1]. However, the low conversion efficiency and low average power of conventional few-kHz near-infrared (NIR) driving lasers limits the photon flux of such sources. Scaling this technique to MHz driving lasers requires strong focusing due to the limited pulse energy, and as a result the interaction volume is greatly reduced. It has been shown that this may be mitigated by restricting HHG to a photonic crystal fiber (PCF) [2, 3]. Here, we explore HHG in the latest generation of negative curvature PCFs [4] and achieve the highest photon energies to date.

Abstract:

The resolution obtained with coherent diffractive imaging (CDI) is limited by a number of factors, one of which is the transverse coherence of the illuminating beam. For a successful reconstruction, it is accepted that the illuminating beam should have a lateral coherence length of at least twice the largest linear dimension of the sample

Abstract:

Driving bright high-order harmonic generation (HHG) with few-μJ pulses is a crucial step towards compact, high average power sources of coherent extreme ultraviolet (XUV) radiation for time-integrated applications including imaging. Unfortunately, reaching a sufficiently strong E-field to perform HHG with these pulses requires tight focusing, greatly reducing the interaction volume. An elegant solution to this problem is to restrict HHG to a hollow waveguide [1] and in particular a photonic crystal fiber [2]. Strong reabsorption in the XUV prohibits the use of multi-atmosphere pressures to achieve phase-matching [3], and instead quasi-phase-matching (QPM) is preferred. Here we demonstrate QPM of HHG for the first time within a gas-filled PCF.

Abstract:

We investigate HHG in gas-filled PCFs with microjoule driving lasers. QPM is implemented for the first time, enhancing the flux at 30 eV by a factor of 60.