Abstract
Few-cycle high peak power laser pulses produced in gas-filled hollow fibres have a EH11 Bessel mode. Control of the intensity and phase-matching conditions requiring no additional dispersion is introduced, and is often achieved by closing a hard aperture around the beam. We use the Huygens–Fresnel diffraction integral to propagate such a beam through a numerical model of a typical attosecond beamline, quantifying the distribution of spatial intensity and the shape of the wavefront through the focal volume as the beam is truncated by finite-diameter optics. State-of-the-art attosecond and single-harmonic experiments combining the fundamental NIR with high-harmonic XUV radiation also employ annular optics, again as material dispersion must be avoided. We simulate the additional changes to wavefront shape and spatial intensity distribution on reflection from a spherical annular mirror for a range of annulus and aperture sizes. Finally we predict the change in intensity and focal position as the aperture is reduced. The model's usefulness as a tool for optimisation of an experimental beamline is therefore highlighted.
Acknowledgements
G.R.A.J. Nemeth acknowledges financial support from EPSRC and STFC. The authors would like to thank the referees for their insightful and constructive comments.