Full characterisation of a focussed extreme ultraviolet beam using a non-redundant array of apertures

摘要

Determination of the beam parameters of a probe beam is essential for many applications across science. Full characterisation of a coherent beam requires numerous measurements of the beam profile both inside and outside the Rayleigh range to determine values of w0, the beam waist size, and M2. In the EUV (extreme ultraviolet, λ<50nm) and X-ray (λ <10nm) regimes, this is particularly difficult because CCD sensor pixels are too large for direct measurement and knife-edge techniques are slow due to low flux or flatness criteria and hence are subject to mechanical drifts over the exposure time. Other conventional wave-front sensing techniques such as Shack-Hartmann [1] sensors are limited either by high absorption in the case of lenses, or by mirror substrate flatness. Hence, a reliable, short exposure technique for beam profiling in these spectral regimes is critical for future cross-field applications at synchrotrons, XFELs (X-ray Free Electron Lasers), and lab-based sources of high energy radiation for future microscopy techniques.