Abstract

Recently the water window region (2.3 nm - 4.4 nm) which holds promise in imaging of biological microstructures has been accessed with xuv high harmonic radiation [1,2]. In this work sub-10fs optical pulses at 1 kHz repetition rate have been focused up to 4^*10¹⁵ W/cm² in helium gas. Resulting high harmonic emission has been characterized with a grating and a Si(Li) detector energy dispersive spectrometer. A spatial coherent xuv beam with photon energies extending to above 0.5 keV shows spectral features which have been predicted theoretically. The measurement of the xuv beam diameter allows to estimate a brightness of 5^*10⁸ photons mm^–2 mrad^–2 s^–1 at the Carbon K edge (4.4 nm) within a bandwidth of 1% [2].

© 1998 IEEE