Legall, H.; Blobel, G.; Stiel, H.; Sandner, W.; Seim, C.; Takman, P.; Martz, D.H.; Selin, M.; Vogt, U.; Hertz, H.M.; Esser, D.; Sipma, H.; Luttmann, J.; Höfer, M.; Hoffmann, H.D.; Yulin, S.; Feigl, T.; Rehbein, S.; Guttmann, P.; Schneider, G.; Wiesemann, U.; Wirtz, M.; Diete, W.: Compact x-ray microscope for the water window based on a high brightness laser plasma source. Optics Express 20 (2012), p. 18362-18369
10.1364/OE.20.018362

Abstract:
We present a laser plasma based x-ray microscope for the water window employing a high-average power laser system for plasma generation. At 90 W laser power a brightness of 7.4 x 10^11 photons/(s x sr x μm^2) was measured for the nitrogen Lyα line emission at 2.478 nm. Using a multilayer condenser mirror with 0.3 % reflectivity 10^6 photons/(μm^2 x s) were obtained in the object plane. Microscopy performed at a laser power of 60 W resolves 40 nm lines with an exposure time of 60 s. The exposure time can be further reduced to 20 s by the use of new multilayer condenser optics and operating the laser at its full power of 130 W.