X-Ray laser: past, present, and future

In this review we concentrate our attention on X-ray laser research and development covering the so called soft X-ray region (down to similar to 10 nm) and the water window region (down to 2.3-4.4 nm). We present the development of soft X-ray lasers (SXLs) and their applications using primarily collisional and recombination schemes. We present the paths towards compact systems and major achievements to date. We discuss conditions for using both schemes to reach the Water window region. In this discussion we also present another possible schemes based on photo-pumping, inner shell transitions in atoms and ions and Doppler Compression of IR laser radiation down to the X-ray region with its intrinsic tunability possibility. A significant part of the review is dedicated to the wide range of applications of SXLs with wavelengths at and above 10 nm. Also, discussed is the potential of extending the range of biological applications for the water window region. [GRAPHICS] Image of wafer with polysilicon lines on silicon (top: 250 nm, bottom: 100 nm widths of lines) (C) 2009 by Astro Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA