Numerical studying of soft x-ray emitted from porous target irradiated by high power subnanosecond laser beam and the effect of plasma opacity

Abstract

This paper presents the results of numerically studying for the enhancement of the soft continuum x-ray yield emitted from porous metal targets irradiated by sub-nanosecond high power pulsed laser beam when considering the effect of plasma opacity. In the calculations, the main emission mechanisms were assumed to be the free–bound and free–free (bremsstrahlung) transitions at water windows wavelengths ranges 2.3-4.4 nm and also wavelength ranges 12.6-14.6 nm which is useful for lithography applications. The free-free, and bound–free transitions were also considered for calculating the opacity. The results show that the opacity may significantly influence the x-ray yield detected by an observer outside the target.