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

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.