Volume effect of laser produced plasma on x-ray emissions

An investigation of x-ray emission from Cu plasma produced by 1.054 μm Nd:glass laser pulses of 5 ns duration, at 2 x 1012 - 2 x 1013 Wcm-2 is reported. The x-ray emission has been studied as a function of target position with respect to the laser beam focus position. It has been observed that x-ray emissions from ns duration plasma show a volume effect similar to subnanosecond plasmas. Due to this effect the x-ray yield increases when target is moved away relative to the best focal plane of the laser beam. This result supports the theoretical model of Tallents and has also been testified independently using suitably modified theoretical model for our experimental conditions. While above result is in good agreement with similar experimental results obtained for sub-nanosecond laser produced plasmas, it differs from result claiming filamentation rather than pure geometrical effect leading to x-ray enhancement for ns plasmas. (author)