Prepulse dependence in hard x‐ray generation from microdroplets

We report on experiments which show that liquid microdroplets are very efficient in hard x‐ray generation. We make a comparative study of hard x‐ray emission from 15 μm methanol microdroplets and a plain slab target of similar atomic composition at similar laser intensities. The hard X‐ray yield from droplet plasmas is about 35 times more than that obtained from solid plasmas. A prepulse that is about 10ns and at least 2% in intensity of the main pulse is essential for hard x‐ray generation from the droplets at about 10¹⁵ W cm⁻². A hot electron temperature of 36 keV is measured from the droplets at 8 × 10¹⁴ W cm⁻²; three times higher intensity is needed to obtain similar hot electron temperature from solid plasmas that have similar atomic composition. We use 1D‐PIC simulation to obtain qualitative correlation to the experimental observations.