Spot size dependent shock wave, plume and ion expansion dynamics of laser produced YBCO plasma

The expansion dynamics of laser produced plasma plumes in gaseous atmospheres exhibit information on plasma-ambient gas interactions which result in plume splitting, shock formation, sharpening and confinement. We investigate laser spot size variation on shock wave, plume, and ion dynamics from laser produced YBa2Cu3O7 (YBCO) plasmas using fast photography and Langmuir probe diagnosis. Changes in plume geometry are observed with varying focal spot size. At smaller spot sizes, lateral expansion of the plume is found to be larger, and plume expansion is spherical, while at larger spot sizes plume expansion is more cylindrical. Shock front formation time, relative intensity, spatial extent and total charge yield (TCY) are all dependent on laser spot size. Total charge yield (TCY) increases as the spot area increases, but decreases beyond a certain value. The width of the ion velocity distribution and the peak velocity decrease with increasing spot size, demonstrate that ions corresponding to larger spot sizes are somewhat more monoenergetic.