Experimental investigation of 1064 nm IR laser induced plasmas in gases and in liquids

Experimental measurements and analysis of pulsed 1064 nm Nd:YAG laser-induced breakdown plasma in air at 760 Torr and in liquid (water) has been carried out and characterized using fast gating and high resolution laser shadowgraphy, two wavelength laser interferometry and optical emission spectroscopy diagnostics¹. Three different experimental laser energies and pulse widths such as 170 mJ at 8 ns, 130 mJ at 7 ns and 65 mJ at 12 ns are studied. The laser pulses were focused down to a ~7 micron spot size in air and the resulting laser flux densities range from 4-14 TW/cm². A 532 nm laser shadowgraphy coupled with high speed and high resolution image capturing diagnostics has been established to investigate spatio-temporal evolution and hydrodynamic behavior of the 1064 nm laser induced plasma and neutral density shock during the formation, expansion and collapsing stages. The observed plasma formations were aspherical due to absorption translation during the initial laser-energy coupling. The aspherical feature seeded the hydrodynamic instability leading to the ultimate destabilization of the hot gaseous core after approximately 10 microseconds. The active plasma lifetime through plasma self-luminescence measurements indicate variations from 200-500 ns for the three laser pulses. Shock propagation velocity and plasma volume for three laser pulse series indicate similarly shaped profiles at different expansion velocities. Early plasma expansion velocities of 20 km/s were measured and using Hugoniot relations the neutral shock pressures and temperatures were inferred and the results at the early plasma expansion stage were found to be over 1000 atmospheres and 4 eV. Laser induced plasma breakdown and its resulting shockwave generation and bubble formation in water was also investigated and characterized. The results of these investigations will be presented.