Electron density of laser plasma produced in liquid under pressure

Plasma produced in liquid under pressure has been studied. The plasma is produced by focusing YAG laser beam, and the electron density of plasma is measured by Mach-Zender interferometer. Ultra pure water and dissolved NaCl 16% are used as a test liquid, and are pressurized up to 15 atm by Nitrogen gas. As a result, the electron density increases with increasing pressure. Then, electron density is proportional to the about 1/3 powers of pressure. The electron density in NaCl aqueous solution also increases with increasing pressure, although the rate of increase is smaller than that in ultra pure water. This implies that dense plasma can be produced using even same laser power. So pressurizing is advantage in production of dense plasma