Investigation of the production of plasmas from liquid droplets

Since laser plasmas have not been created using small, transparent liquid bodies as targets, a preliminary investigation into the phenomena that arise in such plasmas was undertaken. Small (0.1 mm to 1.0 mm diameter) droplets of water freely falling in a partial vacuum (0.1 atm to 0.7 atm) were irradiated by a Q-switched ruby laser (around 10 Mw power at 6943 A wavelength). The resultant plasma was seen to be highly asymmetric; an initial expansion away from the laser was immediately followed by an expansion back towards the laser. Using a moderately simple computer model, these phenomena were seen to be generally explainable in terms of classical geometrical optics, which requires an early focusing of the incident radiation to very high energy densities near the backside of the target droplet