Laser induced breakdown in pulsed helium atmospheric pressure plasma jet

This study connects two fields of research: laser induced plasmas and nonequilibrium low-temperature plasmas by studying effects of preionisation, made by a single-electrode atmospheric pressure plasma jet, on a laser induced breakdown (LIB) in helium. A laser pulse (1064 nm, 4 ns pulse width, 5 Hz repetition rate) was focused into the helium jet flowing into ambient air and synchronized with the discharge (10 kHz repetition rate). The level of preionisation in the focal volume at the moment when the laser pulse arrives was controlled by changing the time delay between voltage and laser pulse. The conditions of the discharge are strongly affecting laser induced plasma by providing initial seed of electrons and promoting the breakdown in helium. Measurements of the absorbed laser pulse energy and optical emission relative intensities were performed for different time delays between voltage and laser pulse. Study of LIB with preionisation is discussed as a potential tool for diagnostics of free plasma jets and jets interacting with various target materials.