Hydrogen Balmer Series Measurements in Laser-Induced Air Plasma

Abstract

Time-resolved spectroscopy is employed to analyze micro plasma generated in laboratory air. Stark-broadened emission profiles for hydrogen alpha and beta allow us to determine plasma characteristics for specific time delays after plasma generation. Stark shift, asymmetry, and full width half maximum measurements are used to infer electron density. The measurements of hydrogen alpha and beta Balmer series line shapes are analyzed using various theory results. Our laser-induced breakdown spectroscopy arrangement uses a Q- switched Nd:YAG laser operating at the fundamental wavelength of 1064 nm that is focused for plasma generation. The hydrogen alpha and beta lines emerge from the free electron background radiation for time delays larger than 0.3 ps and 1.4 ps, respectively. Neutral and ionized nitrogen emission lines allow us to infer electron density for time delays from 0.1 to 10 μs. The electron density values are compared with results obtained from hydrogen Balmer series line shapes.