Time-resolved measurements of laser plasmas interaction during breakdown in normal atmosphere by various wavelengths

摘要

Time-resolved spatial and spectral characteristics of laser plasmas interaction in normal atmosphere are presented. Plasma experiments were performed by using 532 nm (4 ns, 180 mJ) and 1064 nm (5 ns, 360 mJ) pulses from Brilliant B Nd:YAG laser. Laser beams were focused in the opposite directions by lenses with focal distances of 15 mm. Firstly laser breakdown of air by 532 and 1064 nm laser radiation was investigated. Molecular bands, absorption line of atomic oxygen O 777 nm and dip of continuum intensity are recorded at initial instants of laser plasma formation. Mechanisms of plasma expansion are investigated. Relationship of molecular bands, absorption line of atomic oxygen, plasma's UV radiation and fast wave of ionization is discussed. Molecular bands, continuum and line temporal dynamics was investigated during laser plasmas interaction. Three zones of interaction and enhancement of line/continuum ratio is registered. Influence of KrF laser radiation (248 nm, 25 ns, 600 mJ) on parameters of breakdown induced by 532 nm laser radiation is discussed.