Hannover 2020 – scientific programme

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K: Fachverband Kurzzeit- und angewandte Laserphysik

K 5: Laser Systems and Laser Applications

K 5.6: Talk

Wednesday, March 11, 2020, 12:15–12:30, f428

Molecular formation in femtosecond-laser-induced micro-plasmas and their applications — •Anne-Sophie Rother, Peter Kohns, and Georg Ankerhold — Hochschule Koblenz, RheinAhrCampus Remagen, Remagen, Deutschland

Irradiating focused laser-pulses on surfaces can generate local micro-plasmas, in which molecules mostly dissociate into their atomic constituents. These excited atoms and partly ions emit characteristic lines during the plasma cooling phase. Laser-induced breakdown spectroscopy uses these emission spectra to locally analyze the elemental composition of the irradiated surface.

After a few microseconds, the decreasingly excited atoms can recombine and sometimes form new molecules from formerly not bonded constituents, like calcium halides and metal oxides. While some of these molecules improve the elemental analysis by radiating identifying band spectra, others bond without emitting any lines. As we will show, the latter occurs when focusing femtosecond laser pulses on zinc surfaces in ambient air. After the emission of atomic zinc lines, also observable when using nanosecond pulses, only for ultrashort laser pulses crystalline dendrites of zinc oxide are formed and perform scattered second harmonic generation. As we examined, these scattering frequency doublers can be used in an amended optical autocorrelation setup for measuring the duration of ultrashort pulses, which leads to the same results as the much more expensive beta barium borate.