Production and Characterization of Femtosecond-Laser-Induced Air Plasma; Master's Thesis

摘要

The purpose of this research was to produce, characterize, and optimize laser-induced air plasma as a preliminary step in using the plasma as a source of terahertz radiation. An 800 nanometer, 50 femtosecond, 0.75 Watt, pulsed Ti:Sapphire laser system was used as the source infrared beam. A beam expander was used to expand the beam to a diameter of approximately 6.5 mm, and the beam was focused through a 25 mm focal length achromatic lens to produce laser-induced plasma in ambient air. A 40 kHz ultrasonic transducer was used to detect the plasma. A second harmonic generation crystal was placed within the beam expander to generate 400 nm blue light, enabling production of THz in the plasma via four wave mixing; a third-order nonlinear process. While plasma- produced THz was not detected, all the preliminary groundwork was accomplished, including full characterization of the plasma, blue light, and alignment of the system to generate and detect THz. The electro-optic detection apparatus was assembled,aligned and used to successfully detect a diagnostic THz signal.