Studies On Applications Of Laser-induced Breakdown Spectroscopy And Terahertz Emission From Two-color Laser Irradiated Gas Targets

This thesis work consists of two parts, of which the first part is a review on the laser induced breakdown spectroscopy and its technical development and application in liquid samples. The second part is about theoretical and numerical studies of terahertz radiation generated by a two-color laser in gas targets.In the past 50 years, laser-induced breakdown spectroscopy(LIBS) technology has become an important tool for detection of trace elements. Compared with other element detection technologies, LIBS possess many unique advantages, such as no need of sample preparation, remote control, real time and online rapid detection. Therefore LIBS is widely applied for a variety of solid, gas samples. However, compared with its application with solid samples, the LIBS analysis with liquid samples is not effective due to the weak LIBS spectrum intensity. Significant effort has been dovoted to optimizing the signal of the liquid LIBS. Here we mainly introduce the progress of liquid LIBS, common sampling methods, its calibration method and the key applications in industry, daily life, environment detection, biological medicine and many other aspects.In another piece of work, I have studied theoretically and numerically terahertz radiation from gas target irradiated by two-color lasers based upon the ionization current model. Terahertz radiation is a kind of electromagnetic radiation typically at the frequency 0.1-10 THz. The interaction of ultrashort high power lasers with gas targets is an important way to produce high power THz sources.In this work, we mainly consider the case with the 800 nm laser and its sub-harmonic laser(1600nm). It is found that:(1) the ionization current is affected by laser and gas parameters, such as the laser amplitudes, relative phase between the two lasers, and ambient gas density and species, therefore the strength of the THz amplitude can be optimized with proper experiment parameters.(2) The direction of ionization current is affected by polarization direction of 800 nm laser when the angle is less than 72 degrees and the direction is affected by polarization direction of the sub-harmonic laser when the angle is between 72 degrees and 90 degrees.