The Study Of Radiation Enhancement Methods On Laser-induced Soil Plasma

In this paper, the methods of enhancement on laser-induced soil plasma radiation were studied. The laser spectrum analytical system is composed of a high-energy neodymium glass laser (0~25J), a multifunctional and automatic scanning spectrometer, a CCD detector, a delay system, and a spectrum-collected software. A series of national standard soil were used as the target samples. The main subjects are as the following:1. Under room atmospheric pressure, the plasma radiation induced by sequential laser pulse action on the same position of soil sample surface were recorded, the confinement effect of the laser-induced crater on plasma which generated from follow-up laser pulse were researched, and laser high-quality spectroscopy was obtained. The influences of different environmental atmospheres on plasma radiation intensity and signal to noise ratio were studied, and the best condition of environmental atmospheres was determined.2. Volatile additives were added into the soil to improve the sample evaporation, and the relationship between the types of additive and the radiation enhancement of laser-induced plasma were investigated. Through taking the photographs of the plasma excited by a pulse laser, the changes in the size and color of plasma by adding different additives were observed. Laser plasma radiation spectral intensity and background intensity under different additive contents were recorded, and corresponding quality of spectral line were compared.3. Laser-induced plasma belongs to the System of local thermal equilibrium (LTE). Atomic emission spectrometry was used to measure plasma parameter under different experimental conditions. According to the measured excitation temperature, electron density and evaporation capacity, the mechanism of laser-induced soil plasma was investigated and the radiation characteristics of plasma was explained. The optimal experimental conditions conducive to spectral analysis was determined.4. Influence of sample properties on laser-induced soil plasma radiation was studied. NaCl additive and pure ZnO were added into the sample, heavy metals in base soil around the city of Baoding were determined by spectrum quantitative analysis. The results showed that both the contents of these two elements in three base soil did not exceed the second-class soil standard of《Environmental quality standard for soils》(GB 156181995) issued by the State.