State Diagnostic Study Of Laser-produced Air Plasma By Thomson Scattering

The high-temperature and high-density laser-produced plasma?LPP?generated by the high-power density pulse laser(10⁹-10¹³ W/cm²)focusing on the target surface has the characteristics of coexistence of various charge states,complex atomic process,rapid evolution process and large spatial gradient of temperature and density.The diagnosis of laser-produced plasma state parameters and the study of dynamic evolution are hot issues in the field of laser-produced plasma physics.Through the diagnosis investigate of LPP state parameters,we can further understand the dynamic evolution characteristics of LPP,which is of great significance for the research of LPP in the fields of laser ion source,extreme ultraviolet lithography source and astrophysics,etc.The Thomson scattering?TS?method is widely used in the diagnosis of the fusion plasma because of its comprehensive diagnostic information,wide range of diagnostic parameters,high accuracy of diagnostic results and almost no dependence on related theoretical models.Based on the advantages of TS diagnosis,combined with the research needs of the laboratory for laser-produced plasma,a time-resolved TS diagnosis and measurement device is set up in this paper,and a series of researches on the state parameter diagnosis of laser-produced plasma are carried out in air.The time evolution law of electron temperature and electron density of laser-produced air plasma is obtained,and the heating effect of probe laser on plasma is further studied by combining with spectroscopy.The specific work is as follows:?1?A time-resolved TS diagnosis and measurement device is built.The state parameters of LPP in air were diagnosed and measured based on the experimental device.The experimental data are simulated by theoretical calculation,and the electron temperature of air plasma is obtained to decay from 90000 K to 15800 K,and the electron density decreased from 6.6×10¹⁷ cm^-3 to 7.8×10¹⁶ cm^-3.This work has accumulated experimental experience and theoretical basis for the diagnosis of laser-produced target plasma and the interaction between ion beam and plasma in vacuum environment based on TS method.?2?Based on TS diagnostic apparatus,the heating effect of probe beam on LPP with a delay time of 50 ns¹100 ns was studied by means of optical emission spectroscopy?OES?.It is found that the heating effect of probe beam on plasma depends heavily on the energy of probe beam.The higher the energy is,the more obvious the heating effect is.Under the shorter delay time of plasma evolution,the effect of electron temperature of the probe beam on plasma is more lasting.with the increase of delay time,the heating effect gradually weakens until it disappears.Therefore,in order to reduce the influence of probe beam on electron temperature in TS diagnostic experiment,the probe beam should operate at the lowest energy on the premise of ensuring the normal development of the experiment;after the evolution of laser plasma about 1000 ns,the influence of probe beam on plasma is very small or even negligible.No significant effect of probe beam on electron density was observed.This work lays a foundation for further understanding of TS technology and its application in LPP diagnosis.