Studies On The Plasma Diagnosis Technique Based On The Third Harmonic Of Femtosecond Laser

Micro pulsed plasmas are important in applications to industrial and medical fields.Accurate spatio-temporal measurements of microplasma are useful for understanding the mechanism of plasma generation and annihilation and providing guidance for plasma applications.However,there is still a lack of diagnostic techniques adapted to microplasma.In this thesis,a non-destructive,high-sensitivity,and high spatial resolution microplasma diagnostic technique is developed by studying the dependence of the third harmonic intensity of an ultrashort pulse laser on the electron density in the plasma.The analysis shows that the plasma optimizes the quasi-phase matching condition of the axial component of the third harmonic,which greatly increases the spectral intensity of the axial third harmonic.Furthermore,the third harmonic axial component is used as a spectral probe to diagnose pulsed discharge plasma,and the diagnostic scheme is optimized.The diagnostic results show that the third harmonic probe can measure parameters such as the plasma lifetime,the electron density distribution in the plasma,the refractive index gradient of the plasma,the ion velocity and acceleration in the electric field,and the plasma diffusion rate.The third harmonic plasma probe has the advantages of remote diagnostics,high temporal resolution,high spatial resolution,and applicability to harsh environments.The third harmonic plasma probe can provide technical support for plasma diagnostics in the fields of plasma boosting,plasma material modification,plasma pollution control,and pollutant degradation.