Laser produced plasmas for the generation of X-rays

Abstract

Laser Produced Plasmas (LPP) are a better source to increase the energy cut-off of the harmonics generated due to their larger ionisation potential than the conventional neutral gas media, if optimised properly. The experiments detailed in the thesis aim towards the use of LPP as a medium for the generation of bright coherent EUV/XUV table-top sources. A detailed spatio-temporal characterisation of LPP's generated from Al and Cr targets via non-invasive optical emission spectroscopy (OES) and time-resolved plume imaging are performed to investigate plasma features and optimise them. While ns LPP's are spatio-temporally optimised for Al IV/Al III with the irradiation energy as the control parameter, the ps LPP's are optimised for Al III using the single pulse (SP) and double pulse (DP) schemes. Experiments on Cr plasmas are also performed and the changes in plume morphology upon implementing SP and DP schemes are investigated via plume imaging and the abundance of various species in the plume were investigated via time-resolved OES. The DP schemes are investigated in detail to find out the influence of parameters such as the polarisation, delay between the two pulses, energy in the first pulse and the ambient pressure on the plume morphology. Building and extending the experimental setup to conduct the proposed experiments aiming towards increasing the energy cut-off of the harmonics using LPP as the nonlinear medium comprises the second part of the thesis. A High-order Harmonic Generation (HHG) set up is built and tested using harmonics generated in Ar gas. The HHG system developed here would further be modified to take care of the plasma fluorescence as well as to accommodate higher order harmonics. These spatio-temporally optimised LPP's together with the set-up are anticipated to produce HHG sources with higher brilliance than the commercial tabletop sources, adding energy tunability to these sources. Additional experiments on the angle resolved X-ray emissions in the range of 30 keV to 150 keV from LPP from metals (Al and Cr) and their alloys (Al-Cr) are carried out and detailed here; which can also be used as a source of X-ray radiation.