Langmuir probe characterization of spatially confined laser-induced Bismuth plasma

Abstract

The influence of spatial confinement on the laser induced plasma parameters of Bismuth (Bi) at different laser irradiances ranging from 2.9 GWcm−2 to 6.2 GWcm−2 has been investigated using Langmuir probe technique. The spatial confinement is introduced with the help of metallic blocker placing at different distances of 5 mm, 10 mm and 15 mm from the target. It is observed that electron temperature (Te), electron density (ne), and electron thermal velocity (vth,e) of Bi plasma are significantly influenced by laser irradiance, biasing voltage and blocker distances. In the absence of blocker, maximum values of Te, ne, and vth,e, are 13 eV, 1.6 × 1017 cm−3 and 2.4 × 108 cms−1 respectively, whereas, in the presence of blocker these values are significantly enhanced to 31.6 eV, 2.9 × 1017 cm−3 and 3.7 × 108 cms−1 respectively. This enhancement is attributed to increased collisional frequency of plasma species after compression due to reflection of shock waves from blocker. The analytical evaluated values of work done to compress plume vary from 0.7 mJ to 0.2 mJ, whereas, the variation in plasma pressures is from 0.35 MPa to 1.47 MPa and shock pressures variation comes out to be in the range from 0.32 GPa to 0.56 GPa.