Spatial distribution of electron temperature and ion density in laser induced ruby (Al2O3:Cr3+) plasma using Langmuir probe

Abstract

The investigation of laser produced ruby (Al2O3:Cr3+) plasma using a planar copper Langmuir probe is reported in the present paper. The ruby plasma was produced by focusing a high power Q-switched Nd:YAG laser on ruby target in a vacuum chamber at a base pressure of ∼ 10−5 mbar. The effect of probe distance on electron and ion time of flight (TOF) signals were studied. Twin peaks were observed for both ions as well as electron signal, confirming the two velocity components for both these species. A triple peak structure was also observed in case of electron TOF signal due to re-splitting of second peak at 50 and 60 mm probe distance. The electron temperature was estimated using characteristic I-V curve of Langmuir probe. It was found to decay exponentially from 16.0 eV to 4.5 eV with increase in distance from 5 mm to 80 mm w.r.t. target. The ion density was found to first increase from 1.2 × 1012 cm−3 to 1.0 × 1013cm−3 upto 40 mm, and then dropped down to 1.6 × 1012cm−3 at 50 mm and finally shows steady behavior.