Radiative lifetime measurement of excited neutral nitrogen atoms by time resolved laser-induced breakdown spectroscopy

Abstract

Lifetimes of the excited 2P₂ (³P) 3p ⁴S_3/2 level of a nitrogen atom corresponding to transitions to different lower states have been estimated by measuring the line intensity of a transition as a function of the delay time between the Q-switching of the laser and the gating of the window of the ICCD. This novel time resolved laser-induced breakdown spectroscopic technique is explained in the paper. The lifetimes of the upper level 2P₂ (³P) 3p ⁴S_3/2 corresponding to the three transitions to 2P₂ (³P) 3s ⁴P_1/2 (742.346 nm), 2P₂ (³P) 3s ⁴P_3/2 (744.27 nm) and 2P₂ (³P) 3s ⁴P_5/2 (746.851 nm) were measured by this technique. The corresponding average lifetimes (τ) of these transitions were 199 ns, 105 ns and 68 ns. These values compare pretty well with the calculated lifetimes of 203.8 ns, 96.7 ns and 59.2 ns for the above three transitions as reported by Hibbert et al. The plasma temperature (atomic excitation temperature) decay time was found to be 1133 ns. This novel technique of estimating the lifetime of an excited state of an atom/ion is yet another very useful application of LIBS as a versatile analytical tool.