Two-photon absorption laser-induced fluorescence of atomic nitrogen by an alternative excitation scheme

A two-photon absorption laser-induced fluorescence (TALIF) scheme to monitor ground-state atomic nitrogen is described. Excitation at 207 nm to the (3p) 4S°3/2 upper state is demonstrated to be superior to the traditional 211 nm excitation to (3p) 4D°7/2. Most striking is the low quenching rate of the upper (3p) 4S°3/2 state by N2 at kq=6.7(9)×10−11 cm3 s−1, nearly an order of magnitude lower than the traditional technique. The two-photon excitation rate at 207 nm is also measured to be a factor of 3.5 greater than the traditional scheme. The results suggest that the 207 nm excitation scheme should be employed in future N-atom diagnostic work.