Ground state bromine atom density measurements by two-photon absorption laser-induced fluorescence

Ground state bromine atom detection by two-photon absorption laser-induced fluorescence (TALIF) is demonstrated. The (4p⁵) ²Po _3/2 bromine atoms are excited by two-photon absorption at 252.594 nm to the (5p) ⁴So _3/2 state and detected by 635.25 nm fluorescence to the (5s) ⁴P_5/2 state. The atoms are generated in a radio-frequency inductively-coupled plasma in pure HBr. The excitation laser also causes some photodissociation of HBr molecules, but this can be minimized by not focussing the laser beam, still giving adequate signal levels. We determined the natural lifetime of the emitting (5p) ⁴So_3/2 state, _τ ^Br.∗ _f = 30.9 ± 1.4 ns and the rate constant for quenching of this state by collision with HBr molecules, _k^Q _HBr = 1.02 ± 0.07 × 10.15 m³ s^-1.