Detection of Cl in rf plasmas by laser-excited stimulated emission

Laser-excited stimulated emission is used to detect chlorine atoms in a Cl2/Ar rf etching plasma. Two laser photons near 233.3 nm excite the 3p44p 4S0 electronic state of atomic chlorine in a spin-forbidden transition from the 3p5 2P0 ground state. At modest laser fluence stimulated emission is observed from the 3p44p 4S0→3p44s 4P transition. The stimulated emission signals are compared to simultaneously acquired laser-induced fluorescence from the same transition. The strong, collimated stimulated emission provides a means to detect atomic chlorine which only requires a single optical access window.