RESONANCE-ENHANCED COHERENT ANTI-STOKES-RAMAN SCATTERING AND LASER-INDUCED FLUORESCENCE APPLIED TO CH RADICALS - A COMPARATIVE-STUDY

Resonance enhanced CARS and LIF have been applied to the CH radicals i n a microwave excited Ar/H-2/CH4 plasma (p = 21 Pa, P-Mikro = 2.7 kW). Both techniques yield similar nonthermal rotational population distri butions of CH(X(2) Pi(r)) in its vibrational ground state (upsilon = 0 ), which can be described by two rotational temperatures, T-rot,T-1 ap proximate to 600 K being in the order of the gas temperature for rotat ional states with N less than or equal to 7, and a considerably higher T-rot,T-2 for the higher rotational states. This result is in good ag ree ment with previous resonance CARS and LIF measurements in similar plasmas. With resonance CARS additional measurements on CH in the upsi lon = 1 state could be performed yielding a vibrational temperature of 2440 K, the total CH density was about 1.6 x 10(18) m(-3). The detect ion limits of both techniques are determined, in our case about 2 x 10 (8) CH radicals per quantum state in the detection volume, and their a dvantages and disadvantages are discussed.