Laser induced fluorescence in nanosecond repetitively pulsed discharges for CO2 conversion

A CO2 nanosecond repetitively pulsed discharge (NRP) is a harsh
environment for laser induced fluorescence (LIF) diagnostics. The
difficulties arise from it being a strongly collisional system in which
the gas composition, pressure and temperature, have quick and strong
variations. The relevant diagnostic problems are described and
illustrated through the application of LIF to the measurement of the OH
radical in three different discharge configurations, with gas mixtures
containing CO2 + H2O. These range from a dielectric barrier NRP with He
buffer gas, a less hostile case in which absolute OH density measurement
is possible, to an NRP in CO2+H2O, where the full set of drawbacks is at
work. In the last case, the OH density measurement is not possible with
laser pulses and detector time resolution in the ns time scale.
Nevertheless, it is shown that with a proper knowledge of the
collisional rate constants involved in the LIF process, a collisional
energy transfer-LIF methodology is still applicable to deduce the gas
composition from the analysis of LIF spectra.