| Picosecond Coherent Anti-Stokes Raman Scattering (CARS) is used for measurements of nitrogen Q-branch (ΔJ = 0) spectra in several non-equilibrium plasma environments; spectral processing yields vibrational distribution function (VDF), 1st-level vibrational temperature (Tv), and/or rotational-translational temperature (Trot). The implementation of a home built modeless dye laser and portable CARS system is also described.;Simultaneous measurements of Tv and Trot were performed in the 200–370 torr plenum of a nonequilibrium Mach 5 wind tunnel. The nominally high reduced electric field (E/npeak ∼ 500 Td), nsec-pulsed discharge alone results in fairly significant vibrational loading, Tv ∼ 720 K / Trot ∼ 380 K; addition of an orthogonal low E/n (∼10 Td) DC sustainer discharge produces substantial vibrational non-equilibrium, Tv ∼ 2000 K / T rot ∼ 450 K. Injection of CO2, NO, and H 2 downstream of the pulser-sustainer discharge is examined, resulting in vibrational relaxation and simultaneous gas heating, Tv ∼ 800-100 0K / Trot ∼ 600 K.;CARS measurements within very low density flows in the Mach 5 expansion nozzle are also performed, with Tv measured in both the supersonic free-stream and downstream of a bow shock created by a 5 mm diameter cylindrical test object in the Mach 5 flow. Measurements within 300 µm of the cylinder surface show that for pure N2, or N2 with 0.25 torr CO2 injection, no vibrational relaxation is observed behind the bow shock.;A third set of data is reported from measurements of Tv and Trot produced in a plasma assisted combustion reactor. Non-equilibrium vibrational loading is examined for bursts of 40-150 pulses in 100 torr air at T0 = 300 K; vibrational energy is seen to increase quasi-linearly with number of pulses, up to ∼100 pulses, after which vibrational temperature levels off Tv ∼ 1300 K. These results are found to agree well with nsec discharge modeling predictions. Vibrational energy decay is examined in 100 and 300 torr air, for T0 = 300 and 500 K for a variety of discharge burst sizes, and it is noted that the T0 = 500 K condition exhibits vibrational energy decay nearly an order of magnitude faster than that observed for T0 = 300 K. Additionally, Trot was measured for bursts of 50 pulses, at T0 = 500 K, in air as well as C2H4-, CH4-, and H2-air mixtures, for P0 = 100, 200, 300 torr, &phgr; ∼ 0.9-0.36. This analysis shows no significant dependence of Trot on any of the parameters, except for differences between fuel species. Time-resolved thermometry of H2-air excitation and ignition is reported, with ignition delay time and peak temperature found in good agreement with kinetic modeling calculations.;A final data set involved the measurement of VDF and Trot in a single-filament-pulse nsec-duration discharge in 100 torr N2/air. Various energy loading conditions are examined, with high vibrational non-equilibrium observed in all cases. Broadening of the dye laser spectral profile allows simultaneous interrogation of N2(X,v = 0-9). Immediately after the ∼100 nsec pulse moderate vibrational non-equilibrium is observed, with Tv ∼ 600-1000 K, and Trot ∼ 300-400 K for all conditions. Very notable is the presence of a peak in Tv typically occurring ∼100 µsec after the discharge pulse, with Tv(peak) ∼ 1400-2600 K, depending on the discharge energy loading. Total vibrational quanta was also plotted; this peaks at a similar time as Tv, and also exhibits an increase of 2-4 times the value observed immediately after the pulse. |
