Annular phase-matched dual-pump coherent anti-Stokes Raman spectroscopy system for the simultaneous detection of nitrogen and methane

Abstract

The concentration and pressure dependence of dual-pump coherent anti-Stokes Raman spectroscopy (CARS) signals from nitrogen and methane was investigated. CARS spectra were acquired from a gas cell at pressures of 0.007 to 2.24 MPa and methane concentrations of 0.5 to 50%. The square root of the methane signal intensity divided by the nitrogen signal intensity was found to have a near-linear dependence on methane concentration at all pressures investigated. The pressure dependence of this integrated intensity ratio decreased with increasing pressure and became negligible at the highest pressures tested. The shot-to-shot variation at concentrations determined from single-laser-shot measurements was less than 7%. Single-laser-shot CARS spectra of nitrogen and methane were obtained from the cylinder of a firing direct-injection natural gas engine.

Femtosecond coherent anti-Stokes Raman scattering measurement of gas temperatures from frequency-spread dephasing of the Raman coherence

“…For the N 2 band head in nanosecond CARS, the signal increases approximately linearly with pressure above atmospheric pressure because of the effects of overlapping transitions and collisional narrowing. 12 In summary, gas-phase temperature and concentration were determined from the temporal dependence of the femtosecond CARS signal in the first few picosecond after impulsive pump-Stokes excitation. A time-delayed probe beam was used to generate the CARS signal.…”

Nitrogen Vibrational Population Measurements in the Plenum of a Hypersonic Wind Tunnel

“…Most significantly, reduction of the NRB would enable more sensitive detection of weak transitions. To accomplish this, future work will use what is known as unstable-resonator spatially enhanced detection CARS [19,25]. Additionally, increasing laser power would also result in increased detection sensitivity to lower vibrational populations; however, care must be taken to prevent Fig.…”

Dual–pump CARS for the simultaneous detection of N2, O2 and CO in CH4 flames

“…Hence the reported precision holds even in the case of high C 2 concentrations. The accuracy for relative concentration measurements using dual-pump CARS was investigated, e.g., by Green et al 11 to be better than 7%. Carbon monoxide concentration measurements using the contour fitting procedure have been investigated by England et al, 20 the accuracy being assumed to be better than 5%.…”