Rotational redistribution effect on saturated laser-induced fluorescence

Effects of Saturation on Laser-Induced Fluorescence Measurements of Population and Polarization

“…Although the need for quenching rate data is minimized in saturated LIF measurements in flames, these experiments do have a number of compli cations. For example, the possibility of laser-induced chemistry (54--56) or ionization must be considered, complicated models must be used to take into account partial vibrational and rotational relaxation during the laser pulse (43,(57)(58)(59)(60), and extrapolations to complete saturation must be carried out if only partial saturation can be achieved (47,48). In addition, most models of saturation in flames have assumed that the collisional environment of atmospheric flames causes emission to be unpolarized.…”

Optical imaging techniques for hypersonic impulse facilities

“…For example, if the excited absorber undergoes a collision, then a nonradiative transition may occur, known as collisional quenching. Other competing processes, such as rotational energy transfer (RET) (65,66) and vibrational energy transfer (VET) (60,67) need to be considered, but generally speaking, collision-induced transitions add a temperature-and species-dependent factor to the fluorescence signal which complicates interpretation and decreases the magnitude of the signal. RET and VET are generally treated in the same way as collisional quenching, with rate equations, using experimentallydetermined rate coefficients, to describe their contribution to the loss from the upper laser coupled state (68) .…”

The application of coherent anti-Stokes Raman scattering to temperature measurements in a pulsed high enthalpy supersonic flow

“…LIF has been shown to be an extremely useful technique applicable to the measurement of gaseous chemical species concentrations (Stepowski and Cottereau 1981;Dyer and Crosley 1982;Hanson 1987;Hanson et al 1990) rotational and vibrational temperatures (Chan and Daly 1980a;Lee et al 1987) and flow velocities (Hiller and Hanson 1988) in a range of environments, including atmospheric flames, internal combustion engines, nozzle flows and shock wave studies. However, to enable accurate measurements of these parameters from the LIF signals, one must use appropriate rate models that account for excitation dynamics (Chart and Daly 1980b), redistribution of rotational (Berg and Shackleford 1979) and vibrational levels (Campbell 1982), saturation (Seitzmann andHanson 1991;Lucht et al 1990;Carter et al 1987;Lucht et al 1982) and depletion (Campbell 1984) effects and collisional quenching (Barlow and Colligan 1991). Collisional quenching is a very important consideration in the application of LIF to pulsed high enthalpy flows because of the high collision rates in such environments.…”