Abstract

Laser-induced fluorescence (LIF), a nondestructive and sensitive measuring technique, has played an important role in combustion diagnostics. In previous studies,^1–6 temperature measurement using LIF was mainly done by scanning the laser frequency to obtain the ro-vibrational population distribution in the ground electronic state of the molecule, which can only be used for the steady combustion process owing to the time and cost involved in frequency scanning. To meet the needs of measuring an unsteady process, a two-beam LIF technique has been used.⁷,⁸ In the mid-1980s, the thermally assisted fluorescence technique^9,14 was used. D. R. Crosley et al.^12–14 had measured combustion temperature by using the thermally assisted rotational fluorescence of OH radical. However, for smaller rotational frequency separations, a scanning monochrometer with high spectral resolution had to be used to collect the rotational spectra, and it was difficult to use the optical multichannel analyzer (OMA) for the transient temperature measurement.

© 1991 Optical Society of America