Abstract
Distortion of laser-induced fluorescence profiles attributable to optical absorption and saturation broadening was corrected in combination with laser absorption spectroscopy in argon plasma flow. At high probe-laser intensity, saturated absorption profiles were measured to correct probe-laser absorption. At low laser intensity, nonsaturated absorption profiles were measured to correct fluorescence reabsorption. Saturation broadening at the measurement point was corrected using a ratio of saturated to non-saturated broadening. Observed LIF broadening and corresponding translational temperature without correction were, respectively,2.20±0.05 GHz and2510±100 K and corrected broadening and temperature were, respectively,1.96±0.07 GHz and1990±150 K. Although this correction is applicable only at the center of symmetry, the deduced temperature agreed well with that obtained by LAS with Abel inversion.
Highlights
Diode laser-induced fluorescence (DLIF) has a feature of high wavelength resolution on the order of picometers, which makes it useful to obtain translational temperature by measuring Doppler broadening of an atomic line of gases [1, 2] to the same degree as diode laser absorption spectroscopy (DLAS) [3, 4]
The saturation effect in LIF was investigated in earlier studies [8,9,10], in which the laser spectral width was comparable to Doppler broadening, and in which the spectral wing of laser was able to induce substantial fluorescence, causing additional broadening
The broadening was evaluated by using full width at half maximum (FWHM)
Summary
Diode laser-induced fluorescence (DLIF) has a feature of high wavelength resolution on the order of picometers, which makes it useful to obtain translational temperature by measuring Doppler broadening of an atomic line of gases [1, 2] to the same degree as diode laser absorption spectroscopy (DLAS) [3, 4]. Intense lasers with substantial fluorescence that can achieve a high signal-to-noise ratio are preferred, intense lasers are known to cause additional broadening, termed as saturation broadening or power broadening [6]. Correction methods for optical absorption and saturation broadening are demonstrated in an arc-heated argon plasma wind tunnel [14]. The wavelengths of both fluorescence and excitation are 772.42 nm (Ar I, 4s2[1/2]∘−4p2[1/2]). R (1) Absorption of laser (2) Saturated absorption Cross section of axisymmetric plasma
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