Spatially resolved soot-absorption measurements in flames using laser vaporization of particles

Soot absorption in flames is measured with high spatial resolution using a new technique. In this method, the absorption of a probe laser is modulated by vaporization of the soot using a crossed, pulsed pump laser. A detailed analysis shows that the effective beam overlap or interaction length is insensitive to temperature, particle size, or pulsed-laser fluence (energy/area) above a threshold of 5 J/cm(2). The technique has an absorption-coefficient shotnoise-detection limit of roughly 1 x 10(-5) cm(-1) with 0.1-cm spatial resolution using a single laser pulse. Spatially resolved measurements in premixed and in diffusion laminar flames are presented.