Measurement of smoke concentration usingdegenerate four-wave mixing

Abstract

Degenerate four-wave mixing (DFWM) was successfullyused to monitor a wide range of smoke concentrations (0.1-10mg m-3) in sample cells. To the authors' knowledge, thisis the first measurement of smoke by DFWM. The DFWM method isvery sensitive, measuring down to ~0.1 ppb soot volumefraction. To verify the visible laser DFWM system, NO2concentrations from 2 to 200 ppm were measured with a sensitivityof 2 ppm of NO2. Both smoke and NO2 species wereresonantly pumped at 500 nm by an excimer-pumped dye laser(~2 mJ/pulse). The DFWM signal from bothNO2 and smoke showed a squared dependence on concentration.Single-pulse measurements of NO2 and smoke in sample cellsindicate that temporally and spatially resolved in situDFWM measurements are feasible for engine exhausts.