PULSED PHOTOTHERMAL LASER DEFLECTION FOR LOW-LEVEL SMOKE AND NO2 MEASUREMENTS IN ENGINE EXHAUSTS

Pulsed Photothermal Laser Deflection (PLD) is developed to make tempor ally and spatially resolved measurements of NO-2 and smoke. The rapid response PLD signal is produced when a HeNe probe beam is deflected by a thermal lens produced by a pulsed XeCl-excimer laser pumped dye las er. The fast time response (almost-equal-to 30 ns) and good spatial re solution make the PLD method a candidate for future in situ measuremen ts in turbulent engine exhausts. The PLD signals, measured in a sample cell, exhibit a linear response for NO2 concentrations from 3 ppm to 208 ppm and for smoke concentrations from 0.3 mg/m3 to 10 mg/m3. With a low pulse energy of almost-equal-to 4 mJ, single-shot PLD measuremen ts in a sample cell have accuracies of +/- 14 ppm for NO2 indicating a ccuracies of +/- 0.7 mg/m3 for smoke. With increased pulse energy and multi-shot averaging, sensitivities of +/-0.4 ppm of NO2 or +/-20 mug/ m3 of smoke are expected.