PHOTOTHERMAL LASER DEFLECTION AN INNOVATIVE TECHNIQUE TO MEASURE PARTICLES IN EXHAUSTS

AN INNOVATIVE TECHNIQUE TO MEASURE IN REAL-TIME THE MASS CONCENTRATION OF PARTICLES IN EXHAUSTS IS PROPOSED HERE. THE TECHNIQUE IS BASED ON THE DEFLECTION EXPERIENCED BY A LASER BEAM THAT TRAVELS THRU A THERMAL LENS. PHOTOTHERMAL LASER DEFLECTION (PLD) CAN ALSO MEASURE THE CONCENTRATION OF GASEOUS SPECIES SUCH AS NO(X) AND OTHERS. IT THEREFORE HAS THE POTENTIAL TO SIMULTANEOUSLY MEASURE THE PARTICLE CONCENTRATION AND VARIOUS POLLUTANTS SIMULTANEOUSLY. IN THE PROPOSED METHOD A PULSED LASER BEAM LOCALLY HEATS THE PARTICLES PRESENT IN THE EXHAUST THUS CHANGING THE INDEX OF REFRACTION OF THE SURROUNDING GAS AND FORMING A THERMAL LENS. A PROBE CW LASER WHICH TRAVELS THRU THE THERMAL LENS WILL BE DEFLECTED ACCORDINGLY. THE AMOUNT OF DEFLECTION IS PROPORTIONAL TO THE LOCAL MASS CONCENTRATION. THE LASER CAN ALSO BE TUNED TO PUMP A GASEOUS SPECIES OF INTEREST THUS FORMING ALSO A THERMAL LENS. SINCE THE HEAT ABSORBED BY THE PARTICLES IS NOT A STRONG FUNCTION OF THEIR SHAPE, PLD CAN WORK WITH PARTICLE CLUSTERS. BOTH MODELING AND EXPERIMENTAL WORK WILL BE CONDUCTED DURING PHASE I TO ESTABLISH THE FEASIBILITY OF THE PROPOSED TECHNIQUE.