FIRST DEMONSTRATION OF AN ACOUSTO-OPTICALLY MODULATED QUANTUM CASCADE LASER AS A BROADBAND, TIME-RESOLVED COMBUSTION DIAGNOSTIC

We provide the first demonstration of an acousto-optically modulated quantum cascade laser (AOM QCL) system as a diagnostic for combustion by measuring nitric oxide (NO), a highly-regulated emission produced in gas turbines. The system provides time-resolved broadband spectral measurements of the present gas species via a single line of sight measurement, offering advantages over widely used narrowband absorption spectroscopy (e.g., the potential for simultaneous multi-species measurements using a single laser) and considerably faster (>15kHz rates and potentially up to MHz) than sampling techniques which employ FTIR or GC/MS. The developed AOM QCL system yields fast tunable output covering a spectral range of 1725 1930 cm(-1) with a linewidth of 10-15 cm(-1) For the demonstration experiment, the AOM QCL system has been used to obtain time-resolved spectral measurements of NO formation during the shock heating of mixture of a 10% nitrous oxide (N2O) in a balance of argon over a temperature range of 1245 - 2517 K and a pressure range of 3.6 - 5.8 atm. Results were in good agreement with chemical kinetic simulations. The system shows revolutionary promise for making simultaneous time resolved measurements of multiple species concentrations and temperature with a single line of sight measurement.