Development of compact DSP based mid-infrared quantum cascade laser spectrometers

This thesis describes the development of digital signal processor (DSP) and quantum cascade laser (QCL) technology for compact, standalone, integrated, trace gas sensors capable of gas sensing at part-per-billion (ppb) concentration levels. Such sensitivity levels provide the ability to perform precise environmental and emissions monitoring, medical biomarker analysis, and biological/toxic agent detection. Current sensors based on tunable diode laser absorption spectroscopy (TDLAS) frequently require complex optical configurations or cryogenics to produce the proper mid-infrared optical frequencies, a full personal computer based data acquisition system to process data, and assorted nonintegrated support electronics for complete control of the system. In contrast, the developed system employs pulsed distributed feedback (DFB) QCLs to provide frequencies in the mid-infrared wavelengths targeting specific molecular ro-vibrational lines for simple direct absorption spectroscopy, while a custom DSP implementation provides integrated control and processing functions without sacrificing performance. Results show comparable sensitivities compared to traditional techniques, while simultaneously producing compact, robust, low power solutions