QCL-based standoff and proximal chemical detectors

ABSTRACT The development of two longwave infrared quantum cascade laser (QCL) based surface contaminant detection platforms supporting government programs will be di scussed. The detection platforms utilize reflectance spectroscopy with application to optically thick and thin materials including solid and liquid phase chemical warfare agents, toxic industrial chemicals and mate rials, and explosives. Operation at standoff (10s of m) and proximal (1 m) ranges will be reviewed with consideration given to the spectral signatures contained in the specular and diffusely reflected components of the signal. The platforms comprise two va riants: Variant 1 employs a spectrally tunable QCL source with a broadband imaging detector, and Variant 2 employs an ensemble of broadband QCLs with a spectrally selective detector. Each variant employ s a version of the Adaptive Cosine Estimator for detection and discrimination in high clutter environments. Detection limits of 5 P g/cm 2 have been achieved through speckle reduction methods enabling detector noise limited performance. Design considerations for QCL-base d standoff and proximal surface contam inant detectors are discussed with specific emphasis on speckle-mitigated and detector noise limited performance sufficient for accurate detection and discrimination regardless of the surface coverage morphol ogy or underlying surface refl ectivity. Prototype sensors and developmental test results will be reviewed for a ra nge of application scenarios. Future development and transition plans for the QCL-based surface detector platforms are discussed. Key Words: Quantum cascade laser, standoff an d proximal surface contaminant det ection, reflection spectroscopy, chemical warfare agent detection, explosiv es detection, TIC and TIM detection