Multi-spectral mid-infrared laser stand-off imaging.

A multi-spectral mid-IR laser imaging study including system engineering, experiments, and image processing and analysis is described. A 4-lambda scalable system was built with semiconductor lasers, covering from 3.3-9.6 mum. The X-Y scanning system was capable of 2-dimensional (2D) multi-spectral imaging at a stand-off distance from 13-40 m. The system was applied to diverse targets that consist of man-made and natural materials and objects, and shown capable to resolve and distinguish small spectral differences among the various targets. Colorless objects in the visible were shown with "colorful" signatures in the mid-IR. Image processing algorithm based on spectral contrast was shown most effective to exploit the laser sensitivity and accuracy, as opposed to algorithms that operate mainly on the image spatial intensity. The results also showed the complexity of laser imaging phenomenology, involving both spectroscopic and geometrical scattering effects. A demonstration of 3D multi-spectral imaging was also given. The system design is suitable for compact packages with semiconductor lasers, and the results suggest that laser-based multi-spectral imaging can be a unique and powerful technology for target discrimination.