Mid-infrared Backscattering Measurements of Building Materials using a Quantum Cascade Laser

Open-path quantum cascade laser (QCL) systems are being developed for remote environmental monitoring applications for detection of small levels of toxins or pollutant gases in ambient air. In monostatic systems that rely on topographic backscatter, the surface reflection of the target becomes important. To address the feasibility of natural targets in an open-path geometry, we present the backscattering measurements of common urban building materials (aluminum, natural stones, ceramic wall tiles and concrete block) using a distributed feedback (DFB) pulsed QCL. Real surface roughness in the materials was taken into account. In particular, oblique scattering cases which are often unavoidable in field measurements were also investigated. The QCL measurements were evaluated with a FTIR system in which wide frequency range (2.8 mu m -25 mu m) measurements were possible. These results were applied to a total link model to define the potential and range of an open path QCL chemical sensor system.