Characterization of a Quantum Cascade Laser Based Emissivity Monitor for CORSAIR

Abstract

Continuous improvements of quantum cascade laser (QCL) technology have extended the applications in environmental trace gas monitoring, mid-infrared spectroscopy in medicine and life science, law enforcement and homeland security and satellite sensor systems. We present the QCL based emissivity monitor for the CORSAIR blackbody. The emissivity of the blackbody was designed to be better than 0.9999 for the spectral range between 5 to 50µm. To actively monitor changes in blackbody emissivity we employ a QCL-based infrared illumination source. The illumination source consisted of a QCL and thermoelectric cooler (TEC) unit mounted on a copper fixture. The stability of the QCL was measured for 30, 60, and 90s operation time at 1.5A driving current. The temperature distribution along the laser mounting fixture and time dependent system heat dispersion were analyzed. The results were compared to radiative and conductive heat transfer models to define the potential laser operating time and required waiting time to return to initial temperature of the laser mount. The observed cooling behaviour is consistent with a primarily conductive heat transfer mechanism.

Testing of highly accurate blackbodies

“…For the CORSAIR blackbody, a method to monitor emissivity was required, but a heated halo was unlikely to provide enough power under CLARREO-like conditions to measure reflectivity at the required low level. Instead we included an alternative method to monitor emissivity based on a single quantum cascade laser (QCL) to test the concept 2,4 . The design of the monitor is simple; the QCL, with no optics, shines into the blackbody through a small hole near the aperture of the blackbody, and the instrument observing the blackbody is used as a detector.…”