Terahertz Imaging Via a Microbolometer Camera Under the Illumination of a Quantum Cascade Laser

摘要

The terahertz (THz) region of the electromagnetic spectrum has not been fully utilized due to the lack of compact and efficient sources as well as detectors. This thesis aimed on characterizing a quantum cascade laser (QCL) beam and achieving high quality real-time THz imaging using a 160x120 pixel FLIR A20M microbolometer camera designed to operate in long wave infrared range. The FTIR spectroscopy of the QCL beam revealed that lasing could be achieved at 2.85 and 2.91 THz frequencies depending on the bias current. This behavior was analyzed using the longitudinal modes of the laser and found to correspond well with the experimental observations. Real-time imaging of concealed objects in transmission mode was accomplished using the silicon nitride-based microbolometer camera under illumination via the QCL with average power less than 1 mW. The larger extent of the object required the expansion of the narrow laser beam using a parabolic reflector and refocus on the camera using a second parabolic reflector. The standard Ge lens of the camera was replaced by a Tsurupica lens since the earlier lens was opaque to THz radiation. The real-time imaging can be extended to reflection mode as well as longer standoff distances using higher power THz lasers.