Mid-Infrared Quantum Cascade Detectors for Thermal Imaging and EnvironmentalSensors

摘要

There are various photodetector applications in the mid-infrared (MIR) spectral range, both in military and civil applications. Thermal imaging in the MIR is of general interest as the emission of a room temperature black body peaks at a wavelength of 10 μm. Cameras sensitive at this wavelength are thus commonly used in construction to detect thermal bridges, in fire protection to pinpoint pockets of embers, as well as in security and military applications such as missile detection. Dynamic area thermometry is used for breast cancer detection based on the detection of subtle temporal changes of the skin temperature [1]. Heat seeking of hot targets such as aircraft engine exhaust plumes also takes place in the MIR, namely between 3 μm and 8 μm. MIR spectroscopy is an important tool in chemistry and biology, as many molecules and atoms have specific absorption lines between 1 μm and 10 μm. Light detection at 17 μm is of interest for detection of cold interstellar molecular Hydrogen (H_2) using heterodyne spectroscopy [2], as the shortest pure rotational line of H_2 lies at 17.035 μm [3]. Intersubband (ISB) photodetectors detect in the MIR and are well suited for high speed operation in the GHz range. Due to their narrow linewidth, ISB detectors are a promising choice for molecular and atomar spectroscopy, where often only a small part of the spectrum is of interest. The high speed of ISB detectors makes them interesting for heterodyne spectroscopy in the MIR, which allows to distinguish spectrally close absorption lines. Another pecularity of ISB detectors is that their peak detection wavelength is to a large extent fixed by design and not by material. This allows to engineer narrowband ISB detectors across the whole MIR range.