Thermal Imaging: Imaging Outside the Law of Reciprocity

Thermal imaging has completely different characteristics from photonic imaging. The difference is not related to the different wavelength typically used (IR vs. visible or UV) but to the fact that the imaging is done outside the domain of the reciprocity law. This means that the thermal imaging process is controlled by two parameters, energy and power density, while photonic imaging is fully controlled by a single parameter, energy (i.e. exposure) over a surprisingly wide range of power densities (over one billion to one). Adapting visible light imaging architectures to thermal imaging, without considering the need to control power density, severely limits the range of materials that can be used. On the other hand, taking full advantage of this new control parameter opens up a wide range of imaging methods and materials, including inorganic materials, which would have never been considered under the reciprocity law.