Image courtesy of SuKaduna via Pixabay
Mid-infrared (MIR) photodetectors have wide-ranging applications, including medical imaging, security surveillance, and pollution monitoring. However, detecting MIR light has proven challenging because it has a longer wavelength than visible light and therefore carries less energy when it strikes a detector.
Existing methods of detecting MIR light typically require cryogenic cooling or sophisticated device structures, which are inefficient. To avoid these drawbacks, assistant professor of chemical and environmental engineering Peijun Guo and his group at Yale have developed an indirect, all-optical method to detect MIR light.
The principle behind this detection method is that certain materials have properties that change with temperature variation due to the absorption of MIR light. One example of such a material is two-dimensional metal halide perovskite (2D MHP), a type of crystal in which changes in optical reflectance can be measured upon irradiation with MIR light. This change in optical reflectance is analogous to an object changing color upon heating.
This material was selected because it has low thermal conductivity and temperature-dependent reflectance, and it can be easily processed from a solution. Its low thermal conductivity slows dissipation of absorbed heat, making it possible to detect the absorption of MIR light as the change in optical reflectance caused by the MIR-induced temperature rise can be measured.
Guo and his group have developed this technique to precisely detect a wide range of MIR light, utilizing 2D MHPs with a membrane structure and a complex photonic system. In the future, they hope to integrate multiple detectors to image an entire surface, enabling the capture of infrared “images” of objects.