Long wavelength Hg1-xCdxTe at 4.2K as a fast detector for far-infrared nanospectroscopy (Conference Presentation)

We describe the performance of long-wavelength MCT operating at 4.2K as a fast photoconductive detector for far-infrared nanospectroscopy. The technique employs scattering from the tip of an atomic force microscope (AFM) engaged with a sample surface while in "tapping mode" at a frequency f, with the scattered infrared sensed at a higher harmonic, e.g. 2f, 3f or even 4f to improve spatial discrimination. With typical tapping frequencies >100 kHz, the infrared detector requires a bandwidth of 1 MHz or higher, for which thermal-type IR detectors are not sufficiently fast. MCT detectors are usually limited to wavelengths shorter than 25µm when operating at T=77K, but this can be overcome by cooling to 4.2K, in which case the detection threshold wavelength extends to beyond 50 microns. An additional benefit is an overall 5X improvement in S/N. <br/> <br/> *This work supported by the U.S. Department of Energy under contract DE-SC0012704 at NSLS-II and BNL. See ACS Photonics, 10, 4329-4339 (2023), (https://doi.org/10.1021/acsphotonics.3c01148)