Photon-counting microscopy of terahertz radiation

Photon-counting imaging of terahertz radiation is demonstrated with a spatial resolution of 50μm for a free-space wavelength of 132μm by incorporating a quantum-dot single photon detector into a scanning confocal optical system. Terahertz radiation of 10−19–10−16W or 102–105photons∕s is imaged. Applying the microscope to the study of semiconductor quantum Hall devices, a threshold behavior of the cyclotron emission is found and the mechanism is discussed.