Photon-counting microscopy of terahertz radiation

Abstract
Photon-counting imaging of terahertz radiation is demonstrated with a spatial resolution of 50 μ m for a free-space wavelength of 132 μ m by incorporating a quantum-dot single photondetector into a scanning confocal optical system. Terahertz radiation of 10 − 19 – 10 − 16 W or 10 2 – 10 5 photons ∕ 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.