Quantum-dot photon detectors and photon-counting terahertz imaging

Photon-counting microscopy imaging in the terahertz (THz) region has been realized with a resolution of 0.05mm for a free space wavelength of 0.13mm. The system incorporates quantum-dot photon detectors into a scanning confocal optical microscope. Minimal requirements for practical application have been fulfilled by improving the operation speed of photon detection by a factor of 100, expanding the operation temperatures beyond 0.3 K and achieving a dynamic range more than 30dB. We use this microscope to probe extremely weak cyclotron emission with less than femto-watt powers radiated from quantum Hall effect devices, which leads to direct visualization of nonequilibrium electrons generated between Landau levels.