Non-Uniform Absorption of Terahertz Radiation in Superconducting Hot Electron Bolometer Mixers

We present an improved hot spot model that includes the non-uniform absorption of terahertz radiation on a superconducting HEB microbridge. We propose that the terahertz radiation is indeed absorbed mainly in the region of the superconducting microbridge with its energy gap (2Δ), in connection with the local electron temperature, less than the photon energy of the incoming radiation. With this improved hot spot model, we can precisely model LO (Local Oscillator)-pumped current-voltage and LO-pumped resistance-temperature characteristics of superconducting HEB mixers.