Hot Electron Bolometer for detection of fast terahertz pulses from Optical Parametric Oscillator

摘要

Detection of nanosecond pulses by fast and sensitive Hot Electron Bolometer (HEB) is reported. Pulses were generated by an Optical Parametric Oscillator (OPO)-based source. The laser can be tuned in the range 0.7-2.5 THz; its repetition rate equals to 53Hz, duration of the pulse is about 10-20ns, energy is 10nJ and spectral width 50GHz. HEB operates at temperature of about 8.8K in a cryogenic refrigeration system. A sensitive element is a bridge from a 4-mm thick NbN film integrated with a planar logarithmic spiral antenna on a high-resistive silicon. HEB works in 0.3-3THz range with NEP ～3×10~(-13) W/Hz~(1/2) and dynamic range 0.1 uW. Thanks to exploitation of hot electrons in superconducting state, the detector is very fast with minimum response time equals to 50ps. The THz radiation is focused with a silicon lens, and then is coupled to a sensitive bolometer using the planar antenna. THz radiation from the OPO, through a set of mirrors and attenuators, was coupled to the detector. The distance between the source and detector was about 3m. Full Width at Half Maximum of the recorded pulses was about 20 ns. Moreover, we measured linearity of the detector in the range 0.7-2.0 THz by rotation of the polarizer axis. The pulses were averaged and integrated for better stability. We obtained a good similarity to the theoretical curve of the polarizer.