Far infrared detection with Josephson junctions. Final report

The response of Josephson junctions to microwave and far infrared radiation was studied. Junctions are formed by pressing a Nb or Nb-Ti pointed wire onto a Nb thin film which in turn is pressed against the open end of a waveguide. Electromagnetic radiation is applied through the back of the film so that only the wave magnetic field is coupled to the junctions. The change of the dc Josephson current is monitored at different levels of microwave power over a frequency range from 22GHz to 105GHz. The dependence of the responsivity of these current on film thickness over a range from 50 A to 500 A was studied. The observed responsivity agrees very well with that predicted by theory. Higher responsivity is observed for thinner films and lower microwave frequencies.