Skip to Main Content
Shapiro steps have been observed in the I-V characteristics of an NbN tunnel junction illuminated with radiation from an optically pumped far infrared laser. The maximum operating frequency which produced an observable Shapiro step was 2.53 THz. This is a four-fold increase over that previously reported for a thin film Josephson junction. Clear steps were also produced by various laser lines in the frequency range 0.6-1.8 THz.