By observing constant-voltage steps from Josephson junctions at voltages as high as 17 mV we deduce that junctions can generate harmonics up to frequencies as high as 8200 GHz. In consonance with this, submillimeter wave laser detection, harmonic generation, and mixing are demonstrated. These results suggest a model for the upper frequency limit of the Josephson effect.

For mixing in a Josephson junction at infrared frequencies, we have shown that the available power from the junction increases as the intermediate frequency is increased. Following this result an infrared receiver has been developed incorporating a 9-GHz maser preamplifier at the i.f. Using this system, the beat between the 401st harmonic of a high-quality microwave source and a 3.8-THz infrared laser has been observed. Also, for low-order mixing at 3.8 THz, a comparison of beat signals from a Josephson junction and a room-temperature mixer has been made.

Simultaneous irradiation of a Josephson junction with ≈ 10 GHz microwave power and 891-GHz laser radiation produces a 60-MHz beat between the fundamental laser frequency and harmonics of the klystron, ranging from the 84th to the 100th as the klystron is tuned. Observation of such high-order harmonic mixing of klystron and laser signals is unprecedented.

New experimental measurements of the frequency separations of 30 pairs of 12 C 16 0 2 laser lines in the 10.4-jum band and 26 pairs in the 9.4-Mm band have been made with Lamb-dip-stabilized lasers. The use of a Josephson junction as the frequency-mixing element simplified the measurements. Uncertainties in existing rotational constants for the laser vibrational levels were reduced 20 to 30 times and an additional rotational constant H v was determined for the first time.

Coherent detection of applied radiation via a Josephson current step has been achieved with an applied frequency approximately a factor of 3 higher than heretofore reported. The detected signal is at 2.5 THz (118 μ). The inadequacy of existing theory to predict the frequency dependence of the Josephson effect is discussed.