Spectral analysis of a phase locked laser at 891 GHz, an application of Josephson junctions in the far infrared J.S. Wells, D.G. McDonald, A.S. Risley, S. Jarvis et J.D. Cupp Rev. Phys. Appl. (Paris), 9 1 (1974) 285-292 DOI: 10.1051/rphysap:0197400901028500