Patent ID: 8035083

Claim:
An apparatus comprising: a tunable source of terahertz radiation at a fundamental terahertz frequency tunable over a fundamental terahertz frequency range; a first waveguide arranged to receive terahertz radiation from the tunable terahertz source, the first waveguide being arranged to support only a single transverse spatial mode within the fundamental terahertz frequency range; a solid-state frequency multiplier arranged to receive from the first waveguide at least a portion of the terahertz radiation of the tunable terahertz source and to produce harmonic terahertz radiation at a harmonic terahertz frequency, the harmonic terahertz frequency being an integer multiple of the fundamental terahertz frequency; and a second waveguide arranged to receive the harmonic terahertz radiation produced by the frequency multiplier, the second waveguide being arranged to support only a single transverse spatial mode at the harmonic terahertz frequency, wherein: the tunable terahertz source comprises a backward wave oscillator; and the first waveguide includes a splitter portion, and the tunable terahertz source, the first waveguide, and the frequency multiplier are arranged so that measured power of terahertz radiation exiting the splitter portion is greater with the frequency multiplier arranged to receive terahertz radiation from the backward wave oscillator through the waveguide than without the frequency multiplier so arranged.