Terahertz tunable sources, spectrometers, and imaging systems

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;
• the fundamental terahertz frequency range is about 0.10 THz to about 0.18 THz;
• and
• the backward wave oscillator, the frequency multiplier, and the waveguides are arranged so as to exhibit conversion efficiency of the terahertz radiation to the harmonic terahertz radiation that is greater than about 5% for fundamental terahertz frequencies between about 0.11 THz and about 0.17 THz.

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,
• the tunable terahertz source comprises a backward wave oscillator;
• the fundamental terahertz frequency range is about 0.10 THz to about 0.18 THz;
• and
• the backward wave oscillator, the frequency multiplier, and the waveguides are arranged so as to exhibit conversion efficiency of the terahertz radiation to the harmonic terahertz radiation that is greater than about 20% for fundamental terahertz frequencies between about 0.11 THz and about 0.13 THz.

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;
• 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;
• a first beamsplitter arranged to divide the harmonic terahertz radiation into first and second terahertz beams;
• a source of optical radiation in the visible or near-IR wavelength range;
• a second beamsplitter arranged to combine the optical radiation and the first terahertz beam;
• a first non-linear optical medium arranged to generate an optical probe beam from the optical radiation and the first terahertz beam;
• at least one optical element arranged to direct the second terahertz beam to a sample;
• a third beamsplitter for combining a portion of the second terahertz beam that is transmitted by or reflected from the sample with the optical probe beam with the optical radiation;
• a second non-linear optical medium arranged to generate an optical signal beam from the optical radiation and the second terahertz beam;
• an optical filter or polarizer arranged to separate the optical radiation from the optical signal and probe beams;
• and
• an imaging photodetector array for detecting the combined optical signal and probe beams.

A terahertz imaging system comprising:

• a tunable source of terahertz radiation;
• a first beamsplitter arranged to divide the terahertz radiation into first and second terahertz beams;
• a source of optical radiation in the visible or near-IR wavelength range;
• a second beamsplitter arranged to combine the optical radiation and the first terahertz beam;
• a first non-linear optical medium arranged to generate an optical probe beam from the optical radiation and the first terahertz beam;
• at least one optical element arranged to direct the second terahertz beam to a sample;
• a third beamsplitter for combining a portion of the second terahertz beam that is transmitted by or reflected from the sample with the optical probe beam with the optical radiation;
• a second non-linear optical medium arranged to generate an optical signal beam from the optical radiation and the second terahertz beam;
• an optical filter or polarizer arranged to separate the optical radiation from the optical signal and probe beams;
• and
• an imaging photodetector array for detecting the combined optical signal and probe beams.