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Terahertz sources. Left: cw terahertz spectrometer, based on tunable DFB diode technology. Center: fs fiber laser FemtoFiber pro. Right: All-electronic emitter and detector for millimeter-wave imaging

Terahertz Sources

http://www.toptica.com/products/terahertz_generation/terahertz_technologysources_and_thz_generation_methods/terahertz_sources.html

• Electronic systems: High power, ideal for terahertz imaging
• Optoelectronic systems: High bandwidth, ideal for spectroscopy
• Pulsed lasers: Fast measurements, broad spectrum
• cw lasers: Precisely tunable, highest spectral resolution

The spectroscopically interesting frequency band of a 0.5 – 3 THz is not easily accessible. Electronic sources like Gunn or Schottky diodes with subsequent frequency multipliers, provide high output levels (mW range) up to some 100 GHz, yet become inefficient in the submillimeter range. Direct optical sources, like quantum cascade lasers, are usually limited to frequencies > 5 THz, even when operated at cryogenic temperatures.

Optoelectronic terahertz generation is an expression for indirect methods, where near-infrared laser light illuminates a metal-semiconductor-metal structure, generating a photocurrent that becomes the source of a terahertz wave. Both pulsed and continuous-wave (cw) techniques have been realized, and both have their advantages and limitations. Pulsed terahertz radiation offers a higher bandwidth (typically 0.1 .. 5 THz) and permits very fast measurements – a spectrum can be acquired within milliseconds. On the other hand, the frequency resolution is limited to several GHz. Vice versa, a cw system features a somewhat lower bandwidth (typ. 0.1 .. 2 THz) and requires longer measurement times – acquiring a spectrum takes several minutes –, yet the frequency can be controlled with extreme precision (down to single MHz).

TOPTICA offers ultrafast fiber lasers for pulsed terahertz generation, and DFB diode lasers for cw terahertz applications. A cw terahertz spectroscopy kit provides all required components to get an actual measurement started. High-power all-electronic systems operating at 100 GHz or 300 GHz are available for millimeter-wave imaging.