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Imaging spectroscopy with continuous THz-radiation

The technical exploitation of the spectral region between hundred GHz and a few THz has always represented a special challenge. Five years after images were first produce using pulsed THz radiation the world’s first functioning THz spectrometer has been built that operates with continuous radiation.

THz-Transmission images of a specimen of human liver infiltrated with cancer in comparison with conventional photography on the sample. Metastasen appear as light spots on the conventional photograph.

One promising application of THz radiation is imaging various different samples, e. g. in the fields of biomedicine or materials sciences. Transmission images of probed samples deliver information not accessible using other techniques or only by accepting other disadvantages in the measurements, such as, for instance, accepting the radiation load on living organisms for x-ray imaging. Lately, research in the field of THz-spectroscopy is also focussing on image formation with continuous rather than pulsed radiation. Imaging with continuous THz-radiation can be applied at discrete frequencies and achieves better signal-to-noise ratios than the method utilizing pulsed radiation which itself requires integrating over a small region of the pulse spectrum.

The first operative THz-spectrometer with continuous radiation has been constructed by the work group “terahertz-system technology” at the Institute for High Frequency Technology of the Technical University Braunschweig in cooperation with PTB’s Special Laboratory “Semiconductor Structures”. To produce the radiation requires manufacturing photoconductive dipole antennae. The base material is semiconductor GaAs specially processed to create extremely short charge carrier life times. The material and the photoconductive antennae were produced at PTB and optimised for the application.

To demonstrate the potential of the method in a first application related to medical research a THz-transmission image was made of a specimen of human liver infiltrated by cancer. Now that the prototype has been completed further investigations of power and performance and of the new method can be tackled.

Contact at PTB:

Phone: +49-531-592-0