Mapping with Pulsed Terahertz Radiation

7 Mapping with Pulsed Terahertz Radiation 59 Beamsplitter 

3 Romeo, M.J., Dukor, R.K. and Diem, M. (2008) Introduction to spectral imaging, and applications to diagnosis of lymph nodes, in Vibrational Spectroscopy for Medical Diagnosis (eds M. Diem, P.R. Griffiths and ).M. Chalmers), John Wiley Sons, Ltd, Chichester, UK, pp. 1-26. 

14 Griffiths, P.R. and de ttaseth, J.A. (2007) Fourier Transform Infrared Spectrometry, 

Vibrational spectroscopy covers the spectral region from about 0.75 pm ( 13 500cm i) to 1000 pm (10cm ). To this point, we have covered the NIR (0.75-2.5 pm or 13 500-4000 cm ) and mid-infrared (2.5-25pm or 4000-400cm ) regions. The final region is the far-infrared (25-lOOOpm or 

The source for terahertz spectroscopy is an ultrashort-pulsed laser (usually TiiSapphire) that emits a stream of pulses of NIR radiation at 80MHz, with each pulse lasting about 70 fs. The laser pulses are focused on a PC switch, sometimes known as an Auston switch, which is a small semiconductor crystal (often GaAs) on which two planar metal electrodes support a large electric field across its surface [80]. The design of these metal electrodes is that of an antenna. 

The radiation with long wavelength that is generated by this technique can then be collected using a sihcon lens. 

A small fraction of the NIR laser pulse is also used in the detection process. 

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