Terahertz time domain spectroscopy
From Biocrawler, the free encyclopedia.
In terahertz time domain spectroscopy (THz-TDS), picosecond pulses of terahertz radiation are used to probe different materials. The radiation has several distinct advantages over other forms of spectroscopy: it is nonpolar, work on biological tissues, is non-ionizing, and has relatively good resolution.
Generation
Terahertz pulses are produced by a spark discharge between two electrodes patterned on a low temperature gallium arsenide (LT-GaAs) substrate, which have a bias voltage of approximately 40 V placed between them. Usually the electrodes are formed into the shape of a simple dipole antenna and a ~100 fs TiSaph laser pulse provides an extremely large electric field between the leads causing the spark. Terahertz radiation is created by the discharge and short pulses are produced due to the short (500 fs) hole recombination time of the substrate. This is not the only means of generation, but is currently (as of 2005) the most common.
Pulses produced by this method generally have a power level on the order of nanowatts. As one would imagine, the blackbody radiation levels present at room temperature in this frequency range overpower this by a few orders of magnitude so an advanced detection system is also required.
