Continuous Wave (CW) Terahertz Spectroscopy
Most chemical compounds show very strong, highly specific frequency dependent absorption features in the THz range. This is particularly true for gases that have characteristic narrow absorption lines in this range.
What makes continuous-wave terahertz (cw-THz) sources and detectors ideal for gas spectroscopy applications is the fact that many molecules have strong absorption bands in FIR e.g. water, carbon monoxide, and methanol to name a few. Together with a suitable gas cell, this technology is able to detect toxic airborne threats such as hydrogen cyanide, ammonia, hydrogen sulphide, and sulphur dioxide at concentration levels below that of the permissible exposure limit (PEL).
THz radiation also excites the intermolecular modes of many molecules. Liquids and solids have specific frequency dependent absorption and dispersion characteristics in this frequency range also detectable with a CW-THz spectrometer.
In the past ten years, TeraView, in parallel with the developments in pulsed systems, has been increasingly focusing on the generation and detection of continuous wave THz radiation by optical heterodyne techniques, where cw-THz is emitted from a LT-GaAs photomixer device at the difference frequency of two cw optical beams. This technique has many advantages, such as high spectral intensity, and narrow THz linewidth.
Spectroscopy applications of the CW Spectra 400 include:
CW- terahertz spectroscopy of pharmaceutical and energetic (explosive) materials