Inter- and intramolecular vibrations of biomolecules, originating from weak bonds such as hydrogen bonds or van der Waals' force, are known to exist in teraher tzrange. Therefore, tunable sources of coherent terahertz wave can be used for selective excitation of vibrational modes and stimulation of chemical reactions, as well as for recognition of molecules. Two systems for high-power terahertz wave generation are introduced. They are based on difference-frequency generation in Ga Pcrystal. A high-resolution OPO-source system enables measurement of fine structures in spectra, even those resulting from defects in molecules. A conventional Cr: Forsterite-source system is simple, but provides sufficient resolution for measurement at room temperature. Operation principles and construction of the instruments are described in details. Spectrometers which employ these terahertz wave generators were applied to measure absorption spectra of biomolecules. The results demonstrate superiority of these spectrometers in comparison to FTIR and TDS, in range, resolution and sensitivity.
