Coherent terahertz-wave generation from semiconductors and its applications in biological sciences

Coherent terahertz waves are generated by exciting phonon-polariton mode in GaP crystal. We have developed high power, wide frequency tunable terahertz generators and spectrometers, and revealed molecular resonance spectra of biomolecules, such as saccharides, DNA- or RNA-related molecules, amino acids and liquid crystals. It is demonstrated that THz spectral imaging has a possibility to distinguish the cancerous region from the normal tissue. TUNNETT diode, of which fundamental oscillation frequency exceeds 700 GHz, can be utilized for sub-terahertz imaging system for medical and other applications.