| Summary: | This thesis is an investigation of the biological effects of terahertz (THz) radiation at non-thermal power levels. One may loosely define the THz region of the electromagnetic spectrum spanning a range of frequencies between 0.1 and 10 THz. Recent advances in methods of generation and detection have made it possible to build instruments and perform experiments in this relatively unexplored part of he spectrum. Water represents an important constituent of biological systems and strongly absorbs in this frequency range. As a consequence, irradiation at THz frequencies can raise the temperature of biological material and temperature dependent processes can be influenced. THz radiation is non-ionising, with associated photon energies close to the thermal energy level of a metabolically active biological entity. At low power levels, however, a non-linear bio-effect relating to energy transfer from the field to the organism, which is not associated with a temperature rise, may be observed at specific frequencies. The current understanding of the interaction between THz radiation and biological material is. therefore, discussed within the framework of dielectric theory and is considered at both the macroscopic and microscopic levels. A discussion of important biological molecules, cells, tissues and a range of cellular processes is developed within this framework and the complexity of an interaction within a biological system is defined.
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