FEASIBILITY STUDIES IN HIGH RESOLUTION THz SPECTROSCOPY
I. PHYSIKALISCHES INSTITUT
UNIVERSITY OF COLOGNE GERMANY
LABORATORY OF SEMICONDUCTOR DEVICES RADIOPHYSICAL FACULTY
STATE UNIVERSITY OFNIZHNY NOVGOROD RUSSIA
The development of powerful radiation sources and sensitive detector systems plays a key role to achieve good signal to noise ratios for THz spectroscopy. Several spectrometer setups based on heterodyne detection have been explored recently in our laboratory. % which is known as a very sensitive detection %method. % Absorption and emission spectra of D$_2$O have been recorded by the use of the 1.5 THz heterodyne receiver CONDOR }, L33-L36 (2006)}. Different heterodyne setups based on superlattice devices (SL) as mixer elements have also been tested. Further investigations indicate that superconducting NbTiN Hot Electron Bolometers (HEB) can be used as direct detectors with improved sensitivity compared to ordinary InSb bolometers. Also the development of THz-quantum cascade lasers (QCL) make substantial progress. Potential output powers on the order of milliwatts make them very attractive for spectroscopy applications. Phase-stabilized operation of a 1.5 THz QCL has been achieved by using a HEB mixer and a SL multiplier as a reference oscillator, which poses an important step towards their application in high-resolution spectrometers. Prospects of these developments for future THz spectrometers will be discussed.
As millimeter waves (MMWs) are being increasingly used in communications and military applications, their potential effects on biological tissue has become an important issue for scientific inquiry. Specifically, several MMW effects on the whole-nerve activity were reported, but the underlying neuronal changes remain unexplored. This study used slices of cortical tissue to evaluate the MMW effects on individual pyramidal neurons under conditions mimicking their in vivo environment. The applied levels of MMW power are three orders of magnitude below the existing safe limit for human exposure of 1 mW cm −2. Surprisingly, even at these low power levels, MMWs were able to produce considerable changes in neuronal firing rate and plasma membrane properties. At the power density approaching 1 µW cm −2, 1 min of MMW exposure reduced the firing rate to one third of the pre-exposure level in four out of eight examined neurons. The width of the action potentials w...