This paper reports on the development of micromachined pillar arrays for the filtering of terahertz radiation. These pillar
arrays are fabricated using ultraviolet based processing of thick SU8. This micromachining technique enables the array
patterns, dimensions, and consequently the filter characteristics, to be readily defined. In particular, we demonstrate that
by combining individual filter arrays with either different periods or pillar diameters we can isolate individual pass bands
in the 1 to 2 THz region.
Terahertz (THz) spectroscopy of a biomolecule with spatial resolution below the diffraction limit of the radiation has
been achieved by use of an all-optical, contactless transient mirror technique. A resolution of around 50 &mgr;m is
determined by the use of a test sample of gold strip lines deposited on GaAs, and the differential THz time-domain
spectroscopy (THz-TDS) response of biotin has been measured in both the presence and absence of the transient mirror
at room temperature. These preliminary results demonstrate the potential for use of the technique for the chemical
identification and characterisation of biomolecules in small volumes with the ultimate goal being microscopic imaging of
live cells. The technique may find applications in quality control for semiconductor processing, and in identifying
material imperfections, i.e. small cracks in non-destructive testing. We discuss the limitations of the transient mirror
technique along with several advantages over other related techniques.
At the present time the interaction of Terahertz (THz) radiation with random structures is not well understood. Scattering effects are particularly relevant in this spectral regime, where the wavelength, and the size and separation of scattering centres are often commensurable. This phenomenon can both be used to advantage in imaging and sensing, but conversely can have adverse effects on the interpretation of a "fingerprint" spectrum. A new mathematical method, the <i>Phase Distribution Model</i>, is reported here for the calculation of attenuation and scattering of THz radiation in random materials. This uses a Phase Distribution Function to describe the effect of the non-absorbing scatterers within the media. Experimental measurements undertaken using previously published results, data obtained from specially constructed phantoms and from everyday textiles have been compared with the theory. These experimental results encompass both cylindrical and spherical scattering situations. The model has also been compared with exact calculations using the <i>Pendry code</i>.
A new mathematical method, the <i>Phase Distribution Model</i>, is devised for the calculation of attenuation and scattering of THz radiation in random materials. The accuracy of the approximation is tested by comparison with exact calculations and with experimental measurements on textiles and specially constructed phantoms.