The THz/Far-IR Beamline at the Australian Synchrotron was used to demonstrate a novel method of estimating the dielectric properties of homogenous substances in the 1.0 THz to 4.0 THz region. Attenuated total reflection (ATR) coupled with synchrotron sources allow rapid evaluation of samples. The source is incoherent, thus normally only reflectance can be derived, as phase shift data cannot be obtained with this arrangement. A method is presented of deriving the full complex dielectric parameters by a modified frustrated internal reflection technique which reflects the evanescent wave using a gold plated mirror. Oil and alcohol samples were used in the study. With the mirror in situ, the reflectance changed from being enhanced at some frequencies to undergoing a frequency dependent destructive interference at other frequencies. The change in different samples was noted to vary according to the refractive index (but not the absorption coefficient) of the sample.
The THz/Far-IR Beamline at the Australian Synchrotron was used to demonstrate a novel method of estimating the
dielectric properties of water based substances in the 2.0 THz region. The method involves using an ATR apparatus with a
diamond crystal in a way that converts the apparatus to a reflection/transmission mode by using a mirror at a set distance
from the crystal/sample interface to reflect the transmitted portion of the incoming beam back to the detector. The method
can extract the full dielectric properties of a sample. The method is only limited by the frequency range of the source and
the sensitivity range of the detector. It is best suited to studies at 2.0 THz and above with a diamond crystal ATR apparatus,
since the combination of the refractive index of diamond (n=2.40) and water (n=1.95 at 2.0 THz) are in the optimal ratio
to produce excellent contrast. Water and water based gel were used to demonstrate the technique.
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