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Two conformations of the retinal molecule have been studied in order to characterize the molecule's THz transmission spectra in both the ground and metastable states. When subjected to an adequate external excitation the retinal molecule can experience a change in conformation and associated THz transmission spectra. In an attempt to accomplish this characterization, the FTIR system was modified to include a simple off axis excitation source inside of the systems sample chamber. Measurements were made of the retinal molecule's THz spectra both with and without external excitation of the molecule. The results gathered were then compared with the results obtained from simulation. Data obtained from two retinal isomers reveal more spectral features at frequencies ~11 - 15 cm-1 than were predicted for these conformations. The most likely explanation for this is that the material is actually a mixture of several metastable conformations. There is correlation between simulated and measured THz spectra in the ground state at a frequency of 14 cm-1 for all-trans retinal. The strongest vibrational mode frequency predicted for the 9-cis conformation through modeling was 22 cm-1, which correlates quite well with the experimental line at 21.3 cm-1 in the ground state. When the 9-cis samples were exposed to UV illumination there was a noticeable change in the absorption spectra and this line at 21.3 cm-1 almost disappeared which can be related to the transformation of a 9-cis into a more stable all-trans retinal. The absorption spectra of all-trans retinal that is the most stable conformation showed very weak features in experimental spectra, with some of them changing under illumination. [ABSTRACT FROM PUBLISHER]

In this paper, we show that periodic arrays of rectangular slots with subwavelength width provide for local electromagnetic field enhancements due to edge effects in low-frequency range, 10-25 cm-1. Periodic structures of Au, doped Si, and InSb with subwavelength thickness were studied. The half power enhancement width is ~500 nm and less around the slot edges in all cases, thereby possibly bringing terahertz (THz) sensing to the nanoscale. InSb is confirmed to offer the best results with the local power enhancements on the order of 1100 at frequency 14 cm-1. InSb and Si have large skin depths in the frequency range of interest and so the analysis of their structures was done through the Fourier expansion method of field diffracted from gratings. Au, however, has small skin depths at these frequencies compared with the thickness. Surface impedance boundary conditions were employed to model the Au structure, for which the Fourier expansion method was unsuitable owing to the huge magnitude of Au permittivity at these frequencies. The applications possibly include development of novel biosensors, with the strongly enhanced local electromagnetic fields leading to increased detection sensitivity, and monitoring biophysical processes such as DNA denaturation. [ABSTRACT FROM PUBLISHER]