Near-Field Orientation Sensitive Terahertz Micro-Spectroscopy of Single Crystals

We present spectroscopic imaging studies of molecular crystals. These measurements examine the anisotropy of the intra and inter-molecular vibrational modes of single crystals at terahertz frequencies. The method is based on the technique developed in [1-2] for sub-wavelength resolution time domain terahertz spectroscopy (THz TDS), with added polarization orientation dependent measurements and hydration control. This method allows us to study the spectroscopic properties of small single crystals with sizes down to 20 micrometers. In addition, mapping the spectroscopic information at such small spatial scales allows us to reduce the water absorption and interference artifacts that usually affect protein THz TDS measurements. We show the polarization sensitive terahertz absorption spectra in the (0.3-3THz) range of sucrose, oxalic acid and lysozyme protein crystals. \begin{enumerate} \item M. A. Seo, et. al., Opt. Express, 15(19):11781--11789, 09 (2007) \item J. R Knab, et. al., App. Phys. Lett.,97, 031115 (2010) \end{enumerate}