CIRCULAR DICHROISM IN THE FAR INFRARED AND MILLIMETER WAVELENGTH RANGE: NEW TECHNIQUES

Abstract

The measurement of circular dichroism in the long wave length range is of special interest. Such measuremetns would permit the low frequency vibrations to be investigated as probes of molecular stercochemistry. Also the recent theoretical predictions that the circular dichroism is supported by the molecular rotational transitions of chiral molecules can be verified. In the last three years we have been investigating the feasibility of such measurements and identified two different procedures. In this presentation (1) A Martin-puplett interferometer operating in step-integrate mode and incorporated with path difference modulation will be shown to give circular dichroism as Cosine Fourier transform; (2) Tilt tunable waveplates (TTW) in combination with a rotating polarizer will serve as the sources for modulating circular polarization states. Hence dispersive monochromator coupled to TTW can be used to measure circular dichroism in the long wave length range. Necessary theoretical expressions for the above mentioned procedures are developed and will be presented. Preliminary measurements in the $50-1 cm^{-1}$ region have also been carried out, in collaboration with Dr. J. R. Birch, at the National Physical Laboratory in December of 1987.