Knowledge Bank

Vibrational circular dichroism can be measured either with dispersive instruments or with FTIR spectrometers. Using the dispersive approach, commercially available instruments could not be used after approprite modification. Dedicated instruments had to be built in order to account for the weak signals to be measured. On the contrary, FTIR instruments are much more sensitive than dispersive instruments and considerably more expensive than dispersive instruments, so that until now commercially available instruments were equipped with the appropriate auxiliary devices to allow the measurement of VCD. In this paper we wish to describe a dedicated VCD-interferometer, which is designed to minimize the number of optical elements, thus hopefully reducing artifacts in VCD spectra. In the dedicated instrument an off-axis parabolic mirror collects the light of a globar into a parallel beam, which is fed into a modular Michelson interferometer (design adapted from Horlick, Applied Spectroscopy 32 [1978] 38). In our new design the outcoming parallel beam is directly focussed onto the detector, on its way travelling through the linear polarizer, photoelastic modulator and sample. This design thus avoids the possible alteration of the polarization state of the measured light and thus eliminates some important sources of artifacts.