Circular dichroism spectrometer based on a diffractive liquid crystal cell

A simple spectrometer based on a polarization grating has been developed for real time measurements of circular dichroism. The main and unique element is a liquid crystal replica of a polarization grating recorded by means of holographic techniques in thin films of organic materials. This gratings offer long time stability and high diffraction efficiency. Peculiarity of this grating is that the amplitude of the left wave (right wave) associated with the +1(-1) order of the diffracted beam emerging from the grating is proportional to the right polarized (left polarized) component of the incident light beam. Exploiting this feature, the circular dichroism of any system can be easily evaluated measuring only the intensities of the first order diffracted beams, just locating the grating after the investigated system. Due to the spectral selectivity of the grating, the CD at each wavelength can be evaluated at the same time using two linear CCD detectors. It is demonstrate as this method is free from the artifacts introduced by anisotropic samples and non-ideal optical elements in conventional spectrometers [1-4]. References 1.G. Cipparrone, P. Pagliusi, C. Provenzano and A. Mazzulla, "Method and device for measuring circular dichroism in real time" Italian patent n. CS2007A000024 (2007) 2.C. Provenzano, P. Pagliusi, A. Mazzulla, L. Giorgini and G. Cipparrone Appl. Spectrosc., 62, 465 (2008). 3.C. Provenzano, P. Pagliusi, A. Mazzulla, and G. Cipparrone, Opt. Lett., 35, 1822 (2010) 4.P. Pagliusi, E. Lepera, C. Provenzano, A. Mazzulla, G. Cipparrone Polarization gratings allow for real-time and artifact-free circular dichroism measurements, SPIE Proc., 8069 (2011)