MEASUREMENT OF CIRCULAR OR LINEAR, NATURAL OR INDUCED DICHROISM IN INFRARED

Author Institution: Laboratoire d'Optique Physique, EPCI, 10 rue VauquelinWe report on a new dichrometer suitable for measurements in the near infrared (1--5$\mu$). It is, in principle, similar to instruments operating in the visible and UV portions of the spectra. Linearly polarized monochromatic light goes through a birefringence modulator and two orthogonally polarized waves are obtained alternately, (e.g. right and left circular.) After passing through the sample, light goes on to a detector and a signal proportional to dichroism is measured at the modulation frequency. We used a photoelastic modulator operating at 9 KHz, considering KRS 5 as the birefringent material, a quarter wave may be obtained and used up to 10 $\mu$. Infrared detectors are semiconductors or photoresistors with a band pass of 1 MHz. The sensitivity of the instrument is limited by the noise of the detector and of electronic devices to $10^{-3}$ optical density units. However, this should be appreciably improved in the future. Preliminary Magnetic Circular Dichroism results will be shown on $Er^{3+}$ in glasses around $6500 cm^{-1}$