Thermal Lens-Circular Dichroism Spectropolarimeter

Abstract

A novel, ultrasensitive thermal lens-circular dichroism spectropolarimeter (TL-CD) has been developed. In this instrument, a chiral sample is sequentially excited by the left circularly polarized laser light (LCPL) and right circularly polarized laser light (RCPL); both of these excitation beams are derived from the same argon ion laser. The heat generated as a consequence of the sample absorption of the LCPL and RCPL is measured by the probe laser beam collinearly overlapping with the two excitation beams. The TL-CD signal corresponds to the difference in the thermal lens signals produced by the LCPL and the RCPL excitation beams. Compared to characteristics of the conventional spectropolarimeters, the advantages of this TL-CD apparatus include its higher sensitivity, small volume capability, and wider applicability. A detection limit of 5 ng of optically active [Co(en)]3+ complexes whose volume was as small as 8 μL has been estimated for this apparatus with the use of 37 mW excitation power modulated at 1.1 Hz.