Abstract
A novel, ultrasensitive crossed-beam thermal lens-circular dichroism spectropolarimeter (CBTL-CD) has been developed. In this instrument, the two excitation beams, left circularly polarized light (LCPL) and right circularly polarized light (RCPL), were derived from the same argon-ion laser. The chiral sample was sequentially excited by these two beams, and the corresponding thermal lens signals were monitored by a He-Ne probe laser intersecting perpendicularly with the two pump beams inside the sample. The apparatus is about three orders of magnitude more sensitive than the conventional circular dichroism spectropolarimeter. In addition, it can be used to detect chiral samples having very small volumes. A detection limit of 180 ng of optically active Co(en)3 complexes whose volume was as small as 8 μℓ has been estimated for this apparatus using 11-mW excitation laser power modulated at 2.3 Hz. The optics and instrumentation of the apparatus are described in detail.
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