A Microprocessor Controlled Near-Infrared Circular Dichroism Spectrophotometer

A near-infrared circular dichrometer was constructed to cover the wavelength range 0.5 to 2.1 μm. The instrument employed a commercial photoelastic modulator with an infrasil quartz optical element to provide quarter-wave modulation throughout the range of the instrument. An indium antimonide [In(Sb)] doped photovoltaic detector was used at Λ > 1 μm, and a near-IR sensitive photomultiplier detector was used at Λ < 1 μm. Phase- and frequency-sensitive detection was employed and an automatic normalization circuit was used to extract the circular dichroism from the detector signal. The level of artifactual signals was reduced by the use of a passive depolarizing element. The instrument was interfaced with a microprocessor system which provided experimental control and signal enhancement capability. Data were transferred to a minicomputer system which provided bulk storage and both numeric and graphic hard copy output. The instrument, with its computer control capabilities, represents a significant improvement over previously existing instruments operating in this wavelength range in its facility for digital signal enhancement and data analysis.