Optical analysis method and apparatus having programmable rapid random wavelength access

Abstract

The optical reflectance or transmittance concentration analyzer includes an acousto-optical tunable filter (AOTF). The AOTF is tuned by a computer controlled digital-to-analog converter through a tunable sweep oscillator. Tuned beams can be selected according to their direction of propagation or according to their polarization behavior. Therefore, if desired, a pair of crossed polarizers can be used to select one of the tuned monochomatic light beams that pass from a light source through the AOTF. To obtain rapid wavelength change along with electronic chopping or wavelength modulation, the digital-to-analog converter output is combined with the output of a high speed signal generator. The modulated light is conducted directly or through a fiber optic cable to the location of the optical measurement and impinges upon the sample where it is reflected or transmitted. The emerging light is collected onto detector(s). The measurement time interval can be distributed among the required wavelengths or wavelength pairs according to an unequal scheme to decrease the error of the result in a calibration equation. The apparatus is particularly adaptable for use as an on-line concentration monitor in industrial process control because of its stability, efficiency and ability to perform quick analyses.

Dependencies are inferred from the claim text.