Patent ID: 6370407
Filing Date: 2002-04-09
Classification: A61B,G01N

Abstract:
A method for polarimetric measurement of optical rotation of light caused by a concentration of a substance contained in a sample, comprising:(a) providing a laser beam passing through a polarizer and an optical modulator and split into a measurement beam and a reference beam, analyzing the measurement beam and directing it onto a first detector coupled to a first amplifier, and analyzing the reference beam and directing it onto a second detector coupled to a second amplifier; (b) performing identical filtering at integral multiples of a modulation frequency, and performing multiplication and algebraic summing operations on outputs of the first and second amplifiers to produce a first &PSgr;2/2 signal and a first 2&bgr;&PSgr; signal in response to the measurement beam and a second &PSgr;2/2 signal and a second 2&bgr;&PSgr; signal in response to the reference beam, &PSgr; representing a modulation level of light emanating from the optical modulator, and &bgr; representing optical rotation from extinction of the measurement beam or reference beam; (c) stabilizing the measurement beam by i. comparing the second &PSgr;2/2 signal to a first reference signal to produce a first error signal, ii. comparing the second 2&bgr;&PSgr; signal to a second reference signal to produce a second error signal, iii. multiplying the first error signal by a modulation signal to produce a modulation feedback signal and adding it to the second error signal to produce a combined modulation and zeroing feedback signal, and iv. driving the optical modulator in response to the combined modulation and zeroing feedback signal to minimize the first and second error signals; and (d) computing a first value of &bgr; from the first &PSgr;2/2 signal and the first 2&bgr;&PSgr; signal with no sample in a path of the measurement beam and a second value of &bgr; from the first &PSgr;2/2 signal and the first 2&bgr;&PSgr; signal with the sample in the path of the measurement beam, and computing the difference between the first and second values of &bgr;.