MAGNETO-OPTIC ROTATION ANALYZER

• US 3,738,756 A
• Filed: 07/12/1971
• Issued: 06/12/1973
• Est. Priority Date: 07/12/1971
• Status: Expired due to Term

• Current Assignee: Robert L. Chaney
• Original Assignee: Robert L. Chaney
• Inventors: Chaney, Robert L.
• Primary Examiner(s): Corbin, John K.
• Application Number:
  US05/161,846
• Time in Patent Office: 701 Days
• Field of Search: 356/114,117 250/225
• US Class Current: 356/368
• CPC Class Codes: G01N 2021/218 Measuring properties of electrooptical or magnetooptical media
• CPC Class Codes: G01N 21/21 Polarisation-affecting properties G01N21/19 takes precedence
• CPC Class Codes: G02F 1/092 Operation of the cell; Circuit arrangements

Abstract

In a magneto-optic rotation analyzer, a first modulator modulates the magneto-optic rotation, if any, of the probing light beam by the sample at a first modulation frequency and a second reference modulator, independent of the sample, modulates the polarization of the probing light beam at a second reference modulation frequency. Both modulators produce separate modulation components in the output of the photo-multiplier employed to detect the polarization affected probing light beam. The separate sample and reference modulation signal components are separately detected and integrated. The reference signal is utilized to compensate for variations in the parameters of the optical components through the optical path of the analyzer.

Claims

1. In a method for analyzing a sample by detection of magnetooptic rotation, the steps of, probing a sample of matter to be analyzed with a probing light beam having light of a first polarization, applying a magnetic field to the sample with a substantial component of the field being directed along the path of the light beam in the sample to produce magneto-optic rotation of the polarization of the light from the first polarization to a second polarization, modulating the magneto-optic rotation of the polarization at a first modulation frequency to produce a time varying magneto-optic rotation signal of a frequency which is a multiple of the first modulation frequency, modulating the rotation of the polarization of the light beam independently of the magneto-optic rotation at a second modulation frequency to produce a reference signal of a reference frequency which is a multiple of the second modulation frequency, analyzing the polarization of the light beam emerging from the sample as affected by the sample to separate the light of the first polarization from the light of the second polarization, detecting the separated light of one of said polarizations to produce a composite electrical signal having a magneto-optic rotation signal component of a frequency which is a multiple of the first modulation frequency and a reference signal component of a frequency which is a multiple of the second modulation frequency, separating and integrating the magneto-optic rotation signal component of the composite signal, Separating the reference signal component from the composite electrical signal, integrating the magneto-optic rotation signal for a time interval which is responsive to the reference signal, and measuring the integrated magneto-optic rotation signal to obtain a measure of the concentration of preselected constituents of the sample.

2. The method of claim 1 wherein the probing light beam has a first optical bandwidth and including the step of, filtering the light beam as detected by the optical detector to a bandpass of optical frequencies encompassing substantially only the magneto-optic rotation spectrum of the sample constituent to be detected.

3. The method of claim 2 including the step of, substituting different optical filters having differing optical bandpass frequency ranges for detecting different sample constituents having different magneto-optic rotation spectra.

4. The method of claim 1 wherein the step of integrating the magneto-optic rotation signal for a time interval which is responsive to the reference signal includes the steps of, establishing a reference level signal whose magnitude depends on the intensity of the detected light, integrating the reference signal until the integral thereof reaches a level determined by the reference level signal, and employing the integrated reference signal to terminate the integration of the magneto-optic rotation signal.

5. In a magneto-optic rotation analyzer, means for probing a sample of matter to be analyzed with a polarized light beam of a first polarization, means for applying a magnetic field to the sample with a substantial component of the field being directed along the light path in the sample to produce magneto-optic rotation of the polarization of the light from the first polarization to a second polarization, means for modulating the magneto-optic rotation of the polarization at a first modulation frequency to produce a time varying magneto-optic rotation signal of a frequency which is a multiple of the first modulation frequency, means for modulating the rotation of the polarization of the light beam independently of the magneto-optic rotation at a second modulation frequency to produce a reference electrical signal of a reference frequency which is a multiple of the second modulation frequency, means for analyzing the polarization of the light beam emerging from the sample as effected by the sample to separate the light of the first polarization from the light of the second polarization, means for detecting the separated light of one of said polarizations to produce a composite electrical signal having a magneto-optic rotation signal component of a frequency which is a multiple of the first modulation frequency and a reference signal component of a frequency which is a multiple of the second modulation frequency, means for separating the magneto-optic rotation signal component and the reference signal component from the composite electrical signal, means for integrating the magneto-optic rotation signal for a time interval which is responsive to the reference signal, and means for measuring the integrated magneto-optic rotation signal to obtain a measure of the concentration of preselected constituents of the sample.

6. The apparatus of claim 5 wherein the probing light beam has a first optical bandwidth and including, means for filtering the light beam passed to said optical detecting means to a bandpass of optical frequencies encompassing substantially only the magneto-optic rotation spectrum of the sample constituent to be detected.

7. The apparatus of claim 6 including means carried from said filter means for establishing a reference signal level for comparing against the reference signal to derive a comparator output, and said compensating means being responsive to the output of said comparator to compensate the measurement of the magneto-optic rotation signal.

8. The apparatus of claim 5 wherein the means for integrating the magneto-optic rotation signal for a time interval which is responsive to the reference signal includes means for establishing a reference level signal whose magnitude depends on the intensity of the detected light, means for integrating the reference signal, means for comparing the integrated reference signal with the reference level signal to produce an output signal when the integrated reference signal reaches the reference level, means responsive to the output signal for terminating the integration period of the magneto-optic rotation signal, and means for measuring the integrated magneto-optic rotation signal.