ANALYZER EMPLOYING MAGNETO-OPTIC ROTATION

• US 3,740,151 A
• Filed: 08/02/1971
• Issued: 06/19/1973
• Est. Priority Date: 08/02/1971
• Status: Expired due to Term

• Current Assignee: Michael A. Kelly, Robert L. Chaney
• Original Assignee: Michael A. Kelly, Robert L. Chaney
• Inventors: Kelly, Michael A., Chaney, Robert L.
• Primary Examiner(s): Wibert, Ronald L.
• Assistant Examiner(s): Godwin, Paul K.
• Application Number:
  US05/168,332
• Time in Patent Office: 687 Days
• Field of Search: 250/225 350/151 356/116,117
• US Class Current: 356/368
• CPC Class Codes: G01N 2021/218 Measuring properties of electrooptical or magnetooptical media
• CPC Class Codes: G01N 21/1717 with a modulation of one or more physical properties of the sample during the optical investigation, e.g. electro-reflectance
• CPC Class Codes: G01N 21/21 Polarisation-affecting properties G01N21/19 takes precedence
• CPC Class Codes: G02F 1/09 based on magneto-optical elements, e.g. exhibiting Faraday effect

Abstract

A light beam of linearly polarized light is passed through a sample of material to be analyzed to a detector. A magnetic field is applied to the sample to obtain magneto-optic rotation of the polarization of the light by magneto-optically active constituents of the sample. A reference polarization rotator is positioned in the light beam to impart a reference rotation to the polarization of the light. One or both of the polarization rotation effects produced by the sample and the reference are modulated to produce a sideband modulation signal component in the detected output. The sideband signal component is separated and measured to obtain a signal having an amplitude which is a linear function of the quantity of the magneto-optically active material in the sample under analysis. In a preferred embodiment the reference polarization rotator comprises a second magnetooptic cell containing a reference magneto-optically active material corresponding to one of the constituents within the sample under analysis, whereby increased specificity is obtained in the output measurement.

Claims

1. In a method for analyzing a sample by detection of magnetooptic rotation the steps of, disposing a sample of matter to be analyzed to receive a probing light beam having a first polarization and a preselected direction of propogation, applying a magnetic field to the sample with a substantial component of the applied magnetic field being directed along the direction of propagation of the probing light beam within the sample to produce magneto-optic rotation of the polarization of the light by the sample from the first polarization to a second polarization, producing independently of the sample a reference rotation of the polarization of the polarized probing light beam from the first to the second polarization, analyzing the polarization of the probing light beam to separate probing light of the first polarization from probing light of the second polarization, modulating the magneto-optic sample rotation of the polarization at a first non-zero modulation frequency, modulating the reference rotation of the polarization at a second non-zero frequency, detecting the separated light of one of the first and second polarizations to obtain a composite electrical output signal having a time-varying electrical signal component of a sideband frequency corresponding to a sideband of the sample polarization rotation frequency and the reference polarization rotation frequency, and of an amplitude which is responsive to the quantity of material within the sample which is magnetooptically active within a band of optical frequencies of the probing light incident on the sample, separating the electrical signal component of the sideband frequency from the composite electrical output signal to produce a sideband electrical output signal, and measuring the amplitude of the sideband electrical output signal to obtain a measure of the quantity of material within the sample which is magneto-optically active.

2. The method of claim 1 wherein the step of separating the sideband electrical output signal includes the step of synchronously detecting the composite electrical output signal against a reference signal having a frequency which is a preselected function of said sideband frequency.

3. The method of claim 1 wherein the step of producing a reference rotation of the polarization of the polarized probing light beam includes the step of, passing the polarized light beam through a reference magneto-optically active Medium which is the same as that of at least one component of the sample material to be analyzed, and applying a magnetic field to the reference medium to produce the reference rotation of the polarization of the probing light beam.

4. The method of claim 3 wherein the reference magneto-optically active medium comprises a plurality of different reference media disposed along the probing light beam, each of said reference mediums comprising a material to be analyzed within the sample.

5. The method of claim 4 including the step of diffracting the polarization analyzed light beam to spatially separate the polarization analyzed probing light beam into a plurality of separate light beams, each of said separate light beams having a particular band of optical frequencies corresponding to a particular magneto-optic rotation spectral band for different ones of said reference media.

6. The method of claim 4 wherein the step of applying the magnetic field to said reference media comprises the step of applying the magnetic field sequentially to the different ones of said reference mediums to obtain a sequential reference rotation of the polarization of the probing light beam in different bands of optical frequencies.

7. The method of claim 4 wherein the step of applying the magnetic field to said reference media comprises the step of, applying the magnetic field to the different ones of said reference media simultaneously to obtain simultaneous reference rotation of the polarization of the probing light beam within different optical bands corresponding to different reference magneto-optic rotation spectra characteristic of the different reference media.

8. The method of claim 7 including the step of, modulating the magnetic field applied to the different ones of said reference media at different modulation frequencies to produce a plurality of sideband electrical output signals simultaneously at different sideband frequencies in the composite electrical output signal detected at the output of the probing light beam detector.

9. The method of claim 8 including the steps of, separating the plurality of sideband electrical signals and measuring each of the sideband electrical signals to give a measure of the quantity of the particular reference material in the sample under analysis.

10. In a magneto-optic rotation analyzer, means for probing a sample of matter to be analyzed with a probing light beam having a first polarization and a preselected direction of propogation, means for applying a magnetic field to the sample with a substantial component of said field being directed along the direction of propogation of the probing light beam in the sample to produce magneto-optic sample rotation of the polarization of the light from the first polarization to a second polarization, means for producing independently of the sample a reference rotation of the polarization of the polarized probing light beam from the first to the second polarization, means for analyzing the polarization of the probing light beam to separate probing light of the first polarization from probing light of the second polarization, means for modulating the magneto-optic sample rotation of the polarization at a first non-zero modulation frequency, means for modulating the reference rotation of the polarization at a second non-zero frequency, means for detecting the separated light of one of said polarizations to obtain a composite electrical output signal having a time varying electrical signal component of a sideband frequency corresponding to a sideband of the sample polarization rotation frequency and the reference polarization rotation frequency and of an amplitude which is a function of the quantity of material within the sample which is magneto-optically active within the band of optical frequencies of the probing light incident on the sample, means for separating the electrical signal component of the sideband frequency from the composite electrical output signal to produce a sideband electricaL output signal, and means for measuring the amplitude of the sideband electrical output signal to obtain a measure of the quantity of material within the sample which is magneto-optically active.

11. The apparatus of claim 10 wherein said means for separating the sideband electrical signal includes, means for synchronously detecting the composite electrical output signal against a reference signal having a frequency which is a preselected function of the sideband frequency.

12. The apparatus of claim 10 wherein said means for producing a reference rotation of the polarization of the polarized probing light beam includes, means for disposing a reference magneto-optically active medium which is the same as that of at least one component of the sample material to be analyzed in the polarizing light beam, and means for applying a magnetic field to the reference medium to produce the reference rotation of the polarization of the probing light beam.

13. The apparatus of claim 12 wherein said means for disposing the reference magneto-optically active medium in the path of the light beam includes a plurality of reference cell means disposed along the probing light beam, each of said cell means including a different reference medium corresponding to a respective constituent of the sample to be analyzed.

14. The apparatus of claim 12 wherein the reference medium includes a plurality of different reference media, and including, means for diffracting the polarization analyzed light beam to spatially separate the polarization analyzed light beam into a plurality of separate light beams, each of said separate light beams having a particular band of optical frequencies corresponding to a particular magneto-optic rotation spectral band for different ones of said reference media.

15. The apparatus of claim 12 wherein the reference medium comprises a plurality of different reference mediums corresponding to different constituents of the sample material to be analyzed, and wherein said means for applying the magnetic field to said reference media comprises, means for applying the magnetic field sequentially to said different ones of said reference media to obtain a sequential reference rotation of the polarization of the probing light beam.

16. The apparatus of claim 12 wherein said reference medium comprises a plurality of different reference media, and wherein said means for applying the magnetic field comprises, means for applying the magnetic field to the different ones of said reference media simultaneously to obtain simultaneous reference rotation of the polarization of the probing light beam within different optical bands corresponding to different reference magneto-optic rotation spectra characteristic of the different reference media.

17. The apparatus of claim 16 including means for modulating the magnetic field applied to the respective reference media at respectively different modulation frequencies to produce electrical output signals simultaneously at different sideband frequencies in the composite electrical output signal detected at the output of said probing light beam detector means.