ANALYZER EMPLOYING MAGNETO-OPTIC ROTATION

• US 3,738,755 A
• Filed: 07/14/1971
• Issued: 06/12/1973
• Est. Priority Date: 07/14/1971
• Status: Expired due to Term

• Current Assignee: Michael A. Kelly, Robert L. Chaney
• Original Assignee: Michael A. Kelly, Robert L. Chaney
• Inventors: Chaney, Robert L., Kelly, Michael A.
• Primary Examiner(s): Corbin, John K.
• Application Number:
  US05/162,602
• Time in Patent Office: 699 Days
• Field of Search: 356/114,117 250/225
• US Class Current: 356/368
• CPC Class Codes: G01J 4/04 Polarimeters using electric detection means G01J4/02 takes precedence
• CPC Class Codes: G02F 1/092 Operation of the cell; Circuit arrangements

Abstract

A magneto-optic rotation analyzer method and apparatus is disclosed. In the analyzer, a light beam of linearly polarized light, preferably in the ultra-violet region is shown through a sample of a material to be analyzed. A magnetic field is applied to the sample parallel to the light beam to obtain magneto-optic rotation of the polarization of the light by constituents of the sample. The emerging light beam is analyzed as to its polarization to separate light which is rotated from light which has not been rotated. One of the separated light beams is detected by a photodetector. The magneto-optic rotation effect is modulated at a certain modulation frequency and the output signal is synchronously detected against the modulation frequency or a harmonic thereof for improved signal-to-noise ratio. The synchronously detected output is measured to obtain a measurement of the sample under analysis.

Claims

1. In a method for analyzing a sample by detection of magnetooptic rotation the steps of, disposing a sample of matter to be anaylzed to receive a probing light beam having light of a first polarization, applying a magnetic field to the sample with a substantial component of the applied magnetic field being directed along the direction of the path 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, said magnetic field comprising an alternating magnetic field, whereby said alternating magnetic field produces modulation of the magnetooptic rotation at a frequency which is a multiple of the frequency of the applied alternating field, and including the step of, generating a reference signal at a frequency which is a multiple of the frequency of the applied alternating magnetic field, analyzing the polarization of the light emerging from the sample, as affected by sample, to separate the emerging probing light of the first polarization, detecting the separated light of one of said polarizations to obtain a composite electrical output signal having a time varying magneto-optic electrical signal component of a frequency which is a multiple of the frequency of the applied alternating field and of an amplitude which is responsive to the quantity of material within the sample which is magneto-optically active within a band of optical frequencies of the probing light incident on the detector, corelating the composite electrical signal against said reference signal to obtain an output proportional to the time varying magneto-optic rotation electrical signal component and separated from the remainder of the composite electrical singal, and measuring the amplitude of the separated output signal to obtain a measure of the quantity of material within the sample which is magnetooptically active within the band of optical frequencies of light detected by the detector.

2. The method of claim 1 wherein the probing light incident on the sample has a first optical bandwidth broader than the magneto-optic rotation band of a component to be detEcted in the sample, and including the step of, filtering the probing light emerging from the sample at a point between the sample and the optical detector for passing to the optical detector only light within an optical passband less than the bandpass of the incident probing light and 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, changing the optical passband frequencies of the light passed by the filter to the optical detector for detecting magneto-optic rotation of different components of the sample.

4. In an apparatus for analyzing a sample by detection of magneto-optic rotation, means for probing a sample of matter to be analyzed with a light beam having light of a first polarization, means for applying a magnetic field to the sample with a substantial component of applied magnetic field being directed along the direction of the path 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 direction of the first polarization to the direction of a second polarization, said magnetic field comprising an alternating magnetic field, whereby the alternating magnetic field produces a modulation of the magneto-optic rotation at a frequency which is a multiple of the frequency of the applied alternating magnetic field, means for generating a reference signal at a frequency which is a multiple of the frequency of the applied alternating magnetic field, means for analyzing the polarization of the light emerging from the sample as affected by the sample to separate the emerging light of tje first polarization from the emerging light of the second polarizaiton, means for detecting the separated light of one of said polarizations to obtain a composite electrical signal having a time varying magneto-optic rotation electrical component of a frequency which is a function of the frequency of the modulation of the magneto-optic rotation and of an amplitude which is responsive to the quantity of material within the sample which is magneto-optically active within the band of optical frequencies of light incident of said detector, means for correlating the composite electrical signal against said reference signal to obtain an output proportional to the time varying magneto-optic rotation electrical component separated from the remainder of the composite electrical signal, and means for measuring the amplitude of the output to obtain a measure of the quantity of material within the sample which is magneto-optically active within the band of optical frequencies of the light detected by the said detector.

5. The apparatus of claim 4 wherein the probing light beam has a first optical bandwidth broader than the magneto-optic rotation band of a component to be detected in the sample, and including means for filtering the light emerging from the sample at a point between the sample and said light detector means for passing to said light detector means, only light within an optical passband narrower than the bandwidth of the incident probing light and encompassing substantially only the magneto-optic rotation spectrum of the sample constitutent to be detected.

6. The apparatus of claim 5 including means for changing the optical passband of frequencies of the light passed by said filter to said light detector for detecting magneto-optic rotation of different components within the sample.

7. The apparatus of claim 4 wherein said means for detecting the composite electrical signal against said reference signal includes synchronous detector means for synchronously detecting the composite signal against the reference.

8. The apparatus of claim 4 wherein said means for detecting the composite electrical signal against said reference signal comprises a phase sensitive detector means.

9. The apparatus of claim 4 wherein said means for detecting the composite electrical signal agaInst said reference signal comprises, counter means for counting in one direction during certain time periods of the reference quantity and for counting in the opposite direction during remaining periods of the reference quantity and means for subtracting counts in one direction from the counts in the other direction to derive a difference count, said difference count corresponding to an integration of the time varying electrical magneto-optic rotation signal component which is separated from the remainder of the composite electrical signal.