Modulated high sensitivity infrared polarimeter
AssigneeThe United States of America as represented by the Secretary of the Army
InventorsJohn A. Grisham, Frederick W. Clarke, Charles R. Christensen, John L. Stensby
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Abstract
A modulated Faraday rotation signal is produced by passing a linearly polarized laser beam through a semiconductor wafer sample in a modulated magnetic field that is induced in an electromagnet by a sine wave generator and driver coupled thereto. The rotation signal is normalized by dividing by a transmission signal produced by modulating the beam with a chopper that operates at a different frequency from the frequency of the driver. The result is a Faraday rotation measurement with high signal-to-noise ratio and compensation for laser drift in intensity.
Claims2
In a high-sensitivity infrared polarimeter system for measuring the amount of Faraday rotation occurring in a polarized beam as the beam passes through a semiconductor wafer sample in the presence of magnetic field;
- said polarimeter including a chopper revolving at a first frequency to produce a transmission signal;
- an analyzer, a detector and an electromagnet comprised of two co-axial coils, said coils having a space therebetween, the improvement for measuring the normalization signal and Faraday rotation signal simultaneously, said improvement comprising:
- a means for modulating the magnetic field at a second frequency concurrently with the revolution of the chopper;
- a first lock-in amplifier, said first amplifier being coupled between said chopper and said detector for providing a normalization signal;
- and a second lock-in amplifier, said second amplifier being coupled between said detector and said generator for providing the Faraday rotation signal.
Dependencies are inferred from the claim text.