Apparatus and method for measuring optical activity
First Claim
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1. An apparatus for measuring the circular birefringence of a sample comprising:
- (a) a reference polarizer positioned to receive a reference beam having a right circularly polarized (RCP) wave characterized by a first frequency and a left circularly polarized (LCP) wave characterized by a second frequency, the reference polarizer producing a reference heterodyne wave, the reference heterodyne wave characterized by a reference phase, the reference phase representing the difference between the RCP wave and the LCP wave of the reference beam;
(b) a reference detector positioned to receive the reference heterodyne wave and generate a reference signal;
(c) a measurement polarizer positioned to receive a measurement beam exiting the sample, the measurement beam having a RCP wave characterized by the first frequency and a LCP wave characterized by the second frequency, the measurement polarizer producing a measurement heterodyne wave, the measurement heterodyne wave characterized by a measurement phase, the measurement phase representing the difference between the RCP wave and the LCP wave of the measurement beam;
(d) a sample detector positioned to receive the measurement heterodyne wave and generate a measurement signal;
(e) a gain/phase meter connected to the reference detector and sample detector and generating an output signal characterized by a phase difference equal to the difference between the measurement phase and the reference phase; and
(f) a control program capable of execution on a processor, the control program calculating the circular birefringence of the sample based, in part, on the output signal of the gain/phase meter.
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Abstract
The change in the circular birefringence of a sample is measured by passing a light beam comprised of a left circularly polarized (LCP) wave and a right circularly polarized (RCP) wave through a sample and measuring the change in the phase difference between the RCP and LCP waves.
22 Citations
27 Claims
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1. An apparatus for measuring the circular birefringence of a sample comprising:
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(a) a reference polarizer positioned to receive a reference beam having a right circularly polarized (RCP) wave characterized by a first frequency and a left circularly polarized (LCP) wave characterized by a second frequency, the reference polarizer producing a reference heterodyne wave, the reference heterodyne wave characterized by a reference phase, the reference phase representing the difference between the RCP wave and the LCP wave of the reference beam;
(b) a reference detector positioned to receive the reference heterodyne wave and generate a reference signal;
(c) a measurement polarizer positioned to receive a measurement beam exiting the sample, the measurement beam having a RCP wave characterized by the first frequency and a LCP wave characterized by the second frequency, the measurement polarizer producing a measurement heterodyne wave, the measurement heterodyne wave characterized by a measurement phase, the measurement phase representing the difference between the RCP wave and the LCP wave of the measurement beam;
(d) a sample detector positioned to receive the measurement heterodyne wave and generate a measurement signal;
(e) a gain/phase meter connected to the reference detector and sample detector and generating an output signal characterized by a phase difference equal to the difference between the measurement phase and the reference phase; and
(f) a control program capable of execution on a processor, the control program calculating the circular birefringence of the sample based, in part, on the output signal of the gain/phase meter. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
(i) a light beam generator generating a light beam having a first linearly polarized (1LP) wave characterized by a first frequency and a first polarization plane and a second linearly polarized (2LP) wave characterized by a second frequency and a second polarization plane, wherein the first polarization plane is orthogonal to the second polarization plane;
(ii) a quarter-wave plate positioned to receive the light beam and convert the first and second linearly polarized waves to a right circularly polarized (RCP) wave and a left circularly polarized (LCP) wave; and
(iii) a beam splitter positioned to receive the light beam from the quarter-wave plate and produce a measurement beam and a reference beam.
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11. The apparatus of claim 10 wherein the light beam generator is a Zeeman laser characterized by a center frequency and a beat frequency.
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12. The apparatus of claim 11 wherein the Zeeman laser includes a permanent magnet and a stabilizer coil, the stabilizer coil energized to maintain a beat frequency having a variation less than 100 Hz.
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13. The apparatus of claim 10 wherein the measurement polarizer is fixed with respect to rotations about an axis defined by the measurement beam.
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14. The apparatus of claim 11 wherein the beat frequency is less than 200 MHz.
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15. The apparatus of claim 14 wherein the beat frequency is less than 10 MHz.
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16. The apparatus of claim 15 wherein the beat frequency is between 0.5 MHz-4 MHz.
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17. The apparatus of claim 16 wherein the beat frequency is between 1.5 MHz-2.0 MHz.
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18. A method for determining the circular birefringence of a sample comprising the steps of:
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(a) generating a coherent light beam having a left circularly polarized (LCP) wave and a right circularly polarized (RCP) wave, the light beam characterized by a phase;
(b) splitting the light beam into a measurement beam and a reference beam;
(c) passing the measurement beam through a blank sample;
(d) measuring a first phase difference between the measurement beam and reference beam;
(e) replacing the blank with the sample and passing the measurement beam through the sample;
(f) measuring a second phase difference between the measurement beam and reference beam; and
(g) determining the circular birefringence of the sample based, in part, on the first and second phase difference. - View Dependent Claims (19, 20, 21)
(i) passing the measurement beam and reference beam through a polarizer;
(ii) detecting a measurement beam intensity and a reference beam intensity; and
(iii) measuring the phase difference between the measurement beam and reference beam based, in part, on the measurement beam intensity and reference beam intensity.
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22. A method for determining the circular birefringence of a sample comprising the steps of:
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(a) generating a coherent light beam having a left circularly polarized (LCP) wave and a right circularly polarized (RCP) wave, the light beam characterized by a phase;
(b) splitting the light beam into a measurement beam and a reference beam;
(c) passing the measurement beam through a sample;
(d) measuring a phase difference between the measurement beam and reference beam;
(e) repeating steps (c) and (d) at least once thereby measuring a plurality of phase differences; and
(f) determining the circular birefringence of the sample based, in part, on the plurality of phase differences. - View Dependent Claims (23, 24)
(i) passing the measurement beam and reference beam through a polarizer;
(ii) detecting a measurement beam intensity and a reference beam intensity; and
(iii) measuring the phase difference between the measurement beam and reference beam based, in part, on the measurement beam intensity and reference beam intensity.
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24. The method of claim 22 wherein the LCP wave is characterized by a first frequency and the RCP wave is characterized by a second frequency wherein the first frequency is not equal to the second frequency.
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25. A method for measuring the change of the circular birefringence of a sample comprising the steps of:
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(a) propagating a beam through a sample, the beam having a first wave characterized by a first polarization state and a second wave characterized by a second polarization state that is orthogonal to the first polarization state, the beam further characterized by a phase difference between the first and second wave; and
(b) measuring the change of the phase difference of the beam.
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26. An apparatus for measuring the circular birefringence of a sample comprising:
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(a) a light beam generator generating a light beam having a right circularly polarized (RCP) wave characterized by a first frequency and a left circularly polarized (LCP) wave characterized by a second frequency;
(b) a beam splitter positioned to receive the light beam from the beam generator and produce a measurement beam and a reference beam;
(c) a reference polarizer positioned to receive the reference beam and produce a reference heterodyne wave, the reference heterodyne wave characterized by a reference phase, the reference phase representing the difference between the RCP wave and the LCP wave of the reference beam;
(d) a reference detector positioned to receive the reference heterodyne wave and generate a reference signal;
(e) a measurement polarizer positioned to receive the measurement beam exiting the sample and produce a measurement heterodyne wave, the measurement heterodyne wave characterized by a measurement phase, the measurement phase representing the difference between the RCP wave and the LCP wave of the measurement beam;
(f) a sample detector positioned to receive the measurement heterodyne wave and generate a measurement signal;
(g) a gain/phase meter connected to the reference detector and sample detector and generating an output signal characterized by a phase difference equal to the difference between the measurement phase and the reference phase; and
(h) a processor connected to the gain/phase meter, the processor calculating the circular birefringence of the sample based, in part, on the output signal of the gain/phase meter.
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27. An apparatus for measuring the circular birefringence of a sample comprising:
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(a) a light beam generator generating a light beam having a first linearly polarized (1LP) wave characterized by a first frequency and a first polarization plane and a second linearly polarized (2LP) wave characterized by a second frequency and a second polarization plane, wherein the first polarization plane is orthogonal to the second polarization plane;
(b) a quarter-wave plate positioned to receive the light beam and convert the first and second linearly polarized waves to a right circularly polarized (RCP) wave and a left circularly polarized (LCP) wave;
(c) a beam splitter positioned to receive the light beam from the quarter-wave plate and produce a measurement beam and a reference beam;
(d) a reference polarizer positioned to receive the reference beam and produce a reference heterodyne wave, the reference heterodyne wave characterized by a reference phase, the reference phase representing the difference between the RCP wave and the LCP wave of the reference beam;
(e) a reference detector positioned to receive the reference heterodyne wave and generate a reference signal;
(f) a measurement polarizer positioned to receive the measurement beam exiting the sample and produce a measurement heterodyne wave, the measurement heterodyne wave characterized by a measurement phase, the measurement phase representing the difference between the RCP wave and the LCP wave of the measurement beam;
(g) a sample detector positioned to receive the measurement heterodyne wave and generate a measurement signal;
(h) a gain/phase meter connected to the reference detector and sample detector and generating an output signal characterized by a phase difference equal to the difference between the measurement phase and the reference phase; and
(i) a processor connected to the gain/phase meter, the processor calculating the circular birefringence of the sample based, in part, on the output signal of the gain/phase meter.
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Specification