Polarization based interferometric detector
A sensor and method for determining the optical properties of a sample material is disclosed. The sensor comprises a light source that generates a linearly polarized light beam having a predetermined polarization orientation with respect to the plane of incidence. The linearly polarized light beam is reflected off the sample and is split into second and third light beams where the second and third light beam consist of the combined projections of mutually orthogonal components of the first light beam. A signal processor measures the intensity difference between the second and third light beams to calculate the phase difference induced by the sample material.
1. A sensor for determining the optical properties of a sample material, the sensor comprising:
a light source for generating a first light beam having first and second lightwaves, the first lightwave having a first linear polarization and the second lightwave having a second linear polarization, the first and second linear polarizations being substantially orthogonal to each other, the first and second lightwaves being in phase relative to each other;
an optical retarder for providing a substantially 90 degree phase shift between the first and second lightwaves by imposing a relative delay between the first and the second lightwaves;
an optical interface for reflecting the first light beam from the sample material under total internal reflection conditions;
a polarizing beam splitter for splitting the first beam into a second light beam and a third light beam after the first light beam is reflected from the optical interface, the second and third light beams consisting of combined projections of mutually orthogonal polarization components on the main axes of the beam splitter;
a signal processor for measuring the intensity difference between the second and the third light beams to calculate the phase difference induced by the sample material, the signal processor receiving a first intensity measurement from a first detector and a second intensity measurement from a second detector, the first and second detectors measuring the intensities of the second and third light beams, respectively.
2. The sensor of claim 1 wherein the light source comprises a coherent light that is linearly polarized and oriented at a predetermined angle with respect to the plane of incidence.
3. The sensor of claim 2 wherein the light source is a gas laser, a diode pumped solid state laser, an excimer lamp, a vertical cavity surface emitting laser or a laser diode.
4. The sensor of claim 2 wherein the light source is any light source that will provide a linearly polarized coherent light in the 532–680 nanometer wavelength range.
5. The sensor of claim 2 wherein the predetermined angle is substantially 45 degrees to the plane of incidence.
6. The sensor of claim 2 wherein the predetermined angle is η where
tan
η
=
I
P
0
I
P
1
,
and where I 0 P and I 1 P are intensities of the first lightwave before and after reflection from the sample material, respectively.
7. The sensor of claim 1 wherein the polarizing beam splitter is oriented such that the intensity of the second and the third light beams is substantially equal.
8. The sensor of claim 1 wherein the polarizing beam splitter is oriented at a 45 degree angle to the plane of the optical interface.
9. The sensor of claim 1 wherein the optical retarder for providing a substantially 90 degree phase shift is a Fresnel rhomb prism.
10. The sensor of claim 1 wherein the optical retarder for providing a substantially 90 degree phase shift is a right angle prism.
11. The sensor of claim 1 further comprising one or more optical components located in the path of the first beam wherein the one or more optical components convert the polarization of the light beam from substantially elliptical polarization into substantially circular polarization before the light beam is transmitted to the beam splitter.
12. The sensor of claim 1 wherein the sample material is applied to an array of transducers, each transducer containing sensing material.
13. The sensor of claim 1 wherein the sample material is applied to a transducer array chip.
14. The sensor of claim 1 wherein the sample material comprises nucleic acid.
15. The sensor of claim 1 wherein the sample material is selected from the group consisting of proteins and polypeptides.
16. The sensor of claim 1 wherein the sample material comprises viral particles.
17. The sensor of claim 1 wherein the sample material comprises bacteria.
18. The sensor of claim 1 wherein the sensor comprises at least one SPR transducer.
19. A method of determining the optical properties of a sample material, the method comprising:
generating a first light beam having first and second lightwaves, the first lightwave having a first linear polarization and the second lightwave having a second linear polarization, the first and second linear polarizations being orthogonal to each other;
providing a substantially 90 degree phase shift between the first and second lightwaves by imposing a relative delay between the first and the second lightwaves;
reflecting the light beam off the sample material;
splitting the first beam into a second light beam and a third light beam after the first light beam is reflected from the optical interface, the second and third light beams consisting of combined projections of mutually orthogonal polarization components on the main axes of the beam splitter;
measuring the intensity difference between the second and the third light beams to calculate the phase difference induced by the sample material.
20. The method of claim 19 wherein the first light beam is a linearly polarized coherent light beam that is oriented at a predetermined angle with respect to the plane of incidence.
21. The method of claim 20 wherein the predetermined angle is substantially 45 degrees to the plane of incidence.
22. The method of claim 20 wherein the predetermined angle is η where
tan
η
=
I
P
0
I
P
1
,
and where I 0 P and I 1 P are intensities of the first lightwave before and after reflection from the sample material, respectively.
23. The method of claim 19 wherein the intensity of the second and the third light beams is substantially equal.
24. The method of claim 19 further comprising converting the polarization of the first light beam from substantially elliptical polarization into substantially circular polarization before splitting the first light beam into a second light beam and a third light beam.
25. The method of claim 19 wherein the substantially 90 degree phase shift is provided by reflecting the first light beam from two reflection surfaces under total internal reflection conditions.
26. The method of claim 19 wherein the sample material comprises nucleic acid.
27. The method of claim 19 wherein the sample material is selected from the group consisting of proteins and polypeptides.
28. The method of claim 19 wherein the sample material comprises viral particles.
29. The method of claim 19 wherein the sample material comprises bacteria.