# US 7,079,247 B2 · Instantaneous polarization measurement system and method

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- Number: US 7,079,247 B2
- Document ID: US7079247B2
- Status: Granted
- Kind: B2
- Application number: 10/616,328
- Filed: 2003-07-08
- Published: 2005-01-13
- Granted: 2006-07-18
- Earliest claimed: 2003-07-08
- Assignees: Marine Biological Laboratory
- Inventors: Mykhailo Shribak; Rudolf Oldenbourg; Paul J. Cronin; Clifford C. Hoyt; Peter J. Miller
- Web page: https://patentgrep.com/patent/US7079247B2

## CPC

- G01N 21/276: {with alternation of sample and standard in optical path}
- G01J 4/04: Polarimeters using electric detection means (G01J4/02 takes precedence)
- G01N 21/19: Dichroism
- G01N 2021/216: {using circular polarised light}
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)
- G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N)

## Abstract

The invention provides a highly sensitive measurement of retardance and slow axis orientation, accurately and instantaneously, across a full two-dimensional image. There are no moving parts and there need not be any electro-optic tuning as part of the measurement. It is ideally adapted to real-time imaging and is well-suited to use with biological and medical samples, including visualizing structures in oocytes. The invention splits a light beam into several beams, which are analyzed using elliptical polarizers and the resultant intensity is measured. It can be constructed using a single pixilated detector, or several detectors, to achieve high spatial resolution when this is desired.

## Claims

### Claim 1

A system for measuring retardance of a sample, comprising
a sample region for receiving the sample;
a source of substantially circularly polarized illumination light;
illumination optics for directing the illumination light toward the sample region;
analysis optics for receiving incident light from the sample region;
a plurality of photodetector regions;
beamsplitting optics for dividing the incident light into a plurality of sub-beams and for directing each sub-beam to a respective one of the plural photodetector regions;
a plurality of elliptical polarizers disposed in the sub-beams for transmitting incident light whose polarization state lies within a distance ε of a chosen pole on a Poincare sphere; and
a processor for determining retardance from intensity signals generated at the photodetector regions onto which the sub-beams are directed.

### Claim 2 (depends on 1)

The apparatus of claim 1, wherein the sample retardance is 50 nm or less.

### Claim 3 (depends on 1)

The apparatus of claim 1, wherein the sample retardance is 10 nm or less.

### Claim 4 (depends on 1)

The apparatus of claim 1, wherein ε is 35 degrees or less.

### Claim 5 (depends on 1)

The apparatus of claim 1, wherein ε is 20 degrees or less.

### Claim 6 (depends on 1)

The apparatus of claim 1, wherein the beamsplitting optics comprise a beamsplitter configured to operate by partial reflection at an interface for dividing the incident light into the sub-beams.

### Claim 7 (depends on 6)

The apparatus of claim 6, wherein the beamsplitter is substantially polarization neutral.

### Claim 8 (depends on 6)

The apparatus of claim 6, wherein the beamsplitter is a polka-dot type.

### Claim 9 (depends on 1)

The apparatus of claim 1, further comprising an optical retarder disposed adjacent an entrance face of the beamsplitting optics for transforming the polarization state of light passing therethrough.

### Claim 10 (depends on 1)

The apparatus of claim 1, wherein the beamsplitting optics comprises a plurality of prism facets which divide the incident light into the sub-beams according to the area of each facet.

### Claim 11 (depends on 10)

The apparatus of claim 10, wherein the beamsplitting optics comprises a single prism with multiple facets.

### Claim 12 (depends on 10)

The apparatus of claim 10, wherein the beamsplitting optics comprises an assembly of a plurality of prisms.

### Claim 13 (depends on 10)

The apparatus of claim 10, wherein the elliptical polarizers are located between the sample region and the beamsplitting optics.

### Claim 14 (depends on 10)

The apparatus of claim 10, wherein the beamsplitting optics are located between the sample chamber and the elliptical polarizers.

### Claim 15 (depends on 1)

The apparatus of claim 1, wherein at least one of the plural elliptical polarizers comprises a linear polarizer and at least one optical retarder.

### Claim 16 (depends on 15)

The apparatus of claim 15, wherein the optical retarder is an electrically variable retarder.

### Claim 17 (depends on 16)

The apparatus of claim 16, wherein the electrically variable retarder is a liquid crystal cell.

### Claim 18 (depends on 1)

The apparatus of claim 1, wherein at least one of the plural elliptical polarizers comprises a fixed linear polarizer and at least two retarder elements.

### Claim 19 (depends on 18)

The apparatus of claim 18, wherein at least one of the retarder elements is electrically variable.

### Claim 20 (depends on 18)

The apparatus of claim 18, wherein at least two of the retarder elements are electrically variable.

### Claim 21 (depends on 1)

The apparatus of claim 1, wherein the plural detector regions comprise a plurality of detectors.

### Claim 22 (depends on 1)

The apparatus of claim 1, wherein at least two of the plural detector regions comprise different regions on a single pixilated detector.

### Claim 23 (depends on 1)

The apparatus of claim 1, wherein the illumination light source is a pulsed lamp.

### Claim 24 (depends on 23)

The apparatus of claim 23, wherein the illumination light source is a flashlamp.

### Claim 25 (depends on 1)

The apparatus of claim 1, wherein the illumination light source is operable to emit monochromatic light.

### Claim 26 (depends on 25)

The apparatus of claim 25, wherein the illumination light source comprises a broadband light source and a filter.

### Claim 27

A system for real-time imaging of retardance of a sample, comprising
a sample region for receiving the sample;
a source of substantially circularly polarized illumination light;
illumination optics for directing the illumination light toward the sample region;
analysis optics for receiving incident light from the sample region;
a plurality of photodetector regions;
beamsplitting optics for dividing the incident light into a plurality of sub-beams and for directing each sub-beam to a respective one of the plural photodetector regions;
a plurality of elliptical polarizers located in the sub-beams for transmitting incident light whose polarization state lies within a distance ε of a chosen pole on a Poincare sphere; and
a processor for calculating retardance from intensity signals generated at the photodetector regions onto which the sub-beams are directed;
wherein the sample is one of a biological cell, a tissue sample, and an oocyte.

### Claim 28 (depends on 27)

The apparatus of claim 27, wherein the sample is an oocyte.

### Claim 29 (depends on 27)

The apparatus of claim 27, wherein the beamsplitting optics comprise a beamsplitter configured to operate by partial reflection at an interface to divide the incident light into the sub-beams.

### Claim 30 (depends on 29)

The apparatus of claim 29, further comprising a waveplate located between the sample region and the beamsplitting optics.

### Claim 31

The apparatus of 27, wherein the beamsplitting optics comprise a plurality of prism facets which divide the incident light into the sub-beams according to the area of each facet.

### Claim 32 (depends on 31)

The apparatus of claim 31, wherein the plural elliptical polarizers are located between the sample region and the beamsplitting optics.

### Claim 33 (depends on 31)

The apparatus of claim 31, wherein the plural prism facets comprise a single prism with multiple facets.

### Claim 34 (depends on 31)

The apparatus of claim 31, wherein the plural prism facets comprise an assembly of a multiplicity of prisms.

### Claim 35 (depends on 27)

The apparatus of claim 27, further comprising a display unit for providing an image of the sample retardance.

### Claim 36 (depends on 35)

The apparatus of claim 35, wherein the display comprises a head-up display.

### Claim 37 (depends on 35)

The apparatus of claim 35, wherein the sample is viewable with a microscope and wherein the image of sample retardance provided by the display comprises an image viewed from within the eyepiece of the microscope.

### Claim 38

A method for imaging retardance of a sample in real-time, comprising the steps of:
illuminating the sample with light that is substantially circularly polarized;
receiving light that has interacted with the sample;
dividing the received light into N sub-beams, where N≧2;
disposing elliptical polarizers in the N sub-beams, corresponding to states within a distance ε of a pole on a Poincare sphere;
analyzing a polarization state of each of the N sub-beams with the elliptical polarizers;
forming an image of the sample with each sub-beam;
measuring intensity at a plurality of points in the image at each of the N sub-beams; and
calculating the sample retardance based on the N image intensity measurements.

### Claim 39 (depends on 38)

The method of claim 38, further comprising the step of calculating a principal slow axis of the sample at a plurality of points.

### Claim 40 (depends on 38)

The method of claim 38, further comprising the step of taking a background measurement with no sample present.

### Claim 41 (depends on 40)

The method of claim 40, further comprising the step of storing background data derived from the background measurement.

### Claim 42 (depends on 41)

The method of claim 41, further comprising the step of correcting the calculation of retardance using the stored background data.

### Claim 43 (depends on 38)

The method of claim 38, wherein N is 5.

### Claim 44 (depends on 38)

The method of claim 38, wherein N is 4.

### Claim 45 (depends on 44)

The method of claim 44, wherein one of the elliptical polarizers transmits received light that is substantially circular in polarization state.

### Claim 46 (depends on 44)

The method of claim 44, wherein none of the elliptical polarizers transmit received light that is substantially circular in polarization state.

### Claim 47 (depends on 38)

The method of claim 38, wherein N is 3.

### Claim 48 (depends on 38)

The method of claim 38, wherein N is 2.

### Claim 49 (depends on 38)

The method of claim 38, wherein at least one of the elliptical polarizers is electrically variable.

### Claim 50 (depends on 38)

The method of claim 38, further comprising the step of taking calibration images to compensate for variations between optical responses of the N sub-beams.

### Claim 51 (depends on 50)

The method of claim 50, further comprising the step of correcting the image intensity measurements using the calibration images.

### Claim 52 (depends on 50)

The method of claim 50, wherein one of the polarization of the illumination light and the polarization state of at least one of the polarizers is altered between the calibration measurement and the sample measurement.