Method and apparatus for measuring micro structures, anisotropy and birefringence in polymers using laser scattered light

• US 6,097,488 A
• Filed: 06/22/1998
• Issued: 08/01/2000
• Est. Priority Date: 06/22/1998
• Status: Expired due to Fees

• Current Assignee: Princeton University
• Original Assignee: Princeton University
• Inventors: Kennedy, Alan D., Bartolick, Joseph, Grek, Boris
• Primary Examiner(s): Font, Frank G.
• Assistant Examiner(s): STAFIRA, MICHAEL PATRICK
• Application Number:
  US09/102,254
• Time in Patent Office: 771 Days
• Field of Search: 356/364, 356/365, 356/369, 356/370, 356/445, 250/339.11, 250/338.1
• US Class Current: 356/364
• CPC Class Codes: G01J 4/00 Measuring polarisation of light
• CPC Class Codes: G01N 21/23 Bi-refringence

Abstract

A method and apparatus for measuring microstructures, anistropy and birefringence in polymers using laser scattered light includes a laser which provides a beam that can be conditioned and is directed at a fiber or film which causes the beam to scatter. Backscatter light is received and processed with detectors and beam splitters to obtain data. The data is directed to a computer where it is processed to obtain information about the fiber or film, such as the birefringence and diameter. This information provides a basis for modifications to the production process to enhance the process.

Claims

1. An apparatus for measuring birefringence of a moving or static polymer strand during production of the polymer comprising:

laser means for emitting a laser beam directed at the polymer strand, the laser means penetrating the polymer strand and then backscattering therefrom;

modulation means for modulating the laser means;

collection means for collecting forward backscatter from the polymer strand;

beam splitter means for splitting the backscatter into first and second signals;

detector means for receiving first and second signals from the beam splitter; and

computer means interconnected with the modulation means and the detector means for calculating birefringence.

2. The apparatus of claim 1 wherein the laser means, beam splitter, collection means and detection means are contained within a housing and the collection means collects forward backscatter from the polymer strand.

3. The apparatus of claim 1 wherein beam splitter means splits the backscatter into at least three signals with polarization analyzers.

4. The apparatus of claim 3 wherein at least three signals are at 0, 45 and 90 degrees.

5. The apparatus of claim 1 further comprising means for conditioning a laser beam emitted by the laser means.

6. The apparatus of claim 5 wherein the means for conditioning the laser beam comprises a polarizer.

7. The apparatus of claim 5 wherein the means for conditioning the laser beam comprises a chopper.

8. The apparatus of claim 7 wherein a synchronous detection system is interconnected with the detection means.

9. The apparatus of claim 3 wherein the beam splitter means splits the backscatter into additional signals.

10. The apparatus of claim 9 wherein the detector means comprises additional detectors for detecting the additional signals.

11. A method of determining birefringence of a moving polymer strand during production comprising:

directing a laser beam at the polymer strand;

penetrating the polymer strand with the laser beam;

sampling an interior portion the polymer strand with the laser beam;

backscattering the laser beam from the polymer strand;

collecting the backscatter from the polymer strand;

detecting the backscatter; and

calculating the birefringence with a computer.

12. The method of claim 11 wherein the step of calculating the birefringence comprises solving integral equations based on Maxwell'"'"'s formulas.

13. The method of claim 11 wherein the step of calculating the birefringence comprises solving eigenvalue formulas.

14. The method of claim 11 further comprising the step of conditioning the laser beam by polarizing the laser beam.

15. The method of claim 11 further comprising the step of conditioning the laser beam by modulating the laser beam in amplitude and polarization angle.

16. The method of claim 11 wherein the polymer strand comprises a bundle of polymer strands and birefringence of the bundle is determined.

17. A method of measuring micro structures of a moving polymer strand during production comprising:

directing a laser beam at a polymer strand;

allowing the laser beam to penetrate the polymer strand;

scattering the laser beam from the polymer strand;

collecting the scattered light;

analyzing the scattered light;

calculating a value from the scattered light;

utilizing the calculated value to determine properties of the polymer strand.

18. The method of claim 17 further comprising the step of conditioning the laser beam by polarizing the laser beam.

19. The method of claim 17 further comprising the step of conditioning the laser beam by modulating the laser beam in amplitude and polarization.

20. The method of claim 17 wherein the step of collecting the scattered light comprises spitting the scattered light into three signals with polarization analyzers at 0, 45 and 90 degrees.

21. The method of claim 17 wherein the laser beam comprises at least two different wavelengths for removing degeneracy in the measurements.

22. The method of claim 21 further comprising using backscatter from the at least two different wavelengths to calculate birefringence and strand diameter.