Systems and methods for measuring birefringence in glass and glass-ceramics
First Claim
1. A method of optically measuring an amount of birefringence B in a surface of a sample, comprising:
- a) digitally capturing TE and TM angular spectra of intensity versus pixel number for the sample, wherein the digital capturing is defined by pixels having an index resolution;
b) processing the TE and TM angular spectra to minimize differences between respective regions of the TE and TM angular spectra, wherein the respective regions include a rate of change of intensity with angle that is at least 40% of a maximum rate of change of intensity with angle;
c) determining an amount of shift in pixels that best overlaps the processed TE and TM spectra; and
d) determining the amount of birefringence B by multiplying the pixel shift by the index resolution.
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Abstract
Systems and methods of for measuring birefringence and stress in a sample made of ion-exchanged glass or a ceramic are disclosed, wherein the method includes digitally capturing TE and TM angular spectra of intensity versus pixel number for the sample. The TE and TM angular spectra are processed to minimize differences between respective regions of the TE and TM angular spectra. The amount of shift in pixels that best overlaps the processed TE and TM spectra is determined. The birefringence B is calculated by multiplying the pixel shift by the index resolution. The stress is calculated by multiplying the birefringence by the stress-optic coefficient.
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Citations
21 Claims
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1. A method of optically measuring an amount of birefringence B in a surface of a sample, comprising:
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a) digitally capturing TE and TM angular spectra of intensity versus pixel number for the sample, wherein the digital capturing is defined by pixels having an index resolution; b) processing the TE and TM angular spectra to minimize differences between respective regions of the TE and TM angular spectra, wherein the respective regions include a rate of change of intensity with angle that is at least 40% of a maximum rate of change of intensity with angle; c) determining an amount of shift in pixels that best overlaps the processed TE and TM spectra; and d) determining the amount of birefringence B by multiplying the pixel shift by the index resolution. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A method of optically measuring an amount of birefringence B in a surface of a sample made of ion-exchanged glass or a glass-ceramic, comprising:
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a) digitally capturing TE and TM angular spectra of intensity versus pixel number for the sample, wherein the digital capturing is defined by pixels having an index resolution; b) optionally normalizing the TE and TM angular spectra to a total-reflectivity spectrum obtained without sample, representative of an angular distribution of an illumination system; c) processing the TE and TM angular spectra or the optionally normalized TE and TM angular spectra to obtain filtered TE and TM spectra; d) calculating respective derivatives of the filtered TE and TM spectra; e) determining the angular locations of respective maxima of the respective derivatives; and f) determining the shift by the angular separation of the respective derivative maxima.
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16. A system for optically measuring an amount of birefringence B in a surface of a sample made of ion-exchanged glass or a glass-ceramic, comprising:
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a prism optically coupled to the sample surface at a coupling surface and having an input surface and an output surface; a light source that emits light having an operating wavelength in the infrared range, with the light source optically coupled to the prism coupling surface via the input surface and over a first optical path; a photodetector system optically coupled to the prism coupling surface via the output surface over a second optical path and configured to receive TE and TM light representative of TE and TM angular spectra of the sample, wherein the photodetector system includes one or more pixels having an index resolution; and a controller electrically connected to the photodetector system and arranged to receive the TE and TM images, the controller being configured with instructions embodied in a computer-readable medium to process the TE and TM images to minimize differences between respective regions of the TE and TM angular spectra, wherein the respective regions include a rate of change of intensity with angle that is at least 40% of a maximum rate of change of intensity with angle, to determine an amount of pixel shift that best overlaps the processed TE and TM spectra in the respective regions and the amount of birefringence B by multiplying the pixel shift by the index resolution. - View Dependent Claims (17, 18, 19, 20, 21)
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Specification