Stress Profile Measurement Using Combined LSP and RNF Techniques
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Solution Overview
Problem
Current methods for determining central tension and stress profiles, such as light-scattered polarimetry (LSP) and refractive near field (RNF), face challenges with noise, variability, and reliability, particularly in measuring compression regions and across sample thickness.
Innovation Solution
A combined apparatus and method integrating LSP and RNF techniques, using multiple reference blocks and a fluid with specific refractive indices to correct drift and noise, allowing for more accurate and reproducible measurements of refractive index and stress profiles by averaging intensity distributions and excluding noisy edge portions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If light-scattered polarimetry (LSP) is used to measure stress profiles, then stress-based characteristics can be determined, but measurements in compression regions become unreliable and noisy
Solution Approach 1:
The patent combines LSP and RNF measurement techniques into a single integrated system. The LSP apparatus measures stress profiles while the RNF apparatus measures refractive index profiles, and the results are merged to compensate for each other's weaknesses. Specifically, RNF measurements provide reliable data in compression regions where LSP fails, while LSP provides better overall stress profile information. The combined apparatus uses a single sample holder and can switch between or combine both measurement modes to achieve comprehensive and reliable stress characterization.
Solution Approach 2:
The patent introduces refractive index measurement as an intermediary parameter to improve stress profile measurement. By measuring the refractive index profile using RNF technique and using it as a mediator to correct and validate the LSP-based stress measurements, the system can identify and exclude noisy portions of the measurement, particularly in compression regions where the refractive index data provides complementary information.
2Measurement precision
If refractive near field (RNF) method is used to measure stress profiles, then refractive index and birefringence profiles can be obtained, but stress profile magnitude becomes unreliable and drifts over sample thickness
Solution Approach 1:
The patent implements a feedback mechanism where the LSP measurement results are used to validate and correct the RNF measurement results. The system continuously compares the stress profile derived from refractive index changes (RNF) with the direct stress measurement (LSP), and uses this feedback to identify drift and correct the RNF-based stress magnitude. This cross-validation feedback loop ensures that the final stress profile is reliable and free from drift artifacts.
Solution Approach 2:
The patent changes the measurement parameters by using two different physical phenomena (light scattering for LSP and refractive near field for RNF) to measure the same stress profile. By varying the measurement approach and comparing results across different parameter spaces, the system can identify and correct drift in the RNF measurements, as the two methods respond differently to sample variations and systematic errors.
3Measurement precision
If separate LSP and RNF apparatus are used, then comprehensive measurements can be made, but sample handling increases and risk of sample breakage increases
Solution Approach 1:
The patent merges the LSP and RNF apparatus into a single integrated system with a common sample holder, optical table, and control system. This consolidation allows both measurement techniques to be performed on the same sample without removal or repositioning, eliminating the handling risks associated with transferring samples between separate apparatus. The combined system maintains the full measurement capabilities of both individual techniques while simplifying operation and reducing sample stress.
4Area of stationary object
If edge portions of measurements near CT region interface are included, then complete stress profile coverage is achieved, but noise and variability increase
Solution Approach 1:
The patent extracts and excludes the noisy edge portions of the measurement data from the final stress profile calculation. By identifying the regions near the central tension (CT) interface that exhibit excessive noise and variability, the system removes these problematic data points from the analysis. This extraction of harmful data elements allows the remaining clean data to be used for accurate stress profile determination, while still maintaining coverage of the essential measurement regions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The combined approach enhances the reliability and accuracy of stress profile measurements, reduces sample handling risks, and improves the precision of central tension determination by minimizing noise and variability across the sample.
Implementation Method 1
The light polarization is varied continuously between different polarization states using an optical compensator
Implementation Method 2
Stress in the sample causes optical retardation along the light path, with the amount of stress being proportional to the derivative of the optical retardation
Implementation Method 3
The amount of optical retardation can be determined from the detected scattered light intensity distribution, which varies due to the constructive and destructive interference for the different effective path lengths of the detected light
Implementation Method 4
A prism is also used to couple light out of the sample to a transverse electric (TE) mode spectrum and a transverse magnetic (TM) spectrum
Implementation Method 5
A prism is also used to couple light out of the sample
Data Source
AI summary
Apparatus can comprise a cavity at least partially defined by a first major surface of a reference block and configured to receive a sample. The apparatus can comprise a first polarization-switching light source configured to emit a first polarization-switched light beam toward the cavity and a first detector configured to detect a corresponding signal. The apparatus can comprise a second polarization-switching light source configured to emit a second polarization-switched light beam toward the cavity and a second detector configured to detect a corresponding signal. The first reference block can be positioned between the second detector and the second reference block. Methods of determining an estimated stress profile can comprise determining a central tension from a measured retardation profile of the sample. Methods can comprise determining an initial stress profile from a refractive index profile of the sample. Methods can comprise scaling and adjusting stress profiles.