Ultra-Low-NA Refractive Index Profiling With Pinhole Diffraction Filtering
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Solution Overview
Problem
Existing methods for determining the refractive index profile of transparent cylindrical objects suffer from inaccuracies due to diffraction effects caused by material variations, leading to noise and incorrect measurements.
Innovation Solution
A method and system that utilize a pinhole aperture to selectively filter out diffraction orders by scanning the object with and without the aperture, merging deflection functions to create a composite function for accurate refractive index profile calculation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional deflection measurement is performed without filtering, then measurement process is simple, but diffraction effects cause noise and incorrect RIP values
Solution Approach 1:
A pinhole aperture is introduced as an intermediary element in the optical path to filter out diffracted light orders. The pinhole selectively transmits the zero-order beam while blocking higher-order diffraction patterns, thereby eliminating the harmful diffraction effects without requiring complex computational filtering or additional sophisticated optical components
Solution Approach 2:
The harmful diffraction orders are extracted and removed from the measurement system by using the pinhole aperture to block them. Only the useful zero-order beam is allowed to pass through to the detector, separating the desired signal from the harmful diffraction artifacts that would otherwise contaminate the RIP measurement
2Measurement precision
If pinhole aperture is used to filter diffraction orders, then diffraction separation improves, but device complexity increases
Solution Approach 1:
The pinhole aperture serves as a simple intermediary optical element that provides effective diffraction order separation. Rather than using complex gratings, prisms, or computational algorithms, the pinhole provides a straightforward physical filter that achieves the desired separation with minimal added complexity to the optical system
Solution Approach 2:
The pinhole aperture changes the spatial parameter of the optical system by introducing a physical barrier with a specific aperture size. This parameter change effectively filters the optical path, allowing only light within a certain angular range (the zero-order beam) to pass through while blocking diffracted orders at different angles
3Measurement precision
If multiple scanning locations are used to improve measurement coverage, then measurement time increases
Solution Approach 1:
The measurement process performs continuous scanning across multiple locations along the cylindrical object, with the pinhole aperture continuously filtering diffraction orders throughout the scan. This continuous application of the filtering principle ensures that all measurement points benefit from diffraction rejection, maintaining high RIP profile accuracy across the entire measurement range without requiring repeated scans or additional processing time
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 method achieves improved accuracy in refractive index profile determination by effectively separating diffraction orders, reducing noise and enhancing measurement precision.
Implementation Method 1
Microlayer variations in the resulting material lead to significant diffraction when measuring the deflection function
Implementation Method 2
A pinhole aperture is positioned in a path of the one or more optical beams upstream of the cylindrical surface of the optical object
Implementation Method 3
The optical object will deflect the beam(s), and the deflection at each of the scanning locations can be measured to define a deflection angle distribution
Data Source
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AI summary
A method for determining a refractive index profile of an optical object having a cylindrical surface includes: (a) scanning the surface at a first plurality of scanning locations with a pinhole aperture in a path of one or more optical beams; (b) measuring a first deflection function based detecting the optical beams after deflection by the optical object for each of the first plurality of scanning locations; (c) scanning the surface at a second plurality of scanning locations where the path of the optical beams is free of the pinhole aperture; (d) measuring a second deflection function based on detecting the optical beams after deflection by the optical object for each of the second plurality of scanning locations; (e) merging at least portions of the first and second deflection functions to obtain a composite deflection function; and (f) calculating the refractive index profile using the composite deflection function.