Confocal Inspection System Non-Overlapping Annular Regions
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Solution Overview
Problem
Optical inspection systems face challenges in accurately analyzing samples with absorptive or scattering properties due to variations in optical path lengths and overlapping illumination and collection regions, which can lead to unwanted light signals from depths other than the specified depth.
Innovation Solution
A confocal inspection system employing annular illumination and non-overlapping annular collection regions, defined by masks, reconfigurable panels, or software, ensures consistent optical path lengths and rejects signals from undesired depths by using confocal optics and detectors configured to receive light from specific depths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If overlapping illumination and collection regions are used in the pupil, then the system can collect more light from the sample, but unwanted light signals from depths other than the specified depth are included in the analysis
Solution Approach 1:
The pupil is segmented into distinct illumination and collection regions that do not overlap. The illumination region delivers light to the sample while the collection region collects scattered light, and these regions are spatially separated in the pupil plane. This segmentation ensures that only light scattered at specific angles enters the collection path, providing depth resolution while maintaining adequate light collection.
Solution Approach 2:
Different regions of the pupil are assigned different functions: the illumination region is optimized for delivering light to the sample, while the collection region is optimized for collecting scattered light. Each region has specific angular and spatial characteristics that are tailored to its function, with the collection region positioned to receive only light scattered at angles corresponding to the desired depth.
2Device complexity
If a single lens is used for both illumination and collection, then the optical system is simpler, but the optical path lengths vary significantly for different rays
Solution Approach 1:
The single lens is segmented into separate illumination and collection regions in the pupil plane. By assigning different functional zones to different parts of the same lens, the system maintains the simplicity of a single optical element while achieving the optical path length consistency of separate lenses. Rays passing through the collection region all traverse similar path lengths through the sample.
3Illumination intensity
If retroreflected light is included in the collection, then the signal strength is increased, but the accuracy of optical characterization is reduced
Solution Approach 1:
The collection region is positioned and configured to extract only light scattered at specific angles from the sample, excluding retroreflected light that returns along the illumination path. By carefully selecting the angular range and spatial position of the collection region in the pupil plane, the system isolates the desired scattered light signal while rejecting unwanted retroreflected light.
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
This configuration enhances the accuracy of optical characterization by ensuring that only light from the specified depth is analyzed, improving the system's ability to handle absorptive or scattering samples by maintaining consistent optical path lengths and reducing unwanted signal interference.
Implementation Method 1
collect light reflected or scattered from the sample
Implementation Method 2
the optical path length traversed within the sample is nearly the same for all collected rays
Data Source
AI summary
A confocal inspection system can optically characterize a sample. An objective lens, which can be a single lens or a combination of separate illumination and collection lenses, can have a pupil. The objective lens can deliver incident light to the sample through an annular illumination region of the pupil, and can collect scattered light returning from the sample to form collected light. Confocal optics can be positioned to receive the collected light. A detector can be configured with the confocal optics so that the detector generates signals from light received from a specified depth at or below a surface of the sample and rejects signals from light received from depths away from the specified depth. An optical element, such as a mask, a reconfigurable panel, or the detector, can define the annular collection region to be non-overlapping with the annular illumination region in the pupil.