Brewster Angle Illumination for Transparent Substrate Surface Inspection
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Solution Overview
Problem
Current methods for detecting deviations from specified manufacturing dimensions on optically transparent components, such as plane-parallel substrates or coatings, are limited by optical resolution and require longer measurement times, making them inefficient for large-area quality control.
Innovation Solution
A method involving focused illumination with parallel-polarized light at the Brewster angle, where the total intensity of reflected beams is measured and compared to reference values, allowing for sensitive detection of surface defects and coating thicknesses, and distinguishing between geometric waviness and coating changes using intensity and geometric center shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If camera-based inspection systems with multi-mode LED lighting are used for surface inspection, then the inspection coverage can be achieved, but the optical resolution is limited and measurement time is extended
Solution Approach 1:
The patent changes the illumination parameters by using laser light with a narrow aperture angle (half-opening angle of 1° to 3°) at the Brewster angle, instead of multi-mode LED lighting. This parameter change enables higher optical resolution and faster measurement by exploiting the polarization properties and angular selectivity of laser illumination at the Brewster angle, where p-polarized light is completely transmitted and only s-polarized light is reflected.
Solution Approach 2:
The patent introduces dynamic adjustment capabilities for the aperture angle of the illumination beam and the polarization state of the light. By dynamically optimizing these parameters, the system achieves both high resolution and fast measurement speeds, resolving the contradiction between precision and time consumption.
2Measurement precision
If classic spectroscopic ellipsometers are used for characterizing thin flat glass coatings, then nanometer-range thickness measurement is possible, but the method requires significant refractive index difference and is limited to specific objects
Solution Approach 1:
The patent changes the measurement parameters by utilizing illumination at the Brewster angle with controlled polarization, instead of the broad-spectrum, multi-angle illumination used in classic spectroscopic ellipsometers. This approach works effectively for optically transparent objects like flat glass where the refractive index difference method is insufficient, thereby improving versatility while maintaining nanometer-range measurement precision.
Solution Approach 2:
The patent replaces the complex spectroscopic ellipsometry system with a simplified laser-based reflection measurement system. By substituting the mechanical and optical complexity of spectroscopic ellipsometers with a more adaptable laser illumination and detection setup, the system achieves both precision and broad applicability to transparent materials.
3Measurement precision
If high-dynamic mode image acquisition is used to map and measure reflections, then measurement sensitivity is improved, but measurement time increases
Solution Approach 1:
The patent changes the illumination parameters to use laser light with a narrow aperture angle (1° to 3° half-opening angle) at the Brewster angle, which creates a more favorable intensity distribution for reflection measurements. This parameter change improves measurement sensitivity without requiring high-dynamic mode acquisition, thereby maintaining fast measurement speeds and resolving the contradiction between sensitivity and productivity.
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
Enables faster and more cost-effective detection of deviations with improved sensitivity to surface defects and coating conditions, reducing measurement time and hardware complexity compared to camera-based systems.
Implementation Method 1
In a plane of incidence, all of the illumination beams in an angular range converge symmetrically around the Brewster angle of the substrate at a point of the linear illumination section
Implementation Method 2
The illumination beam is polarized parallel to the plane of incidence
Implementation Method 3
The total intensity of at least one measurement beam bundle, which is produced by reflection of the illumination beam bundle on a surface of the substrate layer, is recorded by means of a detector unit
Data Source
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AI summary
The invention relates to a method for detecting modifications to an optically transparent component (1) with a plane-parallel substrate layer (1.1) made of a substrate, wherein an illumination beam is focused onto a front surface (1.2) of the component (1) by means of an illumination unit (2) in a linear illumination section. The illumination beam is collimated along the illumination section and arranged symmetrically around the Brewster angle of the substrate in an incidence plane at half an opening angle of between one and three degrees and is polarized parallel to the incidence plane. The total intensity of at least one measurement beam (5.1, 5.2) reflected at an interface of the component (1) parallel to the substrate layer (1.1) is detected by means of a detector unit (3) and compared with at least one total reference intensity measured on a reference test specimen.