Triple Reflection End Reflector for High Numerical Aperture Interferometry
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing single-shot interferometry methods face challenges in achieving high numerical aperture and robustness, particularly for measuring small wavefront aberrations and ensuring high lateral resolution, especially with end reflector arrangements in interferometers.
Innovation Solution
The proposed solution involves a robust two-beam interferometry arrangement with a triple reflection end reflector designed as a prism or air mirror assembly, allowing for a large aperture angle and high numerical aperture, and using beam-limiting means to adapt the aperture angle, enabling precise measurement of distance, profile, and optical path length on both rough and smooth objects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If end reflector arrangements with three plane mirrors are used in a two-beam interferometer, then the interferometric measurement function is achieved, but the numerical aperture remains limited and cannot reach high values like N.A. = 0.4
Solution Approach 1:
The end reflector is divided into three separate plane mirrors arranged in a specific geometric configuration. This segmentation allows each mirror to be optimized independently for high precision manufacturing while collectively achieving the desired high numerical aperture through their spatial arrangement.
Solution Approach 2:
The solution transitions from a single-plane mirror arrangement to a three-dimensional configuration with mirrors positioned at different orientations and locations. This dimensional expansion enables the system to achieve high numerical aperture by capturing light rays from multiple angular directions simultaneously.
2Measurement precision
If wavefront inversion is performed for interferometric measurement, then measurement of small wavefront aberrations is enabled, but particularly high demands are placed on the upstream beam-forming optics
Solution Approach 1:
The interferometric arrangement performs self-alignment and self-correction through the geometric configuration of the three plane mirrors. The system inherently compensates for certain optical path differences and maintains wavefront integrity without requiring complex upstream beam-forming optics, thereby reducing overall system complexity while maintaining measurement precision.
3Manufacturing precision
If a large aperture angle is achieved for high numerical aperture, then lateral resolution is improved, but the geometric adaptation between reference and object beam paths becomes more difficult
Solution Approach 1:
The three plane mirrors are arranged in an asymmetric configuration where each mirror has a specific orientation and position optimized for the beam path. This asymmetric arrangement naturally adapts the reference and object beams to different aperture angles, allowing high numerical aperture in one path while maintaining proper geometric relationships without requiring additional adaptive components.
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 approach significantly increases the numerical aperture, enhances measurement robustness, and allows for high-resolution displacement measurement, making it suitable for commercial use and inline measurement in manufacturing environments.
Implementation Method 1
The end reflector with three flat reflection surfaces can be designed as a prism mirror or air mirror assembly in order to generate a lateral shear of the amount delta_q between the reference and object bundles
Implementation Method 2
an interferometer in which an end reflector is arranged in the reference beam path, and a detector for detecting an interferogram
Data Source
Figure 1
Figure 2~2a
Figure 3
AI summary
The present invention relates to an arrangement and a method for single-shot interferometry which can be used for detecting distance, profile, shape, undulation, roughness or the optical path length in or on optically rough or smooth objects or else for optical coherence tomography (OCT). The arrangement comprises a light source, an interferometer, in which an end reflector is arranged in the reference beam path, and also a detector for detecting an interferogram. In the reference beam path of the interferometer, the end reflector can be embodied with three plane reflection surfaces as a prism mirror or air mirror assembly in order to generate between reference and object beams a lateral shear of magnitude delta_q for obtaining a spatial interferogram. The embodiment of said assembly with regard to the angles and the arrangement of the reflection surfaces makes possible a large aperture angle for a high numerical aperture. In the method, in the reference beam path it is possible to carry out a reduction of the aperture angle of the reference beam using beam-limiting means in order to achieve an optimum adaptation to the geometrically given aperture angle of the end reflector in the reference beam path, which is designed to be smaller than the aperture angle in the object beam path. The end reflector in the reference beam path can also be used as part of a second interferometer for high-resolution measurement of the displacement of the arrangement for single-shot interferometry, wherein said displacement serves for focusing. The end reflector is embodied as a triple reflection arrangement (e.g. a prism arrangement) having three reflection surfaces. The triple reflection arrangement can have an M- or W-beam path, a non-intersecting zigzag beam path or an intersecting (zigzag) beam path.