Aspheric Secondary Mirror Lens for Ellipsometer Polarization Control
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Solution Overview
Problem
Current lens systems, such as the Schwarzschild lens, face limitations in measurement accuracy and precision due to polarization changes and light blockage, which increase the spot size and require higher numerical apertures, leading to potential system performance issues.
Innovation Solution
A lens system comprising a curved primary mirror and an aspheric secondary mirror with a support member, where the aspheric secondary mirror has a diameter smaller than the primary mirror and is rotationally symmetric, minimizing light blockage and polarization shifts, and a transparent support member connects the aspheric secondary mirror to the housing, reducing aberrations and light obstruction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a Schwarzschild lens is used, then the numerical aperture is increased, but light blockage increases and spot size increases
Solution Approach 1:
The patent employs curved mirrors (primary and secondary mirrors with specific radii of curvature) instead of traditional lens elements. The primary mirror has a radius of curvature between 50-200mm and the secondary mirror has a radius of curvature between 10-50mm, creating a reflective optical path that achieves high numerical aperture without the light blockage inherent in lens-based Schwarzschild designs
Solution Approach 2:
The patent uses an off-axis reflective optical design where the primary and secondary mirrors are positioned asymmetrically relative to the optical axis. This asymmetric configuration eliminates the central obscuration problem of conventional Schwarzschild lenses while maintaining high numerical aperture capability
2Area of moving object
If the angle of incidence is increased, then the spot size is reduced, but polarization changes increase
Solution Approach 1:
The patent replaces refractive optical elements (lenses) with reflective elements (mirrors). By using mirrors instead of lenses, the system achieves spot size reduction through controlled reflection geometry without the polarization-altering effects that occur in refractive systems, particularly at high angles of incidence
3Loss of energy
If a larger secondary mirror is used, then the light blockage is reduced, but the spot size increases
Solution Approach 1:
The patent positions the secondary mirror in a specific spatial arrangement relative to the primary mirror and optical axis, utilizing three-dimensional geometric optimization. The secondary mirror diameter is controlled at 2-10mm with a specific ratio to the primary mirror, and its positioning in space (rather than just size) achieves both low light blockage and small spot size simultaneously
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 proposed lens system enhances measurement accuracy and precision by minimizing polarization errors and reducing the numerical aperture needed, simplifying data analysis and alignment, while maintaining a smaller spot size and lower light blockage compared to traditional designs.
Implementation Method 1
A lens system is provided in a first embodiment. The lens system comprises a primary mirror that is curved, an aspheric secondary mirror
Implementation Method 2
The aspheric secondary mirror shares an optical axis with the primary mirror. The aspheric secondary mirror and the primary mirror are rotationally symmetric with respect to the optical axis
Data Source
AI summary
A lens system includes a curved primary mirror and an aspheric secondary mirror. The aspheric secondary mirror has a diameter smaller than that of the primary mirror and shares an optical axis with the primary mirror. The aspheric secondary mirror and the primary mirror are rotationally symmetric with respect to the optical axis. A support member, which may be transparent over an operating wavelength of the lens system, is disposed on the aspheric secondary mirror.