Aspherical Wavefront Interferometry for Optical Surface Deviation
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Solution Overview
Problem
Conventional interferometer systems face challenges in measuring aspherical optical surfaces with high precision, particularly for non-rotationally symmetrical surfaces, as they require advanced techniques to produce measuring light beams with aspherical wavefronts and struggle with rigorous effects and production-dependent parameters of diffraction gratings.
Innovation Solution
The method employs two diffractive structures, including computer-generated holograms, to reshape the measuring wavefront to match the desired optical surface shape, allowing for precise calibration and measurement of deviations using interferometric techniques, enabling high-precision measurement of any optical surface shape, including non-rotationally symmetrical ones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional interferometer optics are used to produce spherical wavefronts, then measurement of spherical optical surfaces achieves high precision, but measurement of aspherical optical surfaces cannot be performed with the same precision
Solution Approach 1:
The patent changes the wavefront parameter from spherical to aspherical by introducing diffractive structures (computer-generated holograms) that modify the measuring light beam's wavefront shape. This allows the interferometer to adapt to different optical surface shapes while maintaining measurement precision through parameter transformation of the light beam itself.
2Adaptability or versatility
If diffractive structures such as computer-generated holograms are used to produce aspherical wavefronts, then measurement of aspherical surfaces becomes possible, but rigorous effects and production-dependent parameters introduce measurement errors
Solution Approach 1:
The patent applies preliminary calibration by measuring a calibration body with a known aspherical shape before measuring the actual optical surface. This preliminary action characterizes the diffractive structure's actual wavefront transformation properties, allowing subsequent correction of rigorous effects and production-dependent parameters during actual measurements, thereby maintaining precision despite the complexity of diffractive structures.
3Device complexity
If a single diffractive structure is used to reshape the measuring wavefront, then the system remains relatively simple, but calibration errors cannot be fully compensated
Solution Approach 1:
The patent segments the wavefront transformation function into two separate diffractive structures instead of using a single structure. This segmentation allows independent calibration and error characterization of each structure, enabling better compensation of calibration errors through the combined effect of both structures while maintaining manageable system complexity.
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 allows for accurate determination of deviations between actual and desired optical surface shapes with high precision, minimizing errors and improving the measurement accuracy of complex optical surfaces.
Implementation Method 1
providing two diffractive structures which are designed to reshape the wavefront of an arriving wave
Implementation Method 2
The wavefront of the adapted measuring wave is analysed interferometrically after reflection on the optical surface
Data Source
AI summary
An optical element having an optical surface (12; 103), which optical surface has an actual shape, the actual shape deviating from a desired shape by maximum 0.2 nm, wherein the desired shape is either: a free-form surface having a deviation from its best-fitting sphere of at least 5 μm or a substantially rotationally symmetrical surface having a deviation from its best-fitting sphere of at least 0.5 mm.