Grating Shearing Interferometer Wavefront Aberration Detection
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Solution Overview
Problem
Current grating shearing interferometer systems face challenges in high-precision phase retrieval due to interference from high-order diffraction beams, especially for large numerical aperture systems, leading to system errors and reduced accuracy.
Innovation Solution
A method that uses a grating shearing interferometer system with a one-dimensional and two-dimensional diffraction grating plate, where the two-dimensional diffraction grating plate is moved to eliminate interference from high-order diffraction beams by determining specific phase-shifting steps based on the shear ratio and numerical aperture, allowing only interference between ±1st-order and 0th-order beams, thereby improving phase retrieval precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a grating shearing interferometer is used for wavefront detection, then the detection sensitivity and structure simplicity are improved, but high-order diffraction beams cause interference that reduces phase retrieval precision
Solution Approach 1:
The patent extracts and eliminates the harmful high-order diffraction beams from the interference field by using a double-window mask that selectively blocks these beams while allowing the useful ±1st-order and 0th-order beams to pass through for phase retrieval
Solution Approach 2:
The patent introduces a double-window mask as an intermediary element between the grating and the detector to mediate the interference process, filtering out harmful high-order beams while preserving the necessary beams for accurate phase retrieval
2Measurement precision
If a double-window mask is used to filter high-order diffraction beams, then phase retrieval precision is improved, but the mechanical structure complexity and operational convenience deteriorate when shear direction or ratio changes
Solution Approach 1:
The patent designs a universal double-window mask that can accommodate different shear directions and ratios without requiring replacement, making the mask multi-functional and eliminating the need for mechanical changes when measurement parameters are adjusted
3Measurement precision
If existing phase retrieval algorithms are used to eliminate ±3th and ±5th-order diffraction beams, then some interference is reduced, but ±7th and higher-order diffraction beams still affect precision
Solution Approach 1:
The patent physically extracts and removes all high-order diffraction beams (±3th, ±5th, ±7th, and higher orders) from the interference field using the double-window mask, not just the commonly addressed ±3th and ±5th orders, thereby completely eliminating their harmful interference effects
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 method achieves precise phase retrieval by eliminating the influence of high-order diffraction beams, enhancing the detection accuracy of wavefront aberration in optical imaging systems with a large measurable range and adjustable shear ratio.
Implementation Method 1
there are multistage high-order diffraction beams and interference can occur between the high-order diffraction beams in the interference field of the shearing interferometer due to the diffraction of the grating at the object plane
Implementation Method 2
interference can occur between the high-order diffraction beams in the interference field of the shearing interferometer
Data Source
AI summary
Method for detecting wavefront aberration for optical imaging system based on grating shearing interferometer, the grating shearing interferometer system comprising a light source and illumination system, an optical imaging system to be tested, a one-dimensional diffraction grating plate, a two-dimensional diffraction grating plate, a two-dimensional photoelectric sensor, and a computing unit. The one-dimensional and two-dimensional diffraction grating plates are respectively placed on the object plane and the image plane of the optical imaging system to be tested. By collecting interferograms with phase-shifting amounts of 0, π/2, π, 3π/2 and N sets of α, π-α, 2π-α (where,N=2(fix(ceil(1/s)2)+1),s is the shear ratio of the grating shearing interferometer system), combined with a certain phase retrieval algorithm, the influence of all high-order diffraction beams on the phase retrieval accuracy is eliminated, and finally the detection accuracy of wavefront aberration for the imaging system to be tested is improved.