Binary Apodization Mask for Interferometer Wavefront Control
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Solution Overview
Problem
Conventional apodization masks with rotationally symmetric deposition technology are inadequate for advanced interferometers, as they cannot produce uniquely shaped masks and result in undesirable curved wavefronts due to varying optical path lengths, leading to errors in super-precise metrology measurements.
Innovation Solution
A computer-controlled laser or electron beam photolithographic technology is used to create apodization masks with varying dot densities and random placements, eliminating optical path length variations and diffraction effects by employing threshold and spatial randomization to generate any desired mask shape, preventing diffraction rings and ensuring smooth wavefronts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional rotationally symmetric deposition technology is used to create apodization masks, then the masks can be manufactured with standard processes, but they cannot produce uniquely shaped masks required by advanced interferometers and result in varying optical path lengths causing curved wavefronts
Solution Approach 1:
The mask is segmented into multiple discrete elements or dots arranged in specific patterns. Each element can be independently positioned and sized, allowing the mask to achieve complex non-rotationally symmetric shapes while maintaining uniform optical path length through precise control of each segment's location and dimensions.
Solution Approach 2:
The invention deliberately employs asymmetric and non-rotationally symmetric mask patterns to match the specific beam shapes required by advanced interferometers. The mask elements are positioned and sized asymmetrically to achieve the desired apodization function without the constraints of rotational symmetry, thereby improving adaptability while maintaining manufacturing precision through computer-controlled fabrication.
2Ease of operation
If the optical density varies radially in conventional apodization masks, then the beam shaping function is achieved, but the varying optical path length difference of hundreds of nanometers creates unacceptable wavefront distortion for picometer-range interferometers
Solution Approach 1:
Instead of using continuous radial variation in optical density, the mask is divided into discrete segmented elements. Each segment provides local beam shaping contribution while maintaining a uniform substrate thickness, thereby achieving the desired beam shaping function without introducing wavefront distortion that would compromise picometer-range measurement accuracy.
Solution Approach 2:
The invention changes the approach from varying optical density continuously to varying the presence, size, and position of discrete mask elements. This parameter change allows beam shaping to be achieved through spatial distribution of elements rather than optical density gradients, eliminating the optical path length variation that causes wavefront distortion while preserving the beam shaping capability.
3Ease of manufacture
If conventional chemical/ion beam vapor deposition is used, then the mask can be manufactured with existing technology, but it is not suitable for fabricating non-rotationally symmetric mask patterns
Solution Approach 1:
The invention replaces conventional chemical/ion beam vapor deposition with computer-controlled laser or electron beam photolithographic technology. This substitution enables precise positioning and fabrication of non-rotationally symmetric mask patterns by directly writing the desired pattern onto photosensitive materials, thereby achieving both manufacturing feasibility and the flexibility to create uniquely shaped masks required by advanced interferometers.
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 solution provides precise control over apodization and slope, eliminating diffraction effects and optical path length differences, enhancing the smoothness and uniformity of the apodization, thereby improving metrology measurements in interferometers.
Implementation Method 1
computer-controlled laser, electron beam photolithographic technology or other etching and milling technology
Implementation Method 2
the emulsion layer acts as an etching mask to permit the removal by chemical etch of desired portions of the opaque layer
Data Source
AI summary
A method for creating an apodization mask is disclosed. According to the method, a grid is created for the pattern. The grid includes a number of elements. Each element is processed to determine whether the element is to be made transmissive based on a predetermined local optical density and a random value. The predetermined local optical density and the random value are associated with the element. The random value is generated on a random basis. Each element is further processed to determine whether the position of the element is to be shifted. The positional shift is determined on a random basis. The grid with the processed elements is then used to make an apodization mask. The apodization mask may be used in an optical instrument, such as, an interferometer.