Interferometric Measurement of Large Optics Using Immersion Liquid Film
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Solution Overview
Problem
The existing stitching technique for interferometric measurement of large optical elements is costly and time-consuming due to the need for precise surface polishing and complex optical expansions, and it faces challenges with edge errors when measuring large-area test specimens.
Innovation Solution
The method involves using an immersion liquid film between the test specimen's main surfaces and contact bodies that completely cover the measurement area, eliminating the need for precise polishing and relocating edge errors outside the measurement area, allowing for efficient stitching of sub-interferograms into an overall interferogram.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the stitching technique is used to measure large optical elements, then the measurement area is increased, but the cost and time increase due to precise surface polishing requirements
Solution Approach 1:
An immersion liquid with refractive index matching the optical element is introduced as an intermediary between the optical element and the measurement system. This eliminates the need for precise surface polishing by compensating for surface irregularities through refractive index matching, thereby reducing preparation time while maintaining measurement accuracy over large areas
2Area of stationary object
If the stitching technique is used to measure large optical elements, then the measurement area is increased, but the complexity and cost increase due to complex optical expansions
Solution Approach 1:
The refractive index parameter of the measurement medium is changed by introducing an immersion liquid that matches the optical element's refractive index. This parameter change eliminates the need for complex optical expansions, simplifying the measurement system while enabling large area measurements
3Area of stationary object
If the stitching technique is used to measure large optical elements, then the measurement area is increased, but edge errors occur in the measurement results
Solution Approach 1:
The immersion liquid acts as a mediator that extends the effective measurement area by matching refractive indices, allowing the measurement to capture a larger area including edge regions without introducing the edge errors that typically plague stitching measurements. The refractive index matching eliminates refraction effects at boundaries
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 reduces costs and time while maintaining high accuracy and reproducibility by eliminating the need for surface polishing and complex optical expansions, and effectively avoids edge errors in the stitching process.
Implementation Method 1
a film of an immersion liquid is formed between the main surfaces of the test specimen and contact bodies
Implementation Method 2
Interference patterns that arise between a measuring beam passing through the test object and a reference beam are measured and evaluated with an interferometer
Data Source
Figure 1a~1b
Figure 2a~2b
Figure 3~4
AI summary
The invention relates to a method for interferometrically measuring large optics. A combination of a method known as stitching technique , during which the sub-interferograms are determined on partial surfaces of measuring area and are joined in a software-controlled manner and which, as a result, enables the use of small, more cost-effective interferometers, however polished surfaces of the test piece being assumed, together with an immersion method, during which, in fact, lower demands for the surface quality of the test piece exist that, however, is accompanied by edge faults. In order to make this combination possible, a modification of the stitching technique is developed, during which the measuring area (CA) is completely covered by a film consisting of an immersion liquid. A device suited for carrying out this method is characterized by contact bodies, which are made of transparent material, rest upon the main surfaces of the test piece, and which completely cover the measuring area (CA), a film consisting of an immersion liquid being formed between the contact bodies and the main surfaces of the test piece.