Laser Beam Analysis Using Focus-Offset Partial Beams
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Solution Overview
Problem
Conventional wavefront measurement methods, such as Shack-Hartmann sensors, are limited in accurately analyzing thermally induced wavefront changes in laser beams due to inherent geometric reference centers, which interfere with the measurement results, making it difficult to distinguish between actual wavefront modifications and changes in the measurement arrangement's position relative to the laser beam.
Innovation Solution
A method involving the splitting of the laser beam into multiple partial beams with focus offsets, recording measurement images, and performing iterative forward simulations to calculate beam parameters, while utilizing near-field and far-field images to improve wavefront analysis and correction, particularly in EUV laser plasma sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional Shack-Hartmann sensors are used for wavefront measurement, then geometric beam parameters can be measured, but the geometric reference centers of the measurement arrangement interfere with the measurement results and make it difficult to distinguish actual wavefront modifications from position changes of the measurement arrangement
Solution Approach 1:
The patent extracts and removes the harmful geometric reference centers from the measurement arrangement by using a lensless imaging approach. Instead of using a microlens array that introduces reference centers, the invention directly records the focal spot pattern of the laser beam on a sensor, eliminating the coordinate system imprinting effect and enabling reliable distinction between actual wavefront changes and measurement arrangement position changes.
Solution Approach 2:
The patent replaces the mechanical/optical measurement arrangement with fixed geometric reference centers (Shack-Hartmann sensor) with a computational approach. By using lensless imaging and evaluating the focal spot pattern through image processing algorithms, the system substitutes the physical reference center-based measurement with a computational method that operates in the coordinate system of the laser beam itself.
2Measurement precision
If conventional wavefront measurement methods are used, then measurement results can be obtained, but the analysis is too slow to enable immediate correction of wavefront aberrations during operation
Solution Approach 1:
The patent performs preliminary action by pre-calculating and storing the relationship between focal spot patterns and wavefront parameters through forward simulations. During actual measurement, the system only needs to compare the recorded focal spot pattern with the pre-computed reference patterns, significantly reducing the processing time and enabling real-time wavefront correction.
Solution Approach 2:
The patent creates a simplified copy or representation of the wavefront information in the focal spot pattern that can be rapidly evaluated. By encoding the wavefront aberrations into the spatial distribution of focal spots, the system enables quick extraction of wavefront parameters without performing complex iterative reconstructions during real-time operation.
3Adaptability or versatility
If the measurement arrangement position changes relative to the laser beam, then the measurement setup remains flexible, but the measurement results are immediately affected and reliable wavefront analysis becomes difficult or impossible
Solution Approach 1:
The patent inverts the conventional approach by not trying to maintain fixed geometric reference centers, but instead allowing the measurement arrangement to be flexible while extracting wavefront information that is inherently tied to the laser beam's own coordinate system. The focal spot pattern naturally adapts to the beam's position and orientation, eliminating the need for rigid alignment constraints.
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 enables reliable and rapid analysis of wavefront aberrations, allowing for immediate correction of thermally induced aberrations in real-time, enhancing the precision and speed of beam guidance in laser plasma sources.
Implementation Method 1
The beam-splitting optical arrangement has a diffractive structure and is designed to split an incident beam into partial waves having a longitudinal focus offset with respect to one another
Data Source
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AI summary
The invention relates to a method and a device for beam analysis in an optical system, wherein a plurality of beam parameters of a beam propagating along an optical axis (OA) are determined, the method comprising the following steps: splitting the beam into a plurality of partial beams which have a focus offset in the longitudinal direction in relation to the optical axis (OA), capturing a measurement image generated by said partial beams, performing a forward simulation of the beam in the optical system on the basis of estimated initial values for the beam parameters to obtain a simulated image, and calculating a set of values for the beam parameters on the basis of a comparison between the simulated image and the measurement image.