Off-Axis Parabolic Mirror Beam Expander for EUV Laser Alignment
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Solution Overview
Problem
Existing beam guidance devices for generating EUV radiation face challenges in maintaining optimal beam divergence and convergence over long beam paths, especially under varying temperature conditions, leading to potential imaging errors and deposition of target material on optical surfaces.
Innovation Solution
A beam guidance device utilizing two off-axis parabolic mirrors with a movement mechanism to adjust the distance between the mirrors, allowing for precise control of the laser beam's opening angle, thereby influencing its divergence or convergence, and incorporating displaceable deflection mirrors to compensate for beam offsets, ensuring aberration minimization across a wide variation range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the beam diameter is increased to reduce laser radiation intensity on optical surfaces, then the divergence of the laser beam is reduced, but the beam path requires precise alignment through all optical components over long distances
Solution Approach 1:
The patent implements dynamic adjustment of the beam expansion factor by moving at least one parabolic mirror along its axis using a movement device. This allows the system to adapt the beam diameter and divergence in real-time, optimizing both intensity distribution and alignment tolerance for long beam paths. The dynamic capability enables the system to maintain optimal performance under varying thermal conditions and operational requirements.
2Manufacturing precision
If parabolic mirrors are used for beam expansion to achieve error-free imaging, then spherical aberrations are eliminated, but the device complexity increases compared to spherical mirrors
Solution Approach 1:
The patent divides the beam expansion function into two separate parabolic mirrors arranged in a telescope configuration. Each mirror handles a portion of the beam transformation, with the first mirror collimating the divergent beam from the laser and the second mirror expanding it to the desired diameter. This segmentation allows the use of simpler off-axis parabolic segments rather than requiring a single complex mirror, reducing manufacturing and alignment complexity while maintaining imaging quality.
3Adaptability or versatility
If the distance between parabolic mirrors is varied to adjust beam divergence, then the aperture angle can be optimized for long beam paths, but imaging errors may increase
Solution Approach 1:
The system dynamically adjusts the distance between the two parabolic mirrors using a controlled movement device, enabling real-time optimization of beam divergence and aperture angle. This dynamic adjustment allows the system to adapt to different operational conditions and thermal states while maintaining optimal beam quality and minimizing imaging errors throughout the adjustment range.
4Productivity
If CO2 laser is used as driver laser to achieve high conversion efficiency with tin target, then the laser wavelength of 10.6 μm is reflected by rough optical surfaces, but the high radiant power requires large beam diameters
Solution Approach 1:
The patent employs a beam expansion system that transforms the high-power CO2 laser beam into a larger diameter beam with reduced intensity. By adjusting the expansion factor through mirror positioning, the system can optimize the beam parameters to match the requirements of the tin target while maintaining high conversion efficiency. The expandable beam diameter allows flexible adaptation to different power levels and target conditions.
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 solution effectively adjusts the laser beam's characteristics to enhance EUV radiation generation by maintaining low aberrations and ensuring the beam fits through optical components under dynamic thermal conditions, improving the beam's alignment and reducing target material deposition on optical surfaces.
Implementation Method 1
a first off-axis parabolic mirror (15) with a first convexly curved reflective surface (15a) and a second off-axis parabolic mirror (16) with a second concavely curved reflective surface (16a)
Data Source
Figure 1
Figure 2a~2b
Figure 3
AI summary
The invention relates to a beam-guiding device (3) for guiding a laser beam (5) from a driving laser device (2) in the direction of a target position (6), in order to generate EUV radiation, comprising: a device (14) for increasing or reducing the beam diameter (d1) of the laser beam (5), having: a first off-axis parabolic mirror (15) that has a first convexly curved reflective surface (15a), and a second off-axis parabolic mirror (16) that has a second, concavely curved reflective surface (16b). The beam-guiding device (3) comprises a motion device (20) which is designed to alter the opening angle (a) of the laser beam (5) and alter a distance between the first and the second reflective surface (15a, 16a). The invention also relates to a method for adjusting an opening angle (a) of a laser beam (5) in such a beam-guiding device (3).