Wedge-Shaped Polariser Arrangement for EUV Laser Systems
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High-power laser polarizers face challenges with thermal lensing due to absorption in polarization-selective coatings and require significant installation space to prevent interference between plate elements, limiting their compactness and effectiveness in high-power applications.
Innovation Solution
A polarizer arrangement using plate-shaped optical elements with wedge angles aligned at Brewster's angle, allowing for compact design and high extinction of s-polarized radiation without Fabry-Perot interference effects, even at close distances, by ensuring the beam entry and exit surfaces are not parallel, thus minimizing thermal lensing and space requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If multiple plane-parallel plates are arranged at a small distance from one another to reduce installation space, then the polarizer arrangement becomes more compact, but constructive and destructive interference between reflected partial beams occurs
Solution Approach 1:
The patent applies asymmetry by replacing the symmetric plane-parallel plate configuration with asymmetric wedge-shaped plates. The wedge angle introduces a deliberate geometric asymmetry that prevents parallel beam paths, thereby eliminating the conditions for Fabry-Perot interference while maintaining compact spacing between plates.
Solution Approach 2:
The patent changes the geometric parameters of the optical elements from plane-parallel to wedge-shaped with specific wedge angles. This parameter change fundamentally alters the beam propagation characteristics, causing reflected beams to diverge rather than remain parallel, thus preventing interference effects while allowing compact plate arrangement.
2Reliability
If a polarization-selective coating is applied to increase reflectivity for s-polarized radiation, then the polarization separation is strengthened, but absorption of laser radiation causes temperature-dependent refractive index change and thermal lensing
Solution Approach 1:
The patent extracts and eliminates the problematic polarization-selective coating from the system. Instead of using coated surfaces, it relies on the geometric wedge shape of the plates combined with Brewster angle incidence to achieve polarization separation, thereby removing the source of thermal absorption and thermal lensing.
Solution Approach 2:
The patent substitutes the optical coating approach (which relies on material properties and causes absorption) with a geometric-optical approach using wedge angles and Brewster angle incidence. This replacement eliminates the thermal absorption mechanism while maintaining the polarization separation function.
3Reliability
If the distance between plates is increased to prevent interference, then Fabry-Perot effects are avoided, but the polarizer arrangement requires considerable installation space
Solution Approach 1:
The asymmetric wedge geometry fundamentally changes the beam paths of reflected light, causing them to diverge at different angles. This asymmetry ensures that even when plates are closely spaced, the reflected beams do not recombine to form interference patterns, allowing compact arrangement without sacrificing interference prevention.
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 enables a compact, high-extinction polarizer arrangement that effectively suppresses thermal lensing and interference effects, allowing for efficient p-polarization of laser beams in high-power applications with reduced space requirements.
Implementation Method 1
the beam entry surface of a respective plate-shaped optical element (in the respective plane of incidence) is aligned at Brewster's angle to the laser beam
Implementation Method 2
the problem of constructive and destructive interference between partial beams which are reflected at the beam entry surfaces or at the beam exit surfaces of the plane-parallel plates arises
Data Source
Figure 1~2
Figure 3a~3b
Figure 4~5
AI summary
The invention relates to a polariser arrangement (1) for polarisation of a laser beam (2), comprising: a plurality of plate-shaped optical elements (5, 16) which are arranged in the beam path of the laser beam (2) and which each have a beam entry surface (5a, 6a, ...) for the laser beam (2) and a beam exit surface (5b, 6b, ...) for the laser beam (2), wherein the beam entry surface (5a, 6a, ...) of a respective plate-shaped optical element (5, 16) is oriented at the Brewster angle (OB) relative to the laser beam (2). The beam entry surface (5a, 6a, ...) and the beam exit surface (5b, 6b, ...) of the board-shaped optical elements (5, 16) are in each case oriented at least at a wedge angle (γ1, γ2) relative to one another. The invention further relates to an EUV radiation generating device comprising such a polariser arrangement (1).