Gas-Filled Optical Isolator Plasma for EUV Laser Back-Reflection
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Solution Overview
Problem
EUV radiation generating devices face challenges with back-reflection protection and self-lasing, leading to reduced amplification and potential damage to optical components, as conventional optical isolators are limited in power handling and cannot completely suppress back-reflected laser radiation due to thermal lensing and phase shift limitations.
Innovation Solution
A driver laser arrangement with a gas-filled optical isolator that generates a plasma within the chamber to absorb or reflect back-reflected laser radiation, using a plasma ignition threshold adjustable by gas pressure, composition, and excitation laser radiation to effectively suppress back-reflections and self-lasing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional optical isolators (Faraday isolators or electro-optical modulators) are used to filter back-reflected laser radiation, then protection of the beam source is achieved, but the isolators can only handle limited maximum power and would be damaged by high power back-reflected radiation
Solution Approach 1:
The patent changes the physical state of the filtering medium from solid (conventional optical isolators) to plasma (ionized gas). By adjusting gas pressure, composition, and excitation parameters, the plasma can be tuned to absorb or reflect back-reflected laser radiation at high power levels without damage, while allowing forward laser radiation to pass through with minimal attenuation.
2Reliability
If optical isolators based on polarization or phase shift are used, then back-reflected laser radiation can be suppressed, but they can only suppress radiation with specific phase jumps and cannot completely suppress back-reflections from droplets
Solution Approach 1:
The patent uses plasma, whose optical properties (absorption coefficient, reflection coefficient) can be dynamically adjusted by changing gas pressure, composition, and excitation parameters. This allows the plasma to suppress back-reflections across a range of phase conditions, unlike fixed polarization-based isolators.
3Reliability
If the maximum performance limit of the filtering optical element is reached, then back-reflection protection is achieved, but the EUV radiation generating device must be switched off and restarted, causing significant time loss and reduced productivity
Solution Approach 1:
The patent employs dynamically controllable plasma parameters (gas pressure, composition, excitation power) that can be adjusted in real-time to maintain optimal back-reflection suppression without reaching performance limits that would require system shutdown. The plasma can be continuously regenerated and tuned during operation.
4Reliability
If optical isolators are positioned at locations with high laser power (>500 W), then beam source protection is improved, but thermal lensing in the filtering element reduces beam quality and divergence
Solution Approach 1:
The patent uses plasma instead of solid optical isolators, eliminating thermal lensing effects. The plasma's optical properties are controlled by electromagnetic field excitation rather than thermal conduction, allowing high power operation without beam quality degradation.
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 effective plasma back-reflection protection and suppression of self-lasing, preventing damage to optical components and maintaining high amplification efficiency, while allowing for continuous operation without the need for frequent system restarts.
Implementation Method 1
A driver laser arrangement with a gas-filled optical isolator that generates a plasma within the chamber to absorb or reflect back-reflected laser radiation
Implementation Method 2
an optical isolator which includes a polarizer device and a phase shifting device
Implementation Method 3
optical isolators, which are based on the principle of polarization or phase shift
Implementation Method 4
The optical filtering in an optical isolator, which is designed as described above, typically produces a thermal lens in the filtering element of the optical isolator
Implementation Method 5
a plasma generating device for pulsed ignition of a plasma... using a plasma ignition threshold adjustable by gas pressure, composition, and excitation laser radiation
Data Source
Figure 1~4
Figure 5~7
AI summary
The invention relates to a driver laser arrangement (12) for an EUV-radiation-producing device (1), comprising: a radiation source (2) for producing laser radiation (7) propagating in a first direction (R1), an amplifier arrangement (3) comprising at least one optical amplifier (4a-e) for amplifying the laser radiation (7) propagating in the first direction (R1), as well as at least one optical isulator (13). The optical insulator (13) comprises a chamber filled with gas (20), through which the laser radiation (7) propagating in the first direction (R1) passes. The optical insulator (13) also comprises a plasma-generating device (16, 17) designed for the pulsed ignition of a plasma (21) in the gas (20) of the chamber (14), in order to suppress the passage of laser radiation (7a) propagating in a second direction (R2) opposing the first direction, through the chamber (14). The invention also relates to an EUV-radiation-emitting device (1) comprising such a driver laser arrangement (12), a vacuum chamber (11) in which a target material (8) can be arranged, and a beam-guiding device (5) for guiding the laser radiation (7, 7a) propagating in the first direction (R1), from the driver laser arrangement (12) to the target material (8).