EUV Laser Polarization Isolator Retardation Compensation
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Solution Overview
Problem
Current EUV light generation systems face challenges in compensating for retardation occurring in the propagation optical system, which can lead to self-oscillation and limitations in laser amplifier gain, due to the accumulation and transfer of retardation across optical elements.
Innovation Solution
Incorporating a polarization isolator with a reflection retarder that converts the laser beam into an elliptically polarized beam with specific retardation to compensate for the retardation at the propagation optical system, using a reflection retarder disposed to adjust its reflection direction to minimize back reflections and prevent damage to upstream optical components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional propagation optical system is used without retardation compensation, then the device complexity is reduced, but the laser amplifier gain is limited due to self-oscillation caused by accumulated retardation
Solution Approach 1:
A reflection retarder is introduced as an intermediary optical element between the laser amplifier and the propagation optical system. This retarder compensates for the accumulated retardation in the propagation optical system by introducing an equal and opposite retardation, thereby preventing self-oscillation and enabling higher laser amplifier gain without significantly increasing overall system complexity
Solution Approach 2:
The invention changes the polarization state parameter of the laser beam by using a reflection retarder to introduce specific retardation. This parameter change compensates for the retardation accumulated in the propagation optical system, allowing the laser amplifier to operate at higher gains without causing self-oscillation
2Object-affected harmful factors
If the propagation optical system is used without retardation compensation, then the device complexity is minimized, but harmful reflected light reaches upstream components causing potential damage
Solution Approach 1:
The reflection retarder serves as a mediator that not only compensates for retardation but also modifies the polarization state of reflected light. By converting linearly polarized light to elliptically polarized light, the retarder ensures that reflected light does not constructively interfere with upstream components, thereby preventing damage without requiring additional isolation components
Solution Approach 2:
The invention converts the potentially harmful reflected light into a beneficial state by using the reflection retarder to alter its polarization characteristics. The elliptically polarized reflected light no longer causes self-oscillation or damage to upstream components, thus converting a harmful effect into a harmless or even beneficial outcome for system stability
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 prevents returning laser beams from reaching upstream components, reduces the risk of self-oscillation, and increases the gain of the laser amplifier, enabling higher power output by compensating for retardation and preventing damage from reflected light.
Implementation Method 1
a polarizer configured to emit, selecting from the laser beam incident on the polarizer, a laser beam linearly polarized in a predetermined polarization direction
Implementation Method 2
a reflection retarder disposed on an optical path between the polarizer and the propagation optical system to convert, through reflection, the laser beam linearly polarized in the predetermined polarization direction into an elliptically polarized laser beam
Implementation Method 3
having retardation that reduces retardation occurring at the propagation optical system
Data Source
AI summary
A laser apparatus of the present disclosure includes: a master oscillator configured to emit a laser beam; a laser amplifier disposed on an optical path of the laser beam; a propagation optical system disposed on an optical path between the laser amplifier and a target supplied into an EUV chamber in which EUV light is generated; and a polarization isolator disposed on an optical path between the laser amplifier and the propagation optical system. The polarization isolator includes: a polarizer configured to emit, selecting from the laser beam incident on the polarizer, a laser beam linearly polarized in a predetermined polarization direction; and a reflection retarder disposed on an optical path between the polarizer and the propagation optical system to convert, through reflection, the laser beam linearly polarized in the predetermined polarization direction into an elliptically polarized laser beam having retardation that reduces retardation occurring at the propagation optical system.