Laser Unit Polarization Control for EUV Self-Oscillation
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Solution Overview
Problem
The CO2 laser units used in extreme ultraviolet (EUV) light generating systems face issues with self-oscillation due to amplified spontaneous emission (ASE) light, which decreases the amplification factor and affects the output of pulsed laser light and EUV light, and can damage optical components.
Innovation Solution
The laser unit configuration includes a master oscillator and multiple laser amplifiers with discharge electrodes aligned to suppress self-oscillation by using polarization devices and image rotators to control the polarization direction of the ASE light, preventing it from entering the electrodes and reducing reflectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If laser amplifiers are used to increase pulsed laser light output, then the amplification factor increases, but self-oscillation occurs due to ASE light which decreases the amplification factor and can damage optical components
Solution Approach 1:
The patent applies asymmetry by orienting the discharge electrodes in a specific direction that does not align with the polarization direction of the ASE light. This asymmetric configuration prevents the ASE light from being reflected back into the amplifier, thereby suppressing self-oscillation while maintaining high amplification factor and pulsed laser light output.
2Power
If discharge electrodes are added to the laser amplifier, then laser amplification is enabled, but the complexity of the device increases
Solution Approach 1:
The patent applies local quality by specifically orienting only the discharge electrodes in a particular direction relative to the polarization direction of incident light. This localized directional arrangement of electrodes enables the system to suppress self-oscillation without requiring complex overall structural changes, thus achieving laser amplification with minimal increase in device complexity.
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 configuration effectively suppresses self-oscillation, maintaining high output of pulsed laser light and EUV light while protecting optical components, thereby enhancing the performance and reliability of the EUV light generating system.
Implementation Method 1
using polarization devices and image rotators to control the polarization direction of the ASE light, preventing it from entering the electrodes and reducing reflectivity
Implementation Method 2
a laser amplifier disposed between the first polarization device and the second polarization device in the light path of the linearly-polarized incident laser light beam
Implementation Method 3
including a pair of discharge electrodes disposed to oppose each other
Data Source
AI summary
There is provided a laser unit that may include: a master oscillator configured to output a linear-polarized laser light beam; a first polarization device disposed in a light path of the linear-polarized laser light beam and provided with a polarization axis substantially aligned with a polarization direction of the linearly-polarized incident laser light beam; a second polarization device disposed in the light path of the linear-polarized laser light beam and provided with a polarization axis substantially aligned with a direction of the polarization axis of the first polarization device; and a laser amplifier disposed between the first polarization device and the second polarization device in the light path of the linear-polarized laser light beam and including a pair of discharge electrodes disposed to oppose each other, an opposing direction of the pair of discharge electrodes being substantially aligned with the direction of the polarization axis of the first polarization device.