Driver Laser Frequency Shifting for EUV Back-Reflection Suppression
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Solution Overview
Problem
Conventional optical isolators used in driver laser arrangements for EUV radiation generation are susceptible to thermal aberrations and damage at high laser powers, and they cannot completely suppress back-reflected laser radiation, leading to potential damage and incomplete suppression of unwanted power.
Innovation Solution
A driver laser arrangement with a frequency shifting device that reduces the amplification of the first pulse to less than 90% of the maximum amplification, using acousto-optical modulators or other frequency shifting mechanisms to throttle the laser power within the optical amplifiers, allowing for effective suppression of back-reflected radiation by reducing its amplification and power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional optical isolators are used to suppress back-reflected laser radiation, then directional laser radiation suppression is improved, but thermal aberrations and damage occur at high laser powers
Solution Approach 1:
The patent changes the frequency parameter of the laser radiation by introducing a frequency shift between the forward-propagating laser beam and the back-reflected radiation. This frequency differentiation allows the optical isolator to distinguish and suppress the back-reflected radiation without exposing it to the high power conditions that cause thermal damage, as the frequency-shifted radiation can be handled differently by the isolator components.
Solution Approach 2:
The patent introduces a frequency shifting device as an intermediary element between the laser amplifier and the optical isolator. This intermediary shifts the frequency of the back-reflected radiation before it reaches the optical isolator, allowing the isolator to suppress the harmful radiation without directly exposing it to the full power of the amplified laser beam, thereby avoiding thermal damage.
2Reliability
If optical isolators are used to suppress back-reflected laser radiation, then directional control is improved, but complete suppression is not achieved due to power proportion limitations
Solution Approach 1:
The patent applies frequency shifting to change the parameter of the back-reflected laser radiation, creating a frequency difference between the forward and backward propagating beams. This parameter change enables the optical isolator to more effectively differentiate and suppress the back-reflected radiation, reducing the proportion of unwanted power that escapes suppression.
3Productivity
If high laser powers are generated in optical amplifiers, then productivity is improved, but back-reflected radiation causes damage to optical components
Solution Approach 1:
The patent converts the harmful back-reflected laser radiation into a beneficial signal by applying frequency shifting. The frequency-shifted back-reflected radiation can then be suppressed by the optical isolator without damaging the optical amplifier, allowing high power generation to continue safely. The previously harmful reflection becomes a distinguishable signal that can be selectively eliminated.
Solution Approach 2:
The frequency shifting device acts as an intermediary that protects the optical amplifier from damage by modifying the back-reflected radiation before it re-enters the amplifier. This intermediary element enables high power operation by preventing the direct feedback of damaging radiation while maintaining the amplifier's productive function.
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 approach effectively reduces the amplification of back-reflected laser radiation, preventing damage to optical components and ensuring complete suppression of unwanted power, while maintaining high amplification for the main pulse, thereby enhancing the safety and efficiency of the EUV radiation generation process.
Implementation Method 1
at least one frequency shifting device (13) for generating a frequency shift of the laser frequency of the laser radiation (7) relative to a maximum frequency of a frequency-dependent amplification of the at least one optical amplifier (4)
Implementation Method 2
an amplifier arrangement with at least one optical amplifier (4) for amplifying the pulsed laser radiation
Implementation Method 3
frequency-dependent amplification of the at least one optical amplifier
Implementation Method 4
using acousto-optical modulators or other frequency shifting mechanisms to throttle the laser power within the optical amplifiers
Data Source
Figure 1a~1c
Figure 2~3
AI summary
The device relates to a driver laser arrangement (12) for an EUV radiation generation apparatus (1), comprising: a radiation source (2) for generating pulsed laser radiation (7) having a laser frequency (fL), and an amplifier arrangement (3) comprising at least one optical amplifier (4a-c) for amplifying pulsed laser radiation (7). The driver laser arrangement (12) is characterised by at least one frequency shift device (13a-c) for generating a frequency shift of the laser frequency (fL) of the laser radiation (7) relative to a maximum frequency of a frequency-dependent amplification of the at least one optical amplifier (4a-c), and a control device (14), which is designed to set the frequency shift (∆f) such that the amplification (VRED) of the optical amplifier (4a-c) for the laser radiation (7) is reduced to less than 90 %, preferably to less than 70 %, especially preferably to less than 50 % of a maximum amplification (VMAX) of the optical amplifier (4a-c). The invention also relates to an associated method and a computer program product.