Confocal Pulse Stretcher for Laser Systems
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Solution Overview
Problem
Conventional pulse stretchers for high power gas discharge laser systems face limitations in effectively reducing peak power while maintaining pulse length, particularly in integrated circuit manufacture photolithography, where they are sensitive to misalignment and vibrations, and suffer from focusing and re-entry issues.
Innovation Solution
A pulse stretcher design utilizing a multi-pass system with four confocal resonators, each comprising a pair of concave mirrors with a specific radius of curvature, allowing for 12 passes with minimal optics, which is stable and immune to misalignment and vibrations, and includes an optical axis alignment mechanism using a radial mirror positioning mechanism and a wedge optical element to ensure proper alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If conventional pulse stretchers are used to reduce peak power, then pulse length is extended, but the system becomes sensitive to misalignment and vibrations
Solution Approach 1:
The optical delay path is divided into multiple discrete mirror segments (at least four mirrors) arranged in a multi-pass configuration. This segmentation allows the beam to traverse the same optical path multiple times, extending the effective pulse duration while distributing alignment sensitivity across multiple discrete elements rather than a single long path, thereby improving robustness against vibrations and misalignment.
2Duration of action of moving object
If conventional pulse stretchers are used to reduce peak power, then pulse length is extended, but focusing and re-entry issues occur
Solution Approach 1:
The optical path is folded into a multi-dimensional configuration using multiple mirrors arranged in a multi-pass geometry. Instead of a simple linear delay line that suffers from focusing and re-entry problems, the beam traverses a complex three-dimensional path that separates the entry and exit points, eliminating re-entry issues while achieving the required optical delay for pulse length extension.
3Device complexity
If a multi-pass system with minimal optics is used, then device complexity is reduced, but alignment precision requirements increase
Solution Approach 1:
The mirror mounting structures incorporate adjustable elements that allow dynamic alignment of the mirrors during system setup and operation. This dynamic adjustment capability compensates for the high alignment precision requirements inherent in multi-pass configurations, enabling the system to achieve optimal performance while maintaining a compact design with minimal optical elements.
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 design achieves an 80 ns delay with reduced peak power, improved spatial coherence, and increased tolerance to misalignment and vibrations, making it suitable for integrated circuit lithography applications.
Implementation Method 1
Each of the plurality of confocal resonators may comprise a first concave mirror having a radius of curvature and a second concave mirror having the same radius of curvature and separated by the radius of curvature
Implementation Method 2
Each of the plurality of confocal resonators may comprise a first concave mirror having a radius of curvature and a second concave mirror having the same radius of curvature and separated by the radius of curvature
Data Source
AI summary
A gas discharge laser system producing a laser output pulse and a method of operating such a system is disclosed which may comprise a pulse stretcher which may comprise a laser output pulse optical delay initiating optic directing a portion of the laser output pulse along a laser system output pulse optical axis and diverting a portion of the output pulse into an optical delay having an optical delay path and which may comprise a plurality of confocal resonators in series aligned to deliver an output of the optical delay to the laser output pulse optical delay initiating optic; an optical axis alignment mechanism comprising an radial mirror positioning mechanism operable to position the output of the optical delay to the align with the portion of the laser output pulse transmitted along the optical axis of the portion of the laser system output pulse transmitted by the laser output pulse optical delay initiating optic.