Pulse Stretcher Focal Point Relocation
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Solution Overview
Problem
Lithographic apparatuses face optical damage due to high energy density from laser pulses, particularly when using fold mirrors in folded pulse stretching devices, which can shorten the lifespan of optical components.
Innovation Solution
A pulse stretcher design that includes a beam splitter, con-focal mirrors, and a fold mirror, where the input light beam is diverged or converged to create an intermediate focal point away from the fold mirror, reducing energy density-related damage by recombining beams to achieve longer pulse stretching without increasing irradiance on optical elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If pulse stretching is implemented using a folded configuration with fold mirrors, then the pulse stretcher can be compact and achieve longer pulse delay, but the fold mirrors are exposed to high energy density at the intermediate focal point causing optical damage
Solution Approach 1:
The patent relocates the intermediate focal point from a position near the fold mirror to a different spatial location within the optical cavity by adjusting the curvature radii and separation distance of the confocal mirrors. This dimensional repositioning in the optical path allows the focal point to exist in a region away from the fold mirror surface, thereby avoiding high energy density exposure while maintaining the folded compact configuration and achieving the desired pulse delay.
2Device complexity
If the intermediate focal point is positioned near the fold mirror to maximize pulse delay and utilize available space, then the pulse stretcher achieves compact packaging, but unacceptably high irradiance strikes the mirror causing damage or reduced lifespan
Solution Approach 1:
The patent modifies the optical parameters of the confocal mirror system by adjusting the curvature radii (R1, R2) and separation distance (d) to specific relationships (R1=R2=d for maximum delay, or R1=R2>2d for reduced focal spot size). These parameter changes enable the intermediate focal point to be positioned at a safe distance from the fold mirror while maintaining compact packaging, thus preventing optical damage and extending mirror lifespan.
3Productivity
If higher pulse energy is delivered to increase lithographic throughput, then productivity improves, but the energy density on optical components increases causing accelerated degradation
Solution Approach 1:
The patent creates a non-uniform energy density distribution in the optical cavity by positioning the intermediate focal point away from the fold mirror. This local quality adjustment ensures that high energy density regions are spatially separated from sensitive optical components, allowing higher pulse energies to be delivered for improved productivity without accelerating optics 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 effectively extends the usable lifetime of optical components by distributing energy density more evenly, reducing the risk of damage and prolonging the lifespan of fold mirrors and other optics within the pulse stretching device.
Implementation Method 1
a beam splitter configured to split an input light beam into a first beam and a second beam
Implementation Method 2
a con-focal resonator including a first con-focal mirror and a second con-focal mirror
Implementation Method 3
one or more optical elements in an optical path of the input light beam prior to the beam splitter... such that an intermediate focal point of the first beam is formed at a distance away from the fold mirror
Implementation Method 4
the fold mirror is in an optical path between the first and second con-focal mirrors
Implementation Method 5
The one or more optical elements provide divergence of the input light beam prior to the splitting of the input light beam by the beam splitter
Data Source
AI summary
A pulse stretcher includes a beam splitter configured to split an input light beam into first and second beams, a con-focal resonator including first and second con-focal mirrors, and a fold mirror. The beam splitter, con-focal resonator, and fold mirror are optically arranged such that at least a portion of the first beam is recombined with the second beam into a modified beam after an optical delay of the first beam caused by the optical arrangement. The apparatus further includes one or more optical elements in an optical path of the input light beam prior to the beam splitter such that a focal point of the first beam is formed at a distance away from the fold mirror preventing energy density-related damage to the fold mirror. The apparatus can further include one or more additional optical elements to provide re-conditioning of the modified beam. A related method is also disclosed.