Line Narrowing Module With Thermal-Compensated Prism Pair
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Solution Overview
Problem
Existing gas laser devices suffer from chromatic aberration and decreased resolution due to large spectral line widths, which are not adequately addressed by current line narrowing modules, leading to deterioration of beam divergence and spectral line width over time due to thermal distortions in prisms within the expansion optical system.
Innovation Solution
The line narrowing module employs prisms made of materials with opposite temperature coefficients of refractive indices, specifically using calcium fluoride and synthetic quartz for the third and fourth prisms, to control optical path length changes and minimize thermal distortions, ensuring the optical path length difference remains less than half the wavelength of the pulse laser light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a line narrowing module with prisms is used to narrow spectral line width, then spectral line width is reduced, but thermal distortion occurs in prisms causing beam divergence deterioration over time
Solution Approach 1:
The patent applies composite materials by combining prisms made of different materials (calcium fluoride and synthetic quartz) with opposite temperature coefficients of refractive indices. This composite approach allows the thermal distortions of individual prisms to compensate each other, maintaining beam divergence stability while achieving spectral line width narrowing through the grating.
Solution Approach 2:
The patent utilizes parameter changes by selecting materials with opposite temperature coefficients of refractive indices. When temperature changes occur, the refractive indices of the different materials change in opposite directions, causing optical path length changes that compensate for each other, thereby stabilizing beam divergence despite thermal effects.
2Manufacturing precision
If prisms are used to expand beam width for line narrowing, then spectral line width is reduced, but optical path length difference changes with temperature causing wavefront distortion
Solution Approach 1:
The patent employs composite materials by using prisms of different materials (calcium fluoride and synthetic quartz) with opposite temperature coefficients. This combination ensures that temperature-induced optical path length changes in one prism are compensated by opposite changes in the other, stabilizing the optical path length difference and preventing wavefront distortion.
Solution Approach 2:
The patent applies local quality by assigning different material properties to different prisms based on their positions in the optical path. The third prism uses calcium fluoride while the fourth prism uses synthetic quartz, optimizing each local position to contribute to overall thermal compensation of the optical path length difference.
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 wavefront distortion, maintaining stable beam divergence and spectral line width, thereby enhancing the resolution and performance of the gas laser device.
Implementation Method 1
a grating configured to reflect pulse laser light incident thereon
Implementation Method 2
an expansion optical system including a plurality of prisms and configured to cause the pulse laser light to be incident on the grating while expanding a beam width of the pulse laser light
Implementation Method 3
a first closest prism which is closest to the grating and a second closest prism which is second closest to the grating have temperature coefficients of refractive indices opposite in sign to each other
Data Source
AI summary
A line narrowing module to line-narrow pulse laser light having a wavelength in an ultraviolet range includes a grating reflecting pulse laser light incident thereon, and an expansion optical system including prisms and causing the pulse laser light to be incident on the grating while expanding a beam width of the pulse laser light. In the expansion optical system, a first closest prism which is closest to the grating and a second closest prism which is second closest to the grating have temperature coefficients of refractive indices opposite in sign to each other, and an amount of change of an optical path length difference between a case in which a temperature difference in the second closest prism is 0.2° C. or less and a case in which the temperature difference is 0.5° C. or more and 10° C. or less is half or less of the wavelength of the pulse laser light.