Wavelength Separating Element Using Multiple Mirror Reflections
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Solution Overview
Problem
Existing wavelength separating elements for nonlinear frequency conversion (NLFC) devices are inefficient in removing the fundamental beam, leading to poor beam purity and increased costs due to the use of expensive UV transparent materials and bulky designs, especially in the ultra-violet range between 200 nm and 270 nm.
Innovation Solution
A compact wavelength separating element utilizing multiple reflections off mirror surfaces with high reflectivity for the converted beam and low reflectivity for the fundamental beam, combined with a collimating optic and absorbing or scattering surfaces to enhance beam separation and quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If interference filters with multilayer coating are used to remove the fundamental beam, then the fundamental beam can be filtered, but the transmission efficiency of the converted beam is low (as low as 90%) and additional beam separating elements are needed
Solution Approach 1:
The beam separation function is divided into multiple independent mirror surfaces, each contributing to the overall separation. The fundamental beam undergoes multiple reflections at different mirror surfaces (at least three reflections total), with each reflection incrementally reducing the fundamental beam while preserving the converted beam
Solution Approach 2:
Multiple mirror surfaces act as intermediary elements between the NLFC component and the final beam output. These mirrors mediate the separation process by selectively reflecting the fundamental beam while allowing the converted beam to pass through, achieving gradual purification of the converted beam
2Reliability
If prisms are used to separate the beams, then beam separation can be achieved, but the laser devices become bulky and heavy and the cost increases
Solution Approach 1:
The patent replaces expensive, heavy prism materials with simpler, lighter mirror surfaces that can be made from conventional materials. The mirrors achieve the same beam separation function without requiring the bulky UV-transparent prism materials, reducing both weight and cost
Solution Approach 2:
Instead of using a long beam path through a prism in one dimension, the patent uses multiple reflections at mirror surfaces to achieve separation in a more compact configuration, effectively using the reflection dimension to reduce the overall device footprint
3Reliability
If interference filters are used to remove the fundamental beam, then filtering can be achieved, but additional beam separating elements are needed to further reduce the power of the fundamental beam
Solution Approach 1:
The multiple mirror surfaces perform preliminary separation actions in sequence, with each reflection progressively reducing the fundamental beam power before the beam exits the system. This staged approach achieves high rejection ratios without requiring additional post-separation elements
Solution Approach 2:
The beam separation process continues through multiple successive reflections at different mirror surfaces, maintaining continuous useful action throughout the beam path. Each reflection contributes to the overall separation, ensuring the fundamental beam is progressively eliminated without interrupting the converted beam transmission
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
Achieves high transmission efficiency (>95%) and rejection ratio of the fundamental beam, enabling a compact, cost-effective NLFC device with improved beam quality and purity, particularly suitable for deep ultraviolet light generation.
Implementation Method 1
the reflectivity at the mirror surfaces is high for the converted beam and the reflectivity at the mirror surfaces is low for the fundamental beam
Implementation Method 2
The angle of 90 degrees change in polarisation can be exploited to separate the fundamental and converted beams by using Brewster mirror reflection
Implementation Method 3
The most common variation of this technique uses a light beam with fundamental wavelength that is frequency-doubled resulting in a converted beam with half the fundamental wavelength, a process known as second harmonic generation (SHG)
Data Source
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AI summary
A wavelength separating element is provided for separating a converted beam from a fundamental beam in an NLFC device, wherein the converted beam has a wavelength different from a wavelength of the fundamental beam. The wavelength separating element includes a first mirror surface and a second mirror surface opposite to the first mirror surface. The first and second mirror surfaces may have a high reflectivity of the converted beam relative to a reflectivity of the fundamental beam, and the first and second mirror surfaces are configured such that the fundamental and converted beams undergo multiple reflections between the first mirror surface and the second mirror surface to separate the converted beam from the fundamental beam. The fundamental and converted beams undergo at least three reflections at the first and second mirror surfaces, and/or undergo at least two reflections at one of the first mirror surface or the second mirror surface.