UV Laser Frequency Conversion with Crystal Walk-Off Separation
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Solution Overview
Problem
UV-induced deposits on optical surfaces cause losses for both UV and fundamental laser light, particularly in resonators, due to the build-up of contaminants from out-gassing materials, which deteriorate resonance conditions.
Innovation Solution
Spatially separate the fundamental laser light from the generated UV laser light by using a birefringent non-linear crystal with controlled temperature gradients to induce spatial walk-off, ensuring the UV laser light exits at locations separate from the fundamental laser light, thereby preventing contamination from affecting resonance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the fundamental light and frequency-converted UV light exit the non-linear element at a common point, then the optical path is simplified, but UV-induced deposits on optical surfaces cause losses for both UV and fundamental laser light
Solution Approach 1:
The patent divides the non-linear crystal into two distinct portions: a first portion (input end) where phase-matching temperature is maintained for UV generation, and a second portion (output end) where temperature is adjusted to prevent phase-matching. This segmentation allows UV light to be generated only in the first portion and spatially separated from the fundamental beam path in the second portion, eliminating UV-induced deposits on optical surfaces while maintaining efficient frequency conversion.
Solution Approach 2:
Different temperature conditions are applied to different portions of the non-linear crystal. The first portion operates at a temperature providing phase-matching for UV generation, while the second portion operates at a temperature that prevents phase-matching. This local differentiation of thermal conditions enables spatial separation of UV and fundamental beams at the output, resolving the contradiction between optical path simplicity and energy loss prevention.
2Productivity
If UV laser light is generated in a resonant cavity for fundamental laser light, then conversion efficiency is improved, but deposits on optical elements deteriorate the resonator and reduce circulating power
Solution Approach 1:
The non-linear crystal is segmented into two temperature zones: the first portion maintains phase-matching for efficient UV generation within the resonant cavity, while the second portion creates spatial walk-off to separate UV and fundamental beams before they reach the cavity output. This ensures high conversion efficiency while preventing UV-induced deposits from degrading resonator mirrors and optical elements.
Solution Approach 2:
The patent extracts the UV light from the fundamental beam path by creating spatial separation in the second portion of the crystal. The UV light is effectively 'taken out' from the common optical path before reaching the cavity output, preventing it from causing deposits on resonator optical elements while maintaining its generation efficiency in the first portion.
3Productivity
If temperature is uniformly maintained for phase-matching throughout the non-linear crystal, then UV generation efficiency is maximized, but UV light and fundamental light cannot be spatially separated at exit
Solution Approach 1:
The crystal temperature profile is segmented into two zones: the first portion maintains phase-matching temperature for efficient UV generation, while the second portion uses a different temperature to induce spatial walk-off. This thermal segmentation simultaneously achieves high conversion efficiency in the first zone and beam separation in the second zone, resolving the contradiction between productivity and operational ease.
Solution Approach 2:
Different thermal conditions are locally applied to different portions of the crystal. The input end (first portion) has optimized temperature for phase-matching and UV generation, while the output end (second portion) has adjusted temperature to create spatial separation. This local quality differentiation enables both efficient conversion and easy beam separation.
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
Prevents UV-induced contamination from interfering with the fundamental laser light, effectively addressing the UV-induced contamination, enhancing the effectiveness of the technical solution by maintaining resonance conditions for the fundamental laser light.
Implementation Method 1
one way of generating UV laser light is by frequency-doubling of light at 532 nm to obtain UV light at 266 nm
Implementation Method 2
Provided that phase-matching is provided, the amount of frequency-converted light will increase as the fundamental light propagates through the non-linear element
Implementation Method 3
the non-linear crystal exhibits spatial walk-off. The temperature of the non-linear crystal is controlled such that a first portion of the non-linear crystal is maintained at a temperature that provides phase-matching for the conversion of fundamental laser light into UV laser light
Implementation Method 4
It is believed that such deposits form due to photo-fixation or polymerization of various contaminants (particularly carbon-containing contaminants) present in gaseous form at the optical surfaces
Data Source
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AI summary
A frequency conversion apparatus for conversion of one or more fundamental-frequency waves into a frequency-converted wave is disclosed. The frequency conversion apparatus comprises a non-linear element exhibiting spatial walk off between the fundamental-frequency wave(s) and the frequency-converted wave; and at least one temperature control element configured to maintain a first portion of the non-linear element at a first temperature that provides phase matching for the conversion of the fundamental-frequency wave(s) into the frequency-converted wave, and to maintain a second portion of the non-linear element at a second temperature that does not provide phase matching for the conversion of the fundamental-frequency wave into the frequency-converted wave. Thereby, the frequency-converted wave generated in the first portion of the non-linear element is spatially separated from the fundamental-frequency wave by spatial walk off such that the frequency-converted wave and a non-converted portion of the fundamental-frequency wave(s) exit the non-linear element at spatially separated locations.