Cascaded Harmonic Generator Inversion for Efficiency
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Solution Overview
Problem
Existing cascaded harmonic triplers face challenges in achieving high conversion efficiency due to the need for tight focusing, which compromises beam quality and leads to UV-induced degradation of crystals, and using larger spots reduces efficiency significantly.
Innovation Solution
A cascaded harmonic generator configuration that includes a first beam combiner, a third harmonic crystal, and a second harmonic crystal, where the fundamental optical beam enters through a beam combiner and propagates sequentially through both crystals, allowing for improved beam alignment and separate beam splitting to enhance conversion efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If tight focusing is used to improve conversion efficiency, then conversion efficiency is improved, but beam quality is compromised due to beam walk-off effect
Solution Approach 1:
The patent inverts the conventional sequence by performing third harmonic generation first, then using the residual fundamental beam for second harmonic generation. This reversal allows the fundamental beam to traverse the third harmonic crystal without being degraded by tight focusing, preserving beam quality while maintaining high conversion efficiency through optimized crystal positioning and beam parameters.
Solution Approach 2:
The patent optimizes beam parameters including spot size, divergence angle, and crystal length to achieve high conversion efficiency without tight focusing. By adjusting these parameters, the system maintains adequate power density in the third harmonic crystal while avoiding the beam walk-off effects that plague tightly focused configurations.
2Productivity
If tight focusing is used to improve conversion efficiency, then conversion efficiency is improved, but UV-induced degradation of the third harmonic crystal occurs
Solution Approach 1:
By reversing the conversion sequence, the patent ensures that the third harmonic crystal processes the fundamental beam at optimized power densities before the beam undergoes second harmonic conversion. This sequencing, combined with optimized crystal positioning, reduces cumulative UV exposure and prevents the degradation that occurs when beams are tightly focused through multiple crystals.
Solution Approach 2:
The patent adjusts beam spot size and power density parameters to maintain high conversion efficiency while keeping UV power density at the third harmonic crystal facets below degradation thresholds. This parameter optimization allows sustained operation without crystal damage.
3Reliability
If larger spot size is used to improve reliability and reduce UV power density, then crystal lifetime is improved, but conversion efficiency drops significantly
Solution Approach 1:
The inverted sequence allows the fundamental beam to generate third harmonics at optimized power density, then the residual fundamental beam (at lower power) undergoes second harmonic generation. This sequencing enables the use of larger spot sizes that improve reliability while maintaining high overall conversion efficiency, as the most demanding conversion occurs first when beam quality is highest.
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 achieves higher conversion efficiency by optimizing power input and reducing beam walk-off effects, while also minimizing UV-induced crystal degradation, resulting in improved reliability and performance.
Implementation Method 1
a third harmonic crystal 28 coupled to the beam combiner 25 for generating a third harmonic optical beam 23 at a third harmonic frequency 3ω from the fundamental optical beam 21 and the second harmonic optical beam 22
Implementation Method 2
a second harmonic crystal 26 configured to generate the second harmonic optical beam 22 from the residual fundamental optical beam 21A
Data Source
Figure 1~2
Figure 3A~3C
Figure 4
AI summary
Cascaded optical harmonic generators and methods for cascaded optical harmonic generation are disclosed. Relative disposition of individual harmonic generators of a cascaded harmonic generator in an optical path of the fundamental optical beam may be reversed. In a third harmonic generator, the fundamental optical beam may enter the third harmonic crystal first, and the second harmonic crystal second. When the fundamental optical beam enters the third harmonic crystal first, the fundamental light may remain non-depleted by second harmonic generation process.