Multi-pass Laser Amplifier with Varied Dopant Concentration
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Solution Overview
Problem
Conventional laser amplifiers face issues with non-uniform heating and thermal stress due to uniform dopant distribution, leading to excessive amplified spontaneous emission (ASE) and excited state absorption (ESA), which limits gain and causes thermal aberrations, especially in high gain lasers.
Innovation Solution
A laser amplification system with a master oscillator, multi-pass pre-amplifier, and single-pass power amplifier, utilizing ceramic Nd:YAG slabs with varied dopant concentration along length and cross-section, and side-pumped using diode bars with a wider emission bandwidth, allowing for progressive absorption lengths and reduced ASE/ESA thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If uniformly doped gain medium is used, then manufacturing is simple, but non-uniform heating and thermal stress occur causing internal strain
Solution Approach 1:
The patent applies local quality by implementing non-uniform dopant concentration distribution within the gain medium. Specifically, the dopant concentration varies spatially - higher at the edges and lower at the center - to create localized properties that compensate for non-uniform heating patterns during longitudinal pumping, thereby reducing thermal stress and internal strain.
2Use of energy by moving object
If longitudinal pumping with single wavelength is used, then pump efficiency is high, but excessive ASE and ESA occur limiting gain
Solution Approach 1:
The patent applies parameter changes by carefully controlling the pump beam diameter and dopant concentration to optimize the balance between pump absorption efficiency and ASE/ESA suppression. By adjusting these parameters, the system achieves high pump efficiency while maintaining gain medium excitation for desired coherent laser radiation.
3Use of energy by moving object
If high dopant concentration is used, then pump absorption is improved, but ASE and ESA thresholds are reduced
Solution Approach 1:
The patent applies local quality by implementing spatially varying dopant concentration - higher at the edges where pump absorption is needed and lower at the center where ASE/ESA are more problematic. This non-uniform distribution optimizes both pump absorption efficiency and maintains higher ASE thresholds.
4Temperature
If outer surfaces are cooled, then thermal management is improved, but internal stress increases due to temperature gradient
Solution Approach 1:
The patent applies local quality by creating non-uniform dopant concentration that compensates for the temperature gradient caused by external cooling. The varying dopant distribution adjusts the local absorption and gain characteristics to counterbalance the thermal stress induced by cooling the outer surfaces while maintaining internal temperature differences.
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 system achieves reliable operation over a large temperature window, reduces thermal sensitivity, and increases peak and average power levels while minimizing thermally induced aberrations, enabling efficient and compact high-power laser transmission.
Implementation Method 1
The pump source generates a population inversion in the gain medium
Implementation Method 2
the gain medium amplifies light traveling therein
Implementation Method 3
The light in the cavity forms resonant standing waves having a frequency equal to n(c/2D)
Implementation Method 4
a thermoelectric cooler (TEC) controller for stabilizing pump source temperature in a desired absorption band
Data Source
AI summary
A laser amplification system is disclosed that enables reliable operation over large ambient temperature operating window, as well as a significant reduction of laser temperature sensitivity typically associated with diode pumped lasers. The techniques employed by the system effectively eliminate damaging gain hot spots and lower ASE and ESA thresholds, thereby increasing laser peak and average power levels. Additionally, the techniques allow for thermal programming of active gain medium material to minimize thermally induced aberrations. In one particular example embodiment, a variable dopant concentration multi-pass laser amplifier is provided having a customized active ion concentration profile, tailoring the combination of laser absorption and gain distribution using a ceramic YAG host.