Tailored Dopant Profile in Laser Crystals via Float Zone Processing
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Solution Overview
Problem
Existing solid-state lasers with uniform dopant concentration suffer from non-uniform absorption and heat distribution issues, leading to parasitic oscillation, reduced efficiency, and beam quality problems, especially in high-average-power applications.
Innovation Solution
A method of fabricating a single, contiguous laser crystal with a tailored dopant concentration profile using float zone processing, where polycrystalline segments with varying dopant concentrations are arranged to form an ingot, and a heating element creates a moving molten region to achieve a desired dopant distribution along the crystal's length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If high-absorption (highly doped) laser materials are used to achieve efficient pump light absorption, then absorption efficiency is improved, but non-uniform gain distribution and parasitic oscillation occur
Solution Approach 1:
The patent applies local quality by creating a non-uniform dopant concentration profile within the laser crystal, where the dopant concentration varies along the optical axis. Specifically, the concentration is higher at the input end and lower at the output end, optimizing absorption locally at each position rather than using uniform high doping throughout. This resolves the contradiction by maintaining high absorption efficiency at the input while reducing parasitic oscillation at the output.
2Use of energy by moving object
If end pumping geometry is used with high-brightness pump diodes, then pump light absorption is improved, but pump bleaching occurs reducing available ground state ions
Solution Approach 1:
The patent addresses pump bleaching by implementing a dopant concentration gradient that is higher at the input end where pump light intensity is highest. This local increase in dopant concentration compensates for the depletion of ground state ions due to pumping, ensuring sufficient absorption capacity is maintained throughout the crystal length despite the high pumping rates required for end-geometry operation.
3Ease of manufacture
If uniformly doped lasing medium is used, then manufacturing simplicity is maintained, but non-uniform heating and reduced laser efficiency occur
Solution Approach 1:
The patent replaces uniform doping with a tailored dopant concentration profile that varies along the optical axis. This local variation optimizes the balance between pump absorption and heat generation at different positions, improving overall laser efficiency and energy utilization while managing thermal distribution more effectively than uniform doping can achieve.
4Power
If high dopant concentration is used to achieve high gain, then laser output power is improved, but localized heating and mode control problems worsen
Solution Approach 1:
The patent resolves the power-heat contradiction by implementing a dopant concentration gradient that is higher at the input end where pump energy is introduced and lower at the output end where beam extraction occurs. This local differentiation allows high gain and power generation near the pump input while reducing localized heating and maintaining beam quality at the output, preventing thermal lensing and mode distortion.
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 approach results in a lasing medium with uniform heating and emission profiles, enhancing laser efficiency and beam quality by minimizing localized heating and parasitic oscillations, and allowing for the production of high-aspect-ratio slab geometries with improved performance.
Implementation Method 1
moving a heating element along the ingot starting from the first end to a second end of the ingot, the moving heating element creating a moving molten region within the ingot while passing therealong
Implementation Method 2
arranging a plurality of polycrystalline segments together to form an ingot, the polycrystalline segments each having dopant distributed therein
Implementation Method 3
providing a crystal seed at a first end of the ingot
Data Source
AI summary
A lasing medium having a tailored dopant concentration and a method of fabrication thereof is disclosed. The lasing medium has a single crystal having a continuous body having a selected length, wherein the crystal comprises dopant distributed along the length of the body to define a dopant concentration profile. In one embodiment, the dopant concentration profile results in a uniform heating profile. A method of fabricating a laser crystal having a tailored dopant concentration profile includes arranging a plurality of polycrystalline segments together to form an ingot, the polycrystalline segments each having dopant distributed, providing a crystal seed at a first end of the ingot, and moving a heating element along the ingot starting from the first end to a second end of the ingot, the moving heating element creating a moving molten region within the ingot while passing therealong.