Ho:YAG Laser Four-Pass Pumping Reduces Re-absorption Loss
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Solution Overview
Problem
Three-level solid-state lasers face re-absorption loss issues due to reduced pump intensity along the longitudinal axis of the laser medium, leading to lower laser efficiency and output power in single and double-pass end-pumped configurations.
Innovation Solution
A four-pass end-pumped configuration where the pump beam is canted at a small angle and reflected back through the laser gain medium multiple times, allowing it to pass through the medium at least four times, thereby increasing pump intensity and reducing waste.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a single-pass or double-pass end-pumped configuration is used, then the device complexity is reduced, but the pump intensity along the longitudinal axis decreases leading to re-absorption loss and lower laser efficiency
Solution Approach 1:
The patent transforms the conventional single-pass or double-pass linear pump configuration into a four-pass configuration by introducing angular deviation and reflection. The pump beam is deviated from the longitudinal axis at a small angle and reflected back through the gain medium multiple times, effectively increasing the interaction path dimensionality while maintaining compact geometry. This resolves the contradiction by enabling thorough pump absorption without proportionally increasing system complexity.
Solution Approach 2:
The patent introduces reflective surfaces (mirrors or reflective coatings) as intermediary elements to redirect the pump beam through the gain medium four times. These intermediaries enable the complex four-pass configuration without requiring a fundamentally new pump source or gain medium, thus achieving reduced re-absorption loss while keeping the overall device complexity manageable through the use of standard optical components.
2Quantity of substance
If the laser gain medium length is increased to improve pump absorption, then more pump energy can be absorbed, but the pump intensity at the opposite end becomes insufficient to overcome re-absorption loss
Solution Approach 1:
The four-pass configuration ensures continuous and thorough pump energy absorption throughout the entire gain medium length. By having the pump beam traverse the medium four times in succession, the configuration maintains high pump intensity across the entire medium volume, eliminating the intensity drop-off problem at the opposite end that plagues single-pass and double-pass systems.
Solution Approach 2:
The patent uses angular deviation and reflection to create a multi-pass trajectory through the gain medium. This dimensional approach allows the pump beam to interact with the entire medium length multiple times without requiring the beam to simply travel a longer linear distance, thereby maintaining pump intensity while achieving complete energy absorption.
3Productivity
If a double-pass end-pump configuration is used, then laser extraction efficiency increases compared to single-pass, but pump waste remains and efficiency is limited to around 75%
Solution Approach 1:
The patent applies excessive action by implementing a four-pass configuration instead of the conventional two-pass system. This exceeds the minimum required passes to achieve good pump absorption, ensuring that pump waste is minimized to below 10%. The additional passes guarantee thorough energy extraction from the pump beam, pushing the efficiency beyond the 75% limit of double-pass systems.
Solution Approach 2:
The four-pass configuration extends the continuous useful interaction between pump beam and gain medium, ensuring that pump energy is extracted more completely. Each additional pass contributes to reducing pump waste, and the continuous multi-pass action maintains high extraction efficiency throughout the entire pump process, achieving overall efficiency improvements to 81.2% or higher.
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 significantly increases pump intensity and laser output power while minimizing pump waste, achieving higher efficiency compared to traditional double-pass systems, with measured slope efficiency improvements from 75% to 81.2%.
Implementation Method 1
the opposite end of the medium reflects the beam at a small angle from the original beam
Implementation Method 2
the pump intensity is reduced along the longitudinal axis of the laser medium due to absorption by the laser medium of the pump energy
Implementation Method 3
Laser radiation is emitted from the laser gain medium when the lasing threshold of the bulk of the medium is reached. The lasing process can be understood through the familiar three-level or four-level idealizations
Data Source
AI summary
A laser assembly and method of operating the assembly are described in which a pump beam is directed through an end-pumped solid-state laser gain medium four or more times. The pump beam is directed at a slight angle through a first end of the medium, reflects off the inner surface of the second, opposite end (to form a “V”), and then reflected by an external or integrated mirror back through the first end and off the inner surface of the opposite end again (back through the “V”).