Q-switched Laser Device YAG Crystal Axis Arrangement
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Solution Overview
Problem
Existing Q-switched laser devices face challenges in maintaining high pulse laser peak power and linear polarization after wavelength conversion, especially at higher repetition rates, due to thermal issues and birefringence caused by local heating, which limits their application in high-repetition-rate applications like mass imaging devices.
Innovation Solution
The Q-switched laser device arranges the YAG crystallographic axis parallel to the optical axis, combining the excitation volume increase technique and end-cap technique to suppress thermal issues and maintain linear polarization without relying on the low rate excitation technique, allowing for high peak power and efficient wavelength conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the beam diameter of excitation light is expanded to increase total population of inversion, then pulse laser peak power is increased, but the repetition rate cannot be increased simultaneously
Solution Approach 1:
The YAG crystal is segmented into two distinct parts: a doped YAG section for laser oscillation and an undoped YAG section for heat dissipation. This segmentation allows the excitation light to be expanded to increase population of inversion in the doped region while the undoped region handles thermal management, enabling both high peak power and high repetition rate operation
Solution Approach 2:
Different regions of the YAG crystal are given different properties: the doped YAG region contains rare earth elements for laser action, while the undoped YAG region is optimized for thermal conduction. This local differentiation of quality allows simultaneous optimization of laser output and heat dissipation performance
2Power
If excitation light power is increased to raise population of inversion, then pulse laser peak power is increased, but thermal issues and birefringence worsen
Solution Approach 1:
The heat-generating function is extracted from the laser oscillation region. The undoped YAG section is specifically designed to conduct heat away from the doped oscillation region, separating the laser generation function from the thermal management function to prevent thermal issues and birefringence
Solution Approach 2:
The undoped YAG acts as a thermal intermediary between the doped YAG oscillation region and the heat sink. It conducts heat efficiently without containing rare earth elements that would generate additional heat through quantum defect, thus mediating thermal management effectively
3Object-affected harmful factors
If low rate excitation technique is used to suppress thermal issue, then thermal issue is suppressed, but pulse laser peak power and linear polarization deteriorate after wavelength conversion
Solution Approach 1:
The YAG crystal is divided into doped and undoped sections, allowing high-rate excitation of the doped region to maintain high peak power while the undoped region handles heat dissipation, eliminating the need for low-rate excitation and maintaining linear polarization after wavelength conversion
Solution Approach 2:
The laser system uses a composite YAG structure combining doped YAG (for laser oscillation) and undoped YAG (for heat dissipation). This composite approach enables high repetition rate operation with maintained peak power and linear polarization, overcoming the limitations of uniform YAG structures
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 enables the Q-switched laser device to achieve high peak power and maintain linear polarization even at higher repetition rates, making it suitable for applications requiring high-repetition-rate pulse lasers, such as next-generation mass imaging devices.
Implementation Method 1
a laser medium, and a Q-switch arranged on a straight line (i.e., on an optical axis of the laser device) in this order... the laser medium is locally heated within the excitation light irradiation area
Implementation Method 2
The locally heated laser medium causes: local thermal expansion on the laser medium; deformation of the excitation light entrance face
Implementation Method 3
An art that oscillates pulse laser by having a Q-switch inserted in the oscillation system is also known
Implementation Method 4
When the excitation light is entered in the laser medium, the laser medium is heated because of quantum defect
Data Source
AI summary
When an excitation light is entered in a laser medium including a doped (containing rare earth element) YAG, the vicinity of the excitation light entry face is locally heated which generates a birefringence, causing degradation of linear polarization of emitted laser. To avoid such a phenomenon, it was necessary to make the excitation light pulsed and slow down the repetition rate of the pulse. In this device, an undoped YAG is bonded to a excitation light entry face of the laser medium made of a doped YAG. By arranging the YAG <100> axis so as to extend along the optical axis of the laser oscillation system, a linearly polarized pulse laser can be obtained.