Homogeneous Pumping of Crystalline Slab Laser Amplifier
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Solution Overview
Problem
Existing laser amplification systems face limitations in achieving high average powers and adjustable pulse repetition frequencies due to non-linear effects and thermal damage, with complex and bulky designs that hinder efficient pumping of the amplification medium.
Innovation Solution
A compact laser amplifier design featuring a double-pumped optically excited single crystalline slab with a composite pump beam created by overlapping source beams from linear arrays, using an optical assembly with specific lens configurations to ensure uniform pumping and minimize thermal effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a single solid-state crystalline medium is used in MOPA architecture with conventional laser diode bar pumping, then high average powers can be achieved, but non-linear effects and thermal damage limit the maximum pulse energy and power
Solution Approach 1:
The patent segments the pump beam into multiple sub-beams that are spatially separated when entering the amplification medium. This is achieved by using an optical assembly with multiple lenses that divide the pump beam from laser diode bars into several sub-beams, which are then superimposed within the amplification medium to create multiple overlapping pump spots. This segmentation reduces the intensity at any single location, preventing thermal damage and non-linear effects while maintaining high average power.
Solution Approach 2:
The patent creates different local pumping conditions within the amplification medium by generating multiple sub-beams with specific spatial distributions. Each sub-beam creates a localized pump region, and the superposition of these sub-beams creates a homogeneous overall pump distribution. This local quality approach ensures uniform energy deposition throughout the amplification medium, avoiding hot spots and thermal damage.
2Power
If laser diode bars are used for pumping, then high power can be delivered, but the fast-axis divergence and non-uniform absorption lead to beam steering, modal distortion and depolarisation
Solution Approach 1:
The patent segments the pump beam from laser diode bars into multiple sub-beams using an optical assembly. Each sub-beam is individually shaped and directed to create a homogeneous pump distribution within the amplification medium. This segmentation approach transforms the inherently non-uniform laser diode bar output into a uniform pump pattern, eliminating beam steering and modal distortion while maintaining high output power.
Solution Approach 2:
The patent merges multiple sub-beams within the amplification medium to create a homogeneous pump distribution. The optical assembly combines several sub-beams that originate from laser diode bars, superimposing them to achieve uniform energy deposition. This merging process consolidates the pump energy into a homogeneous pattern that maintains beam quality and polarization stability.
3Power
If conventional pumping schemes are used with laser diode arrays, then pumping can be achieved, but the design becomes complex and bulky
Solution Approach 1:
The patent employs a universal optical assembly that can work with various laser diode bar configurations and amplification medium types. The optical assembly with multiple lenses is designed to handle different pump power levels and beam parameters, providing a multi-functional solution that simplifies the overall system design. This universal approach reduces the need for specialized components for different operating conditions, thereby reducing complexity and size.
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 design achieves homogenous pumping and efficient amplification with reduced thermal damage, enabling higher power outputs and adjustable pulse repetition frequencies while maintaining a compact and simplified structure.
Implementation Method 1
an optical assembly located between the emitters and the first facet of the amplification medium; the optical assembly having: adjacent the emitters, a first lens in the fast axis configured to act on the pump beam and an array of second lenses in the slow axis, each second lens configured to act on an individual source beam and a third lens, at a spacing from the first and second lenses, configured to act on the pump beam; wherein the individual source beams overlap at the first facet
Implementation Method 2
The input pulse stimulates emission within the amplifier which is added to the input pulse to create a higher output energy pulse
Data Source
Figure 1~2
Figure 3a~3b
Figure 4a~6(b)
AI summary
An apparatus and method for the amplification of a laser beam by pumping a homogenous composite source beam through an amplification medium. A slab crystalline active medium (14) is side-pumped via a pump module having a laser diode bar (18) and an optical assembly. The optical assembly has a fast axis collimator (34) and a lens (36) in the fast axis and an array (40) of slow axis collimators (42) and the lens (36) in the slow axis. The lenses are spaced so that the individual source beams from the emitters are: imaged upon a first facet (24) of the amplification medium; have a beam waist at or near the first facet; are sized to fill the first facet; substantially overlap on the first facet; and are directed so that peripheral source beams undergo total internal reflection on entering the amplification medium. Embodiments of multiple laser diode bars and optical assemblies are described together with double side pumping arrangements.