Diode-Pumped Solid-State Laser Beam Shaping for Uniform Thin-Disk Pumping
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Solution Overview
Problem
Diode-pumped thin-disk lasers face challenges in achieving a uniform intensity distribution due to the asymmetric output beams from laser diode arrays, which complicates beam homogenization and symmetry, leading to inefficiencies and potential local damage, especially in high-power applications.
Innovation Solution
A diode-pumped solid state laser system utilizing a beam transformation optical element with a continuous twisted surface and a focusing surface to redirect and focus beamlets into a uniform and symmetrized beam, allowing neighboring beamlets to overlap and create a uniform flat top intensity distribution at the focal plane, simplifying the optical train and eliminating the need for precise alignment with emitter pitch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If standard lens arrays are used for beam homogenisation, then the system is simple, but the intensity distribution becomes highly inhomogeneous due to diffraction effects from fast-axis beam properties
Solution Approach 1:
The patent segments the laser diode array into individual emitter beamlets and processes each beamlet separately through the optical train. By treating each beamlet as an independent unit and applying beam transformation to individual elements, the system achieves uniform intensity distribution without the diffraction problems that affect whole-beam approaches.
Solution Approach 2:
The patent applies different optical transformations to different parts of the beam profile. The beam transformation optical element provides local beamlet rotation and offsetting tailored to each emitter's specific characteristics, creating a customized intensity distribution that achieves uniformity across the pump area while accounting for local fast-axis properties.
2Shape
If micro-prisms or micro-lenses are used to rotate divergence of each emitter, then beam symmetrisation is achieved, but the system becomes difficult to manufacture and alignment-sensitive due to pitch dependence
Solution Approach 1:
The patent extracts the beam transformation function from complex discrete optical elements (micro-prisms, micro-lenses) and implements it through a simplified optical train using standard optical components. By removing the pitch-dependent elements, the system achieves beam symmetrisation without manufacturing complexity or alignment sensitivity.
Solution Approach 2:
The patent uses universal optical elements (lenses, mirrors, beam combiners) that can handle multiple functions: collimation, focusing, and beam transformation. These standard components replace specialized pitch-dependent elements, making the system manufacturable and alignment-tolerant while still achieving the required beam symmetrisation.
3Illumination intensity
If fiber-coupled laser diodes or rod homogenisers are used, then intensity homogenisation is achieved, but system complexity and cost increase
Solution Approach 1:
The patent merges the beam transformation and homogenisation functions into a single integrated optical train. By combining multiple operations (collimation, beamlet rotation, offsetting, and focusing) into one compact system using standard optical elements, it achieves intensity uniformity without the complexity of separate fiber-coupled systems or rod homogenisers.
Solution Approach 2:
The patent creates a simplified optical model that replicates the beam transformation effect without using complex physical homogenisation elements. By using standard optical components arranged in a specific configuration, the system copies the intensity-distribution-modifying effect of rod homogenisers and fiber bundles but without their associated complexity and cost.
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 compact, efficient, and uniform pump beam distribution for solid state lasers, enhancing power scaling while minimizing thermal lensing and thermally induced aberrations, and maintaining high beam quality without the complexity and cost of traditional homogenization methods.
Implementation Method 1
an optical train, located between the laser diode array and the solid state laser, comprising: a beam transformation optical element, positioned to intersect the beamlets, the beam transformation optical element including a first continuous twisted surface in which the fast axis gradient varies along the slow axis, causing beamlet redirection in the fast axis
Implementation Method 2
a focusing surface, positioned to intersect the beamlets from the first continuous twisted surface and focus the beamlets into a uniform and symmetrised beam at a focal plane
Data Source
AI summary
A diode-pumped solid state laser system and a method of diode-pumping a solid state laser in which the emitter beamlets in the diode bar are directed at a beam transformation optical element which includes a continuous twisted surface to produce a uniform and symmetrised beam in the fast field which is then focused to match an input pump area of the gain medium of the solid state laser. Embodiments to square and rectangular flat-top intensity distributions are described using a Fourier lens and a set of cylindrical orthogonal lenses.