Thin Disk Laser Resonator Wavefront Error Cancellation
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Solution Overview
Problem
Thin disk lasers face limitations in achieving high power with high beam quality due to lateral lasing parasitics, thermo-optical distortion, and increased threshold gain, which are exacerbated by the need for multiple optical elements that degrade beam quality and introduce wavefront errors.
Innovation Solution
A multipass architecture using pairs of dielectric reflecting mirrors arranged in a re-entrant optical path with cooperative pathways to cancel disk aberrations and reduce wavefront error, allowing for low saturated gain and polarized laser output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple optical elements are added to increase gain length, then threshold gain is reduced, but wavefront error increases and beam quality degrades
Solution Approach 1:
The patent transitions from a conventional linear resonator to a multipass re-entrant resonator configuration, utilizing multiple passes through the gain medium in a folded optical path. This dimensional change allows the beam to interact with the same optical elements multiple times, effectively increasing the gain length without adding more physical components, thereby avoiding cumulative wavefront errors while maintaining beam quality
Solution Approach 2:
The existing optical elements in the resonator are made to serve multiple functions: the same mirrors and gain disk are traversed multiple times during each resonator round trip. This multi-functionality increases the effective interaction length and threshold gain reduction without requiring additional optical surfaces, thus preventing beam quality degradation from extra elements
2Manufacturing precision
If thin disk geometry is used to reduce thermal lensing, then beam quality is improved, but lateral lasing parasitics increase
Solution Approach 1:
The patent employs a re-entrant resonator geometry with specific mirror positioning that creates an optical path where the beam passes through the thin disk at optimized angles and positions. This preliminary configuration of the optical path pre-combats lateral lasing parasitics by confining the beam within the desired longitudinal mode and preventing parasitic lateral oscillations before they can develop
Solution Approach 2:
The patent modifies the resonator parameters including the re-entrant geometry, mirror curvature, and optical path length to create a mode structure that favors the desired longitudinal lasing mode. By changing these resonator parameters, the system suppresses lateral lasing parasitics while maintaining the thermal advantages of thin disk geometry for beam quality
3Object-affected harmful factors
If high outcoupling fraction is used to reduce circulating intensity, then damage and distortion are mitigated, but threshold gain increases
Solution Approach 1:
The multipass re-entrant resonator enables the laser beam to undergo multiple passes through the gain medium and optical elements in a continuous circulating path. This continuity allows the system to maintain lower circulating intensity per pass (reducing thermo-optical distortion and damage risk) while accumulating sufficient total gain through the multiple passes to overcome the threshold, effectively decoupling the relationship between outcoupling fraction and threshold gain
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 effectively reduces wavefront error, improves beam quality, and enables high-power, single-mode resonator design with minimal impact on the resonator layout, while promoting linearly polarized output.
Implementation Method 1
an intra-cavity reflector assembly having a plurality of dielectric reflecting mirrors
Implementation Method 2
a thin disk of lasing material enables large optical pumping densities, efficient extraction, and importantly, minimal thermo-optical distortion of optical beams in the crystal
Implementation Method 3
structural symmetries to cancel disk aberrations and reduce wavefront error buildup
Data Source
Figure 1
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Figure 2B
AI summary
The present embodiment provides a system and method for lowering the saturated gain level of a thin-disk laser oscillator by multipassing each gain generator in such a way to cancel some of the wavefront error contributions from the disk surfaces. Wavefront aberrations introduced on one pass of the gain disk are canceled through symmetry (140) on successive passes (110,120). The reduced wavefront error significantly improves design space for single-mode resonators. Maximum effectiveness is achieved by rotating the gain disk so that the fold plane-of-symmetry reverses the largest wavefront error or specifically chosen functional forms.