Continuous Diffractive Optical Element via Laser-Heated Dielectric Bulges
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Solution Overview
Problem
Existing diffractive optical elements (DOEs) for laser beam shaping face limitations in achieving high diffraction efficiency due to manufacturing complexities and material constraints, particularly for high-power lasers, with prior methods resulting in limited diffraction efficiency and thermal damage issues.
Innovation Solution
A method involving a laser mirror with a layered structure, where focused heating laser beams create bulges in the dielectric layer, allowing for the production of continuous DOEs with extremely high diffraction efficiency, equivalent to over 2500 steps, without the need for additional material addition or removal, and suitable for high-power lasers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If lithographic etching process is used to produce DOE, then diffraction efficiency can be improved by increasing number of steps, but manufacturing complexity and technical effort increase significantly
Solution Approach 1:
The patent replaces the mechanical lithographic etching process with a direct laser writing process that uses photopolymerization to create the microstructures. This substitution eliminates the need for repeated masking, aligning, and etching steps, thereby reducing manufacturing complexity while achieving continuous height profiles for high diffraction efficiency
Solution Approach 2:
The patent changes the manufacturing approach from subtractive etching to additive photopolymerization. By using two-photon polymerization with focused laser beams, the process directly creates the desired microstructure height profile in a single step, avoiding the iterative etching process and achieving continuous profiles without mechanical complexity
2Manufacturing precision
If polymer material is used for quasi-continuous DOE, then diffraction efficiency equivalent to more than 50 steps is achieved, but thermal damage threshold is too low for high-power lasers
Solution Approach 1:
The patent uses composite materials consisting of glass or plastic substrate combined with photopolymerizable material. The final DOE structure integrates the photopolymerized microstructures with the substrate, creating a composite that maintains the high diffraction efficiency of continuous profiles while achieving the high thermal damage threshold of glass or engineered plastics suitable for high-power laser applications
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 method enables the production of DOEs with very high diffraction efficiency, suitable for high-power lasers, by generating finely graded height profiles and maintaining high reflectivity, overcoming the limitations of previous techniques.
Implementation Method 1
creating a plurality of bulges of the dielectric layer by treating the laser mirror with a series of focused heating laser beams
Implementation Method 2
phase modulations of the laser beam occur due to different optical path lengths at the DOE, resulting in interference patterns
Implementation Method 3
The intensity of the laser beam is spatially modulated by constructive and destructive superimposition
Data Source
AI summary
In one aspect, a method for producing a diffractive optical element for beam shaping of a laser beam having a first wavelength of at least 100 nm includes providing a laser mirror, the laser mirror having a layered structure made of a substrate, a dielectric layer and optionally an absorption layer, the dielectric layer resting against the substrate or the absorption layer being located between the substrate and the dielectric layer. The method also includes creating a plurality of bulges of the dielectric layer by treating the laser mirror with a series of focused heating laser beams having a second wavelength (λ2), the plurality of bulges having a height perpendicular to the dielectric layer, and at least one bulge having a height of at least half the first wavelength (λ1).