Photo-Thermo-Refractive Diffractive Optical Element for Laser Beam Homogenization
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Solution Overview
Problem
High average power diode pumped solid state lasers often have non-uniform beam modulation and spatial profiles, which are unsuitable for applications requiring a flat spatial profile in the near or far field, such as pumping other lasers, machining, and laser ablation, as conventional beam homogenizers like microlens arrays and crossed cylindrical lens systems are inefficient and difficult to manufacture.
Innovation Solution
A diffractive optical system using a photo-thermo-refractive material with a diffractive optical element that modifies the laser beam phase, providing a uniform intensity profile through a UV-based exposure and heat treatment process, allowing for the fabrication of diffractive optical elements with continuous refractive index variations, which are more efficient and less prone to structural nonuniformities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional microlens arrays are used for beam homogenization, then beam uniformity can be improved, but structural nonuniformities and intensity variations remain in the output beam
Solution Approach 1:
The patent replaces mechanical microlens arrays with a diffractive optical element that uses diffraction rather than refraction to homogenize the beam. The DOE contains a two-dimensional array of diffractive features with periodic spacing that diffracts light to create a uniform intensity profile, eliminating the structural nonuniformities inherent in microlens arrays.
Solution Approach 2:
The patent changes the operating parameters by using diffraction orders (specifically first and second order diffraction) rather than refraction through lenses. The periodic diffractive structure with spacing on the order of the wavelength of light creates interference patterns that result in uniform beam intensity, fundamentally changing the physical mechanism from geometric optics to wave optics.
2Illumination intensity
If conventional crossed cylindrical lens systems are used for beam homogenization, then beam uniformity can be improved, but the system complexity and manufacturing difficulty increase
Solution Approach 1:
The patent combines the functions of multiple optical elements into a single diffractive optical element. The DOE integrates the beam homogenization function that would otherwise require crossed cylindrical lens systems into one component with a two-dimensional array of diffractive features, reducing system complexity while maintaining beam uniformity.
Solution Approach 2:
The diffractive optical element serves multiple functions simultaneously: it homogenizes the beam intensity profile, controls the diffraction patterns, and creates the desired spatial distribution of light. This single element replaces what would otherwise require multiple separate optical components including cylindrical lenses and condensers.
3Illumination intensity
If diffractive structures on the order of the wavelength of light are used, then beam uniformity and intensity variation reduction are improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent uses a master diffractive element as a template to create additional diffractive optical elements. The master DOE is used to imprint or replicate the diffractive pattern onto substrate materials, allowing precise copying of the wavelength-scale features without requiring direct fabrication at that scale, thereby reducing manufacturing precision requirements while maintaining the fine feature dimensions needed for diffraction.
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 solution achieves higher beam uniformity and efficiency, reducing intensity variations by more than 90% and improving the quality of laser beams for various applications, including laser machining and inertial confinement fusion projects, by providing a flat spatial profile and increasing the damage threshold of the optics.
Implementation Method 1
A diffractive optical system using a photo-thermo-refractive material with a diffractive optical element that modifies the laser beam phase, providing a uniform intensity profile through a UV-based exposure and heat treatment process
Implementation Method 2
Because some embodiments of the present invention utilize diffraction structures on the order of the wavelength of light, such larger structural nonuniformity is avoided in the homogenized output beams produced using embodiments of the present invention
Data Source
AI summary
A method of manufacturing a plurality of diffractive optical elements includes providing a partially transmissive slide, providing a first piece of PTR glass, and directing first UV radiation through the partially transmissive slide to impinge on the first piece of PTR glass. The method also includes exposing predetermined portions of the first piece of PTR glass to the first UV radiation and thermally treating the exposed first piece of PTR glass. The method further includes providing a second piece of PTR glass and directing second UV radiation through the thermally treated first piece of PTR glass to impinge on the second piece of PTR glass. The method additionally includes exposing predetermined portions of the second piece of PTR glass to the second UV radiation, thermally treating the exposed second piece of PTR glass, and repeating providing and processing of the second piece of PTR glass using additional pieces of PTR glass.