Calcium Fluoride Optics Doped with Magnesium for Laser Durability
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Solution Overview
Problem
Calcium fluoride (CaF2) optics used in excimer laser systems degrade quickly due to fluorine migration and the formation of Ca colloids when exposed to high-power ultraviolet radiation, leading to premature failure, which is not adequately addressed by surface coatings alone.
Innovation Solution
Doping CaF2 crystals with specific amounts of dopants such as magnesium (Mg), strontium (Sr), and barium (Ba) to inhibit the formation of Ca colloids and enhance the bulk durability of the optics, thereby extending their lifespan in high-power laser systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If CaF2 optics are used in high-power excimer laser systems, then ultraviolet transparency and large band gap energy are achieved, but the optics degrade quickly due to fluorine migration and Ca colloid formation
Solution Approach 1:
The patent applies parameter changes by doping CaF2 crystals with specific concentrations of dopants (e.g., 0.01-10% by atomic ratio) to fundamentally alter the material's resistance to fluorine migration and Ca colloid formation, thereby improving laser durability while maintaining ultraviolet transparency
Solution Approach 2:
The patent creates composite materials by combining CaF2 with dopants such as Mg, Sr, Ba, or their oxides/carbides/nitrides to form a new material system that exhibits both the desired optical properties and enhanced resistance to laser-induced degradation
2Object-affected harmful factors
If surface coatings are applied to protect CaF2 optics, then surface degradation is reduced, but bulk degradation from Ca colloid formation is not adequately addressed
Solution Approach 1:
The patent applies preliminary action by incorporating dopants into the CaF2 crystal structure during manufacturing, proactively preventing fluorine migration and Ca colloid formation before they can occur during laser operation, rather than merely addressing surface symptoms after the fact
3Productivity
If higher laser fluence is used to increase processing speed, then productivity improves, but optical element failure occurs more rapidly
Solution Approach 1:
The patent changes the material parameters of the optical element by doping, enabling it to withstand higher laser fluences that would otherwise cause rapid failure, thus allowing increased productivity without sacrificing optical element lifespan
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 doped CaF2 optics exhibit improved laser durability, with reduced transmission loss and extended operational life, capable of withstanding high-energy pulses and radiation exposure without significant degradation, as demonstrated by γ-radiation testing and accelerated laser damage testing.
Implementation Method 1
The laser damage is thought to be the result of fluorine migration from the crystal optic interior or bulk to the surface where the fluorine is lost to the atmosphere
Implementation Method 2
The loss of fluorine from the CaF2 crystal optic results in the formation of F centers which can then combine to form Ca colloids near the surface and within the bulk
Implementation Method 3
calcium fluoride crystals and optics made therefrom with improved laser durability that can be used for the transmission of below 250 nanometer (nm) electromagnetic radiation
Data Source
AI summary
The invention is directed to calcium fluoride crystal optics with improved laser durability that can be used for the transmission of below 250 nanometer (nm) electromagnetic radiation. The optics consists of CaF2 as the major component and Mg in an amount in the range of 13 ppm to 20 ppm while Ce and Mn are <0.5 ppm. The doped crystal and optics made therefrom have a ratio of 515/380 nm transmission loss of less than 0.3 after exposure to greater than 2.8 MRads of γ-radiation. Further, the doped crystal and optics made therefrom exhibit a greatly improved lifetime as shown by ALDT testing to at least 1 billion pulses.