Synthetic Diamond Optical Elements with ICP RIE Surface Patterns
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Solution Overview
Problem
Current synthetic diamond optical elements face challenges with high power laser systems due to the limitations of thin film anti-reflective coatings, which are prone to damage and have low laser-induced damage thresholds, and existing methods for forming anti-reflective surface patterns in diamond materials often introduce surface and sub-surface crystal damage, reducing optical performance.
Innovation Solution
An inductively coupled plasma reactive ion etching (ICP RIE) process is used to form anti-reflective and birefringent surface patterns directly in synthetic diamond materials, optimizing periodicity, fill fraction, and aspect ratio to achieve low reflectance, high transmittance, and high laser-induced damage thresholds while minimizing crystal damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If thin film anti-reflective coatings are applied to synthetic diamond optical elements, then reflectance is minimized, but the laser induced damage threshold is reduced
Solution Approach 1:
The patent replaces thin film anti-reflective coatings with a mechanically etched anti-reflective surface pattern directly into the diamond material. This substitution eliminates the weak coating layer that is prone to damage, while maintaining the anti-reflective function through a geometric pattern of grooves or pillars that reduce reflection through gradual refractive index transition.
Solution Approach 2:
The patent creates an anti-reflective surface pattern consisting of an array of grooves or pillars that form a porous-like structure on the diamond surface. This structure gradually transitions the refractive index from air to diamond material, effectively reducing reflectance without requiring a separate coating layer that would have low damage threshold.
2Reliability
If anti-reflective surface patterns are formed directly in diamond material, then laser induced damage threshold is improved, but surface and sub-surface crystal damage is introduced
Solution Approach 1:
The patent optimizes the etching parameters including groove depth (5-20 micrometers), groove width (1-10 micrometers), and spacing between grooves to achieve effective anti-reflective performance while minimizing crystal damage. By carefully controlling these geometric parameters, the etching process removes material only where needed to create the anti-reflective pattern without causing excessive sub-surface damage.
Solution Approach 2:
The patent applies the anti-reflective surface pattern selectively to specific regions of the diamond optical element where reflection reduction is needed, while leaving other regions with intact crystal structure. The localized etching approach ensures that the anti-reflective function is achieved without compromising the overall structural integrity of the diamond material.
3Ease of manufacture
If conventional etching methods are used to form anti-reflective patterns in diamond, then anti-reflective performance is achieved, but optical performance is reduced due to beam aberrations
Solution Approach 1:
The patent replaces conventional chemical or thermal etching methods with a mechanical or precision laser-based etching process that can create clean, well-defined anti-reflective patterns without introducing significant crystal damage or surface irregularities that would cause beam aberrations.
Solution Approach 2:
The patent creates a periodic array of grooves or pillars with regular spacing and consistent geometric dimensions across the diamond surface. This periodic structure provides uniform anti-reflective performance across the optical element, minimizing variations that could cause beam aberrations while maintaining manufacturability through systematic patterning.
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 process effectively reduces reflectance to less than 1% and increases the laser-induced damage threshold, providing high optical performance with minimal beam aberrations and scalability for large areas, suitable for high power laser applications.
Implementation Method 1
inductively coupled plasma reactive ion etching (ICP RIE) process is used to form anti-reflective and birefringent surface patterns
Implementation Method 2
inductively coupled plasma reactive ion etching (ICP RIE) process is used to form anti-reflective and birefringent surface patterns directly in synthetic diamond materials
Data Source
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AI summary
An optical element comprising: synthetic diamond material; and an optical surface pattern formed directly in at least one surface of the synthetic diamond material, wherein the optical surface pattern comprises a plurality of projections separated by trenches, the projections spaced apart with a periodicity d, wherein the periodicity d is between 65 and 99% of a zeroeth order diffraction limit above which non zeroeth diffraction orders are observed at an operating wavelength λ wherein the optical surface pattern has a fill fraction in a range 0.1 to 0.6, the fill fraction defined as [area of projection in one periodic unit]/[area of the periodic unit],and wherein the optical element has an absorption coefficient measured at room temperature of ≤ 0.2 cm-1 at a wavelength of 10.6 μm.