Research on Thermal Effect and Laser-Induced Damage Threshold of 10.6 µm Antireflection Coatings Deposited on Diamond and ZnSe Substrates

At a Glance

Metadata	Details
Publication Date	2025-04-30
Journal	Coatings
Authors	Xiong Zi, Xinshang Niu, Hongfei Jiao, Shuai Jiao, Xiaochuan Ji
Institutions	Tongji University, Shanghai University
Analysis	Full AI Review Included

Technical Documentation & Analysis: High-Power 10.6 µm AR Coatings on CVD Diamond

This document analyzes the findings of the research paper “Research on Thermal Effect and Laser-Induced Damage Threshold of 10.6 µm Antireflection Coatings Deposited on Diamond and ZnSe Substrates” to highlight the superior performance of CVD diamond substrates and connect these requirements directly to 6CCVD’s advanced material capabilities.

Executive Summary

The research conclusively validates CVD diamond as the optimal substrate for high-power 10.6 µm CO₂ laser optics, significantly surpassing the performance of traditional ZnSe.

Superior Thermal Management: The high thermal conductivity of diamond (2000 W/(m·K)) resulted in a 36% reduction in maximum surface temperature rise (62.5 °C) compared to ZnSe (96.63 °C) under continuous wave (CW) laser irradiation.
Enhanced LIDT: Antireflection (AR) coatings deposited on CVD diamond achieved a Laser-Induced Damage Threshold (LIDT) of 15,287 W/cm², representing a 28.5% improvement over the ZnSe baseline (11,890 W/cm²).
Reduced Thermal Distortion: Diamond substrates exhibited a significantly more uniform temperature distribution and lower temperature gradients (reduced from 18.2 °C lateral difference in ZnSe to 0.1 °C in diamond), minimizing thermal lensing and wavefront degradation.
Spectral Efficiency Maintained: The ZnS/YbF₃ 9-layer AR coating achieved excellent spectral properties, maintaining >98% transmittance at the target wavelength of 10.6 µm on both substrates.
Critical Failure Analysis: While diamond offers superior performance, damage under extreme power density was characterized by localized melting, fracture, and the formation of graphite (002) phase, indicating a need for high-purity, defect-free SCD material.

Technical Specifications

The following table summarizes the critical performance metrics and material properties extracted from the study, demonstrating the performance gap between diamond and ZnSe for high-power applications.

Parameter	Diamond (SCD) Substrate	ZnSe Substrate	Unit	Context
Laser-Induced Damage Threshold (LIDT)	15,287	11,890	W/cm²	28.5% improvement using diamond
Maximum Temperature Rise (ΔT)	62.5	96.63	°C	Under 2830 W/cm² CW irradiation
Thermal Conductivity (k)	2000	16	W/(m·K)	Key driver for thermal stability
Maximum Lateral Temp Gradient	0.1	18.2	°C	Diamond minimizes thermal lensing
Transmittance (10.6 µm)	98.04	98.48	%	AR coating performance
Thermal Expansion Coefficient (α)	1.1 x 10^-6	7.1 x 10^-6	K^-1	Low α minimizes stress-induced cracking
Surface Roughness (RMS Ra)	2.3	2.5	nm	Measured post-deposition
Substrate Dimensions Used	Φ25.4 x 1	Φ25.4 x 1	mm	Standard test dimensions

Key Methodologies

The experiment focused on fabricating and characterizing 10.6 µm AR coatings on high-quality CVD diamond and ZnSe substrates under high-power CW laser conditions.

Substrate Selection: CVD single-crystal diamond (SCD) and ZnSe wafers (Φ25.4 x 1 mm) were used.
Coating Design: A 9-layer ZnS/YbF₃ stack, totaling 1.5 µm thickness, was designed using OptiLayer software to achieve high transmittance at 10.6 µm.
Substrate Preparation: Substrates were cleaned using an ion beam (120 V, 40 mA) prior to deposition to enhance film adhesion.
Film Deposition:
- System: Leybold ARES 1110 vacuum deposition system.
- Process Conditions: Vacuum of 8 x 10^-6 mbar; Substrate temperature maintained at 150 °C.
- Materials: ZnS deposited via thermal evaporation (1.0 nm/s); YbF₃ deposited via ion-assisted thermal evaporation (0.5 nm/s) to improve film quality and reduce moisture absorption.
Performance Testing:
- Temperature Rise Test: 50 W CW laser (2830 W/cm²) irradiation for 200 s; temperature monitored via thermocouple.
- LIDT Test: 10.6 µm CW laser, R-on-1 test protocol (60 s irradiation time per step), 1.5 mm spot diameter.
Damage Analysis: Post-irradiation analysis utilized microscopy and X-ray Diffraction (XRD) to confirm damage morphology and the presence of localized graphitization on the diamond surface.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the high-specification diamond materials required to replicate and advance the findings of this research, enabling the next generation of high-power laser systems.

Applicable Materials

To achieve the superior thermal and LIDT performance demonstrated in this study, researchers and engineers require high-purity, low-absorption Single Crystal Diamond (SCD) substrates.

Optical Grade SCD: 6CCVD provides high-quality, low-birefringence SCD wafers, essential for minimizing inherent absorption (extinction coefficient 2.61 x 10^-6 at 10.6 µm) and preventing localized heating that leads to graphitization and fracture under extreme power density.
Polycrystalline Diamond (PCD): For applications requiring larger output windows, 6CCVD offers PCD wafers up to 125 mm in diameter, providing excellent thermal conductivity for scalable high-power systems.

Customization Potential

The study utilized standard 25.4 mm diameter substrates. 6CCVD’s manufacturing capabilities allow for immediate scale-up and precise customization to meet specific system integration needs.

Requirement from Paper	6CCVD Capability	Value Proposition
Substrate Size	Wafers up to 125 mm (PCD) and custom SCD dimensions. Substrate thickness up to 10 mm.	Enables large-aperture output windows for high-power beam delivery systems.
Surface Quality	Guaranteed polishing quality: Ra < 1 nm (SCD) and Ra < 5 nm (Inch-size PCD).	Exceeds the paper’s measured roughness (2.3 nm), minimizing scattering and absorption losses critical for maximizing LIDT.
Coating Interface	Custom metalization services (Au, Pt, Pd, Ti, W, Cu) available.	Allows for integration of specialized bonding layers or electrode structures required for advanced optical assemblies, complementing the ZnS/YbF₃ AR stack.
Thickness Control	SCD thickness range: 0.1 µm to 500 µm.	Provides flexibility for thin optical windows or robust, thick substrates depending on mechanical and thermal requirements.

Engineering Support

The research highlights the critical trade-off between diamond’s superior thermal properties and the risk of localized graphitization under high power. 6CCVD’s in-house PhD engineering team specializes in mitigating these risks.

Material Selection for High-Power CO₂ Systems: We provide consultation on selecting the optimal diamond grade (SCD vs. PCD) and thickness to balance thermal dissipation, mechanical strength, and optical purity for 10.6 µm applications.
Thermal Modeling Assistance: Our team can assist customers in integrating 6CCVD material parameters (k = 2000 W/(m·K), low α) into thermal simulation models to predict and optimize performance, minimizing the risk of thermally induced surface distortion and failure observed in the paper.
Global Supply Chain: 6CCVD ensures reliable, global shipping (DDU default, DDP available) of high-value diamond optics, supporting international research and manufacturing timelines.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

In this study, ZnS/YbF3-10.6 µm antireflection (AR) coatings were fabricated on CVD single-crystal diamond and ZnSe substrates. The spectral characteristics of the coatings and their performance under continuous wave laser radiation at 10.6 µm were systematically investigated. The fabricated AR coatings exhibited excellent spectral properties in the target wavelength range. Both theoretical calculations and experimental results indicated that, at the same power density, the 10.6 µm AR coatings on diamond substrates exhibited a lower temperature rise compared to those deposited on ZnSe substrates. Due to its high thermal conductivity, the diamond substrate is expected to exhibit reduced thermally induced surface distortion. The laser-induced damage threshold (LIDT) test results indicate that the AR coating deposited on the ZnSe substrate exhibits a damage threshold of 11,890 W/cm2, whereas the AR coating on the diamond substrate achieves a threshold of 15,287 W/cm2, representing a 28.5% improvement over the ZnSe substrate. Additionally, graphite formation occurs on the diamond substrate under high power density. These findings provide both theoretical and experimental support for the potential application of diamond materials in high-power laser systems.

Tech Support

Original Source

DOI: https://doi.org/10.3390/coatings15050536

References

2015 - High Precision Materials Processing Using a Novel Q-Switched CO2 Laser [Crossref]
2014 - Dielectric Laser Accelerators [Crossref]
2020 - Microscale Laser-Driven Particle Accelerator Using the Inverse Cherenkov Effect [Crossref]
2023 - Optimization of Extreme Ultra-Violet Light Emitted from the CO2 Laser-Irradiated Tin Plasmas Using 2D Radiation Hydrodynamic Simulations [Crossref]
2025 - Enhancing Surface Properties of Monocrystalline Silicon Wafers via Thermal Annealing for Solar Cell Texturing [Crossref]
2012 - High-Power γ-Ray Flash Generation in Ultraintense Laser-Plasma Interactions [Crossref]
1974 - Optical Distortion of Heated Mirrors in CO2-Laser Systems [Crossref]
1999 - The Potential of CVD Diamond as a Replacement to ZnSe in CO2 Laser Optics [Crossref]
2020 - Power Scaling and Spectral Linewidth Suppression of Hybrid Brillouin/Thulium Fiber Laser [Crossref]