Continuous Innovation: Manufacturing Optical Components with Higher Laser-Induced Damage Thresholds
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Publish time:
2026-02-05
Continuous Innovation:
Manufacturing Optical Components with Higher Laser-Induced Damage Thresholds
Since the invention of the laser in the mid-20th century, laser technology has evolved over decades from a "monochromatic pulse of red light" into a vast and sophisticated field. It continues to advance towards higher power, narrower pulse widths, and shorter wavelengths, finding applications across numerous disciplines. For instance, China's Shenguang II third-harmonic laser system achieves an average power density of 0.66 GW/cm², with a maximum capability of 1 GW/cm². This ecosystem now also includes high-energy picosecond petawatt (PW, 10¹⁵ W) laser systems and ultra-intense femtosecond (10-15 s) laser systems [1]. Continuous-wave lasers, widely used in industrial, scientific, and military applications, have reached power levels of hundreds of kilowatts. This trend towards higher power, shorter pulses, and shorter wavelengths consistently challenges the laser damage resistance of optical components.
Optical components with high laser-induced damage thresholds (LIDT) are primarily applied in laser industrial manufacturing in the following areas:
Optical components with high laser-induced damage thresholds (LIDT) are mainly applied in the following areas of laser industrial manufacturing:
1. 10-kilowatt Fiber Lasers
With the intelligent transformation and upgrading of domestic manufacturing, laser cutting and welding have been widely applied in areas such as automotive manufacturing, aerospace, and the processing of various high-end metals/non-metals. A large number of 10-kilowatt high-power lasers have emerged, correspondingly driving market demand for optical components with high LIDT.
Figure 1. Application of fiber lasers in laser cutting [2]
2. High-Power Ultraviolet Lasers
Ultraviolet lasers offer unique advantages over other lasers. Due to their small heat-affected zone and excellent focusability, they enable high processing precision. UV laser equipment has been applied in ultra-precision processing for high-end markets, such as surface marking and dicing of 3C products and flexible PCBs, as well as microvia and blind hole drilling in silicon wafers. While some materials weakly absorb visible and infrared light leading to low processing efficiency, UV laser photons possess high energy, and most materials absorb UV light efficiently. However, contradictorily, the absorption of laser radiation by optical components in the UV region also limits their LIDT, representing a key "bottleneck" for the development of high-power UV lasers.
Figure 2. Deep engraving using an ultraviolet laser [3]
Definition of Laser-Induced Damage Threshold (LIDT)
The Laser-Induced Damage Threshold (LIDT) is a crucial parameter characterizing the ability of a medium irradiated by a laser to resist laser-induced damage. Laser damage refers to a detectable permanent change in the properties or structure of an optical material or coating caused by laser irradiation. The high concentration of laser energy can cause local deformation or even complete destruction within or on the surface of the medium. The maximum laser power per unit area that a medium can withstand is called its LIDT.
Mechanisms of Laser-Induced Damage
Laser-induced damage to optical components involves various physical mechanisms during the interaction between the laser and the component, including photoionization, impurity absorption, self-focusing, stimulated Brillouin scattering, nonlinear absorption, optical breakdown, and laser-produced plasmas [4]. C.R. Giuliano pioneered the study of laser-induced damage mechanisms in optical materials [5]. In 1973, the damage of optical materials by lasers was summarized into three main causes: particulate inclusions within the material, self-focusing in the material, and damage caused by plasma formation on the surface [6].
For the industrial manufacturing of modern laser optics, the challenges in improving the LIDT of optical components primarily stem from the optical material itself, polishing-induced subsurface damage from cold processing, and coating layer defects:
1) The intrinsic absorption, nonlinear characteristics, and thermal/mechanical properties of the optical substrate material all influence its damage threshold [4].
2) During cold processing (e.g., polishing), subsurface damage can form due to mechanical stress and embedded abrasives. The mechanisms of laser damage induced by subsurface defects are mainly attributed to three aspects: thermal damage caused by absorptive impurities within the defects, field enhancement due to modulation of the incident light field by the defects, and the weakening of the surface mechanical properties of the component, reducing its resistance to laser damage [7].
3) Factors such as slight absorption in the coating materials, microscopic defects within the coating layers, and the electric field distribution inside the coatings can all potentially initiate laser damage under high-intensity laser irradiation.
Based on extensive theoretical research and practical testing, CASTECH has accumulated rich experience regarding the mechanisms of laser damage in optical components. Through standardized damage testing and analysis of damage morphology, our engineering team recognizes that influencing the LIDT involves multiple factors and constitutes a complex systems engineering challenge: material selection, polishing techniques, surface quality, cleaning processes, coating materials, coating design, deposition processes, and post-coating treatments all impact the LIDT. Therefore, improving the process from only one aspect—be it the optical material, polishing, or coating—is insufficient to significantly enhance the overall laser damage resistance of an optical component.
Figure 3. Substrate damage of an optical component under 100x magnification
Figure 4. Coating damage of an optical component under 100x magnification
Control Methods for High-LIDT Products
Guided by systems thinking, CASTECH has developed a comprehensive set of control methods for manufacturing high-power laser components, forming a complete closed-loop processing chain for such products.
1. Material Aspects
For optical components requiring high LIDT, substrate material selection prioritizes parameters such as high damage resistance, low absorption, and low hydroxyl (OH) content. Examples include Corning 7980 ArF, Corning 7980 KrF, Corning 7979, Suprasil 300, etc. The specific glass grade is selected according to the customer's operating wavelength.
2. Polishing Aspects
Specialized ultra-smooth polishing processes are employed. Surface roughness measured by white-light interferometry can be below 1 Å, with no scratches or digs detectable under 100x magnification, achieving a surface quality of 0/0. Polishing is the most critical process determining the quality of an optical component. Extremely low surface roughness and minimal surface impurities/defects effectively enhance the component's resistance to high-power laser damage.
Figure 5. Surface Roughness Measured by Zygo New View 8300
3. Coating Aspects
Utilizing Ion Beam Sputtering (IBS) technology, and by optimizing the coating design and improving deposition process parameters, the coating absorption can be controlled to below 5 ppm. Extremely low coating absorption significantly reduces the thermal effects induced by laser irradiation on the coating, thereby granting the product higher laser damage resistance in high-power laser applications.
Figure 6. Absorption Curve of a 1064nm Anti-Reflection Coating
Testing of Laser-Induced Damage Threshold (LIDT)
LIDT testing is categorized based on the type of laser used, primarily into continuous wave (CW) laser and pulsed laser damage testing.
Damage from continuous wave (CW) lasers is typically caused by thermal effects due to absorption in the optical coating or substrate.
Laser-induced damage from pulsed lasers is usually dominated by dielectric breakdown. For longer pulse widths or high-repetition-rate laser systems, damage results from a combination of thermally induced damage and dielectric breakdown [8].
CASTECH's testing center primarily conducts LIDT testing using pulsed lasers, following ISO 11254 and ISO 21254 standards. In accordance with these ISO international standards and specifications, we have established four LIDT measurement systems for 266nm, 355nm, 532nm, and 1064nm wavelengths. Figure 7 and Figure 8 show the LIDT test systems for 266nm and 1064nm, respectively.
Figure 7. 266 nm Laser-Induced Damage Threshold Test System
Figure 8. 1064 nm Laser-Induced Damage Threshold Test System
CASTECH employs various LIDT test methods, including R-on-1, S-on-1, 1-on-1, and N-on-1. The appropriate method is selected based on the specific characteristics of the product and customer requirements to monitor the damage threshold of substrate materials, polished components, and coating surfaces. Damage testing not only provides a basis for improving and enhancing the product's LIDT but also, by monitoring the consistency of the LIDT across production batches, ensures the excellent performance of laser components under high-power conditions.
Figure 9. Schematic Diagrams of the Four Damage Test Methods [9]
References
[1] ZHU Jian Qiang, CHEN Shao He, ZHENG Yu Xia, et al. Development of the Shenguang II Laser Facility[J]. Chinese Journal of Lasers, 2019, 46(1): 100002.
[2] Shuangcheng Laser. Market and Future Trends of Fiber Laser Cutting Machines[EB/OL]. https://zhuanlan.zhihu.com/p/460886508
[3] Yeyan. Application of Ultraviolet Lasers in Circuit Board Manufacturing[EB/OL]. http://www.diodelaser.com.cn/htm/laser/qtgy/7057.html
[4] QIU Rong. Research on Laser-Induced Damage of Optical Components by High-Power Lasers[D]. China Academy of Engineering Physics, 2013.
[5] Giuliano C R. Laser-Induced Damage to Transparent Dielectric Materials[J]. Applied Physics Letters, 1964, 5(11): 137-142.
[6] Alexander J, Glass A J, Guenther A H. Laser-Induced Damage of Optical Elements: A Status Report[J]. Applied Optics, 1973, 12(3): 637-649.
[7] Feit M D, Rubenchik A M. Influence of Sub-Surface Cracks on Laser-Induced Sub-Surface Damage[R]. Lawrence Livermore National Laboratory Report, UCRL-CONF-155394, 2003: 1-8.
[8] Guanglian Wanwu OPLC. Laser-Induced Damage Threshold (Part 1)[EB/OL]. https://mp.weixin.qq.com/s/3a__mgA8WKHC4MD47TtT4Q
[9] DOU Ru Feng. Study on Damage Mechanisms and Threshold Measurement of Dielectric Thin Films Induced by Long-Pulse Lasers[D]. Nanjing University of Science and Technology, 2009.
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