Key Takeaways & Executive Findings
- •• The fs-ms combined pulse laser (CPL) enhances sapphire ablation efficiency by 28 times compared to fs laser alone, achieving 1.73×10^7 μm³/J. • Ablation efficiency increases with ms peak power and duty ratio, but excessive thermal stress causes fragmentation beyond critical thresholds. • In-situ high-speed imaging reveals a four-stage ablation process: defect-creating, melting and ablation, spattering, and fragmentation within 1.5 ms. • The CPL method offers a promising approach for efficient laser damage of transparent, hard, and brittle materials, addressing the challenge of low optical absorption.
Abstract
High-energy continuous wave (CW) lasers are mostly used in laser damage applications, but efficient laser ablation of transparent materials is challenging due to low optical absorption. Considering the potential of femtosecond (fs) laser-induced air filament for high-peak laser transmission over long distances, femtosecond (fs) laser-induced air filaments are combined with a millisecond (ms) laser to form an fs-ms CPL, enhancing the efficiency of sapphire ablation through synchronized spatial-temporal focusing. Experimental results show that ablation efficiency increases with the ms peak power and duty ratio. Excessive thermal stress leads to fragmentation of the sapphire when the ms duty ratio is over 30% at the peak power of 800 W, or when the peak power is over 500 W at a duty ratio of 100%. Also, the mechanism of high-efficiency damage is revealed through in-situ high-speed imaging. According to it, the ablation process went through 4 stages within 1.5 ms: defect-creating, melting and ablation, spattering, and fragmentation. Finally, the equivalent ablation efficiency of the fs-ms CPL is as high as 1.73×107 μm3/J, about 28 times higher compared to the fs laser only. The CPL damage method explored in this paper can provide theoretical guidance for efficient laser damage of transparent materials.
1. Introduction
With the development of high-energy laser technology, continuous wave (CW) laser with output power exceeding several hundred watts to several kilowatts are available, which provides great possibilities for high-energy laser damage of multiple target types [1−4]. In many application scenarios, transparent, hard, and brittle materials are often used as important structural or functional materials, and their absorption of CW laser is usually extremely low, which is typical of hard-to-damage materials [5]. How to realize high-energy laser damage of transparent media has become a new challenge.
Considering that multiple kinds of processes of laser-matter interaction have different requirements for laser absorption [6, 7], combined pulse laser (CPL) has been proposed and extensively studied [8−10]. By compounding the same or different lasers, CPL can fully regulate the distribution of laser energy in time, space, and frequency, so as to meet the demand for laser energy in different processes of laser-matter interaction [11−15]. Various methods, such as reducing excessive energy heating in the molten state by utilizing assisted shocks, or transiently damaging the target through the introduction of higher thermal stresses, are employed [13, 16, 17]. One prominent approach is the nanosecond-CW CPL method, primarily focused on damaging metal targets. The efficiency of target damage is enhanced by sputtering the melt pool via a shock wave induced by the high pulse energy nanosecond laser [18]. In the current research and development of high-energy laser damage, various types of targets can be damaged through the output of several hundred watts to several kilowatts of CW laser with an irradiation time of 1−10 s [19−22]. However, for transparent materials, due to the limitation of CW laser energy density and the extremely low absorption, the long-pulse laser or CW laser alone cannot effectively ablate such difficult-to-damage materials. Meanwhile, as research progresses, the average power of the CW laser has almost entered the bottleneck, and high-power laser equipment becomes large in size and presents significant power supply challenges.
Loading authentic research manuscript (Pages 1–5)...
Yi Zhao-xi, Jia Xian-shi, Chen Yu-yang, Xu Jun-yang, Guo Chuan, Li Kai, Wang Cong, Li Zhou, Han Kai, Ma Zhuang, Duan Ji-an (2025). Millisecond laser processing of sapphire assisted by femtosecond laser-induced air filament. Journal of Central South University. https://doi.org/10.1007/s11771-025-6061-9
Research & Educational Purpose Only:The translations, structured abstracts, analytical annotations, and data reports provided by SinoTechIntel are intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
Copyright & Intellectual Property Notice: Original copyright of the underlying source articles and experimental data remains with the respective authors, institutions, and original publishing journals. SinoTechIntel claims intellectual property only over its proprietary translations, analytical syntheses, and AEO structured enhancements in accordance with international fair use and academic citation principles.
Frequently Asked Questions
What is the main challenge in laser processing of transparent materials like sapphire?
Transparent materials have extremely low optical absorption for continuous wave (CW) lasers, making efficient laser ablation difficult. The fs-ms combined pulse laser (CPL) addresses this by using femtosecond laser-induced air filaments to assist millisecond laser processing, enhancing absorption and ablation efficiency.
How does the fs-ms combined pulse laser improve sapphire ablation efficiency?
The fs-ms CPL combines femtosecond laser-induced air filaments with a millisecond laser, achieving synchronized spatial-temporal focusing. This enhances the ablation efficiency by 28 times compared to fs laser alone, reaching an equivalent ablation efficiency of 1.73×10^7 μm³/J.
What are the critical parameters affecting ablation efficiency and material integrity?
Ablation efficiency increases with ms peak power and duty ratio. However, excessive thermal stress causes fragmentation when the duty ratio exceeds 30% at 800 W peak power, or when peak power exceeds 500 W at 100% duty ratio.
What are the stages of sapphire ablation observed in the study?
In-situ high-speed imaging revealed four stages within 1.5 ms: defect-creating, melting and ablation, spattering, and fragmentation.
What is the significance of this research for industrial applications?
The CPL method provides theoretical guidance for efficient laser damage of transparent materials, which is crucial for applications in manufacturing, defense, and other fields requiring precise processing of hard, brittle, and transparent materials.
Related Technical Papers & Translations
Direct Repair of the Crystal Structure and Coating Surface of Spent LiFePO4 Materials Enables Superfast Li-Ion Migration
The rapid accumulation of spent LiFePO4 (LFP) cathodes from retired lithium-ion batteries necessitates the development of effective and environmental-friendly recycling strategies. In this context, direct regeneration has emerged as a promising approach for reclaiming LFP cathode materials, offering a streamlined pathway to restore their electrochemical functionality. We report an integrated regeneration protocol that simultaneously repairs the degraded crystal structure and reconstructs the damaged carbon coating in spent LFP. The regenerated cathode material had superfast lithium-ion diffusion kinetics and a stable cathode–electrolyte interface, giving a remarkable rate capability with specific capacities of 122 mAh g−1 at 5C and 106 mAh g−1 at 10C (1C = 170 mA g−1). It also maintained capacities of 110.7 mAh g−1 (5C) and 84.1 mAh g−1 (10C) after 400 cycles. It could be used in harsh environments and could be stably cycled at subzero temperatures (−10 and −20 °C) and in solid-state electrolyte batteries. Life cycle assessment combined with economic evaluation using the EverBatt model reveals that this direct regeneration approach has high economic and environmental benefits.
Oxide Semiconductor for Advanced Memory Architectures: Atomic Layer Deposition, Key Requirement and Challenges
Oxide semiconductors (OSs), introduced by the Hosono group in the early 2000s, have evolved from display backplane materials to promising candidates for advanced memory and logic devices. The exceptionally low leakage current of OSs and compatibility with three-dimensional (3D) architectures have recently sparked renewed interest in their use in semiconductor applications. This review begins by exploring the unique material properties of OSs, which fundamentally originate from their distinct electronic band structure. Subsequently, we focus on atomic layer deposition (ALD), a core technique for growing excellent OS films, covering both basic and advanced processes compatible with 3D scaling. The basic surface reaction mechanisms—adsorption and reaction—and their roles in film growth are introduced. Furthermore, material design strategies, such as cation selection, crystallinity control, anion doping, and heterostructure engineering, are discussed. We also highlight challenges in memory applications, including contact resistance, hydrogen instability, and lack of p-type materials, and discuss the feasibility of ALD-grown OSs as potential solutions. Lastly, we provide an outlook on the role of ALD-grown OSs in memory technologies. This review bridges material fundamentals and device-level requirements, offering a comprehensive perspective on the potential of ALD-driven OSs for next-generation semiconductor memory devices.
Laser powder bed fusion of biodegradable Zn-4Cu alloy: Processing, microstructure and properties
Zn's natural degradability and biocompatibility make it a promising candidate for implants, however, its mechanical properties remain insufficient for bone applications. In this study, the performance of Zn was enhanced by developing Zn-Cu alloys via laser powder bed fusion (LPBF). Optimal LPBF parameters for forming stable tracks were achieved by adjusting laser power and scanning speed. Under optimized conditions of 100 W and 100 mm/s, high-density (99.58%) Zn-Cu alloys with improved hardness (68.2HV) and yield strength (160 MPa) were achieved. These improvements are attributed to solid solution strengthening, segregation strengthening, and grain refinement. The Zn-Cu alloys also demonstrated favorable degradation behavior, with a rate of 0.16 mm/year. This degradation is primarily driven by micro-galvanic corrosion between the CuZn5 phase and Zn matrix, along with refined grains and increased grain boundary density. This work demonstrates a viable strategy for fabricating Zn-based implants with enhanced structural integrity and mechanical performance via LPBF.