Femtosecond Laser Processing Technology for Anti-Reflection Surfaces of Hard Materials

Femtosecond Laser Ablation and Delamination of Functional Magnetic Multilayers at the Nanoscale

Laser nanostructuring of thin films with ultrashort laser pulses is widely used for nanofabrication across various fields. A crucial parameter for optimizing and understanding the processes underlying laser processing is the absorbed laser fluence, which is essential for all damage phenomena such as melting, ablation, spallation, and delamination. While threshold fluences have been extensively studied for single compound thin films, advancements in ultrafast acoustics, magneto-acoustics, and acousto-magneto-plasmonics necessitate understanding the laser nanofabrication processes for functional multilayer films. In this work, we investigated the thickness dependence of ablation and delamination thresholds in Ni/Au bilayers by varying the thickness of the Ni layer. The results were compared with experimental data on Ni thin films. Additionally, we performed femtosecond time-resolved pump-probe measurements of transient reflectivity in Ni to determine the heat penetration depth and evaluate the melting threshold. Delamination thresholds for Ni films were found to exceed the surface melting threshold suggesting the thermal mechanism in a liquid phase. Damage thresholds for Ni/Au bilayers were found to be significantly lower than those for Ni and fingerprint the non-thermal mechanism without Ni melting, which we attribute to the much weaker mechanical adhesion at the Au/glass interface. This finding suggests the potential of femtosecond laser delamination for nondestructive, energy-efficient nanostructuring, enabling the creation of high-quality acoustic resonators and other functional nanostructures for applications in nanosciences.

Editorial for the Topic on Advanced Laser Fabrication Technologies for Cross-Field Applications

The field of laser fabrication technologies has seen remarkable advancements in recent years [...].

High-Transmission Biomimetics Structural Surfaces Produced via Ultrafast Laser Manufacturing

Inspired by periodically aligned micro/nanostructures on biological surfaces, researchers have been fabricating biomimetic structures with superior performance. As a promising and versatile tool, an ultrafast laser combined with other forms of processing technology has been utilized to manufacture functional structures, e.g., the biomimetic subwavelength structures to restrain the surface Fresnel reflectance. In this review paper, we interpret the biomimetic mechanism of antireflective subwavelength structures (ARSSs) for high-transmission windows. Recent advances in the fabrication of ARSSs with an ultrafast laser are summarized and introduced. The limitations and challenges of laser processing technology are discussed, and the future prospects for advancement are outlined, too.

Bioinspired Near-Full Transmittance MgF2 Window for Infrared Detection in Extremely Complex Environments

Due to the extreme complexity of the anti-reflective subwavelength structure (ASS) parameters and the drastic limitation of Gaussian beam manufacturing accuracy, it remains a great challenge to manufacture ASS with ultrahigh transmittance on the surface of infrared window materials (such as magnesium fluoride (MgF₂)) directly by femtosecond laser. Here, a design, manufacturing, and characterization method that can produce an ultrahigh-performance infrared window by femtosecond laser Bessel beam is proposed. Inspired by the excellent anti-reflective and hydrophobic properties of the special structure of dragonfly wings, a similar structural pattern with grid-distributed truncated cones is designed and optimized for its corresponding parameters to achieve near-full transmittance. The desired submicron structures are successfully fabricated by a Bessel beam after effectively shaping the beam. As a practical application, the bioinspired ASS is manufactured on the surface of MgF₂, achieving an ultrahigh transmittance of 99.896% in the broadband of 3-5 μm, ultrawide angle of incidence (over 70% at 75° incidence), and good hydrophobicity with a water contact angle of 99.805°. Results from infrared thermal imaging experiments show that the ultrahigh-transmittance MgF₂ window has superior image acquisition and anti-interference performance (3.9-8.6% image contrast enhancement and more accurate image edge recognition) in an environment with multiple interfering factors, which may play a significant role in facilitating applications of infrared thermal imaging technologies in extremely complex environments.

Hierarchical structure design of sea urchin Shell-Based evaporator for efficient omnidirectional Solar-Driven steam generation

Solar-driven steam generation (SSG) is regarded as a feasible solution to the problem of fresh water scarcity. Although several attempts have been devoted to increase the efficiency of solar-to-steam conversion, it remains difficult to fabricate cost-effective, steady, and multi-angle sunlight-absorbing evaporators from readily available biomass materials. Herein, a novel hierarchical structured SSG evaporator (PDA@Shell-NaClO) is developed through a simple, low-cost, and scalable etching treatment on discarded sea urchin (SU) shells. Attributing to the dedicatedly designed microneedles array structure and porous skeleton structure of the SU shell, this PDA@Shell-NaClO evaporator shows an outstanding average light absorption performance (>90%) in a broad range of angles from 0° to 60° and exceedingly high evaporation rate of 2.81 kg m^-2 h^-1 under one sun condition. Furthermore, the prepared evaporator also maintains an overall stable evaporation performance and exhibits an excellent durability for a long time of up to two weeks in actual seawater. This full-ocean biomass-based SSG evaporator with plentiful raw material availability offers innovative opportunities for large-scale fresh water production.