Laser fabrication of metallic superhydrophobic surfaces (SHSs) for anti-frosting has recently attracted considerable attention. Effective anti-frosting SHSs require the efficient removal of condensed microdroplets through self-propelled droplet jumping, which is strongly influenced by the surface morphology. However, detailed analyses of the condensate self-removal capability of laser-structured surfaces are limited, and guidelines for laser processing parameter control for fabricating rationally structured SHSs for anti-frosting have not yet been established. Herein, a series of nanostructured copper-zinc alloy SHSs are facilely constructed through ultrafast laser processing. The surface morphology can be properly tuned by adjusting the laser processing parameters. The relationship between the surface morphologies and condensate self-removal capability is investigated, and a guideline for laser processing parameterization for fabricating optimal anti-frosting SHSs is established. After 120 min of the frosting test, the optimized surface exhibits less than 70% frost coverage because the remarkably enhanced condensate self-removal capability reduces the water accumulation amount and frost propagation speed (<1 μm/s). Additionally, the material adaptability of the proposed technique is validated by extending this methodology to other metals and metal alloys. This study provides valuable and instructive insights into the design and optimization of metallic anti-frosting SHSs by ultrafast laser processing.

Si₃N₄ ceramics with a microscale rice leaf structure (MRLS) and titanium alloy were connected via brazing, and the influence of the surface microstructure on the ceramic connection was analyzed. MRLS fabrication is an efficient and high-degree-of-freedom method that can be used to change a material’s surface morphology and wettability. The MRLS was obtained at a laser power of 110 W, with line spacings of 100 and 50 μm. The laser-treated surface included nanoparticles and micro particles, exhibiting a coral-like structure after agglomeration. When the MRLS was used to braze the titanium alloy, no defects were observed at the brazing interface, and the formation was excellent. Throughout the brazed joint, the MRLS remained intact and formed a strong metallurgical bond with the brazing filler metal. A finite element analysis was performed to study the cross-sectional morphology after joint fracture; from the load-time curve, it was found that the MRLS on the surface not only helped improve the mechanical occlusion and brazing area at the interface, but also helped generate compressive stress on the Si₃N₄ side. Crack propagation was hindered, thereby increasing the joint strength.

Spot overlapping acts as one of the main concerns in getting ideal results in the laser paint stripping operations. In order to describe the process of paint removal with repetitively pulsed lasers in a scanning scheme, a simplified three-dimensional numerical model is developed and demonstrated to be able to present paint stripping results obtained with movable laser pulses. The influences of spatial overlapping between neighboring pulsed laser spots on the thermal distribution and on the corresponding paint removal are discussed. A series of experiments is designed, and the results agree well with the numerical simulation. It is found that a spot overlapping ratio higher than 50% is able to give uniformly heated zones and hence leads to no paint residues within the stripped region. An experimental linear dependence of laser paint stripping depth on the incident laser energy density is also obtained and may provide a guide for the parameter selection in the laser paint removal operations.

This letter introduces the collinear double-pulse generation method of the electro-optical Q-switched Nd:YAG laser and the rate equations describing its pulse formation dynamics. The two pulses share the same resonator and thus have a natural and highly coaxial characteristic. The effect of the voltage applied on the electro-optic crystal on the pulse energy and temporal waveform was studied. The time interval of the double-pulse laser can be tuned from 80 ns to 10 μs, thus satisfying the needs of a general double-pulse laser. This method is ideal for obtaining a collinear double-pulse laser and can be extended to other lasers.