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In this paper, we report an approach for tuning the surface morphology and phase of Ge2Sb2Te5 (GST) by using an ultrafast laser in a one-step process. Four surface micro/nanostructures with specific phase states were sequentially formed by changing the pulse energy: the modified ripple structure, the completely crystallized structure, the ablated nanodots, and the ablated ripple structure. A high correlation existed between the surface micro/nanostructures and their property. Through integrated property–structure modulation, multifunctional optical recording could be achieved by using modified ripples with specific crystallized phase states. The geometric grating morphology caused by the volume shrinkage effect during crystallization enabled modified ripples to exhibit a structural color based on the grating’s diffraction effect. Moreover, the considerable change in the reflectivity of the crystallized area enabled easy grayscale identification. On the basis of the spatially resolved phase-transition threshold effect, the integrated modulation of the geometric nanograting proportion and degree of crystallization was conducted in multilevel states. Notably, different from the fixed ablated surface structures, the printed modified surface structures could be erased and rewritten by controlling its phase state. This paper presents a promising method for producing dynamic tunable metasurfaces, conducting optical anticounterfeiting, and achieving information storage.

Laser transmission welding (LTW) is an excellent process for joining plastics and is widely used in industry. Numerical simulation is an important method and area for studying LTW. It can effectively shorten the experimental time and reduce research costs, aid in understanding the welding mechanism, and enable the acquisition of ideal process parameters. To enhance understanding of numerical simulation studies on LTW and facilitate research in this area, this paper presents a comprehensive overview of the progress made in numerical simulation of LTW, covering the following aspects: (a) characteristics of the three heat source models for LTW temperature field simulation, including surface heat source model, volumetric heat source model, and hybrid heat source model, along with the methods, results, and applications of temperature field simulation based on these models and experimental validation; (b) numerical simulation of thermal and residual stresses based on the temperature field; (c) numerical simulation of the melt flow field; and (d) predictive simulation of material degradation. The conclusion of the review and the prospects for further research work are eventually addressed.

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