High‐Quality Femtosecond Laser Surface Micro/Nano‐Structuring Assisted by A Thin Frost Layer

Abstract

Femtosecond laser ablation has been demonstrated to be a versatile tool to produce micro/nanoscale features with high precision and accuracy. However, the use of high laser fluence to increase the ablation efficiency usually results in unwanted effects, such as redeposition of debris, formation of recast layer, and heat‐affected zone in or around the ablation craters. Here this limitation is circumvented by exploiting a thin frost layer with a thickness of tens of microns, which can be directly formed by the condensation of water vapor from the air onto the exposed surface whose temperature is below the freezing point. When the femtosecond laser beam is focused onto the target surface covered with a thin frost layer, only the local frost layer around the laser‐irradiated spot melts into water, helping to boost ablation efficiency, suppress the recast layer, and reduce the heat‐affect zone, while the remaining frost layer can prevent ablation debris from adhering to the target surface. By this frost‐assisted strategy, high‐quality surface micro/nano‐structures are successfully achieved on both plane and curved surfaces at high laser fluences, and the mechanism behind the formation of high‐spatial‐frequency (HSF) laser‐induced periodic surface structures (LIPSSs) on silicon is discussed.

Nanoscale Dots, Grids, Ripples, and Hierarchical Structures on PET by UV Laser Processing

“…As ripple generation has been suppressed, this result might be considered experimental evidence that the temperature field is the positive feedback mechanism needed for structure formation, as described in [22,28,64]. Interestingly, cooling of the target silicon surface in [61] had the contrary effect and gave rise to high-spatial-frequency LIPSS. In the future, interesting follow-up experiments would include high-speed camera recording of bubble generation during laser processing, water temperature measurements, physicochemical analysis of the liquid after laser irradiation, and nanostructure analysis upon substrate cooling at various temperatures.…”

“…Similarly, the spatial periods diminished by several times, when LIPSS on metals were produced by a femtosecond laser in liquid environments instead of air [60]. Interestingly, a water film that was generated by melting a thin frost layer on the target silicon surface not only increased the quality of laser-ablated microstructures considerably but also gave rise to high-spatial-frequency LIPSS [61]. These were not generated at all without the frost layer, even when the same processing parameters had been applied.…”

Surface Quality and Material Removal Rate in Fabricating Microtexture on Tungsten Carbide via Femtosecond Laser

“…LIPSS includes low-spatial-frequency LIPSS (LSFL) for the wavelength order and high-spatial-frequency LIPSS (HSFL) for the subwavelength order [ 44 , 45 ]. In femtosecond laser machining, HSFL processing has a strong capability to produce high-efficiency and large-area uniform hierarchical nanotextures [ 46 ]. Typically, the direction of the LSFL texture is perpendicular to the polarization direction of the incident laser, whereas the direction the HSFL texture is parallel to the polarization direction of the incident laser [ 47 ].…”

Scanning Strategies in Laser Surface Texturing: A Review

“…An interesting and original effect of the influence of temperature regime on LST processing and LIPSS formation was presented in the newest work by W. Gao et al [ 123 ]. In this work, it was shown that decreasing the laser-processed surface temperature to below the freezing point has the potential to dramatically change the LST process.…”