Laser-induced graphene (LIG) is an emerging technique for producing few-layer graphene or graphene-like material that has recently received increasing attention, due to its unique advantages. Subsequently, a variety of lasers and materials have been used to fabricate LIG using this technique. However, there is a lack of understanding of how different lasers (wavelengths) perform differently in the LIG conversion process. In this study, the produced LIG on polyimide (PI) under a locally water-cooled condition using a 10.6 μm CO₂ infrared laser and a 355 nm ultraviolet (UV) laser are compared. The experimental investigations reveal that under the same UV and CO₂ laser fluence, the ablation of PI show different results. Surface morphologies with micron-sized and nanometer pores were formed by the UV laser under different laser fluences, whereas micron-sized pores and sheet structure with fewer pores were produced by the CO₂ laser. Energy dispersive spectrometry and three-dimensional topography characterization indicate that the photochemical effects were also involved in the LIG conversion with UV laser irradiation. It is also observed through experiments that the photothermal effect contributed to the formation of LIG under both lasers, and the LIG formed on PI substrates by the CO₂ laser showed better quality and fewer layers.

Bacterial biofilms formed on touchable surfaces such as displays of electronic devices not only reduce the product service life, but also cause human health issues. There is an urgent need to research the biofilm formation mechanism and methodologies to prevent formation of biofilms on human touchable surfaces. It has been reported that laser-induced graphene (LIG) helps resist biofilm growth, which has been attributed to the atomic composition and sharp edges of graphene. However, LIG alone was not able to retard bacterial growth completely. It has been reported that LIG incorporated with silver (Ag) nanoparticles exhibited enhanced surface antibacterial activity. As a heavy metal, overdose of Ag is harmful to human health. Therefore, a new biocompatible antibacterial agent to replace or reduce the use of Ag is highly important. In this study, we investigate and compare the effect of LIG doped with two types of nanocrystals, i.e., ZnO and silver (Ag)-doped ZnO, on antibacterial actions. A 355 nm ultraviolet (UV) laser was used to produce LIG on a watercolor paper substrate. Formation of few-layer graphene has been verified by Raman spectra. Escherichia coli (E. coli), a representative of Gram-negative bacteria and Staphylococcus aureus (S. aureus), a representative of Gram-positive bacteria were employed for the investigation of the bacteriostatic properties of the LIG paper substrate. Results show that with the incorporation of either the ZnO nanocrystals or the silver (Ag)-doped ZnO nanocrystals into LIG, the antibacterial effect became stronger. It is further shown that the Ag-doped ZnO nanocrystals have superior antibacterial performance to that of the ZnO nanocrystals. The Ag-doped ZnO nanocrystals are potentially an effective and biocompatible antibacterial agent and yet have a much reduced and acceptable level of Ag concentration.

Ensuring reliable Fresnel diffractive microlenses (FDMLs) performance in humid and low-temperature environments requires integrating superhydrophobicity, de-icing, and anti-icing. This study proposes a novel strategy for fabricating multifunctional FDMLs by combining femtosecond laser ablation with chemical modification. Laser-induced graphene (LIG) lattice-like microstructures were first generated on polyimide (PI) substrates and subsequently integrated with FDMLs. Surface functionalization with perfluorooctyltrimethoxysilane (F13) imparted the devices with robust superhydrophobicity, photothermal anti-icing capability, and electrothermal de-icing performance. The FDMLs achieved a contact angle of 158.3°, a rolling angle of 4.6°, and a surface adhesion force of only 26.1 μN, ensuring excellent easy-cleaning in diverse liquid environments. Photothermal tests demonstrated that under 1000 W/m2 illumination, the FDMLs surface temperature increased to 69 °C within 600 s, effectively delaying ice formation. In addition, electrothermal heating enabled the surface to reach 175.8 °C in just 60 s at 9 V, resulting in complete de-icing within 21 s. Finite-difference time-domain (FDTD) simulations and experimental validations confirmed that the FDMLs retained high-quality optical imaging and focusing capabilities. This work provides a versatile and scalable approach for producing FDMLs with integrated optical and environmental resilience, paving the way for their deployment in outdoor optical systems operating under harsh conditions.