A Comparative Study of Laser-Induced Graphene by CO2 Infrared Laser and 355 nm Ultraviolet (UV) Laser

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

Laser machining sapphire via Si-sapphire interface absorption and process optimization using an integrated approach of the Taguchi method with grey relational analysis

Laser machining of sapphire faces challenges due to the low laser beam energy absorption. A silicon (Si) plate contacting the rear surface of the sapphire substrate was used as an absorptive material to improve the laser absorption and affect material removal from the rear surface. A near-infrared laser with a wavelength of 1030 nm and pulse duration of 2 ns was focused at the interface, causing Si ablation and generation of a plasma plume with immense recoil pressure. The proposed approach for sapphire machining via enhanced laser absorption at the Si-sapphire interface is illustrated, and a probable material removal mechanism is discussed. Effects of processing parameters on machining depth and surface roughness were investigated using Taguchi L27 orthogonal array design and analysis of variance (ANOVA). It is found that repetition rate has the most significant effect on the machining performance characteristics, among other parameters. Furthermore, a multi-objective optimization was performed to optimize the process by integrating the Taguchi method with Grey Relational Analysis (GRA). The maximum machined depth of 59.1 μm and the minimum surface roughness of 0.145 μm were obtained by conducting confirmation tests at the optimal settings. The optimal processing parameters were obtained corresponding to the repetition rate of 1000 kHz, laser fluence of 1.2 J/cm2, hatching distance of 0.01 mm, scanning speed of 1000 mm/s, and single pass. The integrated Taguchi and GRA methodology offers an alternative for optimizing laser machining processes

Feasibility of ANFIS-PSO and ANFIS-GA Models in Predicting Thermophysical Properties of Al2O3-MWCNT/Oil Hybrid Nanofluid

The main purpose of the present paper is to improve the performance of the adaptive neuro-fuzzy inference system (ANFIS) in predicting the thermophysical properties of Al2O3-MWCNT/thermal oil hybrid nanofluid through mixing using metaheuristic optimization techniques. A literature survey showed that the use of an artificial neural network (ANN) is the most widely used method, although there are other methods that showed better performance. Moreover, it was found in the literature that artificial intelligence methods have been widely used for predicting the thermal conductivity of nanofluids. Thus, in the present study, genetic algorithms (GAs) and particle swarm optimization (PSO) have been utilized to search and determine the antecedent and consequent parameters of the ANFIS model. Solid concentration and temperature were considered as input variables, and thermal conductivity, dynamic viscosity, heat transfer performance, and pumping power in both the internal laminar and turbulent flow regimes were the outputs. In order to evaluate and compare the performance of the models, two statistical indices of root mean square error (RMSE) and determination coefficient (R) were utilized. Based on the results, both of the models are able to predict the thermophysical properties appropriately. However, the ANFIS-PSO model had a better performance than the ANFIS-GA model. Finally, the studied thermophysical properties were developed by the trained ANFIS-PSO model

Supplementary document for Investigation into fabrication and optical characteristics of tunable optofluidic microlenses using two-photon polymerization - 6846205.pdf

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