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Geometric and Surface Analysis of Microchannels Fabricated Using Laser-Induced Plasma Assisted Ablation (LIPAA)
U. Sarma and Shrikrishna N. Joshi

The high transmissivity over a wide range of wavelength makes the laserbased fabrication of microchannels on transparent materials a challenging task and so the application of proper levels of laser parameters viz. pulse power density, pulse duration and pulse repetition rate is of importance. This paper demonstrates the successful fabrication of microchannels on the transparent materials by using a high potential ablation technique known as laser induced plasma assisted ablation (LIPAA). A conventional millisecond Nd:YAG laser was employed to overcome the difficulty of processing a transparent material, polycarbonate (PC) by laser. Full factorial 34 experiments were carried out by varying the laser parameters viz. pulse repetition rate, pulse duration, scanning speed and pulse power density. Their influence on the geometric parameters viz. channel width, channel depth and the channel roughness were studied using response surface methodology (RSM). Analysis of variance (ANOVA) noted that the effect of pulse power density was significant followed by the pulse duration and repetition rate. A microchannel of 250 μm width and 150 μm depth was successfully machined by employing the repetition rate of 40 Hz, pulse duration of 2 ms and pulse power density of 4.79 MW/cm2. Second-order mathematical relations among the input laser parameters, their interactions and the responses were developed. To assess the prediction accuracy of the developed mathematical model, confirmation experiments were planned and performed. The predicted responses obtained by using the mathematical modelling were found in good agreement with the experimental results.

Keywords: Nd:YAG laser, polycarbonate (PC), transparent materials, microchannels, laser induced plasma assisted ablation (LIPAA), response surface methodology (RSM), analysis of variance (ANOVA)

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