The performance of laser ablation generated debris\ud control by means of open immersion techniques have\ud been shown to be limited by flow surface ripple effects\ud on the beam and the action of ablation plume pressure\ud loss by splashing of the immersion fluid. To eradicate\ud these issues a closed technique has been developed\ud which ensured a controlled geometry for both the\ud optical interfaces of the flowing liquid film. This had\ud the action of preventing splashing, ensuring repeatable\ud machining conditions and allowed for control of liquid\ud flow velocity. To investigate the performance benefits\ud of this closed immersion technique bisphenol A\ud polycarbonate samples have been machined using\ud filtered water at a number of flow velocities. The\ud results demonstrate the efficacy of the closed\ud immersion technique: a 93% decrease in debris is\ud produced when machining under closed filtered water\ud immersion; the average debris particle size becomes\ud larger, with an equal proportion of small and medium\ud sized debris being produced when laser machining\ud under closed flowing filtered water immersion; large\ud debris is shown to be displaced further by a given flow\ud velocity than smaller debris, showing that the action of\ud flow turbulence in the duct has more impact on smaller\ud debris. Low flow velocities were found to be less\ud effective at controlling the positional trend of\ud deposition of laser ablation generated debris than high\ud flow velocities; but, use of excessive flow velocities\ud resulted in turbulence motivated deposition. This work\ud is of interest to the laser micromachining community\ud and may aide in the manufacture of 2.5D laser etched\ud patterns covering large area wafers and could be\ud applied to a range of wavelengths and laser types
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