Abstract

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