  This study investigated the formation of multi-voids in polydimethylsiloxane
(PDMS) using a multi-pulse irradiation method and explored the impact of laser
energy, number of pulses per micron (writing speed), and laser spot size (NA)
on the process. The experimental results revealed that multi-void formation
occurred due to multi-pulse irradiation in the bulk of PDMS. Additionally,
increasing laser energy led to an increase in the number of voids, while the
number of voids did not change with an increase in the number of pulses per
micron for a fixed laser parameter. However, the size of the voids increased
with the number of pulses per micron, and tighter focusing conditions (higher
NA) resulted in smaller voids with a shorter distance between them.
Furthermore, Finite-Difference-Time-Domain (FDTD) simulations reproduced the
generation of void arrays in PDMS using a similar multi-laser pulse approach.
By modeling the voids as concentric spheres with densified shells and
simulating the laser interaction with the voids, we showed that void array
generation in PDMS is a linear mechanism. This study provides valuable insight
into the mechanism behind the formation of void arrays in PDMS. The simulation
results agrees well with the experimental results to further validate the model
and gain a better understanding of the physical processes involved in the
generation of void arrays in PDMS.
