Two-photon polymerization (2PP) is an effective technique for the fabrication of complex polymeric 3-D micro/nanofeatures and structures using ultrashort pulses from a NIR laser source. The interaction of laser pulses with photoresponsive resin creates a voxel (volumetric pixel) that defines the resolution of the 2PP process. In this work, we present a mathematical model of the 2PP process that considers the effects of radical diffusion and polymerization kinetics on polymerization dynamics. The increase in temperature during the polymerization process and its effect on polymerization kinetics are considered in the model. The developed model is solved numerically to obtain a better understanding of the polymerization dynamics at various time scales. The effects of diffusion and polymerization kinetics on the growth of voxels are analyzed from the presented simulations. A comparison between high and low pulse repetition rate systems is also presented, showing different polymerization dynamics.
Femtosecond lasers have been widely used for the micro structuring of transparent materials for a wide range of
applications. The local change in refractive index by the irradiation of laser pulse has been exploited for optical
applications ranging from optical data storage to the fabrication of waveguides and couplers. In this work, a Ti:Sapphire
femtosecond laser (800nm, ~150 fs and 1 kHz) is used for the fabrication of three dimensional (3D) waveguides in thick
PMMA substrates. The femtosecond laser microfabrication (FLM) system consists of the laser and three translational (X,
Y and Z) stages and one rotational controlled motorized stages. The coordinated motion of these four stages can be used
to generate desired three dimensional pattern inside the transparent material due to refractive index modification. This
work will present the design of 3D waveguide using commercially available solid modeler, the generation of motion
control codes using a customized post processor and the writing of the developed pattern. Also, control of the laser
process parameters to obtain desired feature quality by minimizing self-focusing and self-trapping in PMMA is
discussed. This FLM system along with the 4-axis machining capability can be effectively used for the fabrication of
complex 3D waveguide circuits in a single step process.
Two Photon Polymerization (2PP) is a powerful technique for the fabrication of 2-D and 3-D microstructures by
focusing ultrashort laser pulses inside a polymer resin mixture consisting of concentration of monomer and photo
initiator. By scanning the focused laser beam in the bulk resin, a complex three dimensional pattern could be fabricated
with micrometer resolution. This work presents the current state of our research towards fabricating microstructures
using 2PP with a Ti:Sapphire femtosecond laser working at 800 nm wavelength and a pulse width of about 150 fs. The
maximum pulse repetition rate of the laser system is 1 kHz, which is much smaller than the MHz systems normally used
for the 2PP process. A mathematical model representing the polymerization process is presented. The governing partial
differential equations for the process are solved numerically and the results are discussed. Characterization experiments
are performed on commercially available acrylate monomer and photoinitiator to evaluate polymerization and damage
threshold. In addition, the effects of self-focusing and self-trapping on the fabrication of microfeatures are presented.