Session: 02-03-01: Session #1: Nanomanufacturing: Novel Processes, Applications, and Process-Property Relationships

Paper Number: 99494

99494 - Fast, Continuous, Projection Multi-Photon 3d Printing 

Multi-photon lithography (MPL) has become the dominant additive manufacturing technique for free-from 3D structuring on the micro/nanoscale. The nonlinearity of the multi-photon absorption process allows for confinement of a polymerized volume, or voxel, to sub-diffraction-limited sizes and for arbitrary placement of the voxel within a volume of photoresist. However, due to the typical point-by-point nature of the MPL process its low throughput often limits it feasibility at the industrial level. Therefore, a focus has been placed on improving the printing rates of MPL.

In this work, a rapid and continuous projection multi-photon lithography system is presented. In the system, a beam from a five kHz amplified femtosecond laser is spatially modulated in amplitude using a digital micro-mirror device (DMD), which allows for high patterning rates. Axial motion control is performed using an air-bearing stage which allows for high translation speeds. Through synchronization of the DMD patterns and stage motion, smooth continuous 3D objects can be printed. The grating effect of the DMD introduces dispersion to the laser pulse. Use of a collecting lens and objective lens in a 4F configuration temporally focuses the pulse at the image plane. This spatiotemporal focusing effect of the laser pulses allows for fabrication of thin, solid 2D layers.

The ability of the system to axially confine polymerization is investigated numerically. The effects of the spatiotemporal focusing process is evaluated by simulating the propagation of the individual component wavelengths of the laser through the optical system, and then combining to obtain the light field about the image plane. This was done using monochromatic coherent Fourier optics with paraxial approximations. Simulation shows spatiotemporal focusing can lead to a light field axially confined to within a one micron thickness. Experimental results also show 2D layers can be printed with micron and sub-micron thicknesses.

Fabrication of 3D structures with arbitrary geometry is demonstrated by printing complex, smooth, curved, aspherical structures. The speed and scalability of the process is shown by printing a millimeter scale structure with a chiral metamaterial-like geometry with a volumetric printing rate greater than 10^-3 mm³ s^-1. The setup can also be used for grayscale digital light processing, by independently varying the patterning rate of the individual DMD mirrors. An application of grayscale printing is demonstrated by locally varying cross-linking density and, as a result, shrinkage in rectangular pillars.

A simulation of the polymerization process is also presented. In this simulation the excited state kinetics of the photoinitiator and the kinetics of the polymerization reaction are modeled. The unknown reaction parameters of the model are determined by fitting simulation results to experimental results from a serial MPL setup. The model is used to analyze the temporal development of the reaction species during photopolymerization. The dominating polymerization reaction species and effects of the photoinitiator excited state kinetics are identified through a sensitivity analysis of the model. The model can be expanded to projection MPL by simulation of the photopolymerization reaction due to the output light field of the Fourier optics simulation discussed above.

Presenting Author: Jason Johnson Purdue University

Presenting Author Biography: Jason E. Johnson is a graduate research fellow at Purdue University pursuing his PhD in Mechanical Engineering under the advisement of Professor Xianfan Xu. His research focuses on the advancement of nanoscale 3D printing, specifically multi-photon lithography.

Authors:

Jason Johnson Purdue University
Paul Somers Purdue University
Zihao Liang Purdue University
Gavin Noel Purdue University
Bryan Boudouris Purdue University
Liang Pan Purdue University
Xianfan Xu Purdue University