Experimental and Theoretical Study of Femtosecond Microscale 3D Light Field Projection and Its Application in Multiphoton 3D Light Field Lithography

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Meta materials are periodic materials that allow microstructure design and are able to provide unique optical, physical, chemical and bio properties that do not exist in natural materials. The meta-materials considered in this project are 3D, where their geometry is described in three dimensions, or 2.5D, where the geometry is defined in a plane, but the plane can stack to make a 3D structure. There is a great desire to have a microfabrication technique that can provide high speed, high resolution fabrication of these structures over large areas. Existing fabrication techniques can provide either sufficiently high resolution to fabricate the 2.5D/3D features, or sufficiently high throughput to cover large areas, but not both simultaneously. An advanced manufacturing process capable of both is critical for the commercialization of the meta-structures. This award will support research on using femtosecond laser enabled 3D virtual object projections into a photoresist (a polymeric material that experiences property changes when exposed to light) as a method to achieve high speed, high resolution fabrication. This is potentially feasible as a femtosecond laser, which can realize over 10,000 focal spots in one 3D light field projection, can enable higher speed processing. Knowledge gaps regarding the complex, non-linear interactions between the 3D projections and the photoresist will be addressed using computational and experimental approaches. If successful bio-sensing/inspection and emission/absorption controlled surfaces may be realized and contribute to U.S. defense and health related interests. The award will also facilitate training of the future workforce as students across all levels will gain exposure to, and experience in 2D and 3D micro fabrication technologies. Additional educational outreach activities include engaging high school teachers in the research, and disseminating the findings through research websites, conference participations and journal publications. The technical objective of this research is to establish a new 3D lithography method based on femtosecond compressed 3D light field projection. If successful it will realize the high-speed (compared with single-spot multiphoton lithography), high-resolution (equal or better than half of the wavelength) fabrication of complicated 2.5D/3D microstructures over a large area. The technical scope of this research includes; 1) a hybrid wave analysis approach combining general astigmatic Gaussian beam tracing and full wave simulation to enable high accuracy wave type analysis of light focusing in large optical systems using minimum computational power, 2) determination of stress/strain fields and the associated deformation of cured photoresist from multiphoton 3D light field lithography, 3) specification and fabrication of a femtosecond compressed 3D light field projector test bed to verify the theoretically predicted size and shape of cured photoresist patterns from femtosecond voxel projections. This proposed research will significantly advance the fundamental understanding in the following areas; non-linear femtosecond light transport/focusing/absorption in photoresists; 3D virtual object reconstructions with femtosecond pulsed light; and the feasibility of femtosecond 3D light field projection in 3D microfabrication of each type of 2.5D/3D microstructures over a large area.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.