Optical Tweezers for High-Resolution Single-Photon Direct Laser Writing

A universal goal of photolithography is to fabricate smaller features, which is achieved by spatially confining a photochemical reaction. This project seeks to improve the resolution of direct laser writing lithography by implementing radiation pressure from an infrared laser to reduce the diffusion of the free-radicals formed during a photo- polymerization reaction. Single-photon polymerization was performed in a liquid acrylate resin with an inexpensive continuous wave 405 nm (UV) diode laser focused to a point using an optical microscope and a high numerical aperture lens. At the same point was also focused a near-IR diode laser at 980 nm, which creates an optical trap. Experiments were performed in poly ethylene glycol diacrylate, dipentaerythritol pentaacrylate esters (SR-399), and low viscosity trimethylolpropane triacrylate (SR-351) resins. The addition of the near-IR beam reduced the minimum UV power required for fabrication and created smaller features than could be achieved with the UV laser alone. Our hope is that this method will enable the fabrication of higher resolution microstructures for lab-on-a-chip devices