MULTIPHOTON ABSORPTION: FABRICATION, FUNCTIONALIZATION AND APPLICATIONS

Abstract

Despite the remarkable progress in micro/nano-scale fabrication that has occurred over the last decades, feature sizes are still restricted by the diffraction limit. The resolution in conventional photolithography is generally constrained to approximately one quarter of a wavelength (lamda) of the light used. Multiphoton absorption polymerization (MAP) offers another option for high-resolution fabrication. Using nonlinear optical and chemical effects, MAP can generate features with a transverse dimension as small as 80 nm using 800-nm laser excitation. MAP has the additional capability of fabricating arbitrary 3D structures, which is essential in many applications. Details of MAP fabrication setup and process are described in this thesis. Novel optical devices have been fabricated with MAP. One drawback of MAP is that the resolution in axial direction remains about three to five times poorer because of the shape of the laser focal point. A novel technique called Resolution Augmentation through Photo-Induced Deactivation (RAPID) lithography has been developed to overcome this issue. With RAPID, resolution of 40 nm in axial direction has been achieved. The aspect ratio of the volume element of MAP has been reduced from about 3 to 0.5.

Selective functionalization of polymeric microstructure has been performed in two ways. In the first approach, microstructures are fabricated with hybrid resists that permits the chemical functionality only applies to one material. The second method is able to pattern both binary and gray-scale functionalities onto polymer surface. The density of the surface functional groups is determined by the intensity of the exposed light.

The nonlinear novelty of multiphoton absorption has not only been realized in MAP, it also shows promise for multiphoton absorption based microscopy. Photoluminescence from noble metal nanostructures has been used for two-photon imaging of living cells. Multiphoton Absorption Induced Luminescence (MAIL) has been used to monitor the targeting and endocytosis of goldnanoparticles to human umbilical vein endothelial cells. Field-enhanced phenomena have been studied with MAIL and MAP.