Nanofabrication and its Applications in Fluorescence Imaging and Quantum Cascade Lasers

Abstract

The research work presented in this thesis includes advanced nanofabrication technique using nanoimprint lithography (NIL) for applications in quantum cascade lasers (QCL) and fluorescence enhancement.

Nanofabrication has enabled rapid development of state-of-the-art

electronic and optical devices. With nanofabricated feature size going down to become comparable, or

even smaller than, the visible wavelength, some unique optical properties, which are

different from their macroscale behaviors, appear. Nanostructure engineering enables us to exploit these unique properties to achieve highly efficient, compact and cheap optical devices.

Quantum cascade lasers was one of the major optical accomplishment of the 20th century. With its wide tuning range and fast response time, QCLs have been adopted in diverse array of applications from environmental monitoring, health, safety, defense to medical diagnostics. Recently, a number of hybrid plasmon polariton waveguides that utilize dielectric structures and metallic components have gained significant interest as they can simultaneously achieve low modal loss and tight confinement. In the first part of the thesis, we have successfully incorporated microfabrication and variety of advanced nanoimprint lithography techniques to fabricate < 200 nm gold nanoholes on top of microridge for application in QCL. The periodic sub-wavelength air surface plasmon waveguide created has potential to improve long wavelength QCL by increasing confinement while maintaining low loss like dielectric waveguide.

In the second part of the thesis, we further use NIL, as a low-cost technology with large-area nanopatterning capacity, to demonstrate a biosensor with high fluorescence enhancement. We fabricated six different nanostructures to study the topological effects of nanostructures on fluorescence enhancement and showed seven-fold higher enhancement just from the topology. Then the effect of topology enhancement was combined with plasmonic nanostructures to increase the overall flruorescence enhancement of the plasmonic biosensor. Finally, we demonstrated regeneration of a highly sensitive biosensor to decrease the time to make the chip ready for testing by more than 90%, breaking a significant barrier for wider real-world use.