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Title: Aperiodic Photonic-Plasmonic Structures with Broadband Field Enhancement for Optical Limiting Applications

Participants: Gary Walsh (PhD ’13) and Professor Luca Dal Negro

Funding: Department of Defense

aperiodic

Top Row (left): Fabricated nanoparticle array with optimized aperiodic geometry for broadband local field enhancement. Top Row (right): Dark-field scattering picture of the device illuminated by white light. Bottom Row (left): Experimental set up for scatterometric characterization of plasmonic nanostructures developed during the project.

Background: Passive photanisotropic dyes can be used in a variety of different applications, including optical communication, data processing, imaging systems, optical sensing, medical diagnostics, precise positioning, guidance systems, etc. For practical applications, there is a need to improve the sensitivity of the passive response of photoanisotropic dyes.

Description: In this research, we utilize plasmonic scattering resonances and strong electromagnetic field enhancement in engineered photonic-plasmonic arrays of metal nanoparticles to selectively enhance the isomerization process efficiency of photosensitive dyes. Our approach combines plasmonic field enhancement and carefully designed resonances in metal-dielectric periodic and aperiodic arrays for the first demonstration of field-enhanced isomerization and minimum background absorption. By combining theory and experiment we analyze the light scattered from periodic and deterministic aperiodic (DA) structures.

Results: In contrast to standard metal-dielectric periodic gratings, the scattering spectra DA structures show multiple resonances spanning across the entire visible spectral range, which are associated to electromagnetic coupling at multiple length scales.

By fabricating such structures using electron-beam lithography on transparent substrates and by coating them with dye doped polymers, the performance of passive photoanisotropic dyes could be dramatically enhanced over a broad spectral region, thereby reducing the required amount of dye.

Website: www.bu.edu/nano

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