Optical antenna design for fluorescence enhancement in the ultraviolet.

Through rational design, we compare the performance of three plasmonic antenna structures for UV fluorescence enhancement. Among the antenna performance metrics considered are the local increase in excitation intensity and the increase in quantum efficiency, the product of which represents the net fluorescence enhancement. With realistic structures in aluminum, we predict that greater than 100× net enhancement can be obtained.

Third-harmonic generation from arrays of sub-wavelength metal apertures.

We measure third-harmonic generation (THG) from arrays of sub-wavelength metal apertures in transmission using fundamental input at 800 nm. Samples with different aperture spacings, sizes, and shapes are used. Strong angular dependence of THG is observed, with maxima located at incidence angles corresponding to extraordinary optical transmission (EOT) for the fundamental. We demonstrate an anomalous scaling of TH intensity with aperture size, where at different EOT peaks, the TH may either increase or decrease with aperture size. The aperture shape is also shown to have a strong effect on TH output.

Beam manipulating by metallic nano-optic lens containing nonlinear media.

Embedding nonlinear media in the slit region of metallic nano-optic lens is proposed as a new method of active modulating the output beam. Two important phenomena, beam deflection and focusing, have been studied in detail. A developed Finite Difference Time Domain (FDTD) method has been performed to account for the nonlinear response. The simulated results show that the deflection angle and focus length can be controlled easily by the intensity of incident light in the structures. The physical principle of the phenomena is explained by the Surface Plasmons (SPs) excitation and Fabry-Pérot (F-P) resonance in the nanoslit.

Optical bistability in subwavelength metallic grating coated by nonlinear material.

A developed two-dimensional Finite Difference Time Domain (FDTD) method has been performed to investigate the optical bistability in a subwavelength metallic grating coated by nonlinear material. Different bistability loops have been shown to depend on parameters of the structure. The influences of two key parameters, thickness of nonlinear material and slit width of metallic grating, have been studied in detail. The effect of optical bistability in the structure is explained by Surface Plasmons (SPs) mode and resonant waveguide theory.

Numerical simulation of nanolithography with the subwavelength metallic grating waveguide structure.

Metallic waveguide theory has been used to design subwavelength metallic grating waveguide structure which can excite the waveguide modes, especially the low frequency coupled surface plasmons mode, to achieve sub-50nm resolution lithography pattern by using the light with 436nm wavelength. The Finite Difference Time Domain method has been performed to analyze the performance of lithography pattern generated by two possible schemes. One named metal-layer scheme utilizes three different modes (two coupled surface plasmons and one non-coupled surface plasmons) on the metal layer to generate the lithography patterns with different resolution and visibility. The other named metal-cladding scheme excites the coupled mode in the metal-cladding region, which utilizes multi-layer coupled effect to generate the field with higher resolution (~ 34nm) and approximately same visibility compared with the metal-layer scheme. The effectively deviated range of grating period is also analyzed to keep the output pattern effective for the lithography.

Investigation of enhanced and suppressed optical transmission through a cupped surface metallic grating structure.

Two-dimensional finite-difference time-domain (FDTD) method has been performed to numerically investigate the transmission through a one-dimension cupped surface metallic grating structure. The concept of coupling of optical modes in the notches and main slits, introduced by Crouse and Keshavareddy [1], is examined further in our work. Unexpected phenomenon is shown that even horizontal surface plasmons (HSPs) are inhibited, the transmission still can be enhanced or suppressed. And the periodicity of transmission depending on the phase change of the light striking on the grating surface is discovered. A hybrid optical mode combined by cavity mode and diffracted evanescent wave mode [2] is introduced to analyze the phenomenon.