We evaluate the potential ability of c-shaped apertures milled in aluminum thin films to reduce the effective
measurement volume and to enhance the fluorescence signal for fluorescence correlation spectroscopy of ATTO655 dye
dissolved in a HEPES buffer solution. Previous studies have shown that by morphing a square aperture into a rectangular
aperture while holding the cross-sectional area constant will yield strong polarization dependence in the reduction of the
effective volume and about a factor of 2-3 enhancement in the fluorescence count rate per molecule. By morphing the
rectangular aperture into a c-shaped aperture we gain further reduction in focal volume while maintaining the count rate
enhancements. In particular, we compare c-shaped apertures to squares with the same cross-sectional area and show that
one can achieve one molecule per focal volume at ~3µM (about a 1000 times reduction in effective volume compared to
confocal FCS) while maintaining a fluorescence count rate per molecule of about an order of magnitude higher than for
bulk diffusing dyes. Two orthogonal polarizations for the incident field have been studied to explore the effects on the
focal volume reduction and fluorescence count rate enhancements.
By using a direct-write e-beam technique with liquid phase epitaxy LiNbO3 thin films, we have successfully produced sub-micron domain structures for achieving dynamically switchable filters in a periodically poled lithium niobate (PPLN) waveguide. Sub-micron domain (~200 nm) structures with a period ~1.2 um are realized in liquid phase epitaxy LiNbO3 films on congruent LiNbO3 substrates by using the direct-write e-beam domain engineering method. In comparison with single crystal congruent LiNbO3 (CLN) and stoichiometric LiNbO3 (SLN), we show that LPE LiNbO3 is the most promising material for producing superior domain regularities and finer domain sizes than single crystals. A physical model is presented to qualitatively explain the observed differences in structure and regularity of the induced periodic domains among the three different materials we studied. We postulate that the higher Li/Nb ratio in LPE LN than in CLN enhances domain inversion initiation. Also, we believe that the vanadium incorporation and distortion due to the lattice mismatch between films and substrates enhance electron localization, domain wall pinning and domain nucleation in LPE materials, giving rise to better structures.