Ultrasmall all-optical plasmonic switch and its application to superresolution imaging

Because of their exceptional local-field enhancement and ultrasmall mode volume, plasmonic components can integrate photonics and electronics at nanoscale, and active control of plasmons is the key. However, all-optical modulation of plasmonic response with nanometer mode volume and unity modulation depth is still lacking. Here we show that scattering from a plasmonic nanoparticle, whose volume is smaller than 0.001 μm3, can be optically switched off with less than 100 μW power. Over 80% modulation depth is observed, and shows no degradation after repetitive switching. The spectral bandwidth approaches 100 nm. The underlying mechanism is suggested to be photothermal effects, and the effective single-particle nonlinearity reaches nearly 10−9 m2/W, which is to our knowledge the largest record of metallic materials to date. As a novel application, the non-bleaching and unlimitedly switchable scattering is used to enhance optical resolution to λ/5 (λ/9 after deconvolution), with 100-fold less intensity requirement compared to similar superresolution techniques. Our work not only opens up a new field of ultrasmall all-optical control based on scattering from a single nanoparticle, but also facilitates superresolution imaging for long-term observation

OMAE2006-92110 RESEARCH ON APPLICABILITY OF NEW MATERIALS TO MARINE STRUCTURES IN TROPICAL CLIMATES -DURABILITY ASSESSMENT OF NEW MATERIALS- Shozo TAKIZAWA Norishige MINEMURA

ABSTRACT New structural members that are light and durable are anticipated to reduce the running and maintenance costs of structures exposed to harsh marine environments, such as offshore oil production facilities, thereby reducing their lifecycle cost. This study aims to investigate the applicability of new materials to marine structures, focusing on their durability. To this end, a 5-year exposure test has been conducted beginning in 1999 on 3 types of specimens (for corrosion observation, tension testing, and joint strength testing) made of 21 selected materials (6 nonferrous metals, 8 steels, 4 composite materials, and 3 rope materials). The specimens have been exposed at 3 sites: Okinotori-shima and Miyako-jima, corrosive environments with high temperature and humidity, and a thermo-hygrostatic room in a laboratory. Having completed the natural exposure tests in 2004, the authors conducted strength tests and observation thereafter toward 2005. This paper summarizes the results of such tests and observation conducted so far, while making a final assessment of each material, and refers to the tasks ahead based on these results. No marked differences were observed between the results of exposure at Okinotori-shima and Miyako-jima. Both islands were therefore found to be similar environments in terms of corrosion. The corrosion states of specimens were classified into five Categories: I (no corrosion), II (slight corrosion), III (light corrosion), IV (corrosion with strength loss), and V (corrosion with significant strength loss). Only reference specimens of ordinary steel were designated as Category V. Those designated as Category IV included textile ropes and Ni steel and coated steel panels with damaged coating film. Most other new materials were designated as Categories III or less with no strength losses. Materials designated as Categories I to III were subjected to surface observation using optical and electron microscopes and element distribution analysis over a cross section using an electron beam probe microanalyzer. The progress of corrosion in each material over the five years has thus been elucidated. Within the range of the 5-year exposure test, most of the selected new materials pose no problems in regard to durability. However, marine structures are more vulnerable to alternate stresses than general structural members on land because of constant waves and pulsating gales on the sea. The authors intend to investigate the durability of structural members under continued or cyclic stress as a subject for the future

Saturated excitation microscopy using differential excitation for efficient detection of nonlinear fluorescence signals

We report a method to increase the efficiency of detecting nonlinear fluorescence signals in saturated excitation (SAX) microscopy. With this method, we compare fluorescence signals obtained under different degrees of saturated excitation to extract the nonlinear fluorescent signal induced by saturated excitation. Compared to conventional SAX microscopy using the harmonic demodulation technique, the detection efficiency of the fluorescence signal can be increased up to 8 and 32 times in imaging using the second-order and the third-order nonlinear fluorescence signals, respectively. We combined this approach with pulsed excitation, which is effective to reduce photobleaching effects, and achieved super-resolution imaging using third-order nonlinear fluorescence signals induced by saturated excitation of an organic dye. The resolution improvement was confirmed in the observations of fluorescent beads, actin-filaments in HeLa cells, and a spine in mouse brain tissue

StayGold photostability under different illumination modes

Abstract StayGold is a bright fluorescent protein (FP) that is over one order of magnitude more photostable than any of the currently available FPs across the full range of illumination intensities used in widefield microscopy and structured illumination microscopy, the latter of which is a widefield illumination-based technique. To compare the photostability of StayGold under other illumination modes with that of three other green-emitting FPs, namely EGFP, mClover3, and mNeonGreen, we expressed all four FPs as fusions to histone 2B in HeLa cells. Unlike the case of widefield microscopy, the photobleaching behavior of these FPs in laser scanning confocal microscopy (LSCM) is complicated. The outstanding photostability of StayGold observed in multi-beam LSCM was variably attenuated in single-beam LSCM, which produces intermittent and instantaneously strong illumination. We systematically examined the effects of different single-beam LSCM beam-scanning patterns on the photostability of the FPs in living HeLa cells. This study offers relevant guidelines for researchers who aim to achieve sustainable live cell imaging by resolving problems related to FP photostability. We also provide evidence for measurable sensitivity of the photostability of StayGold to chemical fixation