We observe coherent resonant coupling of optical whispering-gallery modes in fluorescence from dye doped polymer bispheres with diameters ranging from 2 to 5 mm. By monitoring the frequencies of fluorescence peaks of individual spheres, we sort out two spheres with appropriate size matching and bring them into contact. Wave optics calculation also gives good agreement with the experiment. By taking into account harmonic coupling of the whispering-gallery modes, the obtained features of normal mode splitting are well explained by the tight-binding photon picture. [S0031-9007(99)09349-7] PACS numbers: 42.60.DaManipulation of light path in micrometer length scale has recently attracted considerable attention from both fundamental and application points of view. Conventionally, the manipulation is based on the photonic crystal concept [1][2][3]. In photonic crystals, which have periodic modulation of the refractive index, propagation of the light wave is governed by a weak potential. Correspondingly, such an approach can be referred to as a nearly free photon approach analogous to the nearly free electron approach in band theory. Alternatively the micromanipulation of light can be achieved by exploring the possibility of confining the light in a small unit of the wavelength size. Light propagates through the system of such units due to the coupling between the nearest neighbors. This approach is referred to as the tight-binding photon approach [4]. Within the tight-binding photon approach we can guide the optical waves by connecting the units in the arbitrarily shaped microstructures.The microspheres are the most natural choice of the unit to be employed in the tight-binding photon device. It is known that a dielectric sphere acts as a unique optical microcavity which has very long photon storage time within a small mode volume [5][6][7][8]. In particular, Q factors of the order of 10 10 have been observed for whispering gallery modes (WGM's) in quartz spheres with a diameter of several tens of micrometers [9-13], and the mode structure of a pair of these large spheres in contact has been studied [14]. However, in order to explore the feasibility of micromanipulation of light, one has to confirm the existence of the coherent coupling between spheres of the size of a few times of optical wavelength. Lorenz-Mie theory predicts long photon lifetime even for small spheres, giving, for example, nearly 30 ps for a 4 mm sphere with a refractive index of 1.59. This has allowed one to propose such relatively small spheres to be employed as "photonic atoms" [15] for the tight-binding scheme. However, the coherent coupling between two adjacent microspheres of such size range have not been realized until now. The coherent coupling results in the splitting of the corresponding WGM's and is a manifestation of the well-known phenomena of the normal mode splitting (NMS) in coupled harmonic oscillators. However, although some attempts have been made [16], NMS has not yet been observed because of the difficulty in the precise size con...

We developed a quantitative assay for Caenorhabditis elegans avoidance behavior. This was then used to demonstrate that the worm moved away from toxic concentrations of Cd2+ and Cu2+, but not Ni2+, all ions that prevented development from larval to adult stages. Mutants that have structural defects in ciliated neurons (che-2 and osm-3) as well as worms with three laser-operated neurons (ADL, ASE, and ASH), showed no avoidance behavior from Cd2+ and Cu2+. These results suggest that the avoidance from Cd2+ and Cu2+ are mediated through multiple neural pathways including ADL, ASE, and ASH neurons. We hypothesize that the three sensing neurons provide increased accuracy of the sensory response and a survival advantage in the natural environment of the worm.

It was observed that bi-directional phase changes can be triggered by genuine photoexcitation between two phases with different bond structures in polydiacetylenes. The observed photoinduced phase transition was found to be mediated by photogeneration of charge carriers (and not of excitons). The extremely high efficiency is perhaps due to cooperative interaction between the locally photoconverted domains.

We propose and demonstrate a "bottom-up" approach to constructing photonic structures for photon manipulation. Supermonodispersive polymer microspheres are used as building blocks and a size uniformity better than 0.05% could be obtained by sorting the spheres using spectroscopic methods. The spheres are positioned in a V groove on a silicon substrate and form a photonic chain with resonant coupling of the optical whispering-gallery modes. Photonic band modes are clearly observed in fluorescence and resonant scattering spectra, and an excellent agreement with a tight-binding model calculation is found. Heavy photon states and a group index as high as 40 are obtained.