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Based on electromagnetic calculations, the formation mechanism of the Fano line shape in the attenuated total reflection (far-field) spectrum of a coupled waveguide multilayer structure is studied in detail by tracing back to the behaviors of local electric fields. The Fano line shape of absorptance A directly related to the reflectance by R = 1 − A is shown to be generated by a superposition of a Fano line shape exhibited by local absorption in one of the waveguide layers and a Lorentzian line shape exhibited by local absorption in another waveguide layer. It is also shown that the Fano line shape of the first waveguide layer is generated by a superposition of different Fano line shapes exhibited by local electric fields at different positions inside the waveguide layer. These results unveil the nested mechanisms of the Fano line shape formation hidden in the behaviors of local electric fields. The Fano resonance inside the first waveguide layer is thought to be an example of the multiple Fano resonance arising from the interaction between multiple continua with a discrete state. [ABSTRACT FROM AUTHOR]

The motion of matter containing photoreactive units, such as azo dyes, occurs when the latter undergo cyclic photoisomerization in gradients of light intensity; an effect referred to by photochemical tweezing. Matter motion is polarization sensitive owing to photo-selection of the azo dyes, and it has been described in detail by the recently developed theory of photoinduced vectorial motion of matter (PVMM). Indeed, motion occurs in the direction of the vector gradient of the actinic light with an efficiency that depends on the respective orientations of light polarization and gradient vectors. This paper uses rigorous numerical simulations to reproduce the motion of matter by photochemical tweezing in gradients of intensities produced by a Gaussian beam as well as by an interference pattern resulting from two coherent beams. The simulations are based on the PVMM theory and reproduce very well experimental observations. In particular, and in agreement with the published literature, the parameters used in our simulations impose mobility enhancement of solid azo-polymers by photoisomerization to the viscous flow level, and matter motion is due to the concomitant effects of the enhancement of molecular mobility and the photoisomerization force in the gradients of light fields. [ABSTRACT FROM AUTHOR]

We have succeeded in controlling the line shape of Fano-like resonances in all-dielectric multilayer structures in a wide range by UV light irradiation. Multilayer structures consisting of a waveguide layer supporting a half-leaky guided mode, a spacer layer, and another waveguide layer supporting a planar waveguide mode are known to exhibit Fano-like line shapes in attenuated total reflection spectra due to coupling between the half-leaky guided mode and the planar waveguide mode. Using a photochromic layer, i.e., a layer doped with spiropyran molecules, as one of the waveguide layers, we controlled the amount of light absorption in the waveguide layer by varying the UV irradiation dose. We demonstrated that the line shape changes dramatically depending on the UV dose, from the electromagnetically induced transparency-like to electromagnetically induced absorption-like line shape (or vice versa) passing through the Fano-like line shape. We also demonstrated that the photochromic response induced by UV irradiation in the Fano-resonant multilayer structure is enhanced by a factor of ∼100 relative to that in a single photochromic layer. Our analyses based on electromagnetic calculations suggest that the dramatic line shape change and the enhanced photochromic response are the consequences of enhanced local electric fields inside the photochromic waveguide layer combined with the photoinduced increase in the imaginary part of the dielectric constant. [ABSTRACT FROM AUTHOR]

Active modulation of Fano resonance by light is demonstrated for an all-dielectric multilayer system containing an azo-dye-doped layer. The sample studied consists of a polystyrene layer doped with disperse red 1 (azo dye) molecules, a polyvinyl alcohol layer, and a pure polystyrene layer. In a Kretschmann attenuated-total-reflection configuration, angle-scan reflection spectra of the sample were measured with blue probe light under blue light pumping. The Fano line shape was found to change systematically depending on the intensity of the pump light. Analyses based on electromagnetic calculations of the spectra and field distributions in the layers indicate that the Fano resonance observed is generated by coupling between a broad half-leaky guided mode supported by the azo-dye-doped layer and a sharp planar waveguide mode supported by the pure polystyrene layer. The systematic changes in the Fano line shape under pump light irradiation can be well understood by a systematic decrease in light absorption in the azo-dye-doped polystyrene layer; the decrease in light absorption is due to a decrease in the extinction coefficient of the layer arising from the photoisomerization of azo dye molecules. [ABSTRACT FROM AUTHOR]

Diarylethene-type chromophores were studied to determine photoorientation movement.