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It is shown by the phase calculation that equivalence in guiding principle holds between the in-phase and antiresonant reflection conditions in the one-dimensional and cylindrically symmetric two-dimensional structures with periodic cladding. The in-phase condition is equivalent to a generalized quarter-wave stack (QWS) condition in the Bragg fiber. The generalized QWS condition is formally equivalent to the central gap point in the stratified planar antiresonant reflecting optical waveguide (SPARROW) model. The eigenvalue equations under the generalized QWS condition are identical to those in the limit of an infinite V parameter in the ARROW model. It was confirmed that the confinement loss shows its minima for the generalized QWS condition of the Bragg fiber. The phase calculation is applied to semiquantitatively understand the dependence of confinement and bend losses of the order of photonic bandgap in Bragg and ARROW-type fibers.

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Insight refers to the sudden conscious shift in the perception of a situation following a period of unconscious processing. The present study aimed to investigate the implicit neural mechanisms underlying insight-based recognition, and to determine the association between these mechanisms and the extent of pupil dilation. Participants were presented with ambiguous, transforming images comprised of dots, following which they were asked to state whether they recognized the object and their level of confidence in this statement. Changes in pupil dilation were not only characterized by the recognition state into the ambiguous object but were also associated with prior awareness of object recognition, regardless of meta-cognitive confidence. Our findings indicate that pupil dilation may represent the level of implicit integration between memory and visual processing, despite the lack of object awareness, and that this association may involve noradrenergic activity within the locus coeruleus-noradrenergic (LC-NA) system.

Nonlinear optical frequency conversion has been challenged to move down to the extreme ultraviolet and x-ray region. However, the extremely low signals have allowed researchers to only perform transmission experiments of the gas phase or ultrathin films. Here, we report second harmonic generation (SHG) of the reflected beam of a soft x-ray free-electron laser from a solid, which is enhanced by the resonant effect. The observation revealed that the double resonance condition can be met by absorption edges for transition metal oxides in the soft x-ray range, and this suggests that the resonant SHG technique can be applicable to a wide range of materials. We discuss the possibility of element-selective SHG spectroscopy measurements in the soft x-ray range.