Rigorous analysis of extremely asymmetrical scattering of electromagnetic waves in slanted periodic gratings

Extremely asymmetrical scattering (EAS) is a new type of Bragg scattering in thick, slanted, periodic gratings. It is realised when the scattered wave propagates parallel to the front boundary of the grating. Its most important feature is the strong resonant increase in the scattered wave amplitude compared to the amplitude of the incident wave: the smaller the grating amplitude, the larger the amplitude of the scattered wave. In this paper, rigorous numerical analysis of EAS is carried out by means of the enhanced T-matrix algorithm. This includes investigation of harmonic generation inside and outside the grating, unusually strong edge effects, fast oscillations of the incident wave amplitude in the grating, etc. Comparison with the previously developed approximate theory is carried out. In particular, it is demonstrated that the applicability conditions for the two-wave approximation in the case of EAS are noticeably more restrictive than those for the conventional Bragg scattering. At the same time, it is shown that the approximate theory is usually highly accurate in terms of description of EAS in the most interesting cases of scattering with strong resonant increase of the scattered wave amplitude. Physical explanation of the predicted effects is presented.Comment: 14 pages, 7 figures; v2: corrections to metadata and bibliographical info in preprin

High-resolution deep-tissue optical imaging using anti-Stokes phosphors

We report on the high-resolution deep-tissue imaging using novel water-dispersible upconversion nanoparticles (UCNPs) ?-NaYF4:Yb 3+:Tm3+. Luminescence from the UCNP embedded into tissue-mimicking phantoms at the depth of 4 mm epi-illuminated with 975-nm laser radiation was detected. Fiber-optic detection shows 2-times better resolution compared with that obtained using CCD-based imaging modality. The conversion efficiency of upconversion particles and their cytotoxicity to HeLa cells were also investigated and reported.8 page(s