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Register a new userRefraction and Diffraction of Waves in Electromagnetic (Photonic) Crystals Formed by Anisotropically Scattering Elements
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Added by
Alexandra Gurinovich
Publication date
2012
fields
Physics
and research's language is
English
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Refraction and diffraction of waves in natural crystals and artificial crystals formed by anisotropically scattering centers are considered. A detailed study of the electromagnetic wave refraction in a two-dimensional photonic crystal formed by parallel threads is given by way of example. The expression is derived for the effective amplitude of wave scattering by a thread (in a crystal) for the case when scattering by a single thread in a vacuum is anisotropic. It is established that for a wave with orthogonal polarization, unlike a wave with parallel polarization, the index of refraction in crystals built from metallic threads can be greater than unity, and Vavilov-Chrernkov radiation becomes possible in them. The set of equations describing the dynamical diffraction of waves in crystals is derived for the case when scattering by a single center in a vacuum is anisotropic. Because a most general approach is applied to the description of the scattering process, the results thus obtained are valid for a wide range of cases without being restricted to either electromagnetic waves or crystals built from threads.
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We clarify theoretically that the topological ring-cavity (TRC) modes propagating along the interface between two honeycomb-type photonic crystals distinct in topology can be exploited for achieving stable single-mode lasing, with the maximal intensity larger than a whispering-gallery-mode counterpart by order of magnitude. Especially, we show that the TRC modes located at the bulk bandgap center benefit maximally from the gain profile since they are most concentrated and uniform along the ring cavity, and that, inheriting from the Dirac-like dispersion of topological interface states, they are separated in frequency from each other and from other photonic modes, both favoring intrinsically single-mode lasing. A TRC mode running in a specific direction with desired orbital angular momentum can be stimulated selectively by injecting circularly polarized light. The TRC laser proposed in the present work can be fabricated by means of advanced semiconductor nanotechnologies, which generates chiral laser beams ideal for novel photonic functions.
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The model of nonlinear interaction of proper waves of photonic crystal with plane acoustic wave was developed. The formulation of the model is reduced to the eigenvalue problem, which can be solved by computer simulations. By means of the formulae given in present paper one can predict which polarizations of acoustic wave can result in Bragg diffraction of optical waves of TE or TM polarizations. Computer simulation allows obtaining amplitudes of interaction waves in the case of Bragg diffraction when phase-matching conditions are fulfilled.
We describe a smooth transition from (fully ordered) photonic crystal to (fully disordered) photonic glass that enables us to make an accurate measurement of the scattering mean free path in nanostructured media and, in turn, establishes the dominant role of the density of states. We have found one order of magnitude chromatic variation in the scattering mean free path in photonic crystals for just $sim 3%$ shift around the band-gap ($sim 27$ nm in wavelength).
We experimentally demonstrate how to solve the phase problem of diffraction using multi-wave interference with standard diffraction experimental setups without the need for taking any auxiliary data. In particular, we show that the phases of the Fourier components of a periodic structure can be fully recovered by deliberately choosing a probe wavelength of the diffracting radiation much smaller than the lattice constant. In the course of the demonstration, we accurately determine the refractive index profile of nanocomposite phase gratings by light and neutron diffraction measurements.
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