RESUMO
The transverse magnetic Gaussian beam diffraction from a finite number, equally spaced and rectangular cross section dielectric cylinder row is studied. The infinitely long cylinders' axes are perpendicular to the beam's direction of propagation. The cylinder row, with dielectric constant εc=nc2, is treated as a periodic inhomogeneous film, with period ax and thickness wy, bounded by two semi-infinite homogeneous media. With this restriction, the method is valid only for square or rectangular cross section cylinders. The supercell and the plane wave expansion methods are used to calculate the eigenfrequencies and eigenvectors supported for a one-dimensional photonic crystal. Then, these eigenfrequencies and eigenvectors are used to expand the field in the inhomogeneous film. Numerical results are presented for ax greater than λ (the incident light wavelength), wx (the cylinder width), and wg (Gaussian beam waist). Two cases are studied. In the first (second) case, the unit cell contains one cylinder (a cylinder row), which simulates the scattering from a single cylinder (an inhomogeneous thin film). The total integrated scattering in transmission (reflection) shows three well-defined minima (maxima), which are due to interference effects. Its positions can be approximately obtained with the formula λk=4ncwy/k, with k=3, 4, and 6. The total integrated scattering in transmission decreases linearly as a function of the cylinder number.
RESUMO
We reduce the sidelobes that are present in the bandpass zones of rugate filters, using antireflection coatings to design dichroic rugate filters. Our designs are based on the formalism of equivalent systems that allow us to consider a rugate filter a simple equivalent layer with equivalent optical admittance and equivalent phase thickness functions. Rugate filters with apodization were considered.
RESUMO
We report experimental results of the resonant scattering of light from a prism-glass/Ag/MgF2/air system with use of the attenuated total reflection technique for p and s polarized light. Two MgF2 film thicknesses were used. The system with the thinner dielectric layer supports two transverse magnetic (TM) and two transverse electric (TE) guided modes at a wavelength of 632.8 nm, and the system with the thicker dielectric layer supports three TM and three TE guided modes. In both cases we found dips in the specular reflection as a function of incident angle that is due to excitation of guided modes in the MgF2 film. The scattered light shows peaks at angles corresponding to the measured excitation of the guided modes. These peaks are due to single-order scattering and occur for any angle of the incident light. All features in the scattering response are enhanced in resonance conditions, and the efficiency of injecting light into the guide is reduced.