Broadening the absorption bandwidth based on heavily doped semiconductor nanostructures

Broadband light absorption is a basis for the proper functionality of various materials, microstructures, and devices. Despite numerous studies, however, many aspects of broadband absorption remain uncovered. In this paper, we demonstrate an inverse-problem approach to designing nanostructures with a very low optical reflection and high absorption through a frequency band. Particular emphasis is made on a subwavelength transparent film as a top layer and anisotropic substrate. The polarization-dependent metamaterial absorber based on a subwavelenth semiconductor multicomponent multilayer structure is proposed and numerically investigated. For an illustration, we consider a four-component heavily doped silicon lattice with a thin undoped silicon top layer. The dielectric response of the structure is engineered by controlling the free carrier density and filling factor of each layer. A simulation study reveals a power law dependence of the bandwidth on the maximum reflectivity within the band.

Diffraction of a Gaussian Beam with Limited cross Section by a Volume Phase Grating under Waveguide Mode Resonance

In this work, the diffraction of a Gaussian beam on a volume phase grating was researched theoretically and numerically. The proposed method is based on rigorous coupled-wave analysis (RCWA) and Fourier transform. The Gaussian beam is decomposed into plane waves using the Fourier transform. The number of plane waves is determined using the sampling theorem. The complex reflected and transmitted amplitudes are calculated for each RCWA plane wave. The distribution of the fields along the grating for the reflected and transmitted waves is determined using inverse Fourier transform. The powers of the reflected and transmitted waves are determined based on these distributions. Our method shows that the energy conservation law is satisfied for the phase grating. That is, the power of the incident Gaussian beam is equal to the sum of the powers of the reflected and transmitted beams. It is demonstration of our approach correctness. The numerous studies have shown that the spatial shapes of the reflected and transmitted beams differ from the Gaussian beam under resonance. In additional, the waveguide mode appears also in the grating. The spatial forms of the reflected and transmitted beams are Gaussian in the absence of resonance. It was found that the width of the resonance curves is wider for the Gaussian beam than for the plane wave. However, the spectral and angular sensitivities are the same as for the plane wave. The resonant wavelengths are slightly different for the plane wave and the Gaussian beam. Numerical calculations for four refractive index modulation coefficients of the grating medium were carried out by the proposed method. The widths of the resonance curves decrease with the increasing in the refractive index modulation. Moreover, the reflection coefficient also increases.

Relation between Resonance Parameters of Surface Plasmon-Polariton Waves with Properties of the Dielectric-Metal Film-Dielectric Waveguide

The resonant excitation of the surface plasmon-polariton waves by the prism structure, where a thin silver film was coated on the prism, was studied. New analytical relations between the angular and spectral sensitivities on the change of the medium refractive index, adjacent to the metal film, were obtained. In addition, the analytical relation between the full width at the half maximum of the spectral and angular resonance dependencies were found.

Annealing Effects on Structure and Optical Properties of Diamond-Like Carbon Films Containing Silver

In the present study, diamond-like carbon films with embedded Ag nanoparticles (DLC:Ag) were deposited by reactive magnetron sputtering. Structure of the films was investigated by Raman scattering spectroscopy. Atomic force microscopy was used to define thickness of DLC:Ag films as well as to study the surface morphology and size distribution of Ag nanoparticles. Optical absorbance and reflectance spectra of the films were studied in the 180-1100-nm range. Air annealing effects on structure and optical properties of the DLC:Ag were investigated. Annealing temperatures were varied in the 180-400 °C range. Changes of size and shape of the Ag nanoclusters took place due to agglomeration. It was found that air annealing of DLC:Ag films can result in graphitization following destruction of the DLC matrix. Additional activation of surface-enhanced Raman scattering (SERS) effect in DLC:Ag films can be achieved by properly selecting annealing conditions. Annealing resulted in blueshift as well as significant narrowing of the plasmonic absorbance and reflectance peaks. Moreover, quadrupole surface plasmon resonance peaks appeared. Modeling of absorption spectra of the nanoclusters depending on the shape and surrounding media has been carried out.

Spectroellipsometric characterization and modeling of plasmonic diamond-like carbon nanocomposite films with embedded Ag nanoparticles

Diamond-like carbon nanocomposite films with embedded silver nanoparticles are considered experimentally (spectroellipsometric characterization) and theoretically (modeling of optical properties). Metallic nanocomposite films were synthesized by reactive magnetron sputtering and were studied by transmission electron microscope (TEM) and atomic force microscope (AFM). The optical constants of the films were determined from spectroscopic ellipsometry measurements and were modeled using the Maxwell-Garnett approximations. Comparison between the extended and renormalized Maxwell-Garnett theory was conducted. Surface plasmon resonance peak have been found to be strongly dependent on the shape of nanoparticles and interaction between them.