Narrow Results

The amount of light and its time distribution are key factors determining the performance of scintillators when used as radiation detectors. However most inorganic scintillators are made of heavy materials and suffer from a high index of refraction which limits light extraction efficiency. This increases the path length of the photons in the material with the consequence of higher absorption and tails in the time distribution of the extracted light. Photonic crystals are a relatively new way of conquering this light extraction problem. Basically they are a way to produce a smooth and controllable index matching between the scintillator and the output medium through the nanostructuration of a thin layer of optically transparent high index material deposited at the coupling face of the scintillator. Our review paper discusses the theory behind this approach as well as the simulation details. Furthermore the different lithography steps of the production of an actual photonic crystal sample will be explained. Measurement results of LSO scintillator pixels covered with a nanolithography machined photonic crystal surface are presented together with practical tips for the further development and improvement of this technique.

Gold nanoparticle assemblies show a strong plasmonic response due to the combined effects of the individual nanoparticles’ plasmon modes. Increasing the number of nanoparticles in structured assemblies leads to significant shifts in the optical and physical properties. We use finite-difference time-domain (FDTD) simulations to analyze the electromagnetic response of structurally ordered gold nanorods in monomer and dimer configurations. The plasmonic coupling between nanorods in monomers or dimers configurations provides a unique technique for tuning the spectrum intensity, spatial distribution and polarization of local electric fields within and surrounding nanostructures. This study shows an exponential coupling behavior when two gold nanorods are assembled in end-to-end and side-by-side dimer configurations with a small separation distance. The maximum electric field in the gaps between adjacent nanorods in end-to-end dimer configuration describes a more significant enhancement factor than the individual gold nanorod. Our FDTD simulation on dimer in end-to-end assembly for small separation distance up to $\sim 40$nm can well explain the observed experimental growth dynamics of gold nanorods.

In this paper, we present an analysis and modeling of the interaction of electromagnetic fields with metallic nanostructures using computational tools that allow us to study the phenomena that are produced as an electromagnetic field interacts with the nanostructure. The analysis of dielectric systems including metals can be very complicated because of the metal parameters. For this reason, we propose to integrate the dielectric function of the Lorentz-Drude model with the finite difference time-domain (FDTD) method, which will permit to study the surface and internal effects within the metal nanostructure system added to the dielectric system, and the interaction of electromagnetic fields with atoms, ions or molecules excited up to their resonant frequency, which causes transitions among atomic energy levels. We solved the system and showed the results of the simulation for the following case studies, silver nanosphere of 100nm in diameter, gold nanorod of 12nm in thickness and 30nm in length and gold nanogroove of 70nm.

In this paper, three structures (cylinder, square column, and hexagonal prism) of InGaAsP nanowire arrays are designed based on the excellent light trapping effect of nanostructures. The effects of nanowire aperture, array period, and nanowire height on the light absorption properties are simulated and analyzed using the finite-domain time-difference (FDTD) method. The photoelectron emission capacity of the nanowire arrays was also calculated using MATLAB. The results show that the cylindrical nanowire array has phenomenon of resonance enhancement (absorption peak) in the near-infrared band of 820–1000nm, and the shift of absorption peaks can be achieved by adjusting the geometric parameters. Meanwhile, the quantum efficiency is taken to 9.98%. These simulation results provide some reference for the photocathode design of InGaAsP in the near-infrared band.

In this paper, we systemically and numerically investigate the effects of three types of Nanoparticles on the efficiency of solar cells. Finite Difference Time Domain method has been implemented to compute the absorption spectra in such proposed solar cell structure. High efficiency has been achieved by optimizing the nanoparticles layer by tuning the fraction of nanoparticles on the host layer.

We present a theoretical mechanism for electric field enhancement with SERS of InAs particles of subwavelength apertures under THz excitation. The distribution of electric field confirms that there is a strong enhancement in the InAs particles at THz frequencies. The InAs with a Drude-like behavior in THz range, which is similar to metals at optical frequencies, leads to different SERS when the parameters of these two particles change. The SERS enhancement factor can reach $10^{11}$ under the certain conditions.

The underwater photoelectric detection equipment mainly uses 532 nm laser as the light source, but the corresponding photocathodes like Na₂KSbCs, GaAs and GaAsP have a wide spectral response region and are easily affected by other signals. Thereby, GaAlAs are materials worth developing because of their adjustable band gap, which usually is used as a window layer of GaAs-based photocathode. In this paper, the finite difference time domain (FDTD) method is used to carry out nanostructure design simulations. The results show that GaAlAs with Al component of 0.63 can obtain the cutoff wavelength near 532 nm, which is an excellent photocathode material to meet the requirement of narrow-band spectral response of 532 nm laser. Furthermore, the light absorptance can be improved effectively by the quadrangular prism or cylinder nanostructured array prepared on the Ga${}_{0.37}$Al${}_{0.63}$As emission layer surface, and the maximum light absorptance can reach 96.2% at 532 nm for the cylinder nanostructure array with a height of 900 nm and a base width of 100 nm. Nevertheless, the reflection-mode Ga${}_{0.37}$Al${}_{0.63}$As photocathode with the quadrangular prism nanostructured array can be slightly influenced with incident angle of light.

Finite-difference time-domain (FDTD) method has been successfully developed to model electromagnetic systems in recent years. Since acoustics and electromagnetism share certain undulatory properties, a natural adaptation of this technique has been developed too. Several acoustics problems, such as room acoustics, require the use of fibrous tangles to attenuate the propagation speed of sound waves. Notwithstanding, although free air acoustic propagation is known, FDTD technique is not developed yet to model fibrous materials. To characterize this behavior, only a few and measurable set of parameters must be considered. In this paper, a new approach for modeling fibrous materials analysis using FDTD is presented and validated. A set of simulations covering various packing densities of a real fibrous material is performed. Loudspeaker cabinets, virtual acoustics and room acoustics are situations in which this method can be applied.