Fresnel equations

About: Fresnel equations is a research topic. Over the lifetime, 2770 publications have been published within this topic receiving 54069 citations.

Simulation of light emission from thin-film microcavities

Abstract: In light-emitting devices based on thin-film technology, light waves that are partially or totally reflected at interfaces between different materials interfere and influence the angular distribution of the emitted light. For an electrical dipole transition, the radiation pattern is equivalent to that of an electrical dipole antenna. New theoretical expressions are provided for the radiation, discriminating for polarization, emission angle, absorption, and transmission; and the numerical calculation of discrete modes, narrow modes, and evanescent waves near absorbing media is discussed.

Light-Extraction Enhancement of GaInN Light-Emitting Diodes by Graded-Refractive-Index Indium Tin Oxide Anti-Reflection Contact†

Abstract: tion (AR) coatings, [7–10] and optical resonators. [11] In many cases, however, the unavailability of materials with desired refractive indices, particularly materials with very low refractive indices, prevents the implementation of optical components with very high performance. In addition, the choice of a material with desired refractive index often forces a compromise in other materials properties such as optical transmittance and electrical conductivity that are also important for most optoelectronic applications. Here, we show that oblique-angle deposition can be used to tailor the refractive index of a thinfilm material that is chosen for its desired material properties other than refractive index. The unique ability to control the refractive index of thin film materials allows one to eliminate Fresnel reflection, one of the fundamental limitations in lightextraction efficiency of light-emitting diodes (LEDs), by fabricating coatings whose refractive index gradually decreases from the refractive index of the active semiconductor layer to the refractive index of the surrounding medium. As an example of this concept, we present a six-layer graded-refractiveindex (GRIN) AR coating made entirely of a single material, indium tin oxide (ITO), chosen for its high conductivity, high optical transmittance, and low contact resistance with GaN. Each layer has a refractive index that is individually tuned to form a stack with refractive index graded from its dense ITO value down to the value close to that of air for an optimum AR performance. It is shown that GaInN LEDs with a GRIN ITOAR contact achieve a light-extraction efficiency enhancement of 24.3 % compared to the LEDs with dense ITO coating due to a strongly reduced Fresnel reflection at the ITO– air interface. Oblique-angle deposition is a method of growing porous thin films, and hence thin films with low-refractive index (lown), enabled by surface diffusion and self-shadowing effects during the deposition process. [12–16] In oblique-angle deposition, a random growth fluctuation on the substrate produces a shadow region that the incident vapor flux cannot reach, and a non-shadow region where incident flux deposits preferentially, thereby creating an oriented rodlike structure with high porosity. Figure 1 shows the cross-sectional scanning-electron microscopy (SEM) image of low-n ITO, which is electrically conductive and optically transparent in visible wavelengths, COMMUNICATION

Multiple scattering calculations for technology.

Abstract: A many-flux (discrete ordinate) radiative transfer calculation procedure is described with the goal of making the mathematics easy to learn and use. The major approximation is the neglect of polarization. Emission within the scattering medium is not included, and the formulas are restricted to a scattering medium bounded by parallel planes. The boundary conditions allow for a variety of kinds of illumination, and the surface reflection coefficients at the boundaries of the scattering medium are accurately determined. A comparison is made with the two-flux (Kubelka-Munk) and four-flux calculation methods, and this leads to empirical expressions for the scattering and absorption coefficients in these simple theories, which make them give nearly the same results as exact theories. These empirical expressions provide a very simple method for estimating the absolute reflectance and transmittance of turbid media and greatly increase the utility of the two-flux and four-flux calculation methods. The two-flux equations give excellent results provided the absorption is small compared to scattering and the optical thickness is greater than 5. A comparison with experimental data taken with collimated illumination shows that the four-flux equations give good results at any optical thickness even if the absorption is strong.

Scattering Analysis for the Modeling of THz Communication Systems

Abstract: Modeling propagation channels for future pico-cellular indoor THz communication systems requires the knowledge of the reflective properties of building materials. The reflectivity of smooth, optically thick materials can be modeled with Fresnel equations. In case of materials with a rough surface, diffuse scattering reduces the power reflected in the specular direction. Kirchhoff scattering theory can be employed to derive modified Fresnel equations which account for these losses by introducing a Rayleigh roughness factor calculated from the measured surface height distribution of the sample under observation. Using the resulting, analytically derived reflection coefficient based on material parameter and surface measurements in propagation models enables the simulation of arbitrary configurations. We present a set of calculated and measured reflection coefficients for a selection of common indoor building materials which are in good agreement, thus verifying our modeling approach. Furthermore, we illustrate by ray-tracing simulations the effect of wall and ceiling roughness on propagation in future indoor scenarios. Both, absolute power levels and propagation patterns are shown to be strongly influenced by scattering. In some cases, reflected transmissions with longer propagation paths can be more efficient than the shorter ones in terms of incurred losses.

Interaction of Isotropic Light with a Compact Plant Leaf

Abstract: Diffuse isotropic light interaction with compact corn leaf, using transparent plate model with rough plane-parallel surfaces