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Applications
Published in Akihiro Miyauchi, Nanoimprinting and Its Applications, 2019
Akihiro Miyauchi, Hiroshi Sato
A certain kind of 3D structure, namely a moth eye, has an antireflection property. As shown in Fig. 10.1, a moth eye has a lot of tiny protrusions, several hundred nanometers in size. The principle of antireflection of a moth eye structure is shown in Fig. 10.2. When incident light enters the protrusions, because the size of the protrusions is less than the wavelength of the incident light, the light does not get diffracted. Under the assumption that the protrusions are quadrangular pyramids with the same refractive index as that of the substrate, the refractive index is gradually increased until it reaches the refractive index of the substrate, as shown in Fig. 10.2b. According to the Fresnel equation, reflection occurs at an optical interface, namely an interface between two mediums with different refractive indices. In the moth eye structure, no optical interfaces exist, so reflection does not occur.
The Basics of Lasers
Published in Helmut H. Telle, Ángel González Ureña, Laser Spectroscopy and Laser Imaging, 2018
Helmut H. Telle, Ángel González Ureña
Different phenomena in the gain medium or the laser cavity can be responsible for directional anisotropy and hence for linearly polarized laser emission. These include, for example, the following: (1) the gain medium itself is polarization dependent, as is the case for many laser crystals; or (2) the resonator losses are polarization dependent. For the latter, even a slightly tilted optical component (sometimes merely due to non-optimal alignment) may suffice to result in a preferred linear polarization direction. But more often than not, the polarization dependence of an optical element is inherent, such as wavelength-dependent devices like gratings, prisms, tuning etalons, etc., or Brewster-angled optical surfaces that exhibit near-zero losses for the associated p-polarization direction. Recall that the Fresnel equations predict that light with the p-polarization (i.e., the light wave oscillates in the same plane as the incident ray and the surface normal) will not be reflected provided that the angle of incidence is the so-called Brewster angle θB = tan−1(n2/n1), where n1 is the refractive index of the “incident” optical medium (often air), and n2 is the one for the other optical medium (see Figure 3.25).
Fresnel Equations
Published in Russell A. Chipman, Wai-Sze Tiffany Lam, Garam Young, Polarized Light and Optical Systems, 2018
Russell A. Chipman, Wai-Sze Tiffany Lam, Garam Young
The Fresnel equations describe the behavior of light at an interface between two media. The amplitude of the light divides between the reflected and refracted beam based on the refractive indices of the two media. The resulting amplitude coefficients, described by the Fresnel coefficients, are used within our various polarization matrices to include the effects of reflection and refraction in polarization ray tracing calculations. When wavefronts propagate through optical systems, the resulting polarization effects generate diattenuation and retardance aberrations.
Modeling nanomaterial physical properties: theory and simulation
Published in International Journal of Smart and Nano Materials, 2019
Tanujjal Bora, Adrien Dousse, Kunal Sharma, Kaushik Sarma, Alexander Baev, G. Louis Hornyak, Guatam Dasgupta
To simulate the optical properties of the substrate/sublayers system, the Fresnel equations may be used in combination with a transfer matrix method [35]. Another method is to input the model into a FEM package, such as COMSOL and to solve for the transmitted and reflected fields using Maxwell’s wave equation. As a general requirement for EM FEM calculations, a fine enough meshing (<λ/10) should be used as well as a large enough computational domain (≈λ) (Figure 8) so that numerical artefacts such as unwanted boundary reflections can be avoided. In our FEM simulation, the incidence of the electromagnetic field is kept normal to the surface. The total height of the sublayer stack has been set at 400 nm, bearing in mind that for the visible part of the solar spectrum as a light source, the accuracy of the model is higher for longer wavelengths.
Model development for moisture content and density prediction for non-dry asphalt concrete using GPR data
Published in International Journal of Pavement Engineering, 2023
Lama Abufares, Qingqing Cao, Imad L. Al-Qadi
From field GPR scans, the dielectric constant was calculated using the reflection amplitude (RA) method, Equation 1. This method of calculation is simple, common, and suitable for field applications. It is derived from Fresnel equations for EM waves’ transmission and reflection (Leng et al. 2012). For using this method, only two inputs are needed: reflection amplitude on pavement surface (Ap); and reflection amplitude on top of a perfect reflecting surface (Ac) – a copper plate is used for this purpose.
Study of silicone hydrogel contact lenses’ surface reflection characteristics using confocal microscopy
Published in Journal of Biomaterials Science, Polymer Edition, 2023
Tomasz Suliński, Natalia Nowak, Jędrzej Szymański, Jacek Pniewski
Light incident onto an interface between two media with different refraction indices undergoes reflection, governed by Fresnel equations for reflectance . The greater the difference between refraction indices the bigger reflectance. For normally incident light these equations are reduced to a simple formula