The Importance of Refractive Index When Using Laser Diffraction
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An Atmospheric Radiation Model for Cerro Paranal
Astronomy & Astrophysics manuscript no. nolletal2012a c ESO 2012 May 10, 2012 An atmospheric radiation model for Cerro Paranal I. The optical spectral range⋆ S. Noll1, W. Kausch1, M. Barden1, A. M. Jones1, C. Szyszka1, S. Kimeswenger1, and J. Vinther2 1 Institut f¨ur Astro- und Teilchenphysik, Universit¨at Innsbruck, Technikerstr. 25/8, 6020 Innsbruck, Austria e-mail: [email protected] 2 European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany Received; accepted ABSTRACT Aims. The Earth’s atmosphere affects ground-based astronomical observations. Scattering, absorption, and radiation processes dete- riorate the signal-to-noise ratio of the data received. For scheduling astronomical observations it is, therefore, important to accurately estimate the wavelength-dependent effect of the Earth’s atmosphere on the observed flux. Methods. In order to increase the accuracy of the exposure time calculator of the European Southern Observatory’s (ESO) Very Large Telescope (VLT) at Cerro Paranal, an atmospheric model was developed as part of the Austrian ESO In-Kind contribution. It includes all relevant components, such as scattered moonlight, scattered starlight, zodiacal light, atmospheric thermal radiation and absorption, and non-thermal airglow emission. This paper focuses on atmospheric scattering processes that mostly affect the blue (< 0.55 µm) wavelength regime, and airglow emission lines and continuum that dominate the red (> 0.55 µm) wavelength regime. While the former is mainly investigated by means of radiative transfer models, the intensity and variability of the latter is studied with a sample of 1186 VLT FORS 1 spectra. Results. For a set of parameters such as the object altitude angle, Moon-object angular distance, ecliptic latitude, bimonthly period, and solar radio flux, our model predicts atmospheric radiation and transmission at a requested resolution. -
![Arxiv:1710.01658V1 [Physics.Optics] 4 Oct 2017 to Ask the Question “What Is the RI of the Small Parti- Cles Contained in the Inhomogeneous Sample?”](https://docslib.b-cdn.net/cover/4841/arxiv-1710-01658v1-physics-optics-4-oct-2017-to-ask-the-question-what-is-the-ri-of-the-small-parti-cles-contained-in-the-inhomogeneous-sample-24841.webp)
Arxiv:1710.01658V1 [Physics.Optics] 4 Oct 2017 to Ask the Question “What Is the RI of the Small Parti- Cles Contained in the Inhomogeneous Sample?”
Extinction spectra of suspensions of microspheres: Determination of spectral refractive index and particle size distribution with nanometer accuracy Jonas Gienger,∗ Markus Bär, and Jörg Neukammer Physikalisch-Technische Bundesanstalt (PTB), Abbestraße 2–12, 10587 Berlin, Germany (Dated: Compiled October 5, 2017) A method is presented to infer simultaneously the wavelength-dependent real refractive index (RI) of the material of microspheres and their size distribution from extinction measurements of particle suspensions. To derive the averaged spectral optical extinction cross section of the microspheres from such ensemble measurements, we determined the particle concentration by flow cytometry to an accuracy of typically 2% and adjusted the particle concentration to ensure that perturbations due to multiple scattering are negligible. For analysis of the extinction spectra we employ Mie theory, a series-expansion representation of the refractive index and nonlinear numerical optimization. In contrast to other approaches, our method offers the advantage to simultaneously determine size, size distribution and spectral refractive index of ensembles of microparticles including uncertainty estimation. I. INTRODUCTION can be inferred from measurements of the scattering and absorption of light by the particles. The refractive index (RI) describes the refraction of a A reference case is that of homogeneous spheres de- beam of light at a (macroscopic) interface between any scribed by a single refractive index, since an analytical two materials. Consequently, a variety of experimental solution for the mathematical problem of light scatter- methods exist for measuring the RI of a material that rely ing exists for this class of particles (Mie theory) [12, 13]. on the refraction or reflection of light at a planar interface This makes the analysis of light scattering data feasible between the sample and some other known material, such and at the same time is a good approximation for many as air, water or an optical glass. -
12 Light Scattering AQ1
12 Light Scattering AQ1 Lev T. Perelman CONTENTS 12.1 Introduction ......................................................................................................................... 321 12.2 Basic Principles of Light Scattering ....................................................................................323 12.3 Light Scattering Spectroscopy ............................................................................................325 12.4 Early Cancer Detection with Light Scattering Spectroscopy .............................................326 12.5 Confocal Light Absorption and Scattering Spectroscopic Microscopy ............................. 329 12.6 Light Scattering Spectroscopy of Single Nanoparticles ..................................................... 333 12.7 Conclusions ......................................................................................................................... 335 Acknowledgment ........................................................................................................................... 335 References ...................................................................................................................................... 335 12.1 INTRODUCTION Light scattering in biological tissues originates from the tissue inhomogeneities such as cellular organelles, extracellular matrix, blood vessels, etc. This often translates into unique angular, polari- zation, and spectroscopic features of scattered light emerging from tissue and therefore information about tissue -
Negative Refractive Index in Artificial Metamaterials
1 Negative Refractive Index in Artificial Metamaterials A. N. Grigorenko Department of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, UK We discuss optical constants in artificial metamaterials showing negative magnetic permeability and electric permittivity and suggest a simple formula for the refractive index of a general optical medium. Using effective field theory, we calculate effective permeability and the refractive index of nanofabricated media composed of pairs of identical gold nano-pillars with magnetic response in the visible spectrum. PACS: 73.20.Mf, 41.20.Jb, 42.70.Qs 2 The refractive index of an optical medium, n, can be found from the relation n2 = εμ , where ε is medium’s electric permittivity and μ is magnetic permeability.1 There are two branches of the square root producing n of different signs, but only one of these branches is actually permitted by causality.2 It was conventionally assumed that this branch coincides with the principal square root n = εμ .1,3 However, in 1968 Veselago4 suggested that there are materials in which the causal refractive index may be given by another branch of the root n =− εμ . These materials, referred to as left- handed (LHM) or negative index materials, possess unique electromagnetic properties and promise novel optical devices, including a perfect lens.4-6 The interest in LHM moved from theory to practice and attracted a great deal of attention after the first experimental realization of LHM by Smith et al.7, which was based on artificial metallic structures -
Chapter 19/ Optical Properties
Chapter 19 /Optical Properties The four notched and transpar- ent rods shown in this photograph demonstrate the phenomenon of photoelasticity. When elastically deformed, the optical properties (e.g., index of refraction) of a photoelastic specimen become anisotropic. Using a special optical system and polarized light, the stress distribution within the speci- men may be deduced from inter- ference fringes that are produced. These fringes within the four photoelastic specimens shown in the photograph indicate how the stress concentration and distribu- tion change with notch geometry for an axial tensile stress. (Photo- graph courtesy of Measurements Group, Inc., Raleigh, North Carolina.) Why Study the Optical Properties of Materials? When materials are exposed to electromagnetic radia- materials, we note that the performance of optical tion, it is sometimes important to be able to predict fibers is increased by introducing a gradual variation and alter their responses. This is possible when we are of the index of refraction (i.e., a graded index) at the familiar with their optical properties, and understand outer surface of the fiber. This is accomplished by the mechanisms responsible for their optical behaviors. the addition of specific impurities in controlled For example, in Section 19.14 on optical fiber concentrations. 766 Learning Objectives After careful study of this chapter you should be able to do the following: 1. Compute the energy of a photon given its fre- 5. Describe the mechanism of photon absorption quency and the value of Planck’s constant. for (a) high-purity insulators and semiconduc- 2. Briefly describe electronic polarization that re- tors, and (b) insulators and semiconductors that sults from electromagnetic radiation-atomic in- contain electrically active defects. -
Super-Resolution Imaging by Dielectric Superlenses: Tio2 Metamaterial Superlens Versus Batio3 Superlens
hv photonics Article Super-Resolution Imaging by Dielectric Superlenses: TiO2 Metamaterial Superlens versus BaTiO3 Superlens Rakesh Dhama, Bing Yan, Cristiano Palego and Zengbo Wang * School of Computer Science and Electronic Engineering, Bangor University, Bangor LL57 1UT, UK; [email protected] (R.D.); [email protected] (B.Y.); [email protected] (C.P.) * Correspondence: [email protected] Abstract: All-dielectric superlens made from micro and nano particles has emerged as a simple yet effective solution to label-free, super-resolution imaging. High-index BaTiO3 Glass (BTG) mi- crospheres are among the most widely used dielectric superlenses today but could potentially be replaced by a new class of TiO2 metamaterial (meta-TiO2) superlens made of TiO2 nanoparticles. In this work, we designed and fabricated TiO2 metamaterial superlens in full-sphere shape for the first time, which resembles BTG microsphere in terms of the physical shape, size, and effective refractive index. Super-resolution imaging performances were compared using the same sample, lighting, and imaging settings. The results show that TiO2 meta-superlens performs consistently better over BTG superlens in terms of imaging contrast, clarity, field of view, and resolution, which was further supported by theoretical simulation. This opens new possibilities in developing more powerful, robust, and reliable super-resolution lens and imaging systems. Keywords: super-resolution imaging; dielectric superlens; label-free imaging; titanium dioxide Citation: Dhama, R.; Yan, B.; Palego, 1. Introduction C.; Wang, Z. Super-Resolution The optical microscope is the most common imaging tool known for its simple de- Imaging by Dielectric Superlenses: sign, low cost, and great flexibility. -
Scattering and Absorption by Spherical Particles. Objectives: 1
Lecture 15. Light scattering and absorption by atmospheric particulates. Part 2: Scattering and absorption by spherical particles. Objectives: 1. Maxwell equations. Wave equation. Dielectrical constants of a medium. 2. Mie-Debye theory. 3. Volume optical properties of an ensemble of particles. Required Reading : L02: 5.2, 3.3.2 Additional/Advanced Reading : Bohren, G.F., and D.R. Huffman, Absorption and scattering of light by small particles. John Wiley&Sons, 1983 (Mie theory derivation is given on pp.82-114, a hardcopy will be provided in class) 1. Maxwell equations. Wave equation. Dielectrical constants of a medium. r Maxwell equations connect the five basic quantities the electric vector, E , magnetic r r r vector, H , magnetic induction, B , electric displacement, D , and electric current r density, j : (in cgs system) r r 1 ∂D 4π r ∇ × H = + j c ∂t c r r − 1 ∂ B ∇ × E = [15.1] c ∂ t r ∇ • D = 4πρ r ∇ • B = 0 where c is a constant (wave velocity); and ρρρ is the electric charge density. To allow a unique determination of the electromagnetic field vectors, the Maxwell equations must be supplemented by relations which describe the behavior of substances under the influence of electromagnetic field. They are r r r r r r j = σ E D = ε E B = µ H [15.2] where σσσ is called the specific conductivity ; εεε is called the dielectrical constant (or the permittivity ), and µµµ is called the magnetic permeability. 1 Depending on the value of σ, the substances are divided into: conductors: σ ≠ 0 (i.e., σ is NOT negligibly small), (for instance, metals) dielectrics (or insulators): σ = 0 (i.e., σ is negligibly small), (for instance, air, aerosol and cloud particulates) Let consider the propagation of EM waves in a medium which is (a) uniform, so that ε has the same value at all points; (b) isotropic, so that ε is independent of the direction of propagation; (c) non-conducting (dielectric), so that σ = 0 and therefore j =0; (d) free from charge, so that ρρρ =0. -
Realization of an All-Dielectric Zero-Index Optical Metamaterial
Realization of an all-dielectric zero-index optical metamaterial Parikshit Moitra1†, Yuanmu Yang1†, Zachary Anderson2, Ivan I. Kravchenko3, Dayrl P. Briggs3, Jason Valentine4* 1Interdisciplinary Materials Science Program, Vanderbilt University, Nashville, Tennessee 37212, USA 2School for Science and Math at Vanderbilt, Nashville, TN 37232, USA 3Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA 4Department of Mechanical Engineering, Vanderbilt University, Nashville, Tennessee 37212, USA †these authors contributed equally to this work *email: [email protected] Metamaterials offer unprecedented flexibility for manipulating the optical properties of matter, including the ability to access negative index1–4, ultra-high index5 and chiral optical properties6–8. Recently, metamaterials with near-zero refractive index have drawn much attention9–13. Light inside such materials experiences no spatial phase change and extremely large phase velocity, properties that can be applied for realizing directional emission14–16, tunneling waveguides17, large area single mode devices18, and electromagnetic cloaks19. However, at optical frequencies previously demonstrated zero- or negative- refractive index metamaterials require the use of metallic inclusions, leading to large ohmic loss, a serious impediment to device applications20,21. Here, we experimentally demonstrate an impedance matched zero-index metamaterial at optical frequencies based on purely dielectric constituents. Formed from stacked silicon rod unit cells, the metamaterial possesses a nearly isotropic low-index response leading to angular selectivity of transmission and directive emission from quantum dots placed within the material. Over the past several years, most work aimed at achieving zero-index has been focused on epsilon-near-zero metamaterials (ENZs) which can be realized using diluted metals or metal waveguides operating below cut-off. -
Refractive Index and Dispersion of Liquid Hydrogen
&1 Bureau of Standards .ifcrary, M.W. Bldg OCT 11 B65 ^ecknlcciL ^iote 9?©. 323 REFRACTIVE INDEX AND DISPERSION OF LIQUID HYDROGEN R. J. CORRUCCINI U. S. DEPARTMENT OF COMMERCE NATIONAL BUREAU OF STANDARDS THE NATIONAL BUREAU OF STANDARDS The National Bureau of Standards is a principal focal point in the Federal Government for assuring maximum application of the physical and engineering sciences to the advancement of technology in industry and commerce. Its responsibilities include development and maintenance of the national stand- ards of measurement, and the provisions of means for making measurements consistent with those standards; determination of physical constants and properties of materials; development of methods for testing materials, mechanisms, and structures, and making such tests as may be necessary, particu- larly for government agencies; cooperation in the establishment of standard practices for incorpora- tion in codes and specifications; advisory service to government agencies on scientific and technical problems; invention and development of devices to serve special needs of the Government; assistance to industry, business, and consumers in the development and acceptance of commercial standards and simplified trade practice recommendations; administration of programs in cooperation with United States business groups and standards organizations for the development of international standards of practice; and maintenance of a clearinghouse for the collection and dissemination of scientific, tech- nical, and engineering information. The scope of the Bureau's activities is suggested in the following listing of its four Institutes and their organizational units. Institute for Basic Standards. Applied Mathematics. Electricity. Metrology. Mechanics. Heat. Atomic Physics. Physical Chemistry. Laboratory Astrophysics.* Radiation Physics. Radio Standards Laboratory:* Radio Standards Physics; Radio Standards Engineering. -
4.4 Total Internal Reflection
n 1:33 sin θ = water sin θ = sin 35◦ ; air n water 1:00 air i.e. ◦ θair = 49:7 : Thus, the height above the horizon is ◦ ◦ θ = 90 θair = 40:3 : (4.7) − Because the sun is far away from the fisherman and the diver, the fisherman will see the sun at the same angle above the horizon. 4.4 Total Internal Reflection Suppose that a light ray moves from a medium of refractive index n1 to one in which n1 > n2, e.g. glass-to-air, where n1 = 1:50 and n2 = 1:0003. ◦ If the angle of incidence θ1 = 10 , then by Snell's law, • n 1:50 θ = sin−1 1 sin θ = sin−1 sin 10◦ 2 n 1 1:0003 2 = sin−1 (0:2604) = 15:1◦ : ◦ If the angle of incidence is θ1 = 50 , then by Snell's law, • n 1:50 θ = sin−1 1 sin θ = sin−1 sin 50◦ 2 n 1 1:0003 2 = sin−1 (1:1487) =??? : ◦ So when θ1 = 50 , we have a problem: Mathematically: the angle θ2 cannot be computed since sin θ2 > 1. • 142 Physically: the ray is unable to refract through the boundary. Instead, • 100% of the light reflects from the boundary back into the prism. This process is known as total internal reflection (TIR). Figure 8672 shows several rays leaving a point source in a medium with re- fractive index n1. Figure 86: The refraction and reflection of light rays with increasing angle of incidence. The medium on the other side of the boundary has n2 < n1. -
Electromagnetism - Lecture 13
Electromagnetism - Lecture 13 Waves in Insulators Refractive Index & Wave Impedance • Dispersion • Absorption • Models of Dispersion & Absorption • The Ionosphere • Example of Water • 1 Maxwell's Equations in Insulators Maxwell's equations are modified by r and µr - Either put r in front of 0 and µr in front of µ0 - Or remember D = r0E and B = µrµ0H Solutions are wave equations: @2E µ @2E 2E = µ µ = r r r r 0 r 0 @t2 c2 @t2 The effect of r and µr is to change the wave velocity: 1 c v = = pr0µrµ0 prµr 2 Refractive Index & Wave Impedance For non-magnetic materials with µr = 1: c c v = = n = pr pr n The refractive index n is usually slightly larger than 1 Electromagnetic waves travel slower in dielectrics The wave impedance is the ratio of the field amplitudes: Z = E=H in units of Ω = V=A In vacuo the impedance is a constant: Z0 = µ0c = 377Ω In an insulator the impedance is: µrµ0c µr Z = µrµ0v = = Z0 prµr r r For non-magnetic materials with µr = 1: Z = Z0=n 3 Notes: Diagrams: 4 Energy Propagation in Insulators The Poynting vector N = E H measures the energy flux × Energy flux is energy flow per unit time through surface normal to direction of propagation of wave: @U −2 @t = A N:dS Units of N are Wm In vacuo the amplitudeR of the Poynting vector is: 1 1 E2 N = E2 0 = 0 0 2 0 µ 2 Z r 0 0 In an insulator this becomes: 1 E2 N = N r = 0 0 µ 2 Z r r The energy flux is proportional to the square of the amplitude, and inversely proportional to the wave impedance 5 Dispersion Dispersion occurs because the dielectric constant r and refractive index -
Monte-Carlo Path Tracing Transparency/Translucency
Monte-Carlo Path Tracing Transparency/Translucency Max Ismailov, Ryan Lingg Light Does a Lot of Reflecting ● Our raytracer only supported direct lighting ● Objects that are not light sources emit light! ➔ We need more attention to realism than direct light sources can offer Global Illumination: Shrek Tools to Solve this Problem 1. Appropriate model of reflectance for objects 2. A way to aggregate incoming light sources Formally: We’re Solving the Rendering Equation! Reflectance Models - BRDF’s ● To properly globally illuminate, we need accurate models of light reflectance ○ “Bidirectional Reflectance Distribution Function” ● We already have a few of these! ○ Lambertian ○ Blinn-Phong ○ Many more exist Basic Ingredients of a BRDF Microfaceted Surfaces Subsurface Scattering Aggregating Light Sources ● Ideally, we want to integrate over the light functions contributing to a point. ○ Integrals require an integrand, a function that we can integrate! ■ ...we don’t have this ○ We need something we can do in practice numerically Approximating an Integral ● Recall: an integral is the area under the curve of a function along interval [a,b] ● Rough Area Under a Curve: evaluate the function at a point that looks good, multiply it by the difference in the interval ○ You get a very crude approximation of the integral! Approximating an Integral ● Like most things in calculus: do it a lot, and you get closer to the truth! ● Sample random variable, X ∈ [a,b], from a uniform distribution ● Keep evaluating f(X), average the results, you get a better approximation of the integral ○ This is a “Basic Monte-Carlo Estimator” Approximating an Integral: Non-Uniform Distributions ● In practice, we often sample our random variable from a non-uniform distribution.