DOCSLIB.ORG

Experiment 5 Polarization and Modulation of Light

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Experiment 5 Polarization and Modulation of Light Experiment 5 Polarization and Modulation of Light 1. Objective Understanding the definition of polarized and un-polarized light. Understanding polarizer and analyzer definition, Maluse’s law. Retarding plates definition and application 2. Theory Polarized light: A propagating light (Electromagnetic wave; EM) has its electric and magnetic fields. These fields are perpendicular to one another as well as to the propagation direction. Polarization of an EM wave (light) describes the behavior of the electric field vector of the light as it propagates through a medium. If light wave has E-field oscillating in random directions (but perpendicular to the propagation direction) is called unpolarized. If the direction of E-field oscillation is well defined, it is called polarized (Figure 1). Figure 1. If the E-field oscillates at all time within a well-defined line, it said that EM is linearly polarized. In a linearly polarized light, the E-field vibrations and propagating direction (z axis here) defines a plane of vibrations shown in figure 2.a. The E-field oscillations in the plane of polarization can be represented by the superposition of two fields Ex and Ey with the right magnitude and phase (Figure 2.b, figure 2.c) E (z,t) E cos(t kz) x xo Ey (z,t) Eyo cos(t kz) Where Ø is the phase difference between Ex and Ey , which defines the delay between Ex and Ey . y Plane of polarization E ^ x y Ey ^x ^ xEx Ex y^E E y z E (a) (b) (c) Figure(a) A 2.linearly a) Electric polarized field in awave linearly has polarized its electric wave field oscillates oscillations along a line defined perpendicular along a to line propagation direction. perpendicular to the direction of propagation,z. The field vector E and z define a plane of b)polarization E field oscillations. (b) The are Ein-field the plane os cillations of polarization. are contained c) E-field represented in the plane by ofEx andpolarization. Ey. (c) A linearly polarized light at any instant can be represented by the superposition of two fieldsEx and Ey with the right magnitude and phase. A©n 1999 EM waveS.O. Kasap, (light) Optoelectronics can be polarized (Prentice by passing Hall) through a polarizer such as Polaroid sheet. This polarizer will only pass E-fields oscillating along a preferred direction, called transmission axis. Malus’s law: Suppose that a linearly polarized light from a polarizer is incident on a second identical polarizer as shown in figure 3. By rotating the transmission axis of the second polarizer the polarization state of the incident light can be analyzed. If the transmission axis of the second polarizer is at angle θ to the E-field of the first polarizer then E cosθ of the field will be allowed to pass through the analyzer as in figure 3. As Irradiance or intensity of the light passing through the analyzer is proportional to square of electric field (E cosθ)2 , the irradiance, I, at any angle is then given by Malus’s Law: 퐼(휃) = 퐼(0) 푐표푠2(휃) Malus’s law relates the intensity of a linearly polarized light passing through a second polarizer to the angle between the transmission axis and E-field vector. Figure 3. Randomly polarized light is incident on polarizer 1 with transmission axis TA1. Light is linearly polarized along TA1 and becomes incident on polarizer 2 (called analyzer) with transmission axis TA2 at an angle θ to TA1. Detector at the end measures the intensity of the light. Experimental procedure. 1. Launch the laser into a power meter detector, bolted on the breadboard at a distance about one meter from the laser. Record the maximum power of the laser. 2. Mount the polarizer (Polaroid sheet) in a rotation stage and bolt on the breadboard very close to the laser. Rotate the sheet to get the maximum power. Record this power. Explain the differences in power values? 3. Mount the second polarizer (called analyzer) in between the first one and detector. 4. Rotate the analyzer to get the maximum power. Record the angle on the rotational stage, call it θ = 0. Explain the direction of the transmission axis of the second polarizer with respect to the first one at this point. 5. Rotate the stage of the analyzer in steps of 10° until θ = 90o. Record the powers at each step. 6. Rotate back the stage to θ = 0, check the power. Now rotate the stage in step of -10° until θ = -90o. 7. Estimate the photosensitive device area. Then calculate the light intensity from the data recorded in steps of 5 and 6. 8. Sketch the calculated light intensities with respect to θ. Explain the results. 9. Sketch calculated light intensities with respect to cos2θ. Explain the results. Retarding Plates In crystalline materials the electronic polarization depends on the crystal direction. As a result the refractive index of a crystal, and the velocity of the light in a crystal depends on the direction of light propagation and the on the state of its polarization. Noncrystalline materials like glasses and cubic crystals have the same refractive index in all directions. These materials are called optically isotropic. The refractive index of most crystals depends on the direction of light propagation and the on the state of its polarization. These materials are called optically anisotropic. These materials are also called birefringent (double refraction) because an incident light beam is doubly refracted. There is a special direction in a birefringent crystal which all waves with different polarization experience the same refractive index (travel with the same phase velocity). This axis is called Optic Axis. Optic axis of a crystal is the direction in which a travelling light experience no birefringence (double refraction) and all the waves have the same phase velocity whatever their polarization is (figure 4). Figure 4. a) A birefringent crystal plate with the optic axis parallel to the plate surface. b) Optic axis perpendicular to plate surface. There is a phase difference between E⊥ and Eǁ in the first case. The phase difference of 180° is a half-wavelength retardation which means that E ǁ is delayed by 180° with respect to E ⊥ and is called a half-wave plate retarder. A quarter wave-plate retarder provides quarter wavelength retardation. (Figure 5) Figure 5. Input and output light polarization through half and quarter wave plate retarders. We can build an intensity modulator by inserting a polarizer and an analyzer before and after a retarding plate. (Figure 6) Retarding plate Analyzer Polarizer Figure 6. Intensity Modulator contains 1) Polarizer 2) Retarding plate 3) Analyzer all mounted on rotating stages. Experimental procedure: 1. Mount the polarizer (Polaroid sheet) in a rotation stage and bolt on the breadboard very close to the laser. Turn on the laser, then rotate the polarizer to get the maximum power. Record this power. 2. Mount the second polarizer (called analyzer) in between the first one and detector. Rotate the analyzer until you get the maximum power, record the angle of the analyzer. 3. Remove the analyzer carefully without any rotation. 4. Mount a retarding plate in another rotating stage and bolt it on the breadboard between the polarizer and detector. 3. Rotate the plate to find the optic axis (you should get the maximum power). Record the power and the angle. 4. Mount the analyzer again (at the same position of step 2) in between the retarding plate and detector. What is the power? Explain. 5. Rotate the analyzer to get the maximum power again. Compare the results with previous experiment. Explain what you have observed. .
Load more

Recommended publications
  • Huygen's Explanation of Double Refraction
    06/08/2018 Before this lecture there were two lectures: 1. Introduction about this course. 2. Qualitative description about the various polarizations. Retarders • In retarders, one polarization gets ‘retarded’, or delayed, with respect to the other one. There is a final phase difference between the 2 components of the polarization. Therefore, the polarization is changed. • Most retarders are based on birefringent materials (quartz, mica, polymers) that have different indices of refraction depending on the polarization of the incoming light. 3 Phase shift of half wavelength Quarter Wave plate Circular polarization (IV) 7 How to generate Polarized Light? 1.Dichroic materials 2.Polarizer 3.Birefringent materials 4.Reflection 5.Scattering Wire grid polarizer Polaroid How to generate Polarized Light? 1.Dichroic materials 2.Polarizer 3.Birefringent materials 4.Reflection 5.Scattering Birefringence How to generate Polarized Light? 1.Dichroic materials 2.Polarizer 3.Birefringent materials 4.Reflection 5.Scattering Polarized Reflecting Light • When an unpolarized light wave reflects off a non-metallic surface, it can be completely polarized, partially polarized or unpolarized depending on the angle of incidence. A completely polarized wave occurs for an angle called Brewster’s angle (named after Sir David Brewster) Snell's law Incident Reflected ray ray p n 90o 1 n2 r n1sin P = n2sin r n1sin P = n2sin r = n2sin (90-P) = n2cos P tan P = n2/n1 P = Brewster’s angel Reflection • When an unpolarized wave reflects off a nonmetallic surface, the reflected wave is partially plane polarized parallel to the surface. The amount of polarization depends upon the angle (more later). The reflected ray contains more vibrations parallel to the reflecting surface while the transmitted beam contains more vibrations at right angles to these.
    [Show full text]
  • How to Generate Polarized Light?
    Before this lecture there were two lectures: 1. Qualitative description of polarization and generation of various polarized light. 2. Quantitative derivation and explaining the observations. 08/08/2017 How to generate Polarized Light? 1.Dichroic materials 2.Polarizer 3.Birefringent materials 4.Reflection 5.Scattering Wire grid polarizer Birefringence Polarized Reflecting Light • When an unpolarized light wave reflects off a non-metallic surface, it can be completely polarized, partially polarized or unpolarized depending on the angle of incidence. A completely polarized wave occurs for an angle called Brewster’s angle (named after Sir David Brewster) Snell's law Incident Reflected ray ray p n 90o 1 n2 r n1sin P = n2sin r n1sin P = n2sin r = n2sin (90-P) = n2cos P tan P = n2/n1 P = Brewster’s angel Reflection • When an unpolarized wave reflects off a nonmetallic surface, the reflected wave is partially plane polarized parallel to the surface. The amount of polarization depends upon the angle (more later). The reflected ray contains more vibrations parallel to the reflecting surface while the transmitted beam contains more vibrations at right angles to these. Applications • Knowing that reflected light or glare from surfaces is at least partially plane polarized, one can use Polaroid sunglasses. The polarization axes of the lenses are vertical as the glare usually comes from reflection off horizontal surfaces. Polarized Lens on a Camera Reduce Reflections Polarization by Scattering • When a light wave passes through a gas, it will be absorbed and then re-radiated in a variety of directions. This process is called scattering. y Gas molecule z O Unpolarized x sunlight Light scattered at right angles is plane-polarized Polarization by Scatterings Retarders • In retarders, one polarization gets ‘retarded’, or delayed, with respect to the other one.
    [Show full text]
  • Polarisation
    Polarisation In plane polarised light, the plane containing the direction of POLARISATION vibration and propagation of light is called plane of vibration. Polarisation Plane which is perpendicular to the plane of vibration is called plane of polarisation. The phenomenon due to which vibrations of light waves are restricted in a particular plane is called polarisation. In an ordinary beam of light from a source, the vibrations occur normal to the direction of propagation in all possible planes. Such beam of light called unpolarised light. If by some methods (reflection, refraction or scattering) a beam of light is produced in which vibrations are confined to only one plane, then it is called as plane polarised light. Hence, polarisation is the phenomenon of producing plane polarised light from unpolarised light. In above diagram plane ABCD represents the plane of vibration and EFGH represents the plane of polarisation. There are three type of polarized light 1) Plane Polarized Light 2) Circularly Polarized Light 3) Elliptically Polarized Light Page 1 of 12 Prof. A. P. Manage DMSM’s Bhaurao Kakatkar College, Belgaum Polarisation Huygen’s theory of double refraction According to Huygen’s theory, a point in a doubly refracting or birefringent crystal produces 2 types of wavefronts. The wavefront corresponding to the O-ray is spherical wavefront. The ordinary wave travels with same velocity in all directions and so the corresponding wavefront is spherical. The wavefront corresponding to the E-ray is ellipsoidal wavefront. Extraordinary waves have different velocities in Polarised light can be produced by either reflection, different directions, so the corresponding wavefront is elliptical.
    [Show full text]
  • Conical Diffraction: Complexifying Hamilton's Diabolical Legacy Mike
    Conical Diffraction: Complexifying Hamilton’s Diabolical Legacy Mike R. Jeffrey A thesis submitted to the University of Bristol in accordance with the requirements of the degree of Ph.D. in the Faculty of Science H. H. Wills Physics Laboratory September 2007 word count 32,795 Abstract The propagation of light along singular directions in anisotropic media teems with rich asymptotic phenomena that are poorly understood. We study the refraction and diffraction of light beams through crystals exhibiting biaxial birefringence, optical activity, and dichroism. The optical properties and length of the crystal are related to the beam’s width, wavenumber, and alignment, by just three parameters defined by the effect of the crystal on a paraxial plane wave. Singular axes are crystal directions in which the refractive indices are degenerate. In transparent biaxial crystals they are a pair of optic axes corresponding to conical intersections of the propagating wave surface. This gives rise to the well understood phenomenon of conical diffraction. Our interest here is in dichroic and optically active crystals. Dichroism splits each optic axis into pairs or rings of singular axes, branch points of the complex wave surface. Optical activity destroys the optic axis degeneracy but creates a ring of wave surface inflection points. We study the unknown effect of these degeneracy structures on the diffracted light field, predicting striking focusing and interference phenomena. Focusing is understood by the coalescence of real geometric rays, while geometric interference is included by endowing rays with phase to constitute complex rays. Optical activity creates a rotationally symmetric cusped caustic surface threaded by an axial focal line, which should be easy to observe experimentally.
    [Show full text]
  • ∑ ∑ Discrete Modeling of Homometric and Isovector Divisions
    Crystallography Reports, Vol. 48, No. 2, 2003, pp. 167–170. Translated from Kristallografiya, Vol. 48, No. 2, 2003, pp. 199–202. Original Russian Text Copyright © 2003 by V. Rau, T. Rau. THEORY OF CRYSTAL STRUCTURES Discrete Modeling of Homometric and Isovector Divisions V. G. Rau and T. F. Rau Vladimir State Pedagogical University, Vladimir, Russia e-mail: [email protected] Received April 24, 2001 Abstract—As a further development of the method of discrete modeling of packings, the uniqueness of the division of the packing spaces into homometric (isovector) polyominoes is studied on the basis of the relation between the basic and vector systems of points. The particular criterion of the packing-space division based on the concept of the isovector nature of polyominoes with different numbers of points is formulated. © 2003 MAIK “Nauka/Interperiodica”. Earlier, we suggested a criterion of division of a (periodic basic system). In comparison with the nonpe- two-dimensional space into arbitrarily shaped polyomi- riodic basic system, the periodic basic system has some noes within the framework of the method of discrete additional interpoint distances associated with the modeling of molecules–polyominoes in the periodic translation vectors. The complete set of the interpoint space of a crystal lattice [1]. The criterion based on the distances rij = rj Ð ri = rk transforms the vector system concept of a packing multispace (PMS) of the Nth order of points in both nonperiodic and periodic basic sys- represented as a superposition of the sublattices with tems constructed on the lattice with the same basis vec- the sublattice index N is formulated as follows.
    [Show full text]
  • Technical Journal
    VOLUME XXII JULY, 1943 NUMBER 2 P- 2 S / V 3 THE BELL SYSTEM TECHNICAL JOURNAL DEVOTED TO THE SCIENTIFIC AND ENGINEERING ASPECTS OF ELECTRICAL COMMUNICATION A Mineral Survey for Piezo-Electric Materials —W. L. Bond 145 The Fundamental Equations of Electron Motion (Dynam­ ics of High Speed Particles) . L. A. MacColl 153 Quartz Crystal Applications W. P. Mason 178 Methods for Specifying Quartz Crystal Orientation and Their Determination by Optical Means . W. L. Bond 224 A Note on the Transmission Line Equation in Terms of Im p ed a n ce...........................................................J. R. Pierce 263 Abstracts of Technical Articles by Bell System Authors . 266 Contributors to this I s s u e ..........................................................268 AMERICAN TELEPHONE AND TELEGRAPH COMPANY NEW YORK 50c per copy $1.50 per Year THE BELL SYSTEM TECHNIC AL J OURNAL Published quarterly by the ?OI/ American Telephone and Telegraph Company 195 Broadway, New York, N. Y. EDITORS R. W. King J. O. Perrine EDITORIAL BOARD F. B. Jewett W. H. Harrison O. B. Blackwell O. E. Buckley A. B. Clark H. S. Osborne S. Bracken M. J. Kelly F. A. Cowan SUBSCRIPTIONS Subscriptions are accepted at Si.50 per year. Single copies are 50 cents each. The foreign postage is 35 cents per year or 9 cents per copy. Copyright, 1943 American Telephone and Telegraph Company P R IN T E D IN U . S A. Bell System Technical Journal, July, 1943 For the purposes of record and assistance to librarians, and for the information of subscribers, it is to be noted that there was no April 1943 issue of the Bell System Technical Journal.
    [Show full text]
  • Stokes Parameters in the Unfolding of an Optical Vortex Through a Birefringent Crystal
    Stokes parameters in the unfolding of an optical vortex through a birefringent crystal Florian Flossmann, Ulrich T. Schwarz and Max Maier Naturwissenschaftliche Fakultat¨ II-Physik, Universitat¨ Regensburg, Universitatsstraße¨ 31, D-93053 Regensburg, Germany [email protected] Mark R. Dennis School of Mathematics, University of Southampton, Highfield, Southampton SO17 1BJ, UK [email protected] Abstract: Following our earlier work (F. Flossmann et al., Phys. Rev. Lett. 95 253901 (2005)), we describe the fine polarization structure of a beam containing optical vortices propagating through a birefringent crystal, both experimentally and theoretically. We emphasize here the zero surfaces of the Stokes parameters in three-dimensional space, two transverse dimensions and the third corresponding to optical path length in the crystal. We find that the complicated network of polarization singularities reported earlier – lines of circular polarization (C lines) and surfaces of linear polarization (L surfaces) – can be understood naturally in terms of the zeros of the Stokes parameters. © 2006 Optical Society of America OCIS codes: (260.1440) Birefringence; (260.2110) Electromagnetic Theory; (260.5430) Po- larization; (999.9999) Singular Optics References and links 1. J. F. Nye, Natural focusing and fine structure of light: caustics and wave dislocations, IoP Publishing, 1999. 2. M. S. Soskin and M. Vasnetsov, “Singular optics,” Prog. Opt. 42 219–276 (2001). 3. J.F. Nye, “Lines of circular polarization in electromagnetic wave fields,” Proc. R. Soc. Lond. A 389 279–290 (1983). 4. M.R. Dennis, “Polarization singularities in paraxial vector fields: morphology and statistics,” Opt. Commun. 213 201–221 (2002). 5. M.V.
    [Show full text]
  • Determination of Degree of Anisotropy of Ktp Crystal Using Reflectance Anisotropy Spectroscopy Technique
    DETERMINATION OF DEGREE OF ANISOTROPY OF KTP CRYSTAL USING REFLECTANCE ANISOTROPY SPECTROSCOPY TECHNIQUE By Fekadu Gashaw A THESIS PRESENTED TO THE SCHOOL OF GRADUATE STUDIES ADDIS ABABA UNIVERSITY IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in PHYSICS ADDIS ABABA, ETHIOPIA JUNE 2006 A DDIS ABABA UNIVERSITY DEAPRMENT OF PHYSICS The undersigned hereby certify that they have read and recommend to the Faculty of Science for acceptance a senior project entitled “Determination of Degree of Anisotropy of KTP crystal using Reflectance Anisotropy Spectroscopy Technique ” by Fekadu Gashaw Master of Science. Dated: June 2006 Supervisor: Dr. Araya Asfaw Readers: Dr. Dereje Ayalew Dr. Mebratu G/mariam ii ADDIS ABABA UNIVERSITY Date: June 2006 Author: Fekadu Gashaw Title: Determination of Degree of Anisotropy of KTP crystal using Reflectance Anisotropy Spectroscopy Technique Department: Deaprment of Physics Degree: M.Sc. Convocation: July Year: 2006 Permission is herewith granted to Addis Ababa University to circulate and to have copied for non-commercial purposes, at its discretion, the above title upon the request of individuals or institutions. Signature of Author iii This Work is Dedicated to My parents and Feru iv Table of Contents Table of Contents v List of Tables vii List of Figures viii Acknowledgements x Abstract xi 1 LIGHT AND MATTER 5 1.1 Maxwell’s Equation . 5 1.2 Propagation of Light through Medium . 7 1.2.1 Electromagnetic wave in Isotropic Dielectric Material . 7 1.2.2 Light in Anisotropic Dielectric (crystal) Medium . 12 1.3 Reflection and Refraction of light at plane boundary . 19 1.4 Amplitudes of Reflected and Refracted waves .
    [Show full text]
  • Development, Principles, and Applications of Automated Ice Fabric Analyzers
    MICROSCOPY RESEARCH AND TECHNIQUE 62:2–18 (2003) Development, Principles, and Applications of Automated Ice Fabric Analyzers 1 1 2 3 L.A. WILEN, * C.L. DIPRINZIO, R.B. ALLEY, AND N. AZUMA 1Department of Physics and Astronomy, Ohio University, Athens, Ohio 45701 2EMS Environment Institute and Department of Geosciences, The Pennsylvania State University, University Park, Pennsylvania 16802 3Nagaoka University of Technology, Nagaoka, Niigata 940-2137, Japan KEY WORDS ice fabric; ice texture; c-axes; nearest-neighbor correlation; polygonization; Schmidt plot; Rigsby stage; fabric analysis ABSTRACT We review the recent development of automated techniques to determine the fabric and texture of polycrystalline ice. The motivation for the study of ice fabric is first outlined. After a brief introduction to the relevant optical concepts, the classic manual technique for fabric measurement is described, along with early attempts at partial automation. Then, the general principles behind fully automated techniques are discussed. We describe in some detail the simi- larities and differences of the three modern instruments recently developed for ice fabric studies. Next, we discuss briefly X-ray, radar, and acoustic techniques for ice fabric characterization. We also discuss the principles behind automated optical techniques to measure fabric in quartz rock samples. Finally, examples of new applications that have been facilitated by the development of the ice fabric instruments are presented. Microsc. Res. Tech. 62:2–18, 2003. © 2003 Wiley-Liss, Inc. INTRODUCTION TO ICE FABRIC Shoji and Higashi, 1978). As ice flows, the crystal tex- AND TEXTURE ture and fabric evolve in a way that depends on the The fabric of ice refers to the distribution of crystal deformation rate and symmetry as well as temperature axes of an assemblage of ice crystals.
    [Show full text]