Light Prism

10 Key excerpts on "Light Prism"

• 

  eBook - ePub

  Light and Optics

  Principles and Practices

  • Abdul Al-Azzawi(Author)
  • 2018(Publication Date)
  • CRC Press

    (Publisher)

  11 Prisms 11.1 INTRODUCTION

  The purpose of this chapter is to explain the basic principles that govern light passing through a prism or a combination of prisms. Types of prisms and image formation are also presented. The concept of light passing through prisms is very important to photonics and has significant use in image formation and building optical devices. Particular emphasis will be given to calculating the index of refraction of a prism, producing a rainbow of colours, and mixing a rainbow of colours using a glass rod or tube. Also in this chapter, along with the theoretical presentation, five experimental cases demonstrate the principles of light passing through prisms.

  11.2 PRISMS

  Prisms are blocks of optical material with flat polished faces arranged at precisely controlled angles, as shown in the figure above. In many situations it is necessary to direct a beam of light entering from one side and exiting from the other side of the prism. Light passing through prisms is governed by the laws of light.

  Prisms are widely used in building optical devices, such as a prism spectrometer, which is commonly used to study the wavelengths emitted by a light source. Prisms are also used in building optical fibre devices, such as an opt-mechanical switch, which deflects or deviates an optical signal through a telecommunication system. Prisms can invert or rotate an image, deviate a light beam, disperse light into its component wavelengths, and separate states of polarization. The orientation of a prism (with respect to the incident light beam) determines its effect on the beam. Prisms can be designed for specific applications. The most popular prisms are right angle prisms, Brewster’s angle dispersing prisms, Penta prisms, solid glass retro-reflectors, equilateral dispersing prisms, littrow dispersion prisms, wedge prisms, roof prisms, and Dove prisms. Some of these commonly used prisms are discussed in detail in this chapter.

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  The Science of Imaging

  • Graham Saxby(Author)
  • 2016(Publication Date)
  • CRC Press

    (Publisher)

  The Science of Imaging, Second Edition: An Introduction 14 Prisms When a beam of light passes through a parallel-sided glass block the emergent beam is parallel to the incident beam, but is displaced from it a little. However, if the second surface is not parallel to the first, as in a prism, the beam undergoes a second deviation (Figure 1.17). (a) (b) (c) (d) (e) < c c > c Figure 1.16 Total internal reflection: (a) glass to air; (b) at the critical angle; (c) total internal reflection (TIR); (d) Porro prism for image inversion; (e) corner cube reflector. (a) Refracting angle Angle of deviation i 2 r 2 r 1 i 1 (b) Red Yellow Green Blue Figure 1.17 (a) Path of light through prism; (b) dispersion of light by prism (see Figure 1.9a). The Nature of Light 15 The combined angle of deviation depends on the angle between the prism’s faces (the refracting angle ) and the angle of incidence at the first surface. The deviation is at a minimum when the incident and emergent beams are symmetrical to the prism. This is another property that is useful in optical design. A prism has another important effect on white light. The refractive indices of trans-parent media are greater for shorter wavelengths than for longer ones, and a prism, like a diffraction grating, spreads white light into a spectrum (Figure 1.9a, color plate). Notice that the spectrum produced by a prism is not linear in its spread, and runs in the opposite direction to that produced by a diffraction grating. Newton was the first person to make a proper examination of the spectrum produced by a prism. Perhaps because of the mystical importance of the number seven, he assigned seven hues to the spectrum, namely red, orange, yellow, green, blue, indigo, and violet. This may seem somewhat confusing today, as the dye indigo (used to color denim jeans) is a desaturated color not in the spectrum at all.

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Modern Instrumental Analysis

  • Satinder Ahuja, Neil Jespersen(Authors)
  • 2006(Publication Date)
  • Elsevier Science

    (Publisher)

  The change in refractive index with wavelength is called the dispersion, and substances with large dispersions are valued for preparing prisms. The reflection of a mirror does not depend upon the refractive index, particularly front-coated aluminum mirrors. The result is that parabolic mirrors can achieve the same collimating and focusing functions as lenses. They are superior because they minimize the aberrations due to refractive index effects and also do not decrease the light intensity as much as light passing through a lens. Wherever possible, modern instruments replace lenses with parabolic mirrors. Dispersion devices . Dispersion of light was first achieved using a glass prism. It was discovered that the prism worked because different wavelengths of light had different refractive indices in glass. The result was that each wavelength was ‘‘bent’’ at a different angle when emerg-ing from the prism, producing the separation of white light into the rainbow of colors. This dispersion was not linear and instrument design was very difficult using prisms. Prisms also had the same disadvantage as lenses in that some light was absorbed passing through the prism, decreasing the overall light intensity. Because of their lack of use in modern instruments, further discussion of prisms is omitted. Reflection gratings greatly decreased the problems formerly associ-ated with prisms. In a reflection grating light is dispersed linearly from one end of the spectral region to the other. Gratings being reflective devices also minimize losses due to absorption of light. General principles of spectroscopy and spectroscopic analysis 131 Figure 5.9 shows a reflection grating with rays illustrating just one set of angles for the light source and light output. In this diagram the line segments AB ¼ A 0 B 0 and CD ¼ C 0 D 0 and the line segments BC and B 0 C 0 may or may not be the same length.

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  Optoelectronics Circuits Manual

  • R M MARSTON(Author)
  • 1999(Publication Date)
  • Newnes

    (Publisher)

  dispersion.

  Figure 9.16 Exaggerated diagram showing a prism splitting a beam of white light into its component colours

  When a ray of light passes through air and enters a prism, it bends by an amount determined by its angle of incidence and by the refractive index value of the glass. When the ray leaves the prism again and returns to the air, it bends by an amount determined by its angle of incidence and by the refractive index of the air (1.0) divided by that of the glass (say 1.5), and this value is invariably less than zero (0.667 in this example). Figure 9.17 shows the actual amounts of output refraction that occur on three different prisms that each have a refractive index of 1.5.

  Figure 9.17 Diagram illustrating the phenomenon of total internal reflection in a prism

  In Figure 9.17 , the ray strikes the output surface of prism A at an incident angle of 30° and leaves the prism at a refractive angle of 42°; this prism thus bends the ray downwards by 12°. In the case of prism B, the ray strikes its output surface at an incident angle of 40° and leaves at a refractive angle of 85°, thus bending the ray downwards by 45°.

  Note in the case of prism B that the ray leaves the prism at an angle that is only 5° less than the angle of slope of the prism’s output face, and it is obvious that if the angle of incidence is increased much more the ray will be unable to penetrate the prism’s output surface. The angle of incidence at which this occurs is known as the surface’s critical angle , and is dictated by the n value of the glass; the critical angle is 43° at an n value of 1.5, 36° at an n value of 1.7, and 32° at an n value of 1.9.

  Figure 9.17 shows, in the Prism C diagram, what happens to the light rays when they strike the prism’s output face at an incident angle of 45°, i.e. at an angle greater than the critical angle of the surface. Under this condition a phenomenon known as total internal reflection

  Sign up to read

  Learn more about book
• 

  No longer available |Learn more

  Physics for Scientists and Engineers

  Foundations and Connections, Extended Version with Modern Physics

  • Debora Katz(Author)
  • 2016(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  White light Glass prism B. u i (u t ) red (u t ) violet Vacuum n i Glass n t A. Mopic/Shutterstock.com Copyright 2017 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-300 1224 CHAPTER 38 Refraction and Images Formed by Refraction Unless otherwise noted, all content on this page is © Cengage Learning. A device known as a prism makes use of dispersion to create a color spectrum (Fig. 38.9B). Two angles—the angle of deviation a and the measure of dispersion d—characterize the dispersion of light emerging from a prism (Fig. 38.10). The measure of dispersion (difference between the deviations for violet and red) depends on the difference between n for violet light and n for red light: The greater this difference, the greater the measure of dispersion. Rainbows Artificial devices such as prisms are not the only causes of dispersion. Dispersion also occurs naturally, creating beautiful phenomena such as rainbows (Fig. 38.11A). For you to see a rainbow, there must be water droplets in the air and the Sun must be behind you. Sunlight is refracted and reflected by the water droplets and into your eyes. These droplets are spread out in the air, and the position of each droplet deter- mines which color enters your eyes (Fig. 38.11B). The highest droplets allow red light to enter your eyes, and the lowest ones allow violet light to do so. Drops in between allow other colors to enter your eyes. Sometimes it is possible to see a second rainbow above the first. The second rainbow’s colors are reversed so that violet is on top and red is on the bottom. The reversal occurs because the sunlight that reaches the secondary rainbow’s droplets undergoes two reflections from the back side of each droplet (Fig. 38.11C). The net result is that the violet ray emerges below the red ray. FIGURE 38.10 A. The angle between the original path of the light and the path of the light that emerges from the prism is the angle of deviation a.

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Building Electro-Optical Systems

  Making It All Work

  • Philip C. D. Hobbs(Author)
  • 2021(Publication Date)
  • Wiley

    (Publisher)

  Light of a certain wavelength thus returns along the path of the incident light, with other wavelengths dispersed on one side or the other. Such a prism is nice because it avoids having the beam direction pass through inconveniently arbitrary angles, and leads to a compact light path with few bends. Such prisms are commonly used as cavity mirrors in argon ion lasers, which allows laser line selection: the laser can oscillate only at the wavelength at which the light path retraces itself. Littrow prisms are not particularly vulnerable to etalon fringes, because the front surface reflections go off at large angles. The residual external reflection can be got rid of easily with a beam dump, and the internal one controlled with a patch of black wax, Krylon #1602, or other index-matched absorber placed where it hits the prism surface. There are several types of compound dispersing prisms, of which the Amici prism is representative. It has alternating triangles of high and low dispersion glass cemented together, oriented like the teeth of a bear trap with the low dispersion prisms forming one jaw and the high dispersion ones the other. This allows multiplication of the dispersing power without the beam having to go in circles as with compound gratings (Section 7.7.1). The cemented construction allows the internal surfaces to work near grazing, for high dispersion, without the large surface reflections and sensitivity to figure errors. Such high dispersion prisms have been superseded almost entirely by diffraction gratings except in oddball applications where polarization sensitivity or overlap of grating orders is a problem and the linearity of the dispersion is not critical. 4.9.4 Pentaprisms A pentaprism is an image erecting prism that maintains a constant 90 ∘ deviation between incoming and outgoing rays, inde-pendent of their incidence angle. The physical basis of this is two reflections in one plane, as in the Porro prism.

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Spectroscopy for Amateur Astronomers

  Recording, Processing, Analysis and Interpretation

  • Marc F. M. Trypsteen, Richard Walker(Authors)
  • 2017(Publication Date)
  • Cambridge University Press

    (Publisher)

  Hence the idea to install multiple prisms positioned in angle of minimum deviation to improve the resolving power. Of course other factors, such as the slit width, telescope parameters and pixel size of the camera, influence the theoretical calculated value of R. Nevertheless the value of R, calculated this way, gives a first directive of the achievable performance. For example, by applying Equation {4.15} we can determine an average value for R for the Fraunhofer lines from F to d of an SF2 glass type prism with a base length of 40 mm: R ¼ 1:66124  1:64769 5876  4861  10 7  40 ¼ 5157 The calculated resolving power of 5157 corresponds to a resolution Δλ of 1.14 Å in the yellow wavelength range based on the He I line at λ5876. 4.2.4 Practical Applications of Prisms Today The use of prisms as the main dispersive element in spectro- graphs is very limited nowadays. The main reasons are the limited resolving power, the weight of the prism and the strongly nonlinear spectral output. The main application for using a prism in spectrographs is as a cross dispensing ele- ment in high resolution Echelle spectrographs and in com- bination with gratings in grisms (grating–prism). The advantage of their high transmission efficiency – up to ~98% – is the reason why they are sometimes used in low resolution professional spectrographs. They are very well suited for studying very faint objects. 4.3 The Dispersive Principle of Grating Spectrographs A grating is an optical element used for the dispersion of light. It is composed of a glass plate with parallel lines or grooves on its surface and is covered with a reflecting aluminum or photosensitive coating. Gratings exist in two different types, transmission or reflection. With the former type incident and diffracted light rays are at opposite sites, with the latter they are at the same side as shown in Figure 4.9.

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Optical System Design

  • Rudolf Kingslake(Author)
  • 2012(Publication Date)
  • Academic Press

    (Publisher)

  F. THE PRISM SPECTROGRAPH 2 The simplest form of prism spectrograph consists of a slit at the focus of a collimator lens to give a parallel beam, a prism, and an 2 R. J. Meltzer, Spectrographs and monochromators, in Applied Optics and Optical Engineering (R. Kingslake, ed.), Vol. 5, p. 47. Academic Press, New York, 1969. I. DISPERSING PRISMS 301 Spectrum FIG. 16.4. A typical quartz spectrograph. objective lens to form a spectrum. The spectrum can be recorded on a photographic film, or selected wavelengths can be detected by photo-cells placed appropriately along the spectrum. In spite of the fact that the dispersion can be increased by tilting the prism out of minimum deviation, this is seldom done because the image magnification is then greater than unity, so the resolution is not increased although the dispersion is, and because it is only at mini-mum deviation that the location of the spectrum is independent of slight errors in mounting the prism in the instrument. If the collimator and objective lenses are achromatic, the spectrum is perpendicular to the lens axis, although, because of the presence of secondary spectrum, the ends of the spectrum will be bent slightly backward, particularly at the blue end. For work in the ultraviolet, a Cornu prism with simple quartz lenses is often used, and in that case the blue end of the spectrum is formed much closer to the objective lens than the red end and the whole spectrum is steeply tilted relative to the lens axis (Fig. 16.4). To reduce the size of the instrument and to save one lens, it is possible to use a 30° prism aluminized on the rear surface to autocolli-mate the light. To prevent the spectrum from being obstructed by the Slit Red Ultraviolet FIG. 16.5. A quartz Littrow spectrograph. 302 16. SPECTROSCOPIC APPARATUS incident light, the slit is raised slightly above the plane of the emerging light, and a small mirror is inserted near the slit to bend the beam through a right angle, as shown in Fig.

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  University Physics Volume 3

  • William Moebs, Samuel J. Ling, Jeff Sanny(Authors)
  • 2016(Publication Date)
  • Openstax

    (Publisher)

  Figure 1.24 (a) Different colors emerge in different directions, and so you must look at different locations to see the various colors of a rainbow. (b) The arc of a rainbow results from the fact that a line between the observer and any point on the arc must make the correct angle with the parallel rays of sunlight for the observer to receive the refracted rays. (c) Double rainbow. (credit c: modification of work by “Nicholas”/Wikimedia Commons) Dispersion may produce beautiful rainbows, but it can cause problems in optical systems. White light used to transmit messages in a fiber is dispersed, spreading out in time and eventually overlapping with other messages. Since a laser produces a nearly pure wavelength, its light experiences little dispersion, an advantage over white light for transmission of information. In contrast, dispersion of electromagnetic waves coming to us from outer space can be used to determine the amount of matter they pass through. Chapter 1 | The Nature of Light 27 1.6 | Huygens’s Principle Learning Objectives By the end of this section, you will be able to: • Describe Huygens’s principle • Use Huygens’s principle to explain the law of reflection • Use Huygens’s principle to explain the law of refraction • Use Huygens’s principle to explain diffraction So far in this chapter, we have been discussing optical phenomena using the ray model of light. However, some phenomena require analysis and explanations based on the wave characteristics of light. This is particularly true when the wavelength is not negligible compared to the dimensions of an optical device, such as a slit in the case of diffraction. Huygens’s principle is an indispensable tool for this analysis. Figure 1.25 shows how a transverse wave looks as viewed from above and from the side. A light wave can be imagined to propagate like this, although we do not actually see it wiggling through space.

  Sign up to read

  Learn more about book
• 

  eBook - PDF

  Optics

  Principles and Applications

  • Kailash K. Sharma(Author)
  • 2006(Publication Date)
  • Academic Press

    (Publisher)

  As shown in Principles of Optics by Born and Wolf, the permitted directions of S lie along a cone which touches the optic axis. 1.10.6 Polarizing Prisms There are a number of ways to produce polarized light. We have seen how inci-dence at Brewster angle (Section 1.7.1) on a singly refracting medium generates polarized light. Light scattered by molecules and small particles in directions orthogonal to the direction of the incident light is substantially polarized. Polar-izing prisms exploit the phenomenon of double refraction in uniaxial crystals to produce polarized light. William Nicol developed the first polarizing prism, called the Nicol prism. Its sectional view is shown in Fig. 1.30a. The optic axis lies in the plane of the figure. The cleaved edges of a calcite crystal are inclined at 71 to each other. This angle is reduced to nearly 68 by grinding the sides. The crystal is then cut along the diagonal as shown, and the two halves are cemented together with a thin layer of canada balsam whose index of refraction n = 1 55 lies between the indices n o = 1 6583 and n e = 1 4864 of calcite. The ordinary wave undergoes total internal reflection at the calcite–canada balsam interface, e-wave e-wave o-wave Optic axis Optic axis Optic axis (a) (b) 68 o o-wave Fig. 1.30: Polarizing prisms; (a) Nicol prism, (b) Glan-Thompson prism. 72 Chapter 1: LIGHT WAVES but the extraordinary wave which is polarized in the plane containing the direc-tion of propagation and the optic axis is substantially transmitted. The ordinary wave, after getting reflected, is absorbed at the blackened edge of the prism. The incident beam should be nearly parallel to the upper and lower edges of the prism. For large deviations (more than 10 − 12 ) from this direction, the ordinary and extraordinary waves may not get separated. Absorption of light by canada balsam restricts the use of Nicol prisms down to about 0 35 m.

  Sign up to read

  Learn more about book