Optics Demystified Demystified Series Accounting Demystified Advanced Calculus Demystified Advanced Physics Demystified Advanced Statistics Demystified Algebra Demystified Alternative Energy Demystified Anatomy Demystified Astronomy Demystified Audio Demystified Biochemistry Demystified Biology Demystified Biotechnology Demystified Business Calculus Demystified Business Math Demystified Business Statistics Demystified C++ Demystified Calculus Demystified Chemistry Demystified Circuit Analysis Demystified College Algebra Demystified Complex Variables Demystified Corporate Finance Demystified Databases Demystified Diabetes Demystified Differential Equations Demystified Digital Electronics Demystified Discrete Mathematics Demystified Dosage Calculations Demystified Earth Science Demystified Electricity Demystified Electronics Demystified Engineering Statistics Demystified Environmental Science Demystified Everyday Math Demystified Fertility Demystified Financial Planning Demystified Fluid Mechanics Demystified Forensics Demystified French Demystified Genetics Demystified Geometry Demystified German Demystified Global Warming and Climate Change Demystified Hedge Funds Demystified Investing Demystified Italian Demystified Java Demystified JavaScript Demystified Lean Six Sigma Demystified Linear Algebra Demystified Macroeconomics Demystified Management Accounting Demystified Math Proofs Demystified Math Word Problems Demystified MATLAB? Demystified Medical Billing and Coding Demystified Medical Charting Demystified Medical-Surgical Nursing Demystified Medical Terminology Demystified Meteorology Demystified Microbiology Demystified Microeconomics Demystified Nanotechnology Demystified Nurse Management Demystified OOP Demystified Optics Demystified Options Demystified Organic Chemistry Demystified Pharmacology Demystified Physics Demystified Physiology Demystified Pre-Algebra Demystified Precalculus Demystified Probability Demystified Project Management Demystified Psychology Demystified Quantum Field Theory Demystified Quantum Mechanics Demystified Real Estate Math Demystified Relativity Demystified Robotics Demystified Sales Management Demystified Signals and Systems Demystified Six Sigma Demystified Spanish Demystified Statistics Demystified String Theory Demystified Technical Analysis Demystified Technical Math Demystified Thermodynamics Demystified Trigonometry Demystified Vitamins and Minerals Demystified Optics Demystified Stan Gibilisco Copyright ? 2009 by The McGraw-Hill Companies, Inc. All rights reserved. Printed in the United States of America. Except as permitted under the United States Copyright Act of 1976, no part of this publication may be reproduced or distributed in any or by any means, or stored in a database or retri system, without the prior written permission of the publisher. ISBN: 978-0-07-178215-9 MHID: 0-07-178215-X The material in this eBook also appears in the print version of this title: ISBN: 978-0-07-149449-6, MHID: 0-07-149449-9. All trademarks are trademarks of their respective owners. Rather than put a trademark symbol after every occurrence of a trademarked name, we use names in an editorial fashion only, and to the benefit of the trademark owner, with no intention of infringement of the trademark. Where such designations appear in this book, they have been printed with initial caps. McGraw-Hill eBooks are available at special quantity discounts to use as premiums and sales promotions, or for use in corporate training programs. To contact a representative please e-mail us at

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To Samuel, Tim, and Tony ABOUT THE AUTHOR Stan Gibilisco is an electronics engineer, researcher, and mathematician who has authored numerous titles for the McGraw-Hill Demystified series, along with more than 30 other books and dozens of magazine articles. His work has been published in several languages. Contents Preface CHAPTER 1 The Nature of Light The Speed of Light Newton’s Particle Theory The Wave Theory The Electromagnetic Spectrum Light and Relativity Simultaneity Quiz CHAPTER 2 Classical Optics Reflection Refraction Color Dispersion Lenses Quiz CHAPTER 3 Common Optical Devices Color Mixing Cameras Projectors and Displays Optical Microscopes Optical Telescopes Quiz CHAPTER 4 Common Optical Effects Radiation Pressure Scattering Diffraction Phase and Interference Polarization Quiz CHAPTER 5 Laser Fundamentals What Is Laser Light? The Cavity Laser Semiconductor Lasers Solid-State Lasers Other Noteworthy Lasers Quiz CHAPTER 6 Optical Data Transmission Optical and Image Transducers Modulating a Light Beam Fiberoptics Robotics Applications Quiz CHAPTER 7 Optics in the Field Ranging and Alignment Industrial Applications Other Applications of Lasers Quiz CHAPTER 8 Exotic Optics Holography How Holograms Are Made Photometry and Spectrometry Astronomy beyond the Visible Quiz CHAPTER 9 Optics to Heal and Defend Medical Diagnosis and Treatment Medical Surgery Military Optics Quiz CHAPTER 10 Optical Illusions Lines and Curves Depth and Displacement Size and Shape Ambiguity and “Ghosts” Quiz Final Exam Answers to Quiz and Exam Questions Suggested Additional Reading Index Preface This book is for people who want to learn about optics or refresh their knowledge of the field. The course can be used for self-teaching or as a supplement in a classroom, tutored, or home-schooling environment. Each chapter ends with a multiple-choice quiz. You may (and should) refer back to the text when taking these quizzes. Because the quizzes are “open- book,” some of the questions are rather difficult, but one choice is always best. When you’re done with the quiz at the end of a chapter, give your list of answers to a friend. Have the friend tell you your score, but not which questions you got wrong. The answers are in the back of the book. Stick with a chapter until you get all of the quiz answers correct. The book concludes with a multiple-choice, “closed-book” final exam. Don’t look back into the chapters when taking this test. A satisfactory score is at least 75 answers correct, but I suggest you shoot for 90. With the exam, as with the quizzes, have a friend tell you your score without letting you know which questions you missed. That way, you won’t subconsciously memorize the answers. The questions are similar in at to those you’ll encounter in standardized tests. Suggestions for future editions are welcome. Stan Gibilisco Optics Demystified CHAPTER 1 The Nature of Light The behavior of light has baffled scientists for centuries. Light rays can pass through glass, but are blocked by cardboard. Light rays can be reflected, bent, and split into colors. Light rays act like particle streams in some experiments, and like wave trains in other experiments. The Speed of Light Casual observations suggest that the speed of light is infinite. We can aim a flashlight at a mirror, switch on the light, and instantly see the reflection. Even if we put a large mirror on a distant hill and shine a powerful lantern at it, we’ll see the reflected beam as soon as we activate the lantern. Nevertheless, light rays travel at finite speed. A ray of light takes a little more than 1 second (1 s) to get from the earth to the moon. EARLY EXPERIMENTS The first serious attempt to measure the speed of light was conducted by two people with kerosene lamps and shutters, standing on hilltops several kilometers apart on a direct line of sight. The experimenters agreed that at a certain time, one of them would open the lamp shutter in view of the other. The instant the other person saw the light from the distant hill, he would open the shutter of his lantern. Allowances were made for human reaction time. When the first experimenter opened the shutter, he saw the light from his companion’s lantern immediately. Light traversed the distance between the hills with a round-trip time too short to measure. In the late 1600s, a Danish astronomer named Ole Roemer noted discrepancies in the orbital period of one of Jupiter’s moons. When Jupiter was on the far side of the sun, the timing of the orbit was delayed by several minutes compared to when Jupiter was exactly opposite the sun. This discrepancy was repeated year after year. Roemer attributed this delay to the fact that the light from Jupiter travels farther to reach the earth when Jupiter and the earth are on opposite sides of the sun, as compared to when Jupiter and the earth are on the same side of the sun. He realized that the difference in distances was exactly twice the radius of the earth’s orbit. Unfortunately, Roemer didn’t know the earth’s orbital radius. If he had, he would have come up with a figure of around 227,000 kilometers per second (km/s) for the speed of light through space. THE FIZEAU WHEEL As generations passed, scientists developed increasingly sophisticated schemes for measuring the speed of light. One ingenious machine, devised and built by Armand Fizeau in 1849, had a rotating, serrated wheel through which a focused light beam passed. The rotating wheel broke the light beam up into pulses. The beam was aimed at a mirror several kilometers away, which reflected the rays back through the serrated wheel to the observer’s eye. Before the Fizeau wheel could be operated, the hardware had to be carefully set up and aligned (Fig. 1-1). The distance between the lamp and the mirror had to be considerable. Fizeau correctly reasoned that as he increased this distance, the accuracy of his measurements would improve. Once the device was aligned and working, Fizeau set the wheel so the light beam would pass through one of the notches, out to the mirror, and back again through the same notch. Then the wheel was slowly turned. At first, the rate of rotation was so slow that the light beam returned through the same notch. As the rate of rotation increased, the wheel would rotate enough so the opaque part of the wheel blocked the returning ray. The rotational speed was increased gradually until the light beam reappeared. Then Fizeau knew that he was looking at the reflected beam through the next serration on the wheel. Figure 1-1 Simplified illustration of the Fizeau wheel. As the light ray travels to and from the distant mirror, the wheel rotates from one notch to the next. The significance of point P is discussed in Solution 1-1. Fizeau measured the angular speed of the wheel in rotations per second. He took the reciprocal of that figure, getting the number of seconds per rotation. He divided that result by the number of serrations around the wheel’s circumference, obtaining the number of seconds per serration. He deduced that the resultant figure was equal to the time, in seconds, required for the light beam to make the round trip to and from the mirror. If he called this time interval t, and if he set the distance between the wheel and the mirror to d meters, then the speed of light c, in meters per second, would come out as c = 2d/t When Fizeau conducted his experiment in this way and made his calculations, he obtained a figure of c = 3.13 × 108 meters per second (m/s). Another French physicist, Jean Foucault, built a more sophisticated system that used rotating mirrors rather than a serrated wheel. His results produced a figure of c = 2.98 × 108 m/s—within 1 percent of the value we accept today. TIME AND DISTANCE VERSUS THE SPEED OF LIGHT As published on the Web site of the National Institute of Standards and Technology (NIST) in 2007, the speed of light in a vacuum is c = 2.99792458 × 108 m/s Today, this is taken as an exact value, because c is regarded as a universal constant, inherent in the nature of time and space. It has this value as seen from any nonaccelerating reference frame, regardless of the speed of the observer relative to the source. According to the NIST, 1 s is the length of time required for 9.192631770 × 109 oscillations in the transition between the two hyperfine levels of the ground state of a cesium-133 atom. That’s a lot of jargon, but we can think of it as 9.192631770 × 109 “vibrations” in a certain radioactive material that always behaves in the same way. The cesium atom is considered as an “absolute natural metronome” that beats at a perfectly constant rate at all times. The meter is defined on the basis of the second and the speed of light, taking advantage of the fact that for anything in motion at a constant speed along a straight line, the displacement is equal to the speed multiplied by the elapsed time. One meter (1 m) is thus defined as the distance that a ray of light travels in 1/(2.99792458 × 108) of a second through a vacuum. We have established the values of three important universal constants: the speed of light, the second, and the meter. The relationship among them can be expressed in three ways: t = d/c d = ct c = d/t where t is the elapsed time in seconds, d is the distance in meters that a beam of light travels, and c is the speed of light in meters per second. LARGE DISTANCE UNITS In astronomy, large units of distance are based on the speed of light and the second. One minute (1 min) is precisely 60 s, and one year (1 y) is approximately 3.155693 × 107 s. On that basis, we can calculate distance units called the light-second (lt · s), the light-minute (lt · min), and the light- year . These are as follows, accurate to three significant figures in meters (m), kilometers (km), and statute miles (mi): Of these units, the light-year is the most familiar to lay people. In popular science literature, it’s often quoted in approximate terms such as “10 trillion kilometers” or “6 trillion miles,” where a “trillion” means 1,000,000,000,000 or 1012. PROBLEM 1-1 Imagine that we set up a rotating-wheel apparatus to reenact the experiment of Armand Fizeau. We place a mirror 1.0000 × 104 m (or 10.000 km) from the lamp-and-wheel system. The wheel has 100 evenly spaced notches around its circumference. We switch on a motor, and the wheel begins to rotate. As we gradually increase the angular speed of the wheel, the reflected beam disappears. The reflected beam first reappears when the wheel reaches an angular speed of ρ1 rotations per second (r/s). We increase the angular speed a little more, and the reflected beam remains visible until the wheel reaches the slightly higher angular speed of ρ2 r/s. Beyond that speed, the beam disappears again. We take the average of these two rotation rates (call it ρ) and use it for the purpose of calculating c, the speed of light. Suppose our experiment works out well. Consider c = 3.00 × 108 m/s. What is the value of ρ, the average angular speed of the wheel at which the reflected beam first reappears, in wheel rotations per second (r/s)? Are there other angular speeds at which we should also expect the beam to be visible? If so, what are those angular speeds? SOLUTION 1-1 Let’s find the time interval t between the emission of a light-beam pulse from the wheel and its return from the mirror, just before the beam passes through the wheel again. We use the middle of each pulse as the basis for our timing. Imagine that we place a photovoltaic cell at point P as shown in Fig. 1-1 and then connect an oscilloscope to the cell so we can view the returning light pulses on the oscilloscope display (Fig. 1-2). The distance between P and our eye (the whole length of the wheel apparatus) is negligible compared with the distance between P and the mirror. The time interval t, as we define it, is from the middle of any given pulse to the middle of the next pulse. The distance d between the wheel apparatus and the mirror is 1.0000 × 104 m. We know that c = 3.00 × 108 m/s. We can rearrange the above equation relating distance, time, and the measured speed of light to obtain t = 2d/c Figure 1-2 Oscilloscope display of returned light pulses in a latter-day Fizeau-wheel experiment before passing through the wheel the second time. The horizontal axis portrays time. The vertical axis shows the relative signal strength. When we plug in the numbers, we get t = (2 × 1.0000 × 104)/(3.00 × 108) = (2.0000 × 104)/(3.00 × 108) = 6.67 × 10?5 s There are 100 notches in the wheel. That means the wheel must complete one rotation in a time interval equal to 100t, or 6.67 × 10?3 s, for the returning beam to go precisely through the notch immediately adjacent to the notch it passed through on its way out. The rate of rotation, ρ, in rotations per second, is therefore ρ = 1/(100t) = 1/(100 × 6.67 × 10?5) = 1/(6.67 × 10?3) = 150 r/s This is the slowest angular speed at which the beam will pass cleanly through the wheel on its return (except for when the wheel is stationary). The beam will also be visible at any angular speed equal to a whole-number multiple of ρ. If the angular speed is 2ρ, the beam will return after the wheel has rotated through two notches. If the angular speed is nρ (where n is a whole number), then the beam will return after the wheel has turned through n notches. We will therefore see clean beam returns at angular speeds of 150 r/s, 300 r/s, 450 r/s, 600 r/s, and so on. Newton’s Particle Theory The fact that light travels through a vacuum in straight lines supports the notion that light consists of fast-moving particles or corpus