Classical and Quantum Optics is the first text to cover classical and quantum optics as a single subject with the premise that genuine understanding of light requires mastery of both fields. It addresses all aspects of light equally, including geometric optics, wave optics, electromagnetic optics, and quantum optics. This timely book supplies the tools needed to fully explore the behavior of light.
Classical and Quantum Optics:
Approaches the topic from a conceptual perspective without assuming the reader's knowledge
Includes relatively little math, making it ideal for students in applied sciences and engineering
Starts with well-established hypotheses and builds on them to explain physical effects and experimental observations
Classical and Quantum Optics is suitable for emerging researchers and professionals in optics, natural sciences, engineering, and interdisciplinary fields, as well as students in physics, applied sciences, and engineering.
Dedicated to my family: my daughters, Manasvini and Nakshatra, my wife Latha, and my parents (Gita Mandal and Kartik C. Mandal).
Light can be better represented as a superposition sum of a pure wave function and a pure particle function, ψlight = αψwave + βψparticle
— Partha Pratim Mondal, Self-Thought
Preface
Light has fascinated humans since the beginning of civilization, and observations of celestial objects (stars, pulsars, comets, supernovae, and other galactic phenomena) have been recorded throughout history. It is believed that the universe we see today began with the Big Bang about 13.8 × 109 years ago, and the cosmic microwave background (CMB) is thought to be the leftover radiation from that event. The oldest known supernova explosion (Vela Supernova) occurred about 20 000 years ago. In our galaxy (the Milky Way), several supernova events have been observed, with SN1604 being the most recent to be observed by the naked eye. In 393 CE, the appearance of SN 393 (in the constellation of Scorpius) was observed by the Chinese, and in the year 1006 CE, the observation of SN1006 in.the constellation Lupus was recorded. Many such galactic events have been observed in modern times, primarily due to the technological advances in detecting weak radiation. The observation of the first pulsar was made by Jocelyn Bell Burnell and Antony Hewish in 1967 (Jocelyn Bell Burnell, 1977; and Longair, 1994). Pulsars are spinning magnetic neutron stars that generate highly directed synchrotron radiation. Another optical phenomenon critical for human civilization is photosynthesis, in which light energy is absorbed by chlorophyll molecules in plants to convert CO2 and water into oxygen and carbohydrates. An earlier use of light was by the Greeks (1700–1300 BC), who were known to direct daylight into brightened underground palaces through light wells (shafts). There are numerous other examples of observations of celestial events and the use of light by our ancestors.
Over the centuries, many theories have emerged to explain light and its behavior. However, the first scientifically sound theories of light were independently proposed by Christiaan Huygens and Isaac Newton nearly simultaneously in the 17th century. But the very origins of these two theories were distinct. The corpuscular theory proposed by Newton described light as a stream of microscopic particles called “corpuscles” that travel in a straight line and have finite velocity. On the other hand, Huygens's theory assumed that light behaves more like waves that successfully explain diffraction, interference, and related optical phenomena. The corpuscular theory failed to explain these effects and was, thus, subsequently abandoned in favor of the wave theory. In the 20th century, the behavior of light was revisited and surprisingly was found to possess both particle and wave properties.
Since the 15th century, humanity has been learning how to control and manipulate light. The use of simple optical elements like mirrors and lenses to divert light and magnify images led to the invention of sophisticated instruments (such as microscopes and telescopes). A microscope captures light emerging from a minute (microscopic) object and magnifies it to make it visible to the naked eye. On the other hand, telescopes magnify light collected from objects that are at large, often astronomical, distances from the observer.
In the 21st century, humans have mastered the art of generation, manipulation, concentration, and guided propagation of light. From 1900 to 2000, there was a massive effort to develop bright sources of light. The invention that thrived early on was the incandescent bulb invented by Joseph Swan and Thomas Edison in two different parts of the world. Edison's invention of the electric bulb was more widely adopted primarily due to its longer lifetime. Subsequently, there was a revolution in what can be termed “light engineering.” Light is harvested for our daily activities and scientific investigations in fields ranging from biology to medicine and physics to engineering, including data transmission over optical fibers, and visualization of internal organs through endoscopes in medical practice. It is important to understand that the term “light” is often used to represent the entire electromagnetic spectrum from gamma rays to radio waves. It, therefore, becomes imperative to understand the basic theories and the related effects of light. These theories have been put forward to understand both straightforward and complex properties ranging from those easily observed by the naked eye to subtle quantum effects.
Readers are encouraged to look at some of the spectacular images available on the Internet that have been acquired using imaging systems ranging from microscopes to telescopes. Behind these beautiful images lie several sophisticated optical elements, including sensitive detectors. Optical systems are based on the concrete theories developed over the last four centuries. They range from the simple notion of light as rays/waves to light as particles. Light is currently understood to be an electromagnetic wave that propagates in the form of two mutually coupled vector waves, i.e., electric- and magnetic-field waves. In everyday life, we seldom observe the electromagnetic nature of light. Nevertheless, many optical phenomena can be described by simply assuming that light is a scalar wavefunction. This kind of description does not involve electric or magnetic wave vectors and can be replaced by a single scalar wavefunction. The approximate way of treating light is called scalar wave optics or simply wave optics. However, the wave nature of light is not evident when it interacts with macroscopic objects like lenses and mirrors. It is observed that wave nature is not evident when the light waves propagate through and around objects whose dimensions are larger than the dimension of light (wavelength of light). This further suggests that in such circumstances, light can be treated as a ray and consequently its characteristics can be described by a set of geometrical rules. This simplistic way of treating light is called ray optics. Although classical optics (ray, wave, and electromagnetic optics) provides a broad understanding of light, it fails to explain some of its important properties that are beyond the reach of classical optics. This is due to the fact that light does not always behave as a ray or scalar/electromagnetic wave but rather as particles of well-defined energy called photons. These properties are not described by classical optics but can be accounted for by the specialized treatment of light called quantum optics.
It should, however, be noted that each theory of light has a well-defined domain, and none of them is obsolete. The following four theories succinctly describe light:
Ray optics is a suitable description when the wavelength of light (λ) is small compared with the dimensions of optical elements through/around which it passes.
Wave optics describes the behavior of light when the dimensions of optical elements (such as pinholes, slits, or microscopic objects) are comparable to the wavelength of light.
Electromagnetic optics is a useful way of describing light when it passes through active optical elements (such as quartz and crystals) that are sensitive to the direction of the electric or magnetic fields of light. The electrical properties of the light field are also evident from its coupling to metals at the dielectric–metal interface.
Quantum optics is a more recent description of light that accounts for its behavior as a particle rather than waves. For example, photoelectric and photon bunching effects suggest that light should be treated as packets of finite energy called photons.
Scope
This book provides an introduction to the fundamental properties of light (both classical and quantum) and its peculiar effects, e.g., the Casimir and Hanle effects. Both the wave nature and particle nature of light are explored. Wherever possible, I have incorporated examples and discussed applications. This book is self-consistent, complete, and does not heavily rely on references. This book is designed to serve as a reference for almost all the sciences and engineering disciplines that use light in some way. The scope of the book is as follows:
Understanding the fundamentals of light, beginning from its classical foundations in geometric, wave, and electromagnetic optics to quantum interpretations.
The geometrical effects of light encountered in daily life and its propagation and use in simple optical components and devices.
The wave nature of light responsible for interference and diffraction and its potential for carrying out sensitive measurements (involving interferometers and pinholes).
The electric, magnetic, and electromagnetic effects of light that facilitate the realization of ultra-high-precision instruments and devices.
The quantum behavior of light, i.e., the existence of discrete chunks of energy that explain minuscule optical forces and its utilization for high-precision measurements in atomic systems and detection of ultra-weak signals.
The unusual and surprising effects of light that result from the quantized nature of the radiation field.
In recent decades, the use of light has expanded at a rapid pace and given rise to new interdisciplinary research fields, especially those at the interface of existing disciplines in science and engineering. Due to its non-invasive nature, free-space propagation, and largely neutral behavior, light is expected to be the catalyst for many future developments.
Representative Courses
The chapters can be organized in several ways for use as a crash course or as a complete course for an entire semester. Examples of a few representative courses are as follows:
Principles of classical optics
Ray and Matrix Optics: A Simple Theory of Light
Wave and Fourier Optics
Wave Aspects of Light: Diffraction and Interference
Electromagnetic Optics and Polarization of Light
Fundamentals of quantum optics
Introduction to Quantum Optics
Field Quantization and Hamiltonians
Quantum States of Light
Squeezed States of Light
Bunching, Unbunching, and Antibunching of Light
The Representation Theory of Light
Atom–Field Interaction
Selected Effects in Quantum Optics
Intended Audience
The book Classical and Quantum Optics may serve many purposes and readers ranging from enthusiasts to researchers to industrial experts. Specifically, the book may serve in the following ways:
An introductory textbook for beginners (undergraduates and graduate students) in fields ranging from fundamental to engineering physics.
A reference for enthusiasts from other science disciplines (biologists, chemists, and engineers) who work in interdisciplinary fields.
A complete reference for industrial experts and professionals.
A guide for optical engineers and applied physicists currently working in the fields of optical communications, quantum computing, and other advanced optical technologies.
For medical physicists, biophysicists, and clinical biologists investigating and diagnosing diseases using light as a probe.
For experimentalists primarily using light as a tool for investigation and research.
For innovators for the design and development of novel optical and biomedical devices.
The reader is expected to have a school-level knowledge of mathematics and natural sciences. The book is designed to build the basic concepts, convey essential physics, and bring readers to an advanced level in a gradual manner. The intent is to guide them from a basic to an advanced theory of light that includes quantum effects. In this respect, some of the chapters can be coupled together to constitute separate monograms. With the basics covered, the book can serve as an essential text for advanced research and novel applications.
Acknowledgments
I am indebted to my parent institution (Indian Institute of Science, Bangalore, India) for providing me with the much-needed academic freedom that allowed me to take up this project along with teaching and research.
I drew on numerous science and engineering books and journal articles that influenced the topics covered in this book. Indeed, many figures and illustrations are borrowed, for which appropriate permissions were obtained, and references are cited.
I am grateful to Professor Malvin Carl Teich (Professor Emeritus, Boston University, MA, USA and Columbia University, NY, USA) for providing the necessary references. I am grateful to my friend, Samuel T. Hess (University of Maine, Orono, Maine, USA), for all the friendly discussions on various aspects of light and optics. Many thanks to my mentors, Professor Kanhirodan Rajan (Indian Institute of Science, Bangalore, India), Professor Alberto Diaspro (IIT, Genova and University of Genova, Italy), Professor Peter T. C. So (Massachusetts Institute of Technology, MA, USA), and Professor Richard Gilbert (Northeastern University, MA, USA) for introducing me to optics and imaging. Special thanks to Professor Alberto Diaspro (IIT, Genova, and University of Genova, Italy) and his lab for introducing me to the wonderful field of optics and light microscopy and for the continued support over the years. Over the years, my collaborations with Dr. Franchesca Cella (University of Pisa, Italy), Dr. Subhra Mandal (University of Nebraska, Lincoln, USA), Professor Upendra Nongthomba (Indian Institute of Science, Bangalore, India), Dr. Abhishek Kumar, and Dr. Matthew Parent (Marine Biological Laboratory, Woods Hole, MA, USA) have helped me shape my research.
The book is modeled on the course (IN302: Classical and Quantum Optics) that I teach at my parent institution (Indian Institute of Science, Bangalore, India) and the class notes that I have prepared over the years. The active participation of students in the course has helped me shape the chapters. I am grateful to my research students (Prashant Kumar, Prakash Joshi, Jigmi Basumatary, Arvinth S, and Neptune Baro) for going through the chapters and providing me feedback from a student's perspective. Many of them have gone through the chapters many times and provided me suggestions for minor corrections.
Many thanks to numerous colleagues and fellow faculties from the parent institute (Indian Institute of Science, Bangalore) for collaborative support. Special thanks goes to Dr. Latha Kumari (BMS College of Engineering, Bangalore) for providing scientific feedback and for thoroughly going through the book chapters.
A heartfelt thanks to Duncan Enright (Project Editor), Simina Calin (Commissioning Editor), Martine Felton (Development Editor), Kevin Malone (Senior Content Editor), Michael Lynch (Senior Content Editor), Dina Rabie (Content Editor), and others at AIP Publishing for giving me the opportunity to write this book.
Partha Pratim Mondal
Indian Institute of Science