Photonics, Volume 1

Fundamentals of Photonics and Physics

David L. Andrews

• Publisher: Wiley
• Year: 2015
• Print ISBN: 9781118225530
• eBook ISBN: 9781119009702
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Optics & Light
• Index: Technology & Engineering

Covers modern photonics accessibly and discusses the basic physical principles underlying all the applications and technology of photonics. This volume covers the basic physical principles underlying the technology and all applications of photonics from statistical optics to quantum optics. The topics discussed in this volume are: Photons in perspective; Coherence and Statistical Optics; Complex Light and Singular Optics; Electrodynamics of Dielectric Media; Fast and slow Light; Holography; Multiphoton Processes; Optical Angular Momentum; Optical Forces, Trapping and Manipulation; Polarization States; Quantum Electrodynamics; Quantum Information and Computing; Quantum Optics; Resonance Energy Transfer; Surface Optics; Ultrafast Pulse Phenomena.

• Comprehensive and accessible coverage of the whole of modern photonics
• Emphasizes processes and applications that specifically exploit photon attributes of light
• Deals with the rapidly advancing area of modern optics
• Chapters are written by top scientists in their field

Written for the graduate level student in physical sciences; Industrial and academic researchers in photonics, graduate students in the area; College lecturers, educators, policymakers, consultants, Scientific and technical libraries, government laboratories, NIH.

1
A Photon in Perspective

David L. Andrews

School of Chemistry, University of East Anglia, Norwich, UK

1.1 Introduction

It is a familiar, fundamental truth of modern Physics that light is composed of photons, entities known as elementary particles despite possessing both particle- and wave-like attributes. Readers of these volumes on Photonics will accede with the view that numerous properties and interactions of light are only fully comprehensible when represented and formulated in terms of photons. Indeed, in order to understand certain processes, there simply appears to be no viable alternative. This is not only the case with observations such as the photoelectric effect that have played a pivotal role in familiar scientific history; in optics there is a wealth of recent and developing applications that also hinge on other, specifically photon-borne properties. Many properties of light appear to manifest directly corresponding attributes of the individual photons. Other qualities, of course, reflect ensemble characteristics that can emerge only in a beam comprising numerous photons—but there too we find phenomena dependent on statistical properties which can only make sense by reference to photon distributions. There is a rich and deeply embedded relationship between photons and the modern science of light.

The word photon has not yet reached its centenary; it was in fact coined in 1926 by a thermodynamics researcher named Lewis [1], who surprisingly introduced it to describe “not light but [that which] plays an essential part in every process of radiation.” However, the emergence of a reasonably fully fledged photon concept can be traced back much earlier, to 1905, where it first surfaced in Einstein's explanation of a frequency threshold for photoelectric emission. Using the term Lichtquant, “light quantum,” Einstein wrote: “When a light ray spreads out from a point source, the energy is not distributed continuously over an increasing volume [wave theory of light], but consists of a finite number of energy quanta that are localized at points in space, move without dividing, and can only be absorbed or generated as complete units” [2].

With subsequent success in explaining the line spectra of atoms, this quantum concept rapidly gained an apparently incontrovertible status—and given the passage of time, one might suppose that there would now be little left to discover, little scope for debate over what the photon truly is. However, the nature of that reality has never been simple to explain. It is telling that Lamb, an early pioneer of modern optical spectroscopy, would jest that it should be necessary to be granted a license before being allowed to use the word photon [3]. Following the arrival of the laser [4] and the subsequent emergence of the derivative term “photonics” in the 1960s, the distinctive and sometimes paradoxical nature of the photon has become more than ever evident. The state of knowledge even a quarter of a century ago is a pale shadow of the current understanding; many of the issues discussed in the following were unheard of even at that time [5]. What we now understand about photons has certainly become very much richer, certainly less simple, than Einstein's original conception.

It powerfully illustrates the wide diversity of interpretation that, as more and more exotic phenomena have been identified, specially coined descriptors have been introduced to identify and qualify particular kinds of behavior with which photons can be associated. So we now find in the literature terms that would seem to signify various distinctive kinds of photon, if such a thing were possible. Examples abound: we read of photons whose character is dressed [6], ballistic or snake-like [7, 8], electric or magnetic [9, 10], entangled and heralded [11, 12], dipole or quadrupole [13, 14], real or virtual [15, 16] … there is literature on biphotons [17]—and so the list goes on. Different kinds of system or physical effect certainly manifest different attributes of the photon, but it is evident that various scientific communities and practitioners who share the use of the term would not find themselves in full agreement on every aspect of what a photon is. Far from becoming a fixture in modern physics, the notion of a photon has, if anything, become more of a quandary as time goes by. Many of those who research such matters would be drawn to agree with Loudon, author of one of the classic books on the quantum theory of light, that “it is no longer so straightforward to explain what is meant by a photon” [18].

It is also remarkable that, in the centenary year of the photon concept, 2005, a major international conference with the title What is a Photon? could attract wide-ranging contributions and stimulate debate amongst leading scientists from across the globe [19]. Indeed, that initial meeting spawned an ongoing series of conferences and discussions in which the truth and character of the photon continues to be the subject of highly active deliberation. So it seems fitting, in this first chapter of the series on Photonics, to attempt an objective assessment of which, if any, of those photon attributes are incontrovertible, representing a common ground for interpretation—and also to provide a certain perspective on some of the more intricate and less well-settled issues. As we shall see, even the momentum or information content of a photon, or the existence of its wavefunction, are not entirely uncontroversial.

1.2 Foundations

1.2.1 Modes of Optical Propagation

To lay the foundations for a discussion of the most unequivocal photon properties, it will first be helpful to recall some established ground from classical optics—which will also serve to introduce some key definitions. It has been known, since the pioneering work of Maxwell, that light entails the propagation of mutually associated, oscillatory electric and magnetic induction fields, which we shall call e and b, respectively (lowercase symbols being used, as is common, to signify fields in a microscopic regime). In free space these fields propagate at a speed c, and they oscillate at a common frequency ν, in phase with each other. The simplest case, polarized monochromatic light, can be regarded as a fundamental mode of excitation for the radiation field—an optical mode that is conveniently characterized by two quantities: a wavevector k and a polarization η. The former is a vector in conventional three-dimensional space, pointing in the direction of propagation such that the triad of vectors e, b, and k together form a right-handed, mutually orthogonal set; its magnitude is k = 2πν/c = 2π/λ, where λ is the optical wavelength.

The second mode attribute, the polarization η, which designates the disposition of the electromagnetic oscillations, is most often a label rather than a directly quantifiable variable. Plane (or linear) and circular polarizations are the most familiar forms: circular polarizations in particular occupy a privileged position with regard to some of the ancillary properties to be examined below. The terms “linear” and “circular” are usually taken as referring to a proj...

Table of contents

• List of Contributors
• Preface
• Chapter 1: A Photon in Perspective
• Chapter 2: Coherence and Statistical Optics
• Chapter 3: Light Beams with Spatially Variable Polarization
• Chapter 4: Quantum Optics
• Chapter 5: Squeezed light
• Chapter 6: Electromagnetic Theory of Materials
• Chapter 7: Surface and Cavity Nanophotonics
• Chapter 8: Quantum Electrodynamics
• Chapter 9: Multiphoton Processes
• Chapter 10: Orbital Angular Momentum
• Chapter 11: Introduction to Helicity and Electromagnetic Duality Transformations in Optics
• Chapter 12: Slow and Fast Light
• Chapter 13: Attosecond Physics: Attosecond Streaking Spectroscopy of Atoms and Solids
• Index
• End User License Agreement