**Preface** XI

	- **Part 2 Quantum Phenomena with Laser Radiation 85**

Preface

of light.

The book covers a wide spectrum of research problems concerning quantum theory of light and experiments using its quantum properties. In reference literature one can find a number of definitions for the term "quantum optics" – from the sphere of phenomena revealing the quantum nature of light to the optics section dealing with statistical properties of emission. Such a contradictory situation reflects a complicated way of notion formation. Difficulties of the classical wave concept of light were the basis for formulating new quantum concepts of light emission, propagation, interaction and a new general concept – field concept of matter in the first quarter of the 20th century. In this sense we can speak about quantum optics whenever optical phenomena are considered from the position of quantum theory. That is especially true for the world of phenomena that can be discussed and understood only within the framework of quantum picture. The possibilities of optical experiments have been broadened fantastically by the invention of laser. Since lasers are quantum optical generators, the domain of experiments with laser emission seems to be close to quantum optics. At the same time, strong electromagnetic fields generated by lasers usually manifest their classical properties, so some analysis is necessary for including the observed phenomena into the field of quantum optics. In classical optics, correlation properties of light connected with the statistical nature of a real experiment were discussed in terms of the conception "coherence". In the experiments of Hanbury Brown–Twiss with quantum detecting of light, the process of receiving an electromagnetic emission was considered a usual random process for the first time. Later on, the whole ideology of probability theory and stochastic processes was applied to optical phenomena using quantum detectors for analyzing the statistical (correlation) properties of electromagnetic fields in optics. It gives substantiation for quantum optics identification as a statistical theory

The editor was faced with different interpretations of quantum optics while analyzing the chapter proposals. Upon examining them, he reached the conclusion that all theoretical and experimental papers were welcome if they contributed to our understanding of light as a quantum phenomenon. The accepted approach was to speak about quantum optics in a wide sense, i.e. different phenomena demonstrating the quantum nature of light together with theoretical constructs applied to them; and in the narrow sense, i.e. the statistical theory of light processes and its incarnation with
