The third edition of "Principles of Lasers" by Orazio Svelto provides an updated and revised overview of laser physics, reflecting significant developments in the field since the second edition was published in 1982. The book aims to offer a broad and unified description of laser behavior at the simplest level that is compatible with a correct physical understanding. It is intended for use in classroom teaching and self-study by students in electrical engineering, physics, and chemistry who are interested in understanding the principles of laser operation. The book includes new sections on various types of lasers, including x-ray lasers and new solid-state lasers, as well as an extended description of semiconductor lasers. It also provides a more detailed treatment of laser mode-locking, cavity dumping, and pulse compression. The coherence and statistical properties of laser light are discussed in greater depth, as are the physics of gas discharges and other important topics from conventional optics. The book also includes a historical account of the "Laser" during the Greco-Roman civilization, where it was a plant with remarkable properties, used for medical treatments and as a valuable commodity. The plant was known as "Laser" and was highly valued, leading to its export to both Greeks and Romans. However, it became rare and disappeared around the second century A.D. The book is organized into chapters covering introductory concepts, interaction of radiation with matter, pumping processes, passive optical resonators, continuous wave and transient laser behavior, types of lasers, properties of laser beams, and laser beam transformation. Each chapter includes problems and references for further reading. The book also includes appendices, answers to selected problems, and an index.The third edition of "Principles of Lasers" by Orazio Svelto provides an updated and revised overview of laser physics, reflecting significant developments in the field since the second edition was published in 1982. The book aims to offer a broad and unified description of laser behavior at the simplest level that is compatible with a correct physical understanding. It is intended for use in classroom teaching and self-study by students in electrical engineering, physics, and chemistry who are interested in understanding the principles of laser operation. The book includes new sections on various types of lasers, including x-ray lasers and new solid-state lasers, as well as an extended description of semiconductor lasers. It also provides a more detailed treatment of laser mode-locking, cavity dumping, and pulse compression. The coherence and statistical properties of laser light are discussed in greater depth, as are the physics of gas discharges and other important topics from conventional optics. The book also includes a historical account of the "Laser" during the Greco-Roman civilization, where it was a plant with remarkable properties, used for medical treatments and as a valuable commodity. The plant was known as "Laser" and was highly valued, leading to its export to both Greeks and Romans. However, it became rare and disappeared around the second century A.D. The book is organized into chapters covering introductory concepts, interaction of radiation with matter, pumping processes, passive optical resonators, continuous wave and transient laser behavior, types of lasers, properties of laser beams, and laser beam transformation. Each chapter includes problems and references for further reading. The book also includes appendices, answers to selected problems, and an index.