While preparing the manuscript ofthis book, the author was informed that Profs. H. Dehmelt, Univ. ofWashington, W. Paul, Univ. Bonn and N. F. Ramsey, HarvardUniv. havewontheNobel PrizeinPhysics(1989;fortheirNobellectures, refertoRev.ModernPhysics,Vol.62(l990)pp.525-552).Theirmaincontributions are the pioneering works on the Ramsey resonance method, ion trap, and so on, which are the main topics to be discussed in this book. TherearetwoothergroupspreviouslyawardedwiththeNobelprizeinPhysics for their contributions to laser physics and quantum optics; C. H. Townes, N. G. Basov, and A. M. Prokhorov were awarded a Nobel prize for their works on the inventionofmasers and lasers as well as the basic studiesofquantum electronics; N. Bloembergen and A. L. Schawlow, in 1981, for their works on laser spectros- copy. It is an exceptional case that a branch ofphysics could win the Nobel prize threetimes.Thisfactreflectsandimpliesthatlaserphysicsandphysicsusinglasers are important fields ofbasic study, which relate closely to the quantum optics and atomicphysics. Furthermore,asthecaseofsemiconductorlasers,ithasbecomean importantfield for industrial applications, e.g., opticalcommunicationand optical diskmemories. As shownbythese examples, itcan beconsideredthatthe studyof laser isauniversaloneinscienceandtechnology,coveringawide rangefrombasic physics to industrial applications.