ThisbookiSmotivatedbytheveryfavorablereceptiong~ventothepreviouseditionsaswellasbvtheconsiderablerangeofnewdevelopmentsinthelaserfieldsincethepublicationoflhethirdeditionin1989．Thesenewdevelopmentsinclude，amongothers，Quantum-WellandMultiple．QuantumWelllasers．diode—pumpedsolid—statelasers，newconceptsfofbothstableandunstableresonators，femtosecondlasers，ultra·high—brightnesslasersetc．Thebasicaimofthebookhasremainedthesame，namelytoprovideabroadandunifieddescriptionoflaserbehavioratthesimplestlevelwhichiscompatiblewithacorrectphysicalunderstanding．ThebookiSthereforeintendedasatext-bookforasenior-levelorfirst—yeargraduatecourseand／orasareferencebook．