ABSTRACT
It is not improbable that this monograph may lead one to a conclusion that the possibilities for classical three- and four-level operating schemes are exhausted both from the viewpoints of the traditional problems of expanding the spectral and operating potentialities of crystalline lasers and searching for new laser hosts and activator ions. Indeed, though little attention is paid in this book to the classical principles of stimulated emission (SE) excitation of the Ln3+ ions in insulating crystals, it would be, however, mistaken to think so. Because the search and applied aspects of three- and four-level working systems have been discussed in detail in the extensive literature of quantum electronics, it is hardly reasonable to repeat their analysis in this monograph.
