Peter Walden Milonni

Despite their great variety and range of size, power, wavelength, and temporal, spatial, and polarization characteristics, all lasers involve certain basic concepts, such as gain, threshold, and electromagnetic modes of oscillation 1 ; 2 ; 3 ; 4 ; 5 ; 6 . In addition to these universal characteristics are features, such as Gaussian beam modes, that are important to such a wide class of devices and must be included in any reasonable compendium of important laser concepts and formulas. We have, therefore, included here both generally applicable results as well as some more specific but widely applicable ones.