In our semiclassical treatment of the laser in Chaps. 8-12, we “ Fourieranalyzed” the electric field. This frequency-domain method has much to commend it: explicit expressions for the field are often obtained, the calcu lations generally do not require much computer time, and considerable insight can be gained into the nature of the atom-field interaction which takes place in the laser. There are also shortcomings, however, to the frequency-domain picture. The number of modes which can be treated easily is small, perhaps as few as ten. In general, the mode amplitudes and phases cannot vary ap preciably in the atomic lifetimes (the total field, of course, can vary). Further more the strong-signal theories are rather complicated.