LASERS WITHOUT PHOTONS - OR SHOULD IT BE LASERS WITH TOO MANY PHOTONS

Expanding the fields of a laser cavity in a set of orthonormal modes i s a standard technique in laser theory. Expansion in a normal mode set is also the basis of the concept of ''photons''. A substantial number of practical lasers do not, however, support any kind of normal or or thogonal cavity modes, and thus, their fields cannot be represented (a t least not easily) in terms of normal modes, or photons. This leads t o a number of unusual results, including situations in which the fewes t-order made of a cavity can contain substantially more energy than th e total energy in the cavity, as well as enhanced quantum spontaneous emission far stronger than the ''single extra photon'' level character istic of an ordinary laser oscillator. We review the theoretical origi ns of these unusual effects and present experimental confirmation of g reatly enhanced Schawlow-Townes fluctuations in an unstable-resonator laser with a Petermann-noise enhancement factor of several hundred tim es.