| Popis: |
Ever since the inception of lasers there has been a consistent effort towards reducing their threshold which in general can be achieved by two means: reduction of the active region size and eliminating the residual absorption. Rapid progress in the reduction of size has culminated in quantum well and microcavity lasers [1]. However, elimination of absorption, long used in NH3 masers by the “spatial sorting-out” of excited atoms, is clearly not applicable in solid state lasers. It is only recently that “lasing without inversion”, in which quantum interference causes reduced absorption, has been suggested for semiconductor quantum wells [2]. This method, however, is inherently complicated for reasons such as requiring separate probe and coupling laser beams, etc. |
