Spatio-temporal dynamics of light amplification and amplified spontaneous emission in high-power tapered semiconductor laser amplifiers

We investigate the spatio-temporal light field dynamics in high-power semic onductor lasers with continuous-wave optical injection. The amplification p rocesses that characterize this system occur during the propagation of the injected signal within the active area and can be attributed to spatially d ependent gain and refractive index variations. Those are shown to be determ ined by dynamic interactions between the light fields and the active charge -carrier plasma. This microscopic light-matter-coupling is described by a s patially resolved microscopic theory based on Maxwell-Bloch-Langevin equati ons taking into account many-body interactions, energy transfer between the carrier and phonon system and, in particular, the spatio-temporal interpla y of stimulated and amplified spontaneous emission and noise. Results of ou r numerical modeling visualize the dynamic spatio-spectral beam shaping exp erienced by the propagating light in amplifiers of tapered geometry. This r eveals the microscopic physical processes that are responsible for the part icular amplitude and spatial shape of the light beam at the output facet.