GENERATION OF INTENSE GREEN LIGHT THROUGH AMPLIFIED SPONTANEOUS EMISSION IN ER3+-DOPED GERMANOSILICATE SINGLE-MODE OPTICAL-FIBER PUMPED AT 1.319-MU-M

Generation of intense 525 nm green light through amplified spontaneous emission (ASE) in monomode Er3+-doped germanosilicate fiber pumped by a Nd:YAG laser operated at 1.319 mum is reported. The green emission band around 525 nm corresponds to the H-2(11/2) --> 2I15/2 transition, and the pumping mechanism is accomplished by a first step resonant two-photon absorption exciting 4F9/2 level and a second one-photon step excited-state absorption (4I9/2) which, with the H-2(11/2) state, is populated. The stepwise three-photon frequency upconversion process is enhanced via resonant two- and three-photon transitions connecting ions 4I15/2 ground-state to the 4F9/2 and 4F5/2 excited-states levels, respectively, giving rise to amplified spontaneous emission from the H-2(11/2) level to the 4I15/2 ground-state. Efficient third-harmonic generation at 439 nm in short lengths of fiber, in addition to the ASE mechanism, is presented.