Generation of intense green light through amplified spontaneous emission in Er/sup 3+/-doped germanosilicate single-mode optical fiber pumped at 1.319 /spl mu/m

Generation of intense 525 nm green light through amplified spontaneous emission (ASE) in monomode Er/sup 3+/-doped germanosilicate fiber pumped by a Nd:YAG laser operated at 1.319 /sub /spl mu//m is reported. The green emission band around 525 nm corresponds to the /sup 2/H/sub 11/2//spl rarr//sup 2/I/sub 15/2/ transition, and the pumping mechanism is accomplished by a first step resonant two-photon absorption exciting /sup 4/F/sub 9/2/ level and a second one-photon step excited-state absorption (/sup 4/I/sub 9/2/) which, with the /sup 2/H/sub 11/2/ state, is populated. The stepwise three-photon frequency upconversion process is enhanced via resonant two- and three-photon transitions connecting ions /sup 4/I/sub 15/2/ ground-state to the /sup 4/F/sub 9/2/ and /sup 4/F/sub 5/2/ excited-states levels, respectively, giving rise to amplified spontaneous emission from the /sup 2/H/sub 11/2/ level to the /sup 4/F/sub 15/2/ ground-state. Efficient third-harmonic generation at 439 nm in short lengths of fiber, in addition to the ASE mechanism, is presented.<
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