Ultrashort 1.5-μm laser excited upconverted stimulated emission based on simultaneous three-photon absorption

Simultaneous three-photon excited stimulated emission at (cavityless lasing) similar to610 nm has been achieved in an organic chromophore solution pumped by similar to1.5-mum ultrashort coherent radiation. The stimulated emission can be observed only in the forward and backward directions and is characterized by its high directionality and spectral narrowing. The divergence angle for the backward stimulated emission is considerably smaller than that for the forward stimulated emission, which resembles optical phase conjugation. (C) 2003 Optical Society of America.