Quasi-resonant nonlinear absorption for optical power limiting: solgel-processed Er^3+-doped multicomponent silica glass

We demonstrate optical power limiting by what we believe to be a new mechanism of nonlinear absorption, which involves a quasi-resonant ground-state absorption that is either phonon assisted or assisted by the presence of defect sites (tail absorption). Such a mechanism provides high transmittance at low intensity yet optical limiting under cw conditions. The sample used was a novel solgel-processed Er(3+)-doped multicomponent silica glass. In this system the nonlinear absorption process is achieved because the resonant excited-state ((4)I(13/2) ? (4)S(3/2)) absorption cross section is larger than the quasi-resonant ground-state ((4)I(15/2) ? (4)I(9/2)) absorption cross section.