Using a nonlinear cavity element, a liquefying gallium mirror, we demonstra
te stable, self-starting, passive Q-switching of both erbium and ytterbium
fiber laser cavities operating at wavelengths of 1550 and 1030 nm, respecti
vely. The performance at 1550 nm is shown to be equivalent to that achieved
with a state of the art semiconductor saturable absorber designed to work
at this wavelength. The results highlight the suitability of this tremendou
sly broadband, inexpensive nonlinear medium for a wide range of passive Q-s
witch applications. (c) 1999 American Institute of Physics. [S0003-6951(99)
03524-X].