  In sufficiently strong scattering media, light transport is suppressed and
modes are exponentially localized. Anderson-like localized states have long
been recognized as potential candidate for high-Q optical modes for
low-threshold, cost effective random lasers. Operating in this regime remains
however a challenge since Anderson localization is difficult to achieve in
optics and nonlinear mode interaction compromise its observation. Here, we
exhibit individually each lasing mode of a low-dimension solid-state random
laser by applying a non-uniform optical gain. By undoing gain competition and
cross-saturation, we demonstrate that all lasing modes are spatially localized.
We find that selective excitation reduces significantly the lasing threshold
while lasing efficiency is greatly improved. We show further how their spatial
location is critical to boost laser power-efficiency. By efficiently
suppressing spatial hole burning effect, we can turn on the
optimally-outcoupled random lasing modes. Our demonstration opens the road to
the exploration of linear and nonlinear mode interactions in the presence of
gain, as well as disorder-engineering for laser applications.
