  We discuss a class of lasing modes created by a spatially inhomogeneous gain
profile. These lasing modes are "extra modes", in addition to, and very
different from, conventional lasing modes, which arise from the passive cavity
resonances. These new modes do not have high intensity across the entire gain
region, but instead are localized at the gain boundary and throughout the
gain-free region. They are surface modes, originating from the transmission
resonances of the gain-free region. Using an S-matrix description we connect
these surface modes to the lasing modes in PT-symmetric (balanced gain-loss)
cavities.
