  The gain properties of an oscillator strongly affect its behavior. When the
gain is homogeneous, different modes compete for gain resources in a `winner
takes all' manner, whereas with inhomogeneous gain, modes can coexist if they
utilize different gain resources. We demonstrate precise control over the mode
competition in a mode locked Ti:sapphire oscillator by manipulation and
spectral shaping of the gain properties, thus steering the competition towards
a desired, otherwise inaccessible, oscillation. Specifically, by adding a small
amount of spectrally shaped inhomogeneous gain to the standard homogeneous gain
oscillator, we selectively enhance a desired two-color oscillation, which is
inherently unstable to mode competition and could not exist in a purely
homogeneous gain oscillator. By tuning the parameters of the additional
inhomogeneous gain we flexibly control the center wavelengths, relative
intensities and widths of the two colors.
