The precessional magnetization dynamics of a chromium dioxide$(100)$ film is examined in an all-optical pump-probe setup. The frequency dependence on the external field is used to extract the uniaxial in-plane anisotropy constant. The damping shows a
strong dependence on the frequency, but also on the laser pump fluency, which is revealed as an important experiment parameter in this work: above a certain threshold further channels of energy dissipation open and the damping increases discontinuously. This behavior might stem from spin-wave instabilities.
