  The properties of the light charged sleptons in $\ser\ser$, $\smur\smur$ and
$\stau_1\stau_1$ production are studied within the mSUGRA scenario SPS 1a.
Various method are presented to determine very precisely masses, angular
distributions, spin and couplings as well as the $\stau_1$ polarisation and
mixing parameter in the $\stau$ sector. The analysis is based on a complete
simulation of signal and background reactions assuming experimental conditions
of the TESLA $e^+e^-$ Linear Collider.
