  The development of the next generation of optical phase change technologies
for integrated photonic and free-space platforms relies on the availability of
materials that can be switched repeatedly over large volumes and with low
optical losses. In recent years, the antimony-based chalcogenide phase-change
material Sb$_2$Se$_3$ has been identified as particularly promising for a
number of applications owing to good optical transparency in the near-infrared
part of the spectrum and a high refractive index close to silicon. The
crystallization temperature of Sb$_2$Se$_3$ of around 460 K allows switching to
be achieved at moderate energies using optical or electrical control signals
while providing sufficient data retention time for non-volatile storage. Here,
we investigate the parameter space for optical switching of films of
Sb$_2$Se$_3$ for a range of film thicknesses relevant for optical applications.
By identifying optimal switching conditions, we demonstrate endurance of up to
10$^7$ cycles at reversible switching rates of 20 kHz. Our work demonstrates
that the combination of intrinsic film parameters with pumping conditions is
particularly critical for achieving high endurance in optical phase change
applications.
