  The antimony-based chalcogenide Sb2Se3 is a rapidly emerging material for
photonic phase change applications owing to its ultra-low optical losses at
telecommunication wavelengths in both crystalline and amorphous phases. Here,
we investigate the dynamical response of these materials from nanoseconds to
milliseconds under optical pumping conditions. We apply bichromatic pump-probe
transient reflectance spectroscopy which is a widely used method to study the
optical performance of optical phase change materials. Amorphous regions of
several hundreds of nanometers in diameter are induced by pulsed excitation of
the material using a wavelength of 488 nm above the absorption edge, while the
transient reflectance is probed using a continuous wave 980 nm laser, well
below the absorption edge of the material. We find vitrification dynamics in
the nanosecond range and observe crystallization on millisecond time scales.
These results show a large five-orders of magnitude difference in time scales
between crystallization and vitrification dynamics in this material. The
insights provided in this work are fundamental for the optimisation of the
material family and its employment in photonic applications.
