  We used femtosecond optical spectroscopy to study ultrafast spin and orbital
ordering dynamics in the antiferromagnetic Mott insulator
$\alpha$-Sr$_2$CrO$_4$. This chromate system possesses multiple spin and
orbital ordered phases, and therefore could enable us to study the unique
interplay between these collective phases through their non-equilibrium
response to photoexcitation. Here, by varying the pump photon energy, we
selectively drove inter-site spin hopping between neighboring Cr $t_{2g}$
orbitals and charge transfer-type transitions between oxygen 2$p$ and Cr
$e_{g}$ orbitals. The resulting transient reflectivity dynamics revealed
temperature-dependent anomalies across the N${\textrm{\'e}}$el temperature for
spin ordering as well as the transition temperatures linked to different types
of orbital order. Our results reveal distinct relaxation timescales for spin
and orbital orders in $\alpha$-Sr$_2$CrO$_4$ and provide experimental evidence
for the phase transition at $T_\textrm{O}$, possibly related to antiferro-type
orbital ordering.
