  We study the temperature dependence as well as anisotropy of optical
conductivity ($\sigma_1$) in the pseudocubic single crystal
Pr$_{0.5}$Ca$_{1.5}$MnO$_{4}$ using spectrocopic ellipsometry. Three transition
temperatures are observed and can be linked to charge-orbital ($T_{\rm CO/OO}$
$\sim$ 320 K), two-dimensional-antiferromagnetic (2D-AFM) ($\sim$ 200 K), and
three-dimensional AFM ($T_{\rm N} \sim$ 125 K) orderings. Below $T_{\rm
CO/OO}$, $\sigma_1$ shows a charge ordering peak ($\sim$0.8 eV) with a
significant blue shift as the temperature decreases. Calculations based on a
model that incorporates a static Jahn-Teller distortion and assumes the
existence of a local charge imbalance between two different sublattices support
this assignment and explain the blue shift. This view is further supported by
the partial spectral weight analysis showing the onset of optical anisotropy at
$T_{\rm CO/OO}$ in the charge-ordering region ($0.5-2.5$ eV). Interestingly, in
the charge-transfer region ($2.5-4$ eV), the spectral weight shows anomalies
around the $T_{\rm 2D-AFM}$ that we attribute to the role of oxygen-$p$
orbitals in stabilizing the CE-type magnetic ordering. Our result shows the
importance of spin, charge, and lattice degrees of freedom in this layered
manganite.

Strongly Correlated Electrons