  High-harmonic generation (HHG) is a typical high-order nonlinear optical
phenomenon and can be used to probe electronic structures of solids. Here, we
investigate the temperature dependence of HHG from Pr_{0.6}Ca_{0.4}MnO_{3} in
the range of 7 K to 294 K including the charge ordering (CO) transition and
magnetic transition temperatures. The high-harmonic intensity remains almost
constant in the high-temperature charge-disordered phase. However, as the
temperature is lowered, it starts to gradually increase near the CO transition
temperature where an optical gap related to the CO phase appears. The anomalous
gap energy dependence resembles the one recently reported in a Mott insulator.
We attribute the HHG suppression at high temperatures to the destructive
interference among high-harmonic emissions from thermally activated multiple CO
configurations. Our results suggest that HHG is a promising tool for probing
the fluctuation of local order in strongly correlated systems.
