Differential reflectometry studies were performed on a Cu-17 at.% Al alloy. The differential reflectogram of a short-range ordered versus a disordered specimen shows a pronounced peak at 2.64 eV and a shoulder around 5 eV which is attributed to new structure in the ordered state. No such structure could be observed for a Cu-5 at.% Al alloy, confirming earlier reports in the literature that copper alloys containing less than 9 at.% aluminum undergo very little, if any, short-range ordering transformation. The new structure can be explained using the folding-band concept which yields additional interband transitions. Short-range ordering decreases the energy of one of the peaks in the differential reflectograms by 0.04 eV. This shift is equivalent to an increase in solute concentration amounting to one-half of a percent. © 1980 The American Physical Society.