Photoreflectance (PR) provides an optical means for rapid and precise measurement of near-surface electric fields in semiconductor materials. This article details the use of PR to characterize dopant activation in ultrashallow junction (USJ) structures formed using millisecond annealing processes. USJ structures were formed in silicon using 500 eV B implantation with a dose of 10(15)/cm(2), followed by flash anneals at 1250-1350 degrees C. Reference metrology was performed using secondary ion mass spectrometry and various sheet resistance (R-s) methods. Methods to calibrate PR signals to active carrier concentration in USJ structures, including halo-doped samples, are described. PR is shown to be highly sensitive to active dopant concentrations in USJ structures formed by millisecond annealing.