We have measured far-infrared reflectivity spectra of a single crystal
of AgCl illuminated by the chopped He-Cd laser light with 4416 Angstr
om which is below the exciton energy level of AgCl. In comparison with
the spectrum before the illumination, considerable increase of reflec
tivity in far-infrared region and the increasing or decreasing frequen
cy of TO- or LO-phonon have been observed. These phenomena are interpr
eted by considering the increased defects induced by the illumination.