"Preferably, the optical data storage medium 10 is typically on the order of magnitude of 100 microns in thickness, for instance, about 100-200 ??m, and in particular about 125 ??m and the spacing between Bragg fringes 14 is approximately one thousand times smaller, on the typical order of magnitude of 100 nanometers, for instance about 170 nanometers." . . . . .