Partial erasing of temporal memory by using picosecond accumulated photon echoes in dye doped polymer film

The stimulated photon echo memory using persistent hole-burning materials has been attracting much attention as a possible candidate for high-density data storage. Most studies have been related to the writing and reading processes and little attention has been paid for a partial erasing. We demonstrate for the first time that partial erasing of photon echo memory can be accomplished by simply employing a half-wave plate. In a photon echo memory, the write and data pulses with a time separation /spl tau/ excite a hole-burning material. These pulses create a periodic absorption modulation (periodic hole) with a frequency of l//spl tau/ in the absorption spectrum. When the read pulse excites the sample, a stimulated echo pulse is emitted at /spl tau/ after the read pulse, We note that a bit of data is stored as a periodic hole in the sample. A rotation of a half-wave plate inserted in the data pulse path (which induce a retardation of /spl lambda//2) creates two periodic holes that have the same frequency and opposite phase. Therefore, erasing a periodic hole can be done by rotating the wave plate. A dye (Sulforhodamin 640) doped polymer film (polyvinyl alcohol) cooled at 2 K was used as a persistent hole-burning material.