Two-color recording Holographic data storage

set holographic recording

for two-color holographic recording, reference , signal beam fixed particular wavelength (green, red or ir) , sensitizing/gating beam separate, shorter wavelength (blue or uv). sensitizing/gating beam used sensitize material before , during recording process, while information recorded in crystal via reference , signal beams. shone intermittently on crystal during recording process measuring diffracted beam intensity. readout achieved illumination reference beam alone. hence readout beam longer wavelength not able excite recombined electrons deep trap centers during readout, need sensitizing light shorter wavelength erase them.

usually, two-color holographic recording, 2 different dopants required promote trap centers, belong transition metal , rare earth elements , sensitive wavelengths. using 2 dopants, more trap centers created in lithium niobate crystal. namely shallow , deep trap created. concept use sensitizing light excite electrons deep trap farther valence band conduction band , recombine @ shallow traps nearer conduction band. reference , signal beam used excite electrons shallow traps deep traps. information hence stored in deep traps. reading done reference beam since electrons can no longer excited out of deep traps long wavelength beam.