Thin films of sulfides for high-density optical storage by photon-gated hole burning

In the form of micro-particles europium doped alkaline earth sulfides have been shown to exhibit high density of permanent spectral holes. The photon-gated spectral holeburning (PGHB) in these systems provided the most promising characteristics of any material known to date. These spectral holes can be used as optical memory. However, for any optical storage device either large size single crystals or thin films are required. Thin films of these materials are grown by Pulsed Laser Deposition (PLD) technique. This fast and simple growth technique is superior the single crystal growth or the molecular beam epitaxy (MBE) as far as the holeburning properties are concerned. Transparent glassy MgS:Eu and CaS:Eu films have been grown and tested for the spectral holeburning properties. Critical parameters such as the relative concentration of Eu2+ and Eu3+, and optical quality of thin films have been investigated. Int his paper we report on the growth and the high-density optical holeburning in these films. The density of spectral holes has been further increased by burning in multiple Eu-centers in a material and by depositing multiple layers of thin films of different materials in a stack.