Two-Step Processes and IR Recording in Photorefractive Crystals

Abstract

Abstract. Two-step excitation processes have been used for hologram storage in photorefractive crystals. By this means the interference pattern can be formed with red or near-IR light and nondestructive readout of information is possible. Often shallow levels are involved in the holographic recording process in photorefractive crystals. The shallow levels can be populated by illumination with visible or UV pulses forming states with relatively long lifetimes, thus sensitizing the crystals for holographic recording with IR pulses. In LiNbO3 and LiTaO3 the most important shallow levels have been identified. They result from NbLi 5+ and TaLi 5+ antisite defects (Nb 5+ or Ta 5+ on Li + site). The crystals can also be pre-illuminated with visible light from a cw argon laser or a xenon lamp and holograms can be recorded with red light from a laser diode. The sensitization process is possible for other photorefractive crystals, too. The holograms can be read nondestructively with IR light and can be erased with green light. The hologram lifetime is limited by electron tunneling or by an ionic conductivity. Lifetimes up to years can be achieved. Recording of components for telecommunication applications with IR light allows one to create reconfigurable and thus more versatile devices.

Holographic Spectroscopy: Wavelength-Dependent Analysis of Photosensitive Materials by Means of Holographic Techniques

“…Exposure to light with photon energies in the vicinity of the band edge energy can be applied for the recording of holograms via the mechanism of interband photorefraction [ 35 ]. The tail of this absorption further determines the fundamental absorption in the visible and near-infrared spectrum, and is important for near-infrared recording mechanisms of holograms in lithium niobate [ 36 ].…”

Preparation, Properties, and Applications of Near Stoichiometric Lithium Tantalate Crystals

“…Hence, it is necessary to find more stable materials to make holographic memory. LT crystal has become one of the best choices for holographic storage materials because of its readability, erasure and good optical parameters [52][53][54][55]. LT crystal has a storage density of 10 12 bits/cm 3 , a high transmission speed of 10 9 bits/s, a small proton mobility and has a longer dark storage time [56] than Fe-CLN crystal (1 year).…”