J. J. Amodei

HOLOGRAPHIC PATTERN FIXING IN ELECTRO‐OPTIC CRYSTALS

This paper describes the results of an investigation into techniques for obtaining erasure resistant holograms in electro‐optic crystals. The most successful approach made use of thermally activated ionic drift during or after recording. The samples are heated for about 30 min at 100°C to obtain optically nonerasable holograms with as much as 50% diffraction efficiency in LiNbO3 or in doped Ba2NaNb5O15.

Multiple storage and erasure of fixed holograms in Fe−doped LiNbO3

Holograms were recorded and fixed simultaneously in heated (∼160°C) crystals of Fe−doped LiNbO3. With this procedure the crystals have the erase/write asymmetry required for multiple storage of high−diffraction−efficiency holograms. Five hundred fixed holograms, each with more than 2.5% diffraction efficiency, were recorded.

Improved electrooptic materials and fixing techniques for holographic recording.

This paper describes recent improvements in materials and techniques for storage of high efficiency phase holograms in electrooptic crystals. The storage performance of lithium niobate and barium sodium niobate was greatly enhanced by introducing transition metal impurities or by subjecting the undoped crystals to irradiation treatments. The latest materials combine good sensitivity with diffraction efficiencies that reach well over 50% for sample thickness of a few millimeters. In addition, the fixing techniques that were developed offer a simple means of achieving nondestructive readout for holographic information stored in these crystals.

ELECTRON DIFFUSION EFFECTS DURING HOLOGRAM RECORDING IN CRYSTALS

Diffusion effects are shown to give rise to strong electric fields when insulators with trapped carriers are exposed to holographic interference patterns. A simple physical model is used to calculate the field generated by sinusoidal light intensity distributions of typical wave‐lengths. This phenomenon can be utilized for recording phase holograms in electro‐optic crystals and as means of enhancing the efficiency and permanence of absorption holograms in photochromic materials.

HOLOGRAPHIC STORAGE IN DOPED BARIUM SODIUM NIOBATE (Ba2NaNb5O15)

This paper describes the results obtained using doped crystals of Ba2NaNb5O15 for phase holographic storage. Very short‐lived holograms with less than 1% diffraction efficiencies were obtained in nominally pure crystals. Doping with Fe and Mo yields holograms with much longer decay times and diffraction efficiencies of 67% in a 0.32‐cm‐thick crystal. The energy density required to reach 40% diffraction efficiency was 6 J/cm2.

HOLOGRAMS IN THIN BISMUTH FILMS

Holograms with better than 6% efficiencies and resolutions close to 1000 lines/mm were achieved on Bi films with good linearity and reasonable sensitivity.

Holographic storage performance of iron-doped LiNbO 3

Iron doped LiNbO 3 has been found to give very sensitive performance in holographic storage applications, permitting exposures nearly 1000 times shorter than the undoped crystals. Crystals doped during growth exhibit an interesting combination of increased sensitivity and higher optical erasure resistance, indicating that there is a marked difference between the recording and erasure efficiencies. While the increased erasure resistance is a desirable property in applications requiring repeated non-destructive readout, it is an undesirable feature in dynamic applications requiring fast read-write cycles. Efforts to develop materials that do not exhibit high erasure resistance included double-doping the samples with Fe and various possible charge-compensating centers, and iron-doping by diffusion as opposed to doping the crystals during growth.

Transport Measurements and Holographic Techniques

Abstract Holographic recording in electro-optic crystals has been studied in detail as a very promising approach for high-density information storage. As the physical theories of this phenomenon evolved, it also became clear that these techniques offer potential advantages for performing useful transport measurements in electro-optic materials. Since this latter aspect of holography has not been widely publicized, it is the purpose of this paper to briefly summarize the techniques and discuss some of the measurements that can be performed.