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Contributions to the acoustic signal sensitivity of fiber distributed-feedback (DFB) lasers in air are investigated both theoretically and experimentally. The theoretical results show that the dominant contribution to the laser frequency shift comes from adiabatic temperature shifts in the surrounding air at lower frequencies and from pressure at higher frequencies. The transition frequency was found to be between 5 and 20 kHz, depending on the elastic boundary conditions of the fiber laser. The acoustically induced frequency shifts of two fiber DFB lasers were measured, and the sensitivities varied from 0.61 MHz/Pa at a 100-Hz acoustic frequency to 0.34 kHz/Pa at a 15-kHz acoustic frequency.

The erasure, which occurs during readout of holograms in photochromic or photorefractive media, imposes limitations on the amount of information which can be stored. It is shown that storage of several holograms by varying the angle of incidence of the reference beam is particularly unfavorable. It is much more advantageous to use a large number of bits per page or to store the holograms in separate parts of the sample. If erasure is prevented by some kind of physical or chemical fixing or biasing process, the storage capacity is limited by the bit rate required during readout. This limitation may also be severe, in some cases reducing the storage capacity to several orders of magnitude below the diffraction-limited value.