We show that absorbing photorefractive materials characterized by a space-c
harge exponential relaxation time law exhibit an overall hologram optical e
rasure that is described by the so-called exponential integral function, as
far as self-diffraction can be neglected. This fact is due to the bulk abs
orption producing an exponentially decreasing distribution of the erasure b
eam irradiance along the sample thickness that results in a correspondingly
increasing dielectric relaxation time. The theoretical development in this
paper is experimentally verified by the analysis of the holographic erasur
e in a nominally undoped Bi12TiO20 photorefractive crystal using the 514.5
nm laser wavelength where this material exhibits a relatively strong bulk a
bsorption. Neglecting absorption in this experiment leads to a relaxation t
ime that is about 4-fold larger than the actual value. (C) 2000 Published b
y Elsevier Science B.V. All rights reserved.