The propagation of laser pulses in optically thick samples is investigated
for Pr3 + -ion doped Y-2 SiO5 crystals at low temperatures. We report on se
lf-induced transparency depending on the field polarization and pulse energ
ies. For the interpretation of the data we propose a model based on two cou
pled propagating modes of different field polarization. The Maxwell-Bloch e
quations are applied to pulse propagation in an anisotropic medium. (C) 199
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