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Hologram Recording in GaAs through EL2 Intracentre Absorption,

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Deep donor centre referred to as EL2, is the dominant deep level in melt-grown gallium arsenide crystals. Photoionization of EL2, the subsequent space charge redistribution, and refractive index modulation through the electrooptic effect are responsible for what we call below the photorefractive PR gratings observed in GaAs semi-insulating crystals EL2 centre is also distinguished by a number of specific features including the existence of the excited metastable state EL2 of the same charge. EL2 to EL2 transitions take place under light excitation with photon energy to between 1.0 and 1.3 eV. At low temperatures T approximately 100 K the corresponding cross section sigma and lifetime gamma are sufficiently large sigma approx. 10-17 sm2, gamma 10 according to 2 and hence the metastable state EL2 strongly affects the absorption and photocurrent spectrums, some photoelectrical properties of the material etc. 3,4. Nevertheless, the probable influence of EL2 EL2 transitions on the properties of GaAs crystals as a reversible holographic medium is still in question. The aim of the study reported here was to investigate the possibility of the hologram recording in semi-insulating crystals through a new physical mechanism namely the local modulation of the optical properties of the crystal caused by EL2 EL2 transitions.

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  • Optics
  • Nuclear Physics and Elementary Particle Physics

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