Band-edge photorefractive effect in semiconductors

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Abstract
We report here for the first time, two-beam coupling energy transfer using the Franz–Keldysh electrorefractive effect in photorefractive semiconductors. A large beam coupling gain coefficient (Γ=2.8 cm−1) exceeding the absorption coefficient (α=2.0 cm−1) is obtained in undoped semi-insulating GaAs using the new photorefractive process. The new photorefractive process differs from conventional photorefractivity in that the direction of energy transfer is dictated by the direction of an externally applied electric field. Using a moving grating technique and combining the electrorefractive grating with the conventional electro-optic grating, a very large gain Γ=16.3 cm−1 (α=3 cm−1, crystal length l=4mm) resulting in net amplification by more than a factor of 200 has been demonstrated.