Photovoltaic dependence of photorefractive grating on the externally applied dc electric field

Photovoltaic dependence of photorefractive grating (i.e., space-charge field and phase-shift of the index grating) on the externally applied dc electric field in photovoltaic–photorefractive materials has been investigated. The influence of photovoltaic field (EPhN), diffusion field and carrier concentration ratio r (donor/acceptor impurity concentration ratio) on the space-charge field (SCF) and phase-shift of the index grating in the presence and absence of the externally applied dc electric field have also been studied in details. Our results show that, for a given value of EPhN and r, the magnitude of the SCF and phase-shift of the index grating can be enhanced significantly by employing the lower dc electric field (EON<10) across the photovoltaic–photorefractive crystal and higher value of diffusion field (EDN>40). Such an enhancement in the magnitude of the SCF and phase-shift of the index grating are responsible for the strongest beam coupling in photovoltaic–photorefractive materials. This sufficiently strong beam coupling increases the two-beam coupling gain that may be exceed the absorption and reflection losses of the photovoltaic–photorefractive sample, and optical amplification can occur. The higher value of optical amplification in photovoltaic–photorefractive sample is required for the every applications of photorefractive effect so that technology based on the photorefractive effect such as holographic storage devices, optical information processing, acousto-optic tunable filters, gyro-sensors, optical modulators, optical switches, photorefractive–photovoltaic solitons, biomedical applications, and frequency converters could be improved.

► Effect of photovoltaic field on SCF and phase-shift in presence of EON has been studied.
► For a given value of EPhN, SCF can be enhanced by using crystal of higher EDN▒(>40) and lower EON▒(≪10≪10).
► Higher value of the SCF is responsible for large change in the index of refraction.
► Whereas lower EDN▒(<10) is needed for higher value of the spatial phase-shift in absence of EON.
► Presence of such a higher spatial phase-shift is responsible for strong beam coupling.