Photovoltaic dependence of photorefractive grating on the externally applied dc electric field M.K. Maurya n , R.A. Yadav Laser and Spectroscopy Laboratory, Department of Physics, Banaras Hindu University, Varanasi-221005, India article info Article history: Received 15 August 2012 Received in revised form 13 September 2012 Accepted 18 September 2012 Available online 16 October 2012 Keywords: Photovoltaic–photorefractive materials Space-charge field and external applied dc electric field abstract 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 (E PhN ), 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 E PhN 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 (E ON o10) across the photovoltaic–photorefractive crystal and higher value of diffusion field (E DN 440). 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. & 2012 Elsevier Ltd. All rights reserved. 1. Introduction The miniaturization of electronic circuits is approaching the point where an electromagnetic interaction between neighboring elements affects their reliability. Optical waves are fast and do not interact with each other in linear media, thus optical based components are ideal candidates for expanding the frontier of computation. After the invention of the first laser by T. H. Maiman in 1960 this field of research dealing with optical information processing (photonics) has grown considerably [1,2]. It is, nowa- days, one of the principal areas of development in science and technology [3–8]. Among others, the major advantages of optics with respect to electronics are the intrinsic potential for parallel computation and the much larger bandwidth of optical signals. For the construction of all-optical switching elements the use of nonlinear-optical materials is necessary [5,8]. However, optical computing also depends on the availability of suitable nonlinear material. Requirements depend strongly on the kind of targeted applications. Additional requirements are a controllable photosensitivity and light absorption of the material. Due to its unique nature the photorefractive effect (photorefractive optics) can meet most of these requirements, by an appropriate material selection and a controlled doping treatment [7,8]. The photore- fractive effect is based on light induced charge transport in electro-optic materials. Trapped charges are excited in a mobile state where they can freely move until they re-trapped in an immobile state. In this process an internal space charge field is building up. Through the Pockels effect this spatially modulated field will translate in a refractive index change, which is in turn detected by optical diffraction measurements [8–12]. The advan- tages of photorefractive materials are low power consumption, strong beam coupling at low power levels, real time writing– erasure, storage possibility and parallel processing. Therefore, photorefractive effect play an important role in many fields of science and technology; amplification and oscillation of light beams, phase conjugation, volume holographic storage, and image processing are just a few examples [3,7–18]. In addition to these applications, an important property of a number of photorefractive crystals (among them BaTiO 3 and KNbO 3 ) is the beam-coupling effect—a transfer of energy between two coher- ently intersecting beams inside the crystal [7–12,19]. This unique property of nonreciprocal energy transfer has led to a number of Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/optlastec Optics & Laser Technology 0030-3992/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.optlastec.2012.09.023 n Corresponding author. Tel.: þ91 9452565194. E-mail address: mahendrabhu@gmail.com (M.K. Maurya). Optics & Laser Technology 47 (2013) 10–21