A theoretical model that can efficiently calculate the refractive index response of semiconductors under ultrafast X-ray radiation is established based on the photorefractive effect of ...semiconductors. The proposed model is used to interpret X-ray diagnostics experiments, and the results are in good agreement with experiments. In the proposed model, a rate equation model of free carrier density calculation is adopted with the X-ray absorption cross-sections calculated by atomic codes. The two-temperature model is used to describe the electron-lattice equilibration and the extended Drude model is applied to calculate the transient refractive index change. It is found that faster time response can be achieved for semiconductors with shorter carrier lifetime and sub-picosecond resolution can be obtained for InP and Formula: see text. The material response time is not sensitive to X-ray energy and the diagnostics can be used in the 1-10 keV energy range. This article is part of the theme issue 'Dynamic and transient processes in warm dense matter'.
In the current investigation magnesium (Mg) has been incorporated in the ZnO matrix to induce photo refractivity thereby adding an extra dimension to its already present multi-functionality. Undoped ...and MgxZn1-xO (x = 0.25, 0.30, 0.35, 0.40, 0.45) thin films have been grown using Chemical Solution Deposition (CSD) technique. Obtained X-Ray Diffraction (XRD) spectra exhibits a slight shift in the peak value along (002) plane whereas UV–visible spectra indicates corresponding widening of ZnO band gap values (3.24–3.64 eV) with increase in Mg content. Mg substituted ZnO films were then investigated for their ferroelectric properties using a P-E hysteresis loop tracer. It was noted that ZnO film with 35 % Mg content (x = 0.35) exhibited the high values for saturation (Ps = 1.8 μC/cm2) and remnant (Pr = 0.7 μC/cm2) polarization. Hence the ZnO with same Mg concentration was investigated for nonlinear optical properties (two wave mixing phenomenon) using pump and probe technique. In order to enhance the beam amplification gain and impart stability Au micro-dots were thermally evaporated onto MgxZn1-xO (x = 0.35) films. The maximum beam amplification gain was noted to shoot up to 2.7 post patterning of MgxZn1-xO (x = 0.35) film surface by Au micro-dots.
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•Photo refractivity has been introduced by incorporating Mg in ZnO matrix.•Undoped and Mg substituted ZnO thin films have been grown using chemical solution deposition technique.•Enhanced beam amplification is observed using pump probe technique.•Results obtained with Mg:ZnO films assumes importance because of their potential application in non linear optics.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Spatial solitons in biased photorefractive media due to the photovoltaic effect and the pyroelectric effect are investigated. The pyroelectric field considered is induced due to the heating by the ...incident beam's energy. These solitons can be called screening photovoltaic pyroelectric solitons. It is shown that the solitons can exist in the bright and dark realizations. The conditions for formation of these solitons are discussed. Relevant example is considered to illustrate the self trapping of such solitons. The external electric field interacts with the photovoltaic field and the pyroelectric field to either support or oppose the self trapping.
•Effect of pyroelectric field on screening photovoltaic solitons is studied.•Illumination induced pyroelectric field is considered for the first time.•Self trapping depends on external, pyroelectric and photovoltaic space charge field.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Abstract A convenient way to optical fabricate (2 + 1)-dimensional photonic lattice microstructures was experimentally demonstrated in photorefractive crystal. An improved Billet split lens combined ...with a Fourier transform lens can generate large area interference of multiple plane waves. The (2 + 1)-dimensional square photonic lattice microstructures are optically induced in an iron doped lithium niobate crystal. Induced lattice microstructures are analyzed and validated using several different experimental methods. This method has good flexibility and scalability, stable equipment, and does not require complex adjustment systems. It can be used to optical fabricate more types of (2 + 1)-dimensional lattice microstructures by design and processing of improved Billet split lens reasonably.
Hole-electron competition was induced in an undoped Bi12TiO20 crystal using coherent pre-illumination at 532 nm. Photorefractive recording and erasure at 639.7 nm under the action of external ...electric field E0 were used to theoretically and experimentally investigate the competition within the sample band-gap. The good agreement between theory and experimental data allowed to obtain, in both regimes without and with pre-illumination, the saturation space-charge fields Eq and holes and electrons effective donors concentrations (ND)eff's. The phase shift between the electronic gratings and the hole grating was also computed and revealed a competition behavior between the applied electric field effect of increasing the characteristic lengths of electrons and holes moving in opposite directions in the conduction and valence bands, respectively, and the intensity of decreasing such lengths. The computed holes donor density indicated a strong contribution of the coherent pre-illumination to the hole-electron competition mechanism.
•A strong hole-electron competition is induced in Bi12TiO20 crystal using coherent pre-illumination at 532 nm.•Diffraction efficiency of the holograms increased when the applied electric field increased.•Phase shifts between the holographic gratings revealed a competition between applied electric field and intensities effects.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Direct holographic recording in undoped Bi12TiO20 crystal at 1064 nm is investigated aiming the characterization of diffraction efficiency under action of applied dc electric field (E0). An ...enhancement of 12-fold in the diffraction efficiency was revealed when E0 increased from 0.0 to 4.2 kV/cm. The theoretical dependence of the diffraction efficiency and the holographic erasure time upon E0 was investigated using the standard model of Kukhtarev for photorefractivity and the results showed a good experimental data fitting in both cases, allowing the computation of the effective trap concentration (ND)eff ≈ 5.62 × 1015 cm−3 which is responsible by the recording mechanism into the crystal sample. In particular, the theoretical-experimental investigation using the holographic erasure time also allowed to determine others relevant parameters for Bi12TiO20 such as the diffusion transport length LD, the Maxwell relaxation time τM, and the quantum efficiency Φ that can explain the relatively slow dynamics of photorefractive recording and erasure in near-infrared region. The type of charge carrier involved in the recording mechanism in the near-infrared region is also discussed.
•1064 nm can perform direct recording of phase hologram in undoped Bi12TiO20.•Direct recording in Bi12TiO20 at 1064 nm is dominated by electron photoconductivity.•Phase-sensitive technique detected direct recording in undoped Bi12TiO20 at 1064 nm.•Diffraction efficiency increased when the applied electric field increased.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this work, nonlinear optical (NLO) studies of nickel oxide doped (ranging from 0.2 to 1.0 mol %) Li2SO4–MgO–P2O5 glasses are reported. A combination of femtosecond (fs) laser, as a pumping light ...source and a high-accuracy polarimeter with low power probing laser, is used to investigate the light-induced optical anisotropy (OA) in these glass materials. The light-induced birefringence (LIB) exhibits slow relaxation tendency up to about 10 s suggesting on anisotropic photorefractive effect evidently dominated fast Kerr effect. This behavior is evaluated in the light of other results reported recently and is explained by the glass polymerization mechanisms. The photorefractive birefringence increases with increase of the quantity of NiO up to 0.8 mol% and it is attributed to the enhanced degree of depolymerization of the glass network due to the hike in the concentration of Ni2+ ions that occupy octahedral (Oh) positions. Further increase of NiO content ( > 0.8 mol%) causes, however, a certain decrease of the photorefractive birefringence. Notable change in concentration trend is interpreted by rising of phonon losses due to increasing portion of the nickel ions occupying tetrahedral (Th) sites that facilitates the polymerization of the glass network. The doped glasses with the NiO content of about 0.8 mol% may be considered as optimal in the sense of photorefractive efficiency. Relevant samples exhibit largest magnitudes of the photorefractive birefringence and appear to be favorable for potential applications.
•Nonlinear optical (NLO) studies of NiO doped Li2SO4–MgO–P2O5 glasses are studied.•Combination of femtosecond as pumping source and high-accuracy polarimeter is used.•The light-induced birefringence (LIB) exhibits slow relaxation tendency.•This behavior is explained by the glass polymerization mechanisms.•Glasses with 0.8 mol% NiO content exhibited high photorefractive efficiency.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
To improve the optoelectronic properties for the photorefractive devices can enable the wide application of nanostructured liquid crystal (LC) in optical information processing, optical imaging, and ...optical modulating systems. Especially, the quantum dots (QDs) based on photorefractive effect plays a key role in improving the energy efficiency and color quality for their ability to modify the properties of the bulk materials. In this paper, we propose a QD-doped LC device illuminated by a laser standing evanescent wave (LSEW) field with subwavelength period of 180 nm. Combined with the electric tuning, the obtained optical diffraction pattern of equally spaced light spots indicated that a regular, periodic grating was formed in the QD-doped LC volume. The measured maximum diffraction efficiency of 30 % identified the large change of the refractive index of the nanostructured QD-doped LC device. Our results demonstrate a novel method to design and fabricate rewritable optoelectronic devices with highly precise controlled photorefractive LC structures.
•A novel design method for quantum dots (QDs) doped - LC device with LSEW fields illumination.•Opto-electrical tuning the optical diffraction pattern in the QD-doped LC volume.•The measured diffraction efficiency of 30 % identified the change of the refractive index of the nanostructured QD-doped LC device.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This contribution presents an optofluidic droplet router which is able to route and steer microdroplets using optically induced forces created solely by the bulk photovoltaic effect on a nonlinear ...substrate. The combination of microfluidic tools with the properties of a photorefractive crystal allows for the generation of dielectrophoretic forces that can be either repulsive, leading to virtual barriers, or attractive, creating virtual rails. The sign of these forces is solely determined by the electrical properties of the liquid medium under investigation. Moreover, the induced structures on the bottom of the microfluidic channel are optically reconfigurable, so that the same device can easily be adopted for different purposes. Appropriate droplet‐generating devices are fabricated by UV illumination of SU‐8 and polydimethylsiloxane replica molding of the master structures. The bottom of the channels is formed by an iron‐doped lithium niobate crystal, whose internal electric fields are induced by structured illumination patterns and exert dielectrophoretic forces on droplets in the microfluidic section.
An optofluidic droplet router based on a bulk photovoltaic substrate is presented. This novel tool is able to route and steer micro droplets in optically‐created and hence reconfigurable geometries. The occurring forces can be either repulsive or attractive, depending on the electrical properties of the liquid media. Custom‐made PDMS droplet generators are sealed by a lithium niobate crystal and are used to demonstrate the working principle of the router.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
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