Optical properties of BaCaBO3F crystal

The optical transmission spectra of BaCaBO₃F (abbr. BCBF) crystal have been measured at room temperature. The refractive indices have been measured with the minimum deviation method and fitted to the Sellmeier equations. The nonlinear optical coefficient d₂₂ of BCBF crystal determined by the Maker fringe technique is 0.74d₃₆(KDP).     

Optical bistability and multistability driven by external magnetic field in a dielectric slab doped with nanodiamond nitrogen vacancy centres

Abstract

The theoretical investigation of controlling the optical bistability (OB) and optical multistability (OM) in a dielectric medium doped with nanodiamond nitrogen vacancy centres under optical excitation are reported. The shape of the OB curve from dielectric slab can be tuned by changing the external magnetic field and polarization of the control beam. The effect of the intensity of the control laser field and the frequency detuning of probe laser field on the OB and OM behaviour are also discussed in this paper. The results obtained can be used for realizing an all-optical bistable switching or development of nanoelectronic devices.     

Optical and nonlinear optical properties of orthorhombic BiB3O6

Dispersion of refraction coefficients of orthorhombic BiB₃O₆ in the wavelength range between 435.8 and 1060 nm is studied, nonlinear optical coefficients are determined, and phase matching angles, angular and spectral bandwidths for second harmonic generation processes are calculated. δ-BiBO may be suitable for doubling of lasers with a wavelength in the 1.3 μm region as well as the matrix for self-doubling lasing media.     

Optical bistability and multistability in an open ladder-type atomic system

A novel scheme is proposed for controlling the optical bistability and multistability in an atomic system. In an open ladder-type three-level atomic system, it is shown that, by adjusting the ratio between atomic injections and exit rates from the cavity, the intensity threshold of optical bistability can be controlled. The effect of incoherent pumping field and spontaneously generated coherence (SGC) on optical bistability for different values of exit rates is also discussed. It is found that SGC makes the medium phase dependent, so the optical bistability and multistability threshold can be controlled via relative phase between applied fields. Moreover, it is shown that the optical bistability can be switched to optical multistability, which is favorable for the next generation of all-optical systems and quantum networks.     

Optical bistability of surface plasmon polaritons in nonlinear Kretschmann configuration

Optical bistability based on surface plasmon polaritons in the Kretschmann configuration involving a Kerr nonlinear medium is described by analytical solutions. The conditions of forming the optical bistability with different parameters are explored. The resonant angle of surface plasmon polaritons varying with the incident light intensity also generates the phenomenon of bistability. The system could form optical bistability with the special thickness of the metal film and incident angle. This kind of system has potential application in all-optical networks.     

Domain patterns on ferroelectric Rh:BaTiO3 single crystals

Single crystal growth and domain structure of Rh:Barium titanate (BaTiO₃) have been investigated. Rh doping in BaTiO₃ is effective for the growth of bulk crystals without twin formation. Atomic force microscope (AFM) and optical microscope studies reveal the formation 180° and 90° domains on the grown crystals. It has been observed that the complex 180° domain structure with typical size of around 20 μm exists in the c-domain of {0 0 1} face of Rh doped BaTiO₃ crystals.     

Optical bistability for ZnO–Nb2O5–TeO2 glasses

We examined the optical nonlinear properties of ZnO–Nb₂O₅–TeO₂. The absorption and Raman spectra were measured, the third-order nonlinear susceptibility was determined by degenerated four wave mixing technique. The magnitude of χ⁽³⁾ is about 1.0 × 10⁻¹² esu, larger than that of silica glasses, and the optical bistability was observed in a Fabry–Perot cavity.     

Intrinsic optical bistability in doped polymer

One of the most interesting and applicable effects of nonlinear optics is optical bistability. This phenomenon is exhibited by certain resonant optical structures where it is possible to have two stable steady transmission states for the device, depending on the history of the input. Such a bistable device may be useful for optical computing elements as a result of its memory characteristics. Optical bistability behaviour is usually observed by inserting a nonlinear matter inside a Fabry–Perot interferometer. But in this study, it was shown that this can be achieved without the application of any optical resonator. Two laser beams were used to interact with the photorefractive media (doped PMMA polymer) which resulted in the bistability of the intensity of transmitted wave. Feedback was provided by a periodic grating created in the photorefractive polymer PMMA.     

Growth and characterization of Ca5(BO3)3F fiber crystals, a new nonlinear optical material for UV light generation

For the first time, Ca₅(BO₃)₃F (CBF) fiber crystals were grown by the micro-pulling down technique from LiF-based flux. Regular and transparent fibers were obtained with good optical quality. Characterization by Raman spectroscopy and EDX microprobe showed fibers compositionally homogeneous. The specific heat capacity of the fibers was measured indicating a laser damage threshold slightly lower, at room temperature, than for crystals belonging to the related rare earth calcium oxoborate family.     

Nanocomposite thin films of Ga5Sb10Ge25Se60 chalcogenide glass for optical limiting applications

We report a low-cost, scalable method to fabricate optical grade composite thin films for nonlinear optical applications. The transmission and reflection spectra of prepared Ga₅Sb₁₀Ge₂₅Se₆₀/PVA composite films were investigated. Optical band gap of the thin films were calculated using Tauc’s extrapolation method. The band gap of the nanocomposite thin films were found to be tunable depending on the grain size of the films. Nonlinear optical characterization of samples were studied by the Z-scan technique using an Nd:YAG laser (532 nm, 7 ns, 10 Hz). Sequential Z-scan traces were made in four regimes of intensity for films with three different grain sizes. The Z-scan spectra reveal a strong nonlinear absorption depending on the grain size of the films suggesting that the new materials are promising candidates for the development of nonlinear optical devices and are extremely perspective as optical limiters of intense short pulse radiation.     

Optical properties of graphene based annular photonic crystals

The optical properties of a graphene based annular photonic crystal (APC) are theoretically investigated. The proposed structure is a hollow core cylindrical shell consists of the alternate dielectric layer and graphene monolayer immersed in free space. In order to study the photonic band structures of the APC, we obtained the optical spectra of the graphene based APC by employing the transfer matrix method in the cylindrical waves for both TE and TM polarizations. In this work we study the effect of different geometrical and optical parameters of the structure on the low loss high reflectance graphene induced band gap. It is found that the graphene induced band gap which appeared in the frequency below 10 THz is polarization independent and remains almost invariant with the change in the period number, the radius of the inner core region and the refractive indices of the inner core region and the surrounding medium. However, its width increases by increasing the azimuthal mode number and the chemical potential of the graphene monolayers and decreases by increasing the refractive index and the thickness of the dielectric layers.     

Complementary characterization techniques for identification of ferroelectric domains in KNbO3 single crystals

KNbO₃ single crystals are often utilized for their piezoelectric and optical properties. In this study the domain configurations in as-grown single crystals were investigated using reflected light microscopy, scanning electron microscopy and atomic force microscopy. Using atomic force microscopy it was possible to image the distortion induced on the crystal surface by the domain walls and to quantify the predicted angle between (001)_pc planes across these walls for the cases of both 90° domain walls and S walls. These features can also be imaged using the other two techniques. This direct measurement of surface distortion verifies the geometrical model of domain structures, and suggests that any possible strain energy considerations are minor in predicting the surface topography in the material after phase changes from the growth temperature.     

Observation of paramagnetic point defects in BBO (β-BaB2O4) crystals

The electron paramagnetic resonance (EPR) technique has been used to investigate point defects in single crystals of BBO (β-BaB₂O₄). This borate compound is a widely used nonlinear optical material, especially in the ultraviolet region, and point defects are expected to play a role in its device performance. There were no observable EPR spectra in our as-grown BBO crystals. However, an irradiation at room temperature with X-rays produced two stable EPR signals. One of these spectra, containing ten hyperfine lines when the magnetic field is parallel to the crystal's c axis, is assigned to a hole trapped on an oxygen ion adjacent to a barium vacancy. The ten lines are due to interactions with the two neighboring ¹¹B nuclei. The other radiation-induced spectrum consists of a single line with an effective g value of 2.017 when the magnetic field is along the c axis. We tentatively assign this spectrum to Ni⁺ ions substituting for Ba²⁺ ions. In separate experiments, it was found that heating an as-grown BBO crystal to 760 °C for several hours produced an EPR spectrum due to Cu²⁺ ions. Subsequent exposure at room temperature to X-rays reduces the intensity of the Cu²⁺ spectrum.     

Study of the pumping regimes in Ti-sapphire and Nd0.5La0.5Al3(BO3)4 powders

Stimulated emission without a cavity was obtained (at λ=800 nm) in powders of Ti-sapphire laser crystal and compared to that in Nd_0.5La_0.5Al₃(BO₃)₄. The formation of a narrow channel in a powder sample by a pumping laser beam was found to be advantageous for stimulated emission in Ti-sapphire and disadvantageous in Nd_0.5La_0.5Al₃(BO₃)₄. The effect of the material volume density on stimulated emission in scattering Nd_0.5La_0.5Al₃(BO₃)₄ was experimentally studied. The experimental results are explained in terms of absorption of pumping light in scattering materials, penetration depth for pumping, and residence time for emission photon in the pumped volume.     

Optical, electrical and thermal studies on (As2Se3)3−x(As2Te3)x glasses

Optical properties and conductivity of glassy (As₂Se₃)_3−x(As₂Te₃)_x were studied for 0 ≤ x ≤ 3. The films of the above mentioned compound were prepared by thermal evaporation with thickness of about 250 nm. The optical-absorption edge is described and calculated using the non-direct transition model and the optical band gap is found to be in the range of 0.92 to 1.84 eV. While, the width of the band gap tail exhibits opposite behaviour and is found to be in the range of 0.157 to 0.061 eV, this behaviour is believed to be associated with cohesive energy and average coordination number. The conductivity measurement on the thin films is reported in the temperature range from 280 to 190 K. The conduction that occurs in this low-temperature range is due to variable range hopping in the band tails of localized states, which is in reasonable agreement with Mott's condition of variable range hopping conduction. Some parameters such as coordination number, molar volume and theoretical glass transition temperature were calculated and discussed in the light of the topological bonding structure.     

Impedance spectroscopy study of LaMnO3 modified BaTiO3 ceramics

Ba_0.97Ti_0.97La_0.02Mn_0.04O₃ nanocrystalline powder was prepared by chemical route with the help of soluble tartarate complex of Ti⁴⁺ ion. Preliminary X-ray diffraction analysis of crystal structure showed that a single-phase compound was formed exhibiting tetragonal system. Average crystallite size and particle size were observed to be between 27 and 33 nm, which were analyzed through XRD and transmission electron microscope respectively. Wide range impedance spectroscopy study from 200 to 600 °C showed the presence of both bulk and grain boundary effects up to 500 °C. The bulk conductivity indicated an Arrhenius-type thermally activated process and oxygen vacancies are the possible ionic charge carriers at higher temperatures. The variation of ac conductivity as a function of frequency indicated the possibility of hopping mechanism for electrical process in the system with a non-exponential type of conductivity relaxation.     

Vacuum ultraviolet excited photoluminescence properties of novel Na3Y9O3(BO3)8:Eu phosphor

The novel vacuum ultraviolet (VUV) excited Na₃Y₉O₃(BO₃)₈:Eu³⁺ red phosphor was synthesized and the photoluminescence (PL) properties were investigated. The phosphor showed strong VUV PL intensity, large quenching concentration (40 mol%) and good chromaticity (0.649, 0.351). The Eu³⁺-O²⁻ charge transition (CT) was observed to be at a higher energy (232 nm, 5.35 eV). The host absorption at 127-166 nm was broad and strong when monitoring the Eu³⁺ emission, which indicated that energy transfer from the host-lattice to the Eu³⁺ ions was efficient in Na₃Y₉O₃(BO₃)₈:Eu³⁺. These excellent VUV PL properties were revealed to be correlated with the unique isolated layer-type structure of Na₃Y₉O₃(BO₃)₈ host. The results showed that the Na₃Y₉O₃(BO₃)₈:Eu³⁺ would be a good candidate for VUV-excited red phosphor.     

Experimental observation of low threshold optical bistability in exfoliated graphene with low oxidation degree

We have experimentally investigated low threshold Optical Bistability (OB) and multi-stability in exfoliated graphene ink with low oxidation degree. Theoretical predictions of N-layer problem and the resonator feedback problem show good agreement with the experimental observation. In contrary to the other graphene oxide samples, we have indicated that the absorbance does not restrict OB process. We have concluded from the experimental results and Nonlinear Schrödinger Equation (NLSE) that the nonlinear dispersion – rather than absorption – is the main nonlinear mechanism of OB. In addition to the enhanced nonlinearity, exfoliated graphene with low oxidation degree possesses semiconductors group III–V equivalent band gap energy, high charge carrier mobility and thus, ultra-fast optical response which makes it a unique optical material for application in all optical switching, especially in THz frequency range.     

BaTiO3-SrTiO3 layered dielectrics for energy storage

BaTiO₃-SrTiO₃ (BST) thick films (~ 250-390 μm) with layered structures were fabricated by tape-casting and lamination process. Layered composites with various Ba/Sr ratios were obtained by lamination of BaTiO₃ (BT) and SrTiO₃ (ST) tapes in different spatial configurations (2-2). As-prepared BST ceramics showed much improved sinterability over the laminates of pure BT or pure ST tapes. Dielectric properties of materials were measured in the temperature range of 25 °C to 200 °C. The method of utilizing of layered structures offered flexibility to maximize the energy storage capability at specific operating conditions: (temperature and electric field) by tailoring the dielectric properties through varying the spatial configurations of BT and ST films.     

Electron transfer effect in BaTiO3 and CaTiO3 due to Nb-doping

Using an advanced quantum-chemical method, a study of Nb-doping has been carried out in the BaTiO₃ and CaTiO₃ crystals. The lattice distortion due to the impurity presence is studied in a comparative manner for the two crystals and also considering different crystallographic phases. A new phenomenon of an extra electron transfer from the local energy level within the band-gap to the conduction band is found. This effect is discussed in terms of the available experimental data on electrical conductivity augmentation in these materials.