Upconversion luminescence and optical power limiting effect based on two- and three-photon absorption processes of ZnO crystal

Near-infrared to UV and visible upconversion luminescence was observed in single-crystalline ZnO under an 800 nm infrared femtosecond laser irradiation. The optical properties of the crystal reveal that the UV and VIS emission band are due to the exciton transition (D₀X) bound to neutral donors and the deep luminescent centers in ZnO, respectively. The relationship between the upconversion luminescence intensity and the pump power of the femtosecond laser reveals that the UV emission belongs to three-photon sequential band-to-band excitation and the VIS emission belongs to two-photon simultaneous defect-absorption induced luminescence. A saturation phenomenon and polarization-dependent effect are also observed in the upconversion process of ZnO. A very good optical power limiting performance at 800 nm has been demonstrated. The two- and three-photon absorption coefficients of ZnO crystal were measured to be 0.2018 cm GW⁻¹ and 7.102 × 10⁻³ cm³ GW⁻², respectively. The two- and three-photon cross sections were calculated to be 1.189 × 10⁻⁵¹ cm⁴ s and 1.040 × 10⁻⁸⁰  cm⁶ s², respectively.     

Second- and third-order optical studies of 4-Bromoanilinium hydrogen phthalate single crystal for nonlinear optical device applications

A new organic NLO material 4-Bromoanilinium hydrogen phthalate was grown by slow evaporation technique. The solubility and metastable zone width were determined. The crystal belongs to monoclinic system with space group C2. Optical transmittance spectrum confirms the wide optical window. Absorption coefficient and band gap were calculated from transmittance. The thermal stability, laser-induced surface damage threshold and mechanical behaviour were analysed. The particle size-dependent second harmonic generation efficiency was evaluated by Kurtz–Perry powder method and existence of phase matching. The third-order optical study was measured by Z-scan studies. The dispersion of birefringence behaviour was studied.     

Synthesis, crystal growth and characterization of a metal-organic nonlinear optical tri-allylthiourea mercury chloride single crystals

Metal-organic nonlinear optical material tri-allylthiourea mercury chloride single crystal was grown using low temperature solution growth method. The growth parameters such as pH and temperature were optimized for getting colorless single crystals. The X-ray rocking curve measurement shows that the grown crystal was free from internal structural grain boundaries. The structural, spectral, optical and thermal properties of the grown specimen were studied using various characterization techniques. The defects present in the grown crystals were studied with chemical etching analysis. The results show that the grown crystals are suitable candidates for nonlinear optical applications.     

Theoretical study of diaquamalonatozinc(II) single crystal for applications in non-linear optical devices

The aim of the present paper is to employ theoretical methods to investigate the zero field splitting (ZFS) parameter and to investigate the position of the dopant in the host. These theoretical calculations have been compared with the empirical results. The superposition model (SPM) with the microscopic spin-Hamiltonian (MSH) theory and the coefficient of fractional parentage have been employed to investigate the dopant manganese(II) ion substitution in the diaquamalonatozinc(II) (DAMZ) single crystal. The magnetic parameters, viz. g-tensor and D-tensor, has been determined by using the ORCA program package developed by F Neese et al. The unrestricted Kohn–Sham orbitals-based Pederson–Khanna (PK) as the unperturbed wave function is observed to be the most suitable for the computational calculation of spin–orbit tensor (\(D^{\mathrm{SO}})\) of the axial ZFS parameter D. The effects of spin–spin dipolar couplings are taken into account. The unrestricted natural orbital (UNO) is used for the calculation of spin–spin dipolar contributions to the ZFS tensor. A comparative study of the quantum mechanical treatment of Pederson–Khanna (PK) with coupled perturbation (CP) is reported in the present study. The unrestricted Kohn–Sham-based natural orbital with Pederson–Khanna-type of perturbation approach validates the experimental results in the evaluation of ZFS parameters. The theoretical results are appropriate with the experimental ones and indicate the interstitial occupancy of \(\hbox {Mn}^{2+}\) ion in the host matrix.     

Leaky optical waveguide for high power applications

The available fiber lasers, photonic-crystal fiber (PCF) frequency converters, and hollow-core PCFs are shown to offer realistic practical solutions for an all-fiber format of coherent anti-Stokes Raman scattering (CARS) in the gas phase. In view of the substantial enhancement of CARS in the guided modes of hollow-core PCFs, a broad class of compact ytterbium and erbium fiber laser sources become suitable for the CARS analysis of gas media. The quantum limit of the signal-to-noise ratio, S/N, in all-fiber CARS is shown to scale as λα^-1a^-2 with radiation wavelength λ, fiber loss α, and the fiber core radius,aleading, in the case of a hollow-PCF gas cell, to a dramatic improvement of S/N relative to CARS in the regime of tight focusing. PACS 42.65.Wi; 42.81.Qb     

Nucleation kinetics,growth and characterization of guanidinium 3-nitrobenzoate single crystal

A potential organic nonlinear optical guanidinium 3-nitrobenzoate (Gu-3NB) was synthesized. Solubility of Gu-3NB was determined for various temperatures. Meta stable zone width and induction period values were determined in order to optimize the growth parameters. Nucleation parameters, such as interfacial tension, critical radius and free energy of formation of critical nucleus were evaluated. Optically good quality, bulk single crystal of Gu-3NB was successfully grown by slow evaporation method and slow cooling method with the optimized growth parameters. The etching study was performed to ascertain the growth quality of the crystal. The unit cell parameters and the morphology of Gu-3NB single crystal were determined by X-ray diffraction. The grown crystal was subjected to various characterization studies, such as optical, dielectric measurement and mechanical studies.     

Thin films of metal-organic compounds and metal nanoparticle-embedded polymers for nonlinear optical applications

Thin films based on two very different metal-organic systems are developed and some nonlinear optical applications are explored. A family of zinc complexes which form perfectly polar assemblies in their crystalline state are found to organize as uniaxially oriented crystallites in vapor deposited thin films on glass substrate. Optical second harmonic generation from these films is investigated. A simple protocol is developed for thein-situ fabrication of highly monodisperse silver nanoparticles in a polymer film matrix. The methodology can be used to produce free-standing films. Optical limiting capability of the nanoparticle-embedded polymer film is demonstrated     

Tailoring optical properties of TiO_2 in silica glass for limiting applications

We present the linear and nonlinear optical studies on TiO2-SiO2 nanocomposites with varying compositions. Opti- cal band gap of the material is found to vary with the amount of SiO2 in the composite. The phenomenon of two-photon absorption （TPA） in TiO2/SiO2 nanocomposites has been studied using open aperture Z-scan technique. The nanocom- posites show better nonlinear optical properties than pure TiO2, which can be attributed to the surface states and weak dielectric confinement of TiO2 nanoparticles by SiO2 matrix. The nanocomposites are thermally treated and similar studies are performed. The anatase form of TiO2 in the nanocomposites shows superior properties relative to the amorphous and rutile counterpart. The involved mechanism is explained by rendering the dominant role played by the excitons in the TiO2 nanoparticles.     

Growth and characterization of L-histidinium fumarate fumaric acid monohydrate single crystal: A promising second and third order nonlinear optical material

L-histidinium Fumarate Fumaric acid Monohydrate (LHFFAM), an organic nonlinear optical single crystal[C₁₄H₁₉N₃O₁₁], has been synthesized and grown using aqueous solution by slow evaporation technique at room temperature. Crystal structure details were obtained from single crystal XRD. The coordination of functional groups was identified in the grown crystal by FTIR analysis. The UV-absorption studies evince the transparent nature of the crystal is in the visible region and the optical band gap energy E_g was evaluated. The TG/DSC analyses confirm the thermal stability for the as-grown crystal. The Vickers microhardness test was carried out on the grown crystals and there by Vickers hardness number (H_v), work hardening coefficient (n), yield strength (σ_y), stiffness constant C₁₁ were evaluated. The dielectric behaviour of LHFFAM has been determined in the frequency range 50 Hz to 5 MHz at various temperatures. Kurtz-Perry and Z-scan techniques were performed for the acentric crystal LHFFAM which highlighted good nonlinear response and hence proves it appropriate for frequency conversion process and photonic device fabrications.     

Preparation and optical properties of single crystal thin films of bismuth substituted iron garnets for magneto-optic applications

Single crystal thin films of Bi substituted iron garnets have been grown by the liquid phase epitaxy technique. The growth conditions and compositions are presented together with the segregation coefficients of Bi and Pb as a function of growth temperature. The Faraday rotation and optical absorption have been measured for wavelengths between 0.7 and 0.46 μm. The superior magneto-optic properties (Faraday rotations of up to ten times larger than that observed for Y₃Fe₅O₁₂) make these epitaxial layers attractive for magneto-optic devices. The influence of Pb incorporation on the optical properties of the films is discussed. Compositions of Bi and Ga(Al) substituted Gd₃Fe₅O₁₂, which exhibit a magnetic compensation temperature near room temperature and high Faraday rotation, have also been prepared. The magnetic switching behaviour as a function of temperature has been determined. It shows that these films are especially suited for thermomagnetic recording using an argon ion laser at a wavelength of 5145 Å.     

A double acousto-optic monochromator for the uv region with improved optical characteristics based on a KDP single crystal

A double monochromator is developed and manufactured on the basis of an acousto-optic filter made of a potassium dihydrogen phosphate (KDP) single crystal. The device has an operating range of 260–540 nm and improved optical characteristics: high aperture ratio (an angular aperture of 2° and a linear aperture of 6.5x15 mm), high polarization contrast (～10⁸), and low level of transmission sidelobes (～10³). The spectral resolution of the monochromator at the edges of the operating range is 0.5 and 3 nm, respectively. The control frequency band is 60–150 MHz. Experimentally, it is shown that, for sound beams with equivalent geometric parameters, the diffraction efficiency provided by the KDP-based acousto-optic filter is an order of magnitude higher than that obtained with a noncollinear acousto-optic filter fabricated on the basis of crystalline quartz.     

Wavelength tunability of tandem optical parametric oscillator based on single PPMgOLN crystal

The theoretical analysis and experimental results of the wavelength tunability of a tandem optical parametric oscillator (TOPO) based on a single nonlinear crystal are presented.TOPO is a configuration wherein the signal laser is used as a pump laser to generate secondary optical parametric oscillator (OPO).The cascaded parametric interactions are achieved synchronously in a single-grating-period MgO doped periodically poled lithium niobate (PPMgOLN).Tunable multiple-wavelength mid-infrared (mid-IR) lasers are obtained by changing the temperature of the crystal.When the PPMgOLN crystal with a grating period of 31.2 μm is operated at 148 ℃,the dual OPOs generate an identical mid-IR laser of 2.83 μm.The secondary OPO transforms into an optical parametric amplifier,in which different frequency mixing from the signal laser results in the amplification of the idler laser in the first OPO.TOPO is a useful configuration for multiple laser output,broad tuning range,and high-efficiency mid-IR lasers.     

Low-threshold optical power limiting of cw laser illumination based on nonlinear refraction in zinc tetraphenyl porphyrin

The increasing use of low power cw lasers in various applications calls for the design of optical limiters with low thresholds. To this end, the optical nonlinearity exhibited by zinc tetraphenyl porphyrin at low laser powers is utilized to design an optical limiter for low threshold operation. The basic parameter responsible for limiting action, the nonlinear refractive index of the medium, is measured using the Z-scan technique and found to have a value of at the helium–neon laser wavelength of 632.8 nm. The origin of nonlinearity is explained on the basis of the thermal lens model. It is shown that effective optical limiting at desired threshold values can be achieved by the optimal choice of aperture size and experimental geometry.     

An ultra-short double-wavelength optical power splitter for two waveguides operation based on photonic crystal multimode interference

In this paper, we design an ultra-short 1 × 2 1310/1550 nm double-waveguide optical power splitter based on photonic crystal multimode interference. The device can be used to divide the input beam equally for both 1310 nm and 1550 nm at the same time. The total multimode waveguide length of this device is only about 13 μm, which is one 210th of the conventional dielectric counterparts reported. On the basis of the guided-mode propagation analysis method, the self-imaging effect is discussed for the case of symmetric incidence. The finite-difference time-domain method is used to simulate the propagation of the beam in the multimode interference. The results show that the repetitive appearances of single image and twofold image of the input field occur alternatively in this device.     

Far-infrared optical properties of YVO4 single crystal

Near-normal incident infrared reflectivity spectra of a (001) YVO₄ single crystal have been measured at different temperatures in the frequency region between 100 and 6000 cm^-1. The reflectivity spectra are analyzed with the factorized form of the dielectric function, and the dielectric properties and optical conductivity of the YVO₄ crystal are obtained. From the TO/LO splitting, effective charges at different temperatures are calculated to study the ionicity of YVO₄. The internal modes of the VO₄^3- ion and the external modes of the Y(VO₄) lattice are compared with SiO₄^4- in zircon and with other rare-earth vanadates.     

FIR optical properties of single crystal Ba-and Sr-hexaferrite

Far-infrared reflectivity measurements on single crystal barium and strontium hexaferrite are presented. The infrared active TO, and the associated LO phonon frequencies and the dielectric permittivity functions for E ⊥c have been determined using a fitting procedure based on a four parameter model. The infrared active modes of these compounds (space group D⁴_6h have been determined by group theoretical analysis and the results compared with the spectroscopic measurements.     

Thermally induced nonlinear optical response and optical power limiting of acid blue 40 dye

We report the investigations of thermally induced third-order nonlinear optical and optical limiting characterizations for various concentrations of acid blue 40 dye in N,N-Dimethyl Formamide, studied by employing z-scan technique under cw He–Ne laser irradiation at 633 nm wavelength. The samples exhibited nonlinear absorption and nonlinear refraction under the experimental conditions. For lower concentration, the samples display both saturable absorption (SA) and reverse saturable absorption (RSA); whereas with increase in concentration, RSA behaviour prevails. The estimated values of the effective coefficients of nonlinear absorption β_eff, nonlinear refraction n₂ and third-order nonlinear susceptibility χ⁽³⁾ were found to be of the order of 10^?2 cm/W, 10^?4 esu and 10^?6 esu respectively. Multiple diffraction rings were observed when the samples were exposed to laser beam due to refractive index change and thermal lensing. The effect of concentration and the laser intensity on the self-diffraction ring patterns was studied experimentally. The acid blue 40 dye also exhibited strong optical limiting properties under cw excitation and reverse saturable absorption is found to be the dominant nonlinear optical process leading to the observed nonlinear behaviour.