Third-order Nonlinear Refractive Index Research Articles

Observation of Two-Photon Absorption and Nonlinear Refraction in AlN**Supported by the National Natural Science Foundation of China under Grant Nos 51372267, 51210105026 and 51172270, and the National Basic Research Program of China under Grant No 2013CB932901.

Two-photon absorption (TPA) and nonlinear refraction in AlN single crystals are revealed with the single beam Z-scan technique. A large TPA coefficient of 13±3cm/GW at 355nm and third-order nonlinear refractive indices of −1.91±0.38×10−13 cm2/W at 355 nm, 1.79±0.36×10−13 cm2/W at 532 nm and 1.61±0.32×10−12 cm2/W at 1064 nm are derived. It is inferred that the TPA-generated free carriers are responsible for the large negative nonlinear refractive index at 355 nm, while the oxygen impurity induced bandgap narrowing may account for the large third-order nonlinear refractive indices at 532 nm and 1064 nm. The large nonlinear optical responses of AlN promise wide applications in the deep ultraviolet nonlinear optical devices.

Linear and nonlinear optical properties in spherical quantum dots: Manning-Rosen potential

In this work, we studied the optical properties of spherical quantum dots confined in Manning-Rosen potential with the appropriate centrifugal term included. The approximate solution of the bound state and wave functions were obtained from the Schrodinger wave equation by applying the standard methods. Also, we have used the density matrix formalism to investigate the linear and third-order nonlinear absorption coefficient and refractive index changes.

Effect of the shape of quantum dots on the refractive index changes

We have intensively studied the influence of the shape of quantum dots on the refractive index changes. Within the framework of the effective-mass approximation, numerical results are performed by means of calculation methods of the compact-density-matrix and the matrix diagonalization. We analyze the properties of the linear, third-order nonlinear and total refractive index changes (RICs) as a function of the incident photon energy in circular, elliptic, and triangular shaped quantum dots. The results show that the shape of quantum dots has a significant impact on the refractive index changes.

The effects of germanium addition on properties of Ga-Sb-S chalcogenide glasses

Properties of the glasses are experimentally investigated when Ga is gradually substituted by Ge in Ga8Sb32S60 chalcogenide glass. The glass structure is also studied to elucidate the variations of the properties. While the substitution of Ga by Ge does not remarkably change the glass transition temperature Tg, the thermal stability against crystallization becomes optimum when half of the Ga atoms are replaced by Ge atoms. The short-wavelength absorption edge λS (or optical bandgap Eg) exhibits a remarkable decrease when a small amount of Ge is added, however, its value does not change significantly with further Ga substitution. As Ga is gradually replaced by Ge, the long-wavelength cut-off edge λL, the density ρ, the linear refractive index n, and the third-order nonlinear refractive index n2 decrease. It is shown that the property variations of the glasses could be explained by the evolution of the glass structure.

Third-order nonlinearity and saturable absorbed performance of Cr^4+:Gd_3Ga_5O_12 crystal

In this work, the third-order nonlinear optical properties and saturable absorbed performance of Cr4+-doped Gd3Ga5O12 (Cr4+:GGG) crystal were investigated. By using the Z-scan technique, the third-order nonlinear properties were analyzed systematically. Compared with Cr4+:YAG crystal, Cr4+:GGG crystal has a large third-order nonlinear refractive index, ground-state absorption, and excited-state absorption cross section. It has been successfully employed as a saturable absorber for passively Q-switched and Q-switching mode-locked lasers in this paper. In the Q-switched regime, the maximum average output power of 600 mW was obtained with the shortest pulse width of 4.76 ns and the repetition rate of 41.4 kHz, corresponding to single pulse energy and pulse peak power of 14.5 µJ and 3 kW, respectively. For the Q-switching mode-locking operation, the maximum output power of 468 mW was obtained with a repetition rate of 141.2 MHz. The results indicate that Cr4+:GGG crystal has the potential to be used for passive Q-switching and mode-locking laser generation.

Crystal structure, growth and characterizations of a novel organic third-order nonlinear optical crystal: guanidinium cinnamate

Guanidinium cinnamate (GUCN), a single crystal, was grown by slow evaporation technique. Single-crystal X-ray diffraction study revealed that GUCN crystal belongs to monoclinic crystal system with the space group P21/c. Thermal studies revealed that the GUCN is thermally stable up to 238 °C. The optical transmittance studies were carried out for the crystal, and the lower cutoff wavelength of the grown crystal was observed at 322 nm. The luminescent study showed that the GUCN crystal has high degree of luminescence. Third-order nonlinear refractive index n2, nonlinear absorption coefficient β and susceptibility χ(3) parameters were estimated by Z-scan technique. The four independent tensor coefficients e11, e22, e33 and e13 of dielectric permittivities for monoclinic GUCN were calculated. The mechanical properties of the grown crystals were studied using Vickers micro-hardness tester at different planes.

Optical properties of Fe-doped BaTiO3 films deposited on quartz substrates by sol-gel method

Fe-doped BaTiO3 films were prepared on quartz substrates by sol-gel route. Linearly optical constants of the films were obtained by fitting transmittance spectra with Adachi’s model. With increasing Fe composition, refractive index n at 532 nm increases, single oscillator energy Ec and dispersion energy Ed increase, but optical band gap Eg decreases from 3.78 to 3.63 eV. In addition, nonlinear optical properties of the Fe-doped BaTiO3 films were analyzed by Z-scan method. Nonlinear optical responses of the BaTiO3 films were enhanced by Fe doping. For BaTi0.96Fe0.04O3 film, the third-order nonlinear refractive index coefficient γ, the nonlinear refractive index coefficient n2, the nonlinear absorption coefficient β and the third-order nonlinear susceptibility χ(3) are 1.98 × 10−13 m2/W, 1.03 × 10−6 esu, 1.33 × 10−7 m/W, 2.38 × 10−7 esu respectively. The nonlinearity is predominated by the nonlinear refractive behavior. These results suggest that Fe doping may tune the linear and nonlinear optical properties of BaTiO3 films, which indicates that Fe-doped BaTiO3 films are promising materials for applications in optical devices.

Linear and Nonlinear Optical Properties in Spherical Quantum Dots: Generalized Hulthén Potential

In this work, we studied the optical properties of spherical quantum dots confined in Hulthen potential with the appropriate centrifugal term included. The approximate solution of the bound state and wave functions were obtained from the Schrodinger wave equation by applying the factorization method. Also, we have used the density matrix formalism to investigate the linear and third-order nonlinear absorption coefficient and refractive index changes.

Third-order optical nonlinearity studies of bilayer Au/Ag metallic films

This paper presents nonlinear optical studies of bilayer metallic films of gold (Au) and silver (Ag) on glass substrate prepared using electron beam evaporation. The preparation of Au and Ag nanoparticles (NPs) on the substrate involved the use of electron beam deposition, then thermal annealing at 600 °C and 270 °C, respectively, to produce a randomly distributed layer of Au and a layer of Ag NPs. Observation of field-effect scanning electron microscope images indicated the size of the NPs. Details of the optical properties related to peak absorption of surface plasmon resonance of the nanoparticle were revealed by use of UV–Vis spectroscopy. The Z-scan technique was used to measure the nonlinear absorption and nonlinear refraction of the fabricated NP layers. The third-order nonlinear refractive index coefficients for Au and Ag are (−9.34 and −1.61) × 10−11 cm2 W−1 given lower n2, in comparison with bilayer (Au and Ag) NPs at −1.24 × 10−10 cm2 W−1. The results show bilayer NPs have higher refractive index coefficients thus enhance the nonlinearity effects.

Rashba spin-orbit coupling effects on the optical properties of double quantum wire under magnetic field

We investigate the effects of Rashba spin-orbit interaction on the optical absorption coefficients and refractive index changes associated with transitions between the first two lower-lying electronic levels in double quantum wire. The wire system represented by a symmetric, double quartic-well confinement potential is subjected to a perpendicular magnetic field. The analytical expressions of the linear and third-order nonlinear optical absorption coefficients and refractive index changes are obtained by using the compact-density matrix formalism and iterative scheme. Optical properties are investigated as a function of structural parameter, magnetic field, Rashba spin-orbit interaction and photon energies. Numerical results reveal that competing effects between spin-orbit interaction and magnetic field modify strongly the optical properties and can be altered by these parameters.

Role of Composition and Substrate Temperature on Nonlinear Optical Properties of GeSeTe Thin Films in 0.4–2.4-$\mu \text{m}$ Wavelength Range

The nonlinear optical properties of Ge10Se90– x Te x ( $x = 0$ , 10, 20, 30, 40, 50) thin films have been investigated as a function of composition and substrate deposition temperatures (303, 363, and 423 K). The third-order nonlinear susceptibility and nonlinear refractive index have been estimated. Nonlinearity in refractive index increases with Te content and also with increasing substrate temperature. Among the investigated compositions of Ge10Se90– x Te x , the Ge10Se40Te50 composition shows more prominent nonlinear refractive index in comparison with pure silica. The high third-order susceptibility and nonlinear refractive index may make these materials capable for high-speed communication fibers.

Anisotropically Enhanced Nonlinear Optical Properties of Ensembles of Gold Nanorods Electrospun in Polymer Nanofiber Film.

Polymeric nanofibers containing gold nanorods (GNRs) are aligned in a uniform orientation through electrospinning. The dispersive and absorptive parts of the third-order optical nonlinear optical refractive index of the composite film measured by polarization dependent z-scan method are demonstrated to be anisotropically enhanced. Anisotropic optical response of the aligned GNRs and its connection with the ultrafast electron dynamics are discussed in light of the results of resonant femtosecond pump-probe experiments. The significant appearance of anisotropic nonlinear optical properties of ensembles of GNRs is attributed to the sensitive excitation of longitudinal surface plasmon resonance (LSPR) of highly aligned GNRs. For the macroscopic applications of ensembles of GNRs, such as passive mode-locking and all-optical switching, the experimental results demonstrate that the alignment of GNRs through electrospinning should be very high efficient, and economic.

Interband-transition-modified third-order nonlinear optical properties of Al nanoshells in carbon disulfide

Al nanoshell geometry and the defined parameters used for simulations of linear and nonlinear optical properties.

Large third-order nonlinear refractive index coefficient based on gold nanoparticle aggregate films

Au nanoparticles show large third-order nonlinear effect and ultra-fast response. Here a high nonlinear aggregate film based on self-assembled gold nanoparticles is reported and its third-order nonlinear refractive index coefficient is measured by Z-scan experiment. The third-order nonlinear refractive index coefficient of the Au nanoparticle aggregate film (γ1 = 9.2 × 10−9 cm2/W) is found to be larger than that of an 8-nm-thick sputtered Au film (γ2 = 6.5 × 10−9 cm2/W). This large nonlinear effect can be attributed to the strong field enhancement due to localized plasmon resonances between Au nanoparticles. The result shows that the self-assembled Au nanoparticle aggregate film could be a promising candidate as a third-order nonlinear optical material.

Doped with DR13 molecules TiO2/organically modified silane organic–inorganic hybrid materials with low propagation loss and ultrafast optical response

Disperse red 13 (DR13) azoaromatic chromophores were incorporated into sol-gel derived TiO 2 /organically modified silane matrix to achieve a hybrid material with low propagation loss and ultrafast optical response. The planar waveguide and nonlinear optical properties of the as-derived hybrid films were studied by a prism coupling technique and an optical Kerr shutter technique with an 800-nm femtosecond laser, respectively. Results indicate that the response time of the bulk sample doped with 0.1% DR13 molecules is less than 208 fs, and the third-order nonlinear refractive index is estimated at about 1.141×10 −15 cm 2 /W . The planar waveguide film with a low propagation loss less than 1 dB/cm for both transverse electric and transverse magnetic modes at a wavelength of 1312 nm can be easily obtained by a spin-coating process. It can be concluded from the above results that the as-prepared hybrid materials under present conditions are expected to have potential in ultrafast optical applications.

Synthesis and characterization of semiorganic sodium hydrogen maleate trihydrate (SHMT) single crystal: A third-order nonlinear optical material

Single crystals of semiorganic sodium hydrogen maleate trihydrate (SHMT) were effectively grown from deionized water by solvent evaporation technique. The grown crystals were subjected to single crystal X-ray diffraction to know the precise information about the crystallographic structure. The SHMT crystal belongs to triclinic system with centrosymmetric space group of P-1. TGA/DTA analysis indicates that the grown crystal was thermally stable up to 249.6 °C. The UV–Visible spectrum revealed its high transparency nature and the cut off wavelength was found to be at 290 nm. Its mechanical behavior was assessed by Vickers microhardness measurements. Dielectric measurements were made over a wide range of frequency (50 Hz–1 MHz) at room temperature. Theoretical calculations for polarizability and optical constants were made which are necessary for device fabrication. The third-order nonlinear optical parameters were derived by Z-scan technique. The third-order nonlinear refractive index, absorption coefficient and susceptibility values were found to be −5.04112 × 10−11 cm2/W, 1.08717 × 10−3 cm/W and 6.35585 × 10−7 esu respectively.

Strong Modulation Instability in a Silicon–Organic Hybrid Slot Waveguide

In this paper, we investigate the strong modulation instability (MI) at telecommunication band in a silicon–organic hybrid slot waveguide. The organic material of polymer poly (bis para-toluene sulfonate) of 2, 4-hexadiyne 1, 6 diol (PTS), which has high third-order nonlinear refractive index and very low two-photon absorption, is used to fill the slot of the waveguide. The optical gain can be up to $\sim$ 3600 ${\rm m}^{-1} $ with a low pump peak power of 300 mW. By using Gaussian pulses with width of 10 ps and peak power of 250 mW, deep modulation of the pump is achieved, and the ultrashort pulse trains with the periods of 27 and 24 fs are obtained in the anomalous and normal group-velocity dispersion regions, respectively.

Optical properties of poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene] light-emitting polymer solutions: effects of molarities and solvents

The optical properties of the solutions of the MDMO-PPV light-emitting polymer were investigated. The maximum mass extinction coefficient values of the solutions of the MDMO-PPV for 6.640 and 3.014 µM were found to be 20.874 and 42.009 L g−1 cm−1, respectively. The absorption band edge values of the solutions of the MDMO-PPV shifted from 2.149 to 1.987 eV with increasing molarity. To obtain lower Eg values (2.020, 2.057, 2.083, 2.088 and 2.103 eV, respectively) of the MDMO-PPV can be preferred xylene, toluene, chlorobenzene, chloroform and tetrahydrofuran solvents, respectively. The E g of the solution of the MDMO-PPV was decreased with molarities and solvents. The refractive index values of the MDMO-PPV were controlled with various solvents. The optical parameters such as single oscillator energy, dispersion energy, M −1, M −3 moments, optical oscillator strengths, linear static refractive index, optical linear susceptibility, third-order nonlinear susceptibility and nonlinear refractive index were calculated using Wemple–DiDomenico equation. The highest contrast was obtained with xylene, while the lowest contrast was obtained with chlorobenzene. The MDMO-PPV can be used in the fabrication of the metal–semiconductor contacts due to low optical band gap and suitable optical parameters. Also, the surface morphology properties of the MDMO-PPV polymer film were investigated.

Linear and nonlinear optical properties in asymmetric double semi-V-shaped quantum well

In this present work, the effects of the structure parameters such as the right-well width and the right-barrier height on the linear, third-order nonlinear and total absorption and refractive index changes of asymmetric double semi-V-shaped quantum well are theoretically studied by using the compact-density matrix approach and iterative method. The electronic structure of this system is obtained by solving Schrödinger equation within the framework of effective mass approximation. Numerical results are presented for a typical GaAs/AlxGa1-xAs asymmetric double semi-V-shaped quantum well. The obtained results show that the right-well width and the right-barrier height have great effects on the optical characteristics of these structures.

Spin–orbit interaction effects on the optical properties of quantum wires under the influence of in-plane magnetic fields

In this work, we studied the effects of in-plane magnetic field and Rashba spin–orbit interaction on the intersubband optical absorption coefficients and changes in refractive index for transitions between the first two lower-lying electronic levels of quantum wire represented by a parabolic confining potential. The analytical expressions of the linear and third-order nonlinear optical absorption coefficients and refractive index changes are obtained by using the compact-density matrix formalism and iterative scheme. Optical properties are investigated as a function of quantum wire radius, strength and orientation of magnetic field, strength of Rashba spin–orbit interaction and photon energies. Numerical results reveal that the optical absorption coefficients and refractive index changes are strongly affected and thus can be controlled by these parameters.