Third-order nonlinear optical studies of new anthraquinone derivatives

Four new donor-acceptor-donor anthraquinone derivatives were synthesized and characterized by UV, IR, ¹H NMR and elemental analysis. Their off-resonant third-order nonlinear optical properties were measured using femtosecond laser and degenerate four-wave mixing technique. The third-order nonlinear optical susceptibilities χ⁽³⁾ were 3.36-3.76 × 10⁻¹³ esu. The nonlinear refractive indexes n₂ were 6.19-6.91 × 10⁻¹² esu. The second-order hyperpolarizabilities γ of the molecules were 3.36-3.76 × 10⁻³¹ esu. The response times were 101-115 fs. The results show that these compounds have potential nonlinear optical applications.     

Growth and characterization of semi organic nonlinear optical l-Valine Ferric Chloride single crystal by solution growth technique

l-Valine Ferric Chloride single crystal is a new semi organic nonlinear optical material. It has been grown from a mixture of aqueous solutions of l-Valine and Ferric Chloride by slow evaporation solution growth technique at room temperature for the first time. Single crystal XRD analysis revealed that the crystal system belongs to Cubic P with cell parameters are a = 24.38 Å, b = 24.38 Å, c = 24.38 Å and volume is 14,485 Å³. The UV spectrum shows existence of wide transparency window suitable for optoelectronic applications. Thermal stability and melting temperature of the as grown crystal was identified from TG-DTA analysis. Spectroscopic studies have been carried out for analyzing the presence of functional groups, thermal stability and phase transition of the grown crystal. The dielectric loss and the dielectric constant of the crystals were measured as a function of frequency. Photoluminescence study was carried out for grown crystals and the maximum emission occurs has good optical transmission in the entire visible region. Second harmonic generation (SHG) conversion efficiency has been estimated.     

Effects of deposition temperature on the surface roughness and the nonlinear optical susceptibility of sprayed deposited ZnO:Zr thin films

Zirconium doped zinc oxide thin films were deposited by reactive chemical pulverization spray pyrolysis technique on heated glass substrates at 400 °C, 450 °C and 500 °C using zinc and zirconium chlorides as precursors. The effect of zirconium dopant and surface roughness on the nonlinear optical properties was investigated using atomic force microscopy (AFM) and third harmonic generation (THG). The best value of susceptibility χ⁽³⁾ was obtained from the doped films with less roughness. A strong third order nonlinear optical susceptibility χ⁽³⁾ = 20.49 × 10⁻¹² (esu) of the studied films was found for the 5% doped sample at 450 °C.     

Photophysical and nonlinear optical properties of zincphthalocyanines with peripheral substitutions

Photophysical and nonlinear optical properties of zinc phthalocyanines (ZnPc) bearing peripheral phenoxy substituents containing different functionalized groups were studied. Fluorescence spectra corresponding to the optical transition S₁ → S₀ are found to be appeared at 684 or 686.4 nm. Z-scan technique reveals large nonlinearities, where the absorptive and refractive effects are separately evaluated. Saturation absorption of ZnPc-1 was observed at 632.8 nm, with a very large nonlinear absorption coefficient β = −1.36 × 10⁻² cm/W. However a strong nonlinear refractive effect was found in all ZnPcs (1-4). Transmitted versus incident irradiance measurements carried out on ZnPc-1 and ZnPc-2, showed a very clear optical limiting behavior with irradiance thresholds around be 44 W/cm² and 90 W/cm² respectively.     

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.     

A study of nonlinear optical properties of a negative donor quantum dot

In this paper, we studied the nonlinear optical properties of a negative donor center (D⁻) in a disk-like quantum dot (QD) with a Gaussian confining potential. Calculations are carried out by using the method of numerical diagonalization of Hamiltonian matrix within the effective-mass approximation. A detailed investigation of the linear, third-order nonlinear, total optical absorptions and refractive index changes has been carried out for the D⁻ QD and the D⁰ QD. The linear, third-order nonlinear, total optical absorptions and refractive indices have been examined for a double-electron QD with and without impurity. Our results show that the optical absorption coefficients and refractive indices in a disk-like QD are much larger than their values for quantum wells and spherical QDs and the nonlinear optical properties of QDs are strongly affected not only with the confinement barrier height, dot radius, the number of electrons but also the electron-impurity interaction.     

Polaron effects on linear and nonlinear optical properties of a two-electron quantum dot

The linear and nonlinear optical properties of parabolic quantum dots in which two electrons interact with each other through both coulomb repulsion and longitudinal-optical phonon are studied by using the matrix diagonalization method. With typical semiconducting GaAs-based materials, the linear, third-order nonlinear, total optical absorption coefficients and the optical refractive index have been examined. The effects of different electron-phonon coupling strengths on the linear and nonlinear optical properties are also predicted.     

Electronic structure and optical properties of BiSI crystal

Electronic structure and optical properties of BiSI crystal were investigated by the full potential linearized augmented plane wave (FL-LAPW) method with density functional theory (DFT). The complex dielectric function and optical constants, such as optical absorption coefficient, refractive index, extinction coefficient, energy-loss spectrum and reflectivity, were calculated. The optical properties of BiSI crystal were studied experimentally by spectroscopic ellipsometry. The experimental results were compared with the theoretical spectra of complex dielectric functions and with the spectra of a pseudo-dielectric function (PDF). This method shows that experimental spectra consist of four Laurence lines sum.     

Growth and characterization of pure and doped organic nonlinear optical single crystal: l-Alanine alaninium nitrate (LAAN)

The pure l-alanine alaninium nitrate (LAAN) single crystals and LAAN crystals doped with lanthanum oxide (La₂O₃), sodium chloride (NaCl), urea (CH₄N₂O), glycine (C₂H₅NO₂) and thiourea (CH₄N₂S) were grown by slow evaporation method. The X-ray diffraction analysis, scanning electron microscopy (SEM), energy dispersive X-ray (EDAX) analysis, UV–vis spectral analysis, dielectric studies and powder SHG measurement are studied systematically. The slight changes in the lattice parameters were observed for the doped crystals compared to pure LAAN crystal. The incorporation of doping into the crystal lattice was confirmed by energy dispersive X-ray analysis. There is no change in the transmission window due to doping and the percentage of transmission in doped samples was found to increase as compared to that of pure LAAN crystal. The dielectric constant of pure crystal was found to be less than that of doped crystals. The AC conductivity was found to increase after doping and with the increase in temperature. A green radiation of 532 nm was observed from the pure and doped LAAN crystals confirming the second harmonic generation (SHG) of the crystals.     

Electric field effect on the second-order nonlinear optical properties in semiparabolic quantum wells

Electric field effect on the second-order nonlinear optical properties in semiparabolic quantum wells are studied theoretically. Both the second-harmonic generation susceptibility and nonlinear optical rectification depend dramatically on the direction and the strength of the electric field. Numerical results show that both the second-harmonic generation susceptibility and nonlinear optical rectification are always weakened as the electric field increases where the direction of the electric field is along the growth direction of the quantum wells, which is in contrast to the conventional case. However, the second-harmonic generation susceptibility is weakened, but the nonlinear optical rectification is strengthened as the electric field increases where the direction of the electric field is against the growth direction of the quantum wells. Also it is the blue (or red) shift of the resonance that is induced by increasing of the electric field when the direction of the electric field is along (or against) the growth direction of the quantum wells. Finally, the resonant peak and its corresponding to the resonant energy are also taken into account.     

Investigation of third-order nonlinear optical properties of two azo-nickel chelate compounds

This paper investigates the third-order nonlinear optical properties of two azo-nickel chelate compounds by the optical Kerr gate method at 830 nm wavelength with pulse duration of 120 fs. Both of the two compounds exhibited large third-order optical nonlinearity. The second-order hyperpolarizability,γ, of Compound 1 is of 1.0 × 10^-31 esu. Due to the charge transfer, the γ of Compound 2 with electron donor and acceptor group is 4.9 × 10^-31 esu, which is a four-time enhancement in comparison with Compound i. The absorption spectra show that the electron push-pull effect, which induces intramolecular charge transfer, leads to the increased optical nonlinearity.     

Optimization and limits of optical nonlinear measurements using imaging technique

We report on analytical calculations for a 4f coherent imaging system in presence of a phase object at the entry of the set-up. We give the results of the optimized parameters to be used in this system so as to increase the sensitivity of the measurement of the nonlinear refraction coefficient. Analytical and previously reported simulated image profiles are compared here. Our study also gives the limits of the nonlinear imaging technique with a phase object for relatively high nonlinear phase shifts.     

Single crystal growth,electronic structure and optical properties of Cs2HgBr4

We report on successful synthesis of high-quality single crystal of cesium mercury tetrabromide, Cs₂HgBr₄, by using the vertical Bridgman–Stockbarger method as well as on studies of its electronic structure. For the Cs₂HgBr₄ crystal, we have recorded X-ray photoelectron spectra for both pristine and Ar⁺ ion-bombarded surfaces. Our data indicate that the Cs₂HgBr₄ single crystal surface is rather sensitive with respect to Ar⁺ ion-bombardment. In particular, such a treatment of the Cs₂HgBr₄ single crystal surface alters its elemental stoichiometry. To explore peculiarities of the energy distribution of total and partial densities of states within the valence band and the conduction band of Cs₂HgBr₄, we have made band-structure calculations based on density functional theory (DFT) employing the augmented plane wave+local orbitals (APW+lo) method as incorporated in the WIEN2k package. The APW+lo calculations allow for concluding that the Br 4p states make the major contributions in the upper portion of the valence band, while its lower portion is dominated by contributors of the Hg 5d and Cs 5p states. Further, the main contributors to the bottom of the conduction band of Cs₂HgBr₄ are the unoccupied Br p and Hg s states. In addition, main optical characteristics of Cs₂HgBr₄ such as dispersion of the absorption coefficient, real and imaginary parts of dielectric function, electron energy-loss spectrum, refractive index, extinction coefficient and optical reflectivity have been explored from the first-principles band-structure calculations.     

Laser field effect on the nonlinear optical properties of donor impurities in quantum dots with Gaussian potential

A detailed investigation of optical properties of donor impurities in quantum dots under the influence of laser field with Gaussian potential is performed by using the matrix diagonalization method within the effective mass approximation. Based on the computed energies and wave functions, the dependence of the nonlinear optical properties on the dot size and the potential depth is investigated. The outcome of the calculation suggests that all the factors mentioned above can influence the nonlinear optical properties strongly. We also note that the increase of the laser-dressing parameter leads to important effects on the electronic and optical properties of a quantum dot. This gives a new degree of freedom in various device applications based on the intersubband transition of electrons.     

Impurity and exciton effects on the nonlinear optical properties of a disc-like quantum dot under a magnetic field

A detailed investigation of the nonlinear optical properties of the (D⁺, X) complex in a disc-like quantum dot (QD) with the parabolic confinement, under applied magnetic field, has been carried by using the perturbation method and the compact density-matrix approach. The linear and nonlinear optical absorption coefficients between the ground (L = 0) and the first excited state (L = 1) have been examined based on the computed energies and wave functions. The competition between the confinement and correlation effects on the one hand, and the magnetic field effects on the other hand, is also discussed. The results show that the confinement strength of QDs and the intensity of the illumination have drastic effects on the nonlinear optical properties. In addition, we note that the absorption coefficients of an exciton in QDs depend strongly on the impurity but weakly on the magnetic field. Furthermore, the light and heavy hole excitons should be taken into account when we study the optical properties of an exciton in a disc-like QD.     

Fundamentals of nonlinear optical materials

In this article, we briefly review the fundamental aspects of nonlinear optical materials and their role in modern communication.     

Modulation of spatial spectrum in tunable two crystal optical parametric generator

We report on theoretical and experimental investigations of two crystal traveling-wave optical parametric generator (OPG). It is shown that the efficiency and angular structure of traveling-wave tunable OPG output depends on the distance between the two crystals. Air dispersion driven efficiency modulation at different OPG output wavelengths is observed experimentally and confirmed by theoretical calculations.     

Studies on the electrical, linear and nonlinear optical properties of Manganese mercury thiocyanate bis-dimethyl sulfoxide, an efficient NLO crystal

Manganese mercury thiocyanate bis-dimethyl sulfoxide (MMTD), a novel organo-metallic nonlinear optical (NLO) crystal, was grown by a slow evaporation technique over a period of 30 days. The grown crystal was subjected to single crystal X-ray diffraction to determine the unit cell parameters. The optical properties of MMTD were investigated by UV-Vis-NIR, FTIR and FT-Raman spectroscopic techniques. The second harmonic generation (SHG) efficiency of the sample was measured using a Q-switched, mode-locked Nd:YAG laser and the results were compared with urea and manganese mercury thiocyanate (MMTC). The thermal parameters, such as the thermal diffusivity (α), thermal effusivity (e), thermal conductivity (k) and heat capacity (c_p) of MMTD were measured by the photopyroelectric (PPE) technique and the results are discussed. The dielectric response and mechanical properties of MMTD have also been investigated and reported.     

The nonlinear optical response of new organometallic compounds under picosecond excitation

The nonlinear optical response of three new organometallic compounds was studied by z-scan method under picosecond excitation at 1064 and 532 nm. The compounds showed self-focus effect at both wavelengths, and effective reverse saturation absorption at 532 nm and strong two-photon absorption at 1064 nm occurred. Through calculating and comparing the nonlinear optical indexes of the compounds, we found that the third-order nonlinear susceptibility was enhanced by two-fold for one photon transition resonant effect, and incorporating different heavy metal atoms in the delocalized organic system slightly influenced the nonlinear optical indexes.     

Sum-frequency mixing of optical vortices in nonlinear crystals

Results of theoretical and experimental investigation of the influence of walk-off on sum-frequency mixing of optical vortices in nonlinear crystals are presented. Various phenomena of vortex interaction such as decay of higher order vortices into singly charged vortices, formation of aligned arrays of vortices perpendicular to walk-off direction, particle-like pulling and pushing of vortices, and appearance of pairs of vortices having opposite charges were observed.