Order Nonlinear Optical Coefficients Research Articles

The linear and nonlinear optical properties of a hydrogenic donor impurity in a nanowire superlattice: Effects of laser radiation and hydrostatic pressure

The effects of laser radiation and hydrostatic pressure on the linear and nonlinear optical properties of an impure GaAs/Ga1−xAlxAs nanowire superlattice (NWSL) are analyzed using the finite difference method and compact density-matrix approach. In this regards the transition between ground and first excited states is considered to obtain linear, third order nonlinear and total optical absorption coefficients (ACs) and refractive index (RI) changes. Our calculations show that presence of laser radiation causes an increment in ACs and RI changes and shifts optical spectrum towards lower energies. Additionally, applying pressure leads to a decrement in ACs and RI changes with a small blue shift in the spectrum. Moreover, the nonlinear terms of ACs and RI changes are very sensitive to laser radiation and pressure, and saturation in optical spectrum can be adjusted by magnitudes of laser radiation and pressure.

Anisotropy effect on the linear and nonlinear optical properties of a lased dressed donor impurity in a GaAs/GaAlAs nanowire superlattice

We have developed a finite difference method as well as have used compact density-matrix approach to analyze the effect of laser radiation and geometrical anisotropy on the optical properties of a GaAs/Ga1−xAlxAs nanowire superlattice (NWSL). In this regards the transition between ground and first excited states is considered to obtain the linear, third order nonlinear and total optical absorption coefficients (ACs) and refractive index (RI) changes. Our calculation shows that (I) presence of laser radiation causes an increment in ACs and RI changes and shifts optical spectrum toward lower energies. (II) For small values of volume of QDs the magnitude of optical ACs and RI changes is increased (decreased) by an oblate (a prolate) deviation from spherical QDs whereas for large QDs’ volumes an opposite behavior is observed. (III) The nonlinear terms of ACs and RI changes are very sensitive to laser radiation. Additionally, the saturation in optical spectrum can be adjusted by magnitude of laser radiation and shape of QDs involved in the NWSL.

Anisotropy effect on the nonlinear optical properties of a three-dimensional quantum dot confined at the center of a cylindrical nano-wire

The effect of geometrical anisotropy is numerically investigated on the linear and nonlinear optical properties of a GaAs quantum dot which is located at the center of a Ga1-xAlxAs cylindrical nano-wire. The finite difference approximation has been used for obtaining energy eigenvalues and corresponding wave functions. Also, the compact density matrix formalism is applied to investigate linear, third order nonlinear and total optical absorption coefficients (ACs) and refractive index (RI) changes. The optical properties and oscillator strength are calculated as a function of the incident photon energy for different ellipsoid aspect ratio, dot radius and incident optical intensity for 1–2, 2–3 and 1–3 transitions. The results clearly reveal that the dot anisotropy plays an important role in determining the magnitude of nonlinear AC and RI changes which enable us to adjust saturation condition. We found that the dot anisotropy shifts absorption spectrum towards both lower and higher energies which depend on the shape of dot (spherical, prolate or oblate quantum dot), dot radius and states between which transitions will occur. Additionally, it is shown that the presence of nano-wire (second confinement) causes (I) a large increment in RI changes (II) a decrement in total AC for prolate QDs with respect to the dot radius (III) an increment in third order AC with respect to the ellipsoid aspect ratio and (IV) a blue shift in optical spectrum.

Optical non-linearity in nano- and micro-crystallized glasses

Nonlinear optics is given increasing interest due to its wide applications in the area of laser technology, information processing and data storage technology. This paper mainly reviews our researches on the enhanced optical nonlinearity in nano- and micro-crystallized glasses. Utilizing the surface plasmon resonance of noble metal nanoparticles, we realized the enhancement of third order optical nonlinear coefficient through the controlled deposition of oriented Ag nanorods within the oxide glasses or through Ag ion implantation into the chalcohalide glasses. Furthermore, mainly based on the large interface effect, we further realized the enhancement of second order nonlinear optical coefficient through the incorporation of nano-sized Sb2S3, or CdS semiconductor crystals into silica and silicate glasses. Finally, stable second harmonic generation can be obtained together with the little changed transparency utilizing the controllable nucleation and crystal growth of CdGa2S4, AgGeGaS4 and other infrared double-frequency crystals in chalcogenide glasses.

Polaron Effect of a Two Electron Parabolic Quantum Dot

Polaron induced double electron in a quantum dot is investigated using the exact diagonalization techniques and the compact density-matrix approach. The dependence of nonlinear optical processes on the incident photon energies and the polaronic effect are brought out. The linear, third order non-linear optical absorption coefficients and the refractive index changes of singlet and triplet states as a function of photon energy are obtained with and without the inclusion of polaronic effect. It is found that the geometrical confinement and the effect of polaron have great influence on the optical properties of dots.

Linear and nonlinear optical absorption coefficients and refractive index changes of a spherical quantum dot placed at the center of a cylindrical nano-wire: Effects of hydrostatic pressure and temperature

The combined effects of hydrostatic pressure and temperature on the optical absorption coefficients and refractive index changes of an InAs spherical quantum dot which is located at the center of a GaAs cylindrical nano-wire have been investigated. The wave functions and corresponding eigenvalues are calculated using finite element method in the framework of effective mass approximation. Analytical expressions for the linear and third order nonlinear optical absorption coefficients and refractive index changes are obtained by means of the compact-density matrix formalism. The linear and third order nonlinear absorption coefficient and refractive index changes are presented as a function of the photon energy, dot radius, pressure, temperature, incident photon intensity and relaxation time. It is found from our calculations that the linear and third order nonlinear optical absorption coefficients, refractive index changes and resonance energy are quite sensitive to the dot size, applied hydrostatic pressure and temperature.

Ultrafast third order nonlinear optical properties of water soluble zinc-octacarboxy-phthalocyanine

Synthesis and measurements of third order nonlinear optical (NLO) coefficients of water soluble zinc octacarboxy phthalocyanine (ZnOCPc) are reported here using different laser pulse durations. Nonlinear absorption and refraction behaviour in the nanosecond (ns), picosecond (ps) and femtosecond (fs) time domains were studied in detail. Three-photon absorption was the prevalent mechanism with femtosecond laser excitation whereas strong reverse saturable absorption due to dominant two-photon absorption (TPA) was observed with picosecond and nanosecond excitations. We have evaluated the sign and magnitude of the third order nonlinearity in fs, ps, and ns regimes. We observed large off-resonant second order hyperpolarizability (γ) with ultrafast nonlinear optical response in the femtosecond domain using degenerate four wave mixing (DFWM) technique. We also report the optical limiting characteristics and figure of merit (FOM) of ZnOCPc for optical switching.

Dielectric confinement on exciton binding energy and nonlinear optical properties in a strained Zn1−xinMgxinSe/Zn1−xoutMgxoutSe quantum well

The band offsets for a Zn1−xinMgxinSe/Zn1−xoutMgxoutSe quantum well heterostructure are determined using the model solid theory. The heavy hole exciton binding energies are investigated with various Mg alloy contents. The effect of mismatch between the dielectric constants between the well and the barrier is taken into account. The dependence of the excitonic transition energies on the geometrical confinement and the Mg alloy is discussed. Non-linear optical properties are determined using the compact density matrix approach. The linear, third order non-linear optical absorption coefficient values and the refractive index changes of the exciton are calculated for different concentrations of magnesium. The results show that the occurred blue shifts of the resonant peak due to the Mg incorporation give the information about the variation of two energy levels in the quantum well width.

Size dependent effective band gap, optical absorption coefficients and refractive index changes in a wide ZnS/Zn1−xMgxS strained quantum well

Exciton binding energy of a confined heavy hole exciton is investigated in a Zn1−xMgxS/ZnS/Zn1−xMgxS single strained quantum well with the inclusion of size dependent dielectric function for various Mg content. The effects of interaction between the exciton and the longitudinal optical phonon are brought out. The effect of exciton is described by the effective potential between the electron and hole. The interband emission energy as a function of well width is calculated for various Mg concentration with and without the inclusion of dielectric confinement. Non-linear optical properties are carried out using the compact density matrix approach. The dependence of nonlinear optical processes on the well width is investigated for different Mg concentration. The linear, third order non-linear optical absorption coefficients values and the refractive index changes of the exciton are calculated for different concentration of magnesium content. The results show that the exciton binding energy is found to exceed LO phonon energy of ZnS for x>0.2 and the incorporation of magnesium ions and the effect of phonon have great influence on the optical properties of ZnS/Zn1−xMgxS quantum wells.

Numerical simulation of electronic structure, linear and third order nonlinear optical absorption coefficients in the polymeric nanoheterostructure using imaginary time propagation method

In the effective mass approximation, the charge density, the potential profile, the wavefunctions, and the corresponding energy states for zinc sulfide spherical quantum dot have been self-consistently solved, which is embedded in the polymeric media (PVP) by the imaginary time propagation method. Moreover, for the first time, the oscillator strength, linear, third order nonlinear, and total optical absorption coefficients for the transition between intersubbands 1s-1p, 1p-1d, 1d-1f, 1f-1g, 1g-1h, and 1h-1i are investigated with respect to photon energy and the saturation strength has been calculated for every transition too. Calculated result shows that the oscillator strength and the magnitude of optical absorption coefficients are enhanced for transition between intersubbands with higher energies. Also, calculations show that the total absorption coefficient depends on the strength of incident optical intensity and relaxation time.

Electric field induced exciton binding energy and its non-linear optical properties in a narrow InSb/InGaxSb1−x quantum dot

The effect of electric field on the binding energy, interband emission energy and the non-linear optical properties of exciton as a function of dot radius in an InSb/InGaxSb1−x quantum dot are investigated. Numerical calculations are carried out using single band effective mass approximation variationally to compute the exciton binding energy and optical properties are obtained using the compact density matrix approach. The dependence of the nonlinear optical processes on the dot sizes is investigated for various electric field strength. The linear, third order non-linear optical absorption coefficients, susceptibility values and the refractive index changes of electric field induced exciton as a function of photon energy are obtained. It is found that electric field and the geometrical confinement have great influence on the optical properties of dots.

Second order nonlinear properties of monoclinic single crystal BaTeMo2O9

The second order nonlinear optical properties of BaTeMo2O9 were studied by means of Maker fringe technology and the phase matching method. The value and relative sign of the second order nonlinear optical coefficients were obtained, with the largest being d31 = 9.88 pm/V. At 1064 nm, the crystal can support noncritical phase-matching, and the effective nonlinear coefficient is 10.3 pm/V for phase matching II at (90°, 62.8°) in the x0y plane. The relation between the second order nonlinear properties and the crystal structure is also discussed. All the results show that BaTeMo2O9 is a good candidate for nonlinear optical applications.

Electronic states and the resonant optical non-linearity of exciton in a narrow band InSb quantum dot

Binding energy, interband emission energy and the non-linear optical properties of exciton in an InSb/InGa x Sb 1− x quantum dot are computed as functions of dot radius and the Ga content. Optical properties are obtained using the compact density matrix approach. The dependence of non-linear optical processes on the dot sizes is investigated for different Ga concentrations. The linear, third order non-linear optical absorption coefficients, susceptibility values and the refractive index changes of the exciton are calculated for different concentrations of gallium content. It is found that gallium concentration has great influence on the optical properties of InSb/InGa x Sb 1− x dots.

Accurate determination of second order nonlinear optical coefficients from powder crystal monolayers

An accurate procedure for the determination of second harmonic generation (SHG) efficiency from powder crystal monolayers is proposed. The method is based on the analysis of the dependence of the SHG output on the powder particle size. Unlike with conventional powder methods, the amount of material required is very small, and the scattering of the primary beam by the powder particles is negligible, allowing for an accurate analysis of the collected data. The experimental results demonstrate that the proposed method can provide reliable values for the nonlinear optical coefficients, particularly in the case of phase-matchable uniaxial materials, for which simple analytical expressions can be derived.

Design, synthesis, growth and characterization of 4-methoxy-4′-dimethylamino-benzylidene aniline (MDMABA): A novel third order nonlinear optical material

Synthesis, growth, X-ray crystal structure and characterization of a novel third order nonlinear optical material, 4-methoxy-4′-dimethylamino-benzylidene aniline (MDMABA), are reported for the first time. The asymmetric unit of MDMABA compound contains two crystallographically independent molecules (A and B), and they exist in the E-configuration. The structural perfection of the grown crystal is analyzed by high-resolution X-ray diffraction rocking curve analysis. The functional groups present in MDMABA are investigated by FTIR and FT-Raman spectral analyses. The placement of the protons is determined using HNMR spectrum. The range and percentage of optical transmission were ascertained by recording UV–vis–NIR spectrum. Thermal and mechanical properties are reported. Dielectric study shows that the dielectric constant of the crystal varies with frequency and temperature. The third order nonlinear optical absorption coefficient of the MDMABA crystal is determined by the Z-scan technique.

Second harmonic generation in SiO 2 sol–gel films functionalized with Ethyl-[4-(4-nitro-phenylazo)-phenyl]-(2-oxiranylmethoxy-ethyl)-amine (ENPMA) molecules

High concentrations of Ethyl-[4-(4-nitro-phenylazo)-phenyl]-(2-oxiranylmethoxy-ethyl)-amine (ENPMA) chromophores were linked covalently to two different kinds of SiO 2 matrices prepared by the sol–gel method. The matrices differed in their reticulation level, determined by the organometallic precursor used during the synthesis. The materials were deposited as films by spin-coating. The chromophores in the films were oriented in a non-centrosymmetric way by a modified Corona poling set-up, and the nonresonant second order non-linear optical coefficient d 33(0) of the films was determined by means of the Maker fringe technique. It was found that there is an optimum concentration of chromophores for attaining the highest d 33(0) value in these materials. Their maximum d 33(0) value was found in the films with the least reticulated matrix, that value was equal to 5.2 ± 0.5 pm/V. Besides, the d 33(0) value was more stable in time in the less reticulated materials.

Nonlinear optical properties of a two-dimensional elliptic quantum dot

The linear and third order nonlinear optical absorption coefficient and refractive index changes of an elliptic quantum dot have been investigated, using the compact-density matrix formalism and an iterative method. In this regard, the effect of optical intensity, size and geometry of the dot on the optical absorption coefficient and refractive index changes are investigated. It is found that, not only the light intensity but also the size and the geometry of the dot have a great influence on the optical absorption coefficient and refractive index changes of the system.

DFT/FF study on electronic structure and second-order NLO property of dinuclear gold complex [Au(SeC 2B 10H 11)(PPh 3)] 2

There is a growing interest in the structures and properties of gold complexes because of their especial chemical bonds. The crystal structure of [Au(SeC 2B 10H 11)(PPh 3)] 2 has been determined by X-ray diffraction studies recently. The Au(I)...Au(I) interaction, electronic structures of ligands and nonlinear optical(NLO) properties of systems were discussed by means of DFT and finite field methods in this paper. The calculation results indicate that the second order NLO coefficient of [Au(SeC 2B 10H 11)(PPh 3)] 2 is as high as 10 −29 esu, which is superior to common organic conjugated systems.

Nonlinear optical coefficients and phase-matching conditions in Sn<sub>2</sub>P<sub>2</sub>S<sub>6</sub>

Phase matching conditions and second and third order nonlinear optical coefficients of Sn2P2S6 crystals are reported. The coefficients for second harmonic generation (SHG) are given at lambda = 1542 nm and 1907 nm at room temperature. The largest coefficients at these wavelengths are d111 = 17+/-1.5pm/V and d111 = 12+/-1.5pm/V, respectively. The third-order subsceptibilities chi(3) 1111 = (17 +/- 6) . 10-20m2/V2 and chi(3) 2222 = (9 +/- 3) . 10-20m2/V2 were determined at lambda = 1907 nm. All measurements were performed by the Maker-Fringe technique. Based on the recently determined refractive indices, we analyze the phase-matching conditions for second harmonic generation, sum- and difference-frequency generation and parametric oscillation at room temperature. Phase-matching curves as a function of wavelength and propagation direction are given. Experimental phase-matched type I SHG at 1907 nm has been demonstrated. The results agree very well with the calculations. It is shown that phase-matched optical parametrical oscillation is possible in the whole transparency range up to 8 microm with an effective nonlinear coefficient deff approximately 4pm/V.

Effects of Li + and Nb 5+ cationic sites on macroscopic properties of lithium niobate crystals

A comprehensive study on the role of Li + and Nb 5+ sites in a lithium niobate (LiNbO 3) crystallographic frame using Pauling's rules, Abrahams' empirical model, the bond valence sum model and chemical bond method, is briefly summarized in the present paper. Some physical properties of LiNbO 3 crystals such as calculated dielectric responses (including refractive indices and second order nonlinear optical coefficients), experimental ferroelectric Curie temperature T c, and calculated spontaneous polarization P s, are discussed in this connection. Our results clearly show that Li + site can produce much stronger effects on these physical properties than Nb 5+ site, which is helpful to the further development of various properties of LiNbO 3 crystals.