Third-order Nonlinear Refractive Index Research Articles

Application of Tietz potential to study optical properties of spherical quantum dots

In this work, we study the optical properties of spherical quantum dots by using Tietz potential. In this regard, we have applied Nikiforov–Uvarov (NU) technique and numerically solved the Schrodinger equation to obtain energy levels and wave functions. Then, by using the density matrix method, we have derived expressions for the changes in linear and third-order nonlinear absorption coefficients and refractive index. According to the results obtained from this work, it is deduced that: (i) the total refractive index and the absorption coefficients increase and shift towards higher energies as v0 increases; (ii) the total absorption coefficient and refractive index decrease and also shift towards lower energies as r0 increases.

δ-BiB3O6:Pr3+: polymer nanocomposites deposited on substrates with silver nanoparticles for nonlinear optics

Composites containing nanocrystallites of novel rare earth doped borate δ-BiB3O6 and polyvinyl alcohol (PVA) polymer are reported. Experimental studies of the third-order nonlinear refractive index n2, absorption coefficient β and second-order nonlinearity for δ-BiB3O6:Pr3+(7.5 at.%) large-size nanocrystallites embedded into PVA polymer matrices and deposited on gallium-doped zinc oxide substrates modified with silver nanoparticles (Ag-NPs) using Z-scan technique and second harmonic generation (SHG) method were performed. The complex SHG and Z-scan measurements for different sizes of Ag-NPs were done. It was shown that the polymer composite of PVA containing particles of orthorhombic bismuth triborate doped with praseodymium (7.5 at.%) reveals optically nonlinear response. It was shown that the studied composites possess both coherent and non-coherent component of nonlinear optics. The Z-scan measurements were done with use of 5 ns Nd:YAG laser and the second harmonic generation was measured using the 25 ns Nd:YAG laser with frequency repetition about 10 Hz. The measurements showed that both second as well as third-order susceptibilities are sensitive to the sizes of the Ag-NPs. The obtained results confirm a principal role of the Ag-NPs in influencing the output susceptibilities.

Characterization of ultrafast optical nonlinearities of ZnS in the presence of group velocity dispersion

The ultrafast nonlinear optical response of a 3-mm-thick polycrystalline zinc sulfide (ZnS) is investigated using the combination of Z-scan technique and time-resolved pump-probe technology with a phase object. The temporal broadening of femtosecond pulse induced by group velocity dispersion (GVD) is clearly observed in the ZnS crystal. A unified expression of pulse-propagating equations taking account of GVD is proposed, which fits the experiment results well and properly explains the observed pulse broadening. The dispersion coefficient k 2, third-order nonlinear refractive index n 2z and three-photon absorption coefficient α 3 of ZnS are determined quantitatively, which are 5.5 × 10−24 s2/m, (0.76 ± 0.8) × 10−5 cm2/GW and (1.8 ± 0.3) × 10−3 cm3/GW2, respectively. The obtained results imply that GVD has a significant impact on the ultrafast nonlinearities of ZnS.

Nonlinear optical properties of CdTe nanocrystals synthesized by a green room temperature solution method

The CdTe nanocrystals were successfully synthesized using a facile room temperature method with non-toxic and environmentally friendly capping agent. The obtained CdTe nanocrystals were characterized by UV–Vis absorption spectroscopy, transmission electron microscopy, and z-scan technique. A photoluminescence peak with full width at half maximum of around 15 nm could be obtained, which indicates a homogeneous and narrow size distribution for the CdTe nanocrystals. The magnitude and sign of the third-order nonlinear refractive index (n 2) and nonlinear absorption coefficient (β) of the CdTe nanocrystals were determined by using of the closed- and open-aperture z-scan at different intensities, respectively. The negative sign of n 2 indicated that there is a self-defocusing effect in the sample. The nonlinear refractive index, n 2, and the nonlinear absorption coefficient, β, were in order of 10−7 cm2W−1 and 10−2–10−3 cmW−1, respectively.

The linear and nonlinear optical properties of a bulged GaAs nanowire

It is well-known that the optical properties of semiconductor nanostructures are so sensitive to alteration of confinement while the nanostructure’s morphology often determines the confinement. Accordingly existence of a bulge on the wire surface will affect the specifications of the nanowire. However, bulge existence effects are significant for ultrafine nanowires and negligible for wires with large radius. In the present work we consider a GaAs ultrafine nanowire with a bulge on the middle of wire axis. The linear, third-order nonlinear and total absorption coefficient and refractive index changes variations are investigated as functions of bulge and nanowire radius. Also the effects of bulge and wire radius on saturation are studied. It has been found that increment in wire (bulge) radius leads to a red shift (blue shift) in absorption coefficient and refractive index changes curves. Additionally, alteration of wire and bulge radii, changes the corresponding incident photon intensity that saturation occurs at it.

Threshold pump intensity effect on the refractive index changes in InGaN SQD: Internal constitution and size effects

In the present paper, internal composition and size-dependent threshold pump intensity effects on on-center impurity-related linear, third-order nonlinear and total refractive index changes are investigated in wurtzite (In,Ga)N/GaN unstrained spherical quantum dot. The calculation is performed within the framework of parabolic band and single band effective-mass approximations using a combination of Quantum Genetic Algorithm (QGA) and Hartree–Fock–Roothaan (HFR) method. According to the results obtained, (i) a significant red-shift (blue shift) is obtained as the dot size (potential barrier) increases and (ii) a threshold optical pump intensity depending strongly on the size and the internal composition is obtained which constitutes the limit between two behaviors.

Optical properties of amorphous In-doped GeSe2 films for all-optical applications

In-doped GeSe2 films were prepared by magnetron co-sputtering method. Amorphous behavior of as-deposited films was confirmed by the X-ray diffraction. The linear optical properties of the films have been derived by analyzing transmission spectra. The experimental results show that linear refractive index rises and optical band gap reduces from 2.04eV to 1.66eV with increasing In content. The proper In content of 13.18 at.% is obtained by optimizing the composition of the films. The nonlinear optical properties of the films were studied at 800nm by using femto-second Z-scan measurement. Experimental results show that the third-order nonlinear refractive index and nonlinear susceptibility of In13.18(GeSe2)86.82 film are up to 8.50×10−16m2/W and 1.41×10−9esu, respectively, almost two orders larger than those of the GeSe2 film. These excellent properties indicate that In-doped GeSe2 films are perspective in the aspect of all-optical applications.

Sol-gel Preparation and Optical Properties of TiO2/Organically Modified Silane Hybrid Material Containing DR13

Disperse red 13 (DR13) azoaromatic chromophores were incorporated into sol-gel derived TiO2/organically modified silane matrix to achieve a hybrid material doped with dye molecules. Nonlinear optical properties of the asprepared hybrid material were investigated by an optical Kerr shutter technique with an 800-nm femtosecond laser. It is obtained 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 cm2/W. It is also found that the sample of material with higher DR13 content could be with higher third-order nonlinear susceptibility. The linear refractive index and the thickness of the hybrid films derived by a spin-coating process were also studied by a prism coupling technique. It is found that with an increasing of the baking temperature, both the refractive index and the thickness of the hybrid films decrease. Absorption spectra, microstructural and morphological properties of the hybrid films were also characterized by UV–Vis absorption spectroscopy, thermal gravimetric analysis, Fourier-transform infrared spectroscopy and atomic force microscopy. Results indicate that the as-prepared hybrid material is expected to be potential in ultrafast photonic applications.

Extended π-conjugated ruthenium zinc-porphyrin complexes with enhanced nonlinear-optical properties.

Zinc porphyrin dimers and trimers, in which the porphyrins are connected via a ruthenium metal core, exhibit large third-order nonlinear optical absorption coefficients and refractive indices. These properties are a result of the presence of multiple porphyrins, which lead to an extension of the π-conjugated system and the octupolar effect.

Structure and Third-order Optical Nonlinearity Performance of Ge-Sn-Se Doped TiO$lt;inf$gt;2$lt;/inf$gt; Glass-ceramics at 1550 nm

TiO2 manifested as nucleating agent was introduced in Ge-Sn-Se ternary chalcogenide glass by heat-melt method. Then the samples were heat-treated for different time. The experiment results indicated that heat treatment process can lead to the precipitation of GeSe2 monoclinic crystals and SnSe2 hexagonal crystals in the TiO2 doped Ge-Sn-Se glass with the heat treatment time increasing. The variety of UV cut-off wavelength, optical band gap and Urbach energy revealed that the number of defect units in glass-ceramic samples increased with the increment of heat treatment time. The third-order optical nonlinearity of all samples was measured by Z-scan technology at 1550 nm. The results showed that the formation of nano-crystals in glass-ceramic samples can improve the third-order nonlinear refraction index significantly due to the strong local field effect. The largest value of nonlinear refraction index reached 5.75×10 -16 m 2 /W, and the sample heat-treated for 3 h was considered as a high-quality nonlinear optical mate-

Synthesis, characterization and theoretical investigations of the structure, electronic properties and third-order nonlinearity optics (NLO) of M(DPIP)2

Three complexes of M(DPIP)2 (M=Cu, Co, Zn as 1, 2, 3) were synthesized and characterized by elemental analysis, IR, UV–Vis, thermogravimetry, and X-ray diffraction. Their nonlinear optical properties were measured by the Z-scan technique and yielded a normalized transmittance of about 70% for complex 1 (45μJ pulse), and 93% for complex 3 (68μJ pulse at the focus point). The nonlinear absorption coefficient, β, is 1.4×10−11m/W for 1 and 5.6×10−13m/W for 3, and the third-order nonlinear refraction index, n2, is 1.0×10−18m2/W for 3. Complex 1 shows self-defocusing property, while complex 3 exhibits self-focusing property. The thermogravimetric results show that the frame structure of compounds 1–3 begin to collapse at 400, 250 and 280°C, respectively, which suggests that they elicit excellent thermal stability. This research aims to provide better understanding of these compounds, and offer preliminary explanations for the significant differences between compounds 1–3, in order to potentially help in the designing of future novel materials with NLO properties.

Large femtosecond third-order optical nonlinearity of Bi3.15Nd0.85Ti3O12 ferroelectric thin films

Both the linear and nonlinear optical properties of Bi3.15Nd0.85Ti3O12 (BNT0.85) ferroelectric thin films deposited on quartz substrates were investigated. The fundamental optical constants were determined as a function of light wavelength by optical transmittance measurements. By performing single-beam Z-scan experiments with femtosecond laser pulses at a wavelength of 800 nm, the two-photon absorption (TPA) coefficient β and third-order nonlinear refraction index γ were measured to be 1.15 × 102 cm/GW and −8.15 × 10−3 cm2/GW, respectively. The large TPA is attributed to an indirect transition process via the intermediate energy levels and the large refractive nonlinearity is the result of the electronic polarization and ferroelectric polarization arisen from the femtosecond midinfrared radiation. The results indicate that the BNT0.85 thin film is a promising candidate for applications in nonlinear photonic devices.

The effects of intense laser field and applied electric and magnetic fields on optical properties of an asymmetric quantum well

This paper presents the results of the theoretical study of the effects of non-resonant intense laser field and electric and magnetic fields on the optical properties (the linear and third-order nonlinear refractive index and absorption coefficients) in an asymmetric quantum well. The electric field and intense laser field are applied along the growth direction of the asymmetric quantum well and the magnetic field is oriented perpendicularly. To calculate the energy and the wave functions of the electron in the asymmetric quantum well, the effective mass approximation and the method of envelope wave function are used. The asymmetric quantum well is constructed by using different aluminium concentrations in both right and left barriers. The confinement in the quantum well is changed drastically by either the effect of electric and magnetic fields or by the application of intense laser field. The optical properties are calculated using the compact density matrix approach. The results show that the effect of the intense laser field competes with the effects of the electric and magnetic fields. Consequently, peak position shifts to lower photon energies due to the effect of the intense laser field and it shifts to higher photon energies by the effects of electric and magnetic fields. In general, it is found that the concentration of aluminum, electric and magnetic fields and intense laser field are external agents that modify the optical responses in the asymmetric quantum well.

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

In this paper, we have studied optical properties of spherical quantum dots by using Rosen-Morse potential. In this regard, we have first solved the Schrodinger equation and obtained energy levels and wave functions by applying Nikiforov-Uvarov (NU) method. Then, by using density matrix method, we have applied analytical expressions for the linear and third-order nonlinear absorption coefficient and refractive index changes. The results show that the total refractive index changes and the absorption coefficients increase and shift towards higher by enhancing height potential.

Electric field and shape effect on the linear and nonlinear optical properties of ellipsoidal finite-potential quantum dots

In this work, the optical properties of ellipsoidal finite-potential quantum dot with an on-center shallow hydrogenic impurity in the presence of an external electric field have been studied. A variational procedure in the framework of perturbation theory was employed within the effective-mass approximation. Numerical results on typical GaAs/AlxGa1−xAs materials show that, besides incident light intensity, the electric field and dot shape have an important influence on the peak positions and magnitudes of linear and third-order nonlinear absorption coefficients and refractive index changes.

Ultrafast optical Kerr gate of bismuth–plumbum oxide glass for time-gated ballistic imaging

We demonstrated the time-gated ballistic imaging technique using a femtosecond optical Kerr gate (OKG) of bismuth–plumbum oxide glass, the nonlinear optical properties of which were also investigated. The third-order nonlinear refractive-index n2 of the bismuth–plumbum oxide glass was measured to be 2.19 × 10−15 cm2/W, and the nonlinear response time was estimated to be shorter than 180 fs. For the time-gated ballistic imaging, the maximum measurable optical density of turbid media using the OKG of bismuth–plumbum oxide glass was 9.3, while only 7.0 for the OKG of quartz glass. And the intensities of the images for the bismuth–plumbum oxide glass were approximately two orders of magnitude higher than that for the quartz glass. The experimental results indicated that the bismuth–plumbum oxide glass was an excellent optical material for nonlinear optical applications.

Relaxation time and impurity effects on linear and nonlinear refractive index changes in (In,Ga)N–GaN spherical QD

By means of a combination of Quantum Genetic Algorithm and Hartree–Fock–Roothaan method, the changes in linear, third-order nonlinear and total refractive index associated with intra-conduction band transition are investigated with and without shallow-donor impurity in wurtzite (In,Ga)N–GaN spherical quantum dot. For both cases with and without impurity, the calculation is performed within the framework of single band effective-mass and parabolic band approximations. Impurity׳s position and relaxation time effects are investigated. It is found that the modulation of the refractive index changes, suitable for good performance optical modulators and various infra-red optical device applications can be easily obtained by tailoring the relaxation time and the position of the impurity.

Simultaneous Effects of External Electric Field and Conduction Band Nonparabolicity on Optical Properties of a GaAs Quantum Dot Embedded at the Center of a GaAlAs Nano-Wire

An investigation of the optical properties of a GaAs spherical quantum dot which is located at the center of a Ga1−xAlxAs cylindrical nano-wire has been performed in the presence of an external electric held. The band nonparabolicity effect is also considered using the energy dependent effective mass approximation. The energy eigenvalues and corresponding wave functions are calculated by finite difference approximation and the reliability of calculated wave functions is checked by computing orthogonality. Using computed energy eigenvalues and wave functions, the linear, third-order nonlinear and total optical absorption coefficients and refractive index changes are examined in detail. It is found that (i) Presence of electric field causes both blue and red shifts in absorption spectrum; (ii) The absorption coefficients shift toward lower energies by taking into account the conduction band nonparabolicity; (iii) For large values of electric field the effect of conduction band nonparabolicity is less dominant and parabolic band is estimated correctly; (iv) In the presence of electric field and conduction band nonparabolicity the nonlinear term of absorption coefficient rapidly increases by increasing incident optical intensity. In other words, the saturation in optical spectrum occurs at lower incident optical intensities.

High-energy ion treatments of amorphous As40Se60 thin films for optical applications

The treatment of 100MeV Ag swift-heavy ion (SHI) irradiation with five different fluences (3×1010, 1×1011, 3×1011, 1×1012, and 3×1012ions/cm2) was used to design optical and structural properties of amorphous (a-) As40Se60 chalcogenide thin films. Swanepoel method was applied on transmission measurements to determine the changes in optical bandgap, Tauc parameter and linear optical parameters, i.e., linear optical absorption, extinction coefficient and linear refractive index. Dispersion of the material was determined by Wemple–DiDomenico relation. Changes in nonlinear optical parameters of third-order optical susceptibility and nonlinear refractive index were determined using semi-empirical relations. Changes in surface morphology of the films were investigated using SEM observation, which indicated that fluence 3×1012ions/cm2 was upper threshold limit for these films for ion treatment. It is observed that optical bandgap reduces from 1.76eV to 1.64eV, and nonlinear refractive index increases from 1.31×10−10 [esu] to 1.74×10−10 [esu]. Linear refractive index initially increases from 2.80 to 3.52 (for fluence 3×1010ions/cm2) and then keeps decreasing. The observed changes in optical properties upon irradiation were explained in terms of structural rearrangements by Raman measurement. The study was compiled with the previous literature to propose SHI as an effective optical engineering technique to achieve desired changes according to the need of optical/photonic applications.

Nonlinear optical response of semiconductor-nanocrystals-embedded photonic band gap structure

Colloidal CdSe/ZnS core/shell nanocrystals (NCs), which were dispersed in SiO2 sol, were utilized to fabricate a SiO2:NCs/TiO2 all-dielectric photonic band gap (PBG) structure. The third-order nonlinear refractive index (n2) of the PBG structure was nearly triple of that of the SiO2:NCs film due to the local field enhancement in the PBG structure. The photoinduced change in refractive index (Δn) could shift the PBG band edge, so the PBG structure would show significant transmission modification, whose transmission change was ∼17 folds of that of the SiO2:NCs film. Under excitation of a 30 GW/cm2 femtosecond laser beam, a transmission decrease of 80% was realized.