Optoelectronic and nonlinear optical processes in low dimensional semiconductors

Spatial confinement of quantum excitations on their characteristic wavelength scale in low dimensional materials offers unique possibilities to engineer the electronic structure and thereby control their physical properties by way of simple manipulation of geometrical parameters. This has led to an overwhelming interest in quasi-zero dimensional semiconductors or quantum dots as tunable materials for multitude of exciting applications in optoelectronic and nonlinear optical devices and quantum information processing. Large nonlinear optical response and high luminescence quantum yield expected in these systems is a consequence of huge enhancement of transition probabilities ensuing from quantum confinement. High quantum efficiency of photoluminescence, however, is not usually realized in the case of bare semiconductor nanoparticles owing to the presence of surface states. In this talk, I will focus on the role of quantum confinement and surface states in ascertaining nonlinear optical and optoelectronic properties of II–VI semiconductor quantum dots and their nanocomposites. I will also discuss the influence of nonlinear optical processes on their optoelectronic characteristics.     

Second-order nonlinear optical properties of mexylaminotriazine-functionalized glass-forming azobenzene derivatives

The second-order nonlinear optical coefficients of thin films of mexylaminotriazine-functionalized azobenzene molecular glass derivatives were measured using second harmonic generation. The thin films were poled using a custom corona poling set-up and the second harmonic light from a pulsed 1064-nm laser was detected. Four out of the six tested compounds showed optical nonlinearity and a maximum coefficient of 75 pm/V was obtained. The time dependence of the nonlinear coefficients was studied under ambient light and under dark; the second harmonic generation intensity stayed constant for thiazole-containing derivatives while a significant decay was measured for the other compounds.     

Thermally stable chromophores for nonlinear optical applications

Three thermal organic second-order nonlinear optical chromophores were synthesized. The decomposition temperature was determined by DSC, and the absorption spectra was measured. The second-order polarizabilities at zero energy and the dispersion of second-order polarizabilities were measured by solvatochromic method.     

Monodisperse ceria nanospheres: Synthesis,characterization, optical properties,and applications in wastewater treatment

Monodisperse ceria nanospheres have been synthesized by a facile solvothermal method, and their morphology and microstructures have been revealed by a combination of X-ray diffraction (XRD), scanning electron microscopy, high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy and N₂ adsorption. It is demonstrated that the as-synthesized powders are highly uniform CeO₂ in spherical shape with cubic fluorite structure. HRTEM and XRD studies show that each ceria nanosphere is composed of dozens of nanocrystals with the average size of 8.5 nm. The direct optical band gap of the ceria nanospheres estimated from the ultraviolet–visible absorption spectrum is 2.7 eV, which is evidently red-shifted with respect to the bulk material (E_g = 3.19 eV); the reduced band gap could be resulted from the high concentration of grain boundaries and defects present in the ceria nanospheres. In addition, the ceria nanospheres exhibit a strong blue luminescence at 504 nm and a broad orange luminescence centered at 645 nm. As a result of the large specific surface area, ceria nanospheres are revealed to be an excellent sorbent for the removal of poisonous pollutants present in water, such as chromium ions and rhodamine B. The removal efficiency of chromium ions is as high as ∼94%.     

非线性光学材料聚二乙炔及其衍生物的制备及应用

非线性光学材料聚二乙炔及其衍生物的研究已引起国内外的广泛关注。本文总结了近年来聚二乙炔及其衍生物的合成方法 ,综述了聚二乙炔及其生物在非线性光学方面的研究进展 ,并且对聚二乙炔及其衍生物在非线性光学领域的进一步应用提出了展望。     

Large nonlocal nonlinear optical response of castor oil

The nonlocal nonlinearity of castor oil was investigated using the Z-scan technique in the CW regime at 514 nm and in femtosecond regime at 810 nm. Large negative nonlinear refractive indexes of thermal origin, thermo-optical coefficients and degree of nonlocality were obtained for both laser excitation wavelengths. The results indicate that the electronic part of the nonlinear refractive index and nonlinear absorption were negligible. Our results suggest that castor oil is promising candidate as a nonlinear medium for several nonlocal optical applications, such as in spatial soliton propagation, as well as a dispersant agent in the measurement of absorptive properties of nanoparticles.     

Crystal structure and third-order nonlinear optical property study of a copper complex constructed by DMIT ligand

A copper complex constructed by the ligand: 1,3-dithiole-2-thione-4,5-dithiolato (DMIT) has been synthesized and its crystal structure has been determined by means of X-ray single crystal diffraction. The central copper(II) ion coordinates with two DMIT which constructed a square environment. Intermolecular C–H?S hydrogen bonds between cation groups and ligands lead to the formation of a two-dimensional supramolecular network. Its third-order nonlinear optical property has been studied using Z-scan technique at different peak laser irradiance with 20 picosecond (ps) pulses at wavelength 1064 nm. Its molecular second hyperpolarizability γ was determined to be 4.03 × 10⁻⁵⁷ m⁴ C V⁻³.     

非线性光学含氟PI/SiO2杂化波导纳米材料的研究

以含氟的二胺5,5'-(六氟异丙基)-二-(2-氨基苯酚)及二酐4,4'-(六氟异丙基)-苯二酸酐为单体.首先合成了经酰胺化的主链上带有活性羟基的含氟聚酰亚胺,再通过Mitsunobu反应将活性生色分子分散红1共价链接到聚酰亚胺的侧链骨架上,合成了二阶非线性光学(NLO)含氟聚酰亚胺.采用溶胶-凝胶技术,利用偶联剂APTES制备带有发色团的及含有硅氧烷端分子的聚酰胺酸,其中的Si(OR)3基经水解、缩合后,与正硅酸乙酯在催化剂作用下反应,经杂化、凝胶后,得到热稳定性高的杂化材料.将制得的含氟聚酰亚胺/SiO2杂化材料,利用FT-IR、SEM、TEM、XRD、DSC等手段对其进行了表征.杂化材料的玻璃化转变温度(Tg)为382℃,比纯聚酰亚胺的Tg(306℃)高76℃,表现出优良的高温热稳定性.     

Structural and nonlinear optical behavior of Ag-doped ZnO films

We present the structural and nonlinear optical behavior of Ag-doped ZnO (AZO) films prepared by magnetron sputtering. The structural of AZO films are systematically investigated by X-ray diffraction (XRD) and scanning electronic microscopy (SEM), respectively. The results show that AZO films can still retain a wurtzite structure, although the c-axis as preferred orientation is decreased by Ag doping. As the amounts of the Ag dopant were increased, the crystallinity as well as the absorptivity and optical band gap were increased. Moreover, the nonlinear optical characterized of the AZO films was studied using Z-scan technique. These samples show self-defocusing nonlinearity and good nonlinear absorption behavior which increases with increasing Ag volume fraction. AZO is a potential nanocomposite material for the development of nonlinear optical devices with a relatively small limiting threshold.     

Synthesis and nonlinear optical properties of Lead Telluride nanorods

Lead Telluride (PbTe) nanorods have been uniformly grown on silicon substrates, using the thermal evaporation technique under high vacuum conditions. The structural and morphological studies are done using X-ray diffraction and scanning electron microscopy. Optical nonlinearity studies using the open aperture z-scan employing 5 ns and 100 fs laser pulses reveal a three-photon type absorption. For nanosecond excitation the nonlinear absorption coefficients (γ) are in the order of 10⁻²² m³ W⁻² and for femtosecond excitation it is in the order of 10⁻²⁹ m³ W⁻². The role of free carriers and excitons in causing the nonlinearity in both excitation time domains is discussed. Results indicate that PbTe nanorods are good optical limiters with potential device applications.     

The effect of aggregation on the nonlinear optical absorption performance of indium and gallium phthalocyanines in a solution and co-polymer host

The nonlinear optical properties (NLO) of Pcs can be modified by substituting different metal atoms into the ring or altering peripheral and axial functionalities. In this study, nonlinear optical absorption properties of tetra-substituted gallium and indium phthalocyanine complexes both in solution and polymeric film have been investigated by open aperture Z-scan measurements with nanosecond pulses at 532 nm. All investigated compounds exhibited reverse saturable absorption for both solution and film experiments. The investigated compounds in the solution showed better nonlinear optical absorption properties than polymeric films. The observed nonlinear optical absorption differences depending on the aggregation are discussed using the ultrafast dynamics and decay processes of excited states found from femtosecond pump-probe spectroscopy with white light continuum experiments.     

Third order nonlinear optical susceptibility of fluorescein-containing polymers determined by electro-absorption spectroscopy

Novel polymers containing xanthene groups with high dye concentrations were prepared, and their third order nonlinear optical properties were studied by electroabsorption spectroscopy technique. The polymers were amorphous with refractive indices above 1.6 in the non-resonant region. The UV-Visible absorption spectra indicate the fluoresceins molecules in the polymers are H-aggregated. They showed third order nonlinear susceptibility, χ⁽³⁾ (−ω:ω, 0, 0), of 2.5-3.5 × 10⁻¹² esu.     

Preparation and nonlinear optical response of novel palladium-containing micellar nanohybrids

The synthesis and characterization of novel micellar nanohybrids with controllable sizes consisting of palladium nanosized core and covered by well-defined poly(lauryl methacrylate)-block-poly(2-(acetoacetoxy)ethyl methacrylate) (pLauMA-b-pAEMA) diblock copolymers are reported. Their nonlinear optical (NLO) response (i.e. nonlinear refraction and absorption and the third-order susceptibility χ⁽³⁾) is also studied under 35 ps laser excitation both in the visible and in the infrared and found to be insensitive to the size of the micelles while it was found to be greatly affected by the molar fraction of the AEMA block. To the best of our knowledge it is the first time that such Pd micellar nanohybrids are synthesized and investigated towards their NLO properties. The magnitude of the nonlinear optical response of these nanohybrids renders them promising candidates for potential optoelectronic applications.     

Support Vector Regression control charts for multivariate nonlinear autocorrelated processes

Statistical process control charts are one of the most widely used techniques in industry and laboratories that allow monitoring of systems against faults. To control multivariate processes, most classical charts need to model process structure and assume that variables are linearly and independently distributed. This study proposes to use a nonparametric method named Support Vector Regression to construct several control charts that allow monitoring of multivariate nonlinear autocorrelated processes. Also although most statistical quality control techniques focused on detecting mean shifts, this research investigates detection of different parameter shifts. Based on simulation results, the study shows that, with a controlled robustness, the charts are able to detect the different applied disturbances. Moreover in comparison to Artificial Neural Networks control chart, the proposed charts are especially more effective in detecting faults affecting the process variance.     

Studies on lithium l-ascorbate dihydrate: An interesting chiral nonlinear optical crystal

Lithium l-Ascorbate dihydrate (LLA) is a new metal organic nonlinear optical crystal belonging to the saccharide family. Single crystals of LLA were grown from aqueous solution. Solubility of the crystal has a positive temperature coefficient facilitating growth by slow cooling. Rietveld refinement was used to confirm the phase formation. The crystal has prismatic habit with (010), (001) and (10−1) prominent faces. Thermal analysis shows that the crystal is stable up to 102 °C. Transmission spectrum of the crystal extends from 302 nm to 1600 nm. Dielectric spectroscopic analysis revealed Cole–Cole behaviour and prominent piezoelectric resonance peaks were observed in the range of 100–200 kHz. Second harmonic generation (SHG) conversion efficiency of up to 2.56 times that of a phase matched KDP crystal was achieved when the (010) plate of LLA single crystal was rotated about the +ve c axis, by 9.4° in the clockwise direction. We also observed SHG conical sections which were attributed to noncollinear phase matching. The observation of the third conical section suggests very high birefringence and large nonlinear coefficients. A detailed study of surface laser damage showed that the crystal has high multiple damage thresholds of 9.7 GW cm⁻² and 4.2 GW cm⁻² at 1064 nm and 532 nm radiation respectively.     

Influence of defects on the quality and optical studies of sodium p-nitrophenolate dihydrate, a nonlinear optical material

Nonlinear optical material of sodium p-nitrophenolate dihydrate was synthesized by employing the technique of controlled evaporation and the effect of temperature on growth morphology was investigated. Single crystal XRD analysis confirms that the crystals with different morphologies have the same lattice parameters. The high-resolution X-ray diffraction curves recorded by a multicrystal X-ray diffractometer revealed the presence of very low angle tilt boundaries. The green emission band at 524 nm is due to the existence of defects on the crystal which corroborated with HRXRD studies. The wide band gap of the SPND crystals confirms the large transmittance in the visible region.     

Fabrication of photo-cross-linked stable organic-inorganic hybrid second-order nonlinear optical films

A photo-cross-linked stable organic-inorganic hybrid second-order nonlinear optical (NLO) film was fabricated by sol-gel process with silicon sol linking aromatic diazonium group (SOD) and Chromophore molecule 2-({4-[4-(2-carboxy-2-cyano-vinyl)-phenylazo]-phenyl}-methyl-amino)-ethyl acid (DRCB). The films were poled under 50 DC voltage electric field at room temperature at the existence of solvents. After the solvents volatilized completely and upon UV irradiation under the electric field, the ionic bonds converted to stable covalent bonds in the system, the orientations of the chromophores were fixed by the photo-cross-linked structures. The order parameter of the fabricated film can retain 99% after 17 days at room temperature. The stable organic-inorganic hybrid photo-cross-linked NLO films fabricated in this paper had large potential to be applied in electric-optic devices.     

Concentration dependence of the optical limiting and nonlinear light scattering in aqueous suspensions of detonation nanodiamond clusters

Optical limiting (OL) is observed for detonation nanodiamond clusters (ND) suspended in water with mass concentrations of 3–0.01%. By using nanosecond Z-scan measurements at 1064 nm we demonstrate that the nonlinear light scattering strongly contributes to the OL in a wide range of ND concentrations. Moreover we show that the ratio of the nonlinear and linear extinction that can be seen as figure of merit for an optical limiter is a non-monotonous function of the ND concentration. Our analysis reveals that the concentration that corresponds to the optimum OL performance essentially depends on the incident intensity.     

Growth and nonlinear optical properties of Zn-doped LiB3O5 crystals

Zn-doped LiB₃O₅ (LBO) single crystals with high quality were successfully grown from the Li₂O–MoO₃–ZnF₂ ternary system by the top-seeded solution growth method. The suitable region for LBO crystal growth was investigated by growth experiments, as well as viscosity and volatility measurements, which confirmed that the optimal molar ratio of Li₂O:MoO₃:ZnF₂ was 1:1.5:0.2. The second-harmonic generation efficiency of Zn-doped LBO crystal increased by 16% compared with that of the LBO crystals grown from the MoO₃ flux. The optical homogeneity was at 10⁻⁶ cm⁻¹. Optical absorption at the critical wavelengths of 1064 nm was measured to be 15 and 18 ppm cm⁻¹, respectively.     

Magnetic field induced optical gain in a dilute nitride quaternary semiconductor quantum dot

Effects of magnetic field strength on the electronic and optical properties are brought out in a Ga_0.661In_0.339N_0.0554As_0.9446/GaAs quantum dot for the applications of desired wavelength in opto-electronic devices. The band alignment is obtained using band anticrossing model and the model solid theory. The magnetic field dependent electron-heavy hole transition energies with the dot radius in a GaInNAs/GaAs quantum dot are investigated. The magnetic field induced oscillator strength as a function of dot radius is studied. The resonant peak values of optical absorption coefficients and the changes of refractive index with the application of magnetic field strength in a GaInNAs/GaAs quantum dot are obtained. The magnetic field induced threshold current density and the maximum optical gain are found in a GaInNAs/GaAs quantum dot. The results show that the optimum wavelength for fibre optical communication networks can be obtained with the variation of applied magnetic field strength and the outcomes may be useful for the design of efficient lasers based on the group III-N-V semiconductors.