Third-order optical nonlinearities of an organometallic complex: Bis(tetra-n-propylammonium)bis(2-thioxo-1,3-dithiole-4,5-dithiolato)cuprate(II) doped in solid PMMA films

An organometallic complex, bis(tetra-n-propylammonium)bis(2-thioxo-1,3-dithiole-4,5-dithiolato)cuprate(II), [(C₃H₇)₄N]₂[Cu(dmit)₂] (dmit^2?=4,5-dithiolate-1,3-dithiole-2-thione), abbreviated as PrCu, was synthesized. The films of PrCu were prepared using spin coating method. The third-order nonlinear optical properties of PrCu in acetone solution and PMMA films were investigated by Z-scan technique at 1064 nm with laser duration of 20 ps. The Z-scan spectra reveal that the composite films exhibit large negative nonlinear refractive indices of the order of 10^?15 m²/W, which are three orders larger than that in acetone solution. The nonlinear absorption coefficients were calculated to be 9.416×10^?10 m/W. For the composite films, the figure of merit, W and T, meet the requirement of all-optical switching devices. The experimental results show that the PrCu-doped PMMA films have potential applications for nonlinear optical devices.     

The study on the nonlinear optical response of Sudan I

The nonlinear optical properties of Sudan I were investigated by a single beam Z-scan technique. The Sudan I ethanol solution exhibited large nonlinear refractive indices under both CW and pulse laser excitations. The nonlinear refractive indices of Sudan I were in the order of ?10^?8 cm²/W under CW 633 nm excitation and ?10^?6 cm²/W under CW 488 nm excitation, respectively. Under the excitation of a pulse 532 nm laser, the nonlinear refractive index n₂ was calculated to be 1.19 × 10^?14 cm²/W. It was discussed that the mechanism accounting for the process of nonlinear refraction was attributed to the laser heating for the CW laser excitation and the electronic effect for the pulse excitation. Moreover, the second hyperpolarizability of Sudan I was also estimated in this paper.     

Investigation of third-order nonlinear optical properties of NNDC-doped PMMA thin films by Z-scan technique

A novel chalcone derivative, (2E)-1-(2,4-di- chloro-5-fluorophenyl)-3-[4-dimethylamino)phenyl]prop-2-en-1-one, abbreviated as NNDC, was prepared and characterized by elemental analyses, infrared (IR) and proton nuclear magnetic resonance (¹H NMR) spectrum, and thermal analyses. The NNDC-doped poly(methyl methacrylate) (PMMA) thin films with five different doping concentrations by weight were prepared by using a spin-coating method. Their linear optical properties were investigated by using a prism coupling measuring system. The third-order nonlinear optical properties of NNDC in 1,2-dichloroethane (NNDC/1,2-dichloroethane) solution and NNDC-doped PMMA (NNDC/PMMA) films were investigated by using the laser Z-scan technique with 20 ps pulses at 532 nm. A self-focusing effect was observed from the Z-scan curves for solution and thin films and the nonlinear refractive index of the film increases with the increase of the doping concentration. In addition, nonlinear absorption was negligible for all samples. The magnitude of third-order nonlinear refraction index n ₂ and the third-order nonlinear susceptibility χ ⁽³⁾ for thin films were 10⁻¹⁵ m²/W and 10⁻⁹ esu, respectively, which are about three orders larger than that of NNDC/1,2-dichloroethane solution. Some necessary analyses were presented. The results show that this material is a promising candidate for application in the nonlinear optical devices at 532 nm.     

Nonlinear optical study of palladium Schiff base complex using femtosecond differential optical Kerr gate and Z-scan techniques

A femtosecond differential optical Kerr gate (DOKG) and Z-scan techniques, have been applied to investigate the third-order optical nonlinearity of composite film of the coordination complex [PdLPPh₃] (L=N-(2-pyridyl)-N′-(salicylidene)hydrazine, PPh₃=triphenylphosphine). Film exhibits superior nonlinear optical properties in the near-infrared spectral region. The nonlinear response time and third-order nonlinear optical susceptibility of complex were found to be≤90 fs and 3.9×10^?10 esu, respectively. The Z-scan result shows that saturable absorption property of the film and its nonlinear absorption coefficient of the sample was found to be ?23 cm/GW.     

Atomic force microscopy enabled roughness analysis of nanostructured poly (diaminonaphthalene) doped poly (vinyl alcohol) conducting polymer thin films

The Atomic Force Microscopy (AFM) helps in evaluating parameters like amplitude or height parameters, functional or statistical parameters and spatial parameters which describe the surface topography or the roughness. In this paper, we have evaluated the roughness parameters for the native poly (vinyl alcohol) (PVA), monomer diaminonaphthalene (DAN) doped PVA, and poly (diaminonaphthalene) (PDAN) doped PVA films prepared in different solvents. In addition, distribution of heights, skewness and Kurtosis moments which describe surface asymmetry and flatness properties of a film were also determined. At the same time line profiles, 3D and 2D images of the surface structures at different scanning areas i.e. 5 × 5 μm² and 10 × 10 μm² were also investigated. From the roughness analysis and the surface skewness and coefficient of Kurtosis parameters, it was concluded that for PVA film the surface contains more peaks than valleys and the PDAN doped PVA film has more valleys than peaks. It was also found that the PDAN doped PVA film with acetonitrile solvent was used for substrate in electronics applications because the film gives less fractal morphology. Thus, the AFM analysis with different parameters suggested that the PDAN doped PVA films are smooth at the sub-nanometer scale.     

Third-order nonlinear optical response of newly synthesized accepter/donor substituted propylidene aryloxy acet hydrazide

A class of organic compounds namely propylidene aryloxy acet hydrazide derivatives were synthesized. The third-order nonlinear optical properties and optical limiting studies of the compounds were investigated using the single beam Z-scan technique at 532 nm. The Z-scan study reveals that the compounds exhibit a self-defocusing effect at 532 nm. The calculated values of nonlinear refractive index, third-order nonlinear optical susceptibility and second order molecular hyperpolarizability are of the order of 10^?11 esu, 10^?13 esu and 10^?31 esu, respectively. The compounds exhibit good optical limiting properties at the wavelength used.     

Effect of Ag addition on the third-order nonlinearity and physicochemical property of chalcohalide glass

In this work, the 70GeS₂–20In₂S₃–10CsI glass introduced with 0–10 mol% Ag₂S were prepared by the vacuumed melt-quenching technique. The physicochemical properties, such as glass transition temperature, density, refractive index, transmittance, hardness as well as third-order nonlinearity are investigated with the increasing Ag₂S contents. It was found that the refractive index (@632.8 nm), density, and hardness of glasses increase distinctly from 2.204 to 2.270, from 3.520 to 3.675 g cm⁻³ and from 180.9 to 227.9 kg mm⁻², respectively. Meanwhile, the nonlinear refractive index increases from 3.2 × 10⁻¹⁸ to 4.6 × 10⁻¹⁸ m²/W due to the increased refractive index. Finally, the Raman spectra are performed to structurally illustrate the role of Ag addition on the changes of the physicochemical properties. With the Ag₂S contents increasing, the vibration intensity of the [InS₄] and [InS₃I] tetrahedrons increases and the heavy Ag atoms result in the increased density and refractive index, as well as the nonlinear refractive index. The Ag-containing glass, which exhibited good thermal stability, excellent infrared transparency and ultrafast nonlinear optical properties, can be find applications for the IR window material or ultrafast infrared optics.     

Characterization and nonlinear optical properties of PVP/TiO2 nano-fibers doping with Ag colloid nano-particles

We synthesized PVP/TiO₂ nano-fibers doping with Ag colloid nano-particles by electro-spinning method. These nano-fibers were characterized by UV/visible/NIR spectroscopy, SEM and XRD. The image of SEM showed that the synthesized nano-fibers were monotonous and without knot and had a diameter about 150 nm. We also measured the nonlinear refractive and absorption indexes of the sample in three different intensities using the single beam Z-scan method by a continuous wave (CW) He–Ne laser at 632.8 nm wavelength. The nonlinear refraction indexes of these nano-fibers were measured in order of 10⁻⁷ (cm²/W) with negative sign and the nonlinear absorption coefficient was obtained in order of 10⁻³ (cm/W).     

Non-linear optical properties and all optical switching of Congo red in solution

We present the results from investigations of the nonlinear properties of Congo red solutions using Z-scan technique with a continuous wave argon ion laser at 514 nm. The magnitude and sign of the third-order nonlinear refractive index n₂ of aqueous solution of Congo red were determined. The nonlinear refractive index was found to vary with concentration. Third-order nonlinearity is dominated by nonlinear refractive index, which leads to strong self-defocusing and self diffraction in the samples studied. A pump and probe technique was used to investigate the origin of nonlinearity. Furthermore the nonlinear refractive index effect was utilized to demonstrate all optical switching. The optical limiting behavior based on nonlinear refractive index was investigated.     

Synthesis of oligomeric poly[(1, 2-propanediamine)-alt-(oxalic acid)] and anomalous proton conductivities of the thin films

New proton-conductive polyamide oligomers, oligomeric poly[(1, 2-propanediamine)-alt-(oxalic acid)], were synthesized to investigate the proton transport properties of bulk and thin films. The obtained oligomers were characterized by the X-ray diffraction, FT-IR spectra, ¹H NMR, Matrix Assisted Laser Desorption/Ionization Time of Flight (MALDI-TOF) mass spectrum, and electrical conductivity measurements. The bulk proton conductivity is 3.0 × 10^? 4 S cm^? 1 at the relative humidity (RH) of 80%. The proton conductivity of thin film is relatively higher than that of bulk sample. Thickness dependence of the proton conductivity was observed in these thin films. The maximum proton conductivity of the thin film is 4.0 × 10^? 3 S cm^? 1 at the relative humidity (RH) of 80%, which is higher one order magnitude than that of the bulk sample. The activation energies of bulk and 200 nm thick film are 1.0 and 0.69 eV at the RH of 60%, respectively.     

Quick response PZT/P(VDF-TrFE) composite film pyroelectric infrared sensor with patterned polyimide thermal isolation layer

The fabrication method and the pyroelectric response of a single element infrared sensor based lead zirconate titanate (PZT) particles and polyvinylidene fluoride P(VDF-TrFE) copolymer composite thick film is reported in this paper. A special thermal insulation structure, including polyimide (PI) thermal insulation layer and thermal insulation tanks, was used in this device. The thermal insulation tanks were fabricated by laser micro-etching technique. Voltage responsivity (R_V), noise voltage (V_noise), noise equivalent power (NEP), and detectivity (D^*) of the PZT/P(VDF-TrFE) based infrared sensor are 1.2 × 10³ V/W, 1.25 × 10⁻⁶ V Hz^1/2, 1.1 × 10⁻⁹ W and 1.9 × 10⁸ cm Hz^1/2 W⁻¹ at 137.3 Hz modulation frequency, respectively. The thermal time constant of the infrared sensor τ_T was about 15 ms. The results demonstrate that the composite infrared sensor show a high detectivity at high chopper frequency, which is an essential advantage in infrared detectors and some other devices.     

Nonlinear optical properties of a series of azobenzene liquid-crystalline materials

The nonlinear optical properties of a series of azobenzene liquid-crystalline materials, which have different side-chain lengths in their molecular structure from one to another, were investigated using Z-scan method under picosecond pulse laser at 532 nm, 1064 nm and CW 488 nm excitation. The mechanism accounting for the process of nonlinear refraction was discussed under different laser excitations. The polymer films possess very large nonlinear refraction at all the three different laser excitations. Especially, the nonlinear refractive index becomes larger as the length of side-chain, where azobenzene group is contained, increases under pulse excitation at 1064 nm.     

Structural,optical, thermal and mechanical characterization of an organic nonlinear optical material: 4-methyl-3-nitrobenzoic acid single crystal

Organic single crystals of 4-methyl-3-nitrobenzoic acid (4M3N) have been grown by slow evaporation solution growth technique at room temperature. The single crystal X-ray diffraction study reveals that 4M3N crystallizes in monoclinic system with space group P21/n. The crystalline perfection of the crystal was analyzed by high resolution X-ray diffraction (HRXRD) measurements. The functional groups present in 4M3N have been identified from FT-IR and FT-Raman spectra. The lower cut-off wavelength of 4M3N is found to be 404 nm and the optical band gap is calculated as 2.91 eV. The refractive index shows normal behavior with wavelength. The physio chemical changes, decomposition and stability of the 4M3N compound were established by TG-DTA studies. Vickers microhardness measurement concludes that 4M3N belongs to soft material (n=2.5) category. The LDT value is found to be higher than that of KDP and some of the important organic NLO materials. The third order nonlinear refractive index and nonlinear absorption coefficient of the 4M3N have been measured by Z-scan studies. The imaginary and real parts of the third-order susceptibility values were determined as Im χ³=9.129×10⁻¹¹ esu and Re χ³=1.4034×10⁻⁹ esu respectively. The dislocation density was calculated to be 3.0448×10⁶ cm⁻² which indicates the quality of the crystal.     

Nonlinear refractive index of some anthraquinone dyes in 1294-1b liquid crystal

Third order nonlinear refractive index of three anthraquinone dyes, i.e., Solvent Blue 59, Solvent Blue 35 and Solvent Green 3 doped in 1294-1b nematic liquid crystal (NLC) were studied by the single beam Z-scan technique using a continuous-wave He–Ne laser at 632.8 nm. The negative nonlinear refractive index (n₂) in the order of 10^? 5 cm²/w for all samples was obtained. We believe that, this large nonlinearity is owing to Janossy effect and the difference in the nonlinear refractive index of our dyes can be described by the structures of dyes and the interactions between dyes and 1294-1b molecules. So as to understand the effect of dye structure on nonlinearity enhancement, the dichroic ratio of these dyes in 1294-1b was measured using polarized spectroscopy.     

Preparation and nonlinear characterization of zinc selenide nanoparticles embedded in polymer matrix

Nanocomposites of ZnSe nanoparticles embedded in polyvinyl alcohol (PVA) matrix have been prepared by in-situ synthesis. ZnSe/PVA nanocomposites are characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and UV/Vis spectra. The nanocomposite structure is confirmed by the blue-shift of the absorption edge. The nonlinear refractive index and two-photon absorption (TPA) coefficient are measured by the Z-scan technique using low power CW He–Ne laser light. The results show that the ZnSe nanocomposite films show large optical nonlinearity and the magnitude of the third-order nonlinear susceptibility χ⁽³⁾ is calculated to be 2.62×13^?11 m²/V².     

Measurement of optical and surface properties of PLZT thin films

Lanthanum-modified lead zirconate titanate (Pb_0.93La_0.07(Zr_0.3Ti_0.7)_0.93O₃, PLZT7/30/70) thin films with and without a seeding layer of PbTiO₃ (PT) were successfully deposited on indium-doped tin oxide (ITO) coated glass substrate via spin coating in conjunction with a sol–gel process, and a top transparent conducting thin film of SnO₂ was also prepared in the same way. The thicknesses of PLZT and PT layers are 0.5 μm and 24 nm, respectively. The retardance of PLZT film was measured by a new heterodyne interferometer and enhanced by application of a seeding layer of PT. The Pockels linear electro-optical coefficient of PLZT film with a PT layer was determined to be 3.17 × 10^?9 m/V when the refractive index is considered as 2.505, which is one order larger than 1.4 × 10^?10 m/V for PLZT12/40/60 doped with Dy reported in the literature. The root-mean-square (rms) roughness of PLZT thin film with a PT layer (R_rms = 6.867 nm) was larger than that of PLZT film (R_rms = 0.799 nm). From the comparisons, the average transmittance of PLZT film with a PT seeding layer was 77.01%, which was a little smaller than that of PLZT film (around 80.75%). Experimental results imply that the PT seeding layer plays a key role in the increase of retardance value, leading to a higher Pockels coefficient.     

Ionic conductivity of polymer electrolyte membranes based on polyphosphazene with oligo(propylene oxide) side chains

A polyphosphazene [NP(NHR)₂]_n with oligo[propylene oxide] side chains − R = –[CH(CH₃)–CH₂O]_m–CH₃ (m = 6 – 10) was synthesized by living cationic polymerisation and polymer-analogue substitution of chlorine from the intermediate precursor [NPCl₂]_n using the corresponding primary amine RNH₂. The polymer had an average molecular weight of 3.3 × 10⁵ D. Polymer electrolytes with different concentrations of dissolved lithium triflate (LiCF₃SO₃) were prepared. Mechanically stable polymer electrolyte membranes were formed using UV radiation induced crosslinking of the polymer salt mixture in the presence of benzophenone as photoinitiator. The glass transition temperature of the parent polymer was found to be − 75 °C before cross linking. It increases after crosslinking and with increasing amounts of salt to a maximum of − 55 °C for 20 wt.% LiCF₃SO₃. The ionic conductivity was determined by impedance spectroscopy in the temperature range 0–80 °C. The highest conductivity was found for a salt concentration of 20 wt.% LiCF₃SO₃: 6.5 × 10^− 6 S·cm^− 1 at 20 °C and 2.8 × 10^− 4 S cm^− 1 at 80 °C. The temperature dependence of the conductivities was well described by the MIGRATION concept.     

Conductivity and thermal studies of blend polymer electrolytes based on PVAc–PMMA

The polymer electrolytes comprising blend of poly(vinyl acetate) (PVAc) and poly(methylmethacrylate) (PMMA) as a host polymer and LiClO₄ as a dopant are prepared by solution casting technique. The amorphous nature of the polymer–salt complex has been confirmed by XRD analysis. The DSC thermograms show two T_g's for PVAc–PMMA blend. A decrease in T_g with the LiClO₄ content reveals the increase of segmental motion. Conductance spectra results are found to obey the Jonscher's power law and the maximum dc conductivity value is found to be 1.76 × 10^− 3 S cm^− 1 at 303 K for the blend polymer complex with 20 wt.% LiClO₄, which is suitable for the Li rechargeable batteries. The conductivity–temperature plots are found to follow an Arrhenius nature. The dc conductivity is found to increase with increase of salt concentration in the blend polymer complexes.     

The nonlinear optical property and photoinduced anisotropy of?a?novel azobenzene-containing fluorinated polyimide

A novel azobenzene-containing fluorinated polyimide was synthesized. The nonlinear optical property and photoinduced birefringence of a polyimide thin film were investigated. Large third-order nonlinear refraction (n ₂=−4.49×10⁻¹¹ cm²/W) was observed in the polyimide thin film by carrying out Z-scan measurement. The polyimide thin film exhibited larger nonlinear refraction than that of a mono-azo dye doped PMMA thin film (n ₂=−1.63×10⁻¹² cm²/W). The photoinduced birefringence of the polyimide thin film (▵ n∼10⁻²) under different pump intensities was investigated; it was much larger than that of the mono-azo dye doped PMMA thin film (▵ n∼10⁻³). Moreover, the time constants for birefringence growth and relaxation processes were determined.     

A Boubaker polynomials expansion scheme (BPES)-related protocol for measuring sprayed thin films thermal characteristics

Measurements of In₂S₃ and ZnIn₂S₄ sprayed thin films thermal characteristics have been carried out using the photodetection technique. The thermal conductivity k and diffusivity D were obtained using a new protocol based on photothermal signal parameters analysis. Measured values of k and D were respectively, (15.2 ± 0.85) W m⁻¹K⁻¹ and (69.8 ± 7.1) × 10⁻⁶ m²s⁻¹ for In₂S₃, (7.2 ± 0.7) W m⁻¹K⁻¹ and (32.7 ± 4.3) × 10⁻⁶ m²s⁻¹ for ZnIn₂S₄. These values are extremely important since similar compounds are more and more proposed as Cd-free alternative materials for solar cells buffer layers.