Linear and nonlinear optical properties of plasma-enhanced chemical-vapour deposition grown silicon nanocrystals

We provide a systematic study on the linear and nonlinear optical properties of silicon nanocrystals (Si-nc) grown by plasma-enhanced chemical vapour deposition (PECVD). Linear optical properties, namely absorption, emission and refractive indices are reported. The sign and magnitude of both real and imaginary parts of third-order nonlinear susceptibility X(³) of Si-nc are measured by the Z-scan method. Closed aperture Z-scan reveals a positive nonlinearity for all the samples. From the open aperture measurements, nonlinear absorption coefficients are evaluated and attributed to two-photon absorption. Absolute values of X(³) are in the order of 10^-9 esu and show systematic correlation with the Si-nc size, due to quantum confinement related effects. A correlation has been made between X(³), nanocrystalline size, linear refractive index and optical band gap.     

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.     

Nonlinear optical and optical limiting properties of phthalocyanines in solution and thin films of PMMA at 633 nm studied using a cw laser

We present our results on nonlinear optical (NLO) and optical limiting properties of Tetra tert-butyl phthalocyanine and Zinc tetra tert-butyl phthalocyanine studied at 633 nm using a continuous wave laser. We have evaluated the sign and magnitude of the third-order nonlinearity from the closed aperture Z-scan data while the nonlinear absorption properties were assessed using the open aperture data. We have observed low power optical limiting, with low limiting thresholds, based on nonlinear refraction in both the samples. We also present results on the NLO properties of the same dyes doped in Polymethylmethacrylate (PMMA). These studies indicate that both the phthalocyanines are potential candidates for low power optical limiting applications.     

Nonlinear optical properties of p-(N,N-dimethylamino)dibenzylideneacetone doped polymer

A bis-chalcone derivative, p-(N,N-dimethylamino) dibenzylideneacetone was synthesized. Its third-order nonlinear susceptibility was determined to be as high as 10⁻¹² esu by employing single beam Z-scan and degenerate four wave mixing techniques using Nd:YAG 7 ns laser pulses at 532 nm. The compound was doped in to poly(methylmethacrylate) matrix and the third-order nonlinearity was investigated by using Z-scan technique. The nonlinear refractive index of the doped polymer is found to be negative, and its magnitude is of the order of 10⁻¹⁰ esu. The results show that the compound exhibits strong reverse saturable absorption and a good optical limiting property and hence may be used as a promising dopant material. The study on concentration dependence of nonlinear optical parameters has been presented.     

Solvent effect on the third order optical nonlinearity and optical limiting ability of betanin natural dye extracted from red beet root

We report on the solvent effect on the third order optical nonlinearity of betanin natural dye extracted from red beet root and their third order nonlinear optical (NLO) properties have been studied using a Q-switched Nd:YAG laser at 532 nm. The third order nonlinearity of these samples are dominated by nonlinear absorption, which leads to strong optical limiting and their strength is influenced by the solvent used, suggesting that betanin natural dyes are promising candidate for the development of photonic nonlinear optic devices.     

Synthesis and nonlinear optical properties of Lif films containing gold nanoparticles

We have studied the structure and optical properties of a thin lithium fluoride (LiF) film containing nanosized gold particles, which has been obtained by the thermal evaporation of LiF and Au followed by deposition onto the surface of a glass substrate heated to 590 K. Data of scanning electron microscopy and X-ray diffraction (XRD) showed that the composite film possesses a polycrystalline structure with an average LiF grain size of about 170 nm. The formation of gold nanoparticles in the film was confirmed both by XRD data and the presence of plasmon resonances in the optical absorption spectrum, which is close to the spectra obtained by model calculations for a LiF matrix with 20- to 40-nm-sized gold particles. Using the Z-scan technique, it is shown that the composite film exhibits nonlinear absorption of pulsed laser radiation with a wavelength of 780 nm and pulse duration of 150 fs at a power exceeding 100 mW. The magnitude of this effect is comparable to that observed previously for various single-crystalline matrices containing gold nanoparticles.     

Linear and nonlinear optical properties of RF sputtered (Pb,La)(Zr,Ti)O<Subscript>3</Subscript> ferroelectric thin films

Linear and nonlinear optical properties of (Pb,La)(Zr,Ti)O₃ (PLZT) ferroelectric thin films were presented in this paper. The PLZT ferroelectric thin films have been in situ grown on quartz substrates by radio-frequency (RF) magnetron sputtering at 650 °C. Their crystalline structure and surface morphologies were examined by X-ray diffraction and atomic force microscopy, respectively. It can be found that the PLZT thin films exhibit well-crystallized perovskite structure and good surface morphology. The fundamental optical constants (the band gap energy, linear refractive index, and linear absorption coefficient) were obtained through the optical transmittance measurements. A Z-scan technique was used to investigate the optical nonlinearity of the PLZT thin films on quartz substrates. The films display the strong third-order nonlinear optical effect. A large and negative nonlinear refractive index n ₂ is determined to be 1.21 × 10⁻⁶ esu for the PLZT thin films. All results show that the PLZT ferroelectric thin films have potential applications in optical limiting, switching, and modulated-type optical devices.     

Nonlinear optical properties of mercury dithizonate in a polymer film

Abstract

The absorption spectra of trans and cis isomers of mercury dithizonate in a doped poly(methyl methacrylate) film are measured, and the optical properties of the two isomers are analysed. The properties indicate that different isomers of mercury dithizonate can convert into each other when irradiated by light of appropriate wavelength. With the Z-scan method, the nonlinear optical properties of mercury dithizonate are investigated, and experimental data on the nonlinear refractive index and the change in refractive index are obtained. The changes in refractive index as a function of wavelength are obtained by the Kramers-Kronig transformation.     

Study of nonlinear optical properties of organic dye by Z-scan technique using He–Ne laser

Laser induced nonlinear absorption coefficient of Brilliant Green solution was measured by single beam open aperture Z-scan technique using a continuous wave He–Ne laser at the wavelength of 632.8 nm. It was found that the material exhibits multiphoton absorption type optical nonlinearity. Significant optical nonlinearity is an indicative that Brilliant Green dye is prominent material for low power nonlinear applications. Ultraviolet–visible and photoluminescence (PL) spectra of Brilliant Green solutions are also recorded. A strong linear absorption band with a peak at 625 nm has been observed, while the PL intensity was found to decrease due to quenching effect on increasing the concentration.     

Energy dependent saturable and reverse saturable absorption in cube-like polyaniline/polymethyl methacrylate film

Solid films of cube-like polyaniline synthesized by inverse microemulsion polymerization method have been fabricated in a transparent PMMA host by an in situ free radical polymerization technique, and are characterized by spectroscopic and microscopic techniques. The nonlinear optical properties are studied by open aperture Z-scan technique employing 5 ns (532 nm) and 100 fs (800 nm) laser pulses. At the relatively lower laser pulse energy of 5 μJ, the film shows saturable absorption both in the nanosecond and femtosecond excitation domains. An interesting switchover from saturable absorption to reverse saturable absorption is observed at 532 nm when the energy of the nanosecond laser pulses is increased. The nonlinear absorption coefficient increases with increase in polyaniline concentration, with low optical limiting threshold, as required for a good optical limiter.     

Nonlinear optical properties of thin iron films grown on MgO (100) by pulsed laser deposition

Thin films of iron were fabricated on MgO (100) substrates using pulsed laser deposition technique. The crystalline property and surface roughness of the films were investigated by X-ray diffraction and atomic force microscopy, respectively. It was found that the morphology of the Fe film deposited at room temperature was characteristic of continuous metal film. Increasing the deposition temperature caused the smooth Fe film to break up, and nanoscale Fe islands were formed. We performed the z-scan measurements to study the third-order optical nonlinearity of the continuous approximately 9-nm-thick iron film. The results show that the ultrathin iron film exhibits large nonlinear refractive coefficient, n₂=7.09×10⁻⁵ cm²/kW, and nonlinear absorption coefficient, β=−5.52×10⁻³ (cm/W), at the wavelength of 532 nm.     

Optical properties of Cu and Ag nanoparticles synthesized in glass by ion implantation

Metal nanoparticles synthesized by sequentially ion-implanted Ag and Cu into silica glasses have been studied. The implantation doses (×10¹⁶ ions/cm²) were 5Ag, 5Cu and 5Ag/5Cu, respectively. The optical and microstructural properties of the nanoparticles were characterized by optical absorption spectra and transmission electron microscopy (TEM), respectively. Fast nonlinear optical refraction and nonlinear optical absorption coefficients were measured at 1064 nm of wavelength using Z-scan technique. Results in this paper indicate that the nonlinear refractive index for the Ag/Cu implanted system has a higher value compared to single Ag or Cu implantation nanoparticles.     

Two-photon Absorption and Nonlinear Optical Properties of A New Organic Dye DEASPI

A new organic dye trans-4- [p-(N,N-diethylamino) styryl]-N-methylpyridinium iodide (abbreviated' as DEASPI thereafter) with large two-photon absorption (TPA) cross section and excellent upconverted lasing properties was synthesized. The melting point and decompound point were measured to be 230 degreesC and 264.7 degreesC respectively. The molecular TPA cross section was measured to be sigma (2)=6.9x10(-48) cm(4).s/photon at 1064 nm by using an open aperture Z-scan system. The linear and nonlinear optical properties of this dye were systematically studied. The highest net upconversion efficiency from the absorbed pump energy to the output upconverted lasing energy is as high as 18.6% at the pump energy of 2.17 mJ from a mode-locked Nd:YAG ps laser. The nonlinear transmittance at the wavelengths from 720 to 1100 nm was measured. The dye solution also shows a clear optical power limiting effect.     

Tunable emission and excited state absorption induced optical limiting in Tb2(MoO4)3: Sm3+/Eu3+ nanophosphors

Photoluminescence properties and optical limiting behavior of pure and Sm³⁺/Eu³⁺ doped Tb₂(MoO₄)₃ nanophosphors are investigated. The prepared nanophosphors exhibit excellent emission when excited by UV light. Color-tunable emissions in Tb_2−xSm_x(MoO₄)₃ and Tb_2−xEu_x(MoO₄)₃ are realized by employing different excitation wavelengths or by controlling the doping concentration of Sm³⁺ and Eu³⁺. Luminescence quantum yield and CIE chromatic coordinates of the prepared phosphors were also presented. Optical limiting properties of the samples are investigated by open aperture Z-scan technique using 5 ns laser pulses at 532 nm. Numerical fitting of the measured Z-scan data to the relevant nonlinear transmission equations reveals that the nonlinear absorption is arising from strong excited state absorption, along with weak absorption saturation and it is found that the optical nonlinearity of Tb₂(MoO₄)₃ increases with Sm³⁺/Eu³⁺doping. Parameters such as saturation fluence, excited state absorption cross section and ground state absorption cross section of the samples have been determined numerically, from which the figure of merit for nonlinear absorption is calculated. The excited state absorption cross-section of the samples is found to be one order of magnitude higher than that of the ground state absorption cross-section, indicating strong reverse saturable absorption. These results indicate that Sm³⁺/Eu³⁺ doped Tb₂(MoO₄)₃ nanophosphors are efficient media for UV/n-UV pumped LEDs, and are also potential candidates for designing efficient optical limiting devices for the protection of human eyes and sensitive optical detectors from harmful laser radiation.     

Synthesis,z-scan and degenerate four wave mixing characterization of certain functionalized photosensitive polyesters containing ortho-hydroxyazo chromophores

The preparation and NLO characterization of photosensitive polyesters containing azoaromatic residues in the molecular backbone, functionalized with orthohydroxy chromophores is presented. Samples were studied for its UV–vis absorption, FT-IR and intensity dependent nonlinear absorption properties. Nonlinear characterization was carried out with z-scan using frequency doubled, Q-switched Nd:YAG laser operating at 532 nm. The closed aperture z-scan spectra reveal the self defocusing effects of the samples with negative nonlinearity coefficient (n₂) showing values as high as −1.28 × 10⁻¹⁰ (esu) for certain samples and the corresponding third order susceptibility coefficient of the order of 29.9 × 10⁻¹² (esu). Degenerate four wave mixing technique was employed to substantiate the findings. The numerical fits show that the molecules exhibit reverse saturable absorption. A study of beam fluence dependence of nonlinear absorption coefficient (β_eff) has been presented. All phenomena indicate that molecules are reverse saturable absorbers whose optical limiting property gets enhanced with increasing conjugation length.     

Nonlinear optical properties of laser deposited CuO thin films

In this work we investigate the third-order optical nonlinearities in CuO films by Z-scan method using a femtosecond laser (800 nm, 50 fs, 200 Hz). Single-phase CuO thin films have been obtained using pulsed laser deposition technique. The structure properties, surface image, optical transmittance and reflectance of the films were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and UV-vis spectroscopy. The Z-scan results show that laser-deposited CuO films exhibit large nonlinear refractive coefficient, n₂ = − 3.96 × 10^− 17 m²/W, and nonlinear absorption coefficient, β = − 1.69 × 10^− 10 m/W, respectively.     

Microstructure and nonlinear optical characterization of a poly(aryl ether ketone) containing cobalt phthalocyanine

Poly(aryl ether ketone) containing cobalt phthalocyanine (PAEK-CoPc) is synthesized. The resulting polymer has good solubility and thermal stability. It shows optical absorption in the visible region, and exhibits blue photoluminescence. SEM images reveal that cotton morphology is shown when a solution of PAEK-CoPc in CHCl₃ is mixed with 4 equiv of Bipy, and then dried on a substrate. The third order nonlinear optical property of PAEK-CoPc solution is characterized by Z-scan measurement at 532nm with 4.5ns pulses and the third order nonlinear optical susceptibility χ⁽³⁾ is 1.11 × 10^{− 11}esu in the non-resonant region.     

Optical properties of chalcogenide glasses with ion-synthesized copper nanoparticles

Substrates of chalcogenide glassy semiconductors As₂S₃ and Ge_15.8As₂₁S_63.2 are implanted with Cu⁺ ions (energy 40 keV, radiation dose 1.5 × 10¹⁷ ion/cm², fixed current density in the ion beam 1 μA/cm²). The composite layers are analyzed by measuring linear optical transmittance and recording nonlinear optical absorption using the Z-scan technique at 780 nm (probe laser radiation with 150-fs pulses; intensity of 25–100 mW). It is ascertained for the irradiated materials that (1) the linear transmission characteristic of the optical surface plasmon resonance (SPR) band, which indicates the formation of copper nanoparticles in the near-surface region, has emerged and (2) there are simultaneously saturated and two-photon nonlinear absorption types; the latter prevails as the intensity of laser irradiation is increased.     

Donor/acceptor effects on the nonlinear optical properties of 1,3 diphenyl propenones

Employing the single beam Z-scan technique with nanosecond laser pulses at 532 nm, the refractive and absorptive nonlinearities of donor and acceptor substituted (2E)-1-(3,4-dimethoxyphenyl)-3-phenylprop-2-en-1-one have been studied. The sign of the nonlinear index of refraction (n ₂) is found to be negative and the magnitude of n ₂ is in the order of 10^?11 esu. The second-order molecular hyperpolarizability (γ_h) is calculated to be in the order of 10^?32 esu. The variation of nonlinear absorption coefficient (β_eff) with input intensity (I ₀) is studied and the nonlinear absorption mechanism is found to be reverse saturable absorption (RSA). The enhancement of nonlinearity due to the donor and acceptor substitution is in accordance with the variation in π electron delocalization in the molecules. The compounds exhibit good optical limiting as well.     

Studies on synthesis,growth and characterization of a novel third order nonlinear optical 4-Dimethylaminopyridinium p-Toluenesulfonate single crystal

Good quality single crystals of 4-Dimethylaminopyridinium p-Toluenesulfonate (4DMAPPTS) possessing third order nonlinearity were grown by slow evaporation solution technique (SEST). Single crystal X-ray diffraction analysis reveals that 4DMAPPTS belongs to monoclinic crystal system with centrosymmetric space group P2₁/n. FT-IR spectral studies were carried out to identify the functional groups present in 4DMAPPTS. NMR spectral study confirms the molecular structure of the grown crystal. Dielectric measurements were made over a wide range of frequencies for different temperatures. The grown crystal was subjected to Vickers microhardness test to study the mechanical property. The etching studies reveal the growth pattern and dislocations present in the grown title crystal. The important optical parameters such as absorption coefficient, extinction coefficient, refractive index and optical band gap were estimated from UV–Visible spectral analysis. The negative third order nonlinear optical parameters like refractive index (n₂), absorption coefficient (β) and susceptibility (χ⁽³⁾) were estimated by Z-scan studies.