Nonlinear optical characterization of LaEr(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript> thin films using the <Emphasis Type="BoldItalic">Z</Emphasis> -scan technique

The nonlinear optical properties of thin films of LaEr(MoO₄)₃ were studied using a ∼30 ps Nd:YAG laser at 532 nm with a repetition rate of 250 Hz. Closed aperture Z-scan measurement revealed a negative nonlinearity in the LaEr(MoO₄)₃. The nonlinear refractive index γ=1.38×10^-10 cm²/W and nonlinear absorption coefficient β=16.8×10^-6 cm/W were calculated from the Z-scan data. The fluorescent upconversion spectra were recorded with 980 nm excitation. An optical switching mechanism based on nonlinear absorption is also presented experimentally. PACS 81.15.Fg; 77.84.Bw; 33.50.Dq; 42.70.Mp     

Solvatochromic and nonlinear optical properties of Eosin B in solvents and AOT/water/Heptane

The third-order susceptibility and second-order hyperpolarizability and the two-photon absorption coefficient of Eosin-B in AOT/water/Heptane were investigated by using the Z-Scan technique. The droplets were prepared with an AOT/water droplet in a continuous phase of Heptane. The droplets size changes with the amount of water and the droplet concentration decreases with the increase of Heptane concentration. To study the nonlinear optical properties of Eosin-B, the Z-scan measurements were performed by means of a laser at 532 nm and 80 mW power. The nonlinear refractive and the nonlinear absorption coefficient indices were found to be in the order of 10^?12 (cm² W^?1) and 10^?7 (cm W^?1), respectively. The change of nonlinear optical properties of Eosin-B by droplet size and concentration is due to the change of dye aggregation and thermal conductivity and thermo-optic coefficient of samples. The absorption of Eosin-B changes with the polarity of the medium (dielectric constant and refractive index). It has been shown that the intensity of emission spectra of Eosin-B in AOT/water/Heptane is enhanced compared to that of aqueous solution. By the Bilot and Kawski theory, the ratio between the excited state and the ground state of the dipole moments (μ_e/μ_g) of Eosin-B both in water and in droplets is extracted.     

Nonlinear optical properties of an azo-based dye irradiated by picosecond and nanosecond laser pulses

The nonlinear optical properties of an azo-based dye were investigated using Z-scan technique employing 38 ps pulses at 532 and 1064 nm, and 6 ns laser pulses at 532 nm. Large nonlinear absorption and nonlinear refraction were observed at both ps and ns 532 nm in the azoic dye. When excited at ps 1064 nm, this dye displayed a large two-photon absorption cross-section (σ₂=1810 GM). Meanwhile, the optical nonlinearity mechanism was discussed in terms of molecular structure, excitation wavelength, and pulse width.     

Broadband optical limiting in the suspensions of lead sulfide nanoparticles

Nanoparticles of lead sulfide (PbS) have been prepared by a surfactant micelle template-inducing reaction. These nanoparticles were dispersed in ethanol and investigated for their nonlinear optical properties by nanosecond laser pulses. Broadband optical limiting effects have been observed at the wavelengths of 355, 1064, and 430 nm and every 30 nm from 470 to 620 nm. The nonlinear light-scattering process in the suspensions of PbS nanoparticles was characterized at the wavelength of 532 nm. Nonlinear absorption and nonlinear scattering were deduced to be the mechanisms for the broadband optical limiting performance. The origins of the nonlinear scattering were discussed.     

Picosecond nonlinearity of GeO2–Bi2O3–PbO–TiO2 glasses at 532 and 1,064 nm

The third-order optical properties of GeO₂–Bi₂O₃–PbO–TiO₂ glasses at 532 nm and 1,064 nm were studied to evaluate their potential for optical limiting and all-optical switching. The Z-scan technique was used to determine the nonlinear (NL) refractive index, n ₂, and the NL absorption coefficient, α ₂, of samples with different amounts of the constituent oxides. Values of n ₂ ≈ + 0.7 × 10^?14 cm²/W at 1,064 nm and ≈+1.5 × 10^?14 cm²/W at 532 nm were measured. The NL absorption coefficient, α ₂, was smaller than the minimum that our apparatus can measure (α ₂ < 0.01 cm/GW) in the near-infrared (1,064 nm); in the visible region (532 nm), we obtained α ₂ ≈ 4.4 cm/GW. The set of NL parameters measured indicates the potential usefulness of the GeO₂–Bi₂O₃–PbO–TiO₂ glasses for all-optical switching at 1,064 nm and for optical limiting at 532 nm.     

Picosecond Z-scan study of bound electronic Kerr effect in LiNbO3 crystal associated with two-photon absorption

3 crystal have been measured using Z-scan technique with picosecond pulses at 532 nm. The nonlinear absorption coefficient and nonlinear refractive index are determined to be 2.5×10^-10 cm/W and 5.3×10^-15 cm²/W, respectively. Both sign and magnitude of the measured refractive nonlinearity are considerably different from the reported Z-scan results in LiNbO₃ obtained with cw laser beam at 514 nm. The nonlinearities in LiNbO₃ induced by 532 nm picosecond pulses are believed to be mainly due to two-photon absorption and bound electronic Kerr effect associated with the two-photon absorption. Received: 4 July 1996     

Third order nonlinear optical properties of oligophenylene dyads by open-aperture Z-scan technique

The third order nonlinear optical response of some oligophenylene dyads were obtained at 30 ps, 532 nm using the Z-scan technique. The large nonlinearity of oligomers deriving from different substituted anisole is attributed to its rigid planar and intrachain charge transfer within the structure. The nonlinear absorption has been attributed to reverse saturable absorption-type behavior of the samples, while the imaginary part of the third order nonlinear susceptibility found has been of the order of 10 $^{-13}$ esu.     

Z-scan determination of the third-order optical nonlinearities of an azo dye using diode-pumped Nd:Yag laser

Optical nonlinearity of dye solutions are studied with considerable interest for their wide spread applications ranging from gain media in lasers to all-optical processing signal devices. The third-order nonlinear optical properties of Brilliant Crocein dye was measured by the Z-scan technique and measurements were carried out for different concentrations. The negative sign of the nonlinear refractive index n₂ indicates that this material exhibits self-defocusing optical nonlinearity and purely saturation absorption at the wavelength 532 nm of the diode-pumped Nd:YAG. These results show that Brilliant Crocein has potential applications in nonlinear optics.     

Non-linear optical properties of (Pb<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)TiO<Subscript>3</Subscript> thin films

Thin films of (Pb_1−x Sr _x )TiO₃, x=0,0.5,1.0 have been prepared on glass substrates by the chemical-solution method using the spin-coating technique. The optical nonlinearity in the visible spectral region is investigated using short (5 ns) laser pulses at the off-resonant wavelength of 532 nm employing the open aperture z-scan technique. It is found that the third order nonlinear absorption is dependent on the lead content of the films, with the compositions x=0, 0.5 exhibiting large values (β∼10⁻⁷ m/W), thereby suggesting the possible use of these materials as optical limiters. No optical nonlinearity is observed for the composition with x=1.0.     

Third-Order Nonlinear Optical Susceptibility of Indium Phosphide Nanocrystals

InP nanocrystals synthesized by refluxing and annealing of organic solvent are determined from XRD measurements to have an averse granularity of 25 nm. The nonlinear optical properties of the InP nanocrystals studied by using laser Z-scan technique with 50 ps pulses at 532nm are found to reveal strong nonlinear optical properties and two-photon absorption phenomenon. Also, the nonlinear absorption coeffcient, the nonlinear refractive index and the third-order nonlinear optical susceptibility are determined by experiments, in which the nonlinear refractive index is three orders of magnitude larger than that of bulk InP.     

Nonlinear optical studies of 1-3-diaryl-propenones containing 4-methylthiophenyl moieties

The third-order nonlinear optical properties of chalcone derivatives have been studied using the single beam Z-scan technique. The dependence of χ⁽³⁾ on different donor and acceptor type substituents demonstrates the electronic nonlinearity of compounds. The largest value of nonlinear refractive index, n₂, measured for a high electron donor substituted molecule is −2.033 × 10⁻¹¹ esu. These molecules exhibit a strong two-photon absorption and interesting optical limiting of nanosecond laser pulses at 532 nm.     

Femtosecond optical nonlinearity of Au nanoparticles under their excitation in nonresonant relative to surface plasmon conditions

Nonlinear optical response of Au island films to femtosecond laser pulses is studied in the vicinity but not exactly at the surface plasmon absorption peak (λ _spr = 560 nm). The third-order nonlinear optical susceptibility is shown to be Reχ ⁽³⁾ = +1.7 × 10^?7 esu and Reχ ⁽³⁾ = +1 × 10^?7 esu at the wavelengths 800 and 460 nm, respectively. Kinetics of the optical nonlinear response has been studied for wavelengths 400 and 800 nm. It is believed that the origin of nonlinearity at the wavelengths is related to the free-electron heating in the conduction band and their further thermalization via electron–electron scattering, but at 400 nm the contribution to the nonlinear susceptibility because of interband d → s, p transitions is also possible.     

Nonlinear Optical Properties of Nanosized Rare-Earth–Doped Strontium Barium Niobate Ceramics

Nanosized, undoped and rare-earth–doped Sr_0.5Ba_0.5Nb₂O₆ (SBN) ceramic systems were synthesized by an aqueous organic gel route. The precursor gel on calcinations at 800°C for 2 hr produces undoped and rare-earth–doped SBN systems of pure tungsten bronze lattice structure. These systems have been characterized for their structure by XRD, SEM, and TEM. The nonlinear absorption behavior of the undoped and rare-earth–doped SBN ceramic systems was investigated by use of the open-aperture Z-scan technique using 532 nm, 5 ns laser pulses. The authors found that these materials are potential optical limiters at this excitation wavelength.     

Z-scan and optical limiting properties of Hibiscus Sabdariffa dye

The intensity-dependent refractive index n ₂ and the nonlinear susceptibility χ ⁽³⁾ of Hibiscus Sabdariffa dye solutions in the nanosecond regime at 532 nm are reported. More presicely, the variation of n ₂, β, and real and imaginary parts of χ ⁽³⁾ versus the natural dye extract concentration has been carried out by z-scan and optical limiting techniques. The third-order nonlinearity of the Hibiscus Sabdariffa dye solutions was found to be dominated by nonlinear refraction, which leads to strong optical limiting of laser.     

Optical and nonlinear optical properties of copper nanocomposite glasses annealed near the glass softening temperature

Copper nanocomposite glasses have been prepared by the ion-exchange method, and annealed at different temperatures up to and above the glass softening temperature. The absorption spectra, fluorescence spectra, and nonlinear optical transmission of the samples at 532 nm for nanosecond laser pulses, have been investigated. The optical and nonlinear optical properties of the glasses are found to be distinctly different below and above the glass softening temperature. For instance, thermal annealing up to the glass softening temperature makes the samples behave like saturable absorbers, while annealing at higher temperatures makes them behave like optical limiters. Such flexibility in controlling the optical nonlinearity in these materials makes them potential candidates for photonic applications.     

Te/TeO2-SiO2复合薄膜的吸收和非线性光学特性研究

应用分光光度计测量Te/TeO₂-SiO₂复合薄膜的透射光谱和吸收光谱, 在480nm附近观察到Te颗粒引起的等离子体共振吸收峰; 采用Z扫描技术研究了共振(激发波长为532 nm)和非共振情况下(激发波长1064 nm) 不同电位制备薄膜的Te颗粒状态与复合薄膜的三阶非线性极化率的关系. 基于有效介质理论对复合薄膜的三阶非线性效应进行分析, 研究Te颗粒大小对Te/TeO₂-SiO₂复合薄膜的非线性光学性质的影响及其产生机理. 结果表明薄膜制备过电位增大, Te的粒径减小, 颗粒数量多, 颗粒分布趋于均匀, 使得金属颗粒的表面等离子体共振峰红移, 吸收强度增强, 导致三阶非线性光学效应增强, χ⁽³⁾由1064 nm的5.12×10^-7 esu增大为532 nm的8.11×10^-7 esu. 关键词： 碲 二氧化碲 复合薄膜 三阶非线性     

Optical and structural properties of nanocrystalline PbS thin film grown by CBD on Si(1 0 0) substrate

PbS nanocrystalline thin film was prepared by chemical bath deposition on Si(1?0?0) substrate at bath temperatures of 25, 45 and 65 °C. Triethanolamine was added to the aqueous solution, which decreased the grain size and increased the luminescence of the nanocrystalline PbS thin film. PbS nanocrystals were identified using XRD, TEM and AFM. The crystalline size of the PbS film deposited at different bath temperatures was estimated by XRD and TEM to be 7–12 nm. The growth mechanism of the PbS crystallites were described at different bath temperatures. The confinement was reflected in the absorption spectra, photoluminescence excitation and photoluminescence spectra. The luminescence of Si(1?0?0) substrate and PbS nanocrystalline film deposited on Si(1?0?0) were compared, and the results revealed that the PbS nanocrystals altered and notably enhanced the emission features of the Si(1?0?0) substrate. The shifting of the maximum photoluminescence emission wavelength of PbS nanocrystals with a change in bath temperature and the variation in photoluminescent intensity of PbS nanocrystals prepared at 25 °C versus deposition time were investigated. A single-peak fit of a Gaussian function was employed to discern the photoluminescence of PbS on Si(1?0?0) substrate.     

Third-order nonlinear optical properties in [(C4H9)4N]2[Cu(C3S5)2]-doped PMMA thin film using Z-scan technique in picosecond pulse

An organometallic complex, [(C₄H₉)₄N]₂[Cu(C₃S₅)₂], abbreviated as BuCu, was synthesized. Then the BuCu-doped polymethylmethacrylate (PMMA) thin film with a doping concentration 1% by weight (1 wt.%) was fabricated using a spin-coating method and its third-order nonlinear optical properties were characterized using the Z-scan technique with 20 ps pulse duration at 532 and 1064 nm, respectively. The Z-scan curves have revealed that the material exhibits a self-defocusing effect at both wavelengths. Saturable absorption at 532 nm and two-photon absorption at 1064 nm were also found, respectively. Additionally, the calculated results of the material in film were compared with that of acetone solution, which indicated that the values in film were larger than that of acetone solution for about two orders in magnitude. The origins were analyzed of the difference between the two wavelengths. Our results suggest that considerable nonlinear optical properties were confirmed in BuCu-doped PMMA film. The material can easily be doped into PMMA film and forms a waveguide mode. So this material should be considered to be manufactured into devices and applied in all-optical switching, laser locking-mode, optical limiting fields etc.     

PbS纳米颗粒复合的溶胶凝胶薄膜的飞秒非线性光学特性

通过光Kerr效应研究了PbS半导体纳米颗粒的三阶光学非线性响应。在较低的激发强度下,单激子态的饱和吸收和双激子效应的激发态吸收对非线性的贡献同时存在;而在高激发强度下,双激子效应是主要的。计算了高激发强度下(4mJ/cm²)PbS半导体纳米颗粒的三阶非线性光学极化率为5.1×10^-10esu。     

The nonlinear optical response of a fluorine-containing azoic dye

The nonlinear optical nonlinearities of a fluorine-containing azoic dye in tetrahydrofuran have been investigated by using Z-scan technique with picosecond and nanosecond lasers. The experimental results reveal that the azoic dye has large optical nonlinearity under the excitations of picosecond and nanosecond 532 nm. At the picosecond 532 nm the solution presents negative nonlinear refraction due to the electronic effect, while the larger nonlinear refraction under nanosecond laser excitation is induced by thermal effect. Moreover, the different nonlinear absorption behavior under picosecond and nanosecond excitations is analyzed.