Femtosecond Z-scan measurements of nonlinear refraction in nonlinear optical crystals

We report an investigation of third-order optical nonlinearities in several nonlinear optical crystals using the Z-scan technique with femtosecond laser pulses at 780 nm wavelength. The crystals studied include LiNbO₃:MgO, KTiOAsO₄, KTiOPO₄, β-BaB₂O₄ and LiB₃O₅, which are extensively used for ultrashort-pulse second-harmonic generation and optical parametric oscillation. The nonlinear refractive index n₂ in these crystals has been determined to be in the range from 10⁻¹⁶ to 10⁻¹⁵ cm²/W. No two-photon absorption has been observed. The experimental results are compared with the two-band model for the bound electronic Kerr nonlinearity. It is shown that the measured n₂ values in β-BaB₂O₄ and LiB₃O₅ are one order of magnitude smaller than those of LiNbO₃:MgO, KTiOAsO₄, KTiOPO₄, which is in agreement with the theoretical prediction.     

Structural, optical, and nonlinear optical absorption/refraction studies of the manganese nanoparticles prepared by laser ablation in ethanol

The structural, optical, and nonlinear optical properties of the manganese nanoparticles prepared by laser ablation in various liquids were investigated using the 532 and 1064 nm, 50 ps laser pulses. The TEM and spectral measurements showed temporal dynamics of size distribution of Mn nanoparticles in solutions. The nonlinear absorption (β = 2 × 10⁻¹⁰ and 4 × 10⁻¹¹ cm W⁻¹) and positive nonlinear refraction (γ = 8 × 10⁻¹⁵ and 2 × 10⁻¹⁴ cm² W⁻¹) of picosecond radiation were observed in the Mn colloidal suspensions using the 1064 and 532 nm radiation, respectively     

Fabrication of Ag and Cu nanowires by a solid-state ionic method and investigation of their third-order nonlinear optical properties

Ag and Cu nanowires were separately fabricated in a direct current electric field using a solid-state ionic method, and characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Their optical nonlinearities induced by 8 ns laser pulses from a frequency-doubled, Nd:YAG laser at 532 nm, were investigated using the Z-scan technique. Experimental results indicate the metal nanowires have obvious positive refractive nonlinearities and reverse saturated absorption behaviors. The self-focusing behaviors of Ag and Cu nanowires can be attributed to Kerr-induced self-focusing of laser radiation, the nonlinear refractive indexes of Ag and Cu nanowires are n₂ = 1.7 × 10^− 11 esu and n₂ = 2.4 × 10^− 11 esu respectively, and the two-photon process of Ag and the one-photon process of Cu are responsible for the difference between Ag and Cu nanowires suspended in de-ionized water in nanosecond nonlinear absorptions.     

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.     

Optical nonlinearities of Fe2O3 nanoparticles investigated by Z-scan technique

The single beam Z-scan technique has been used to measure the third-order nonlinear refractive index, γ, the two-photon absorption coefficient, ß, and the variation of refractive index per unit photoexcited carrier density σ_r, and the free carrier absorption cross section σ_ab for quantum-confined Fe₂O₃ nanoparticles coated by a layer of organic molecular in toluene and bare particles in hydrosol. For coated Fe₂O₃ nanoparticles, the ratio γ/ß is enhanced by a factor of five compared to the bare sample. Their figures of merit related to linear and two-photon absorption for ultrafast all-optical devices application were determined.     

Coating of TiO2 nanoparticles with PbS thin films and preparation of PbS nanoparticles using a one-pot sonochemical reaction under the multibubble sonoluminescence conditions

Preparations of PbS-coated titanium dioxide (TiO₂) and lead sulfide (PbS) nanoparticles under ultrasonic field at the multibubble sonoluminescence (MBSL) conditions were tested in water solutions. Under the optimal MBSL conditions (20 kHz and 220 W power input), PbS nanoparticles (diameter = 40-50 nm) were prepared by treating lead nitrate and thioacetamide for 20 min in water solutions. The size of PbS nanoparticles was found to be easily increased to about 90 nm in diameter by increasing the reactant concentration twice. A similar sonochemical reaction with TiO₂ nanoparticles (about 20-30 nm in diameter) gave rise to PbS-coated TiO₂ nanoparticles with a core/shell structure. The PbS thin film coating was quite uniform and the average coating depth of PbS on the TiO₂ nanoparticles was about 2-3 nm under the described conditions. It is interesting to note that the coating depth was found to be controlled to 2-10 nm range by increasing the amounts of reactants for Pb and S twice with a sonication time of 30 min.     

Z-scan的基础理论及技术回顾

由Sheik-Bahe于1989年提出的Z-scan技术已经成为在非线性光学和材料科学领域里的一项非常有用的测量方法,它能简单而灵敏地测量非线性光折射率和吸收率.本文概要地讨论了Z-scan技术并介绍了它的最新进展,其中着重讨论了高斯分解法对此项技术的理论研究.     

Study on the nonlinear optical properties of three azo dyes by Z-scan measurements

The nonlinear optical properties of p-aminoazobenzene (PAAB), methyl orange (MO) and p-dimethylamino benzene arsenic acid (PDBAA) were investigated by a single beam Z-scan technique, respectively. Their solution samples all exhibited large nonlinear refractive indices under the excitation of a 633 nm laser. Among the three azo dyes, PDBAA showed the largest value of nonlinear refractive index. Moreover, the process of nonlinear refraction induced by the laser thermal effect was also analyzed in this paper.     

Fluorescence and nonlinear optical properties of non-aggregating hexadeca-substituted phthalocyanine

Highly non-aggregating hexadeca-substituted phthalocyanine (Pc) complexes were prepared and their fluorescence and nonlinear optical properties were studied. Three visible fluorescence bands were observed when the Pc complexes were excited at 355 nm and found to be concentration dependent. They are attributed to the optical transitions S₂ → S₀ at 415 nm, T₂ → T₁ at 630 nm, and S₂ → S₁ at 755 nm. Nonlinear absorptive and refractive effects were measured with the help of Z-scan technique. Saturation absorption was observed at 632.8 nm where the nonlinear absorption coefficient is found to be very large (β = −2.8 × 10⁻² cm/W) and the refractive nonlinear coefficient γ = −9.5 × 10⁻¹¹ cm²/W. In the transparency domain at 532 nm, reverse absorption saturation is observed and β and γ are found to be 17.5 and 15.5 times smaller, respectively. Optical limiting performances are measured in the absorption and transparency domains. Purely refractive-based optical limiting at 632.8 nm is found to have a threshold of 0.16 kW/cm², lower than the reverse absorption saturation and refractive-based optical limiting of 0.90 kW/cm² at 532 nm.     

Light control through a nonlinear lensing effect in a colloid of biosynthesized gold nanoparticles

Biosynthesis of four samples of colloidal suspensions of gold nanoparticles is achieved using hydroalcoholic extract and three different separated compounds of the plant Bacopa procumbens. The nonlinear optical properties of each sample are characterized with the Z-scan technique. In all cases, the Z-scan curves indicate a negative or self-defocusing response, which is mainly attributed to thermal effects. Among the four samples, the hydroalcoholic extract was noted to have the highest nonlinear optical response and was selected to demonstrate the formation of self-collimated beams (SCBs). This kind of beams are obtained when a convergent CW laser, with only few tens of milliwatts of optical power, is introduced into the sample and induces a negative-lens effect that shifts the focal spot forward. As a result, the otherwise highly focused beam propagate with little divergence over lengths of up to 10?mm. Moreover, an SCB is capable of controlling and steering a weak probe beam of a different wavelength, since the probe experiences the lensing induced by the pump. Noteworthy, the response time of the material was found to be less than 0.07?s, which makes it a plausible candidate for photonic applications.     

掺杂PbS纳米粒子的有机改性硅酸盐玻璃

本文报道了用溶胶 凝胶法将表面修饰的 Ｐｂ Ｓ纳米粒子均匀固化于有机改性硅酸盐玻璃中的制备方法, 制得的 Ｐｂ Ｓ在改性硅酸盐玻璃中的掺杂浓度为０.５ｗｔ％ , Ｈ Ｒ Ｔ Ｅ Ｍ 显示 Ｐｂ Ｓ 纳米粒子的尺寸为３～４ｎｍ在吸收光谱中, 可以观察到明显的量子尺寸效应, 吸收边蓝移     

Microwave heating synthesis of HgS and PbS nanocrystals in ethanol solvent

A novel route was developed to prepare PbS and HgS nanocrystals in ethanol solvent in the presence of sodium hydroxide by microwave heating method. PbS and HgS nanocrystals were obtained with an average size of approximately 10 and 6 nm, respectively. In the reaction, mercury acetate and lead acetate were used as mercury and lead source; sulfur powder was employed as chalcogenide source. The products were characterized by X-ray powder analysis (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV–Vis absorption spectroscopy. The probable mechanism was presented.     

Linear and nonlinear optical refractions of CR39 composite with CdSe nanocrystals

Hybrid composites of CdSe nanocrystals embedded in allyl diglycol carbonate (CR39) matrices have been prepared and characterized. The measurements show that the linear refractive index of the composite decreases as the CdSe nanocrystal’s weight-percentage concentration increases at the laser wavelengths of 632.8 nm and 532 nm. The room temperature nonlinear optical properties of the hybrid composites were investigated using a single-beam Z-scan technique with femtosecond laser pulses at the wavelengths of 794 nm and 397 nm. The experimental data reveals that the Kerr nonlinear refractive index n₂ of the composite increase at these wavelengths when the CdSe nanocrystal’s weight-percentage concentration increases. Also, the nonlinear refractive index n₂ of the CdSe/CR39 hybrid composites exhibit dispersion from a positive value at 794 nm (below the band gap) to a positive value at 395 nm (above the band gap). The measured dispersion of n₂ is roughly consistent with the Sheik-Bahae’s theory for the bound electronic nonlinear refraction resulting from the two-photon resonance.     

Nonlinear optical properties of two oxazine dyes in aqueous solution and polyacrylamide hydrogel using single beam Z-scan

The nonlinear optical properties of the two oxazine dyes, i.e. oxazine 720 (OX720) and oxazine 750 (OX750), in aqueous solution and in polyacrylamide hydrogel (PAA) matrix were studied by Z-scan technique using CW He–Ne laser at 632.8 nm. All the polymeric and aqueous samples showed a negative nonlinearity and large nonlinear refractive index of the order of 10⁻⁸ cm²/W. The concentration-dependent nonlinear refractive index was also investigated. In the case of PAA–dye systems, two types of transit (fast) and steady state (slow) nonlinear effects were observed. It is believed that these effects are due to the thermo-optical induced refractive index gradient and a concentration gradient induced by a temperature gradient present in a medium.     

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.     

表面具有孔洞的硫化铅微立方体的制备及表征

运用水热法再经过高温煅烧处理制备出了表面具有孔洞的硫化铅立方体.立方体的边长在10μm左右,表面孔洞的直径在1～2μm之间.考察了反应条件对产物的影响规律,结果表明反应时间对产物的形貌有着重大的影响,随着反应时间的增加,PbS晶体由完整的微立方体逐步转变为表面具有孔洞的立方体结构,同时体系中葡萄糖的存在对于这种新颖结构的形成也起到了至关重要的作用,运用X射线粉末衍射(XRD)、扫描电子显微镜(SEM)、高分辨透射电镜(HRTEM)、电子衍射(ED)等对所得产物进行了系统的表征.并对其生长机理进行了初步的探讨.     

Size-dependent nonlinear weak-field magnetic behavior of maghemite nanoparticles

The magnetic behavior at room temperature of maghemite nanoparticles of variable sizes (from 7 to 20 nm) is compared using a conventional super quantum interference device (SQUID) and a recently patented technology, called MIAplex. The SQUID usually measures the magnetic response versus an applied magnetic field in a quasi-static mode until high field values (from -4000 to 4000 kA m(-1)) to determine the field-dependence and saturation magnetization of the sample. The MIAplex is a handheld portable device that measures a signal corresponding to the second derivative of the magnetization around zero field (between -15 and 15 kA m(-1)). In this paper, the magnetic response of the size series is correlated, both in diluted and powder form, between the SQUID and MIAplex. The SQUID curves are measured at room temperature in two magnetic field ranges from -4000 to 4000 kA m(-1) (-5T to 5T) and from -15 to 15 kA m(-1). Nonlinear behavior at weak fields is highlighted and the magnetic curves for diluted solutions evolve from quasi-paramagnetic to superparamagnetic behavior when the size of the nanoparticles increases. For the 7-nm sample, the fit of the magnetization with the Langevin model weighted with log-normal distribution corresponds closely to the magnetic size. This confirms the accuracy of the model of non-interacting superparamagnetic particles with a magnetically frustrated surface layer of about 0.5 nm thickness. For the other samples (10-nm to 21-nm), the experimental weak-field magnetization curves are modeled by more than one population of magnetically responding species. This behavior is consistent with a chemically uniform but magnetically distinct structure composed of a core and a magnetically active nanoparticle canted shell. Accordingly the weak-field signature corresponds to the total assembly of the nanoparticles. The impact of size polydispersity is also discussed.     

全氟羧酸离子交换膜内硫化铅超微粒的光学非线性研究

在全氟羧酸阳离子交换膜中制备出不同颗粒尺寸的ＰｂＳ超微粒，并由吸收光谱及电镜测量结果获得证实。用飞秒激光脉冲对ＰｂＳ超微粒复合膜进行了时间分辨光克尔效应测定，发现ＰｂＳ超微粒具有三阶光学非线性，三阶光学非线性极化率Ｘ（３）约为１０（－１２）ｅｓｕ，光克尔效应响应时间小于１６５ｆｓ，并且发现ＰｂＳ超微粒的光学非线性随着超微粒颗粒尺寸的减小而增大，显示出量子限域效应对于超微粒子光学非线性的贡献。