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.     

A freeform optics design with limited data for extended LED light sources

Abstract

This paper proposes an optimization method for designing a freeform lens which can produce a good uniform circular illumination distribution and obtain high efficiency on the target plane. The initial surface profile of the freeform lens is calculated based on the laws of reflection and the energy conservation law, and then is fitted using the non-uniform rational basis spline (NURBS) method. The control points and weights are applied to parameterize the shape of freeform lens. The merit function for the optimization is defined as relative standard deviation (RSD) of the simulated illumination from the desired illumination and the efficiency of the lens. The simulation results indicate that the RSD is shown to be lower than 0.157, and maximum efficiency can be as high as 83.9%. In addition, it is demonstrated that this algorithm can obtain high uniform illumination distribution on the target plane with less variables. Compared with the conventional method, the simulation results show that the modified algorithm converges with less variables, good uniformity and high efficiency. Moreover, a freeform lens with different lighting patterns and non-rotational symmetry can be produced by the proposed method.     

电光源频闪测试技术研究

采用经V(λ)修正后的硅光电接收器模拟人眼接收光信号,高速A/D采样,使用傅里叶变换理论及其改进算法处理采样数据,实现电光源频闪频谱和波动深度的准确、快速测试。运用方法学考证,设计了验证实验并取得理想的验证结果。在对常用电光源进行了大量测试研究的基础上,提出了电光源频闪特性的参数及限量指标的建议,给出典型电光源的频闪数据。     

Composition dependent structural,Raman and nonlinear optical properties of PVA capped Zn1-x-yCdxCuyS quantum dots

Composition dependent structural, optical nonlinear and limiting properties of PVA capped Zn_1-x-yCd_xCu_yS quantum dots at different Cu:Zn ratio synthesized by insitu technique is subjected to detailed investigation. Cubic phase of the quantum dots were identified from XRD with particle size in the range 2.5 nm–3.5 nm find excellent correlation with the particle size measured from TEM. With increase in Cu concentration: systematic increment in lattice parameter, red shift in absorption edges and luminescence quenching is observed. Raman scattering reveals good photoactivity evidenced by intensity variation and shifting of LO and TO phonon modes. The intensity dependent third order nonlinearity is studied using Q switched Nd: YAG laser with 532 nm irradiation. Progressive increase in 3 PA coefficient indicated that prepared samples exhibit good nonlinear and optical limiting properties.     

Biological behaviour of buccal cells exposed to blue light

Blue light is used in dental practise to cure resin-based materials, but the path of the light often includes oral tissues such as gingival tissues. While adverse effects of blue light exposure on cells – such as retina cells – are well known, few studies have investigated the impact of blue light exposure on oral cells. The aim of the present in vitro study was to assess the biological effects of blue light emitted by two dental curing devices (a plasma-arc and a light-emitting diode curing unit) on human gingival fibroblasts. Light intensities and light-induced temperature rise were respectively measured with a radiometer and a thermocouple. Cellular response to blue light exposure was assessed by the observation of cell morphology (scanning electron microscopy) and the estimation of cell mitochondrial activity (MTT assay). Light intensities measured at the clinical distance were 488 ± 42 mW/cm² for the plasma-arc unit and ranged from 61 ± 5 to 140 ± 16 mW/cm² for the light-emitting diodes unit, according to the curing program used. The highest temperature rise was 0.5 and 3.5 °C for exposure to the plasma-arc light and to the light-emitting diodes light, respectively. Results showed no differences between exposed- and non-exposed cells in regards to cell morphology. However, cells exposed to blue light presented an increased mitochondrial activity compared to control cells (non-exposed), and mostly those exposed to plasma-arc light.     

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.     

有机生色团和极化聚合物二阶非线性光学系数的非激光评估方法

讨论了有机生色团和极化聚合物膜的二阶非线性光学特性的非激光测试和评估方法，它包括测定生色团分子一阶超极化率（β）的溶剂化变色法、测定极化膜的ｄ值的电子吸收光谱法和偏振红外光谱法以及相应的简化估算公式，在此基础上还提出了极化膜进行应用试探的筛选标准。方法简便易行，无需复杂昂贵的激光测试系统，而且结果有较高的精度，适用于普通化学实验室进行样品的评估和筛选。     

Single-mode fluorotellurite glass fiber

By multi-stage rod-in-tube fiber drawing process, a single-mode fluorotellurite glass fiber was fabricated and reported for the first time. Benefiting from chemical–physical dehydration process to remove water and OH⁻ groups, the propagation loss was decreased to 1.9 dB/m at 1550 nm and the infrared window is extended from 2.8 μm to 4.2 μm, i.e. a new kind of mid-infrared glass fiber. The fiber is with a small core of 3.52 μm in diameter to meet single-mode condition, and the effective nonlinear parameter γ was estimated to be 236.7 W⁻¹ km⁻¹ at 1550 nm by using continuous-wave self-phase modulation method. © 2015 Elsevier B.V. All rights reserved.     

Study of the nonlinear optical properties and behavior in phenoxy-phthalocyanines liquid at nanosecond laser pulses

The nonlinear optical properties of 2,9,16,23-phenoxy-phthalocyanine (Pc1) and 2,9,16,23-phenoxy-phthalocyanine-zinc (Pc2) in solution were investigated under excitation with nanosecond laser pulses at 532 nm. Based on five-level model, the nonlinear absorption in nanosecond regime was theoretically analyzed. The A-OS and OL behavior of Pc1 and Pc2 were further investigated with the pump–probe technique and transmission measurement technique. The results show that the A-OS response time is determined by the lifetime of the first triplet excited state of molecule, and Pc1 and Pc2 exhibit strong optical limiting effect at nanosecond laser pulses. These studies make the samples a promising possibility for device realization.     

Propagation properties of Airy–Gaussian beams in centrosymmetric photorefractive media

Based on the biased centrosymmetric photorefractive media, we investigate numerically the propagation and interaction properties of Airy–Gaussian beams. The single Airy–Gaussian beam forms the one-component breather with the help of the photorefractive nonlinearity. The interaction properties of two Airy–Gaussian beams can be controlled by adjusting the relative parameters, such as photorefractive nonlinearity, transverse distance and relative phase of two incident beams. The two-component breather with ladder structure can be observed for both the in-phase and out-of-phase cases when the self-acceleration property is balanced by the photorefractive nonlinearity. The one- or three-component breathers can be observed for the in-phase case only when the transverse distance takes a certain range.     

Organic and inorganic hybrid film with second-order nonlinear optical and pyroelectric properties

An organic and inorganic hybrid material was prepared from a nonlinear optically active imidazole derivative 4-(nitrophenyl)-2,4-Bis-(4,4′-[N,N-bis-(2-hydroxyethyl)aminophenyl]) imidazole and metal alkoxide of Nb(V) via sol-gel process. The second-order nonlinear optical and pyroelectric properties of the hybrid film were investigated in terms of the second harmonic generation (SHG) and pyroelectric coefficient measurement. The SHG coefficient d₃₃ was found to be 29.3 pm/V at the fundamental wavelength of 1064 nm and the pyroelectric coefficient P was found to be 1.47 × 10^− 6 C/cm² K.     

Incoherent triggering of picosecond pulse pumped supercontinuum

We numerically study spectral and noise properties of picosecond pulse pumped supercontinuum using an incoherent continuous wave trigger with 1% pump intensity. We have swept the trigger central wavelength from 1404 to 1724?nm, and observe obvious improvement in the SC bandwidth and moderate enhancement of SNR when the ASE-based CW-trigger is located at a proper wavelength range. We also varied the trigger bandwidth from 0.5 to 6?nm and find a reduced effect of the trigger when its associated coherence time decreases below the duration of the temporal pump pulse. Finally, we have varied the pump pulse peak intensity from 20 W to 120 W to demonstrate the power dependency of the suggested CW triggering technique.     

Structural,photoluminescence and picosecond nonlinear optical effect of In-doped ZnO nanowires

In-doped ZnO (IZO) nanowires were grown using the chemical vapour deposition method. The IZO nanowires have been characterized by scanning electronic microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and UV–Visible spectroscopy. The PL results demonstrated a larger band-gap for the IZO nanowires in comparison to the undoped ZnO. Two major emission peaks were observed for the IZO nanowires, one originated from the free exciton recombination (ultraviolet emission) and another possibly related to the deep-level emission (visible emission). Furthermore, the nonlinear optical characteristic of the nanowires was studied using picosecond Z-scan technique. The experimental results show that the two and three-photon absorption coefficient of samples were able to be observed. These studies make the promising potential applications of the samples in the development of multifunctional all-optical devices.     

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.     

Glass formation and third-order optical nonlinear characteristics of bismuthate glasses within Bi2O3–GeO2–TiO2 pseudo-ternary system

Glass-forming region of Bi₂O₃–GeO₂–TiO₂ (BGT) pseudo-ternary system was determined by using melt-quench method. A series of high transparent glass samples were selected and their structural characteristics were investigated by FT-IR and Raman spectra. By employing Z-scan and optical Kerr shutter techniques with femtosecond laser pulses as excitation source, third-order optical nonlinearities (TON) of the BGT glasses as well as the TON response time were investigated at wavelength of 800 nm. The ultrafast nonlinear response and high figure of merit suggest great potentials of BGT glasses in applications of all-optical switching or related optical devices.     

Preparation and nonlinear optical properties of hybrid films containing dicyanomethylenepyran-based chromophores

A new nonlinear optical (NLO) chromophore 4-dicyanomethylene-2-methyl-6- {4-[4-(N-ethyl-N-hydroxyethylamino)phenylazo]}styryl-4H-pyran (AZP), which features extended conjugated chain based on DCM laser dye, was synthesized and functionalized with alkoxysilane for materials processing. Hybrid films containing chromophore AZP and DCM were prepared via a sol-gel processing. The d₃₃ values of films containing AZP are 39-48 pm/V varying with concentration of chromophores, which is similar to that containing DCM. By tuning the organic content, the thermal stability of d₃₃ values can be significantly improved by about 30 °C, about 15 °C higher than those containing DCM. The residual rotational stress, along with cavity between chromophores and matrix, is proposed to contribute to the stability of NLO activity of hybrid films.