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     

Nonlinear optical and optical limiting studies of alkoxy phthalocyanines in solutions studied at 532 nm with nanosecond pulse excitation

We report our results on the nonlinear optical and optical limiting properties of two alkoxy phthalocyanines namely 2,3,9,10,16,17,23,24-octakis-(heptyloxy) phthalocyanine and 2,3,9,10,16,17,23,24-octakis-(heptyloxy) phthalocyanine zinc(II) studied at a wavelength of 532 nm using 6 ns pulses. Using the standard Z-scan technique we observed that both the phthalocyanines exhibited negative nonlinearity as revealed by the signature of closed aperture data. The magnitude of the nonlinear refractive index n₂ evaluated from the closed aperture data was ∼ 1.61×10^-11 cm²/W for the free-base phthalocyanine and ∼ 1.56×10^-11 cm²/W for the metallic phthalocyanine. Open aperture Z-scan data indicates strong nonlinear absorption in both the phthalocyanines with measured nonlinear coefficients of ∼ 1650 cm/GW and ∼ 1850 cm/GW respectively. We also report optical limiting properties of these phthalocyanines with limiting thresholds (I_1/2) of ∼ 0.5 J/cm². Our studies suggest that these phthalocyanines are one of the best molecules for nonlinear optical applications studied recently. PACS 42.65.-k; 42.70.Jk, 42.65.Jx     

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.     

Preparation and optical properties of sol–gel neodymium-doped germania/γ-glycidoxypropyltrimethoxysilane organic–inorganic hybrid thin films

Germania/γ-glycidoxypropyltrimethoxysilane organic–inorganic hybrid spin-coating thin films doped with neodymium ions are prepared by a sol–gel technique and a spin-coating process. Acid-catalyzed solutions of γ-glycidoxypropyltrimethoxysilane mixed with germanium isopropoxide are used as matrix precursors. Thermal gravimetric analysis, UV–visible spectroscopy, and Fourier transform infrared spectroscopy are used to study the structural and optical properties of the hybrid thin films. The results indicate that films that are crack-free and have a high transparency in the visible and near-infrared range can be obtained; a strong UV absorption region at short wavelength ∼200 nm, accompanied with a shoulder peaked at ∼240 nm, due to the neutral oxygen monovacancy defects, is also identified. Upconversion emission properties of the transparent dried gel and the thin films heated at different heat treatment temperatures and doped with different neodymium ion concentrations are studied; a relatively strong room-temperature yellow to violet upconversion emission at 397 nm (⁴ D _3/2→⁴ I _13/2) is observed under a xenon lamp excitation with yellow light at the wavelength of 580 nm (⁴ I _9/2→⁴ G _5/2). The effect of Nd³⁺ doping concentration and heat treatment temperature on upconversion emission of the thin films is also studied. The mechanism of the upconversion is proposed. PACS 81.05.Kf; 81.20.Fw; 78.55.Hx     

Z-Scan studies of KYW, KYbW, KGW, and Ba(NO3)2 crystals

We present the studies of nonlinear refraction and nonlinear absorption in promising crystals which are extensively used in Raman lasers or as solid-state laser host materials: Ba(NO₃)₂, KGW, KYW, and KYbW. The single-beam z-scan technique with 1 ps laser pulses at 790 and 395 nm has been applied for the study. Nonlinear refraction-index intensity-coefficients and two-photon absorption coefficients have been determined for the crystals. The considerable enhancement of nonlinear refraction is observed in the crystals at 395 nm.     

Linear and nonlinear optical properties of rare earth doped of Ba0.7Sr0.3TiO3 thin films

Ba_0.7Sr_0.3TiO₃:Eu ferroelectric films were deposited on quartz substrates by pulsed laser deposition. The linear absorption coefficient and the linear refractive index calculated from the transmission spectrum at 532 nm were found to be 1.67×10⁴ cm^?1 and 1.82 respectively. The room temperature photoluminescence shows the characteristic emission of Eu³⁺ ions. The nonlinear optical properties of the film were investigated by a single beam Z-scan setup. The negative nonlinear refractive index and two photon absorption coefficient was found to be ?1.508×10^?6 m²/GW and 240 m/GW respectively. The real and imaginary part of the third order susceptibility of the thin films is 2.58×10^?17 m²/V² and 1.16×10^?16 m²/V² respectively. The BST:Eu thin films show good optical limiting property.     

Nonlinear refraction and photoinduced birefringence in chlorophosphonazo I doped polymer thin films

The nonlinear refraction and photoinduced birefringence of chlorophosphonazo I (CPA I ) doped PVA thin films were investigated. The single-beam Z-scan measurement showed that CPA I doped PVA thin film possessed a large value of nonlinear refractive index (n₂=1.82×10⁻¹² cm²/W) under a pulse 532 nm excitation, and the mechanism accounting for the process of nonlinear refraction was discussed in term of resonant electronic effect. Moreover, fast and stable molecular reorientation was observed when investigating the photoinduced birefringence of CPA I doped PVA thin film with a CW 532 nm laser as pump light and a CW 650 nm laser as probe light.     

Nonlinear refraction of silver nanowires from nanosecond to femtosecond laser excitation

In order to investigate the effect of pulse width and solvent on the nonlinear properties of metal nanostructures, silver nanowires were fabricated in a direct current electric field (DCEF) using a solid-state ionic method and characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The nonlinear refractive index (γ) of silver nanowires suspended in ethanol was measured using the Z-scan technique and laser radiation of various (femto-, pico-, and nanosecond) pulse durations. Experimental results indicated that silver nanowires have obvious positive refractive nonlinearities and γ (the Kerr-induced self-focusing) increases as the pulse duration increases from 7.4×10⁻⁸ cm²/GW at 110 fs to 1.6×10⁻⁴ cm²/GW at 8 ns, due to the additional influence of the atomic reorientational Kerr effect in the case of longer pulses. Due to the solvent dependence of the nonlinear behavior of the silver nanowires, the nonlinear absorption and refraction of silver nanowires suspended in de-ionized water are smaller than those of silver samples suspended in ethanol. The thermal nonlinearities are insignificant in our experimental conditions.     

生物大分子杂化处理的CdSe/ZnS核/壳量子点多层膜的超快三阶非线性研究

利用静电自组装技术，以生物大分子材料壳聚糖杂化处理具有稳定结构的CdSe/ZnS核/壳量子点，形成复合多层薄膜. 与薄膜的吸收谱线比较，在375nm飞秒激光激发下测量的量子点的光致发光谱存在Stokes位移. 采用Z扫描技术，利用790nm飞秒激光研究了其三阶非线性吸收和折射特性，发现饱和吸收信号来自CdSe/ZnS量子点，而自聚焦的折射信号则部分来自壳聚糖. 测出多层膜的三阶非线性系数分别是β＝6.5×10^-6cm/W，n₂＝1.5×10^-10cm²/W. 关键词： CdSe/ZnS量子点 非线性性能 光致发光谱     

Critical current densities of high pressure oxygen sputtered thin films of YBa2Cu3O7−x by non-resonant rf absorption method

The critical current densities (J _c) have been measured at 77K in high pressure oxygen sputtered thin films of YBa₂Cu₃O_7−x superconductor using the non-resonant rf absorption technique. High values ofJ _c (∼ 10⁵ A/cm²) are observed in these relatively large area (∼ 1·2 cm²) films.     

Nonlinear optical absorption and refraction in Ru, Pd, and Au nanoparticle suspensions

We present the results of studies of the nonlinear optical properties of Pd, Ru, and Au nanoparticles. We studied the nonlinear refraction and nonlinear absorption of suspensions of these nanoparticles at 1064-nm wavelength. A relatively strong nonlinear absorption of the Pd nanoparticles was observed in the case of 1064-nm, 50-ps pulses (β=2×10⁻⁹ m W⁻¹). The Ru and Pd nanoparticles showed weak negative nonlinear refraction (γ∼−(6–8)×10⁻¹⁶ m² W⁻¹) in this spectral range. In the case of the Au nanoparticles, a saturated absorption at 532 nm dominated over other nonlinear optical processes.     

Nonlinear optical properties in SrTiO3 thin films by pulsed laser deposition

Well-crystallized 250 nm-thick SrTiO₃ thin films on fused-quartz substrate were prepared by pulsed laser deposition. The band-gap of SrTiO₃ thin film by transmittance spectra is equal to 3.50 eV, larger than 3.22 eV for the bulk crystal. The nonlinear optical properties of the films were examined with picosecond pulses at 1.064 μm excitation. A large two-photon absorption (TPA) with absorption coefficient of 87.7 cm/GW was obtained, larger than 51.7 cm/GW for BaTiO₃ thin films. The nonlinear refractive index n₂ is equal to 5.7×10⁻¹⁰ esu with a negative sign, larger than 0.267×10⁻¹¹ esu for bulk SrTiO₃. The large TPA is attributed to intermediate energy levels introduced by the grain boundaries, and the optical limiting behaviors stemming from both TPA and negative nonlinear refraction were also discussed.     

Aerosol deposition of detonation nanodiamonds used as nucleation centers for the growth of nanocrystalline diamond films and isolated particles

The aerosol deposition of detonation nanodiamonds (DNDs) on a silicon substrate is comprehensively studied, and the possibility of subsequent growth of nanocrystalline diamond films and isolated particles on substrates coated with DNDs is demonstrated. It is shown that a change in the deposition time and the weight concentration of DNDs in a suspension in the range 0.001–1% results in a change in the shape of DND agglomerates and their number per unit substrate surface area N _s from 10⁸ to 10¹¹ cm⁻². Submicron isolated diamond particles are grown on a substrate coated with DND agglomerates at N _s ≈ 108 cm⁻² using microwave plasma-enhanced chemical vapor deposition. At N _s ≈ 10¹⁰ cm⁻², thin (∼100 nm) nanodiamond films with a root-mean-square surface roughness less than 15 nm are grown.     

Patterning of PLZT and PSZT thin films by excimer laser

The patterning of lanthanum-doped lead zirconate titanate (PLZT) and strontium-doped lead zirconate titanate (PSZT) thin films has been examined using a 5-ns pulsed excimer laser. Both types of film were deposited by rf magnetron sputtering with in situ heating and a controlled cooling rate in order to obtain the perovskite-structured films. The depth of laser ablation in both PSZT and PLZT films showed a logarithmic dependence on fluence. The ablation rate of PLZT films was slightly higher than that of PSZT films over the range of fluence (10–150 J/cm²) and increased linearly with number of pulses. The threshold fluence required to initiate ablation was ∼ 1.25 J/cm² for PLZT and ∼ 1.87 J/cm² for PSZT films. Individual squares were patterned with areas ranging from 10×10 μm² up to 30×30 μm² using single and multiple pulses. The morphology of the etched surfaces comprised globules which had diameters of 200–250 nm in PLZT and 1400 nm in PSZT films. The diameter of the globules has been shown to increase with fluence until reaching an approximately constant size at ≤ 20 J/cm² in both types of film. The composition of the films following ablation has been compared using X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy. PACS 79.20.Ds; 82.80.Pv; 82.80.Ej     

氧压对Ba0.6Sr0.4TiO3薄膜晶格常数的影响及BaTiO3/Ba0.6Sr0.4TiO3超晶格的制备

采用脉冲激光沉积(PLD)技术,经一系列的优化实验成功地制备了BaTiO₃(BT)和Ba_0.6Sr_0.4TiO₃(BST)单层膜.X射线衍射分析表明,在LaAlO₃(001)单晶平衬底上生长的BT和BST薄膜都是沿[001]取向的近外延生长.且随着氧压在10^-3—25 Pa范围内逐渐增大,BST薄膜的晶格常数与氧压之间近似满足Boltzmann函数关系.其次,在此优化条件下还 关键词： 超晶格 晶格常数 激光感生热电电压 脉冲激光沉积     

Thermal tuning of surface plasmon resonance: Ag gratings on barium strontium titanate thin films

Surface plasmon tuning via thermally induced refractive index changes in ferroelectrics is investigated. Epitaxial (Ba_0.7Sr_0.3)TiO₃ (BST) thin films were deposited on MgO (001) substrates by pulsed laser deposition. The refractive index of BST thin films measured by the prism-coupling technique was found to increase from 2.3932 (TE)/1.9945 (TM) at room temperature to 2.3949 (TE)/1.9965 (TM) at 66°C. Then 30-nm-Ag gratings with periodicity 750 nm and width 300 nm were fabricated on BST by soft ultraviolet nanoimprint lithography and subsequent lift-off process. The reflection spectra from 500 to 1000 nm with incident angle from 5° to 60° were measured at room temperature and 66°C, with a collimated and p-polarized light incident perpendicularly to the grating direction. Several modes were observed from the spectra. At 66°C, a red shift of a dip at about 850 nm by 2 nm was obtained at an incident angle of 15°. Calculations confirmed that the observed modes belong to the (−1), (2), (−2) and (3) surface plasmon modes from the Ag and BST interfaces and localized mode; the red shift by thermal tuning is also confirmed. The results indicate the feasibility of active modulation in surface plasmon resonance in solid-state structures.     

Microstructures and dielectric properties of compositionally graded (Ba1-xSrx) TiO3 thin films prepared by pulsed laser deposition

Compositionally graded (Ba_1-xSr_x)TiO₃ (BST) (x:0.0∼0.25) thin films were grown on Pt (111)/TiO₂/SiO₂/Si (100) substrates using layer-by-layer pulsed laser deposition in the temperature range 550–650 °C. Both downgraded (Ba/Sr ratio varying from 100/0 at the bottom surface to 75/25 at the top surface) and upgraded (Ba/Sr ratio varying from 75/25 at the bottom surface to 100/0 at the top surface) BST films were prepared. Their microstructures were systematically studied by X-ray diffractometry and scanning electron microscopy. A grain morphology transition from large ‘rosettes’ (>0.30 μm) to small compact grains (70–110 nm) was observed in the downgraded BST films as the deposition temperature was increased from 550 to 650 °C. No such grain morphology transition was detected in the upgraded BST films. Dielectric measurements with metal electrodes revealed an enhanced dielectric behavior in the downgraded films. This enhancement is mainly attributed to the large compressive stress field built up near the interface between the downgraded film and substrate. Furthermore, the BaTiO₃ layer in the downgraded BST films not only serves as a bottom layer but also as an excellent seeding layer for enhancing the crystallization of the subsequent film layers in the downgraded films. Received: 10 December 2001 / Accepted: 12 March 2002 / Published online: 19 July 2002 RID="*" ID="*"Corresponding author. Fax: 86-25/359-5535, E-mail: xhzhu@public1.ptt.js.cn     

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.     

Production and characterization of Nd,Cr:GSGG thin films on Si(001) grown by pulsed laser ablation

Nd,Cr:Gd₃Sc₂Ga₃O₁₂ (GSGG) thin films have been produced for the first time. They were grown on Si(001) substrates at 650 °C by pulsed laser ablation at 248 nm of a crystalline Nd,Cr:GSGG target rod. The laser plume was analyzed using time-of-flight quadrupole mass spectroscopy, and consisted of elemental and metal oxide fragments with kinetic energies typically in the range 10 to 40 eV, though extending up to 100 eV. Although films deposited in vacuum using laser fluences of 0.8±0.1 J cm⁻² reproduced the Nd,Cr:GSGG bulk stoichiometry, those deposited using fluences above ≈3 J cm⁻² resulted in noncongruent material transfer and were deficient in Ga and Cr. Attempts to grow films using synchronized oxygen or oxygen/argon pulses yielded mixed oxide phases. Under optimal growth conditions, the films were heteroepitaxial, with GSGG(001)[100]∥Si(001)[100], and exhibited Volmer–Weber-type growth. Room-temperature emission spectra of the films suggest efficient non-radiative energy transfer between Cr³⁺ and Nd³⁺ ions, similar to that of the bulk crystal. Received: 1 October 1999 / Accepted: 15 October 1999 / Published online: 23 February 2000     

溶胶-凝胶法制备的Ba0.8Sr0.2TiO3薄膜的结构及铁电性质研究

采用0.05mol/L的前驱体溶液,利用溶胶-凝胶法成功制备了室温下具有优良铁电性质的Ba_0.8Sr_0.2TiO₃ (BST)薄膜.X射线衍射分析表明,制得的BST薄膜室温下呈四方相,场发射扫描电子显微观测显示BST薄膜表面平整、致密、无裂纹出现,薄膜晶粒呈柱状结构、尺寸在150nm左右.电学测量表明制备的BST薄膜室温下具有优良的铁电性能.薄膜的剩余极化P_r约为35μC/cm²,矫顽电场E关键词：