The origin of the super-resolution via a nonlinear thin film

In laser applications, resolutions beyond the diffraction limit can be obtained with a thin film of strong optical nonlinear effect. The optical index of the silicon thin film is modified with the incident laser beam as a function of the local field intensity n(r)∼E²(r). For ultrathin films of thickness d?λ, the transmitted light through the film forms a profile of annular rings. Therefore, the device can be related to the realization of super-resolution with annular pupils. Theoretical analysis shows that the focused light spot appears significantly reduced in comparison with the diffraction limit that is determined by the laser wavelength and the numerical aperture of the converging lens. Analysis on the additional optical transfer function due to the thin film confirms that the resolving power is improved in the high spatial frequency region.     

Ultra-fast reconfigurable spatial switching between a quadratic solitary wave and a weak signal

Experimental and numerical investigations of an ultra-fast reconfigurable spatial switch based on the nonlinear interaction between a weak wave (the signal) and a solitary wave (the control) at 1548 nm are reported. The non-collinear interaction in a quadratic nonlinear film waveguide gives birth to a third switched optical beam (the idler). This beam could be steered according to the transverse spatial position of the control beam. PACS 42.65.Ky; 42.65.Re; 42.65.Wi     

Transmission property for a one-dimensional photonic crystal containing a subwavelength layer and a nonlinear layer

Using the transfer matrix method, we investigate the transmission property of a one-dimensional photonic crystal doped with a linear subwavelength layer and a Kerr-type nonlinear layer. We find that a thin film of subwavelength layer can significantly modify the characteristic of optical bistability. We also find that the sequence of the thin film and the nonlinear layer has a major impact on the hysteretic behavior. With the investigations to the linear defect mode and the electric field distribution in the nonlinear material, we explain these phenomena. PACS 42.65.Pc; 42.25.Bs; 42.70.Qs; 42.65.-k; 78.66.-w     

Ultra-fast saturable absorber through spatial self-trapping and filtering in Ti:PPLN film waveguides

Numerical and experimental investigations on ultra-fast all-optical saturable absorber on picosecond optical pulses at 1547 nm using spatial self-trapped propagation in a quadratic nonlinear film waveguide combined with spatial filtering are reported. The influences of phase-mismatch, pulse intensity and spatial filtering on the temporal reshaping mechanism are discussed to derive the optimum parameters. PACS 42.65.Ky, 42.65.Re, 42.65.Wi     

Tetracene film morphology: Comparative atomic force microscopy, X-ray diffraction and ellipsometry investigations

X-ray diffraction, atomic force microscopy and spectroscopic ellipsometry were used to study tetracene thin films as a function of deposition rate. A comparative analysis of the thickness and roughness values allows for detailed modelling of the film morphology. An interdigitated growth mode is established for the coexisting thin film and bulk phases. By comparison with the respective quinone-derivative of tetracene, we were additionally able to identify reaction products by their optical response.     

A superresolution optical disk with a combination of optical path filtering and saturable absorption techniques

Calculations have been done for the modulation transfer function of a superresolution optical disk with a combination of optical path filtering and saturable absorption techniques. The results reveal that optical path filtering alone can only equalize, to a certain degree, the spatial frequency response of the opticaldisk system, but it can not attain any response beyond the cutoff frequency. With an additional saturable absorption layer in-between the substrate and the information layer, it is found that the optical response both under and beyond the cutoff frequency can be greatly improved.     

Second harmonic generation in zinc oxide nanorods

Second-order optical nonlinearities of zinc oxide (ZnO) nanorods grown on quartz substrate were determined by optical second harmonic generation (SHG) measurements at 1064 nm fundamental wavelength. The average length of the zinc oxide nanorods ranged from 50 nm to 700 nm. By employing the Maker fringes technique, we obtained the second-order nonlinear optical coefficients d₃₃₃ and d₃₁₁. Their magnitudes and ratio are compared with that of zinc oxide thin film fabricated by different techniques. We see variations of the second-order nonlinear optical coefficients with respect to the aspect ratio of the nanorods. This is attributed to local field effects. PACS 42.65.Ky; 78.67.-n; 81.07.-b     

Pattern formation by spatially incoherent light in a nonlinear ring cavity

Modulation instability and pattern formation by spatially incoherent light is investigated experimentally in a nonlinear ring cavity using a photorefractive strontium barium niobate crystal as the nonlinear medium. A step-like threshold for the onset of pattern formation is observed experimentally for the case of high optical feedback. When compared to the case without feedback, this threshold is shifted towards smaller nonlinearities and a significant increase of the modulation degree of the obtained patterns is obtained. Our measurements also show that, above threshold, the dominating spatial frequency of the patterns decreases monotonically with both increasing nonlinearity and increasing feedback. PACS 42.65.Tg; 42.65.Sf; 89.75.Kd     

Mesoscale structures in luminescent conjugated polymer thin films studied by near-field scanning optical microscopy

We report the studies of various conjugated polymer thin films with near-field scanning optical microscopy, NSOM. Firstly, it is shown that MEH-PPV thin film undergoes significant changes in film morphology upon thermal annealing. The once homogeneous morphology becomes inhomogeneous after annealing. Secondly, polarization near-field measurements reveal mesoscale polymer ordering in PPV thin film. The average domain size and the coefficient for linear dichroism were studied as a function of film thickness. Finally, phase separation in polymer blend film was directly observed by transmission NSOM. Time-resolved fluorescence spectra indicate that the phase domains are decomposed of different fractions of the two constituent polymers. The near-field optical microscopy was also used to write lithographic patterns with a resolution of 100 nm, exceeding the diffraction limit.     

Shaping of ultrashort pulses using bulk acousto-optic filter

Our paper deals with temporal shaping of ultrashort pulses by direct spectral filtering performed with bulk acousto-optic filters using noncollinear geometry. This geometry allows arbitrary optical pulse repetition rate and high diffraction efficiency at relatively large optical apertures. A theoretical model of the pulse shaper is presented, emphasizing the degrees of freedom in this shaping technique. Phase and angular dispersion effects are analyzed, and experimental results on generating controllable pulse trains are presented. PACS 42.65.Re; 42.79.J     

Optically nonlinear phonon-polariton modes in a three-layered structure

A theory is presented for the propagation of phonon-polariton modes arising when phonons are coupled to electromagnetic waves in multilayered structures. A multi-layered structure consists of a thin film surrounded symmetrically by a bounding media. Numerical calculations are given for s-polarized phonon-polariton modes in the case where the bounding media are assumed to be semi-infinite layers with nonlinear dielectric functions of ionic crystal type supporting optical phonon modes and the thin film is characterized by a Kerr-type nonlinear dielectric function. The phonon-polaritons were found to have distinct branches characteristic of optical phonons and showing features that are different from those of plasmon-polaritons [S. Baher, M.G. Cottam, Surf. Rev. Lett. 10 (2003) 13]. The parameters that modify the modes are the in-plane wave vector, the thickness of the film, the phonon frequency and the nonlinearity of each layer. It was found that by increasing the film thickness and nonlinearity coefficient, the curves move to the left and the number of the branches increases without changing the pattern of the curves.     

Optical and electrical properties of aluminum zinc oxide (AZO) nanostructured thin film deposited on polycarbonate substrate

Transparent polymer materials, due to their unique properties, such as light weight, optical transparency, and electrical and mechanical properties, have become very attractive as a replacement for inorganic glass substrates in a wide range of optoelectronic applications. In this research, aluminum zinc oxide nanostructured thin film was deposited on polycarbonate polymer substrates using a magnetron sputtering technique. The structure, morphology, and surface composition of the thin film were investigated by X-ray diffraction and field emission scanning electron microscopy. The optical and electrical properties of the thin film were investigated by UV–VIS-NIR spectrophotometer, ellipsometer, and four point probe method. The X-ray diffraction pattern showed that the aluminum zinc oxide thin film had a polycrystalline structure. The optical and electrical results indicated that the refractive index, band gap, and sheet resistance of the aluminum zinc oxide thin film were 1.8, 3.2 eV, and 265 Ω/sq, respectively.     

可用于光存储和光学信息处理的SrS（Eu,Sm）电子俘获薄膜的研究

报道用电子束蒸发法制备的ＳｒＳ（Ｅｕ，Ｓｍ）电子俘获薄膜的特性，给出了这种薄膜的Ｘ射线衍射图、原子力显微镜（ＡＦＭ）形貌观察结果、光谱及存储的图像照片等。结果表明所制备的电子俘获薄膜具有很好的光学特性，具有应用在光存储和光学信息处理上的能力。     

有机聚合物的非线性光学

有机聚合物是一类非常重要的非线性光学材料,这是因为它在光通信和高密度光存储等高技术领域中有良好的应用前景。有机聚合物的非线性光学性质是过去２０年来理论和实验的重要研究课题。文章在简要介绍非线性光学之后,着重论述了有机聚合物光学非线性的来源和这些材料中二阶、三阶非线性光学效应及非线性光吸收的特点。最后,简要介绍了作者在有机聚合物非线性光学研究中几个近期结果,如“全光极化、三阶光学非线性的激发态增强、     

Localized structures in an optical feedback interferometer: properties and interactions

The occurrence of localized structures in a nonlinear optical experiment is a robust phenomenon, persisting in a wide region of the parameter space. We demonstrate how different control parameters determine several properties of localized structures; among these of particular relevance are the contrast and the amplitude and frequency of the oscillations appearing on the tails of the structures. Tuning these oscillations modifies the interactions between pairs of localized structures, thus resulting in a substantial modification of their bound-state spectrum. PACS 42.65.Tg; 05.45.Yv; 42.65.Sf     

CuO薄膜的三阶非线性光学特性研究

采用脉冲激光沉积技术在Si(100)和熔石英基片上制备了单相的CuO薄膜.通过X射线衍射仪,拉曼光谱仪,场发射扫描电镜和紫外可见光光度计对薄膜的结构,表面形貌和光学性质进行了表征. 场发射扫描电镜结果表明CuO薄膜中晶粒排列致密且分布均匀,其尺寸约为45nm.结合飞秒激光(800nm,50fs)和Z扫描方法测量了薄膜的三阶非线性光学特性,结果表明CuO薄膜具有超快的非线性光学响应且非线性折射率和非线性吸收系数均为负值,其大小分别为-3.96×10^-17 m^{2< 关键词： CuO薄膜 Z-扫描')" href="#">Z-扫描 三阶光学非线性}     

Theoretical assessment of optical resolution enhancement and background fluorescence reduction by three-dimensional nonlinear structured illumination microscopy using stimulated emission depletion

Three-dimensional structured illumination microscopy (SIM) enlarges frequency cutoff laterally and axially by a factor of two, compared with conventional microscopy. However, its optical resolution is still fundamentally limited. It is necessary to introduce nonlinearity to enlarge frequency cutoff further. We propose three-dimensional nonlinear structured illumination microscopy based on stimulated emission depletion (STED) effect, which has a structured excitation pattern and a structured STED pattern, and both three-dimensional illumination patterns have the same lateral pitch and orientation. Theoretical analysis showed that nonlinearity induced by STED effect, which causes harmonics and contributes to enlarging frequency cutoff, depends on the phase difference between two structured illuminations and that the phase difference of π is the most efficient to increase nonlinearity. We also found that undesirable background fluorescence, which degenerates the contrast of structured pattern and limits the ability of SIM, can be reduced by our method. These results revealed that optical resolution improvement and background fluorescence reduction would be compatible. The feasibility study showed that our method will be realized with commercially available laser, having 3.5 times larger frequency cutoff compared with conventional microscopy.     

Synthesis of CdZnO thin film as a potential candidate for optical switches

Cadmium doped zinc oxide thin films have been prepared using a thermal decomposition technique. The influence of Cd as a doping agent on the structure, optical and nonlinear optical properties was carefully investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and a UV-vis spectrophotometer. A deep correlation has been found between the surface roughness and the optical properties. The roughness is found to deteriorate the nonlinear response, such that the highest nonlinear susceptibility χ⁽³⁾ is obtained for the smoothest layer. The third-order nonlinear susceptibility χ⁽³⁾ has been calculated using the Frumer model, and is estimated to be 3.37×10⁻¹⁰ esu. The dispersion of the refractive index of the prepared thin film is shown to follow the single electronic oscillator model. From the model, the values of oscillator strength (E_d), oscillator energy (E_o) and dielectric constant (ε_∞) have been determined. The conductivity has been measured as a function of the energy of the photons, revealing marginal change at energies below 3.15 eV, while above this value there is a large increase in the conductivity. This suggests that CdZnO is a potential candidate for applications in optical devices such as optical limiter and optical switching.     

Effects of the ZnSe concentration on the structural and optical properties of ZnSe/PVA nanocomposite thin film

This study investigated the effects of ZnSe nanoparticles (NPs) on the structural and (linear and nonlinear) optical properties of polyvinyl alcohol (PVA) thin film. Three samples of ZnSe NP-doped PVA thin films with different concentrations of ZnSe were produced on a glass substrate. The ZnSe NPs were synthesized by pulsed laser ablation of the ZnSe bulk target immersed in distilled water using a 1064 nm wavelength and a high frequency pulsed Nd:YAG laser. The optical bandgap energies of the films were extracted from their UV-Vis-NIR absorption spectra. The corresponding energy bandgaps of the nanocomposite films declined as the ZnSe NPs doping concentration increased. X-ray diffraction analysis was used to characterize the crystalline phases of the ZnSe/PVA nanocomposite films. The concentration-dependent nonlinear optical absorption and nonlinear refraction behaviors of the films after exposure to 532-nm nanosecond laser pulses were investigated using the Z-scan technique. The nonlinear absorption response of the films was positive when measured using an open aperture scheme, which was attributed to the two-photon absorption mechanism. In addition, the nonlinear refraction indices had a negative value and they increased as the concentration of ZnSe NPs in the films increased.     

Microstructured Ultrathin HDPE Films Prepared by Selective Oriented Recrystallization

The recrystallization behavior of surface-modified melt-drawn HDPE thin films having a vacuum-evaporated carbon layer was studied by means of transmission electron microscopy and electron diffraction. The results show that, by surface modification with the carbon layer, the orientation of the melt-drawn highly oriented HDPE film can be preserved after complete melting and subsequent recrystallization for any condition. Based on the orientation maintenance phenomenon of the carbon-coated preoriented HDPE films, micrometer-structured, thin HDPE films with well-defined oriented and nonoriented structures were prepared by selectively coating the melt-drawn-oriented HDPE thin film with the help of a micrometer-structured mask and subsequent melt recrystallization. A potential application of the thus prepared micrometer-structured HDPE thin films stems from the fact that they exhibit conspicuous different birefringence between the areas with and without carbon coating under polarized optical microscopy. This may provide us with a new route toward polarization-dependent displays.