Tunable beam focusing based on optical bistability with a composite Kretschmann configuration involving a Kerr medium

A beam focuser with a composite Kretschmann configuration involving a Kerr medium is investigated theoretically. The structure employs a silver film with four slits filled with the Kerr medium. Optical bistability and beam focusing are demonstrated, and changes to the incident intensity result in optical bistability characteristics in the reflection, focused intensity, spot size, and depth of focus. The proposed structure has the potential to be applied for optical switching and nano-illumination.     

Optical bistability of surface plasmon polaritons in nonlinear Kretschmann configuration

Optical bistability based on surface plasmon polaritons in the Kretschmann configuration involving a Kerr nonlinear medium is described by analytical solutions. The conditions of forming the optical bistability with different parameters are explored. The resonant angle of surface plasmon polaritons varying with the incident light intensity also generates the phenomenon of bistability. The system could form optical bistability with the special thickness of the metal film and incident angle. This kind of system has potential application in all-optical networks.     

Bistability of a self-standing film caused by photothermal displacement

We report on the bistability of a self-standing thin film caused by photothermal displacement. The sample consisted of a self-standing thin film placed in front of a mirror. By irradiating the self-standing thin film with continuous wave laser light, the self-standing thin film deflected with thermoelastic bending moment. Since a standing wave of the laser light was generated by the reflection of the mirror, the bending moment generated on the film was periodic along the optical axis. The displacement of the film was found to be bistable with the laser light intensity. Simultaneously, the light intensity reflected from the sample was also bistable. These phenomena are explained by the photothermal displacement of thin film in the standing wave of laser light.     

Mirrorless optical bistability in a semiconductor-doped-glass plate as a result of oblique incidence

A procedure to obtain optical bistability in a third-order nonlinear film (or parallel plate) of low refractive index without any external mirrors is investigated both theoretically and experimentally. If an s-polarized light is incident obliquely at a large angle of incidence on the film, the generation of optical bistability can be expected because of the resulting increase in the reflectivity at the surfaces. Arigorous analysis of the stationary transmission characteristics of the nonlinear film is done for both positive and negative nonlinear coefficients with a plane-wave model. In the experimental demonstration, a CdS(x)Se(1-x)doped glass (Hoya Y-52) plate and a cw Ar(+) laser are used as the nonlinear material and the light source, respectively. It is shown that three operations of optical bistability, optical limiting, and differential gain can be easily obtained through adjustment of the angle of incidence as an initial detuning. The measured nonlinearity is thermal, and the magnitude and sign of the nonlinear refractive index are determined.     

Atomic layer deposition of nanocrystallite arrays of copper(I) chloride for optoelectronic structures

Zinc blende structure γ-copper(I) chloride is a wide bandgap semiconductor with high exciton and biexciton binding energies. γ-CuCl has applications in UV-wavelength optoelectronic structures which can exploit these characteristics, such as 4-wave mixing and optical bistability. For these purposes, a controllable method of achieving thin films and nanocrystallite arrays is necessary. Atomic layer deposition (ALD) of nanocrystallites and thin films of γ-CuCl under restricted conditions has previously been demonstrated. This paper greatly extends the previous work and unequivocally confirms that ALD growth takes place over a range of deposition parameters, as characterised by growth saturation with increasing precursor dose, deposition rate independent of temperature and linear growth rate once a complete film has been formed. Arrays of nanocrystallites of different sizes can be controllably deposited by varying the number of ALD cycles within the initial nucleation region. In this region two distinct growth regimes have been observed depending on the length of the post-chloride precursor purge pulse. Long purge time results in retarded nucleation whereas short pulse time shows enhanced nucleation compared to a strictly linear process. The zinc blende γ-CuCl phase was confirmed with both X-ray analysis and also the signature excitonic Z_1,2 and Z₃ peaks in optical absorption, with no evidence of other impurities. This demonstrates that ALD is a suitable technique for the controllable deposition of thin films and arrays of nanocrystallites of CuCl which may facilitate the use of CuCl in thin film or nanocluster form for further exploration in optoelectronic and photonic applications.     

碲氧溅射薄膜的光学性质

碲氧薄膜是很有希望的可擦写光盘介质材料。本文用射频溅射技术制备碲氧系统的薄膜。测定热处理前后薄膜的光学特性(光透过率、反射率、折射指数、光吸收系数和光能隙)和 X 射线衍射特性,并研究了这些性能与靶材的组份关系,还测定了这些薄膜激光喇曼光谱,并讨论它们的结构特征。     

Development of thickness measurement program for transparent conducting oxide thin films

The gallium doped zinc oxide has been one of the candidates for the transparent conducting oxide thin film electrode. It is not suitable to use a conventional light interference method to measure the thickness of the gallium doped zinc oxide thin film because the refractive index and extinction coefficient of the thin film is unknown during the optimization of the deposition conditions. In this paper, we report on the details of the film thickness program which uses the measured optical and electric properties and relationship between the plasma frequency and the optical constant of the film. The obtained film thickness of the prepared gallium doped zinc oxide thin film using the program was comparable with thicknesses measured by a cross-sectional analysis of the atomic force microscopy and the surface profiler. Moreover, the optical constant of refractive index and extinction coefficient of the film could also be estimated.     

光学薄膜的激光诱导损伤与材料带隙的关系

采用多光子吸收电离模型讨论了光学薄膜的激光诱导损伤与其材料带隙的关系,报实际光学薄膜存在大量的非化学计量比化合物缺陷时,损伤阈值的变化,给出了光汪膜的损伤阈民其材料带隙的关系曲线,理论上解释了实际光学薄膜较理想光学薄膜的损伤阈值的主要原因可能是实际光学薄膜中存在大量的非化学计量比化合物缺陷。     

Mikroskop-photometrische Untersuchungen des Wachstums von Silbersulfidschichten

Microscopic-Photometric Investigations of the Growth of Silver Sulfide Films. Corrosion phenomena are often characterized by the presence of thin surface films the thickness of which may be very important for determining either the behaviour of the base material or that of the corrosion film itself. The paper describes an optical method for investigating the film thickness and the growth of absorbing surface films. With the aid of a microscopic-photometric method the spectral reflectivity of thin films, at perpendicular incidence of light, is determined and compared with theoretically calculated curves with the optical constants of the base material and film material being known. This method proved suitable for investigating the tarnishing process of silver in a sulphurous atmosphere. Films as from a thickness of approx. 1 nm could be measured. Growth curves for silver sulfide films at different temperatures are given and the phenomenon of tarnishing is discussed in more detail.     

Characterization of vapor-deposited l-leucine nanofilm

X-ray reflective measurements (XRR), atomic force microscopy and single wavelength ellipsometry were used to investigate the optical properties of thin l-leucine films deposited onto silicon substrates. The ellipsometry data (Ψ,Δ) were fitted with a four-layer-model, and the optical refractive index of the l-leucine film measured with ellipsometry was determined to be 1.37. With the conventional effective medium approximation theory and the ellipsometry results, the density of the l-leucine nanofilm was determined to be 70% (0.81 g/cm³) of crystalline l-leucine. This value was in good agreement with the density of 69% (0.80 g/cm³) obtained with XRR measurement. The ellipsometry measurements also enabled us to estimate the surface roughness or absorption layer of the film. This procedure of combined XRR and ellipsometry measurements could be a powerful tool for the determination of the (otherwise hard-to-determine) refractive index in thin organic material films with a rough surface layer.     

CuInS2 thin films obtained by spray pyrolysis for photovoltaic applications

Copper indium disulphide, CuInS₂, is a promising absorber material for thin film photovoltaic which has recently attracted considerable attention due to its suitability to reach high efficiency solar cells by using low-cost techniques. In this work CuInS₂ thin films have been deposited by chemical spray pyrolysis onto glass substrates at ambient atmosphere, using different composition solutions at various substrate temperatures. Structural, chemical composition and optical properties of CIS films were analysed by X-ray diffraction, energy dispersive X-ray spectroscopy and optical spectroscopy. Sprayed CIS films are polycrystalline with a chalcopyrite structure with a preferential orientation along the <112> direction and no remains of oxides were found after spraying in suitable conditions. X-ray microanalysis shows that a chemical composition near to stochiometry can be obtained. An optical gap of about 1.51 eV was found for sprayed CIS thin films.     

MnBi films for magnetooptic recording

Progress made during the past years in the area of magnetooptic data storage by the computer industry has been most impressive. Many material media and physical phenomena have been developed for this particular application. It now appears that a large capacity (gsim 10^{10}bits) magnetooptic data store possessing major advantages over the conventional recording techniques could be developed. Of the many materials and techniques advanced to date, the use of thin films of MnBi for thermomagnetic writing, erasing, and magnetooptic reading has received particularly intensive study because of the many unique properties of this film medium. In order to provide an assessment of the potential of this medium for optical memory application, we have included in this review the pertinent material physical properties of MnBi; the memory characteristics in regard to read, write, and erase operation; the physical process involved in the writing and erasure by thermomagnetic technique; the technique for detection of written information; and the utilization of this medium for magnetic holographic storage. Emphasis is given to the material properties and physical phenomena, rather than the systems considerations in using MnBi films for optical memory.     

Study of structural,optical and electrical parameters of ZnSe powder and thin films

Nanocrystalline ZnSe powder and thin film forms have been synthesized via chemical bath deposition technique. The ZnSe thin films are deposited onto ultrasonically clean glass substrates in an aqueous alkaline medium using sodium selenosulphate as Se^2? ion source. The ZnSe powder and thin film are characterized by structural, optical and electrical properties. It is confirmed from X-ray diffraction study that cubic phase is present in ZnSe thin film form with (111) as preferred orientation and hexagonal phase is present in ZnSe powder form with (100) as preferred orientation. Optical absorption measurement indicates the existence of direct allowed optical transition with a wide energy gap and blue shift in the fundamental edge has been observed in both cases. The optical band gap of ZnSe powder is greater than the thin film. The electrical conductivity (both dark and photoconductivity) measurements are also carried out in different temperature range and variation in activation energy has been calculated.     

Isomerization and optical bistability of DR1 doped organic–inorganic sol–gel thin film

To investigate the isomerization process of the disperse red 1 (DR1) doped TiO₂/ormosil thin film, both the photo-isomerization and the thermal isomerization of the thin films were observed as a change of the absorption spectrum. Under a real-time heat treatment, the change of the linear refractive index shows a thermal stable working temperature range below T_g. The optical bistability (OB) effect of the DR1 doped thin films based on different matrices was studied and measured at a wavelength of 532 nm. Results indicate that the TiO₂/ormosils based thin film presents a better OB-gain than that of the poly (methyl methacrylate) (PMMA) based thin film due to its more rigid network structure. Moreover, it is also noted that higher titanium content is helpful for enhancing the OB-gain of the as-prepared hybrid thin films.     

Electro-reflectance and electro-transmittance in thin films of gold

The electro-reflectance and electro-transmittance of gold films have been measured using an electrolytic cell technique and the spectral variation of the effect has been established as a function of the film thickness. The electrolytic electric field causes a shift of the electro-reflectance peak to lower photon energies as the film becomes less than 20 nm thick. A relationship has been established between the normal reflectance and transmittance of the system and the changes in these with electric field. These effects have been predicted quantitatively with a theoretical model which takes into account only the modulation of the first surface of the charge carrier enhanced layer and uses the free electron component contribution to the optical constants together with interference within a thin absorbing film. This model has been used to predict the electro-reflectance effects previously observed with silver.

With very thin films (less than 10 nm) discrepancies arise due to the fact that the optical properties of the thin film material are no longer those of the bulk. In this case it has been shown that on the same model it is possible to use the derivative of the reflectance of the thin film with respect to frequency to obtain a prediction of the electro-reflectance exhibited.     

高功率脉冲磁控溅射制备ZnO薄膜的研究进展

氧化锌薄膜材料由于具有高电导率、良好的光学透过率、原料储存丰富、成本低廉的特点,被认为是最具有潜力的透明导电薄膜.特别是其宽禁带(3.37eV)和高达60meV的激子束缚能,使其在环境温度制备同质结发光器件、太阳能电池电子传输层具有巨大的应用前景.然而,传统制备方法难以实现薄膜质量的综合调控,存在p-ZnO稳定性差、制...     

Review of the fundamentals of thin-film growth

The properties of a thin film of a given material depend on the film's real structure. The real structure is defined as the link between a thin film's deposition parameters and its properties. To facilitate engineering the properties of a thin film by manipulating its real structure, thin-film formation is reviewed as a process starting with nucleation followed by coalescence and subsequent thickness growth, all stages of which can be influenced by deposition parameters. The focus in this review is on dielectric and metallic films and their optical properties. In contrast to optoelectronics all these film growth possibilities for the engineering of novel optical films with extraordinary properties are just beginning to be used.     

Optical bistability and multistability in an open ladder-type atomic system

A novel scheme is proposed for controlling the optical bistability and multistability in an atomic system. In an open ladder-type three-level atomic system, it is shown that, by adjusting the ratio between atomic injections and exit rates from the cavity, the intensity threshold of optical bistability can be controlled. The effect of incoherent pumping field and spontaneously generated coherence (SGC) on optical bistability for different values of exit rates is also discussed. It is found that SGC makes the medium phase dependent, so the optical bistability and multistability threshold can be controlled via relative phase between applied fields. Moreover, it is shown that the optical bistability can be switched to optical multistability, which is favorable for the next generation of all-optical systems and quantum networks.     

Preparation of ZnO:Al thin film on transparent TPT substrate at room temperature by RF magnetron sputtering technique

Aluminum doped ZnO thin films (ZnO:Al) deposited on flexible substrates are suitable to be used as transparent conductive oxide (TCO) thin films in solar cells because of the excellent optical and electrical properties. TPT films are a kind of composite materials and are usually used as encapsulation material of solar panels. In this paper, ZnO:Al film was firstly deposited on transparent TPT substrate by RF magnetron sputtering. The structural, optical, and electrical properties of the film were investigated by X-ray diffractometry (XRD), scanning electron microscope (SEM), UV–visible spectrophotometer, as well as Hall Effect Measurement System. Results revealed that the obtained film had a hexagonal structure and a highly preferred orientation with the c-axis perpendicular to the substrate. Also, the film showed a high optical transmittance over 80% in the visible region and a resistivity of about 3.03 × 10^? 1 Ω·cm.     

环形腔中非线性周期结构介质的双稳态和光限

研究了环腔中的非线性周期结构介质的光学双稳态和光限现象，建立了输入光强与输出光强关系的表达式。理论上给出了临界入射光强低达１０＾７Ｗ／ｃｍ＾２的光学双的条件和非常有效的限光作用的条件。