Optical constants of gold in the soft-x-ray region from reflection and transmission measurements

The optical constants of gold deposited on 300-nm-thick freestanding polyimide films have been measured in the energy range of 40-1350 eV. The optical constants of the polyimide films were known from a previous investigation. By performing both transmission measurements with Kramers-Kronig analysis and multiangle reflection measurements with analysis by fitting to a Fresnel multilayer model including roughness, one could carry out a detailed error analysis. In the energy range above 500 eV systematic deviations between the results obtained by both methods were found. For gold films the discrepancies can be attributed to deviations from Beckmann-type behavior at small grazing-incidence angles.     

Optical transmission measurements of silver, silver-gold alloy and silver-gold segmented nanorods in thin film alumina

Silver nanorods have been grown by electrodeposition into thin film porous alumina. Transmission measurements show two peaks related to the transverse and longitudinal resonance of the nanorods. The behaviour of the longitudinal resonance peak is found to vary with nanorod length and the spectral position to depend on nanorod diameter. As the distance between the nanorods is decreased a small blue-shift of the longitudinal peak is observed. Depositing a small gold cap on top of the silver nanorods causes a red-shift of the longitudinal peak whilst, conversely, the longitudinal peak of gold nanorod arrays is comparatively insensitive to the deposition of a silver cap. Gold-silver alloy nanorods were also deposited from a mixed salt bath and a linear dependence of the transverse peak position on alloy composition was observed.     

Improved method for determination of optical constants of organic thin films from reflection and transmission measurements

A new technique for determining the optical properties of organic thin films is presented. A detailed evaluation of the accuracy of the determined optical constants has been performed, and the best combination of measured values yielding the smallest errors in the index of refraction for realistic experimental uncertainties has been found. The proposed method utilizes the fact that optical constants are smooth continuous functions, which reduces the possibility of encountering multiple solutions. The method consists of two steps. In the first step the optical constants at all wavelengths and the film thickness are determined. In the second step the thickness and the imaginary part of the index of refraction are kept fixed while we reevaluate the real part of the index of refraction by using a different objective function with improved sensitivity to the refractive index. After verifying that the proposed method is capable of an accurate estimation of optical constants, we determine the index of refraction data of vanadyl-phthalocyanine in the visible spectral range.     

Optical constants in the IR from thin film interference and reflectance: the reststrahlen region of muscovite mica

A new technique for determining the IR optical constants of materials that can be formed into thin films is presented. At a given wavelength the thickness of the film t, the index of refraction n, and the extinction coefficient k combine to produce interference effects in the film, which in turn control reflectance from the film. When reflectance is plotted vs thickness the resultant curve is a unique function of n and k. Values of n and k are determined by curve fitting. The technique is illustrated using thin films of muscovite mica, and values of n and k are reported for wave numbers from 1200 to 400 cm-1, which include the reststrahlen region of mica.     

Optical constants of the nano-crystal and polymer composite thin film PbTiO3/PEK-c

Composite thin films of PbTiO₃ nano-crystals and high transparency PEK-c polymer were prepared by spin coating. The size of PbTiO₃ nanocrystals was evaluated to be 30–40 nm. The transparency spectra of PEK-c composite thin film in 360–800 nm were measured. The optical constants n, k of the film in the wavelength range 400–620 nm were investigated by the transmission spectrum. The dispersion of refractive index fits well to a three-term Sellmeier relation. At 633 nm wavelength the refractive index of PbTiO₃/PEK-c film was measured to be 1.6628 by a prism coupling method and showed a good agreement with the calculated value using the Sellmeier relation.     

Integrated transmission lines for magnetic thin film memories

The pulse transmission properties of integrated strip lines are examined for a structure that has been proposed for application in a large capacity, high-speed magnetic film memory. The lines are vacuum-deposited onto an insulated ground plane and are characterized by low impedances. Previous analyses, such as those given by Eastman and Chang, McQuillan, and Harloff, examine the effects of skin-depth losses in lines which are assumed to be perfectly terminated. In general, this type of analysis is insufficient for lines which are lossy and which have resistive terminations. The present analysis considers skin-effect losses in the ground plane and in the strip conductors separately and also includes the effect of reflections from resistive terminations. The influence of heavy magnetic loading of the transmission line due to the presence of magnetic film devices is examined in detail. A computer program, similar to the one described by Bertin, has been used to obtain numerical results for the pulse response of the transmission lines. Data are presented which demonstrate the influence of line geometry and material properties.     

Optical tomographic image reconstruction from ultrafast time-sliced transmission measurements

Optical imaging and localization of objects inside a highly scattering medium, such as a tumor in the breast, is a challenging problem with many practical applications. Conventional imaging methods generally provide only two-dimensional (2-D) images of limited spatial resolution with little diagnostic ability. Here we present an inversion algorithm that uses time-resolved transillumination measurements in the form of a sequence of picosecond-duration intensity patterns of transmitted ultrashort light pulses to reconstruct three-dimensional (3-D) images of an absorbing object located inside a slab of a highly scattering medium. The experimental arrangement used a 3-mm-diameter collimated beam of 800-nm, 150-fs, 1-kHz repetition rate light pulses from a Ti:sapphire laser and amplifier system to illuminate one side of the slab sample. An ultrafast gated intensified camera system that provides a minimum FWHM gate width of 80 ps recorded the 2-D intensity patterns of the light transmitted through the opposite side of the slab. The gate position was varied in steps of 100 ps over a 5-ns range to obtain a sequence of 2-D transmitted light intensity patterns of both less-scattered and multiple-scattered light for image reconstruction. The inversion algorithm is based on the diffusion approximation of the radiative transfer theory for photon transport in a turbid medium. It uses a Green s function perturbative approach under the Rytov approximation and combines a 2-D matrix inversion with a one-dimensional Fourier-transform inversion to achieve speedy 3-D image reconstruction. In addition to the lateral position, the method provides information about the axial position of the object as well, whereas the 2-D reconstruction methods yield only lateral position.     

Retrieval of optical constants and thickness of thin films from transmission spectra

We discuss a new method to estimate the absorption coefficient, the index of refraction, and the thickness of thin films using optical transmission data only. To solve the problem we used a pointwise constrained optimization approach, defining a nonlinear programming problem, the unknowns of which are the coefficients to be estimated, with linear constraints that represent prior knowledge about the physical solution. The method applies to all kinds of transmission spectra and does not rely on the existence of fringe patterns or transparency. Results on amorphous semiconductor thin films and gedanken films are reported. They show that the new method is highly reliable.     

Determination of the orthotropic elastic constants of thin PET film by an ultrasonic micro-spectrometer

The elastic constants of a thin polyethylene terephthalate (PET) film, whose thickness was 12 mum, were determined from the acoustic reflection coefficients. The reflection coefficients were measured by an ultrasonic micro-spectrometer (UMSM), and all of the elastic constants were obtained through the fitting of a theory to the dip points of the magnitude of the reflection constants where leaky Lamb waves were excited. As a result, the film was found to be an orthotropic material, and the observed elastic constants were consistent with those measured by tensile tests. Besides, the in-plane shear modulus was found to be much larger than the out-of-plane shear moduli. Then, the reflection coefficients were calculated using the obtained stiffness matrix. The calculated values reproduced not only the dip points but also the change in magnitude of measured reflection coefficients depending on the frequency and the incident angle. These agreements suggest that the stiffness matrix components were determined accurately.     

光学薄膜及其发展现状

介绍了传统光学薄膜的原理,并对反光膜、增透膜、纳米光学薄膜等传统光学薄膜的研究现状及应用情况,以及几种新型光学薄膜如高强度激光器、金刚石及类金刚石膜、软X射线多层膜、光电通信用光学薄膜的研究现状及应用进行了详细分析;最后对光学薄膜的发展前景进行了展望。     

Optical constants of float glass, nickel, and carbon from soft-x-ray reflectivity measurements

Angular-dependent reflectivity was measured with a dynamic range of 5-6 orders of magnitude at ~20 different photon energies in the range from 40 to 800 eV with the HASYLAB reflectometer with synchrotron radiation. Several float-glass substrates and a number of sputtered Ni and C films were investigated to improve the accuracy. The optical constants were obtained from least-squares fits of theoretical reflectivity curves, taking into account the influence of film thicknesses and surface and interface roughnesses. All samples with Ni and C films were produced on float-glass substrates, with Ar as the sputter gas, in the low-pressure triode-assisted sputtering facility of the Sincrotrone Trieste.     

Optical constants of thermally evaporated amorphous GeSe3 thin films

The optical transmission spectra of amorphous Ge-Se films of chemical composition GeSe₃, prepared by thermal evaporation, are measured overthe 300 nm to 2500 nm spectral region. A simple, straightforward procedure suggested by Swanepoel, which is based on the use of interference fringes, has been applied in order to derive the real and imaginary parts of the complex refractive index, and also the film thickness. Furthermore, thickness measurements made by a surface-profiling stylus are also carried out to cross-check the results obtained by the present optical method, employing only T(). The dispersion of n is discussed in terms of the single-oscillator Wemple and DiDomenico model, and the optical band gap E _g ^opt has been determined from the absorption coefficient values, using the Tauc procedure.     

Optical properties of NAEC-PMMA nonlinear polymeric thin film

Novel guest nonlinear optical (NLO) chromophore molecules (4-nitrobenzene)-3-azo-9-ethylcarbazole (NAEC) were doped in poly (methyl methacrylate) (PMMA) host with a concentration of approximately 15% by weight. For a useful macroscopic electro-optic (EO) effect, these NLO molecules NAEC were arranged in a noncentrosymmetric structure in the host polymer by corona-onset poling at elevated temperature (COPET). For applying NAEC-PMMA polymer in optical devices such as EO switch, its optical properties have been investigated. The UV/Visible absorption spectra for the unpoled and poled polymer film were determined. The refractive index of the film was also determined from measurements of the coupling angles with the reflective intensity at 632.8 nm wavelength. Using the simple reflection technique, the EO coefficient ₃₃ value was measured as 60 pm/V at 632.8 nm wavelength. The second-order nonlinear coefficient d ₃₃ was characterized by the second-harmonic-generation (SHG) experimental setup and the calculated d ₃₃ value reached 18.4 pm/V at 1064 nm wavelength. The relation between the second-order nonlinear coefficients d ₃₃ and d ₁₃ for the poled polymer film was also discussed in detail and the ratio d ₃₃/d ₁₃ value was obtained as 3.3.     

Optical constants of CdS thin films prepared by spray pyrolysis

CdS thin films were prepared by spray pyrolysis techniques. Variable angle spectroscopic ellipsometry was used for optical constant calculations. Multiple angle measurements were taken in the most sensitive angle of incidence region. The sensitive regions of angle of incidence were obtained theoretically using 3-dimensional graph ofδψ andδΔ. Real partn and imaginary partk of the complex refractive index of the samples were calculated in the wavelength range 470–650 nm, taking into account surface roughness. Bruggeman’s effective medium approximation is used for analysis of the surface rough layer of the thin films.