Determination of optical parameters of very thin (λ/50) films

2008 ◽  
Vol 47 (28) ◽  
pp. 5117 ◽  
Author(s):  
Petya Gushterova ◽  
Peter Sharlandjiev ◽  
Boian Hristov
Keyword(s):  
Optical Parameters

Computer-Assisted High-Re Solution TEM

1990 ◽  
Vol 48 (1) ◽  
pp. 162-163
Author(s):  
F.A. Ponce ◽  
H. Hikashi
Keyword(s):  
Signal To Noise Ratio ◽  
Accurate Determination ◽  
Computer Software ◽  
Video Camera ◽  
Image Contrast ◽  
Objective Lens ◽  
Computer Assisted ◽  
Optical Parameters ◽  
Astigmatism Correction

The determination of the atomic positions from HRTEM micrographs is only possible if the optical parameters are known to a certain accuracy, and reliable through-focus series are available to match the experimental images with calculated images of possible atomic models. The main limitation in interpreting images at the atomic level is the knowledge of the optical parameters such as beam alignment, astigmatism correction and defocus value. Under ordinary conditions, the uncertainty in these values is sufficiently large to prevent the accurate determination of the atomic positions. Therefore, in order to achieve the resolution power of the microscope (under 0.2nm) it is necessary to take extraordinary measures. The use of on line computers has been proposed [e.g.: 2-5] and used with certain amount of success.We have built a system that can perform operations in the range of one frame stored and analyzed per second. A schematic diagram of the system is shown in figure 1. A JEOL 4000EX microscope equipped with an external computer interface is directly linked to a SUN-3 computer. All electrical parameters in the microscope can be changed via this interface by the use of a set of commands. The image is received from a video camera. A commercial image processor improves the signal-to-noise ratio by recursively averaging with a time constant, usually set at 0.25 sec. The computer software is based on a multi-window system and is entirely mouse-driven. All operations can be performed by clicking the mouse on the appropiate windows and buttons. This capability leads to extreme friendliness, ease of operation, and high operator speeds. Image analysis can be done in various ways. Here, we have measured the image contrast and used it to optimize certain parameters. The system is designed to have instant access to: (a) x- and y- alignment coils, (b) x- and y- astigmatism correction coils, and (c) objective lens current. The algorithm is shown in figure 2. Figure 3 shows an example taken from a thin CdTe crystal. The image contrast is displayed for changing objective lens current (defocus value). The display is calibrated in angstroms. Images are stored on the disk and are accessible by clicking the data points in the graph. Some of the frame-store images are displayed in Fig. 4.

scholarly journals Radiative forcing of the desert aerosol at Ouarzazate (Morocco)

2018 ◽  
Vol 37 ◽  
pp. 03004
Author(s):  
Abdelouahid Tahiri ◽  
Mohamed Diouri
Keyword(s):  
Optical Properties ◽  
Atmospheric Aerosol ◽  
Radiative Forcing ◽  
Cloud Formation ◽  
Optical Parameters ◽  
Aerosol Radiative Forcing ◽  
Daily Average ◽  
Definition Of ◽  
Aerosol Radiative

The atmospheric aerosol contributes to the definition of the climate with direct effect, the diffusion and absorption of solar and terrestrial radiations, and indirect, the cloud formation process where aerosols behave as condensation nuclei and alter the optical properties. Satellites and ground-based networks (solar photometers) allow the terrestrial aerosol observation and the determination of impact. Desert aerosol considered among the main types of tropospheric aerosols whose optical property uncertainties are still quite important. The analysis concerns the optical parameters recorded in 2015 at Ouarzazate solar photometric station (AERONET/PHOTONS network, http://aeronet.gsfc.nasa.gov/) close to Saharan zone. The daily average aerosol optical depthτaer at 0.5μm, are relatively high in summer and less degree in spring (from 0.01 to 1.82). Daily average of the Angstrom coefficients α vary between 0.01 and 1.55. The daily average of aerosol radiative forcing at the surface range between -150W/m2 and -10 W/m2 with peaks recorded in summer, characterized locally by large loads of desert aerosol in agreement with the advections of the Southeast of Morocco. Those recorded at the Top of the atmosphere show a variation from -74 W/m2 to +24 W/m2

Photo-acoustic determination of optical parameters of tissue-like media with reference to opto-acoustic diffraction

1997 ◽  
Vol 12 (4) ◽  
pp. 357-363 ◽  
Author(s):  
S. Lohmann ◽  
Chr. Ruff ◽  
Chr. Schmitz ◽  
H. Lubatschowski ◽  
W. Ertmer
Keyword(s):  
Optical Parameters ◽  
Acoustic Diffraction

Simple method for the determination of optical parameters of inhomogeneous thin films

1999 ◽  
Vol 342 (1-2) ◽  
pp. 153-159 ◽  
Author(s):  
Liberato De Caro ◽  
Maria Cristina Ferrara
Keyword(s):  
Thin Films ◽  
Optical Parameters ◽  
Simple Method

scholarly journals Diffuse Interstellar Bands – The Unidentified Part of the Interstellar Absorption Spectrum

1989 ◽  
Vol 135 ◽  
pp. 67-86 ◽  
Author(s):  
Jacek Krełowski
Keyword(s):  
Absorption Spectrum ◽  
Line Of Sight ◽  
Optical Parameters ◽  
Interstellar Matter ◽  
Molecular Absorption ◽  
Interstellar Clouds ◽  
Diffuse Interstellar Bands ◽  
Intensity Ratios ◽  
Molecular Abundances

The unidentified (since 1921) diffuse interstellar bands (DIBs) are discussed together with their relations to other interstellar absorptions sucn as: continuous extinction, polarization and atomic or molecular absorption lines. It is shown that DIBs do not form the absorption spectrum of one agent, but probably of several (3 or more). DIBs as well as other interstellar absorptions are usually formed in several clouds along a line-of-sight. Thus, they suffer Doppler splitting; the first high resolution profiles free of the latter effect are described. Since single interstellar clouds may differ not only in radial velocities but also in many physical (optical) parameters, the observed interstellar absorptions are ill-defined averages over all clouds situated along any line-of-sight. It is of basic importance to determine not only the single cloud profiles of diffuse bands, but also their relations to other interstellar absorptions in the same clouds. Intensity ratios of DIBs are shown to be sensitive to the shapes of extinction curves, depletion patterns of elements and molecular abundances in the considered clouds. The sensitivity of the DIBs to the variation in polarization is less documented but probably also present. Thus the diffuse lines are presented as the unidentified part of the absorption spectrum of interstellar matter. Their identification depends on the determination of their relations to other interstellar absorptions which must be determined precisely.

Study of temperature sensitive optical parameters and junction temperature determination of light-emitting diodes

2012 ◽  
Vol 100 (20) ◽  
pp. 202108 ◽  
Author(s):  
Yue Lin ◽  
Yu-Lin Gao ◽  
Yi-Jun Lu ◽  
Li-Hong Zhu ◽  
Yong Zhang ◽  
...  
Keyword(s):  
Light Emitting Diodes ◽  
Junction Temperature ◽  
Temperature Sensitive ◽  
Optical Parameters ◽  
Light Emitting ◽  
Temperature Determination

Determination of optical parameters of organic and inorganic thin films using both surface plasmon resonance and Abelès-Brewster methods

Optik ◽  
2017 ◽  
Vol 142 ◽  
pp. 426-435 ◽  
Author(s):  
Y.M. Espinosa-Sánchez ◽  
D. Luna-Moreno ◽  
M. Rodríguez-Delgado ◽  
A. Sánchez-Álvarez
Keyword(s):  
Thin Films ◽  
Surface Plasmon Resonance ◽  
Surface Plasmon ◽  
Plasmon Resonance ◽  
Optical Parameters ◽  
Inorganic Thin Films
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