Search results for "Attenuation coefficient"
showing 10 items of 62 documents
Optimization of a polarization imaging system for 3D measurements of transparent objects
2009
This paper presents a multispectral imaging system for 3D reconstruction of transparent objects based on "shape from polarization" technique. The originality of this work relies on a multispectral active lighting system which enables to cope with the two ambiguities on the zenith angle and azimuth angle. A calibration step allows optimising the polarimetric measurements. Example of a reconstructed transparent object is presented.
Effects of spatial dispersion and damping on exciton absorption
1986
Exciton absorption is studied in the spatially dispersive case. The energy-propagation properties of the medium are used to define the absorption coefficient. The interplay of dispersion and damping in determining the absorption coefficient is discussed and a critical value of the damping above which the dispersion effects disappear is derived analytically. Furthermore, the dependence of the spectral and of the integrated absorption coefficient on the auxiliary boundary condition is discussed.
Electronic structure and optical properties of CdTe rock-salt high pressure phase
2003
This paper reports on optical absorption and reflectance measurements in thin CdTe samples up to 15 GPa. All studied samples become virtually opaque at the pressure transition between the zinc-blende and rock-salt phases (3.9 GPa). As pressure increases up to 10 GPa, a relative transparency region is observed between 1.2 eV and 2.4 eV, whose high energy edge shifts to higher photon energies. Above 10 GPa the transparency region gradually shrinks and disappears at about 11 GPa. The low energy side of the absorption spectrum is attributed to free carrier absorption, as electronic structure calculations show that rock-salt CdTe is a semimetal or a low gap semiconductor. Band filling effects lo…
Spectroscopic ellipsometry applied to phase transitions in solids: possibilities and limitations
2009
The possibilities of in situ spectroscopic ellipsometry applied to phase transitions investigation in oxide thin films and crystals are examined in this work, along with the use of various parameters calculated from ellipsometric data (band gap energy Eg, refractive index n and surface roughness) together with the directly measured main ellipsometric angles psi and Delta, for the detection of phase transitions. The efficiency of spectroscopic ellipsometry on "surface" phase transition and its sensitivity to surface defects are also demonstrated.
On the Semiconductor Spectroscopy for Identification of Emergent Contaminants in Transparent Mediums
2021
In this chapter, we present a theoretical study of photoelectronic processes in experimental silicon \({n}^{+}{\text{-}}p{\text{-}}{n}^{+}\) structures with applications in identifying emergent contaminants in aqueous medium. Contribution due to various mechanisms of photon absorption to the total photocurrent is calculated. Various mechanisms, such as the influence of tunneling on the spectral characteristic and selective spectral photosensitivity of samples under investigation were investigated. The nature of the relationship between energy parameters of the absorbed waves and the structural parameters is revealed. Expressions are obtained for photocurrent with and without external diffus…
Excitonic absorption and Urbach's tail in bismuth sulfide single crystals
1988
The absorption coefficient of bismuth sulfide single crystals has been measured through more than four orders of magnitude and in the range of energies from 1.25 to 1.70 eV. A detailed study as a function of temperature has been carried out from 29 to 300 K. An Urbach tail for low values of absorption has been found. This tail and its temperature evolution fit the expression for ionic materials. An excitonic region appears at low temperature and the shape of the exciton peak is Gaussian, which corresponds to a strong exciton-phonon coupling. The exciton binding energy is estimated (28±3 meV) and then the energy gap at 29 K is obtained (Eg=1.523±0.003 eV). The fundamental electronic transiti…
A thin absorbing layer at the center of a Fabry-Pérot interferometer
1994
The influence of a dye (Rhodamin B) dissolved in solution or adsorbed at an interface at the center of a Fabry-Perot interferometer on the transmission was investigated both experimentally and theoretically. We show that (i) spectra of extremely thin films are measurable at sub-monolayer concentration (one monolayer reduces the transmission by ≃50%), (ii) the transmission is sensitive to the location of an extremely thin film within nm range and (iii) the absorption coefficient is determined quantitatively by comparison between theory and experiment thus permitting one to estimate the local concentration. The results are relevant for the use of dye probes to monitor changes of organic inter…
Attenuation of the fourth sound in liquid helium II via extended thermodynamics
2004
Abstract This work continues a study begun in previous works, where a non-standard model of liquid helium II is proposed, in which a small entropy transfer is associated with the superfluid component. In this work the influence of this superfluid entropy on the propagation of the fourth sound is analyzed. From experimental data for velocities and attenuations of the first and second sound, the model provides speed and attenuation coefficient of the fourth sound in a porous medium as a function of the ratio ss/s between the superfluid entropy ss and the total entropy s. These values are determined in the two limiting cases ss/s=0 and =0.02, for various values of temperature and pressure.
Monte Carlo calculation of dose rate distributions around 192Ir wires.
1997
Monte Carlo calculations of absolute dose rate in liquid water are presented in the form of away-along tables for 1 and 5 cm 192 Ir wires of 0.3 mm diameter. Simulated absolute dose rate values can be used as benchmark data to verify the calculation results of treatment planning systems or directly as input data for treatment planning. Best fit value of attenuation coefficient suitable for use in Sievert-integrals-type calculations has been derived based on Monte Carlo calculation results. For the treatment planning systems that are based on TG43 formalism we have also calculated the required dosimetry parameters.
Suppression of the frequency drifts in polarization modulational instability spectra by means of a photon reservoir
2012
By appropriately combining the effects of second- and fourth-order dispersion, and by carefully choosing the pump power, we create a photon reservoir which suppresses the drifts of sidebands in the spectra of polarization modulational instability