Optimization of a perfect absorber multilayer structure by genetic algorithms

Background: An increasing interest has been recently grown in the development of nearly perfect absorber materials for solar energy collectors and more in general for all the thermophotovoltaic applications. Methods: Wide angle and broadband perfect absorbers with compact multilayer structures made of a sequence of ITO and TiN layers are here studied to develop new devices for solar thermal energy harvesting. Genetic Algorithms are introduced for searching the optimal thicknesses of the layers so to design a perfect broadband absorber in the visible range, for a wide range of angles of incidence from 0° to 50°, and for both polarizations. Results: Genetic Algorithms allow to design several optimized structures with 6, 8, and 10 layers reaching a very high average absorbance of 97%, 99% and 99.5% respectively together with a low hemispherical total emissivity (<20%) from 200 °C till 400 °C. Conclusions: The proposed multilayer structures use materials with high thermal stability, and high melting temperature, can be fabricated with simple thin film deposition techniques, appearing to have very promising applications in solar thermal energy harvesting

Optimization of Perfect Absorbers with Multilayer Structures

We study wide-angle and broadband perfect absorbers with compact multilayer structures made of a sequence of ITO and TiN layers deposited onto a silver thick layer. An optimization procedure is introduced for searching the optimal thicknesses of the layers so as to design a perfect broadband absorber from 400nm to 750 nm, for a wide range of angles of incidence from 0◦ to 50◦, for both polarizations and with a low emissivity in the mid-infrared. We eventually compare the performances of several optimal structures that can be very promising for solar thermal energy harvesting and collectors

Picosecond time scale imaging of mechanical contacts

By means of an ultrafast opto-acoustic technique we study the nanoindentation of thin chromium films on sapphire substrates using a ceramic ball bearing. Acoustic pulses at 40 GHz returning from the film–indenter interface allow the film indentation profiles to be probed to sub-nanometer resolution over contact areas 25 lm in radius. The deformation of the films during loading is hereby revealed. Furthermore, thermal wave imaging of the contact at megahertz frequencies is simultaneously achieved

A realistic interpretation of quantum wavefunctions as temperature dependent vacuum polarization waves

We discuss in this paper a novel interpretation of Born rule as an approxi-mated thermodynamic law which emerges from the interaction of a quantumsystem with a non-stationary thermal bath associated to vacuum fluctuationsinduced by external environment radiation. In particular we assume thatvacuum polarization is a real non relativistic phenomena caused by hiddenvacuum charge oscillations which diffuses heat energy in a dispersive and dis-sipative dielectric medium with a temperature dependent speed of propaga-tion. We propose a model which couples vacuum wavefunctions to vacuumcharge fluctuations and we deduce a temperature dependent running finestructure constant function proportional, at first approximation, to thesquared of the effective electron charge and compatible with known experi-mental data. We interpret the vacuum symmetry breaking energy fluctuationsinduced in scattering experiments of particle physics and in laser assisted nu-clear reactions as thermal quasi-monochromatic beams produced by the de-cay of hidden non equilibrium massive photons propagating with a variablelight speed. We suggest, exploiting an old analogy between plasmons andpseudo Goldstone bosons, to interpret heat diffusion of this non relativisticpolarized vacuum as a real De Broglie electromagnetic scalar wave associatedto the radiation emitted by the hidden massive photons with accelerationproportional to vacuum Unruh like temperature. We predict a temperaturedependent deviation from Coulomb law and a generalized dispersive law ofthese hidden unstable photons that could be revealed as not stationary col-oured noise in experiments on anomalous heat diffusions associated to thedecay of unstable accelerated pairs produced in nuclear physics experiments.We discuss then how our proposal of a temperature dependent non relativis-tic vacuum polarization might be applied to deduce a dynamic generalizationof Born rule based on a realistic interpretation of quantum wavefunctions as averaged electromagnetic waves of hidden massive photons. Finally we sug-gest to test our time asymmetric model looking for very fast oscillating po-larization thermal waves emitted during the not instantaneous wavefunctioncollapse and revealed as not stationary bulk heating effects in experiments onaccelerated conductors and nanoconductor

A note on the history of photoacoustic, thermal lensing, and photothermal deflection techniques

We review the history of photoacoustic, thermal lensing, and photothermal deflection techniques from early experiments to the current time. The paper also describes the main fields of application in chronological order, showing the primary advantages and listing initial technological development

Optimization of transparent metal structures by genetic algorithms

In this article the general problem of designing high performances Transparent Metal structures is deeply discussed. In particular the Genetic Algorithms are introduced as useful tool for searching the optimal thicknesses of the layers. The article deeply analyses the effect of all parameters of the Genethic Algorithms so to optimize the computational time in the optical filter design. As an example the article reviews the basic steps for the design of a particular metallo/dielectric multilayer structure made of nine layers

Optimization of thermochromic VO2 based structures with tunable thermal emissivity

In this paper, we design and simulate VO2/metal multilayers to obtain a large tunability of the thermal emissivity of infrared (IR) filters in the typical mid wave IR window of many infrared cameras. The multilayer structure is optimized to realise a low emissivity filter at high temperatures useful for military purposes. The values of tunability found for VO2/metal multilayers are larger than the value for a single thick layer of VO2. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4739489

Relationship between corneal temperature and i0ntraocular pressure in healthy Individuals. a clinical thermographic analysis

To study the geographical distribution of corneal temperature (CT) and its influence on the intraocular pressure (IOP) of healthy human volunteers. Materials and Methods. Fifteen subjects (7 M, 8 F), 33.8 +/- 17.4 years old, were enrolled in this pilot, cross-sectional study. Measurements of CT were taken after one hour with closed eyelids (CET) or closed eyelids with a cooling mask (cm-CET) and compared to baseline. Results. If compared to baseline, after CET, average CT significantly increased by 0.56 degrees C in the RE and by 0.48 degrees C in the LE (p < 0.001) and IOP concomitantly significantly increased by 1.13 mm Hg and 1.46 mm Hg, respectively, in each eye (p < 0.001). After cm-CET, average CT significantly decreased by 0.11 degrees C and 0.20 degrees C, respectively, in the RE and LE (RE p = 0.04; LE p = 0.024), followed by a significant IOP decrease of 2.19 mm Hg and 1.54 mm Hg, respectively, in each eye (RE p < 0.001; LE = 0.0019). Conclusion. Significant variations of CT occurred after CET and cm-CET and were directly correlated with significant differences of IOP. It can be speculated that both oxidative stress and sympathetic nerve fiber stimulation by temperature oscillations may affect the regulation of AH vortex flow and turnover, thus influencing IOP values

Light scattering from a rough metal surface: theory and experiment

There is still great interest in the determination of microtopographic properties of rough metallic surfaces from light scattering measurements. According to Beckmann–Kirchhoff theory a clear relationship is established between the in-plane angular scattered light intensity and the statistical properties of the surface. We discuss one way to invert this relationship, and we introduce a new iterative procedure to retrieve the height autocorrelation function even for a very rough metallic surface (rms surface roughness of the same order of the optical wavelength). The procedure is eventually applied to the experimental data of a known metallic surface for validation

Method for thermal diffusivity measurements based on photothermal deflection

The thermal diffusivity measurement through pulsed photodeflection in a modified collinear configuration is presented and discussed; comparison between theory and experiment is also shown