Mirage Effect Research Articles

Graded photonic crystals curve the flow of light: An experimental demonstration by the mirage effect

We report the experimental demonstration of a beam curvature in graded photonic crystals via a spectacular mirage effect. A two-dimensional structure of metallic rods is constructed to produce this effect in the microwave domain near 10GHz. Experimental results are in excellent agreement with theoretical predictions, thus, proving the versatility of graded photonic crystals in view of their integration in future photonic circuits.

Determination of thermal conductivity and diffusivity of soaked steels using the “Mirage effect” method

In this work, we intend to study the thermal properties of the soaked steels like XC48 and their evolution according to the heating temperature and for different soaking media, using the “Mirage effect” method which permits the simultaneous determination of thermal conductivity and diffusivity. We have observed a discontinuity of thermal conductivity and diffusivity at the temperature of the ferro-paramagnetic transition.

Optical and thermal properties of doped semiconductor

The knowledge of doping effects on optical and thermal properties of semiconductors is crucial for the development of optoelectronic compounds. The purpose of this work is to investigate theses effects by mirage effect technique and spectroscopic ellipsometry SE. The absorption spectra measured for differently doped Si and GaAs bulk samples, show that absorption in the near IR increases with dopant density and also the band gap shifts toward low energies. This behavior is due to free carrier absorption which could be obtained by subtracting phonon assisted absorption from the measured spectrum. This carrier absorption is related to the dopant density throw a semi-empirical model.

Photothermal investigations of thermal and optical properties of liquids by mirage effect

In this paper, the “mirage effect” detection technique was used in order to determine the thermal diffusivity and the absorption spectrum of liquids. Experiments were more particularly realized with paraffin oil. Generally, since the thermal diffusion length is relatively short in liquids, the different parts of the probe beam are differently deflected by the heat flow. So, a new mathematical expression of the deflection related to the probe beam dimensions was established to calculate the “effective” deflection in liquids. Such an expression was used to measure the thermal diffusivity of paraffin oil. Then, the “mirage effect” technique was also used to obtain indirectly the optical spectrum of paraffin oil through the measurement of the absorption of a carbon black layer immersed in this liquid.

Electromagnetic analysis of cylindrical invisibility cloaks and the mirage effect

We present a finite-element analysis of a diffraction problem involving a coated cylinder enabling the electromagnetic cloaking of a lossy object with sharp wedges located within its core. The coating consists of a heterogeneous anisotropic material deduced from a geometrical transformation as first proposed by Pendry [Science 312, 1780 (2006)]. We analyze the electromagnetic response of the cloak in the presence of an electric line source in p polarization and a loop of magnetic current in s polarization. We find that the electromagnetic field radiated by such a source located a fraction of a wavelength from the cloak is perturbed by less than 1%. When the source lies in the coating, it seems to radiate from a shifted location.

Thermal Lensing in a Supercritical Water Medium

A pulsed, two-beam, thermal lensing experiment was performed to determine the concentration of aqueous solutes above the critical point of water. Despite a very significant mirage effect due to thermal gradients in the cell and absorption by water itself, the thermal lensing signal strength for aqueous benzoic acid in supercritical water was found to be linear with concentration in the sub-millimolar range. Although thermal lensing experiments in aqueous media are notoriously insensitive, the sharp density gradient near the critical point considerably improves the signal intensity. In this study a short-pulse pump 266 nm YAG laser and continuous low-power probe Ar ion beam were both focused into a supercritical water cell, giving a lensing signal whose strength could be maximized by changing the overlap of the two beams.

Photothermal measurement with mirage effect for investigation of LiNbO3single crystals

Results of measurements of the thermal diffusivity of pure and doped lithium niobate single crystals are presented. A reference sample was a pure crystal. The others were doped with: Cu (0.05%at.), Dy (0.1 %at., 1.0%at., and 1.7%at.), and Er + Yb (1.0%at. Er + 1.0%at. Yb) ions. Thermal properties were determined in [100], [120] and [001] crystallographic directions. Experimental studies were carried out using photothermal method based on mirage effect. This method based on determination of a phase lag connected with propagation ofa thermal wave in investigated sample. Obtained results showed considerable anisotropy of the thermal diffusivity of pure crystal and doped samples. The thermal properties in [001] direction (c-axis) is higher than in directions perpendicular to it. Unexpectedly, anisotropy of the thermal diffusivity in plane (001) was also observed.

Princípio e utilização da técnica de efeito miragem de concentração

The aim of this work is to present the theoretical and experimental aspects of the mirage effect technique. We are especially interested in the concentration mirage effect, which is a powerful tool in the study of electrochemical reactions that produce ionic movements close to electrodes and to get some fundamental information on mass transport and charge transfer during electrochemical processes. Limitations of this technique are discussed as well as the recent attempts to overcome them.

Simultaneous determination of thermal conductivity and diffusivity of solid samples using the “Mirage effect” method

We propose in this work a new method based on the “Mirage effect” which permits the simultaneous determination of thermal conductivity and diffusivity. This method consists in comparing the experimental photothermal signal variation with the square root of the modulation frequency to the corresponding theoretical one. The coincidence between the experimental and theoretical curves will permit to deduce the values of thermal diffusivity and conductivity. The obtained values of thermal conductivity and diffusivity are in good agreement with those existing in literature (Table 1).

Vibration focusing in two dimensions: Constructing elliptical mirrors on the nanoscale

Concentrated vibrational energy transfer from one of the focal points of an elliptically shaped Ar island, adsorbed on different metal surfaces, into the second focus at finite temperatures is demonstrated. A comparison to a free Ar cluster of the same shape is made. A possible influence on the electronic quantum mirage effect is discussed.

Mirage and superbending effect in two-dimensional graded photonic crystals

We present a study of graded photonic crystals presenting a mirage effect. This light bending is understood through parametric studies of the isofrequency curves. We derive a model based on the effective index computation and on the Eikonal equation in order to demonstrate that photonic mirages originate from the same physical principles as atmospheric mirages. A graded photonic crystal presenting a superbending effect is proposed for designing a bent waveguide.

Characterization of metallic atomic structures using the mirage effect

A combined theoretical and experimental method has been developed to characterize the crystal structures of metals and alloys. This method is based on the mirage effect and can be applied to study unknown defect and heat-treated structures. Using a laser beam with a Gaussian distribution made it possible to design a simple algorithm to describe the frequency response of a crystal structure to a modulated thermal action for the case of photothermal deflection. This algorithm can establish the most probable crystalline modification of the structure to be tested. Samples of quenched and annealed steels have been studied. This method should finally be verified by studying a material subjected to substantially different heat treatments.

Liquid–Solid Interface Waves with Laser Ultrasonic and MirageEffect

We experimentally investigate the transparent-liquid/solid(water/aluminum or steel) interface waves generated by laser pulses anddetected by the Mirage effect. It is shown that nearly all kinds ofliquid/solid interface waves in water are detected, both their measuredwave velocities and characteristic of shape are in good agreement withtheoretical predictions.

The interferometric mirage effect method: The determination of the thermal diffusivity of CdMnTe

A Michelson interferometer was used as a precise detector in the Mirage effect configuration in order to determine the thermal diffusivity of the diluted magnetic semiconductor Cd1−xMnxTe, in the concentration range 0<x<0.6 at room temperature. This zinc-blende ternary alloy exhibits an almost linear behavior of the thermal diffusivity as a function of Mn concentration. This trend is similar to that of the energy gap against Mn concentration, which increases linearly as the nominal x value increases. The latter result was tested by electrolytic electroreflectance measurements.

Doping effect on thermal diffusivity of pyrochlore Sm2-xSrxMo2O7

Doping effects on thermal diffusivity have been investigated in pyrochlore Sm 2-x Sr x Mo 2 O 7 (0.2≤x≤0.6) by means of mirage effect at 300K. Substitution of the Sr ions for Sm ions increases the value of the thermal diffusivity from 0.49 cm 2 /s at x=0.2 to 0.58 cm 2 /s at x=0.6. The increase of the thermal diffusivity is ascribed to the variation of the structure of the pyrochlore.

Investigation of the critical behavior at lyotropic systems by collinear mirage technique

We investigate the behavior of the thermal diffusivity (D) in the vicinity of the nematic to isotropic (N - I) and uniaxial to biaxial (N - N) phase transitions for different lyotropic liquid crystals. For the first time, collinear mirage effect technique is used to observe that the presence of a peak in the thermal diffusivity is accomplished by a phase transition due to the variation at the sample's temperature. Furthermore, we show that our experimental setup is sensitive to both first and second order transitions in lyotropic systems. We also propose a critical exponent related to the thermal diffusivity.

Superior mirage effect in supercritical CO 2: Experiment and model

At temperatures near T c, supercritical CO 2 is highly compressible and it follows that a small temperature gradient will create a large density gradient. We established stable density gradients by maintaining the bottom of a sc-CO 2-cell cooler than its other sides. That created a large refractive index gradient that bent a laser beam through an angle that is roughly proportional to the density gradient. Such light bending causes, for example, the mirage of water on a hot road. A He–Ne laser beam traversed a 7.62 cm long cell and was deflected downward as much as 5.9°. The magnitude of the beam deflections agreed within 3% with a model that used only fundamental geometrical optics and known PVT data, but that employed no adjustable parameters.

Thermodiffusion study in ferrofluids through collinear mirage effect

We studied some thermodiffusion effects for ferrofluid samples with two different kinds of surfactant by mirage effect technique. We focused a laser beam in the sample introducing a heat gradient that provoked ferroparticles mobility (thermodiffusion) and analyzed the behavior of the mirage signal as a function of the pump laser beam intensity, for a fixed frequency. The main results showed that for the ferrofluid with anionic surfactant no thermodiffusion variation was verified, even for the most concentrated sample. On the other hand, for the cationic one we observed an increase in the thermodiffusion with greater ferroparticles concentration. Therefore, we showed that collinear mirage effect technique can be used for detecting Soret effect generated by the thermal interactions between the laser radiation and the highly absorbing material.

Electropolymerization of 3-methylthiophene studied by multiflux convolution

The electropolymerization of 3-methylthiophene (3-MeTh) in LiClO 4 + CH 3CN is monitored by in situ probe beam deflection (Mirage effect). Analysis of current and beam deviation dependences with time at constant potential (chronoamperometry and chronodeflectometry) is made by using a new treatment based on parallel convolutions with transfer functions specific to each species moving between the electrode and the solution. Considered species are monomers arriving at the electrode, oligomers and protons produced by the polymerization reaction and anions coming from the electrolyte for balancing the oxidation of the polymer. The mechanism of P(3-MeTh) formation is confirmed and quantitative determination of reaction and transport properties is made, allowing an estimation of the proportion of oligomers undertaking deposition onto the electrode with respect to oligomers released towards the solution.

Analysis of laser-induced vibrations to detect non-adhesive regions of coatings

A method is presented to find areas in coatings, which show no adhesion to the substrate. The combination of a Q-switched Nd : YAG laser as a non-destructive excitation tool and a laser-doppler-vibrometer as a contact-free measuring device was found to be useful for gaining information about qualitative adhesion conditions. We made use of two different mechanisms to excite the samples: direct irradiation generates thermoelastic waves, whereas ignition of a breakdown in air leads to shock wave generation and indirect excitation of the sample. We give evidence that the vibrations of areas that show no adhesion to the substrate correlate with membrane vibrations. In addition we show how the Mirage effect becomes visible in our experimental setup.