Mirage Effect Research Articles

Transformation design of in-plane elastic cylindrical cloaks, concentrators and lenses

We analyse the elastic properties of a class of cylindrical cloaks deduced from linear geometric transforms x→x′ in the framework of the Milton–Briane–Willis cloaking theory [New Journal of Physics 8, 248, 2006]. More precisely, we assume that the mapping between displacement fields u(x)→u′(x′) is such that u′(x′)=A−tu(x), where A is either the transformation gradient Fij=∂xi′/∂xj or the second order identity tensor I. The nature of the cloaks under review can be three-fold: some of them are neutral for a source located a couple of wavelengths away; others lead to either a mirage effect or a field confinement when the source is located inside the concealment region or within their coated region (some act as elastic concentrators squeezing the wavelength of a pressure or shear polarized incident plane wave in their core); the last category of cloaks is classified as an elastic counterpart of electromagnetic perfect cylindrical lenses. The former two categories require either rank-4 elastic tensor and rank-2 density tensor and additional rank-3 and 2 positive definite tensors (A=F) or a rank-4 elasticity tensor and a scalar density (A=I) with spatially varying positive values. However, the latter example further requires that all rank-4, 3 and 2 tensors be negative definite (A=F) or that the elasticity tensor be negative definite (and non fully symmetric) as well as a negative scalar density (A=I). We provide some illustrative numerical examples with the Finite Element package Comsol Multiphysics when A is the identity.

Super-localisation of a point-like emitter in a resonant environment: Correction of the mirage effect

<p style='text-indent:20px;'>In this paper, we show that it is possible to overcome one of the fundamental limitations of super-resolution microscopy: the necessity to be in an <i>optically homogeneous</i> environment. Using recent modal approximation results from [<xref ref-type="bibr" rid="b10">10</xref>, <xref ref-type="bibr" rid="b7">7</xref>], we show, as a proof of concept, that it is possible to recover the position of a single point-like emitter in a <i>known resonant environment</i> from far-field measurements, with a precision two orders of magnitude below the classical Rayleigh limit. The procedure does not involve solving any partial differential equation, is computationally light (optimisation in <inline-formula><tex-math id="M1">\begin{document}$ \mathbb{R}^d $\end{document}</tex-math></inline-formula> with <inline-formula><tex-math id="M2">\begin{document}$ d $\end{document}</tex-math></inline-formula> of the order of <inline-formula><tex-math id="M3">\begin{document}$ 10 $\end{document}</tex-math></inline-formula>) and is therefore suited for the recovery of a very large number of single emitters.</p>

IR photothermal and spectroscopic analysis of proton-irradiated 4H-SiC

The effect of the proton irradiation dose on thermal transport anisotropy, free carrier density, and defect formation in 4H-SiC is studied by thermal wave scattering and infrared spectroscopy. Thermal waves are generated by infrared laser pulses, and the in-plane and cross-plane thermal diffusion length are measured using the deflection of a laser probe beam due to the mirage effect. The effect of proton irradiation dose on in-plane and cross-plane thermal diffusivity is measured as a function of depth. Proton irradiation is shown to cause significant damage primarily in the direction perpendicular to the sample surface. Irradiation-induced free carriers contributing to heat transport in the sample plane are revealed by Kramers-Kronig analysis of the infrared reflectivity spectra of the studied samples. Measurements of thermal diffusion lengths in the irradiated samples are converted to depth profiles of defect density. It is shown that the highly damaged zone in irradiated 4H-SiC thickens and approaches the proton reaching depth with increasing the irradiation dose. Thermal wave scattering complemented by infrared spectroscopy is proposed as an effective approach for the directional analysis of irradiation-induced changes in physical and structural properties of materials.

Minimization of spatial cover times for impaired self-avoiding random walks: the mirage effect

Self-avoidance is a common mechanism to improve the efficiency of a random walker for covering a spatial domain. However, how this efficiency decreases when self-avoidance is impaired or limited by other processes has remained largely unexplored. Here we provide a numerical study in regular lattices for the case when the self-avoiding signal left by a walker both (i) saturates after successive revisits to a site, and (ii) evaporates, or disappears, after some characteristic time. We surprisingly reveal that the mean cover time becomes minimum for intermediate values of the evaporation time, leading to the existence of a nontrivial optimum management of the self-avoiding signal. We show that this is a consequence of a complex dynamics arising from the interplay between signal evaporation and signal saturation, in which evaporation has the capacity of creating some sort of mirages (sites or regions that the walker see as unvisited, though in fact they are not) that enhance the searcher mobility, so contributing to a more efficient exploration of the lattice that counteracts the effects of signal saturation. Remarkably, we argue both through scaling arguments and from numerical results, that this mirage effect will become more and more significant as long as the domain size increases.

Pulse Dynamics of Flexural Waves in Transformed Plates

AbstractCoordinate‐transformation‐inspired optical devices have been mostly examined in the continuous‐wave regime: the performance of an invisibility cloak, which has been demonstrated for monochromatic excitation, is likely to deteriorate for short pulses. Here, pulse dynamics of flexural waves propagating in transformed plates is investigated. A practical realization of a waveshifter and a rotator for flexural waves based on the coordinate transformation method is proposed. Time‐resolved measurements reveal how the waveshifter deviates a short pulse from its initial trajectory, with no reflection at the bend and no spatial and temporal distortion of the pulse. Extending the strategy to cylindrical coordinates, a wave rotator is designed. It is demonstrated experimentally how a pulsed plane wave is twisted inside the rotator, while its wavefront is recovered behind the rotator and the pulse shape is preserved, with no extra time delay. The realization of the dynamical mirage effect is proposed, where an obstacle appears oriented in a deceptive direction.

Laser beam steering in a variable gradient index nematic liquid crystal structure

We have fabricated a parallel slab of nematic liquid crystal with hybrid alignment that provides “longitudinal” gradient of refractive index for the extraordinary polarized beam. This in turn generates continuously changing angular separation between ordinary and extraordinary beams while propagating inside the slab, like the optical mirage effect. For the moment the output separation angle is not large (below 1°), but it can be further optimized to obtain larger separation angles and consequently more effective electrical control.

Mid-IR photothermal measurement of substantial heat transport by surface waves of polar amorphous films supported on silicon

We present measurements of significant thermal diffusivity by surface electromagnetic waves of an ultra-thin polar and amorphous dielectric film deposited on silicon (Si). We used a photothermal-beam-deflection technique with a modulated mid-infrared heating source to excite and launch surface electromagnetic waves onto the surface of an amorphous silicon carbide (a-SiC) film deposited on Si and generate periodic temperature and refractive index gradients above the sample surface. These gradients are capable of periodically deflecting a probe beam, passing very close to the surface, at the modulation frequency of the heating beam. We have fitted the measured probe beam deflection to an analytical model for the mirage effect that takes into account the thermal anisotropy of the measured sample to infer the contribution of the surface electromagnetic waves of the a-SiC film to thermal diffusivity in the plane of the sample under study. We found that reducing the thickness of the a-SiC film promotes the interaction between the surface electromagnetic waves propagating on either side of the a-SiC film, which significantly enhances thermal diffusivity in the plane of the measured sample. We also found that in-plane thermal diffusivity by surface electromagnetic waves on an amorphous silicon carbide film a few nanometers thick is several orders of magnitude greater than thermal diffusivity by phonons in silicon. We believe that the results obtained provide a better understanding of the physics of electromagnetic waves confined to solid surfaces.

Direct measurements of the magnetocaloric effect of Fe49Rh51 using the mirage effect

The magnetocaloric effect in the Fe49Rh51 alloy was systematically studied using three different approaches: in-field differential scanning calorimetry, standard direct measurement of the adiabatic temperature change, and a non-contact method based on a thermo-optical phenomenon, the mirage effect, which was able to directly test the magnetocaloric response induced by a fast magnetic field variation. The metamagnetic phase transition of Fe49Rh51 was studied in the temperature range of 290–330 K at magnetic fields up to 1.8 T through magnetic and calorimetric measurements. The estimated parameters of phase transition were comparable with the literature data. The values of adiabatic temperature change obtained with the three methods (calorimetry, standard direct measurement, and mirage-based technique), which explore three different time scales of the field variation (static field, 1 T s−1, 770 T s−1), were consistent, proving the absence of dynamic constraints in the first-order magnetostructural transition at the maximum field sweep rate.

Kondo-free mirages in elliptical quantum corrals

The quantum mirage effect is a fascinating phenomenon in fundamental physics. Landmark experiments on quantum mirages reveal atomic-scale transport of information with potential to remotely probe atoms or molecules with minimal perturbation. Previous experimental investigations are Kondo-effect based; the quantum mirages appear only near the Fermi energy. This strongly limits the exploration of the mechanism and potential application. Here we demonstrate a Kondo-free quantum mirage that operates in a wide energy range beyond Fermi energy. Together with an analytical model, our systematic investigations identify that the quantum mirage is the result of quantum interference of the onsite electronic states with those scattered by the adatom at the focus of elliptical quantum corrals, where two kinds of scattering paths are of critical importance. Moreover, we also demonstrate the manipulation of quantum mirages with pseudo basic logic operations, such as NOT, FANOUT and OR gates.

Key signal contributions in photothermal deflection spectroscopy

We report on key signal contributions in photothermal deflection spectroscopy (PDS) of semiconductors at photon energies below the bandgap energy and show how to extract the actual absorption properties from the measurement data. To this end, we establish a rigorous computation scheme for the deflection signal including semianalytic ray tracing to analyze the underlying physical effects. The computation takes into account linear and nonlinear absorption processes affecting the refractive index, thus leading to a deflection of the probe beam. We find that besides the linear mirage effect, nonlinear absorption mechanisms make a substantial contribution to the signal for strongly focused pump beams and sample materials with high two-photon absorption coefficients. For example, the measured quadratic absorption contribution exceeds 5% at a pump beam intensity of about 1.3×105W/cm2 in Si and at 5×104W/cm2 in GaAs. In addition, our method also includes thermal expansion effects as well as spatial gradients of the attenuation properties. We demonstrate that these effects result in an additional deflection contribution that substantially depends on the distance of the photodetector from the readout point. This distance dependent contribution enhances the surface related PDS signal up to two orders of magnitude and may be misinterpreted as surface absorption if not corrected in the analysis of the measurement data. We verify these findings by PDS measurements on crystalline silicon at a wavelength of 1550 nm and provide guidelines on how to extract the actual attenuation coefficient from the PDS signal.

Direct measurement of the magnetocaloric effect on micrometric Ni-Mn-(In,Sn) ribbons by the mirage effect under pulsed magnetic field

In this work, we report on the direct measurement of the magnetic field induced temperature change in a series of micrometric thick ribbons of Ni-Mn-In-Sn Heusler alloys, performed with an innovative experimental technique based on the thermo-optical “Mirage Effect.” The technique combines very fast measurement time, 1 T pulsed magnetic field in the millisecond range, and contactless temperature detection. These features make the technique ideal for the characterization of thin samples with a thickness down to a few micrometers. In this work, we demonstrate this by directly measuring the magnetocaloric effect (MCE) of micrometric-thick ribbons of Heusler alloys at the Curie transition, which was tuned on a wide temperature range by varying the Sn to In ratio. The direct test of the MCE in thin samples is fundamental for the development of refrigerant elements with a large heat-transfer coefficient and for the design of solid state micro devices for cooling and energy harvesting.

Spin-wave beam propagation in ferromagnetic thin films with graded refractive index: Mirage effect and prospective applications

Using analysis of iso-frequency contours of the spin-wave dispersion relation, supported by micromagnetic simulations, we study the propagation of spin-wave (SW) beams in thin ferromagnetic films through the areas of the inhomogeneous refractive index. We compare the transmission and reflection of SWs in areas with gradual and step variation of the SW refractive index. In particular, we show the mirage effect for SWs with narrowing SW beam width, and an application of the gradual modulation of the SWs refractive index as a diverging lens. Furthermore, we study the propagation of SWs in ferromagnetic stripe with modulated refractive index. We demonstrate that the system can be considered as the graded-index waveguide, which preserves the width of the SW beam for a long distance-the property essential for prospective applications of magnonics.

Thermal Characterization of Clay Roof Tile Using Photothermal Deflection Technique

In this research, a non-destructive, simple and rapid method, photothermal deflection technique or the so-called “mirage effect”, is setup. A flat and smooth sample is heated by a modulated 532 nm 14 mW pump beam on the surface. The heat flow induced by the surface layer is detected by the 632 nm 0.14 mW probe beam. The frequency-dependent signal in the range of 1 - 800 Hz is measured by lock-in amplifier in term of amplitude and phase. The clay roof tile with and without the waterproof glaze layer on top are the measured samples. The results give the thermal diffusivities of the clay roof tile and the waterproof glaze layer of 0.67 mm2s-1 and 2.32 mm2s-1, respectively.

One-way self-collimated acoustic beams in two-dimensional asymmetric sonic crystals with circulating fluids

We theoretically realized the one-way self-collimation effect of acoustic beams in two-dimensional sonic crystals (SCs), which are composed of irregular rigid rods surrounded by circulating fluids. The parity symmetry (P symmetry) and time-reversal symmetry (T symmetry) of the circulating-fluid SCs (CFSCs) are broken by the asymmetric crystal lattice and the circulating fluids. A large isolation of >30 dB with a maintained wavefront and frequency is realized for output acoustic beams launched in opposite directions. By applying the gradient angular velocities of the circulating fluids, the one-way self-collimated acoustic beams can be bent gradually, yielding an acoustic mirage effect. The one-way self-collimation in CFSCs provides an avenue for manipulating acoustic beams independently of the nonlinearity and mode conversion.

Millisecond direct measurement of the magnetocaloric effect of a Fe2P-based compound by the mirage effect

We present direct measurements of the magnetocaloric effect on a Fe2P-based compound induced by a milliseconds pulsed magnetic field of 1 T to test their possible use in high frequency (up to 100 Hz) thermomagnetic cycles. The reported measurements were performed with an innovative and versatile non-contact set up based on the mirage effect. The adiabatic temperature change of a MnFeP0.45As0.55 sample is presented and compared with measurements performed varying the same magnetic field in a time interval of 1 s and 100 ms. These results demonstrate the absence of kinetic constraints in the first-order phase transition of this sample induced on the milliseconds time scale. The study of the materials' response to millisecond magnetic field pulses represents a fundamental test for the development of more powerful and efficient magnetic refrigerators.

Investigations of Thermal, Optical, and Electric Properties as a Function of Composition for $$\hbox {ZnS}_{x}\hbox {Se}_{1-x}$$ ZnS x Se 1 - x Crystals

$$\hbox {ZnS}_{x}\hbox {Se}_{1-x}$$ single crystals with different S contents were examined. The crystals were grown by the modified Bridgman method. Thermal, optical, and electrical measurements for a solid solution of $$\hbox {ZnS}_{ x}\hbox {Se}_{1-x}$$ crystals are presented and analyzed to determine the influence of composition on the thermal diffusivity, the electrical resistivity, the relative permittivity, and the energy gap. The thermal measurement was based on the thermal wave method with detection using the mirage effect. For interpretation of the experimental data, a thermal model of a layered system was adopted. The results showed that the thermal diffusivity of samples decreases with an increase of the S content $$x$$ . The electrical resistivity of investigated samples was measured by the constant voltage method. The relative permittivity was determined by dielectric spectroscopy and decreased with increasing sulfur content in the ZnSe. Further, the optical bandgap of $$\hbox {ZnS}_{ x}\hbox {Se}_{1-x}$$ was determined from photoluminescence spectra. Possible correlations between the thermal diffusivity, the optical bandgap, and electrical properties were studied. The obtained results showed a clear dependence of those parameters on the S concentration in the sample.

A study of optothermal and AC impedance properties of Cr-doped Mn3O4 sprayed thin films

Chrome-doped Mn3O4 thin films were grown on the glass substrates by the spray pyrolysis technique at 350°C. XRD diffraction and Raman spectroscopy analysis revealed that all samples have tetragonal spinel structure with a preferred orientation along the direction (101). Absorption coefficient has been measured using both transmission and mirage effect. The band gap energy decreases from 2.2 to 1.9eV with Cr content while Urbach energy value increases from 354 to 473meV. Also, thermal conductivity was evaluated. Finally, physical properties have been evaluated and discussed in terms of alteration of the band gap edges, electrical patterns and mirage effect.

Physical investigations on NiMn2O4 sprayed magnetic spinel for sensitivity applications

NiMn2O4 ternary nickel manganese oxide thin films spinels have been grown on glass substrates at 350°C through spray pyrolysis technique. X-ray diffraction and Raman spectroscopy analyses show that the synthesized film has mainly cubic spinel structure with a preferred orientation along (111) plane. Some optical constants such as the refractive index (n), extinction coefficient (k), Urbach energy (EU=342eV) and optical energy band gap (Eg=1.07eV) have been calculated from reflection-transmission spectra. The mirage effect technique has been used to estimate the thermal conductivity (Kc). Its value is Kc=25Wm−1K−1. The real part of the ac the conductivity behaviour has been investigated in the frequency range 100Hz to 1MHz. It was found that the real conductivity follows a power law (Aωs). The dc conductivity has been studied in the temperature range from 250°C to 375°C and supports the variable range hopping model proposed by Mott. The activation energy value estimated from the relaxation frequency is Ea~0.32eV. Moreover, the temperature dependency of the resistance indicates that conduction was well described by a variable range hopping model, in which electron transfer takes place between Mn3+ and Mn4+ ions.

Formation and characterisation of copper oxide coating for absolute radiant laser power measurement absorbing cavity

The aim of this work is to optimise the different parameters for realisation of an absorbing cavity to measure the incident absolute laser energy. Electrochemical oxidation is the background process that allowed the copper blackening. A study of the blackened surface quality was undertaken using atomic force microscopy (AFM) analysis and ultraviolet-visible-infrared spectrophotometry using a Shimadzu spectrophotometer. A two-dimensional and three-dimensional microscopy of the formed oxide coating made by AFM shows that the copper surfaces became porous after electrochemical etching with different roughnesses. This aspect becomes more and more important with decreasing current density anodisation. In a 2 mol.L−1 NaOH solution at a temperature of 90°C and using a 16 mA/cm² constant density current, copper oxide formed has a reflectivity of around 5% in the spectral range between 300 nm and 1800 nm. Using 'mirage effect' technique, the obtained Cu2O diffusivity and thermal conductivity are, respectively, equal to (11.5 ± 0.5) 10−7 m2s−1 and (350 ± 20) Wm−1K−1. This allows us to consider that our Cu2O coating is a good thermal conductor. The results of optical and thermal study dictate the choice of the cavity design. The absorbing cavity is a hollow cylinder machined to its base at an angle of 30°. If the included angle of the plan is 30° and the interior surface gives specular reflection, an incoming ray parallel to the axis will undergo six reflections before exiting the device. So, the absorption of the surface becomes closely near 0.999999.

Study and characterization of porous copper oxide produced by electrochemical anodization for radiometric heat absorber.

The aim of this work is to optimize the different parameters for realization of an absorbing cavity to measure the incident absolute laser energy. Electrochemical oxidation is the background process that allowed the copper blackening. A study of the blackened surface quality was undertaken using atomic force microscopy (AFM) analysis and ultraviolet-visible-infrared spectrophotometry using a Shimadzu spectrophotometer. A two-dimensional and three-dimensional visualization by AFM of the formed oxide coating showed that the copper surfaces became porous after electrochemical etching with different roughness. This aspect is becoming more and more important with decreasing current density anodization. In a 2 mol L -1 of NaOH solution, at a temperature of 90°C, and using a 16 mA cm2 constant density current, the copper oxide formed has a reflectivity of around 3% in the spectral range between 300 and 1,800 nm. Using the ‘mirage effect’ technique, the obtained Cu2O diffusivity and thermal conductivity are respectively equal to (11.5 ± 0.5) 10 to 7 m2 s-1 and (370 ± 20) Wm-1 K-1. This allows us to consider that our Cu2O coating is a good thermal conductor. The results of the optical and thermal studies dictate the choice of the cavity design. The absorbing cavity is a hollow cylinder machined to its base at an angle of 30°. If the included angle of the plane is 30° and the interior surface gives specular reflection, an incoming ray parallel to the axis will undergo five reflections before exit. So the absorption of the surface becomes closely near 0.999999.