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  • 1
    Electronic Resource
    Electronic Resource
    Thermal diffusivity measurements on solids using collinear mirage detection (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 1539-1547 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A report on the adequacy of the collinear mirage technique for thermal diffusivity measurements on bulk homogeneous solids is presented. A 3D theoretical model for collinear deflection has been developed from which two simple linear relations between measurable parameters and the thermal diffusivity have been obtained. Two methods, the so-called zero-crossing and phase methods, are discussed in detail. The second one seems to be a promising tool for thermal diffusivity determination. It has been validated by means of experimental measurements on a set of samples with known thermal diffusivities. The technique is restricted to semitransparent solids but is also valid for materials with either high or low thermal diffusivities, being specially useful for this last group.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354854
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  • 2
    Electronic Resource
    Electronic Resource
    Photothermal detection and characterization of a horizontal buried slab by the mirage technique (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 3031-3037 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a theoretical and experimental analysis of the mirage detection and measurement of a semi-infinite horizontal buried slab of air within opaque solids. A detailed study on the effects introduced by the mirage parameters (pump and probe beam sizes, probe beam height) as well as by the surface features is discussed. We use pump and probe beams orthogonally superimposed, and detection is made of the amplitude and phase of the normal component of the mirage deflection. Air slabs with a thickness (e2) as low as 0.1 μm and located down to a depth (e1) of 0.3(square root of)ks (ks is the thermal diffusivity of the material) can be easily observed. Detection improves as the pump radius (a) and probe height (z0) increase, although a compromise is necessary because of signal attenuation. Determination of e1 and e2 through the model fitting, requires an independent control of a and z0. The use of low frequencies avoids the effects of surface features on the slab detection. However, for surface planar horizontal steps, their height must be incorporated into the model as a variation of z0 in order to characterize the slab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349334
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  • 3
    Electronic Resource
    Electronic Resource
    Thermal diffusivity measurements in solids by the "mirage'' technique: Experimental results (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 1216-1223 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This work provides the experimental confirmation of a generalized theory for thermal diffusivity measurements of solid samples using the "mirage'' technique presented by the authors in a previous paper [A. Salazar, A. Sanchez-Lavega, and J. Fernandez, J. Appl. Phys. 65, 4150 (1989)]. Moreover the influence of different effects on such determinations has been analyzed, and the limits of validity of the method have been established. The most important influence relies on the finite nature of two parameters: the height of the probe beam above the sample surface h and the radius of the exciting beam a. Such effects in all solids are discussed in detail according to their bulk thermo-optical properties and for two ways of measuring: "bouncing'' (probe beam sent to the sample surface at a small angle) and "skimming'' (probe beam parallel and grazing the surface). The first way of measuring gives reliable results while the second one must be managed with care. In any case, significant shifts in the thermal diffusivity measurement for nonzero values of h and a are specially observed when the thermal diffusivity of the sample is much lower than that of the deflecting medium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347306
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  • 4
    Electronic Resource
    Electronic Resource
    Photothermal measurements near a 90° edge. I. Mirage deflection by a free edge (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 536-547 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The presence of a 90° edge (corner) modifies substantially the photothermal signal generated by a focused and modulated laser beam incident on an opaque sample. A 3-D model has been developed in order to calculate the ac thermal fields in the sample and adjacent gas, as well as the mirage deviations in the gas. This model incorporates the effects introduced by the finite size of the Gaussian pump beam, and the height and size of the Gaussian probe beam. The experimental measurements of the mirage normal (φn) and transverse (φt) deflections confirm the theoretical predictions. The spatial symmetric forms, of both functions, relative to the exciting point, are broken by the thermal wave scattering produced by the edge. In particular, the inner (close to the edge) parts of φn and φt show an enhancement in their magnitude and phase. For imaging inspection (scanning the sample with probe and pump beams centered), there is an elevation in the magnitude of φn but a drop in its phase at distances smaller than the sample's thermal diffusion length. However, the most prominent change takes place in φt (both in magnitude and phase), which gives the signature of the presence of the edge.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355266
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  • 5
    Electronic Resource
    Electronic Resource
    Photothermal measurements near a 90° edge. II. Characterization of subsurface rectangular voids and close planar cracks (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 548-557 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigate the scattering of spherical thermal waves by planar subsurface structures located close to the corner of an opaque and thermally thick sample. Two kinds of planar features have been studied theoretically and experimentally: isolating rectangular holes and weakly scattering thermal barriers. We have modeled by means of the Green's function method the temperature of the heated surface for each case, incorporating the Gaussian shape of the exciting beam and the strength (thermal resistance) of the barrier. The resulting thermal field is the convolution of that produced by the scattering by the subsurface structure and by the 90° edge. Good qualitative agreement is found between the theoretical surface temperature and the photothermal signal measured with a mirage device on fabricated structures on a niquel sample. We discuss how the scattering processes influence the spatial forms of the normal (φn) and transverse (φt) mirage deviations, and how they are also modified when probe and pump beams are centered and fixed for imaging inspection. These results can be employed not only to detect and separate the effect of the corner from that of the feature, but also to characterize the subsurface structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355268
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  • 6
    Electronic Resource
    Electronic Resource
    General solution for the thermal wave scattering in fiber composites (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 1087-1098 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this article we present a general solution for the ac temperature field generated from a modulated heating in an opaque material containing a series of aligned subsurface cylinders. The model includes the multiple scattering effects suffered by the plane thermal wave, generated by a planar heat source, when interacting with the cylinders and with the sample surfaces. A series solution to the heat diffusion equation and a matrix formulation to solve the scattering coefficients are used. There are no restrictions on the cylinders number, on their size and position inside the material, nor on the thermal properties of cylinders and sample. For completeness the case of coated cylinders is also investigated. Numerical calculations for the case of nonconducting cylinders illustrate the effect of the multiple scattering of the incident thermal wave on the sample surface temperature. A specific case of interest of the model is its application to the thermal characterization and nondestructive evaluation of fiber reinforced composites. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1421633
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  • 7
    Electronic Resource
    Electronic Resource
    Multiple scattering effects of thermal waves by two subsurface cylinders (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 2600-2607 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a theoretical model and experimental measurements of the temperature field produced by the multiple scattering of thermal waves between two close subsurface cylinders and the material surface. The thermal waves are excited at the surface of an opaque material by an extended modulated optical beam. The cylinders are taken as thermal insulating holes and the model is run for a variety of modulation frequencies, thermal properties of the sample, and geometric properties of the cylinders (sizes, depths, mutual separation). The photothermal signal obtained using an infrared radiometry technique on calibrated samples validate our model predictions. The model is used to address the question of the spatial resolving power in photothermal wave experiments and introduce a novel resolution criterion. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372225
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  • 8
    Electronic Resource
    Electronic Resource
    Comments on "On the photothermal method applied to low thermal diffusivity measurements'' [Rev. Sci. Instrum. 64, 1576 (1993)] (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 275-276 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: It is shown theoretically and experimentally that the method recently proposed by Bertolloti et al. to measure low thermal diffusivity samples presents errors of the same order as other "mirage'' photothermal techniques previously proposed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145279
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  • 9
    Electronic Resource
    Electronic Resource
    Effective thermal diffusivity of layered materials measured by modulated photothermal techniques (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 3031-3041 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Modulated photothermal techniques provide useful methods based on linear relations to measure the thermal diffusivity of homogeneous materials. We have analyzed theoretically the applicability of such linear relations to two particular cases of layered composites, i.e., two-layer materials and superlattices. In order to measure the through-thickness and in-plane thermal diffusivities of these anisotropic materials, planar and pointlike excitations have been studied. The main result of this article is that the linear relations encountered for homogeneous materials still hold for layered composites, although their slopes do not always give the effective thermal diffusivities of the sample parallel and perpendicular to the layers, as derived from the in-parallel and in-series thermal resistors models, respectively. However, an "apparent" thermal diffusivity is obtained from which the thermal parameters of each layer can be retrieved. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.368457
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  • 10
    Electronic Resource
    Electronic Resource
    Low temperature thermal diffusivity measurements of gases by the mirage technique (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 98-103 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In this article a cryogenic mirage setup to perform thermal diffusivity measurements of gases in the temperature range 77–500 K is presented. The device was calibrated by measuring the temperature dependence of the thermal diffusivity of pure nitrogen and pure helium that have very different thermal properties. The ability of the device was demonstrated by measuring the thermal diffusivity of gas binary mixtures that fit very well the theoretical values obtained from the kinetic theory. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149548
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