Time-resolved thermal mirror technique with top-hat cw laser excitation.

A theoretical model was developed for time-resolved thermal mirror spectroscopy under top-hat cw laser excitation that induced a nanoscale surface displacement of a low absorption sample. An additional phase shift to the electrical field of a TEM(00) probe beam reflected from the surface displacement was derived, and Fresnel diffraction theory was used to calculate the propagation of the probe beam. With the theory, optical and thermal properties of three glasses were measured, and found to be consistent with literature values. With a top-hat excitation, an experimental apparatus was developed for either a single thermal mirror or a single thermal lens measurement. Furthermore, the apparatus was used for concurrent measurements of thermal mirror and thermal lens. More physical properties could be measured using the concurrent measurements

An open-photoacoustic-cell method for thermal characterization of a two-layer system

In the present work, we use an open-photoacoustic-cell (OPC) operating at high frequency to measure thermal properties of two-layer system samples. Photothermal deflection technique is also employed to measure the samples. The effective thermal diffusivity measured using the OPC method is interpreted using the concept of effective thermal resistance for a series two-layer system. The results show the reliability of the photoacoustic method for a complete thermal characterization of the samples. In addition, by varying the sample effective thickness, the thermal diffusivity and conductivity of each layer are precisely determined. The effective thermal diffusivity, thermal conductivity, and specific heat of a porous catalyst layer (thickness varying from 13 to 53 \u3bcm) deposited on an aluminum foil (53 \u3bcm in thickness) were thus measured and found to be (3.7+-0.3)x10 12\ub3 cm\ub2 / s, (7.5+-0.7)x10 12\ub3 W/cm K, and (1.6+-0.2) J /gK, respectively.Peer reviewed: YesNRC publication: Ye

Vpliv robnih učinkov na lasersko induciran pomik površine neprozornih materialov s fototermalno interferometrijo

We demonstrate the influence of edge effects on the photothermal-induced phase shift measured by a homodyne quadrature laser interferometer and compare the experiments with rigorous theoretical descriptions of thermoelastic surface displacement of metals. The finite geometry of the samples is crucial in determining how the temperature is distributed across the material and how this affects the interferometer phase shift measurements. The optical path change due to the surface thermoelastic deformation and thermal lens in the surrounding air is decoded from the interferometric signal using analytical and numerical tools. The boundary/edge effects are found to be relevant to properly describe the interferometric signals. The tools developed in this study provide a framework for the study of finite size effects in heat transport in opaque materials and are applicable to describe not only the phase shift sensed by the interferometer but also to contribute to the photothermal-based technologies employing similar detection mechanisms.Prikažemo vpliv robnih učinkov na fototermalno inducirani fazni premik, ki ga merimo s homodinskim kvadraturnim laserskim interferometrom in poskuse primerjamo z eksaktnimi teoretičnimi opisi termoelastičnih površinskih premikov kovin. Končna geometrija vzorcev je ključnega pomena pri določanju, kako se temperatura porazdeli po materialu in kako to vpliva na merjenje faznega premika interferometra. Razliko optične poti zaradi površinske termoelastične deformacije in termalne leče v okoliškem zraku dekodiramo iz interferometričnega signala s pomočjo analitičnih in numeričnih orodij. Mejni/robni učinki so pomembni za pravilen opis interferometričnih signalov. Orodja, razvita v tej študiji, nudijo okvir za preučevanje učinkov zaradi končnih dimenzij pri prenosu toplote v neprozornih materialih in niso uporabna le za opisovanje faznega premika, ki ga zazna interferometer, temveč prispevajo tudi k fototermalnim tehnologijam, ki uporabljajo podobne mehanizme zaznavanja

Generation and detection of thermoelastic waves in metals by a photothermal mirror method

We investigate the thermoelastic waves launched by a localized heat deposition. Pulsed laser excitation is used to generate mechanical perturbations in metals that are detected using the photothermal mirror method. This method detects the wavefront distortion of the probe beam reflected from the perturbed sample surface. Nanometer scale expansion of the material is induced just under the irradiated surface releasing transient thermoelastic waves of much smaller amplitudes on the surface. Numerical predictions and the experimental results are in a good agreement and represent both the thermal diffusion of the large amplitude, long-lasting outward bulge, and the released elastic waves

Temperature coefficients of the refractive index for hydrocarbons and binary mixtures

Temperature coefficients of the refractive index (dn/dT) for nine hydrocarbons and two sets of binary mixtures were investigated in this work. The measured 12dn/dT values for the pure hydrocarbons were found to be inversely proportional to their molar volumes (Vm) and molecular weights (M). Experimental data for binary mixtures show that 12dn/dT varies linearly with volume and mass fractions, consistent with theory derived from the linear relationships of 12dn/dT with 1/Vm and 1/M for individual hydrocarbons. This study should aid the interpretation of the observed correlations of dn/dT with physical and combustion properties of diesel fuels.Peer reviewed: YesNRC publication: Ye

Spectroscopic investigation and heat generation of Yb3+/Ho3+ codoped aluminosilicate glasses looking for the emission at 2 μm

Energy transfer (ET) and heat generation processes in Yb3+/Ho3+-codoped low-silica calcium aluminosilicate glasses were investigated using thermal lens (TL) and photoluminescence measurements looking for the emission around 2.0 μm. Stepwise ET processes from Yb3+ to Ho3+, upon excitation at 0.976 μm, produced highly efficient emission in the mid-infrared range at around 2.0 μm, with high fluorescence quantum efficiency (η1 ∼ 0.85 and independent of Ho3+ concentration) and relatively very low thermal loading (<0.4) for concentration up to 1.5% of Ho2O3. An equation was deduced for the description of the TL results that provided the absolute value of η1 and the number of emitted photons at 2.0 μm per absorbed pump photon by the Yb3+ ions, the latter reaching 60% for the highest Ho3+ concentration. These results suggest that the studied codoped system would be a promising candidate for the construction of photonic devices, especially for medical applications.PRONEX/FAPEAL (2009-09-006)FINEPCNPqInstituto Nacional de Ciência e Tecnologia de NanoBioEstruturas & Simulação NanoBioMolecular (INCT NANO(BIO)SIMES)CAPES (02727/09-9)Fundação AraucáriaCAPES / COFECU

Razkritje sevalnih sil na površini in v notranjosti dielektrične tekočine

Precise control over light-matter interactions is critical for many optical manipulation and material characterization methodologies, further playing a paramount role in a host of nanotechnology applications. Nonetheless, the fundamental aspects of interactions between electromagnetic fields and matter have yet to be established unequivocally in terms of an electromagnetic momentum density. Here, we use tightly focused pulsed laser beams to detect bulk and boundary optical forces in a dielectric fluid. From the optical convoluted signal, we decouple thermal and nonlinear optical effects from the radiation forces using a theoretical interpretation based on the Microscopic Ampère force density. It is shown, for the first time, that the time-dependent pressure distribution within the fluid chiefly originates from the electrostriction effects. Our results shed light on the contribution of optical forces to the surface displacements observed at the dielectric air-water interfaces, thus shedding light on the long-standing controversy surrounding the basic definition of electromagnetic momentum density in matter.Natančen nadzor interakcij med svetlobo in snovjo je ključnega pomena za številne metodologije optičnih manipulacij in karakterizacij materialov. Poleg tega igra zelo pomembno vlogo tudi v številnih nanotehnoloških aplikacijah. Kljub temu pa je potrebno temeljne vidike interakcij med elektromagnetnim poljem in snovjo še nedvoumno določiti v smislu gostote gibalne količine elektromagnetnega polja. Za zaznavanje sevalnih sil na površini in v notranjosti dielektrične tekočine smo uporabili tesno fokusirane laserske bliske. Iz zapletenega optičnega signala smo z uporabo teoretične interpretacije, ki temelji na gostoti mikroskopske Ampèrove sile, ločili toplotne in nelinearne optične učinke od sevalnih sil. Prvič je prikazano, da časovno odvisna porazdelitev tlaka znotraj tekočine izvira pretežno iz elektrostrikcijskih učinkov. Naši rezultati osvetljujejo prispevek optičnih sil k površinskim pomikom, opaženih na dielektrični meji zrak-voda, s čimer osvetljujejo dolgoletno polemiko o osnovni definiciji gostote gibalne količine elektromagnetnega polja v snovi