Modeling for thermal conductivity measurements of thin films using photothermal deflection with obliquely crossed configuration

Received: 21 December 1996     

The locality problem in quantum measurements

The locality problem of quantum measurements is considered in the framework of the algebraic approach. It is shown that contrary to the currently widespread opinion one can reconcile the mathematical formalism of the quantum theory with the assumption of the existence of a local physical reality determining the results of local measurements. The key quantum experiments: double-slit experiment on electron scattering, Wheeler’s delayed-choice experiment, the Einstein-Podolsky-Rosen paradox, and quantum teleportation are discussed from the locality-problem point of view. A clear physical interpretation for these experiments, which does not contradict the classical ideas, is given.     

Thermal diffusivity measurements in porous ceramics by photothermal methods

Received: 16 September 1996/Accepted: 6 January 1997     

Continued fraction method in inverse problem of photothermal diagnostics

Received: 1 July 1996/Accepted: 16 October 1996     

Influence of substrate in photothermal measurements of thin film absorption

In photothermal measurements of low optical absorption coefficients, as in the case of thin films of amorphous semiconductors, the substrate absorption can play a non-negligible role. In this paper, the substrate influence is discussed and generalized on the basis of a theoretical model of a two-layer absorbing sample, and the interaction of the thermal and optical parameters which control the photothermal process in the sample is shown. Some experimental results obtained on thin films of amorphous silicon carbide deposited on different substrates are presented and discussed.     

An improved photothermal gas analyser: Monitoring of simultaneous thermal diffusivity and thermal effusivity

In this paper we describe a new, simple and fast photothermal method for characterizing simultaneously the thermal diffusivity and thermal effusivity. The improved PTGA essentially combines a photoacoustic cell and a thermal wave pyroelectric cell enclosed in a single compact gas analyzer. The photo- acoustic cell is kept filled with nitrogen and sealed. The pyroelectric cell is also filled with nitrogen and after some warm up time, the nitrogen is exchanged to the gas of interest. It is shown that the analysis of the transient and saturation signals of both photoacoustic and pyroelectric cells are capable of measuring the thermal properties with an accuracy of 5%. The measurements were performed for hydrocarbons as ethane and propane, which are combustible gases. Knowing thermal diffusivity and effusivity, others important properties can be determinate: the thermal conductivity and the volumetric thermal capacity.     

Explicit and approximate theories of photothermal deformation in surface thermal lens technique

An explicit thermoelastic model is developed to describe the photothermal deformation of a coated sample excited by a cw modulated laser beam with a top-hat profile. The surface displacement obtained with this explicit model is compared to that obtained by an approximate model developed by Reichling and Gr?nbeck (J. Appl. Phys. 75, 1914 (1994)). Both thermoelastic models are then applied in a Fresnel diffraction based surface thermal lens (STL) theory. Numerical calculations are performed to investigate the differences between the explicit and approximate models in both surface displacement and STL signal. The simulation results show that the approximate model over-estimates the surface displacement and the corresponding STL signal amplitude. A decrease in the thermal diffusion length reduces the differences between the results obtained with the two thermoelastic models.     

Two-temperature plane strain problem in a semiconducting medium under photothermal theory

In this investigation, we study the two-temperature problem with two-dimensional (2-D) deformations for a semi-infinite semiconducting medium at the free surface with the influence of mechanical force through a photothermal process. The harmonic wave method (Normal Mode analysis) has been used to get the exact expression of normal displacement, normal force stress, carrier density, and temperature distribution, and also the two-temperature coefficients ratios has been obtained analytically. The effects of several parameters as thermoelastic and thermoelectric coupling parameters and two-temperature parameter of this force on the displacement component, force stress, carrier density, and temperature distribution have been depicted graphically.     

低温下固体接触热阻与接触电阻的实验研究

在低温工程中,两个接触固体之间存在着接触热阻与接触电阻,将对低温实验中热量及电流的传输产生显著的影响,是进行低温下物性研究的关键。自行研制了一套可同步实现固体接触热阻和接触电阻的测量装置,该系统具有较高的精度,可实现外界力、温度等对接触热阻的测量,同时具备接触电阻的实时测量功能。在此基础上,开展了外界压力、温度、电流对接触热阻和接触电阻的实验研究。实验结果显示:随着压力的增大,接触热阻与接触电阻随之减小;低温下,随着温度的增大接触热阻与接触电阻增大,接触电阻增大的速率要比接触热阻快。温度平衡时,20mA范围内的电流变化对接触电阻的影响显著,对接触热阻影响非常小。当界面温度达到室温后,首次观测到接触热阻和接触电阻会随着温度的增大而减小。     

Pulsed photothermal radiometry for noncontact spectroscopy,material testing and inspection measurements

Photothermal radiometry (PTR) is a sensitive technique for noncontact spectroscopy and inspection. Its principle is the following: a modulated beam of photons (or other particles) produces temperature transients in a sample; the corresponding transients in the IR thermal radiation emitted from the sample are analyzed. This can provide absolute absorption coefficients, as well as information on thermal diffusivity, layered structure and dimensions. Variations of PTR are possible with continuously-modulated or pulsed excitation, and with transmission or back-scattering detection. These variations are reviewed. The recent technique of pulsed PTR with back-scattering detection is described in more detail, and some important single-ended remote-sensing applications are discussed.     

固-固接触界面热传输研究

提出了固-固接触热传导接触界面层的概念并进行了解释。接触界面层的建立,把微结构的散射和辐射热传导机制统一于界面层内,通过对接触界面层、接触界面层的厚度和界面层热导率等的讨论,初步揭示了接触界面层热传导的机制。在界面层微观传热的机制上,建立了接触界面层热阻预测模型,并把模型预测接触热阻值与扩散失陪模型(DMM)以及实验值进行了比较。结果显示该模型克服了DMM模型预测值偏低的缺陷,这些将对接触界面层的微尺度热分析有一定的帮助。     

Pulsed photothermal laser deflection for low-level smoke and NO2 measurements in engine exhausts

Pulsed Photothermal Laser Deflection (PLD) is developed to make temporally and spatially resolved measurements of NO₂ and smoke. The rapid response PLD signal is produced when a HeNe probe beam is deflected by a thermal lens produced by a pulsed XeCl-excimer laser pumped dye laser. The fast time response (30 ns) and good spatial resolution make the PLD method a candidate for future in situ measurements in turbulent engine exhausts. The PLD signals, measured in a sample cell, exhibit a linear response for NO₂ concentrations from 3 ppm to 208 ppm and for smoke concentrations from 0.3 mg/m³ to 10 mg/m³. With a low pulse energy of 4 mJ, single-shot PLD measurements in a sample cell have accuracies of ± 14 ppm for NO₂ indicating accuracies of ±0.7 mg/m³ for smoke. With increased pulse energy and multi-shot averaging, sensitivities of ± 0.4 ppm of NO₂ or ± 20 µg/m³ of smoke are expected.     

On quantum systems in thermal contact

It is shown that under rather general conditions two K.M.S. states ₁ and ₂ of systemsS ₁ andS ₂, respectively, can be simultaneously extended to a K.M.S. state of a system composed ofS ₁ andS ₂, provided both systems have equal temperatures. This result gives further support to the conjecture that K.M.S. states are equilibrium states. In the second part, a model of thermal coupling is constructed which satisfies the assumptions of the first part, thereby showing that the result is also valid in the interesting case of systemsS ₁ andS ₂ in thermal contact.     

Quantitative measurements of optical absorption in CVD-grown ZnS with the phase-shift photothermal method

A technique of measuring weak bulk optical absorption at a wavelength of 10.6 μm in polished plates made of CVD-grown polycrystalline ZnS was developed on the basis of the phase-shift photothermal method. The results obtained are in good agreement with the data on the absorption of the samples under investigation, calculated from calorimetric and transmittance measurements. The possibility of highly sensitive local quantitative measurements of the optical-absorption coefficient using the phase-shift photothermal method is demonstrated.     

Phase (interferometric) photothermal method for separate measurements of surface and volume absorption

The possibility of separately measuring the surface and volume absorption by a phase photothermal method is demonstrated with ZnSe polished samples. A theory developed allows us to directly relate the signal amplitude to the coefficients of surface and volume absorption. From the experimentally found dependence of the temperature oscillation amplitude at the sample surface on the angle of incidence, the position of the absorbing surface layer relative to the interface is determined and a mechanism of interaction between the pumping radiation and the target material is assessed.     

An investigation of the photothermal deflection spectroscopy technique for temperature measurements in a flame

The technique of photothermal deflection spectroscopy (PTDS) is investigated for temperature measurements in a flame. The spatial distribution of temperature is measured in two different types of burners operating with methane and oxygen, and methane and air. The spatial distributions of the temperature are in qualitative agreement with our expectations. At two points, the temperatures measured by PTDS have been compared with those measured by Boltzmann distributions. The measurements agree within their uncertainties. All the effects that affect the reliability of this technique are investigated and discussed. Finally, the pros and cons of the PTDS technique for temperature measurement are discussed. Received: 31 January 2002 / Published online: 8 August 2002     

The measurements of thermal neutron flux distribution in a paraffin phantom

The term ‘thermal flux’ implies a Maxwellian distribution of velocity and energy corresponding to the most probable velocity of 2200 m s^???1 at 293.4 K. In order to measure the thermal neutron flux density, the foil activation method was used. Thermal neutron flux determination in paraffin phantom by counting the emitted rays of indium foils with two different detectors (Geiger–Muller counter and NaI(Tl)) was the aim of this project. The relative differences of the outcome of the experiments were between 2.5% and 5%. The final results were compared with MCNP4C outputs and the best agreement was generated using NaI(Tl) by a minimum discrepancy of about 0.6% for the foil placed 8.5 cm from the neutron source.     

Discriminating thermal effect in nonlinear-ellipse-rotation-modified Z-scan measurements

We report that a modified Z-scan method by nonlinear ellipse rotation (NER) can be used to discriminate true nonlinear refraction from thermal effect in the transient regime and steady state. The combination of Z-scan and NER allows us to measure the third-order nonlinear susceptibility component without the influence of thermal-optical nonlinearity. The experimental results of pure CS(2) and CS(2) solutions of nigrosine verify that the transient thermal effect can be successfully eliminated from the NER-modified Z-scan measurements. This method is also extended to the case in which thermal-optical nonlinearities depend on a high repetition rate of femtosecond laser pulses for the N,N-dimethylmethanamide solutions of graphene oxide.     

Investigation into the processes of thermal and photothermal destruction of F-color centers in alkali-halide crystal phosphors

Using the concept of thermal and photothermal destruction of color centers in alkali-halide phosphors as an ion mechanism, certain formulas are examined which represent these processes. The phenomenon of thermal and photothermal destruction of F-color centers is investigated experimentally for the case of NaCl-Ag. A comparison of the experimental results obtained with the theory enabled an estimate to be made of a number of kinetic characteristics of the processes in question.The results obtained confirm the usefulness of the idea of ion processes in explaining the phenomena of relaxation in alkali-halide crystal phosphors.