An inverse solution of the two-layer thermal wave problem has been derived, which allows us to determine the relevant thermal transport parameters, the thermal diffusion time and the thermal reflection coefficient, respectively, the ratio of the effusivities of the two layers, deduced from the relative minimum or maximum of the calibrated phase lags measured between the periodically modulated excitation of the thermal wave and the detected thermal response. Applying a functional transformation by multiplying the calibrated phase lags with the variable (1∕f1∕2)q, where f is the modulation frequency of excitation and q a positive or negative real number close to zero, the inversion method is extended to other values of the calibrated phase lags measured in the neighborhood of the phase minimum or maximum. The application potential of these two solution methods is studied by analyzing the phase lags measured as a function of frequency for two-layer systems of technological importance, e.g., different plasma-deposited hard coatings on tool steel, coated cutting tools after friction wear, and a sample of a shape memory alloy (NiTi) after mechanical surface treatment.

Lycopene that imparts red color to the tomato fruit is the most potent antioxidant among carotenes, an important nutrient and also used as a color ingredient in many food formulations. Since cooked and processed foods derived from tomatoes were shown to provide optimal lycopene boost, products such as paste, puree, juice, etc. are nowadays gaining popularity as dietary sources. The analysis of lycopene in tomato paste ͑partially dehydrated product prepared by vacuum concentrating tomato juice͒ is carried out using either high pressure liquid chromatography ͑HPLC͒, spectrophotometry, or by evaluating the color. The instability of lycopene during processes of extraction, etc., handling, and disposal of organic solvents makes the preparation of a sample for the analysis a delicate task. Despite a recognized need for accurate and rapid assessment of lycopene in tomato products no such method is available at present. The study described here focuses on a direct determination of a total lycopene content in different tomato pastes by means of the laser optothermal window ͑LOW͒ method at 502 nm. The concentration of lycopene in tomato paste ranged between 25 and 150 mg per 100 g product; the results are in excellent agreement with those obtained by spectrophotometry. The time needed to complete LOW analysis is very short, so that decomposition of pigment and the formation of artifacts are minimized. Preliminary results indicate a good degree of reproducibility making the LOW method suitable for routine assays of lycopene content in tomato paste.

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Coatings prepared by reactive magnetron sputtering of approximately equal thermal transport properties but differing coating thicknesses are analyzed by means of non‐contact non‐destructive modulated IR radiometry. For the quantitative interpretation, the measured thermal wave signals are calibrated, using the signals measured for a homogenous opaque solid of smooth surface. The relative minima of the inverse calibrated phase lag signals are interpreted with respect to the effective thermal transport properties and to the coating thickness using an inverse solution of the two‐layer thermal wave problem. Based on measurements of various coatings, the limitations of this thermal wave method and the errors of measurement for the coating thickness are discussed by comparing with microscopic measurements.

Multifunctional coatings consisting of transition metal oxycarbides and oxynitrides deposited by physical vapour deposition techniques on tool steel are analysed in this work by means of modulated IR radiometry (MIRR), a non-contact non-destructive thermal wave measurement technique, with respect to the thermal transport properties relevant for time-dependent surface heating processes of coating–substrate systems. In order to interpret the measured data quantitatively, an inverse solution of the two-layer thermal wave problem is applied, which relies on the thermal wave phase lag data measured as a function of modulation frequency of the periodically modulated laser beam heating intensity. Based on these measurements and their quantitative interpretation, correlations between the thermal transport properties of the coatings and their deposition conditions have been found, which can be used to monitor deposition processes. For a second objective of this work, namely to determine the film thickness by means of MIRR, different sets of thin films of approximately constant thermal transport properties, but differing film thickness, have been measured. To discuss the limitations and error limits of these non-contact non-destructive measurements of the coating thickness, the results obtained by MIRR are compared with the coating thickness determined by destructive measurements.