The optical and thermophysical parameters of starch films (obtained by extrusion) were determined in order to obtain input data for photothermal studies of water migration in such films. The optical spectra, sorption isotherm, and volume change were measured for samples equilibrated at different levels of relative humidities. The photopyroelectric method was used to measure thermal parameters as a function of water content and temperature. The thermal conductivity, thermal effusivity, and volume specific heat all increase with water content while the thermal diffusivity remains almost constant. The temperature behaviour of the thermal parameters in the -15+70 °C temperature range was measured for samples with different water contents. No phase transition was observed at 0 °C, which proves either that water in the starch matrix is not in a free form, or the fact that water dissolved other particles shifting the melting point to a lower temperature.

We propose a new definition of the thermal thickness of a specific layer in a multilayer system. which takes into account the ratio of the thermal effusivities at the interfaces with the adjacent layers. The concept of effective thermal thickness is illustrated in some practical cases by comparison with experimental data. Finally, it is shown that the new definition is useful for the design of photothermal experiments for the characterisation of thin self-supporting films in air.

The photopyroelectric method in a non contact detection configuration is proposed to study water migration in starch sheets. This allows the exchange of humidity between the moist atmosphere and the starch sample during the experiment. The sensitivity for the total water content measurement was about 0.3%. A theoretical model was developed, taking into account a continuous depth profile of humidity in the starch sample. A water profile in the material and its evolution in time were evidenced when exposing one side of the sample to a humid atmosphere.

Some near-field experimental methods use laser excitation inducing thermal effects that are often neglected or incompletely estimated (1,2). We particularly investigate the case of a Scanning Tunneling Microscope (STM). The thermal response of the tip and of the sample are studied and the thermal ability of the STM are defined.

The photopyroelectric method was used for measuring the thermal parameters of starch sheets as a function of water content and temperature. The thermal conductivity, thermal effusivity and volume specific heat are increasing with water content while the thermal diffusivity remains almost constant. The temperature behaviour of the thermal parameters in the -15+70 degrees C temperature range was measured for samples with different water contents. No phase transition was observed at 0 degrees C, which proves either that water is bound in the starch matrix, or the fact that water has dissolved other particles that shifted the melting point to a lower temperature.

The aim of this study was to determine the depth-dependent water migration profile in starch sheets using a photothermal method. It is found that the distribution of the absorbed water is exponential, depending markedly on the duration of contact between sample and liquid water.

The photopyroelectric (PPE) method in different experimental configurations was thermophysical characterisation of agricultural and biological samples. The study appears important due to the relation of thermal parameters to the quality of foodstuffs (connected to their preservation, storage and adulteration), migration profiles in biodegradable packages, and the mechanism of desiccation tolerance of seeds. Results are presented on the thermal parameters measurement and their dependence on temperature and water content for samples such as: honey, starch, seeds.

Introduction Fruits and vegetables used in various processed products, as well as in fresh market sales, are expected to comply with the certain quality standards. However. quality is everything but a single parameter state and, therefore, a variety of subjective and objective measurements are usually performed. In particular, the firmness and maturity are considered important attributes to the quality of fruits and vegetable crops. Presently. these parameters are usually determined either destructively (by a pressure tester) or by means of ultrasound; a development of alternative methods has been strongly encouraged in the recent years.

The photopyroelectric (PPE) technique in two different configurations (back, BPPE; front, FPPE) has been used in order to measure the room temperature values of ail static and dynamic thermal parameters of some food products (vegetable oils, fats, water-containing foodstuffs). As a second application, the BPPE technique was applied to study the changes in the thermal parameters of a 10% human red blood cell suspension exposed to different electron irradiation levels. The results obtained for the temperature dependence of the thermal diffusivity indicate an increase of the disorder of the system at the red cell level, due to irradiation.

The temperature dependence of the green cathodoluminescence (CL) of an Er3+-doped calcium difluoride crystal has been studied by means of a scanning electron microscope; it shows good sensitivity to temperature in a wide range. In order to quantify with accuracy the thermal effects induced by the electron beam itself, a model based on both Monte-Carlo and finite element calculations was developed. A first attempt made to use the thermal behaviour of the Er3+ green CL as a local temperature probe under different conditions of excitation showed good agreement with the simulations.

Cathodoluminescence (CL) of Er3+-doped alkaline earth fluorides is investigated in order to elaborate a thermal probe with micrometer spatial resolution. The green luminescence of Er3+ ions represents a good candidate for such a purpose since this emission is due to the thermally coupled S-4(3/2) and H-2(11/2) levels. The evolution of the CL intensity ratio from these levels with temperature is found very sensitive over a wide range. In order to take into account the heating induced by the electron beam in the target material, Ne develop a numerical model based on both Monte-Carlo and thermal calculations. This model allows the determination of the field of temperature in the region submitted to excitation in both stationary and non-stationary modes. Using the electron beam as heating source and the CL emission as local probe by exciting areas with different size, we experimentally determine some differences of heating which are very close to those predicted by calculations.

Photothermal methods are well adapted to thin multilayer material analysis. In the particular case of biological materials, which are thermally fragile, low excitation power is required. We have studied whole human blood sedimentation by using photothermal radiometry and a photopyroelectric technique. Results obtained with random- and sine-modulated excitation are discussed. Evolution laws of plasma thicknesses and optical absorption coefficients during the process have been determined by identifying the parameters using different estimation methods. It appears that results are consistent with theoretical predictions of our 2D-thermophysical model and also with the values measured by the well-known Westergreen reference method, usually used in clinical analysis. Finally, in order to extend the investigation field of the pyroelectric method, particularly in the domain of biological materials, we have analysed the possibility of using the sensitive pyroelectric sensors without direct thermal contact with the sample and detecting the temperature changes at the sample surface through a thin air monolayer.

The photopyroelectric (PPE) technique is usually used as a contact photothermal method to characterize thin solid materials. We performed theoretical and experimental investigations of a non-contact PPE configuration to analyse the effects of an air gap between the thermal source and a PVDF sensor using a modulated laser beam as optical excitation. The detection of the thermal wave developed within the sample was possible across an air gap of up to 15 mm. The PPE signal was described well thanks to a two-dimensional (2D) model with axial symmetry, which could be reduced in some particular cases to a simpler 1D propagation model. Border effects can be artificially taken into account in the calculations by increasing the adiabatic lateral limits in the model, keeping the active sensor area constant. Despite there being strong attenuation with increasing modulation frequency, the PPE method can be used as well as can other non-contact photothermal techniques. New perspectives for the application of the PPE technique have been opened.

Traditionally, the photopyroelectric (PPE) technique is a contact photothermal method. The work investigates the signal characteristics of the non-contact PPE configuration. Below the modulation frequency of 5 Hz a two-dimensional theoretical approach is necessary due to axial and lateral heat flow, whereas at higher frequency a one-dimensional model is convenient as well.

After demonstrating recently the possibilities of scanning photothermal radiometry for wear crack detection (Bodnar et al., J. Phys. IV, 4 (1994) 591–594), we now study its possibilities for dimensional characterization of these kinds of flaws. In this respect, we present here the results obtained from our study of two types of emerging cracks, i.e. thin and shallow cracks in samples with a reflecting surface as well as wider and deeper cracks in samples with an absorbing surface.

The study of a new approach using photopyroelectric method, for measuring the interface locations of erythrocyte sedimentation in whole blood is presented. A simple instrument is described, composed of a small vessel with the bottom made of a pyroelectric material. The liquid sample is irradiated from above with modulated light which is absorbed mainly at the interface between the clear component and the sediment. The PPE signal phase and amplitude contain informations on the sedimentation dynamics. The cell was tested with water and latex spheres 3 μm diameter and then with blood particles like erythrocytes.

Using a mobile photothermal probe we show that it is possible to detect rapidly different type of cracks (emerging ones or not), their width being a few micrometers and their depth being some hundredths of micrometers.

Photothermal radiometry is a thermal method leading to the measurement of thermal diffusivity. In this paper we use a pseudo-random excitation. The measurement is accomplished by comparing the experimental results in phase, with some curves, calculated by a mathematical modelling (bidimensionnal and axisymetrical).