Antonio M. Mansanares

Photosynthetic O2 evolution in maize inbreds and their hybrids can be differentiated by open photoacoustic cell technique

Abstract Photosynthetic efficiency is considered one of the traits potentially suitable to differentiate hybrids from their inbred lines. Previous evaluations concerning photosynthetic efficiencies of maize (Zea mays L.) plants in the field have shown inconsistent and contradictory data. In this work, we attempted to study photosynthetic O2 evolution through photoacoustic spectroscopy in intact undetached leaves of dark-adapted seedlings of inbreds and their hybrids. The results indicate that photosynthetic efficiencies of inbreds and hybrids can be differentiated by photoacoustic measurements of oxygen evolution, providing a parameter that might prove useful in evaluating plant genotypes.

AN APPLICATION OF THE FRONT PHOTOPYROELECTRIC TECHNIQUE FOR MEASURING THE THERMAL EFFUSIVITY OF SOME FOODS

ABSTRACT Photopyroelectric calorimetry, in the front (inverse) configuration (with thermally thick sensor and sample, and optically opaque sensor), was applied to measure the thermal effusivity of some fats and water-based juice products. The information was obtained via a frequency scan of the phase of the pyroelectric signal; the measurements need no calibration. The main advantages of this configuration above the other two previously proposed front schemes are: (i) it does not require the use of very thin foils or expensive semitransparent sensors; (ii) the information is contained in the phase of the signal (and not in the amplitude as usual), which is independent of the power fluctuations of the radiation source and, consequently, the results are more accurate and reproducible.

Thermal diffusivity measurements in vegetable oils with thermal lens technique

Using a thermal lensing experimental setup the thermal properties of several vegetable oils were obtained. The samples were oils from Amazonian species and olive (the popular identifications are piqui, copaiba, buriti, and babacu). The two lasers mismatched mode experimental configuration was used, with a He–Ne laser as the probe and an Ar+ laser as the excitation one. The time resolved spectra were measured using an automatic system, and fitting the aberrant theoretical model to the data, the characteristic relaxation time were obtained, and knowing this value, the thermal property of each oil was solved.

Thermal lens spectrometry to study complex fluids

We describe applications of Thermal Lens Spectrometry to study optical and thermal properties of lyotropic liquid crystal. In particular, we refer to methods for measurements of thermal diffusivity anisotropy at different temperatures and as a function of the ferrofluids doping. The theoretical basis for quantitative measurements is discussed together with the advantages and limitations as compared with conventional methods. Finally, future developments of photothermal techniques for these applications are assessed.

GEOMETRICAL ANISOTROPY DEPENDENCE OF THERMAL DIFFUSIVITY IN LYOTROPIC NEMATICS : MODE MISMATCHED THERMAL LENS MEASUREMENTS

In this work the quantitative theoretical treatment for two beam mode mismatched thermal lens spectrometry is applied to investigate the thermal diffusivity anisotropy of two lyotropic mixtures: (1) potassium laurate, decanol and water and (2) potassium laurate, potassium chloride and water in the nematic calamitic phase. The ratio between the thermal diffusivities parallel and perpendicular to the director has been shown to be smaller than those reported for thermotropic liquid crystal. This observation is explained by using a simple model where this ratio is correlated to the micellar shape anisotropy.

Open photoacoustic cell : Applications in plant photosynthesis studies

Abstract In this article, we review the applications of the open photoacoustic cell (OPC) technique in studies of photosynthetic activity in plant leaves. The ability to perform in vivo and in situ measurements makes this technique particularly suitable for monitoring photosynthesis of plants subjected to specific treatments. Therefore, our objective in the present article is to describe, in more detail, the principles of the OPC technique and to follow the historical path of its applications related to the study of plants and photosynthesis, including recent results. It will be shown that the technique has been used to observe spectroscopic responses to herbicide application and to soil toxicity, in the study of photosynthesis induction, gas exchange, photochemical loss, photoinhibition, photosynthesis saturation, and photosynthetic responses to changes in parameters such as temperature, atmospheric conditions, and nutrient availability. Recent results have demonstrated its usefulness in the determination of the action spectrum directly from oxygen evolution measurements.

Photothermal and electroreflectance images of biased metal-oxide-semiconductor field-effect transistors: Six different kinds of subsurface microscopy

Six different configurations for metal-oxide-semiconductor field-effect-transistor reflectance microscopy are presented, each one revealing a particular contrast of the operating structure. These different images are obtained by interchanging the modulation of gate-source and drain-source potentials, as well as by varying the probe beam intensity. Three main components were identified in the signal, their relative importance depending on the experimental configuration: the electroreflectance component, the photoinjected carrier (probe-induced) component and the bias current (Joule effect) component. The high ability of the technique to detect defects in these structures is also demonstrated.

Subsurface microscopy of biased metal-oxide-semiconductor field-effect-transistor structures: photothermal and electroreflectance images

Abstract In this work we used reflectance microscopy to investigate biased metal-oxide-semiconductor field-effect-transistor (MOSFET) structures. A resolution of micrometer is achieved by using visible laser light to probe the gate surface, and both electroreflectance and thermoreflectance components were found in the signal. Image contrast depends upon the bias configuration, and a total of six different types of images can be obtained. The high ability of the technique to detect subsurface defects is also demonstrated.

PHOTOSYNTHETIC ENERGY STORAGE AND OXYGEN EVOLUTION DETERMINED THROUGH AN OPEN PHOTOACOUSTIC CELL TECHNIQUE

Abstract Recently, a new open photoacoustic cell (OPC) has been developed for the determination of both optical and thermal properties of the sample. The OPC can also be applied for the determination of photosynthetic parameters as energy storage and oxygen evolution for in vivo and in situ plant leaves. However, the membrane of the microphone used in this cell inserts a spurious component in the photoacoustic signal of non-opaque samples such as plant leaves. The membrane signal is added to the sample signal, making the analysis more complicated. In the present work, we discuss this problem and propose a simple method to eliminate it.

Contrast enhancement in the detection of defects in transparent layered structures: The use of optothermal interference technique in solar cell investigation

This article shows the enhanced sensitivity of the optothermal interference technique in the detection of local differences (nonhomogeneity in thickness and optothermal parameters), compared to the conventional optical interference, when investigating layered transparent structures. The measured signal is sensitive to the reflectance variation at the distinct interfaces, function of temperature, as well as to the optical phase lag between the reflected beams. Measurements made on solar cells show contrast of the order of 100% in the optothermal interference, while the conventional optical interference presents a contrast of only 15%. A model based on the reflectance variation at each interface describes the signal behavior as a function of modulation frequency. Theoretical calculation based on this model evidences the influence of the optothermal parameters in the signal contrast.