Infrared imaging is a well-known non-invasive technology that in recent years has gained great interest in precision agriculture field. Plants are subjected to a wide range of biotic stresses caused by pathogenic bacteria, fungi, nematodes, and viruses that reduces productivity. In this work wild rocket (Diplotaxis tenuifolia) plants inoculated with the soil-borne pathogens Rhizoctonia solani Kühn, Sclerotinia sclerotiorum (Lib.) and Fusarium oxysporum f. sp. raphani were monitored daily in laboratory by means of the infrared imaging. Plant monitoring was performed with both active and passive approaches. The results obtained showed that the infrared imaging methods tested are promising for early diagnosis of soil-borne diseases by allowing their detection a few days before they are detectable through a visual analysis. These findings open up the possibility of developing new imaging systems for both proximal and remote sensing.
Plants are subjected to a wide range of stresses which reduces the productivity of agricultural crops. In the case of cereal cultivations, climate change impacts on their production mainly through abiotic and biotic stress due for example to heat and water stress but also to pathogens such as bacteria, fungi, nematodes and others. The area under cereal cultivation is increasing worldwide, but, due to these problems, the current rates of yield growth and overall production are not enough to satisfy future demand. For this motivation, there is the needs to monitor and to control the cultivations, also developing new technological solutions useful to better optimize the management strategies, increasing both the quality of products and the quantity of the annual cereal harvest. Infrared imaging is a well-known non-invasive and non-contact technique that represents an outstanding approach of analysis applied in many fields: engineering, medicine, veterinary, cultural heritage and others. In recent years it has been gaining great interest in agriculture as it is well suited to the emerging needs of the precision agriculture management strategies. In this work, we performed an in-field multispectral infrared monitoring of different cereal crops (durum wheat and common wheat) through the use of both LWIR and MWIR cameras. The monitoring carried out made it possible to identify, among the crops analyzed, those subject to higher stress levels and their response to the different spectral ranges used. The results obtained open to the possibility of identifying new figures of merit useful for an effective monitoring of cereal crops and measurable through remote instrumentation.
Active Thermography (AT) is a well-known non-contact and non-invasive imaging technique that has gained great interests in agriculture in recent years. It has been used to evaluate physical and physiological characteristics of plants such as: transpiration rates, heat capacity of the leaves, local water content, response to UV interaction and it fits well with emerging demands of the precision agriculture management strategy. According to this technique, the surface of the sample under investigation is stimulated using an external heat source and its thermal response is detected and recorded using infrared camera. Different strategies can be used for both the measurement protocol and for data analysis. Copper has been widely used in agriculture as a fungicide and bactericide for many decades. Applied on leaf, copper based fungicide (CBF) remains deposited and it is not absorbed into plant tissues, causing accumulation problems that needs to be monitored and controlled, also by using modern technologies. In this work, we test and compare different AT methods to detect and to monitor the presence of CBF on leaves. Our experimental results demonstrate that methodological approaches based on AT can be used to engineer effective remote tools to evaluate in real-time the presence of copper on plants, allowing a tentative of quantification and, therefore, to optimize its use in the agricultural practices.
Composites represent the evolution of the material science and technologies. They are obtained by combining two or more materials of different nature with the aim of exploiting any synergies between the characteristic performances of the raw materials. Their properties, in fact, are influenced by those of the starting components but also by the quality of the interface generated between the combined phases as well as by their mutual distribution. The interphase, even if of minimal extension with respect to the main phases constituting the composite, plays a significant role in the control of the damage mechanisms, determines the breaking strength and the stress / deformation behavior of composite materials. In this work we study the effect of low pressure plasma treatment on intrinsically hydrophilic flax fiber fabrics to improve their adhesion to a hydrophobic polypropylene matrix. The fibers are treated using nitrogen (N2) plasma with four different exposure times. The interfacial adhesion actually achieved was indirectly quantified by interlaminar shear strength measurements. After this, the damaged areas were measured with non-destructive techniques, i.e. Electron Speckle Pattern Interferometry and Lock-in thermography.
The diagnostic of artworks represents a topic of high interest and at the same time a critical task. The development of effective tools based on advanced technologies for investigating and monitoring health-state of item of interest for cultural heritage is essential to assuring their preservation and restoration. In fact, detecting and preventing the formation of damages or assessing them for an accurate pre-restoration analysis are the main objectives of non-destructive investigation. In this study the combined use of Electronic Speckle Pattern Interferometry and Pulse Thermography Analysis, as complementary tools for cultural heritage artifacts diagnostics have been employed on poplar panels painted reproducing original painting methods adopted during the 16th and 17th centuries. Both techniques are full field, contactless, non-invasive and can provide relevant information about state of conservation. The concurrent investigations, allow to expand understanding the results of each individual technique, from which, in many cases, no exclusive assumption is possible. The applications include detection of detachments, micro-cracks, inclusions, and hidden damages. It is also possible the real time monitoring of the behaviour of the object according to the environment thermo-hygrometric changes. The porpoise of this work is to optimize the parameters of such NDT methods on the samples that were specially made by reproducing in high fidelity the structural properties and materials of the artwork. Results show that the employed diagnostic protocols, by speckle interferometry and pulse thermography, are a powerful tool in assessing the pre-restoration health-state and suitable for in situ analysis of wood artworks. Examples of analysis on different artworks are shown.
We utilize Digital Speckle Pattern Interferometry and Square Pulse Thermography Analysis, as complementary tools for
cultural heritage artifacts diagnostics. The concurrent utilization of two methods provide the possibility to complement
and validate the effective understanding of each individual technique results, that are not always easy to interpret. Both
techniques are non-invasive and can be applied on almost any type of archaeological finds, providing relevant
information about their state of conservation. The applications include the whole structure analysis, as well as the
detection of detachments, micro-cracks, hidden damages. The diagnostic investigation can be carried out before, during
and after a restoration. It is also possible the real time monitoring of the behavior of the object according to the
environment thermo-hygrometric changes. Examples of analysis on different artworks are illustrated.
A noniterative image reconstruction method is proposed by the subtraction of diffraction intensity patterns based on the Fraunhofer diffraction theory. According to the linearity theorem of the Fourier transform, the process of the noniterative image reconstruction is performed by numerical calculation, that is, the object wavefront can be extracted by the subtraction of three diffraction intensity patterns of an object and two hybrid masks. Furthermore, the way the noise impacts the quality of the reconstructed image is evaluated and the noise is suppressed by a median filtering algorithm. The results certify that the reconstructed image is consistent with the image of the object. The method provides us with an easy way for retrieving the wavefront with high quality in a wide class of wave fields such as optical, X-ray, electron, and atomic waves.
Electrically Induced Bragg Reflectors can be very attractive to realize programable waveguides networks. Their
practical realization is nevertheless intrinsically connected to the capability to make a peculiar comb-structure electrode
on the top of the waveguides with typical period of 200 nm (corresponding to the Bragg length) and a tolerance of few
nanometers. In this work, the experimental fabrication of these comb-structure electrodes by means of electron beam
lithography is described. We fabricated large areas 1D periodic gold structures with nanometer resolution by using a
high resolution electron beam lithography (EBL) process and a post-processing technique based on lift-off. These
electrodes can be employed as Induced Bragg Reflectors in a multilayer structure for a not permanent periodically
modulation of the effective refractive index of the guiding structure. The desired structures are obtained with
nanometric resolution by means of EBL, digging furrows of rectangular section in both a polymetilmethacrylate
(PMMA) and in α-chloromethacrylate and α-methylstyrene (ZEP) layer spin-coated on silicon, then evaporating a metal
layer (Au) on the top and then by lift-off of metal. The EBL technique allows a very accurate control of the dielectric
distribution of the exposed area able to produce feasible, high efficiency periodic and photonic band-gap structures.
The resulting 1D gratings are made of metal lines 100 nm wide with a period of 200 nm and, 120 nm wide with a
period of 250 nm, respectively. Large area structures (up to 1 mm x 6 μm) have been realized with nanometre resolution
and they have been characterized by scanning electron microscopy (SEM).
These structures will be used in a future work of ours to realize 40 GHz switching speed modulator by inducing a Bragg
Reflector with a reverse biased vertical InP/InGaAsP p-i-n diode according to the predictions of the grating reflectivity
spectra and of the transient response.
Light beam propagation at a prism-magnetic fluid film interface is experimentally studied. The magnetic fluid is made
through dispersion of synthesized cigar-shaped sub-micron particles of Fe2O3 in an oil solution. This was injected into a
glass cell with an active area of 10mm2 and a depth ranging from 10 microns to 30 microns whose base is a glass
microscope slide and on the top it was covered with a glass prism. The set up was developed by one of the authors to
measure light switching at a prism-liquid crystal interface in a previous publication.1 Polarized Light (TE or TM) from a
He-Ne laser impinges at the prism-magnetic film interface. The external reflected light is detected by a photodiode
connected to a data acquisition system. Since the properties of the magnetic fluid can be modulated by external magnetic
fields, we investigated the effects of the magnetic field on the refractive index of the magnetic fluid.
For our magnetic fluid, the reflection of light has been investigated as a function of particles concentration and thickness
of the films with a wavelength of 633nm and both TE and TM polarization, and applied magnetic fields up to 25 Oe. It
was found that the intensity of reflected light increases with increasing magnetic field up to 4 times the initial value, and
saturates at 20 Oe for TE light, while decreases with increasing magnetic field up to 4 times less for TM light with the
same saturation value. Moreover, under a given magnetic field, the output light increases with the increasing film
thickness in TE polarization, and decreases with the increasing film thickness in TM case. The refractive index of the
magnetic fluid depends on the concentration of the dilute oil-based magnetic fluid under zero field.
These behaviors are explained in terms of the organization of the submicron particles when the magnetic field is
applied.2 The cigar-shaped sub-micron particles are oriented along their long axis to form an organized mesostructure.
The different aggregation ability of the magnetic fluid particle is responsible for the variation of the optical properties
under different magnetic fields and for different polarization of the incident light.
It is noteworthly that the magnetically modulated refractive index of the magnetic fluid film could have great potential in
electro-optical applications. In particular, according to the experimental results, we believe that the fluid films that we
are proposing, thanks to the optical responses and the relative times, is a very good candidate to design Fiber Optical
Sensors (FOS) for magnetic fields.
A new metallomesogen (MOM) was prepared aiming to the realization of liquid crystalline materials. A traditional Polymer Dispersed Liquid Crystal (PDLC) has been considered as a reference point in order to compare it with an other one obtained with the inclusion of MOM. We analyzed the thermo- and electro-optical properties of the reference PDLC and of MOM based PDLC. We focused our attention on the light transmittivity when an electric field is applied to the sample and evaluated the contrast ratio of both materials. Furthermore, a detailed morphological analysis is performed to better understand their behavior. A comparison between the PDLC with and without MOM is presented. Our experimental results demonstrated the possibility to use MOM in order to improve the transmittivity characteristic as a function of an electric field for application such as displays or windows.
Integrated optical devices based on liquid crystal's (LC) features have been generally discarded for a long period mainly due to very high scattering losses. However, in the 90's this situation is rapidly changing. A better understanding of the physical phenomena underlying the observed effects, the use of new materials with improved performances, the discovery of new electro-optical and nonlinear optical effects make the applications of LC in integrated optics more and more attractive. We present here some recently obtained results in this field. In particular, we have designed and realized an integrated device in a three-stage planar waveguide, having as middle stage a nematic liquid crystal (NLC) film. We studied the device performance in different geometries using TE polarized light. By a proper choice of the material parameters we measured time responses in the microsecond rage. Our experimental results confirm the possibility of employing such a device working as an optical switch and/or beam deflector.
We analyzed the self-transparency effect of a laser beam traveling in a sample of an unsaturated polyester. Polymer Dispersed Liquid Crystal. This effect is of thermal nature and occurs when a change of the refractive index of the considered composite material is induced by variations of the local temperature due to the incident light power. We studied the mechanism governing this phenomenon and report a detailed 3D map showing how the transmitted beam profile changes as a function of both incident power and time. It is discussed how light intensity and temperature can be used as control parameters for the nonlinear part of the refractive index. Our experimental results indicates the possibility of employing this material to design thermal sensors as devices working as optical switch.
Electro-optical properties of an epoxy-based polymer dispersed liquid crystal (PDLC) have been investigated. A morphological analysis has been performed by optical microscopy in order to estimate initially the average diameter of the liquid crystal microdroplets dispersed in the polymeric matrix. We present the observation of an electro-optical switching effect from an opaque to a transparent state occurring at a threshold value of the applied field in a PDLC. Optical responses of the composite film under the conditions of an externally applied ac electric field and a film thickness of 50μm, were determined using an Argon laser. The experimental result showed promising switching times with a rise time of 200 μsec and a decay time of 2.2 msec and an exceptionally high contrast ratio up to 410. These result demonstrate the validity of employing this new PDLC in electro-optical devices.
A guided light wave can be modulated by coupling it into a ferroelectric liquid crystal (FLC) waveguide. The FLC, which changes its optical properties under the application of an electric field, acts as active medium. With a carefully chosen aligned configuration, the large change in refractive index induced by the electric field, gives a good contrast ratio in the optical response. The optical and electro- optical properties of liquid crystals can be modified by the propagating light and these effects can be enhanced by the addition of a suitable absorbing dye in the liquid crystal. Thus changes in the guiding conditions of the light can be induced also by the guided light itself.
The integrated optical devices represent the most innovative result of the research in the photonics field. New horizons can be open by introduction of new materials and advanced techniques. The applications depend on the properties of the considered materials and their response times to external applied field. In this article we present an integrated device in a three-stage planar waveguide, having as middle stage a nematic liquid crystal film. We studied the device performance with TE polarized input light. By a proper choice of the material parameters and of the driving voltages we got time response in the microsecond range. Our experimental results confirm the possibility of employing such a device working as optical switch and/or beam deflector. A further analysis is in progress in order to explain an anomalous electro-optical behavior occurred for higher applied voltages.
An integrated electro-optical switch based on a planar nematic liquid crystal waveguide has been realized and tested. To achieve this goal, we fabricated and measured a number of step-index waveguides, using RF sputtering and sol-gel deposition techniques. A summary of their characteristics is presented. The design of electro-optical switch is reported, together with the analysis of the problems met in order to optimize the manufacturing process. Finally, we present the experimental results obtained with a three-stages device, having as middle stage a thin nematic LC film and two glass waveguides as other stages. The electro-optical behavior and the response times have been studied for different configurations. The experimental findings show that an additional bias voltage can improve both the transmittivity and the response time of the device, leading to very promising results in the frame of new integrated electro-optical switches.
The design procedure is described of integrated optical switches to be fabricated by inserting a liquid-ciystal cell into a glass planar waveguide. Two configurations are analysed, corresponding to ON-OFF and OFF-ON operation, respectively. Preliminary experimental data on the waveguide characteristics and device fabrication process are also presented.
A first molecular, morphological and thermo-optical characterisation of a new type of Polymer Dispersed Liquid Crystal (PDLC) is presented. The chemical and structural properties are investigated by transmission FT4R spectra. The photopolymerisation process is analysed with optical monitoring, in order to obtain the best curing conditions. An experimental study on the transmithvity as a function of the temperature shows a seff-transparency effect, which occurs near the phase transition. An interpretation of the experimental results in tenns of a nonlinearity of thermal origin is given, using the theory of nonlinear scattering in heterogeneous media. The temperature switch, obtained in such a condition, suggests the
possibility of employing such a material to realise a new type of all-optical temperature sensors and open the horizon to a new class ofthermo-optical devices.
The problem of propagation of guided light in hybrid integrated planar waveguides is afforded in terms of Local Normal Modes. The approach is then generalized taking into account reflected modes arising when index discontinuity between adjacent guiding steps is significant. This is crucial for liquid crystal based waveguide devices. Transmission features in homogeneous as well as inhomogeneous and anisotropic waveguides have been considered in numerical computations. One of the worked examples can well explain previously reported experimental results.
The light beam propagation at a prisms-liquid crystal interface is studied both theoretically and experimentally making a comparison between a theoretical model based on the Berreman formalism and the experimental results. Our results suggest the possibility of employing such interface as a new electooptical device for detecting magnetic fields.
The propagation of cw laser beams oppositely travelling in a polymeric blend (PMMA-EVA) is analyzed in order to study the thermo-optical behavior of such a material. The experimental results show optical bistability due to the mutual self-action of counterpropagating beams. The thermal coefficient of the refractive index dn/dt of PMMA-EVA is calculated by a simple theoretical model. This value is in well agreement with that one obtained by us using an interferometric method.
In order to investigate laser effects on biological specimens, Hydra, a coelenterate with high regeneration rate, was observed for ten days during regeneration after CO2 laser cutting. Control animals were cut with a razor blade immediately below the tentacle whorl under a dissecting microscope while they were in small glass petri dishes. They regenerated tentacles completely 8 to 10 days from the cutting. Hydra were cut in the same position with CO2 laser. As a first step, we studied the effect of the laser beam on the normal behaviour of hydra. For the cutting, we used four different power intensities: 0.5, 1.0, 1.5 and 2.0 W. At different power intensities the animals regenerated the tentacles. However in about 20% of the animals the amputation performed with 1 and 1.5 W originated a quicker regeneration of tentacles. No effect was observed on asexual reproduction of the polyps and therefore also no change of the bud index.
The physical properties of the PMMA-EVA , a poly (methylmetacrylate) with 7% by wt. of poly
(ethylene-covinylacetate) blend,have been investigated with a photoacoustic technique, which allows us
to analyse the absorption as a function of the wave length. The informations obtained from the absorption
spectra of this blend are useful in interpreting the behaviour of such a novel material subjected to thermal
variations.
In recent years, polymer and polymeric blends with high order susceptibility have attracted a great deal of
attention in nonlinear optics field. We propose a novel polymeric blend for optical investigation, a poly
(methylmetacrylate (PMMA) with 7% by wt. of poly (ethylene-co-vinylacetate) (EVA) blend, and present
a simple characterization of this material by photoacoustic technique. This blend is polymerized by an
unique technique in which the acrylic matrix is polymerized in the presence of dissolved EVA copolymer.
The resulting blend is characterized by an intimate dispersion of rubbery droplets (diameter 1 jim) in an
acrylic rubbery particles. The PMMA-EVA thermograph in the temperature range - 50 °C to 220 °C
exhibits a phase transition at 50 °C, when 10% of EVA melts. Since this polymeric blend suffers an
abrupt diffusion near the temperature of the phase transition (- 50 °C), we used the photoacoustic
spectroscopy (PAS) in order to compare the absorption spectra at several temperatures. This technique,
based on the photoacoustic effect, makes possible the analysis of samples with high absorption and/or
scattering.
A novel polymeric material a poly (methylmetacrylate) (PMMA) with 7 by wt. of poly (ethylenecovinylacetate) (EVA) blend is presented. The PMMAIEVA thermograph in the temperature range -50 to 220 C exhibits a phase transition at 50 C. During this transition the typical hysteresis of the polymeric transitions has been noted. We show the behaviour of the optical transmission as a function of the temperature and present some physical properties of this material. In the frame of a research on the preparation and characterization of high mechanical performances PMMA-based blends we conducted several optical tests in order to verify the potential applications of such blends in devices of integrated optics. Tough transparent PMMA is industrially produced by a multistage process of incorporation of rubbery particles in a methacrylic matrix. The rubbers are obtained by a suspension process in which a shell of cross-linked rubbery buthyl acrylate-styrene copolymer is polymerized around a PMMA matrix. The core-shell structure (fig. 1) is necessary in order to assume a good stress transfer between the phases and at the same time a better matching of the refractive indices of the two phases. To achieve the desired level of toughening high amounts (20-30 by wt) of rubber are necessary with an unavoidable diminution of elastic modules. In our procedure an amorphous ethylene-co-vinylacetate copolymer (EVA 20 by wt of VA) is used as rubbery component 1 The synthetic process
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