Spectroscopic investigation and heat generation of Yb3+/Ho3+ codoped aluminosilicate glasses looking for the emission at 2 ��m

Energy transfer (ET) and heat generation processes in Yb3+/Ho3+-codoped low-silica calcium aluminosilicate glasses were investigated using thermal lens (TL) and photoluminescence measurements looking for the emission around 2.0 ��m. Stepwise ET processes from Yb3+ to Ho3+, upon excitation at 0.976 ��m, produced highly efficient emission in the mid-infrared range at around 2.0 ��m, with high fluorescence quantum efficiency (��1 ��� 0.85 and independent of Ho3+ concentration) and relatively very low thermal loading (<0.4) for concentration up to 1.5% of Ho2O3. An equation was deduced for the description of the TL results that provided the absolute value of ��1 and the number of emitted photons at 2.0 ��m per absorbed pump photon by the Yb3+ ions, the latter reaching 60% for the highest Ho3+ concentration. These results suggest that the studied codoped system would be a promising candidate for the construction of photonic devices, especially for medical applications.

Luminescence quantum efficiency at 1.5 ��m of Er3+- doped tellurite glass determined by thermal lens spectroscopy

Erbium doped tellurite glasses (TeO2 + Li2O + TiO2) were prepared by conventional melt-quenching method to study the influence of the Er3+ concentration on the luminescence quantum efficiency (��) at 1.5 ��m. Absorption and luminescence data were used to characterize the samples, and the �� parameter was measured using the well-known thermal lens spectroscopy. For low Er3+ concentration, the measured values are around 76%, and the concentration behavior of �� shows Er-Er and Er-OH- interactions, which agreed with the measured lifetime values.

Multiwavelenght study of cluster mergers and consequences for the radio emission properties of galaxy clusters

In the present thesis a thourough multiwavelength analysis of a number of galaxy clusters known to be experiencing a merger event is presented. The bulk of the thesis consists in the analysis of deep radio observations of six merging clusters, which host extended radio emission on the cluster scale. A composite optical and X���ray analysis is performed in order to obtain a detailed and comprehensive picture of the cluster dynamics and possibly derive hints about the properties of the ongoing merger, such as the involved mass ratio, geometry and time scale. The combination of the high quality radio, optical and X���ray data allows us to investigate the implications of the ongoing merger for the cluster radio properties, focusing on the phenomenon of cluster scale diffuse radio sources, known as radio halos and relics. A total number of six merging clusters was selected for the present study: A3562, A697, A209, A521, RXCJ 1314.4���2515 and RXCJ 2003.5���2323. All of them were known, or suspected, to possess extended radio emission on the cluster scale, in the form of a radio halo and/or a relic. High sensitivity radio observations were carried out for all clusters using the Giant Metrewave Radio Telescope (GMRT) at low frequency (i.e. ��� 610 MHz), in order to test the presence of a diffuse radio source and/or analyse in detail the properties of the hosted extended radio emission. For three clusters, the GMRT information was combined with higher frequency data from Very Large Array (VLA) observations. A re���analysis of the optical and X���ray data available in the public archives was carried out for all sources. Propriety deep XMM���Newton and Chandra observations were used to investigate the merger dynamics in A3562. Thanks to our multiwavelength analysis, we were able to confirm the existence of a radio halo and/or a relic in all clusters, and to connect their properties and origin to the reconstructed merging scenario for most of the investigated cases. ��� The existence of a small size and low power radio halo in A3562 was successfully explained in the theoretical framework of the particle re���acceleration model for the origin of radio halos, which invokes the re���acceleration of pre���existing relativistic electrons in the intracluster medium by merger���driven turbulence. ��� A giant radio halo was found in the massive galaxy cluster A209, which has likely undergone a past major merger and is currently experiencing a new merging process in a direction roughly orthogonal to the old merger axis. A giant radio halo was also detected in A697, whose optical and X���ray properties may be suggestive of a strong merger event along the line of sight. Given the cluster mass and the kind of merger, the existence of a giant radio halo in both clusters is expected in the framework of the re���acceleration scenario. ��� A radio relic was detected at the outskirts of A521, a highly dynamically disturbed cluster which is accreting a number of small mass concentrations. A possible explanation for its origin requires the presence of a merger���driven shock front at the location of the source. The spectral properties of the relic may support such interpretation and require a Mach number M < ��� 3 for the shock. ��� The galaxy cluster RXCJ 1314.4���2515 is exceptional and unique in hosting two peripheral relic sources, extending on the Mpc scale, and a central small size radio halo. The existence of these sources requires the presence of an ongoing energetic merger. Our combined optical and X���ray investigation suggests that a strong merging process between two or more massive subclumps may be ongoing in this cluster. Thanks to forthcoming optical and X���ray observations, we will reconstruct in detail the merger dynamics and derive its energetics, to be related to the energy necessary for the particle re���acceleration in this cluster. ��� Finally, RXCJ 2003.5���2323 was found to possess a giant radio halo. This source is among the largest, most powerful and most distant (z=0.317) halos imaged so far. Unlike other radio halos, it shows a very peculiar morphology with bright clumps and filaments of emission, whose origin might be related to the relatively high redshift of the hosting cluster. Although very little optical and X���ray information is available about the cluster dynamical stage, the results of our optical analysis suggest the presence of two massive substructures which may be interacting with the cluster. Forthcoming observations in the optical and X���ray bands will allow us to confirm the expected high merging activity in this cluster. Throughout the present thesis a cosmology with H0 = 70 km s���1 Mpc���1, m=0.3 and =0.7 is assumed.

Planktonic potential CO2 emission calculation: preliminary results by applying an adapted enzymatic methodology to marine ecosystems

<p>[EN]Isocitrate Dehydrogenase (IDH) is a key enzyme in the Krebs cycle, being responsible for the production of one of the three CO2 molecules related to cellular respiration. In order to measure the potential CO2 production linked to the marine planktonic community we have adapted an enzymatic methodology. Preliminary results show that different proportions of autotrophs, heterotrophs and mixotrophs and their metabolic pathways, lead to different relationships between potential CO2 emission and potential O2 consumption during cellular respiration. Although more experiments need to be made, this methodology is leading to a better understanding of cellular respiration in marine samples and their impact on the food chain, vertical Carbon flux and the current sequestering capacity for anthropogenic CO2.</p>

Design and Characterization of New Luminescent Sensors and Labels

The aim of this Ph.D. project has been the design and characterization of new and more efficient luminescent tools, in particular sensors and labels, for analytical chemistry, medical diagnostics and imaging. Actually both the increasing temporal and spatial resolutions that are demanded by those branches, coupled to a sensitivity that is required to reach the single molecule resolution, can be provided by the wide range of techniques based on luminescence spectroscopy. As far as the development of new chemical sensors is concerned, as chemists we were interested in the preparation of new, efficient, sensing materials. In this context, we kept developing new molecular chemosensors, by exploiting the supramolecular approach, for different classes of analytes. In particular we studied a family of luminescent tetrapodal-hosts based on aminopyridinium units with pyrenyl groups for the detection of anions. These systems exhibited noticeable changes in the photophysical properties, depending on the nature of the anion; in particular, addition of chloride resulted in a conformational change, giving an initial increase in excimeric emission. A good selectivity for dicarboxylic acid was also found. In the search for higher sensitivities, we moved our attention also to systems able to perform amplification effects. In this context we described the metal ion binding properties of three photoactive poly-(arylene ethynylene) co-polymers with different complexing units and we highlighted, for one of them, a ten-fold amplification of the response in case of addition of Zn2+, Cu2+ and Hg2+ ions. In addition, we were able to demonstrate the formation of complexes with Yb3+ an Er3+ and an efficient sensitization of their typical metal centered NIR emission upon excitation of the polymer structure, this feature being of particular interest for their possible applications in optical imaging and in optical amplification for telecommunication purposes. An amplification effect was also observed during this research in silica nanoparticles derivatized with a suitable zinc probe. In this case we were able to prove, for the first time, that nanoparticles can work as ���off-on��� chemosensors with signal amplification. Fluorescent silica nanoparticles can be thus seen as innovative multicomponent systems in which the organization of photophysically active units gives rise to fruitful collective effects. These precious effects can be exploited for biological imaging, medical diagnostic and therapeutics, as evidenced also by some results reported in this thesis. In particular, the observed amplification effect has been obtained thanks to a suitable organization of molecular probe units onto the surface of the nanoparticles. In the effort of reaching a deeper inside in the mechanisms which lead to the final amplification effects, we also attempted to find a correlation between the synthetic route and the final organization of the active molecules in the silica network, and thus with those mutual interactions between one another which result in the emerging, collective behavior, responsible for the desired signal amplification. In this context, we firstly investigated the process of formation of silica nanoparticles doped with pyrene derivative and we showed that the dyes are not uniformly dispersed inside the silica matrix; thus, core-shell structures can be formed spontaneously in a one step synthesis. Moreover, as far as the design of new labels is concerned, we reported a new synthetic approach to obtain a class of robust, biocompatible silica core-shell nanoparticles able to show a long-term stability. Taking advantage of this new approach we also showed the synthesis and photophysical properties of core-shell NIR absorbing and emitting materials that proved to be very valuable for in-vivo imaging. In general, the dye doped silica nanoparticles prepared in the framework of this project can conjugate unique properties, such as a very high brightness, due to the possibility to include many fluorophores per nanoparticle, high stability, because of the shielding effect of the silica matrix, and, to date, no toxicity, with a simple and low-cost preparation. All these features make these nanostructures suitable to reach the low detection limits that are nowadays required for effective clinical and environmental applications, fulfilling in this way the initial expectations of this research project.

Quantitative Aspekte der Anziehungskraft von Stra��enbeleuchtungen auf die Emergenz aus nahegelegenen Gew��ssern (Ephemeroptera, Plecoptera, Trichoptera, Diptera: Simuliidae, Chironomidae, Empididae) unter Ber��cksichtigung der spektralen Emission ve

Beim Beobachten von n��chtlichen Insektenschw��rmen an Stra��enbeleuchtungen kommt es zur Frage, inwieweit von einer Bedrohung eines geordneten Naturkreislaufes durch dieses Ph��nomen gesprochen werden kann. Am Beispiel der bedrohten Artenvielfalt aquatischer Insekten im Bereich anthropogen bedingt verschmutzter Flie��gew��sser wurde die Problematik umfassend untersucht. Die Freilandtests erstreckten sich von Sommer 1998 bis Sommer 2000. Die vorliegende Arbeit geht mehreren Fragestellungen nach:1. - Wie hoch ist der Anteil aquatischer Insekten, der von dem Ort seiner Emergenz aus von einer naheliegenden Stra��enlaterne angezogen wird ?2. - Welcher Lampentyp lockt weniger Insekten an: OSRAM HQL (Wei��-Mischlicht) oder PHILIPPS SON (gelbes Licht) ?3. - Welche Wellenl��ngenbereiche des Lichts sind beim Anflug an die Lampe von besonderer Pr��ferenz ? zu 1. - Aquatische Insekten wiesen kein einheitliches Verhalten im Anflug an k��nstliches Licht auf. In den Sommermonaten kam es bei einigen Insektengruppen, wie z.B. den Trichopteren, zu einem massenhaften Anflug an die eine, im Untersuchungsgebiet aufgestellte Stra��enlaterne. In dieser Zeit ergaben sich im Mittelwert Fangzahlen in einer Nacht am Licht, die der Emergenz von 25 Metern Bachufer/72 Stunden entsprachen. Bei den Dipteren ergab der mittlere Wert eine Emergenz von knapp 10 Metern Uferl��nge/72 Stunden. Aufgrund hoher Fangzahlen konnten folgende Ergebnisse auf Artniveau bei den Chironomiden erzielt werden. Bei den zehn h��ufigsten Arten aus Emergenz und Lichtfang zeigten sich starke Schwankungen: Der Fang am Licht entsprach im Maximum einer Schlupfrate von 61 Metern Ufer/ 72 Stunden bei einer Art, bei einer anderen Art wurde z.B. ein Lichtfang erzielt, der lediglich die Emergenz von 0,3 Metern/72 Stunden umfa��te.zu 2. - In dem ohne Lichtkonkurrenz stattfindenden Vergleich zwischen PHILIPPS SON 70W und OSRAM HQL 125W ergab sich eine Fangrelation von 1:1,6 (SON:HQL). Bei einem Parallelfang (30 Metern Abstand der Leuchten) mit SON/HQL flogen wesentlich mehr Tiere an die HQL: Hier betrug die Relation 1:3,97 (SON:HQL). Es fand somit bei Lichtkonkurrenz eine Abwanderung der Insekten zur 'attraktiveren' Lampe statt.zu 3. - Zuletzt wurde die Anlockwirkung dreier Farbspektren mit den Intensit��tsmaxima einer Wellenl��nge von 437nm, 579nm und 599nm getestet. 437nm war die in der HQL gemessene Intensit��tsspitze im niedrigwelligen Bereich und nach verbreiteter Auffassung von besonderer Anlockwirkung. Der Wellenl��ngenbereich um 579nm stellte das Intensit��tsmaximum der SON-Lampe dar (gelbes Licht); 599nm war als Alternative f��r anlockschwache Beleuchtungen ausgew��hlt worden. Hier ergab sich bei abwechselndem Fang (ohne Lichtkonkurrenz) eine Fangrelation von 1,8 : 3,4 : 1 (437nm : 579nm : 599nm).

Development of the optimal estimation method for inversion of stratospheric emission spectra and validation of HNO3 profiles

This doctoral thesis focuses on ground-based measurements of stratospheric nitric acid (HNO3)concentrations obtained by means of the Ground-Based Millimeter-wave Spectrometer (GBMS). Pressure broadened HNO3 emission spectra are analyzed using a new inversion algorithm developed as part of this thesis work and the retrieved vertical profiles are extensively compared to satellite-based data. This comparison effort I carried out has a key role in establishing a long-term (1991-2010), global data record of stratospheric HNO3, with an expected impact on studies concerning ozone decline and recovery. The first part of this work is focused on the development of an ad hoc version of the Optimal Estimation Method (Rodgers, 2000) in order to retrieve HNO3 spectra observed by means of GBMS. I also performed a comparison between HNO3 vertical profiles retrieved with the OEM and those obtained with the old iterative Matrix Inversion method. Results show no significant differences in retrieved profiles and error estimates, with the OEM providing however additional information needed to better characterize the retrievals. A final section of this first part of the work is dedicated to a brief review on the application of the OEM to other trace gases observed by GBMS, namely O3 and N2O. The second part of this study deals with the validation of HNO3 profiles obtained with the new inversion method. The first step has been the validation of GBMS measurements of tropospheric opacity, which is a necessary tool in the calibration of any GBMS spectra. This was achieved by means of comparisons among correlative measurements of water vapor column content (or Precipitable Water Vapor, PWV) since, in the spectral region observed by GBMS, the tropospheric opacity is almost entirely due to water vapor absorption. In particular, I compared GBMS PWV measurements collected during the primary field campaign of the ECOWAR project (Bhawar et al., 2008) with simultaneous PWV observations obtained with Vaisala RS92k radiosondes, a Raman lidar, and an IR Fourier transform spectrometer. I found that GBMS PWV measurements are in good agreement with the other three data sets exhibiting a mean difference between observations of ~9%. After this initial validation, GBMS HNO3 retrievals have been compared to two sets of satellite data produced by the two NASA/JPL Microwave Limb Sounder (MLS) experiments (aboard the Upper Atmosphere Research Satellite (UARS) from 1991 to 1999, and on the Earth Observing System (EOS) Aura mission from 2004 to date). This part of my thesis is inserted in GOZCARDS (Global Ozone Chemistry and Related Trace gas Data Records for the Stratosphere), a multi-year project, aimed at developing a long-term data record of stratospheric constituents relevant to the issues of ozone decline and expected recovery. This data record will be based mainly on satellite-derived measurements but ground-based observations will be pivotal for assessing offsets between satellite data sets. Since the GBMS has been operated for more than 15 years, its nitric acid data record offers a unique opportunity for cross-calibrating HNO3 measurements from the two MLS experiments. I compare GBMS HNO3 measurements obtained from the Italian Alpine station of Testa Grigia (45.9�� N, 7.7�� E, elev. 3500 m), during the period February 2004 - March 2007, and from Thule Air Base, Greenland (76.5��N 68.8��W), during polar winter 2008/09, and Aura MLS observations. A similar intercomparison is made between UARS MLS HNO3 measurements with those carried out from the GBMS at South Pole, Antarctica (90��S), during the most part of 1993 and 1995. I assess systematic differences between GBMS and both UARS and Aura HNO3 data sets at seven potential temperature levels. Results show that, except for measurements carried out at Thule, ground based and satellite data sets are consistent within the errors, at all potential temperature levels.

Size-selective investigations of spectral and emission properties of small particles and nanotubes

In dieser Arbeit wurde die Elektronenemission von Nanopartikeln auf Oberfl��chen mittels spektroskopischen Photoelektronenmikroskopie untersucht. Speziell wurden metallische Nanocluster untersucht, als selbstorganisierte Ensembles auf Silizium oder Glassubstraten, sowie ferner ein Metall-Chalcogenid (MoS2) Nanor��hren-Prototyp auf Silizium. Der Hauptteil der Untersuchungen war auf die Wechselwirkung von fs-Laserstrahlung mit den Nanopartikeln konzentriert. Die Energie der Lichtquanten war kleiner als die Austrittsarbeit der untersuchten Proben, so dass Ein-Photonen-Photoemission ausgeschlossen werden konnte. Unsere Untersuchungen zeigten, dass ausgehend von einem kontinuierlichen Metallfilm bis hin zu Clusterfilmen ein anderer Emissionsmechanismus konkurrierend zur Multiphotonen-Photoemission auftritt und f��r kleine Cluster zu dominieren beginnt. Die Natur dieses neuen Mechanismus` wurde durch verschiedenartige Experimente untersucht. Der ��bergang von einem kontinuierlichen zu einem Nanopartikelfilm ist begleitet von einer Zunahme des Emissionsstroms von mehr als eine Gr����enordnung. Die Photoemissions-Intensit��t w��chst mit abnehmender zeitlicher Breite des Laserpulses, aber diese Abh��ngigkeit wird weniger steil mit sinkender Partikelgr����e. Die experimentellen Resultate wurden durch verschiedene Elektronenemissions-Mechanismen erkl��rt, z.B. Multiphotonen-Photoemission (nPPE), thermionische Emission und thermisch unterst��tzte nPPE sowie optische Feldemission. Der erste Mechanismus ��berwiegt f��r kontinuierliche Filme und Partikel mit Gr����en oberhalb von mehreren zehn Nanometern, der zweite und dritte f��r Filme von Nanopartikeln von einer Gr����e von wenigen Nanometern. Die mikrospektroskopischen Messungen best��tigten den 2PPE-Emissionsmechanismus von d��nnen Silberfilmen bei ���blauer��� Laseranregung (h��=375-425nm). Das Einsetzen des Ferminiveaus ist relativ scharf und verschiebt sich um 2h��, wenn die Quantenenergie erh��ht wird, wogegen es bei ���roter��� Laseranregung (h��=750-850nm) deutlich verbreitert ist. Es zeigte sich, dass mit zunehmender Laserleistung die Ausbeute von niederenergetischen Elektronen schw��cher zunimmt als die Ausbeute von h��herenergetischen Elektronen nahe der Fermikante in einem Spektrum. Das ist ein klarer Hinweis auf eine Koexistenz verschiedener Emissionsmechanismen in einem Spektrum. Um die Gr����enabh��ngigkeit des Emissionsverhaltens theoretisch zu verstehen, wurde ein statistischer Zugang zur Lichtabsorption kleiner Metallpartikel abgeleitet und diskutiert. Die Elektronenemissionseigenschaften bei Laseranregung wurden in zus��tzlichen Untersuchungen mit einer anderen Anregungsart verglichen, der Passage eines Tunnelstroms durch einen Metall-Clusterfilm nahe der Perkolationsschwelle. Die elektrischen und Emissionseigenschaften von stromtragenden Silberclusterfilmen, welche in einer schmalen L��cke (5-25 ��m Breite) zwischen Silberkontakten auf einem Isolator hergestellt wurden, wurden zum ersten Mal mit einem Emissions-Elektronenmikroskop (EEM) untersucht. Die Elektronenemission beginnt im nicht-Ohmschen Bereich der Leitungsstrom-Spannungskurve des Clusterfilms. Wir untersuchten das Verhalten eines einzigen Emissionszentrums im EEM. Es zeigte sich, dass die Emissionszentren in einem stromleitenden Silberclusterfilm Punktquellen f��r Elektronen sind, welche hohe Emissions-Stromdichten (mehr als 100 A/cm2) tragen k��nnen. Die Breite der Energieverteilung der Elektronen von einem einzelnen Emissionszentrum wurde auf etwa 0.5-0.6 eV abgesch��tzt. Als Emissionsmechanismus wird die thermionische Emission von dem ���steady-state��� hei��en Elektronengas in stromdurchflossenen metallischen Partikeln vorgeschlagen. Gr����enselektierte, einzelne auf Si-Substraten deponierte MoS2-Nanor��hren wurden mit einer Flugzeit-basierten Zweiphotonen-Photoemissions-Spektromikroskopie untersucht. Die Nanor��hren-Spektren wiesen bei fs-Laser Anregung eine erstaunlich hohe Emissionsintensit��t auf, deutlich h��her als die SiOx Substratoberfl��che. Dagegen waren die R��hren unsichtbar bei VUV-Anregung bei h��=21.2 eV. Eine ab-initio-Rechnung f��r einen MoS2-Slab erkl��rt die hohe Intensit��t durch eine hohe Dichte freier intermedi��rer Zust��nde beim Zweiphotonen-��bergang bei h��=3.1 eV.

Biogenic emission of halocarbons

Within this doctoral thesis, biogenic emissions of several globally relevant halocarbons (methyl chloride, methyl bromide, methyl iodide, dibromomethane, chloroform and bromoform) have been investigated in different environments. An airborne study was focused on the tropical rainforest ecosystem, while shipborne measurements investigated naturally occurring oceanic plankton blooms. Laboratory experiments using dried plant material were made to elucidate abiotic production mechanisms occurring in organic matter. Airborne measurements over the tropical rainforest of Suriname and French Guyana (3 - 6 ��N, 51 - 59 ��W) revealed net fluxes of 9.5 (�� 3.8 2��) ��g m-2 h-1 methyl chloride and 0.35 (�� 0.15 2��) ��g m-2 h-1 chloroform emitted in the long dry season (October) 2005. An extrapolation of these numbers to all tropical forests helped to narrow down the range of the recently discovered and poorly quantified methyl chloride source from tropical ecosystems. The value for methyl chloride obtained (1.5 (�� 0.6 2��) Tg yr-1) affirms that the contribution of the tropical forest ecosystem is the major source in the global budget of methyl chloride. The extrapolated global net chloroform flux from tropical forests (56 (�� 23 2��) Gg yr-1) is of minor importance (5 - 10 %) compared to the global sources. A source of methyl bromide from this region could not be verified. The abiotic formation of methyl chloride and methyl bromide from dead plant material was tested in a laboratory study. The release from plant tissue representative of grassland, deciduous forest, agricultural areas and coastal salt marshes (hay, ash, tomato and saltwort) has been monitored. Incubations at different temperatures (25 - 50 ��C) revealed significant emissions even at ambient temperature, and that the emissions increased exponentially with temperature. The strength of the emission was found to be additionally dependent on the availability of halide and the methoxyl group within the plant tissue. However, high water content in the plant material was found to inhibit methyl halide emissions. The abiotic nature of the reaction yielding methyl halides was confirmed by its high activation energy calculated via Arrhenius plots. Shipborne measurements of the atmospheric mixing ratios of methyl chloride, methyl bromide, methyl iodide, dibromomethane and bromoform have been conducted along a South Atlantic transect from the 27.01. - 05.02.2007 to characterize halocarbon emissions from a large-scale natural algae bloom encountered off the coast of Argentina. Mixing ratios of methyl chloride and methyl bromide were not significantly affected by the occurrence of the phytoplankton bloom. Emissions of methyl iodide, dibromomethane and bromoform showed pronounced mixing ratio variations, triggered by phytoplankton abundance. Methyl iodide was strongly correlated with dimethyl sulfide throughout the sampled region. A new technique combining satellite derived biomass marker (chlorophyll a) data with back trajectory analysis was successfully used to attribute variations in mixing ratios to air masses, which recently passed over areas of enhanced biological production.

Main characteristics of the emission from elliptical galaxies

Elliptical galaxies are one of the most characteristic objects we can find in the sky. In order to unveil their properties, such as their structure or chemical composition, one must study their spectral emission. In fact they seem to behave rather differently when observed with different eyes. This is because their light is mainly brought by two different components: optical radiation arises from its stars, while the X emission is primarly due to a halo of extremely hot gas in which ellipticals seem to be embedded. After a brief classification, the two main processes linked to these phenomena will be described, together with the informations we can collect thanks to them. Eventually, we will take a quick look at the other regions of the electromagnetic spectrum.