967 resultados para INFRARED DETECTORS
Resumo:
A system comprised of a Bomem interferometer and a LT3-110 Heli-Tran cryostat was set up to measure the reflectance of materials in the mid-infrared spectral region. Several tests were conducted to ensure the consistency and reliability of the system. Silicon and Chromium, two materials with well known optical properties were measured to test the accuracy of the system, and the results were found to be in good agreement with the literature. Reflectance measurements on pure SnTe and several Pb and Mn-doped alloys were carried out. These materials were chosen because they exhibit a strong plasma edge in the mid infrared region. The optical conductivity and several related optical parameters were calculated from the measured reflectance. Very low temperature measurements were carried out in the far-infrared on Sn9SMn2Te, and the results are indicative of a spin glass phase at 0.8 K. Resistivity measurements were made at room temperature. The resistivity values were found, as expected, to decrease with increasing carrier concentration and to increase with increasing manganese concentration.
Resumo:
A system comprised of a Martin-Puplett type polarizing interferometer and a Helium-3 cryostat was developed to study the transmission of materials in the very-far-infrared region of the spectrum. This region is of significant interest due to the low-energy excitations which many materials exhibit. The experimental transmission spectrum contains information concerning the optical properties of the material. The set-up of this system is described in detail along with the adaptations and improvements which have been made to the system to ensure the best results. Transmission experiments carried out with this new set-up for two different varieties of materials: superconducting thin films of lead and biological proteins, are discussed. Several thin films of lead deposited on fused silica quartz substrates were studied. From the ratio of the transmission in the superconducting state to that in the normal state the superconducting energy gap was determined to be approximately 25 cm-1 which corresponds to 2~/kBTc rv 5 in agreement with literature data. Furthermore, in agreement with theoretical predictions, the maximum in the transmission ratio was observed to increase as the film thickness was increased. These results provide verification of the system's ability to accurately measure the optical properties of thin low-Tc superconducting films. Transmission measurements were carried out on double deionized water, and a variety of different concentrations by weight of the globular protein, Bovine Serum Albumin, in the sol, gel and crystalline forms. The results of the water study agree well with literature values and thus further illustrate the reproducibility of the system. The results of the protein experiments, although preliminary, indicate that as the concentration increases the samples become more transparent. Some weak structure in the frequency dependent absorption coefficient, which is more prominent in crystalline samples, may be due to low frequency vibrations of the protein molecules.
Resumo:
A new Ultra-High Vacuum (UHV) reflectance spectrometer was successfully designed, making use of a Janis Industries ST-400 sample cryostat, IR Labs bolometer, and Briiker IFS 66 v/S spectrometer. Two of the noteworthy features include an in situ gold evaporator and internal reference path, both of which allow for the experiment to progress with a completely undisturbed sample position. As tested, the system was designed to operate between 4.2 K and 325 K over a frequency range of 60 - 670 cm~^. This frequency range can easily be extended through the addition of appUcable detectors. Tests were performed on SrTiOa, a highly ionic incipient ferroelectric insulator with a well known reflectance. The presence and temperatmre dependence of the lowest frequency "soft" mode were measured, as was the presence of the other two infrared modes. During the structural phase transition from cubic to tetragonal perovskite, the splitting of the second phonon mode was also observed. All of the collected data indicate good agreement with previous measurements, with a minor discrepency between the actual and recorded sample temperatures.
Resumo:
The optical response to far infrared radiation has been measured on a mosaic of heavy fermion CeCoIns single crystals. The superconducting transition temperature of the crystals has been determined by van der Pauw resistivity and ac-susceptibility measurements as Tc = 2.3 K. The optical measurements were taken above and below the transition temperature using a ^He cryostat and step and integrate Martin-Puplett type polarizing interferometer. The absolute reflectance of the heavy fermion CeCoIns in the superconducting state in range (0, 100)cm~^ was calculated from the measured thermal reflectance, using the normal state data of Singley et al and a low frequency extrapolation for a metallic material in the Hagen-Rubens regime. By means of Kramers-Kronig analysis the absolute reflectance was used to calculate the optical conductivity of the sample. The real part of the calculated complex conductivity a{u)) of CeCoIns indicates a possible opening of an energy gap close to 50 cm~^.
Resumo:
Measurements of the optical reflectivity of the normal incident light along c-axis [0001] have been made on a Gadolinium single crystal, for temperatures between 50 K and room temperature just above the Curie temperature of Gd, which is 293 K. And covering the spectrum range between 100 -11000 cm-I . This work is the first study of Gd in the far infrared range. In fact it fills the gap below 0.2 eV which has never been measured before. Extreme attention was paid to the fact that Gadolinium is a very reactive metal with air. Thus, the sample was mechanically polished and carefully handled during the measurement. However, temperature dependent optical measurements have been made in the same frequency range for a sample of Gd2O3. For comparison, both samples of Gd and Gd2O3 were examined by X-Ray diffraction. XRD analysis showed that the sample was pure gadolinium and the oxide layer either does not exist, or is very thin. Furthermore, this fact was supported by the absence of any of Gd2O3 features in the Gd sample reflectivity. Kramers Kronig analysis was applied to extract the optical functions from the reflectance data. The optical conductivity shows a strong temperature dependence feature in the mid-infrared. This feature disappears completely at room temperature which supports a magnetic origin.
Resumo:
Infrared thermography is a non-invasive technique that measures mid to long-wave infrared radiation emanating from all objects and converts this to temperature. As an imaging technique, the value of modern infrared thermography is its ability to produce a digitized image or high speed video rendering a thermal map of the scene in false colour. Since temperature is an important environmental parameter influencing animal physiology and metabolic heat production an energetically expensive process, measuring temperature and energy exchange in animals is critical to understanding physiology, especially under field conditions. As a non-contact approach, infrared thermography provides a non-invasive complement to physiological data gathering. One caveat, however, is that only surface temperatures are measured, which guides much research to those thermal events occurring at the skin and insulating regions of the body. As an imaging technique, infrared thermal imaging is also subject to certain uncertainties that require physical modeling, which is typically done via built-in software approaches. Infrared thermal imaging has enabled different insights into the comparative physiology of phenomena ranging from thermogenesis, peripheral blood flow adjustments, evaporative cooling, and to respiratory physiology. In this review, I provide background and guidelines for the use of thermal imaging, primarily aimed at field physiologists and biologists interested in thermal biology. I also discuss some of the better known approaches and discoveries revealed from using thermal imaging with the objective of encouraging more quantitative assessment.
Resumo:
Les naines brunes sont, en termes de masse, les objets astrophysiques intermédiaires entre les planètes géantes gazeuses et les étoiles de faible masse. Elles se forment de la même manière que les étoiles, par contraction gravitationnelle d’un fragment de nuage de gaz moléculaire ayant atteint la limite de Jeans, mais se différencient par leur incapa- cité à produire les réactions de fusion de l’hydrogène dans leur cœur. Les naines brunes sont par conséquent des objets qui se refroidissent graduellement, et dont les propriétés spectrales évoluent au cours du temps. Ce mémoire présente la recherche de nouvelles candidates de type spectral T tardif et Y, dans le but de compléter le relevé des naines brunes du voisinage solaire. Cette recherche est motivée par deux objectifs principaux. Premièrement, un échantillon com- plet des objets de faible masse est nécessaire pour contraindre correctement la limite aux faibles masses de la fonction de masse initiale des nuages interstellaires, problème clé en astrophysique actuellement. Deuxièmement, les naines brunes de types spectraux tardifs sont les objets stellaires dont les propriétés atmosphériques sont les plus semblables à celles des planètes géantes gazeuses. Par conséquent, la recherche de nouvelles naines brunes permet indirectement d’améliorer nos connaissances des exoplanètes, sans être contraints par la proximité d’étoiles brillantes. À partir du WISE All-Sky Source Catalog, nous avons établi un échantillon de 55 candidates naines brunes répondant aux critères photométriques attendus. Parmi ces can- didates, 17 ont fait l’objet d’un suivi photométrique en bande J à l’Observatoire du Mont-Mégantic, et 9 ont pu être détectées. De ces 9 détections, 4 objets présentent des mouvements propres cohérents avec ceux de naines brunes.
Resumo:
En opération depuis 2008, l’expérience ATLAS est la plus grande de toutes les expériences au LHC. Les détecteurs ATLAS- MPX (MPX) installés dans ATLAS sont basés sur le détecteur au silicium à pixels Medipix2 qui a été développé par la collaboration Medipix au CERN pour faire de l’imagerie en temps réel. Les détecteurs MPX peuvent être utilisés pour mesurer la luminosité. Ils ont été installés à seize différents endroits dans les zones expérimentale et technique d’ATLAS en 2008. Le réseau MPX a recueilli avec succès des données indépendamment de la chaîne d’enregistrement des données ATLAS de 2008 à 2013. Chaque détecteur MPX fournit des mesures de la luminosité intégrée du LHC. Ce mémoire décrit la méthode d’étalonnage de la luminosité absolue mesurée avec les détectors MPX et la performance des détecteurs MPX pour les données de luminosité en 2012. Une constante d’étalonnage de la luminosité a été déterminée. L’étalonnage est basé sur technique de van der Meer (vdM). Cette technique permet la mesure de la taille des deux faisceaux en recouvrement dans le plan vertical et horizontal au point d’interaction d’ATLAS (IP1). La détermination de la luminosité absolue nécessite la connaissance précise de l’intensité des faisceaux et du nombre de trains de particules. Les trois balayages d’étalonnage ont été analysés et les résultats obtenus par les détecteurs MPX ont été comparés aux autres détecteurs d’ATLAS dédiés spécifiquement à la mesure de la luminosité. La luminosité obtenue à partir des balayages vdM a été comparée à la luminosité des collisions proton- proton avant et après les balayages vdM. Le réseau des détecteurs MPX donne des informations fiables pour la détermination de la luminosité de l’expérience ATLAS sur un large intervalle (luminosité de 5 × 10^29 cm−2 s−1 jusqu’à 7 × 10^33 cm−2 s−1 .
Resumo:
The vibrational overtone spectra 0f the liquid phase 1,2-dichloroethane and 1,2-dibromoethane in the spectral regions of CH stretching local mode overtones corresponding to delta v CH= = 2 to delta v CH=5 are reported. The observed spectral features are assigned using the local mode model. LocaI mode frequencies WCH and diagonal local mode anharmonicities XCH are obtained from an analysis of the spectra. The local-local combinations observed are interpreted on the basis of a coupled CH oscillator model hamiltonian. Local-normal combinations show complex structures and their possible assignments are given.
Resumo:
Vibrational overtone spectra of styrene (liquid) and polystyrene (solid), studied by the laser-induced thermal lens (for ΔV=6) and the conventional near infrared absorption (for ΔV=3–5) techniques, are reported. For polystyrene, the overtone energy-bond length correlation predicts that the aryl CH bonds are ∼0.0005 Å longer than that in benzene, while no such conclusions could be drawn on styrene. Thesp 3 CH overtones in polystyrene are observed on the low energy side of the aryl CH overtones.