Intermediate band to conduction band optical absorption in ZnTeO

ZnTe doped with high concentrations of oxygen has been proposed in previous works as an intermediate band (IB) material for photovoltaic applications. The existence of extra optical transitions related to the presence of an IB has already been demonstrated in this material and it has been possible to measure the absorption coefficient of the transitions from the valence band (VB) to the IB. In this study, we present the first measurement of the absorption coefficient associated with transitions from the IB to the conduction band (CB) in ZnTeO. The samples used are 4-mum-thick ZnTe layers with or without O in a concentration ~10 19 cm -3, which have been grown on semiinsulating GaAs substrates by molecular beam epitaxy (MBE). The IB-CB absorption coefficient peaks for photon energies ~0.4 eV. It is extracted from reflectance and transmittance spectra measured using Fourier transform infrared (FTIR) spectroscopy. Under typical FTIR measurement conditions (low light intensity, broadband spectrum), the absorption coefficient in IB-to-CB transitions reaches 700 cm -1. This is much weaker than the one observed for VB-IB absorption. This result is consistent with the fact that the IB is expected to be nearly empty of electrons under equilibrium conditions in ZnTe(O).

The XMM deep survey in the CDF-S. VI. Obscured AGN selected as infrared power-law galaxies

Context. Accretion onto supermassive black holes is believed to occur mostly in obscured active galactic nuclei (AGN). Such objects are proving rather elusive in surveys of distant galaxies, including those at X-ray energies. Aims. Our main goal is to determine whether the revised IRAC criteria of Donley et al. (2012, ApJ, 748, 142; objects with an infrared (IR) power-law spectral shape), are effective at selecting X-ray type-2 AGN (i.e., absorbed N_H > 10^22 cm^-2). Methods. We present the results from the X-ray spectral analysis of 147 AGN selected by cross-correlating the highest spectral quality ultra-deep XMM-Newton and the Spitzer/IRAC catalogues in the Chandra Deep Field South. Consequently it is biased towards sources with high S/N X-ray spectra. In order to measure the amount of intrinsic absorption in these sources, we adopt a simple X-ray spectral model that includes a power-law modified by intrinsic absorption at the redshift of each source and a possible soft X-ray component. Results. We find 21/147 sources to be heavily absorbed but the uncertainties in their obscuring column densities do not allow us to confirm their Compton-Thick nature without resorting to additional criteria. Although IR power-law galaxies are less numerous in our sample than IR non-power-law galaxies (60 versus 87 respectively), we find that the fraction of absorbed (N_H^intr > 10^22 cm^-2) AGN is significantly higher (at about 3 sigma level) for IR-power-law sources (similar to 2/3) than for those sources that do not meet this IR selection criteria (~1/2). This behaviour is particularly notable at low luminosities, but it appears to be present, although with a marginal significance, at all luminosities. Conclusions. We therefore conclude that the IR power-law method is efficient in finding X-ray-absorbed sources. We would then expect that the long-sought dominant population of absorbed AGN is abundant among IR power-law spectral shape sources not detected in X-rays.

The effect of certain dissolved substances on the infra-red absorption of water,

"Reprinted from the Physical review, n.s., vol. XX., no. 5, Novermber, 1922."

Spectral modification of type IA fibre Bragg gratings by high-power near-infrared lasers

We report the first experimental measurements on the spectral modification of type IA fibre Bragg gratings, incorporated in an optical network, which result from the use of high-power, near-infrared lasers. The fibre grating properties are modified in a controlled manner by exploiting the characteristics of the inherent 1400 nm absorption band of the optical fibre, which grows in strength during the type IA grating inscription. If the fibre network is illuminated with a high-power laser, having an emission wavelength coincident with the absorption band, the type IA centre wavelength and chirp can be modified. Furthermore, partial grating erasure is demonstrated. This has serious implications when using type IA gratings in an optical network, as their spectrum can be modified using purely optical methods (no external heating source acts on the fibre), and to their long-term stability as the grating is shown to decay. Conversely, suitably stabilized gratings can be spectrally tailored, for tuning fibre lasers or edge filter modification in sensing applications, by purely optical means. © 2006 IOP Publishing Ltd.

Wavelength drift of PMMA-based optical fiber bragg grating induced by optical absorption

The transmission loss in polymer optical fiber (POF) is much higher than that in silica fiber. Very strong absorption bands dominate throughout the visible and near infrared. Optical absorption increases the internal temperature of the polymer fiber and reduces the wavelength of any POF Bragg grating (POFBG) inscribed within the fiber. In this letter, we have investigated the wavelength drift of FBGs inscribed in poly(methyl methacrylate)-based fiber under illumination at different wavelengths. The experiments have shown that the characteristic wavelength of such a POFBG starts decreasing after a light source is applied to it. This decrease continues until equilibrium inside the fiber is established, depending on the surrounding humidity, optical power applied, and operation wavelength.

IRAS 00183-7111: ALMA and X-ray view of an ultra luminous infrared galaxy

The aim of this Thesis work is to study the multi-frequency properties of the Ultra Luminous Infrared Galaxy (ULIRG) IRAS 00183-7111 (I00183) at z = 0.327, connecting ALMA sub-mm/mm observations with those at high energies in order to place constraints on the properties of its central power source and verify whether the gas traced by the CO may be responsible for the obscuration observed in X-rays. I00183 was selected from the so-called Spoon diagnostic diagram (Spoon et al. 2007) for mid-infrared spectra of infrared galaxies based on the equivalent width of the 6.2 μm Polycyclic Aromatic Hydrocarbon (PAH) emission feature versus the 9.7 μm silicate strength. Such features are a powerful tool to investigate the contribution of star formation and AGN activity in this class of objects. I00183 was selected from the top-left region of the plot where the most obscured sources, characterized by a strong Si absorption feature, are located. To link the sub-mm/mm to the X-ray properties of I00183, ALMA archival Cycle 0 data in Band 3 (87 GHz) and Band 6 (270 GHz) have been calibrated and analyzed, using CASA software. ALMA Cycle 0 was the Early Science program for which data reprocessing is strongly suggested. The main work of this Thesis consisted in reprocessing raw data to provide an improvement with respect to the available archival products and results, which were obtained using standard procedures. The high-energy data consists of Chandra, XMM-Newton and NuSTAR observations which provide a broad coverage of the spectrum in the energy range 0.5 − 30 keV. Chandra and XMM archival data were used, with an exposure time of 22 and 22.2 ks, respectively; their reduction was carried out using CIAO and SAS software. The 100 ks NuSTAR are still private and the spectra were obtained by courtesy of the PI (K. Iwasawa). A detailed spectral analysis was done using XSPEC software; the spectral shape was reproduced starting from simple phenomenological models, and then more physical models were introduced to account for the complex mechanisms that involve this source. In Chapter 1, an overview of the scientific background is discussed, with a focus on the target, I00183, and the Spoon diagnostic diagram, from which it was originally selected. In Chapter 2, the basic principles of interferometry are briefly introduced, with a description of the calibration theory applied to interferometric observations. In Chapter 3, ALMA and its capabilities, both current and future, are shown, explaining also the complex structure of the ALMA archive. In Chapter 4, the calibration of ALMA data is presented and discussed, showing also the obtained imaging products. In Chapter 5, the analysis and discussion of the main results obtained from ALMA data is presented. In Chapter 6, the X-ray observations, data reduction and spectral analysis are reported, with a brief introduction to the basic principle of X-ray astronomy and the instruments from which the observations were carried out. Finally, the overall work is summarized, with particular emphasis on the main obtained results and the possible future perspectives.

Multiscale photoacoustic tomography using reversibly switchable bacterial phytochrome as a near-infrared photochromic probe.

Photoacoustic tomography (PAT) of genetically encoded probes allows for imaging of targeted biological processes deep in tissues with high spatial resolution; however, high background signals from blood can limit the achievable detection sensitivity. Here we describe a reversibly switchable nonfluorescent bacterial phytochrome for use in multiscale photoacoustic imaging, BphP1, with the most red-shifted absorption among genetically encoded probes. BphP1 binds a heme-derived biliverdin chromophore and is reversibly photoconvertible between red and near-infrared light-absorption states. We combined single-wavelength PAT with efficient BphP1 photoswitching, which enabled differential imaging with substantially decreased background signals, enhanced detection sensitivity, increased penetration depth and improved spatial resolution. We monitored tumor growth and metastasis with ∼ 100-μm resolution at depths approaching 10 mm using photoacoustic computed tomography, and we imaged individual cancer cells with a suboptical-diffraction resolution of ∼ 140 nm using photoacoustic microscopy. This technology is promising for biomedical studies at several scales.

Near-infrared Instrumentation For Rapid-response Astronomy

Ɣ-ray bursts (GRBs) are the Universe's most luminous transient events. Since the discovery of GRBs was announced in 1973, efforts have been ongoing to obtain data over a broader range of the electromagnetic spectrum at the earliest possible times following the initial detection. The discovery of the theorized ``afterglow'' emission in radio through X-ray bands in the late 1990s confirmed the cosmological nature of these events. At present, GRB afterglows are among the best probes of the early Universe (z ≳ 9). In addition to informing theories about GRBs themselves, observations of afterglows probe the circum-burst medium (CBM), properties of the host galaxies and the progress of cosmic reionization. To explore the early-time variability of afterglows, I have developed a generalized analysis framework which models near-infrared (NIR), optical, ultra-violet (UV) and X-ray light curves without assuming an underlying model. These fits are then used to construct the spectral energy distribution (SED) of afterglows at arbitrary times within the observed window. Physical models are then used to explore the evolution of the SED parameter space with time. I demonstrate that this framework produces evidence of the photodestruction of dust in the CBM of GRB 120119A, similar to the findings from a previous study of this afterglow. The framework is additionally applied to the afterglows of GRB 140419A and GRB 080607. In these cases the evolution of the SEDs appears consistent with the standard fireball model. Having introduced the scientific motivations for early-time observations, I introduce the Rapid Infrared Imager-Spectrometer (RIMAS). Once commissioned on the 4.3 meter Discovery Channel Telescope (DCT), RIMAS will be used to study the afterglows of GRBs through photometric and spectroscopic observations beginning within minutes of the initial burst. The instrument will operate in the NIR, from 0.97 μm to 2.37 μm, permitting the detection of very high redshift (z ≳ 7) afterglows which are attenuated at shorter wavelengths by Lyman-ɑ absorption in the intergalactic medium (IGM). A majority of my graduate work has been spent designing and aligning RIMAS's cryogenic (~80 K) optical systems. Design efforts have included an original camera used to image the field surrounding spectroscopic slits, tolerancing and optimizing all of the instrument's optics, thermal modeling of optomechanical systems, and modeling the diffraction efficiencies for some of the dispersive elements. To align the cryogenic optics, I developed a procedure that was successfully used for a majority of the instrument's sub-assemblies. My work on this cryogenic instrument has necessitated experimental and computational projects to design and validate designs of several subsystems. Two of these projects describe simple and effective measurements of optomechanical components in vacuum and at cryogenic temperatures using an 8-bit CCD camera. Models of heat transfer via electrical harnesses used to provide current to motors located within the cryostat are also presented.

Towards near-infrared photoactivation of anticancer metal complexes.

171 p.

X-ray analysis of local mid-infrared selected Compton-thick AGN candidates

Cosmic X-ray background synthesis models (Gilli 2007) require a significant fraction of obscured AGN, some of which are expected to be heavily obscured (Compton-thick), but the number density of observationally found obscured sources is still an open issue (Vignali 2010, 2014). This thesis work takes advantage of recent NuSTAR data and is based on a multiwavelength research approach. Gruppioni et al. 2016 compared the AGN bolometric luminosity, for a sample of local 12 micron Seyfert galaxies, derived from the SED decomposition to the same quantity obtained by the 2-10 keV luminosity (IPAC-NED). A difference up to two orders of magnitude resulted between these quantities for some sources. Thus, the intrinsic X-ray luminosity obtained correcting for the obscuration may be underestimated. In this thesis we have tested this hypothesis by re-analysing the X-ray spectra of three of the sources (UGC05101, NGC1194 and NGC3079), for which observations from NuSTAR and Chandra and/or XMM-Newton were available. This is meant to extend our analysis to energies above 10 keV and thus estimate the AGN column density as reliable as possible. For spectral fitting we made use of both the commonly used XSPEC package and the two very recent MYtorus and BNtorus physical models. The available wide bandpass allowed us to achieve new and more solid insights into the X-ray spectral properties of these sources. The measured absorption column densities are highly suggestive of heavy obscuration. Once corrected the X-ray AGN luminosity for the obscuration estimated through our spectral analysis, we compared the L(X) values in the 2-10 keV band with those derived from the MIR band, by means of the relation by Gandhi, 2009. As expected, the values derived from this relation are in good agreement with those we measured, indicating that the column densities were underestimated in the previous literature works.

QUANTIFICATION OF CALCIUM IN SPARKLING WINES BY INFRARED SPECTROSCOPY

Markets are increasingly competitive and the companies feel the urge to improve their manufacturing processes. Blending that with a larger control of quality and safety it was created a need to develop new methods of analysis each time more accurate, faster and with lower costs. Alentejo is a region with a wide variety of soils, most of them are rich in calcium and potassium. In the production of sparkling wine many wineries use encapsulated yeast in alginate beads, instead of the traditional method, champenoise. The first method is faster, allowing a more versatile production, reducing the risk of contamination and features organoleptic characteristics similar to the traditional method (yeast free). However, encapsulated yeast spheres should be only used if the base wine matches a number of features, among them calcium content. In this study the calcium content in the wine was determined by atomic absorption spectroscopy (AAS) and by near-infrared spectroscopy. The AAS is a high sensitivity method clearly produces a reliable result, however it is very time consuming and produces great quantities of environmental waste, therefore the possibility of using near-infrared spectroscopy as a method was studied to be a fast, simple and clean alternative to the AAS. It was obtained a calibration model with a variation coefficient higher than 0.80 which indicates that the near-infrared spectroscopy as an adequately alternative the ASS.

Near-infrared spectroscopic study of basic aluminum sulfate and nitrate

The tridecameric Al-polymer [AlO4Al12(OH)24(H2O)12]7+ was prepared by forced hydrolysis of Al3+ up to an OH/Al molar ratio of 2.2. Under slow evaporation crystals were formed of Al13-nitrate. Upon addition of sulfate the tridecamer crystallised as the monoclinic Al13-sulfate. These crystals have been studied using near-infrared spectroscopy and compared to Al2(SO4)3.16H2O. Although the near-infrared spectra of the Al13-sulfate and nitrate are very similar indicating similar crystal structures, there are minor differences related to the strength with which the crystal water molecules are bonded to the salt groups. The interaction between crystal water and nitrate is stronger than with the sulfate as reflected by the shift of the crystal water band positions from 6213, 4874 and 4553 cm–1 for the Al13 sulfate towards 5925, 4848 and 4532 cm–1 for the nitrate. A reversed shift from 5079 and 5037 cm–1 for the sulfate towards 5238 and 5040 cm–1 for the nitrate for the water molecules in the Al13 indicate that the nitrate-Al13 bond is weakened due to the influence of the crystal water on the nitrate. The Al-OH bond in the Al13 complex is not influenced by changing the salt group due to the shielding by the water molecules of the Al13 complex.

New dimeric supramolecular structure of mixed (phthalocyaninato)(porphyrinato)-europium(III) sandwiches : preparation and spectroscopic characteristics

The mixed double-decker Eu\[Pc(15C5)4](TPP) (1) was obtained by base-catalysed tetramerisation of 4,5-dicyanobenzo-15-crown-5 using the half-sandwich complex Eu(TPP)(acac) (acac = acetylacetonate), generated in situ, as the template. For comparative studies, the mixed triple-decker complexes Eu2\[Pc(15C5)4](TPP)2 (2) and Eu2\[Pc(15C5)4]2(TPP) (3) were also synthesised by the raise-by-one-story method. These mixed ring sandwich complexes were characterised by various spectroscopic methods. Up to four one-electron oxidations and two one-electron reductions were revealed by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). As shown by electronic absorption and infrared spectroscopy, supramolecular dimers (SM1 and SM3) were formed from the corresponding double-decker 1 and triple-decker 3 in the presence of potassium ions in MeOH/CHCl3.

Electronic and vibrational spectra of gaspeite

Visible, near-infrared, IR and Raman spectra of magnesian gaspeite are presented. Nickel ion is the main source of the electronic bands as it is the principal component in the mineral where as the bands in IR and Raman spectra are due to the vibrational processes in the carbonate ion as an entity. The combination of electronic absorption and vibrational spectra (including near-infrared, FTIR and Raman) of magnesian gaspeite are explained in terms of the cation co-ordination and the behaviour of CO32– anion in the Ni–Mg carbonate. The electronic absorption spectrum consists of three broad and intense bands at 8130, 13160 and 22730 cm–1 due to spin-allowed transitions and two weak bands at 20410 and 30300 cm–1 are assigned to spin-forbidden transitions of Ni2+ in an octahedral symmetry. The crystal field parameters evaluated from the observed bands are Dq = 810; B = 800 and C = 3200 cm–1. The two bands in the near-infrared spectrum at 4330 and 5130 cm–1 are overtone and combination of CO32– vibrational modes. For the carbonate group, infrared bands are observed at 1020 cm–1(1 ), 870 cm–1 (2), 1418 cm–1 (3) and 750 cm–1 (4), of which3, the asymmetric stretching mode is most intense. Three well resolved Raman bands at 1571, 1088 and 331 cm–1 are assigned to 3, 1 and MO stretching vibrations.