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We present an analysis of the properties of HI holes detected in 20 galaxies that are part of “The HI Nearby Galaxy Survey” (THINGS). We detected more than 1000 holes in total in the sampled galaxies. Where they can be measured, their sizes range from about 100 pc (our resolution limit) to about 2 kpc, their expansion velocities range from 4 to 36 km/s, and their ages are estimated to range between 3 and 150 Myr. The holes are found throughout the discs of the galaxies, out to the edge of the HI disc; 23% of the holes fall outside R25. We find that shear limits the age of holes in spirals; shear is less important in dwarf galaxies which explains why HI holes in dwarfs are rounder, on average than in spirals. Shear, which is particularly strong in the inner part of spiral galaxies, also explains why we find that holes outside R25 are larger and older. We derive the scale height of the HI disc as a function of galactocentric radius and find that the disc flares at large radii in all galaxies. We proceed to derive the surface and volume porosity (Q2D and Q3D) and find that this correlates with the type of the host galaxy: later Hubble types tend to be more porous. The size distribution of the holes in our sample follows a power law with a slope of a=−2.9. Assuming that the holes are the result of massive star formation, we derive values for the supernova rate (SNR) and star formation rate (SFR) which scales with the SFR derived based on other tracers. If we extrapolate the observed number of holes to include those that fall below our resolution limit, down to holes created by a single supernova, we find that our results are compatible with the hypothesis that HI holes result from star formation. We use HI data from THINGS, 8μm, 24μm, 70μm and HI maps from SINGS, CO(2–1) data from HERACLES and FUV data from NGS to present a visual comparison of these maps with respect to the locations of HI holes. We find that the vast majority of HI holes are also prominent in the 8μm map and to some extent in the 24μm map. There is a lack of molecular gas from the interior of nearly all the holes, which is consistent with the idea that the latter are filled with hot gas. About 60% of young holes have FUV emission detected in their interiors highlighting the presence of the parent OB association. In addition, FUV is detected on the rims of some of the older HI holes, presumably due to the dispersion of the OB association with respect to the gas. We describe the development of a 2–D cross-correlation method to compare multi-wavelength maps in a quantitative way (quantified by Ccoef ) and give some first results from the application of this method to the nearby galaxy NGC2403. We find that the all the dust tracers are well correlated (Ccoef > 0.7) with the 8μm–24μm correlation being the highest (Ccoef > 0.88). Similarly all the star formation tracers are well linked as expected (Ccoef > 0.6). With respect to the relations between star formation and dust tracers we found that most are well matched (Ccoef > 0.7) as dust grains are heated by radiation in star forming regions. At smaller scales (15") FUV correlates poorly (Ccoef ~ 0.3) with the dust tracers, a direct consequence of the absorption of FUV photons by dust. We find that the HI is reasonably well correlated with the 8μm emission (Ccoef ~ 0.6) illustrating the fact that HI is mixed with PAH’s. Interestingly, the HI map shows some correlation with the SF map (Ccoef ~ 0.4) even though FUV and HI emissions were found to be completely uncorrelated (Ccoef ~ 0).

The two SCUBA HAlf-Degree Extragalactic Survey (SHADES) fields are amongst the richest places in the sky in terms of multi-wavelength coverage. They comprise an eastern section of the Lockman Hole (LH) and the central portion of the Subaru- XMM/Newton Deep Field (SXDF). In this thesis, I have obtained extremely deep, multi-frequency radio imaging of the SHADES fields using the GiantMetre-wave Radio Telescope (GMRT) and the Very Large Array (VLA), at 610MHz and 1.4GHz, respectively. These data are used to analyse the nature of the sub-milliJansky (sub-mJy) radio population, which has been hotly debated in the last few years: are they powered by star-forming or nuclear activity? To tackle the problem, I employ different approaches making use of the large variety of multi-wavelength data in the SHADES fields. I begin by analysing the spectral index, α610MHz 1.4GHz , of radio sources detected in the LH, to explore the dominant emission mechanism. Based on a robust 10 σ detection criterion, I find a constantmedian spectral index of α610MHz 1.4GHz ≈ −0.6 to −0.7 for sources between S1.4GHz ≈ 200 μJy and 10mJy. This result suggests that the galaxy population in the sub-mJy regime is powered by optically-thin synchrotron emission – starforming galaxies or lobe-dominated active galactic nuclei (AGN). Making use of X-ray observations in the LH, I show that the fraction of radio sources detected in the hard X-ray band (between 2 and 10 keV) decreases from 50 to 15 per cent between S1.4GHz ≈ 1mJy and . 100 μJy, which strongly suggests a transition from AGN to star-forming galaxies. Based on the deep, multi-wavelength coverage of the SXDF, I explore the behaviour of the far-infrared (FIR)/radio correlation as a function of redshift. I combine the q24 factor – the logarithmic flux density ratio between Spitzer 24-μm and VLA 1.4- GHz flux densities – with available photometric redshifts and find strong evidence that the correlation holds out to z ≈ 3.5. Based on M82-like k-corrections and using a high-significance (S1.4GHz > 300 μJy) radio sub-sample, I find a mean and scatter of q24 = 0.71 ± 0.47. Monte-Carlo simulations based on these findings show that fewer sources deviate from the correlation at fainter flux densities (i.e. fewer radioloud AGN). I predict that the radio-loud fraction drops from 50 per cent at ∼ 1mJy to zero at . 100 μJy. The validity of the FIR/radio correlation out to very high redshifts adds credibility to identifications of sub-millimetre (submm) galaxies (SMGs) made at radio wavelengths. Based on a sample of 45 radio-identified SMGs in the LH, I find a median radio spectral index of α610MHz 1.4GHz = −0.72 ± 0.07, which suggests that optically-thin synchrotron is the dominant radio emission mechanism. Finally, as anAppendix I include a theoretical treatment that constrains the average geometry of the dusty, torus-like structures believed to obscure a large fraction of the AGN population. I use the distribution of column densities (NH) obtained from deep ∼ 1Msec X-ray observations in the Chandra Deep Field South. I find that to reproduce the wide observed range of NH, the best torus model is given by a classical “donut”- shaped distribution with an exponential angular dependency of the density profile.

Cette thèse vise à montrer rapport d'un lidar multispectral, en particulier en ajoutant des longueurs d'onde dans le proche infrarouge proche, pour la caractérisation des aérosols. En effet par rapport à un lidar mono-longueur d'onde, l'information contenue dans les profils multispectraux permet de remonter aux propriétés microphysiques des aérosols (distribution en aille et composition). Pour cela un simulateur de signaux lidar multispectraux a été adapté à notre étude afin de pouvoir développer et tester deux méthodes permettant de retrouver les propriétés microphysiques des aérosols le long de la ligne e visée à partir de signaux lidar synthétiques. La première méthode, basée sur l'inversion des signaux lidar, permet de retrouver la répartition en taille des aérosols et donc d'en déduire notamment leur concentration et leur rayon modal. Cette méthode nécessite des informations a priori sur les aérosols. Un bilan d'erreur a été réalisé en introduisant des incertitudes sur ces paramètres a priori et montre que les résultats obtenus sur la concentration et le rayon modal sont précis (respectivement 16% et 17% d'erreur). Cette méthode présente l'avantage de ne pas nécessiter d'étalonnage absolu de l'instrument. La deuxième méthode est basée sur la minimisation de l'écart entre des signaux simulés et les signaux que l'on étudie. Même si la précision obtenue sur la répartition en taille retrouvée est plus faible (35% et 40 % d'erreur sur la concentration t le rayon modal) et que la constante d'étalonnage de l'instrument doit être connue, cette méthode a l'avantage de retrouver la composition des aérosols dans 74 % des cas. / The purpose of this thesis is to show the contribution of a multispectral Iidar for the characterisation of aerosols, in particular hen wavelengths in near infrared are added. Indeed, compared with a mono-wavelength Iidar, the information contained in multispectral profiles allow to retrieve the microphysical properties of aerosols (particule size distribution and composition). To this end, we adapted a multispectral Iidar signal simulator to our study in order to develop and test two methods which objective is to obtain the microphysical properties of aerosol along the line-of-sight from synthetic lidar signals. The first method, based on the inversion of lidar signals, enables to find the length distribution of aerosols and therefore to educe their concentration and their modal radius. This method requires a priori information about the aerosols. An error budget was made by introducing uncertainties on the a priori parameters. It shows that the results obtained regarding the concentration and modal radius are accurate (respectively 16% and 17% uncertainty). The advantage of this method is that it does not require absolute calibration of the instrument. The principle of the second method is to minimize the difference between the studied and the simulated signals. Even if the accuracy on the size distribution is lower (35% and 40% on the concentration and modal radius) and the calibration constant of the instrument has to be known, this method has the advantage to find the concentration of the aerosols in 74% of the cases. Finally, the first method was validated on real data, coming from a collaboration with the RSLab (Barcelona), by comparing ur results with those obtained by this team (7% difference on the modal radius).

Thin-film inorganic solar cells, such as CdTe, have demonstrated the most promise to date for a viable low-cost renewable energy resource. Their current performance, however, is far from the theoretical limit suffering from significant charge recombination losses due to grain boundaries and point defects. It is likely that the microscopic compositions of grain bulk and grain boundaries are significantly different and not optimal for the overall device performance. Good understanding of charge transport along and across the grain boundaries and other microscopic interfaces is lacking, preventing the development of reliable and predictive device models. The insufficient microscopic understanding hinders efficient characterization of photovoltaic materials and also holds back the development of process control techniques. We first show preliminary results for a novel technique, quantum-dot electron-beam induced current to characterize semiconductors in the near-field. We also propose the use of near-field optical scanning microscopy for high precision optical excitation and for local, high-resolution characterization. These imaging techniques are examined with the goal of synthesizing information obtained by both methods, of material phenomena at the relevant length scales, to other measurement methods. The most important nanoscale phenomena being the separation of compositional and electrical effects.

Current methodologies for characterization of tympanic membranes (TMs) have some limitations. They: are qualitative rather than quantitative, consist of single point mobility measurements, or only include one-dimensional deformation measurements. Furthermore, none of the current clinical tools for diagnosis of hearing losses have the capability to measure the shape of TM, which is very useful for anatomical or pathological investigations. The multi-wavelength lensless digital holography system (MLDHS) reported in this work consists of laser delivery (LD), optical head (OH), and computing platform (CP) subsystems, with capabilities of real-time, non-contact, full-field of view measurements. One version of the LD houses two tunable near-infrared external-cavity diode lasers with central wavelengths of 780.24nm and 779.74nm respectively, an acousto-optic modulator, and a laser-to-fiber mechanism. The output of the LD is delivered to an ultra-fast MEMS-based fiber optic switch and the light beam is directed to the OH, which is arranged to perform imaging and measurements by phase-shifting holography. The second LD version subsystem contains one tunable near-infrared diode laser in the range from 770nm to 789nm, an anamorphic prism pair, an acousto-optic modulator, a half-wave plate, and a fiber coupler assembly. The output of the LD is delivered to the OH directly. The OH is designed by 3D optical ray tracing simulations in which components are rotated at specific angles to overcome reflection issues. A high-resolution digital camera with pixel size of 6.7μm by 6.7μm in the OH is used for image recording at high-rates while the CP acquires and processes images in either time-averaged or double-exposure modes. The choice of working version depends on the requirements of the measurement and the sample under test. MLDHS can obtain shape and one-dimensional deformations along one optical axis (z-axis). In order to recover 3D deformations, assumptions based on elasticity theory are prerequisites for the calculations: (a) the TM is analyzed as a thin shell; (b) shape before and after deformation is considered nearly the same since acoustic pressure typically introduces nanometer scale deformations; and (c) normal vectors remain perpendicular to the deformed mid-plane of the TM. Another part of this Thesis is the design and prototyping of the MLDHS, which translates this holographic platform into a simple and compact holographic instrument for measurements of the visible tympanic-membrane motions in live patients. Therefore, the OH subsystem needs to be light and portable, as it can be mounted on a robotic arm be near the ear canal, while the LD subsystem needs to be stable and safely protected. Preliminary results of acoustically induced 3D deformations and shape measurements by a single instrument that demonstrate the capabilities of the devices developed in this Thesis are presented.

The work in this thesis concerns the host galaxies of a class of luminous, yet heavily-obscured, quasars at z$\sim$2 - a peak epoch of both star formation and black hole accretion. Here, we seek to characterise the star-forming properties of these obscured quasars to improve our understanding of galaxy-quasar coevolution. A key issue facing host galaxy studies among populations of the most luminous quasars is being able to disentangle the galaxy emission from that of the quasar. With combined observations from the Dark Energy Survey (DES), the VISTA Hemisphere Survey (VHS) and the UKIDSS Large Area Survey (ULAS), we exploit the quasar dust extinction in our sample to demonstrate that the quasar and galaxy emission can be separated via SED-fitting in these systems. By isolating the galaxy emission in this way, we estimate instantaneous SFRs for the galaxies in our sample, based on the restframe UV emission. In general, we find obscured quasars to reside in prodigiously star forming hosts with 25 $\lesssim$ SFR$_{\rm{UV}}$ $\lesssim$ 365 M$_{\rm{\odot}}$yr$^{-1}$. Furthermore, we show that the most luminous quasars reside in the most actively star-forming galaxies, potentially indicating the same gas supply is fuelling both star formation and accretion on to the black hole. Having isolated the galaxy emission via SED-fitting, we test our ability to model the restframe-UV emission of obscured z$\sim$2 quasar hosts in 2D. Until now, morphological studies of luminous quasar hosts have typically been limited to low redshifts or relied on space-based imaging. By making use of a multi-band modelling code however, we demonstrate that it is possible to accurately infer several galaxy properties (i.e. the position of the galaxy in the image, (X,Y), its radius, R$_{\rm{eff}}$, axis ratio, q$_{\rm{GAL}}$, angle of orientation, $\theta$, and S\'rsic index, $n$), based on current ground-based imaging, accross the full range of galaxy and quasar luminosities considered in our sample. This potentially opens the door to future ground-based morphological studies of obscured quasars at high redshift. At sub-mm wavelengths, thermal emission from cold dust peaks, meaning these wavelengths can be used to probe the dust heating by star formation, effectively giving a measure of the obscured star formation in the galaxy. Using targeted observations from SCUBA-2, we trace the 850$\mu$m emission in a sample of obscured quasars, finding evidence for prodigious star formation $ > $ 2400 M$_$yr$^$ in three of the 19 quasars in our sample. The detection rate of our obscured quasar sample is found to be consistent with that of both more heavily-obscured Hot-DOGs and UV-luminous quasars, once the samples have been matched in luminosity and redshift. Furthermore, we find evidence that several of the obscured quasars lie in overdense regions of the sky ($\sim$ 3 times denser than sub-mm blank fields).

This thesis utilized pulse shaping and Gerberg-Saxton algorithm to develop high power tunable narrowband terahertz radiation and applications. By the way of using Freezing algorithm and Gerberg-Saxton, pulse width, pulse duration, pulse position and pulse number can be controlled. The pulse train can be pumping source of high power tunable narrowband terahertz radiation, by avoid the saturations and different pulse duration. The simulation shown the result can have 5GHz narrowband width closing to commercial product. Besides, we demonstrated the THz multi-wavelength interference method by using THz-TDS (terahertz time domain spectroscopy) to measure the liquid crystal cell gap. We have also used THz-TDS to investigate the complex optical constants and birefringence of cholesteric liquid crystal mixture BL006. The extraordinary (ne) and ordinary (no) indices of refraction at are 1.784-1.817 and 1.516-1.555 giving rise to a birefringence of 0.25¡V0.29 in 0.2THz~1.6THz.

Since their initial demonstration in 1994, quantum cascade lasers (QCLs) have become prominent sources of mid-infrared radiation. Over the years, a large scientific and engineering effort has led to a dramatic improvement in their efficiency and power output, with continuous wave operation at room temperature and Watt-level output power now standard. However, beyond this progress, new functionalities and capabilities need to be added to this compact source to enable its integration into consumer-ready systems. Two main areas of development are particularly relevant from an application standpoint and were pursued during the course of this thesis: wavelength control and wavefront engineering of QCLs. The first research direction, wavelength control, is mainly driven by spectroscopic applications of QCLs, such as trace gas sensing, process monitoring or explosive detection. We demonstrated three different capabilities, corresponding to different potential spectroscopic measurement techniques: widely tunable single longitudinal mode lasing, simultaneous lasing on multiple well-defined longitudinal modes, and simultaneous lasing over a broad and continuous range of the spectrum. The second research direction, wavefront engineering of QCLs, i.e. the improvement of their beam quality, is relevant for applications necessitating transmission of the QCL output over a large distance, for example for remote sensing or military countermeasures. To address this issue, we developed plasmonic lenses directly integrated on the facets of QCLs. The plasmonic structures designed are analogous to antenna arrays imparting directionality to the QCLs, as well as providing means for polarization control. Finally, a research interest in plasmonics led us to design passive flat optical elements using plasmonic antennas. All these projects are tied together by the involvement of Fourier analysis as an essential design tool to predict the interaction of light with various gratings and periodic arrays of grooves and scatterers. / Engineering and Applied Sciences

abstract: Dual-wavelength laser sources have various existing and potential applications in wavelength division multiplexing, differential techniques in spectroscopy for chemical sensing, multiple-wavelength interferometry, terahertz-wave generation, microelectromechanical systems, and microfluidic lab-on-chip systems. In the drive for ever smaller and increasingly mobile electronic devices, dual-wavelength coherent light output from a single semiconductor laser diode would enable further advances and deployment of these technologies. The output of conventional laser diodes is however limited to a single wavelength band with a few subsequent lasing modes depending on the device design. This thesis investigates a novel semiconductor laser device design with a single cavity waveguide capable of dual-wavelength laser output with large spectral separation. The novel dual-wavelength semiconductor laser diode uses two shorter- and longer-wavelength active regions that have separate electron and hole quasi-Fermi energy levels and carrier distributions. The shorter-wavelength active region is based on electrical injection as in conventional laser diodes, and the longer-wavelength active region is then pumped optically by the internal optical field of the shorter-wavelength laser mode, resulting in stable dual-wavelength laser emission at two different wavelengths quite far apart. Different designs of the device are studied using a theoretical model developed in this work to describe the internal optical pumping scheme. The carrier transport and separation of the quasi-Fermi distributions are then modeled using a software package that solves Poisson's equation and the continuity equations to simulate semiconductor devices. Three different designs are grown using molecular beam epitaxy, and broad-area-contact laser diodes are processed using conventional methods. The modeling and experimental results of the first generation design indicate that the optical confinement factor of the longer-wavelength active region is a critical element in realizing dual-wavelength laser output. The modeling predicts lower laser thresholds for the second and third generation designs; however, the experimental results of the second and third generation devices confirm challenges related to the epitaxial growth of the structures in eventually demonstrating dual-wavelength laser output. / Dissertation/Thesis / Ph.D. Electrical Engineering 2011