Physics

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The 15-43 GHz parsec-scale circular polarization of 41 active galactic nuclei
(Oxford University Press, 2008) Vitrishchak, V. M.; Gabuzda, Denise; Algaba, Juan Carlos; Rastorgueva, E. A.; O'Sullivan, Shane P.; O'Dowd, A.
We present the results of parsec-scale circular-polarization measurements based on Very Long Baseline Array data for a number of radio-bright, core-dominated active galactic nuclei obtained simultaneously at 15, 22 and 43 GHz. The degrees of circular polarization m(c) for the Very Long Baseline Interferometry (VLBI) core region at 15 GHz are similar to the values reported earlier at this wavelength, with typical values of a few tenths of a per cent. We find that mc as often rises as falls with increasing frequency between 15 and 22 GHz, while the degree of circular polarization at 43 GHz is in all cases higher than at 22 and 15 GHz. This behaviour seems contrary to expectations, since the degree of circular polarization from both synchrotron radiation and the Faraday conversion of linear to circular polarization - the two main mechanisms considered thus far in the literature - should decrease towards higher frequencies if the source is homogeneous. The increase in mc at 43 GHz may be due to the presence of regions of both positive and negative circular polarization with different frequency dependences ( but decreasing with increasing frequency) on small scales within the core region; alternatively, it may be associated with the intrinsic inhomogeneity of a Blandford-Konigl like jet. In several objects, the detected circular polarization appears to be near, but not coincident with, the core, although further observations are needed to confirm this. We find several cases of changes in sign with frequency, most often between 22 and 43 GHz. We find tentative evidence for transverse structure in the circular polarization of 1055+018 and 1334-127, that is consistent with their being generated by either the synchrotron mechanism or the Faraday conversion in a helical magnetic field. Our results confirm the earlier finding that the sign of the circular polarization at a given observing frequency is generally consistent across epochs separated by several years or more, suggesting stability of the magnetic-field orientation in the innermost jets.
The 2015 edition of the GEISA spectroscopic database
(Elsevier, 2016-06-23) Jacquinet-Husson, N.; Armante, R; Scott, N. A.; Chedin, A.; Crepeau, L.; Boutammine, C.; Bouhdaoui, A.; Crevoisier, C.; Capelle, V.; Boonne, C.; Poulet-Crovisier, N.; Barbe, A.; Benner, D. C.; Boudon, V.; Brown, L. R.; Buldyreva, J.; Campargue, A.; Coudert, L. H.; Devi, V. M.; Down, Michael J.; Drouin, B. J.; Fayt, A.; Fittschen, C.; Flaud, J. M.; Gamache, R. R.; Harrison, J. J.; Hill, Colin; Hodnebrog, O.; Hu, S. M.; Jacquemart, D.; Jolly, A.; Jimenez, E.; Lavrentieva, N. N.; Liu, A. W.; Lodi, L.; Lyulin, O. M.; Massie, S. T.; Mikhailenko, S.; Muller, H. S. P.; Naumenko, O. V.; Nikitin, A.; Nielsen, C. J.; Orphal, J.; Perevalov, V. I.; Perrin, A.; Polovtseva, E.; Predoi-Cross, A.; Rotger, M.; Ruth, Albert A.; Yu, S. S.; Sung, K.; Tashkun, S. A.; Tennyson, J.; Tyuterev, V. I. G.; Auwera, J. V.; Voronin, B. A.; Makie, A.; Centre National d’Etudes Spatiales; Institut National des Sciences de l'Univers, Centre National de la Recherche Scientifique; National Science Foundation; Russian Foundation for Basic Research; Science Foundation Ireland; Horizon 2020; European Commission; Fonds De La Recherche Scientifique - FNRS; Natural Sciences and Engineering Research Council of Canada
The GEISA database (Gestion et Etude des Informations Spectroscopiques Atmosphériques: Management and Study of Atmospheric Spectroscopic Information) has been developed and maintained by the ARA/ABC(t) group at LMD since 1974. GEISA is constantly evolving, taking into account the best available spectroscopic data. This paper presents the 2015 release of GEISA (GEISA-2015), which updates the last edition of 2011 and celebrates the 40th anniversary of the database. Significant updates and additions have been implemented in the three following independent databases of GEISA. The “line parameters database” contains 52 molecular species (118 isotopologues) and transitions in the spectral range from 10−6 to 35,877.031 cm−1, representing 5,067,351 entries, against 3,794,297 in GEISA-2011. Among the previously existing molecules, 20 molecular species have been updated. A new molecule (SO3) has been added. HDO, isotopologue of H2O, is now identified as an independent molecular species. Seven new isotopologues have been added to the GEISA-2015 database. The “cross section sub-database” has been enriched by the addition of 43 new molecular species in its infrared part, 4 molecules (ethane, propane, acetone, acetonitrile) are also updated; they represent 3% of the update. A new section is added, in the near-infrared spectral region, involving 7 molecular species: CH3CN, CH3I, CH3O2, H2CO, HO2, HONO, NH3. The “microphysical and optical properties of atmospheric aerosols sub-database” has been updated for the first time since 2003. It contains more than 40 species originating from NCAR and 20 from the ARIA archive of Oxford University. As for the previous versions, this new release of GEISA and associated management software facilities are implemented and freely accessible on the AERIS/ESPRI atmospheric chemistry data center website.
3d absorption-spectra of Sr I through Sr IV
(American Physical Society, 1995) McGuinness, C.; O'Sullivan, G.; Carroll, P. K.; Audley, D.; Mansfield, Michael W. D.
The extreme ultraviolet photoabsorption spectra of neutral to three-times-ionized strontium have been recorded in a comprehensive series of experiments with the dual laser-produced plasma technique. Striking differences were found in the spectra, which can be attributed to the transfer of oscillator strength from 3d→np to 3d→nf transitions at Sr2+ due to nf wave-function contraction. In Sr and Sr+, 3d→5p transitions dominate; in Sr2+, 3d→nf transitions are most intense, while in Sr3+ the 4p subshell opens and 3d→4p transitions are the strongest features. Partial cross sections for 3d→ɛf and 3d→ɛp photoionization were calculated and compared with experiment.
42.6 Gbit/s fully integrated all-optical XOR gate
(Institution of Engineering and Technology, 2009-09) Dailey, James M.; Ibrahim, Selwan K.; Manning, Robert J.; Webb, Rod P.; Lardenois, Sébastien; Maxwell, Graeme D.; Poustie, Alistair J.; Science Foundation Ireland
We demonstrate an SOA-based all-optical high-speed Mach-Zehnder interferometer exclusive- OR (XOR) gate fabricated in a silica III-V hybrid-integration technology platform. The device includes integrated time delays for rapid differential operation as well as integrated phase shifters for fine tuning of power splitters and interferometer bias enabling highly optimized XOR gate operation. XOR functionality is verified through inspection of the output pulse sequence and the carrier-suppressed output spectrum. A 2.3 dB penalty for a 42.6 Gb/s RZ-OOK signal at a 10-9 bit error rate is observed.
Absolute photoionization cross-section measurements of the Kr I isoelectronic sequence
(American Physical Society, 2007) Kilbane, D.; Folkmann, F.; Bizau, J. -M.; Banahan, C.; Scully, S.; Kjeldsen, H.; van Kampen, P.; Mansfield, Michael W. D.; Costello, John T.; West, J. B.
Photoionization spectra have been recorded in the 4s, 4p, and 3d resonance regions for the Kr I isoelectronic sequence using both the dual laser produced plasma (DLP) technique (at DCU) to produce photoabsorption spectra, and the merged ion beam and synchrotron radiation technique (at ASTRID) to measure absolute photoionization cross sections. Profile parameters are compared for the 4s-np resonances of Rb+ and Sr2+. Many 4p -> ns, md transitions are identified with the aid of Hartree-Fock calculations, and consistent quantum defects are observed for the various ns and md Rydberg series. Absolute single and double photoionization cross sections recorded in the 3d region for Rb+ and Sr2+ ions show preferential decay via double photoionization. This is only the second report to our knowledge where both the DLP technique and the merged-beam technique have been used simultaneously to record photoionization spectra, and the advantages of both techniques (i.e., better resolution in the case of DLP and values for absolute photoionization cross sections in the case of the merged-beam technique) are highlighted.
Accurate effective-one-body waveforms of inspiralling and coalescing black-hole binaries
(American Physical Society, 2008) Damour, Thibault; Nagar, Alessandro; Hannam, Mark; Husa, Sascha; Bruegmann, Bernd
The effective-one-body (EOB) formalism contains several flexibility parameters, notably a(5), upsilon(pole) and (a) over bar (RR). We show here how to jointly constrain the values of these parameters by simultaneously best-fitting the EOB waveform to two, independent, numerical relativity (NR) simulations of inspiralling and/or coalescing binary black-hole systems: published Caltech-Cornell inspiral data (considered for gravitational wave frequencies Mw <= 0.1) on one side, and newly computed coalescence data on the other side. The resulting, approximately unique, "best-fit" EOB waveform is then shown to exhibit excellent agreement with NR coalescence data for several mass ratios. The dephasing between this best-fit EOB waveform and published Caltech-Cornell inspiral data is found to vary between -0.0014 and +0.0008 radians over a time span of similar to 2464M up to gravitational wave frequency Mw = 0.1, and between +0.0013 and -0.0185 over a time span of 96M after Mw = 0.1 up to Mw = 0. 1565. The dephasings between EOB and the new coalescence data are found to be smaller than: (i) +/- 0.025 radians over a time span of 730M (11 cycles) up to merger, in the equal-mass case,and (ii) +/- 0.05 radians over a time span of about 950M ( 17 cycles) up to merger in the 2:1 mass-ratio case. These new results corroborate the aptitude of the EOB formalism to provide accurate representations of general relativistic waveforms, which are needed by Currently operating gravitational wave detectors.
Acoustic deformation potentials of n -type PbTe from first principles
(American Physical Society, 2018-08-03) Murphy, Aoife R.; Murphy-Armando, Felipe; Fahy, Stephen B.; Savić, Ivana; Science Foundation Ireland; Marie-Curie Action COFUND
We calculate the uniaxial and dilatation acoustic deformation potentials Lu and Ld of the conduction band L valleys of PbTe from first principles, using the local density approximation (LDA) and hybrid functional (HSE03) exchange-correlation functionals. We find that the choice of a functional does not substantially affect the effective band masses and deformation potentials as long as a physically correct representation of the conduction band states near the band gap has been obtained. Fitting of the electron-phonon matrix elements obtained in density functional perturbation theory (DFPT) with the LDA excluding spin-orbit interaction (SOI) gives L u = 7.0 eV and L d = 0.4 eV. Computing the relative shifts of the L valleys induced by strain with the HSE03 functional including SOI gives L u = 5.5 eV and L d = 0.8 eV, in good agreement with the DFPT values. Our calculated values of L u agree fairly well with experiment (∼3–4.5 eV). The computed values of L d are substantially smaller than those obtained by fitting electronic transport measurements (∼17–22 eV), indicating that intravalley acoustic phonon scattering in PbTe is much weaker than previously thought.
Advanced processing strategies for site-controlled pyramidal quantum dots
(University College Cork, 2021-10-07) Varo, Simone; Pelucchi, Emanuele; Science Foundation Ireland
Today, the world is on the verge of a new technological breakthrough that has been called the “second quantum revolution”: much like the understanding of semiconductor physics paved the way for the development of integrated circuits and ushered the age of information technology, the development of the first working quantum computers might start a profound change in the way we process information, and pave the way for much anticipated technological breakthrough. In my thesis, I have investigated the applications of Pyramidal Quantum Dots (PQDs) as potential sources of single and entangled photons, with a particular focus on improving their quality and brightness, and explored new approaches for their processing that would make them suitable for integration in future quantum devices. In order to address the limits of the conventional InGaAs in GaAs PQDs in relation to resonant pumping of the biexcitonic state, I contributed to the development of two new families of dots: GaAs in AlGaAs PQDs and GaAs dots confined by superlattice barriers. For the former, only results of growths on templates of smaller size were reported in the literature, while the latter is a completely new family of PQDs altogether. Results reported in this thesis indicate a surprising uniformity in spectral features for either family, and demonstrate that resonant excitation can indeed be achieved due to the binding biexcitonic state. In collaboration with Prof. Di Falco’s group in the University of St. Andrews (UK), we have demonstrated potential applications in the field of semiconductor non-classical light sources of the Electron Beam Induced Deposition technique, which allowed us to fabricate complex dielectric nanostructures directly above the quantum emitters. Our work showed how this approach doesn’t cause any significant degradation in the emission spectra, and was complemented by a large number of simulations to elucidate the underlying mechanisms that allow SiO_2 nanostructures to boost light extraction efficiency form the semiconductor matrix depending on their shape. A more promising approach to boost the brightness of our dots was also developed, in the form of a self-aligning technique that allows to fabricate micro and nanopillars using dry etching, and that allowed us to achieve our own record of brightness. Furthermore, an approach to compensate for the effects of the excitonic fine structure splitting on the level of entanglement was devised: the model we have developed complements similar proposals that have previously appeared in the literature, but is also extremely intuitive due to its sequential logic gate structure. Finally, for the first time transmission electron microscopy of PQDs was achieved in a joint effort with Queen’s University Belfast, a success in large part made possible by the new processing strategies devised in this thesis, and whose preliminary results are here reported.
Aligning VLBI images of active galactic nuclei at different frequencies
(Oxford University Press, 2008) Croke, S. M.; Gabuzda, Denise
Many important techniques for investigating the properties of extragalactic radio sources, such as spectral-index and rotation-measure mapping, involve the comparison of images at two or more frequencies. In the case of radio interferometric data, this can be done by comparing the CLEAN maps obtained at the different frequencies. However, intrinsic differences in images due to the frequency dependence of the radio emission can be distorted by additional differences that arise due to source variability (if the data to be compared are obtained at different times), image misalignment, and the frequency dependence of the sensitivity to weak emission and the angular resolution provided by the observations (the resolution of an interferometer depends on the lengths of its baselines in units of the observing wavelength). These effects must be corrected for as best as possible before multifrequency data comparison techniques can be applied. We consider the origins for the aforementioned factors, outline the standard techniques used to overcome these difficulties, and describe in detail a technique developed by us, based on the cross-correlation technique widely used in other fields, to correct for misalignments between maps at different frequencies.
All magnetic phenomena are NOT due to electric charges in motion
(American Association of Physics Teachers, 2021-12-21) Fahy, Stephen B.; O'Sullivan, Colm T.
All optical systems for terabit network era
(University College Cork, 2016) Fabbri, Simon; Ellis, Andrew D.; Peters, Frank H.
The continuous growth of the network capacity demand drives the development of the optical fiber networks. Since optical super-channels carrying multi- Terabit/s transmissions are the next evolution of the optical links, future transmitters and receivers systems will be required to handle vast volume of information while maintaining reasonable power consumption and cost. In addition, when point-to-point links are approaching the fundamental limit of standard fiber, the efficient use of the entire transmission window for optical networks will only be achieved through flexible superchannels compatible with flexible optical nodes. This thesis describes the research work carried out to investigate the future optical systems that will support the Terabit era networks. All-optical systems are presented, allowing for high spectral efficiency in future networks, from the comb sources to the optical nodes. The following manuscript firstly reports on the development of optical combs based on external modulators to provide transmitters with a large number of optical carriers. Then, the implementation of an experimental all-optical super-channel through the use of optical signals and wavelength manipulations is described. Finally, a novel all-optical node called Terabit Interferometric add, Drop, and Extract (TIDE) is presented. With a management of the super-channel components in the optical domain, the optical node offers transparency and flexibility while maintaining the high spectral efficiency of the super-channel carrying links. An optical frequency comb source was developed, generating a high quality 9-line comb with a spectral flatness < 0.3 dB and side-mode suppression ratio > 20 dB. A single Mach-Zehnder modulator was driven with a low power multi- harmonic electrical signal. Furthermore, a large 36 line comb was obtained by the addition of a two cascaded modulators comb source driven with a 90 GHz signal The implementation of an alloptical Orthogonal Frequency Division Multiplexing (OFDM) super-channel, using a high quality single sideband modulation scheme based on a dual-parallel Mach-Zehnder modulator, allowed for the development and test of the all-optical TIDE node. The interferometer-based structure was capable of managing (add, drop, and extract) channel from a super-channel strictly in the optical domain. In this manuscript, we prove that it is possible to extract channels even with overlapping spectrum super-channel aggregation for both single and dual quadrature modulation formats.
All-optical header processing in a 42.6Gb/s optoelectronic firewall
(IEEE, 2011) Webb, Rod P.; Dailey, James M.; Manning, Robert J.; Maxwell, Graeme D.; Poustie, Alistair J.; Lardenois, Sébastien; Harmon, Robert; Harrison, James; Kopidakis, Georgios; Athanasopoulos, Elias; Krithinakis, Antonis; Doukhan, Francis; Omar, Mohamed; Vaillant, Dominique; Di Nallo, Frédéric; Koyabe, Martin; Di Cairano-Gilfedder, Carla; Science Foundation Ireland; European Commission
A novel architecture to enable future network security systems to provide effective protection in the context of continued traffic growth and the need to minimise energy consumption is proposed. It makes use of an all-optical pre-filtering stage operating at the line rate under software control to distribute incoming packets to specialised electronic processors. An experimental system that integrates software controls and electronic interfaces with an all-optical pattern recognition system has demonstrated the key functions required by the new architecture. As an example, the ability to sort packets arriving in a 42.6Gb/s data stream according to their service type was shown experimentally.
All-optical modulation converter for on-off keying to duobinary and alternate-mark inversion at 42.6 Gbps
(IEEE, 2011-05) Dailey, James M.; Power, Mark J.; Webb, Rod P.; Manning, Robert J.; Science Foundation Ireland
Advanced modulation formats have become increasingly important as telecoms engineers strive for improved tolerance to both linear and nonlinear fibre-based transmission impairments. Two important modulation schemes are Duobinary (DB) and Alternate-mark inversion (AMI) [1] where transmission enhancement results from auxiliary phase modulation. As advanced modulation formats displace Return-to-zero On-Off Keying (RZ-OOK), inter-modulation converters will become increasingly important. If the modulation conversion can be performed at high bitrates with a small number of operations per bit, then all-optical techniques may offer lower energy consumption compared to optical-electronic-optical approaches. In this paper we experimentally demonstrate an all-optical system incorporating a pair of hybrid-integrated semiconductor optical amplifier (SOA)-based Mach-Zehnder interferometer (MZI) gates which translate RZ-OOK to RZ-DB or RZ-AMI at 42.6 Gbps. This scheme includes a wavelength conversion to arbitrary output wavelength and has potential for high-level photonic integration, scalability to higher bitrates, and should exhibit regenerative properties [2].
All-optical technique for modulation format conversion from on-off-keying to alternate-mark-inversion
(Optical Society of America, 2010-10-10) Dailey, James M.; Webb, Rod P.; Manning, Robert J.; Science Foundation Ireland
We propose and numerically investigate for the first time a novel all-optical on-off-keying to alternate-mark-inversion modulation format converter operating at 40 Gbps employing a semiconductor optical amplifier (SOA)-based Mach-Zehnder interferometer (MZI). Wedemonstrate that this SOA-MZI operates as a pulse subtractor, and in the absence of patterning will produce perfectly phase inverted pulses regardless of the individual SOA phase excursions. We use a comprehensive computer model to illustrate the impact of patterning on the output phase modulation which is quantified through the definition of the phase compression factor.
Alternate two-dimensional quantum walk with a single-qubit coin
(American Physical Society, 2011) Di Franco, Carlo; Mc Gettrick, M.; Machida, T.; Busch, Thomas; Irish Research Council for Science, Engineering and Technology; Science Foundation Ireland
We have recently proposed a two-dimensional quantum walk where the requirement of a higher dimensionality of the coin space is substituted with the alternance of the directions in which the walker can move [C. Di Franco, M. Mc Gettrick, and Th. Busch, Phys. Rev. Lett. 106, 080502 (2011)]. For a particular initial state of the coin, this walk is able to perfectly reproduce the spatial probability distribution of the nonlocalized case of the Grover walk. Here, we present a more detailed proof of this equivalence. We also extend the analysis to other initial states in order to provide a more complete picture of our walk. We show that this scheme outperforms the Grover walk in the generation of x-y spatial entanglement for any initial condition, with the maximum entanglement obtained in the case of the particular aforementioned state. Finally, the equivalence is generalized to wider classes of quantum walks and a limit theorem for the alternate walk in this context is presented.
Analysing curved optical waveguides using the finite difference beam propagation method
(University College Cork, 2020-09-01) Murphy, Tommy; Peters, Frank H.; Science Foundation Ireland
Photonic integrated circuits (PICs) integrate optical components on a single semiconductor chip. As time has progressed, advances have been made allowing the components of these PICs to become smaller and smaller. It is now possible to place many of these components on a single PIC. As these components can contain, or be connected by, bending waveguides, it is desirable to make these waveguide bends with as small a radius of curvature as possible to allow many components to fit on the single PIC. Unfortunately, as the radius of curvature decreases, the power loss through the bend increases due to the waveguide’s fundamental mode shifting towards the outside of the bend, causing large loss from the transition between the straight and curved waveguides. The power from the shifted mode also leaks as the fields propagate through the bend. Therefore, the aim of this thesis was to reduce the loss caused by these bends at small radii of curvature, allowing the bends to take up less space on a PIC. This involved designing the waveguide bends to have curvature profiles other than the conventional circular waveguide bend. The propagating fields through the bends were then analysed by numerical simulations using a program utilising the 3D finite difference beam propagation method, which was created and optimised over the course of the research, to investigate if the different curvature profiles could reduce the loss caused by bends in ridge waveguides. It was found that much lower loss could be achieved for curved deep-etched ridge waveguides with small radii of curvature by designing the bend to have a section where the curvature of the waveguide linearly changes.
Analysing the transverse structure of the relativistic jets of active galactic nuclei
(Oxford University Press, 2013) Murphy, Eoin Gerard; Cawthorne, T. V.; Gabuzda, Denise; Irish Research Council for Science, Engineering and Technology
This paper describes a method of fitting total intensity and polarization profiles in very long baseline interferometry (VLBI) images of astrophysical jets to profiles predicted by a theoretical model. As an example, the method is used to fit profiles of the jet in the active galactic nucleus (AGN) Mrk 501 with profiles predicted by a model in which a cylindrical jet of synchrotron plasma is threaded by a magnetic field with helical and disordered components. This fitting yields model Stokes Q profiles that agree with the observed profiles to within the 1-2 sigma uncertainties; the I model and observed profiles are overall not in such good agreement, with the model I profiles being generally more symmetrical than the observed profiles. Consistent fitting results are obtained for profiles derived from 6-cm VLBI images at two distances from the core, and also for profiles obtained for different wavelengths at a single location in the VLBI jet. The most striking success of the model is its ability to reproduce the spine-sheath polarization structure observed across the jet. Using the derived viewing angle in the jet rest frame, delta' similar or equal to 83 degrees, together with a superluminal speed reported in the literature, beta(app) = 3.3, yields a solution for the viewing angle and velocity of the jet in the observer's frame, delta similar or equal to 15 degrees and beta similar or equal to 0.96. Although these results for Mrk 501 must be considered tentative, the combined analysis of polarization profiles and apparent component speeds holds promise as a means of further elucidating the magnetic field structures and other parameters of parsec-scale AGN jets.
Analysis and optimisation of semiconductor reflective modulators for optical networks
(University College Cork, 2014) Naughton, Alan J.; Townsend, Paul D.; Science Foundation Ireland; European Commission
Reflective modulators based on the combination of an electroabsorption modulator (EAM) and semiconductor optical amplifier (SOA) are attractive devices for applications in long reach carrier distributed passive optical networks (PONs) due to the gain provided by the SOA and the high speed and low chirp modulation of the EAM. Integrated R-EAM-SOAs have experimentally shown two unexpected and unintuitive characteristics which are not observed in a single pass transmission SOA: the clamping of the output power of the device around a maximum value and low patterning distortion despite the SOA being in a regime of gain saturation. In this thesis a detailed analysis is carried out using both experimental measurements and modelling in order to understand these phenomena. For the first time it is shown that both the internal loss between SOA and R-EAM and the SOA gain play an integral role in the behaviour of gain saturated R-EAM-SOAs. Internal loss and SOA gain are also optimised for use in a carrier distributed PONs in order to access both the positive effect of output power clamping, and hence upstream dynamic range reduction, combined with low patterning operation of the SOA Reflective concepts are also gaining interest for metro transport networks and short reach, high bit rate, inter-datacentre links. Moving the optical carrier generation away from the transmitter also has potential advantages for these applications as it avoids the need for cooled photonics being placed directly on hot router line-cards. A detailed analysis is carried out in this thesis on a novel colourless reflective duobinary modulator, which would enable wavelength flexibility in a power-efficient reflective metro node.
An analysis of 1.55 mu m InAs/InP quantum dash lasers
(AIP Publishing, 2008) Heck, Susannah C.; Healy, Sorcha B.; Osborne, Simon; O'Reilly, Eoin P.; Lelarge, Francois; Poingt, F.; Accard, A.; Pommereau, F.; Le Gouezigou, O.; Dagens, B.; Sixth Framework Programme; Science Foundation Ireland
Calculations show that electron states are not confined in the dashes in 1.55 mu m InAs/InP quantum dash-in-a-well laser structures. The combination of strain and three-dimensional confinement reduces the calculated density of states (DOS) near the valence band maximum, with the conduction and valence DOS then almost equal close to the band edges. Calculations and photoabsorption measurements show strongly polarized spontaneous emission and gain spectra. Experimental analysis shows the room temperature threshold current is dominated by nonradiative current paths. (C) 2008 American Institute of Physics. (DOI: 10.1063/1.2952194)
Analysis of an 18O and D enhanced water spectrum and new assignments for HD18O and D218O in the near-infrared region (6000–7000 cm−1) using newly calculated variational line lists
(Elsevier, 2012-12) Down, Michael J.; Tennyson, Jonathan; Orphal, Johannes; Chelin, Pascale; Ruth, Albert A.; Environmental Protection Agency; European Research Council; Natural Environment Research Council, United Kingdom
An experimental infrared spectrum due to Orphal and Ruth (2008) [10] recorded using isotopically enriched water in the 6000–7000 cm−1 region is analysed and assigned. The assignment procedure is based on the use of known transition frequencies for H216O and H218O, existing variational line lists for HD16O and D216O, and newly calculated variational line lists for HD18O and D218O. These new variational line lists are presented herein. The main absorption comes from HD16O and HD18O, for which there are few previous assignments in the region. Assignments to 426 new HD18O lines are presented. In all 3254 of the 4768 lines observed in the spectrum are assigned, resulting in a number of newly determined energy levels. These assignments are in agreement with the recent work of Mikhailenko et al. (2012) [41].

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