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Sample records for lcls-s1 optical transition

  1. Patterning via optical saturable transitions

    NASA Astrophysics Data System (ADS)

    Cantu, Precious

    For the past 40 years, optical lithography has been the patterning workhorse for the semiconductor industry. However, as integrated circuits have become more and more complex, and as device geometries shrink, more innovative methods are required to meet these needs. In the far-field, the smallest feature that can be generated with light is limited to approximately half the wavelength. This, so called far-field diffraction limit or the Abbe limit (after Prof. Ernst Abbe who first recognized this), effectively prevents the use of long-wavelength photons >300nm from patterning nanostructures <100nm. Even with a 193nm laser source and extremely complicated processing, patterns below ˜20nm are incredibly challenging to create. Sources with even shorter wavelengths can potentially be used. However, these tend be much more expensive and of much lower brightness, which in turn limits their patterning speed. Multi-photon reactions have been proposed to overcome the diffraction limit. However, these require very large intensities for modest gain in resolution. Moreover, the large intensities make it difficult to parallelize, thus limiting the patterning speed. In this dissertation, a novel nanopatterning technique using wavelength-selective small molecules that undergo single-photon reactions, enabling rapid top-down nanopatterning over large areas at low-light intensities, thereby allowing for the circumvention of the far-field diffraction barrier is developed and experimentally verified. This approach, which I refer to as Patterning via Optical Saturable Transitions (POST) has the potential for massive parallelism, enabling the creation of nanostructures and devices at a speed far surpassing what is currently possible with conventional optical lithographic techniques. The fundamental understanding of this technique goes beyond optical lithography in the semiconductor industry and is applicable to any area that requires the rapid patterning of large-area two or three

  2. Turbulent Transitions in Optical Wave Propagation

    NASA Astrophysics Data System (ADS)

    Pierangeli, D.; Di Mei, F.; Di Domenico, G.; Agranat, A. J.; Conti, C.; DelRe, E.

    2016-10-01

    We report the direct observation of the onset of turbulence in propagating one-dimensional optical waves. The transition occurs as the disordered hosting material passes from being linear to one with extreme nonlinearity. As the response grows, increased wave interaction causes a modulational unstable quasihomogeneous flow to be superseded by a chaotic and spatially incoherent one. Statistical analysis of high-resolution wave behavior in the turbulent regime unveils the emergence of concomitant rogue waves. The transition, observed in a photorefractive ferroelectric crystal, introduces a new and rich experimental setting for the study of optical wave turbulence and information transport in conditions dominated by large fluctuations and extreme nonlinearity.

  3. Enhanced optical transmission at the cutoff transition.

    PubMed

    Laux, E; Genet, C; Ebbesen, T W

    2009-04-27

    The phenomenon of extraordinary transmission in the optical regime for circular hole arrays in optically thick metal films is studied as a function of hole size and depth. In the limit of small holes compared to the depth, the transmission properties follow a waveguide type behavior. By describing the transmission process as resulting from the interference between a resonant and a non-resonant contribution, a transition is clearly revealed through the specific spectral variations of the resonance at a given hole depth. This transition is associated to a change in the attenuation through the hole as its size increases, and corresponds to the optimal condition for surface plasmon excitation.

  4. Turbulent Transitions in Optical Wave Propagation.

    PubMed

    Pierangeli, D; Di Mei, F; Di Domenico, G; Agranat, A J; Conti, C; DelRe, E

    2016-10-28

    We report the direct observation of the onset of turbulence in propagating one-dimensional optical waves. The transition occurs as the disordered hosting material passes from being linear to one with extreme nonlinearity. As the response grows, increased wave interaction causes a modulational unstable quasihomogeneous flow to be superseded by a chaotic and spatially incoherent one. Statistical analysis of high-resolution wave behavior in the turbulent regime unveils the emergence of concomitant rogue waves. The transition, observed in a photorefractive ferroelectric crystal, introduces a new and rich experimental setting for the study of optical wave turbulence and information transport in conditions dominated by large fluctuations and extreme nonlinearity.

  5. Interband optical transitions in ellipsoidal shaped nanoparticles

    NASA Astrophysics Data System (ADS)

    Kereselidze, Tamaz; Tchelidze, Tamar; Devdariani, Alexander

    2017-04-01

    The optical properties of crystalline semiconductor nanoparticles with ellipsoidal shape are investigated and discussed as a function of the shape-anisotropy parameter. The optical transition-matrix elements are calculated in the dipole approximation using perturbation theory and with a direct diagonalization of the appropriate Hamiltonian. The matrix elements involving the ground and first excited states are monotonic functions of the shape-anisotropy parameter, whereas matrix elements involving the highly excited states have zeros and extrema that are reflected in the behaviour of the corresponding transition probabilities. Moreover, some matrix elements involving the excited states have discontinuity. We demonstrate that, nanoparticles with ellipsoidal shape can be grown with the infrared as well as ultraviolet features.

  6. Optical angular momentum: Multipole transitions and photonics

    SciTech Connect

    Andrews, David L.

    2010-03-15

    The premise that multipolar decay should produce photons uniquely imprinted with a measurably corresponding angular momentum is shown in general to be untrue. To assume a one-to-one correlation between the transition multipoles involved in source decay and detector excitation is to impose a generally unsupportable one-to-one correlation between the multipolar form of emission transition and a multipolar character for the detected field. It is specifically proven impossible to determine without ambiguity, by use of any conventional detector, and for any photon emitted through the nondipolar decay of an atomic excited state, a unique multipolar character for the transition associated with its generation. Consistent with the angular quantum uncertainty principle, removal of a detector from the immediate vicinity of the source produces a decreasing angular uncertainty in photon propagation direction, reflected in an increasing range of integer values for the measured angular momentum. In such a context it follows that when the decay of an electronic excited state occurs by an electric quadrupolar transition, for example, any assumption that the radiation so produced is conveyed in the form of 'quadrupole photons' is experimentally unverifiable. The results of the general proof based on irreducible tensor analysis invite experimental verification, and they signify certain limitations on quantum optical data transmission.

  7. Theory of optical transitions in curved chromophores

    NASA Astrophysics Data System (ADS)

    Barford, William; Marcus, Max

    2016-09-01

    Using first order perturbation theory in the Born-Oppenheimer regime of the Frenkel-Holstein model, we develop a theory for the optical transitions in curved chromophores of π-conjugated polymers. Our key results are that for absorption, A, and emission, I, polarized parallel to the 0-0 transition, I01/I00 ≃ A01/A00 = S(N), where S(N) = S(1)/IPR is the effective Huang-Rhys parameter for a chromophore of N monomers and IPR is the inverse participation ratio. In contrast, absorption and emission polarized perpendicular to the 0-0 transition acquires vibronic intensity via the Herzberg-Teller effect. This intensity generally increases as the curvature increases and consequently I01/I00 increases (where I01 is the total 0-1 emission intensity). This effect is enhanced for long chromophores and in the anti-adiabatic regime. We show via DMRG calculations that this theory works well in the adiabatic regime relevant to π-conjugated polymers, i.e., ħ ω/|J| ≲ 0.2.

  8. Optical pulsations from a transitional millisecond pulsar

    NASA Astrophysics Data System (ADS)

    Ambrosino, F.; Papitto, A.; Stella, L.; Meddi, F.; Cretaro, P.; Burderi, L.; Di Salvo, T.; Israel, G. L.; Ghedina, A.; Di Fabrizio, L.; Riverol, L.

    2017-10-01

    Millisecond pulsars are neutron stars that attain their very fast rotation during a 108-109-yr-long phase of disk accretion of matter from a low-mass companion star1,2. They can be detected as accretion-powered millisecond X-ray pulsars if towards the end of this phase their magnetic field is strong enough to channel the in-flowing matter towards their magnetic poles3. When mass transfer is reduced or ceases altogether, pulsed emission generated by magnetospheric particle acceleration and powered by the star rotation is observed, preferentially in the radio4 and gamma-ray5 bands. A few transitional millisecond pulsars that swing between an accretion-powered X-ray pulsar regime and a rotationally powered radio pulsar regime in response to variations of the mass in-flow rate have been recently identified6,7. Here, we report the detection of optical pulsations from a transitional millisecond pulsar. The pulsations were observed when the pulsar was surrounded by an accretion disk, and originated inside the magnetosphere or within a few hundreds of kilometres from it. Energy arguments rule out reprocessing of accretion-powered X-ray emission and argue against a process related to accretion onto the pulsar polar caps; synchrotron emission of electrons in a rotation-powered pulsar magnetosphere8 seems more likely.

  9. Resolved Atomic Interaction Sidebands in an Optical Clock Transition

    DTIC Science & Technology

    2011-06-24

    Resolved Atomic Interaction Sidebands in an Optical Clock Transition M. Bishof,1 Y. Lin,1 M.D. Swallows,1 A.V. Gorshkov,2 J. Ye,1 and A.M. Rey1 1JILA...Institute of Technology, Pasadena, California 91125, USA (Received 4 February 2011; published 22 June 2011) We report the observation of resolved atomic ...interaction sidebands (ISB) in the 87Sr optical clock transition when atoms at microkelvin temperatures are confined in a two-dimensional optical lattice

  10. Black Hole Advective Accretion Disks with Optical Depth Transition

    SciTech Connect

    Artemove, Y.V.; Bisnovatyi-Kogan, G.S.; Igumenshchev, I.V.; Novikov, I.D.

    2006-02-01

    We have constructed numerically global solutions of advective accretion disks around black holes that describe a continuous transition between the effectively optically thick outer and optically thin inner disk regions. We have concentrated on models of accretion flows with large mass accretion rates, and we have employed a bridging formula for radiative losses at high and low effective optical depths.

  11. Optical transition radiation beam emittance diagnostics

    SciTech Connect

    Fiorito, R.B.; Rule, D.W.

    1994-10-10

    We have developed several analytic and experimental techniques to measure the divergence and emittance of charged particle beams, which employ optical transition radiation (OTR) produced from thin intercepting foils. OTR`s directionality, promptness, linearity, polarization, and the sensitivity of its angular distribution to energy and divergence, can be all exploited to diagnose the spatial distribution, energy, and emittance of a charged particle beam. We describe the techniques we have developed to separately determine the {ital x} and {ital y} emittances of a beam at an {ital x} or {ital y} waist using OTR from a single foil or a two foil OTR interferometer. These methods have proven to be especially valuable for diagnosing low emittance electron beams produced by FEL accelerators, which range in energy from 17 to 110 Mev. However, we have shown that there is no inherent theoretical limit to the utility of these methods for much higher energy lepton or hadron beams. The advantages of OTR methods over those commonly used to diagnose beam properties are described.

  12. All-optical OXC transition strategy from WDM optical network to elastic optical network.

    PubMed

    Chen, Xin; Li, Juhao; Guo, Bingli; Zhu, Paikun; Tang, Ruizhi; Chen, Zhangyuan; He, Yongqi

    2016-02-22

    Elastic optical network (EON) has been proposed recently as a spectrum-efficient optical layer to adapt to rapidly-increasing traffic demands instead of current deployed wavelength-division-multiplexing (WDM) optical network. In contrast with conventional WDM optical cross-connect (OXCs) based on wavelength selective switches (WSSs), the EON OXCs are based on spectrum selective switches (SSSs) which are much more expensive than WSSs, especially for large-scale switching architectures. So the transition cost from WDM OXCs to EON OXCs is a major obstacle to realizing EON. In this paper, we propose and experimentally demonstrate a transition OXC (TOXC) structure based on 2-stage cascading switching architectures, which make full use of available WSSs in current deployed WDM OXCs to reduce number and port count of required SSSs. Moreover, we propose a contention-aware spectrum allocation (CASA) scheme for EON built with the proposed TOXCs. We show by simulation that the TOXCs reduce the network capital expenditure transiting from WDM optical network to EON about 50%, with a minor traffic blocking performance degradation and about 10% accommodated traffic number detriment compared with all-SSS EON OXC architectures.

  13. Aqueous medium induced optical transitions in cerium oxide nanoparticles

    SciTech Connect

    Inerbaev, Talgat M.; Karakoti, Ajay S.; Kuchibhatla, S. V. N. T.; Kumar, Amit; Masunov, Artem E.; Seal, Sudipta

    2015-03-07

    Experimental and theoretical investigations were performed to investigate the effect of water on optical properties of nanoceria as a function of Ce3+ concentration. Theoretical studies based on density functional plane-wave calculations reveal that the indirect optical transitions in bare ceria nanoparticles are red-shifted with an increase in the concentration of Ce3+. However, ceria nanoparticles model with adsorbed water molecules show a blue shift in the indirect optical spectra under identical conditions. Direct optical transitions are almost independent of Ce3+ concentration but show a pronounced blue shift in the aqueous environment relative to the bare nanoparticles. The theoretical study is consistent with our experimental observation in difference of shift behaviour in bare and aqueous suspended ceria nanoparticles. This change from red- to blue-shift in indirect optical transitions is associated with the polarization effect of water molecules on f-electron states.

  14. Physics: Optical transition seen in antihydrogen

    NASA Astrophysics Data System (ADS)

    Ulmer, Stefan

    2017-01-01

    Precise measurements of antimatter systems might cast light on why the Universe is dominated by matter. The observation of a transition in an antihydrogen atom heralds the next wave of high-precision antimatter studies. See Letter p.506

  15. Electronic structure and optical transition of semiconductor nanocrystallites

    NASA Astrophysics Data System (ADS)

    Xia, Jian-Bai; Cheah, K. W.

    1997-11-01

    The electronic states and optical transition properties of three semiconductor nanocrystallites, Si, GaAs, and ZnSe, are studied using the empirical pseudopotential homojunction model. The energy levels, wave functions, optical transition matrix elements, and lifetimes are obtained for quadratic prisms with widths from 11 to 27 Å. It is found that the three kinds of prism have different quantum confinement properties. For Si prisms, the energy gaps vary with the equivalent diameter d as 0953-8984/9/45/013/img1, in agreement with previous theoretical calculations. For the same d the energy gaps are slightly different for different shapes: large for the prism with large aspect ratio; small for the prism with small aspect ratio. The exponent of d depends on the boundary barrier height, i.e. the extent of penetration of the wave function into the vacuum. The wave function of the LUMO states consists mainly of bulk X states. The optical transition matrix elements are much smaller than those of direct transition, and increase with decreasing width. The corresponding lifetimes decrease from the millisecond range to the microsecond range, and the change is abrupt depending on the symmetry and composition of the wave function of the LUMO and HOMO states. For GaAs prisms, the energy gap is also pseudo-direct, but the optical transition matrix elements are larger than those of Si prisms by two orders of magnitude for the same width. For ZnSe prisms, the energy gap is always direct, and the optical transition matrix elements are comparable with those of direct energy gap bulk semiconductors. In some cases the symmetry of the HOMO state changes, resulting in an abrupt decrease of the transition matrix element. The calculated lifetimes of the Si prism and the positions of PL peaks are in agreement with experimental results for porous Si.

  16. Optical Control of Spin Polarization in Monolayer Transition Metal Dichalcogenides.

    PubMed

    Chen, Xi; Yan, Tengfei; Zhu, Bairen; Yang, Siyuan; Cui, Xiaodong

    2017-02-28

    Optical excitation could generate electrons' spin polarization in some semiconductors with the control of the field polarization. In this article, we report a series of spin-resolved photocurrent experiments on monolayer tungsten disulfide. The experiments demonstrate that the optical excitations with the same helicity could generate opposite spin polarization around the Fermi level by tuning the excitation energy. The mechanism lies in the valley-dependent optical selection rules, the giant spin-orbit coupling, and spin-valley locking in monolayer transition metal dichalcogenides (TMDs). These exotic features make monolayer TMDs promising candidates for conceptual semiconductor-based spintronics.

  17. Isotropically sensitive optical filter employing atomic resonance transitions

    DOEpatents

    Marling, John B.

    1981-01-01

    An ultra-high Q isotropically sensitive optical filter or optical detector employing atomic resonance transitions. More specifically, atomic resonance transitions utilized in conjunction with two optical bandpass filters provide an optical detector having a wide field of view (.about.2.pi. steradians) and very narrow acceptance bandwidth approaching 0.01 A. A light signal to be detected is transmitted through an outer bandpass filter into a resonantly absorbing atomic vapor, the excited atomic vapor then providing a fluorescence signal at a different wavelength which is transmitted through an inner bandpass filter. The outer and inner bandpass filters have no common transmission band, thereby resulting in complete blockage of all optical signals that are not resonantly shifted in wavelength by the intervening atomic vapor. Two embodiments are disclosed, one in which the light signal raises atoms contained in the atomic vapor from the ground state to an excited state from which fluorescence occurs, and the other in which a pump laser is used to raise the atoms in the ground state to a first excited state from which the light signal then is resonantly absorbed, thereby raising the atoms to a second excited state from which fluorescence occurs. A specific application is described in which an optical detector according to the present invention can be used as an underwater detector for light from an optical transmitter which could be located in an orbiting satellite.

  18. Microscopic Studies of Quantum Phase Transitions in Optical Lattices

    NASA Astrophysics Data System (ADS)

    Bakr, Waseem S.

    2011-12-01

    In this thesis, I report on experiments that microscopically probe quantum phase transitions of ultracold atoms in optical lattices. We have developed a "quantum gas microscope" that allowed, for the first time, optical imaging and manipulation of single atoms in a quantum-degenerate gas on individual sites of an optical lattice. This system acts as a quantum simulator of strongly correlated materials, which are currently the subject of intense research because of the technological potential of high--T c superconductors and spintronic materials. We have used our microscope to study the superfluid to Mott insulator transition in bosons and a magnetic quantum phase transition in a spin system. In our microscopic study of the superfluid-insulator transition, we have characterized the on-site number statistics in a space- and time-resolved manner. We observed Mott insulators with fidelities as high as 99%, corresponding to entropies of 0.06kB per particle. We also measured local quantum dynamics and directly imaged the shell structure of the Mott insulator. I report on the first quantum magnetism experiments in optical lattices. We have realized a quantum Ising chain in a magnetic field, and observed a quantum phase transition between a paramagnet and antiferromagnet. We achieved strong spin interactions by encoding spins in excitations of a Mott insulator in a tilted lattice. We detected the transition by measuring the total magnetization of the system across the transition using in-situ measurements as well as the Neel ordering in the antiferromagnetic state using noise-correlation techniques. We characterized the dynamics of domain formation in the system. The spin mapping introduced opens up a new path to realizing more exotic states in optical lattices including spin liquids and quantum valence bond solids. As our system sizes become larger, simulating their physics on classical computers will require exponentially larger resources because of entanglement build

  19. Hyper-Ramsey spectroscopy of optical clock transitions

    SciTech Connect

    Yudin, V. I.; Taichenachev, A. V.; Oates, C. W.; Barber, Z. W.; Lemke, N. D.; Ludlow, A. D.; Sterr, U.; Lisdat, Ch.; Riehle, F.

    2010-07-15

    We present nonstandard optical Ramsey schemes that use pulses individually tailored in duration, phase, and frequency to cancel spurious frequency shifts related to the excitation itself. In particular, the field shifts and their uncertainties can be radically suppressed (by two to four orders of magnitude) in comparison with the usual Ramsey method (using two equal pulses) as well as with single-pulse Rabi spectroscopy. Atom interferometers and optical clocks based on two-photon transitions, heavily forbidden transitions, or magnetically induced spectroscopy could significantly benefit from this method. In the latter case, these frequency shifts can be suppressed considerably below a fractional level of 10{sup -17}. Moreover, our approach opens the door for high-precision optical clocks based on direct frequency comb spectroscopy.

  20. Optical & Infrared Spectroscopy of Transiting Exoplanets

    NASA Astrophysics Data System (ADS)

    Griffith, C. A.; Tinetti, G.

    2010-10-01

    Two types of spectra can be measured from transiting extrasolar planets. The primary eclipse provides a transmission spectra of the exoplanet's limb as the planet passes in front of the star. These data probe the gas and particle composition of the atmosphere, as well as the atmospheric scale height. The secondary eclipse measures the emission of mainly the planet's dayside atmosphere from the planet plus star's emission minus the emission of star alone, when it eclipses the planet. These data probe the temperature and composition structure of the exoplanet. Only in the past 3 years, have infrared transmission and emission spectroscopy revealed the presence of the primary carbon and oxygen species (CH4, CO2, CO, and H2O). Efforts to constrain the abundances of these molecules are hindered by degenerate effects of the temperature and composition in the emission spectra. Transmission spectra, while less sensitive to the atmospheric temperatures, are difficult to interpret because the composition derived depends delicately on the assumed radius at a specified pressure level. This talk will discuss the correlations in the degenerate solutions that result from the radiative transfer analyses of both emission and transmission spectroscopy. The physical implications of these correlations are assessed in order to determine the temperature and composition structure of extrasolar planets, and their significance with respect to the exoplanet's chemistry and dynamics.

  1. Isotropically sensitive optical filter employing atomic resonance transitions

    DOEpatents

    Marling, J.B.

    An ultra-high Q isotropically sensitive optical filter or optical detector is disclosed employing atomic resonance transitions. More specifically, atomic resonance transitions utilized in conjunction with two optical bandpass filters provide an optical detector having a wide field of view (approx. 2 ..pi.. steradians) and very narrow acceptance bandwidth approaching 0.01A. A light signal to be detected is transmitted through an outer bandpass filter into a resonantly absorbing atomic vapor, the excited atomic vapor than providing a fluorescence signal at a different wavelength which is transmitted through an inner bandpass filters have no common transmission band, therby resulting in complete blockage of all optical signals that are not resonantly shifted in wavelength by the intervening atomic vapor. Two embodiments are disclosed, one in which the light signal raises atoms contained in the atomic vapor from the ground state to an excited state from which fluorescence occurs, and the other in which a pump laser is used to raise the atoms in the ground state to a first excited state from which the light signal then is resonantly absorbed, thereby raising the atoms to a second excited state from which fluorescence occurs. A specific application is described in which an optical detector according to the present invention can be located in an orbiting satellite.

  2. Optical properties of transition metal oxide quantum wells

    NASA Astrophysics Data System (ADS)

    Lin, Chungwei; Posadas, Agham; Choi, Miri; Demkov, Alexander A.

    2015-01-01

    Fabrication of a quantum well, a structure that confines the electron motion along one or more spatial directions, is a powerful method of controlling the electronic structure and corresponding optical response of a material. For example, semiconductor quantum wells are used to enhance optical properties of laser diodes. The ability to control the growth of transition metal oxide films to atomic precision opens an exciting opportunity of engineering quantum wells in these materials. The wide range of transition metal oxide band gaps offers unprecedented control of confinement while the strong correlation of d-electrons allows for various cooperative phenomena to come into play. Here, we combine density functional theory and tight-binding model Hamiltonian analysis to provide a simple physical picture of transition metal oxide quantum well states using a SrO/SrTiO3/SrO heterostructure as an example. The optical properties of the well are investigated by computing the frequency-dependent dielectric functions. The effect of an external electric field, which is essential for electro-optical devices, is also considered.

  3. Optical properties of transition metal oxide quantum wells

    SciTech Connect

    Lin, Chungwei; Posadas, Agham; Choi, Miri; Demkov, Alexander A.

    2015-01-21

    Fabrication of a quantum well, a structure that confines the electron motion along one or more spatial directions, is a powerful method of controlling the electronic structure and corresponding optical response of a material. For example, semiconductor quantum wells are used to enhance optical properties of laser diodes. The ability to control the growth of transition metal oxide films to atomic precision opens an exciting opportunity of engineering quantum wells in these materials. The wide range of transition metal oxide band gaps offers unprecedented control of confinement while the strong correlation of d-electrons allows for various cooperative phenomena to come into play. Here, we combine density functional theory and tight-binding model Hamiltonian analysis to provide a simple physical picture of transition metal oxide quantum well states using a SrO/SrTiO{sub 3}/SrO heterostructure as an example. The optical properties of the well are investigated by computing the frequency-dependent dielectric functions. The effect of an external electric field, which is essential for electro-optical devices, is also considered.

  4. Spectroscopy of intraband optical transitions in anisotropic semiconductor nanocrystals

    NASA Astrophysics Data System (ADS)

    Turkov, Vadim K.; Baimuratov, Anvar S.; Rukhlenko, Ivan D.; Baranov, Alexander V.; Fedorov, Anatoly V.

    2013-09-01

    We propose a new type of optical spectroscopy of anisotropic semiconductor nanocrystals, which is based on the welldeveloped stationary pump-probe technique, where the pump and probe fields are absorbed upon, respectively, interband and intraband transitions of the nanocrystals' electronic subsystem. We develop a general theory of intraband absorption based on the density matrix formalism. This theory can be applied to study degenerate eigenstates of electrons in semiconductor nanocrystals of different shapes and dimentions. We demonstrate that the angular dependence of intraband absorption by nonspherical nanocrystals enables investigating their shape and orientation, as well as the symmetry of quantum states excited by the probe field and selection rules of electronic transitions.

  5. Optical Properties in Non-equilibrium Phase Transitions

    SciTech Connect

    Ao, T; Ping, Y; Widmann, K; Price, D F; Lee, E; Tam, H; Springer, P T; Ng, A

    2006-01-05

    An open question about the dynamical behavior of materials is how phase transition occurs in highly non-equilibrium systems. One important class of study is the excitation of a solid by an ultrafast, intense laser. The preferential heating of electrons by the laser field gives rise to initial states dominated by hot electrons in a cold lattice. Using a femtosecond laser pump-probe approach, we have followed the temporal evolution of the optical properties of such a system. The results show interesting correlation to non-thermal melting and lattice disordering processes. They also reveal a liquid-plasma transition when the lattice energy density reaches a critical value.

  6. Clock Shifts of Optical Transitions in Ultracold Atomic Gases

    SciTech Connect

    Yu Zhenhua; Pethick, C. J.

    2010-01-08

    We calculate the shift, due to interatomic interactions, of an optical transition in an atomic Fermi gas trapped in an optical lattice, as in recent experiments of Campbell et al.[Science 324, 360 (2009)]. Using a pseudospin formalism to describe the density matrix of atoms, we derive a Bloch equation which incorporates both spatial inhomogeneity of the probe laser field and interatomic interactions. Expressions are given for the frequency shift as a function of pulse duration, detuning of the probe laser, and the spatial dependence of the electric field of the probe beam. In the low temperature semiclassical regime, we find that the magnitude of the shift is proportional to the temperature.

  7. Resolved Atomic Interaction Sidebands in an Optical Clock Transition

    SciTech Connect

    Bishof, M.; Lin, Y.; Swallows, M. D.; Ye, J.; Rey, A. M.; Gorshkov, A. V.

    2011-06-24

    We report the observation of resolved atomic interaction sidebands (ISB) in the {sup 87}Sr optical clock transition when atoms at microkelvin temperatures are confined in a two-dimensional optical lattice. The ISB are a manifestation of the strong interactions that occur between atoms confined in a quasi-one-dimensional geometry and disappear when the confinement is relaxed along one dimension. The emergence of ISB is linked to the recently observed suppression of collisional frequency shifts. At the current temperatures, the ISB can be resolved but are broad. At lower temperatures, ISB are predicted to be substantially narrower and useful spectroscopic tools in strongly interacting alkaline-earth gases.

  8. Quantum phase transitions in optical lattices beyond the Bogoliubov approximation

    NASA Astrophysics Data System (ADS)

    Kleinert, H.; Narzikulov, Z.; Rakhimov, Abdulla

    2012-06-01

    We study the quantum phase transition from a superfluid to a Mott insulator in optical lattices using a Bose-Hubbard Hamiltonian. For this purpose we develop a field theoretical approach in terms of path integral formalism to calculate the second-order quantum corrections to the energy density as well as to the superfluid fraction in cubic optical lattices. Using the present approach, the condensate fraction and ground-state energy are calculated as functions of the s-wave scattering length. In contrast to the Bogoliubov model, which is, technically speaking, a one-loop approximation, we carry the calculation up to two loops and improve the result further by variational perturbation theory. The result suggests that the quantum phase transition exists.

  9. Structural Phase Transitions of Vortex Matter in an Optical Lattice

    SciTech Connect

    Pu, H.; Yi, S.; Baksmaty, L.O.; Bigelow, N.P.

    2005-05-20

    We consider the vortex structure of a rapidly rotating trapped atomic Bose-Einstein condensate in the presence of a corotating periodic optical lattice potential. We observe a rich variety of structural phases which reflect the interplay of the vortex-vortex and vortex-lattice interactions. The lattice structure is very sensitive to the ratio of vortices to pinning sites and we observe structural phase transitions and domain formation as this ratio is varied.

  10. Older Persons’ Transitions in Care (OPTIC): a study protocol

    PubMed Central

    2012-01-01

    Background Changes in health status, triggered by events such as infections, falls, and geriatric syndromes, are common among nursing home (NH) residents and necessitate transitions between NHs and Emergency Departments (EDs). During transitions, residents frequently experience care that is delayed, unnecessary, not evidence-based, potentially unsafe, and fragmented. Furthermore, a high proportion of residents and their family caregivers report substantial unmet needs during transitions. This study is part of a program of research whose overall aim is to improve quality of care for frail older adults who reside in NHs. The purpose of this study is to identify successful transitions from multiple perspectives and to identify organizational and individual factors related to transition success, in order to inform improvements in care for frail elderly NH residents during transitions to and from acute care. Specific objectives are to: 1. define successful and unsuccessful elements of transitions from multiple perspectives; 2. develop and test a practical tool to assess transition success; 3. assess transition processes in a discrete set of transfers in two study sites over a one year period; 4. assess the influence of organizational factors in key practice locations, e.g., NHs, emergency medical services (EMS), and EDs, on transition success; and 5. identify opportunities for evidence-informed management and quality improvement decisions related to the management of NH – ED transitions. Methods/Design This is a mixed-methods observational study incorporating an integrated knowledge translation (IKT) approach. It uses data from multiple levels (facility, care unit, individual) and sources (healthcare providers, residents, health records, and administrative databases). Discussion Key to study success is operationalizing the IKT approach by using a partnership model in which the OPTIC governance structure provides for team decision-makers and researchers to participate

  11. Optical characterization of phase transitions in pure polymers and blends

    SciTech Connect

    Mannella, Gianluca A.; Brucato, Valerio; La Carrubba, Vincenzo

    2015-12-17

    To study the optical properties of polymeric samples, an experimental apparatus was designed on purpose and set up. The sample is a thin film enclosed between two glass slides and a PTFE frame, with a very thin thermocouple placed on sample for direct temperature measurement. This sample holder was placed between two aluminum slabs, equipped with a narrow slit for optical measurements and with electrical resistances for temperature control. Sample was enlightened by a laser diode, whereas transmitted light was detected with a photodiode. Measurements were carried out on polyethylene-terephtalate (PET) and two different polyamides, tested as pure polymers and blends. The thermal history imposed to the sample consisted in a rapid heating from ambient temperature to a certain temperature below the melting point, a stabilization period, and then a heating at constant rate. After a second stabilization period, the sample was cooled. The data obtained were compared with DSC measurements performed with the same thermal history. In correspondence with transitions detected via DSC (e.g. melting, crystallization and cold crystallization), the optical signal showed a steep variation. In particular, crystallization resulted in a rapid decrease of transmitted light, whereas melting gave up an increase of light transmitted by the sample. Further variations in transmitted light were recorded for blends, after melting: those results may be related to other phase transitions, e.g. liquid-liquid phase separation. All things considered, the apparatus can be used to get reliable data on phase transitions in polymeric systems.

  12. Energy spectra and optical transitions in germanene quantum dots

    NASA Astrophysics Data System (ADS)

    Herath, Thakshila M.; Apalkov, Vadym

    2016-04-01

    The band gap of buckled graphene-like materials, such as silicene and germanene, depends on external perpendicular electric field. Then a specially design profile of electric field can produce trapping potential for electrons. We study theoretically the energy spectrum and optical transitions for such designed quantum dots (QDs) in graphene-like materials. The energy spectra depend on the size of the QD and applied electric field in the region of the QD. The number of the states in the QD increases with increasing the size of the dot and the energies of the states have almost linear dependence on the applied electric field with the slope which increases with increasing the dot size. The optical properties of the QDs are characterized by two types of absorption spectra: interband (optical transitions between the states of the valence and conduction bands) and intraband (transitions between the states of conduction/valence band). The interband absorption spectra have triple-peak structure with peak separation around 10 meV, while intraband absorption spectra, which depend on the number of electrons in the dot, have double-peak structure.

  13. Optical characterization of phase transitions in pure polymers and blends

    NASA Astrophysics Data System (ADS)

    Mannella, Gianluca A.; Brucato, Valerio; La Carrubba, Vincenzo

    2015-12-01

    To study the optical properties of polymeric samples, an experimental apparatus was designed on purpose and set up. The sample is a thin film enclosed between two glass slides and a PTFE frame, with a very thin thermocouple placed on sample for direct temperature measurement. This sample holder was placed between two aluminum slabs, equipped with a narrow slit for optical measurements and with electrical resistances for temperature control. Sample was enlightened by a laser diode, whereas transmitted light was detected with a photodiode. Measurements were carried out on polyethylene-terephtalate (PET) and two different polyamides, tested as pure polymers and blends. The thermal history imposed to the sample consisted in a rapid heating from ambient temperature to a certain temperature below the melting point, a stabilization period, and then a heating at constant rate. After a second stabilization period, the sample was cooled. The data obtained were compared with DSC measurements performed with the same thermal history. In correspondence with transitions detected via DSC (e.g. melting, crystallization and cold crystallization), the optical signal showed a steep variation. In particular, crystallization resulted in a rapid decrease of transmitted light, whereas melting gave up an increase of light transmitted by the sample. Further variations in transmitted light were recorded for blends, after melting: those results may be related to other phase transitions, e.g. liquid-liquid phase separation. All things considered, the apparatus can be used to get reliable data on phase transitions in polymeric systems.

  14. Optical Sensor for Characterizing the Phase Transition in Salted Solutions

    PubMed Central

    Claverie, Rémy; Fontana, Marc D.; Duričković, Ivana; Bourson, Patrice; Marchetti, Mario; Chassot, Jean-Marie

    2010-01-01

    We propose a new optical sensor to characterize the solid-liquid phase transition in salted solutions. The probe mainly consists of a Raman spectrometer that extracts the vibrational properties from the light scattered by the salty medium. The spectrum of the O – H stretching band was shown to be strongly affected by the introduction of NaCl and the temperature change as well. A parameter SD defined as the ratio of the integrated intensities of two parts of this band allows to study the temperature and concentration dependences of the phase transition. Then, an easy and efficient signal processing and the exploitation of a modified Boltzmann equation give information on the phase transition. Validations were done on solutions with varying concentration of NaCl. PMID:22319327

  15. Stimulated emission on impurity – band optical transitions in semiconductors

    SciTech Connect

    Bekin, N A; Shastin, V N

    2015-02-28

    This paper examines conditions for population inversion and amplification in the terahertz range using impurity – band electron transitions in semiconductors and semiconductor structures. Our estimates indicate that stimulated emission on such transitions under optical excitation of impurities can be obtained in a semiconductor with a sufficiently high doping level if electron heating is restricted. At a CO{sub 2} laser pump power density near 0.2 MW cm{sup -2} (photon energy of 117 meV), the gain in n-GaAs may exceed the loss by 50 cm{sup -1} provided the electron gas temperature does not exceed 40 K. We analyse the influence of the carrier effective mass and doping compensation on the gain coefficient and briefly discuss the use of resonance tunnelling for obtaining stimulated emission on impurity – band transitions in quantum cascade heterostructures. (terahertz radiation)

  16. Transition-metal-nitride films for optical applications

    NASA Astrophysics Data System (ADS)

    Ribbing, Carl-Gustaf; Roos, Arne

    1997-10-01

    The three transition metal nitrides TiN, ZrN and HfN have remarkably high stability due to their bonding: a mixture of covalent and ionic contributions. The optical properties of these nitride compounds are free-electron like to a surprisingly large extent, in particular in comparison with the corresponding carbides. It is argued that the interband optical excitations of the d-electrons are restricted by selection rules, resulting in a Drude like behavior of these d-electron compounds. Hitherto, one of the main optical applications has been as opaque, wear-resistant replacements for gold-coatings. This review includes the efforts to study, understand and enhance the optical selectivity of group IVB transition metal nitrides as the selective surface in high temperature thermal solar absorbers, as the metal layer in LE-coatings on energy-efficient or solar control windows and as a Langmuir probe coating. The reflectance edge is not in the optimum position for absorber applications and attempts to shift it with alloying were unsuccessful. Recent development of inhomogeneous, cermet- type nitrides hold some promise. The LE-coatings will not reach as high selectivity as the current noble metal based multilayers, but many find use in aggressive environments because of their excellent stability.

  17. Stimulated electronic transition concept for an erasable optical memory

    NASA Technical Reports Server (NTRS)

    Albin, Sacharia; Satira, James D.; Livingston, David L.; Shull, Thomas A.

    1992-01-01

    A new concept for an erasable optical memory is demonstrated using stimulated electronic transition (SET). Large bandgap semiconductors are suitable materials for the SET medium. The properties of MgS:Eu,Sm and SrS:Eu,Sm as possible media for the SET process are investigated. Quantum storage is achieved in the form of charges in deep levels in the medium and stimulated radiative recombination is used as the reading process. Unlike magneto-optic (M-O) and phase change (PC) processes, optical writing, reading and erasing are achieved without localized heating. The SET process will have an inherently faster data transfer rate and a higher storage density, and the medium will be more durable than the M-O and PC media. A possible application of the SET process in neural networks is also discussed.

  18. Advances in the optical imaging transition-edge sensory array

    NASA Astrophysics Data System (ADS)

    Bay, Thomas Joel

    Our universe contains many faint, compact objects that have an optical magnitude which can vary over the millisecond time scale, such as pulsars, low- mass X-ray binaries or cataclysmic variables. Maximally probing the detailed physics of these objects requires single photon detection with extremely high time and energy resolution. This regime is unaccessible to current conventional detectors. Transition-edge sensors are superconducting-based microcalorimeters that are able to measure the energy and time-of-arrival for single photons at high count rates. A constant voltage-bias stably maintains the TESs in the sharp transition region between the superconducting and normal states. The absorption of a photon will heat the detector, thereby raising its resistance. Using an inductor placed in series with the TES to couple it to a flux-locked SQUID readout, we can measure the resulting change in current, and hence, measure the energy and time-of-arrival of single photons. This thesis describes the first imaging TES detector designed to be sensitive to optical wave-length photons. Using thin-film tungsten TESs, we have demonstrated less than microsecond time resolution and energy resolution as low as 0.15 eV over the near-IR/optical/near-UV wave-length range with count rates of up to 30 kHz per pixel. To construct a working and useful detector array many challenges had to be overcome. The most significant challenge was to minimize unwanted infrared power loading on the array while maintaining an acceptable in-band throughput. I discuss the process of choosing a proper filter set and describe my contributions to the redesign of the 50 mK base stage in this context. Other topics discussed are the physics of transition-edge sensors, the fabrication of the tungsten TESs, the experimental apparatus and single and multiple pixel results.

  19. Evolution of molecular crystal optical phonons near structural phase transitions

    NASA Astrophysics Data System (ADS)

    Michki, Nigel; Niessen, Katherine; Xu, Mengyang; Markelz, Andrea

    Molecular crystals are increasingly important photonic and electronic materials. For example organic semiconductors are lightweight compared to inorganic semiconductors and have inexpensive scale up processing with roll to roll printing. However their implementation is limited by their environmental sensitivity, in part arising from the weak intermolecular interactions of the crystal. These weak interactions result in optical phonons in the terahertz frequency range. We examine the evolution of intermolecular interactions near structural phase transitions by measuring the optical phonons as a function of temperature and crystal orientation using terahertz time-domain spectroscopy. The measured orientation dependence of the resonances provides an additional constraint for comparison of the observed spectra with the density functional calculations, enabling us to follow specific phonon modes. We observe crystal reorganization near 350 K for oxalic acid as it transforms from dihydrate to anhydrous form. We also report the first THz spectra for the molecular crystal fructose through its melting point.

  20. Direct band gap carbon superlattices with efficient optical transition

    NASA Astrophysics Data System (ADS)

    Oh, Young Jun; Kim, Sunghyun; Lee, In-Ho; Lee, Jooyoung; Chang, K. J.

    2016-02-01

    We report pure carbon-based superlattices that exhibit direct band gaps and excellent optical absorption and emission properties at the threshold energy. The structures are nearly identical to that of cubic diamond except that defective layers characterized by five- and seven-membered rings are intercalated in the diamond lattice. The direct band gaps lie in the range of 5.6-5.9 eV, corresponding to wavelengths of 210-221 nm. The dipole matrix elements of direct optical transition are comparable to that of GaN, suggesting that the superlattices are promising materials as an efficient deep ultraviolet light emitter. Molecular dynamics simulations show that the superlattices are thermally stable even at a high temperature of 2000 K. We provide a possible route to the synthesis of superlattices through wafer bonding of diamond (100) surfaces.

  1. Optical lattice polarization effects on hyperpolarizability of atomic clock transitions.

    PubMed

    Taichenachev, A V; Yudin, V I; Ovsiannikov, V D; Pal'chikov, V G

    2006-10-27

    The light-induced frequency shift due to hyperpolarizability (i.e., terms of second-order in intensity) is studied for a forbidden optical transition, J = 0 --> J = 0. A simple universal dependence on the field ellipticity is obtained. This result allows minimization of the second-order light shift with respect to the field polarization for optical lattices operating at a magic wavelength (at which the first-order shift vanishes). We show the possibility for the existence of a magic elliptical polarization, for which the second-order frequency shift vanishes. The optimal polarization of the lattice field can be either linear, circular, or magic elliptical. The obtained results could improve the accuracy of lattice-based atomic clocks.

  2. Optical fingerprint of non-covalently functionalized transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Feierabend, Maja; Malic, Ermin; Knorr, Andreas; Berghäuser, Gunnar

    2017-09-01

    Atomically thin transition metal dichalcogenides (TMDs) hold promising potential for applications in optoelectronics. Due to their direct band gap and the extraordinarily strong Coulomb interaction, TMDs exhibit efficient light-matter coupling and tightly bound excitons. Moreover, large spin orbit coupling in combination with circular dichroism allows for spin and valley selective optical excitation. As atomically thin materials, they are very sensitive to changes in the surrounding environment. This motivates a functionalization approach, where external molecules are adsorbed to the materials surface to tailor its optical properties. Here, we apply the density matrix theory to investigate the potential of non-covalently functionalized monolayer TMDs. Considering exemplary molecules with a strong dipole moment, we predict spectral redshifts and the appearance of an additional side peak in the absorption spectrum of functionalized TMDs. We show that the molecular characteristics, e.g. coverage, orientation and dipole moment, crucially influence the optical properties of TMDs, leaving a unique optical fingerprint in the absorption spectrum. Furthermore, we find that the molecular dipole moments open a channel for coherent intervalley coupling between the high-symmetry K and K\\prime points which may create new possibilities for spin-valleytronics application.

  3. On the character of the optical transitions in closed-shell transition metal oxides doped with Bi(3).

    PubMed

    Amer, M; Boutinaud, P

    2017-01-18

    A criterion is introduced to achieve the assignment of the optical features observed in the excitation spectra of Bi(3+) ions incorporated in closed-shell transition metal oxides. The model is based on the calculation of the energy associated with the lowest (1)S0 → (3)P1 intra-ionic transition of Bi(3+) (A-like transition), the metal-to-metal charge transfer (D-like transition) and the Stokes shift of the corresponding emission.

  4. Coherent Magnetic Response at Optical Frequencies Using Atomic Transitions

    NASA Astrophysics Data System (ADS)

    Brewer, Nicholas R.; Buckholtz, Zachary N.; Simmons, Zachary J.; Mueller, Eli A.; Yavuz, Deniz D.

    2017-01-01

    In optics, the interaction of atoms with the magnetic field of light is almost always ignored since its strength is many orders of magnitude weaker compared to the interaction with the electric field. In this article, by using a magnetic-dipole transition within the 4 f shell of europium ions, we show a strong interaction between a green laser and an ensemble of atomic ions. The electrons move coherently between the ground and excited ionic levels (Rabi flopping) by interacting with the magnetic field of the laser. By measuring the Rabi flopping frequency as the laser intensity is varied, we report the first direct measurement of a magnetic-dipole matrix element in the optical region of the spectrum. Using density-matrix simulations of the ensemble, we infer the generation of coherent magnetization with magnitude 5.5 ×10-3 A /m , which is capable of generating left-handed electromagnetic waves of intensity 1 nW /cm2 . These results open up the prospect of constructing left-handed materials using sharp transitions of atoms.

  5. Optical transition radiation interferometry for the A0 photoinjector

    SciTech Connect

    Kazakevich, G.; Edwards, H.; Fliller, R.; Nagaitsev, S.; Ruan, J.; Thurman-Keup, R.; /Fermilab

    2008-06-01

    Optical Transition Radiation Interferometry (OTRI) is a promising diagnostic technique and has been successfully developed and used for investigation of relativistic beams. For mid-energy accelerators the technique is traditionally based on thin polymer films (the first one is being transparent for visible light), which causes beam multiple scattering of about 1 mrad. A disadvantage of those films is unacceptable vacuum properties for photoinjectors and accelerators using superconducting cavities. We have studied the application of thin mica sheets for the OTRI diagnostics at the A0 Photoinjector in comparison with 2.5 {micro}m thick Mylar films. This diagnostic is also applicable for the ILCTA-NML accelerator test facility that is planned at Fermilab. This report discusses the experimental setups of the OTR interferometer for the A0 Photoinjector and presents comparisons of simulations and measurements obtained using Mylar and mica-based interferometers.

  6. Precision spectroscopy of acetylene transitions using an optical frequency synthesizer.

    PubMed

    Ahtee, V; Merimaa, M; Nyholm, K

    2009-09-01

    An optical frequency synthesizer is used for saturation spectroscopy of acetylene near 1540 nm. In the synthesizer, a user-specified frequency is generated from an atomic time base by phase locking the second harmonic of a cw near-IR external-cavity diode laser (ECDL) to a Ti:sapphire frequency comb. By stepping the repetition rate of the frequency comb, the ECDL frequency is swept over an acetylene transition in a saturated absorption spectroscopy setup. Hence, a spectral lineshape is measured with an absolute frequency scale. Line-center frequencies determined by fitting theoretical line profiles to the measured data are in good agreement with values measured with the ECDL stabilized to acetylene by third-harmonic locking and with the values recommended by the International Committee for Weights and Measures (CIPM).

  7. Resolution of Transverse Electron Beam Measurements using Optical Transition Radiation

    SciTech Connect

    Ischebeck, Rasmus; Decker, Franz-Josef; Hogan, Mark; Iverson, Richard H.; Krejcik, Patrick; Lincoln, Melissa; Siemann, Robert H.; Walz, Dieter; Clayton, Chris E.; Huang, Chengkun; Lu, Wei; Deng, Suzhi; Oz, Erdem; /Southern California U.

    2005-06-22

    In the plasma wakefield acceleration experiment E-167, optical transition radiation is used to measure the transverse profile of the electron bunches before and after the plasma acceleration. The distribution of the electric field from a single electron does not give a point-like distribution on the detector, but has a certain extension. Additionally, the resolution of the imaging system is affected by aberrations. The transverse profile of the bunch is thus convolved with a point spread function (PSF). Algorithms that deconvolve the image can help to improve the resolution. Imaged test patterns are used to determine the modulation transfer function of the lens. From this, the PSF can be reconstructed. The Lucy-Richardson algorithm is used to deconvolute this PSF from test images.

  8. Vibrational states and optical transitions in hydrogen bonds

    NASA Astrophysics Data System (ADS)

    Johannsen, P. G.

    1998-03-01

    Proton energies in hydrogen bonds are mostly calculated using a double Morse potential (the DMP model). This form, however, does not reproduce the experimentally observed correlation between the proton stretching frequency and the bond length in an extended bond-length region sufficiently well. An alternative potential is proposed in the present paper. The quantum states of this non-symmetric double-well potential are calculated numerically using the Numerov (Fox-Goodwin) algorithm. It is shown that the optical spectra of hydrogen bonds in various substances can be well approximated on the basis of the transition frequencies and intensities predicted by the present model. For weakly interacting OH impurities in 0953-8984/10/10/008/img1, the overtone spectrum and line intensities are well reproduced, whereas the line broadenings and the decrease of the fundamental stretching frequencies in intermediate and strong hydrogen bonds are traced back to the influence of the reduced height of the central barrier. The model is also extrapolated to the range of symmetric hydrogen bonds, and the calculated transition frequencies are discussed with respect to most recent infra-red experiments on ice under strong compression. A possible artificial infra-red signal from strained diamond anvils is thereby noted.

  9. The Older Persons’ Transitions in Care (OPTIC) study: pilot testing of the transition tracking tool

    PubMed Central

    2013-01-01

    Background OPTIC is a mixed method Partnership for Health System Improvement (http://www.cihr-irsc.gc.ca/e/34348.html) study focused on improving care for nursing home (NH) residents who are transferred to and from emergency departments (EDs) via emergency medical services (EMS). In the pilot study we tested feasibility of concurrently collecting individual resident data during transitions across settings using the Transition Tracking Tool (T3). Methods The pilot study tracked 54 residents transferred from NHs to one of two EDs in two western Canadian provinces over a three month period. The T3 is an electronic data collection tool developed for this study to record data relevant to describing and determining success of transitions in care. It comprises 800+ data elements including resident characteristics, reasons and precipitating factors for transfer, advance directives, family involvement, healthcare services provided, disposition decisions, and dates/times and timing. Results Residents were elderly (mean age = 87.1 years) and the majority were female (61.8%). Feasibility of collecting data from multiple sources across two research sites was established. We identified resources and requirements to access and retrieve specific data elements in various settings to manage data collection processes and allocate research staff resources. We present preliminary data from NH, EMS, and ED settings. Conclusions While most research in this area has focused on a unidirectional process of patient progression from one care setting to another, this study established feasibility of collecting detailed data from beginning to end of a transition across multiple settings and in multiple directions. PMID:24330805

  10. Determination of the liquid crystals phase transition temperatures using optical rotation effect

    NASA Astrophysics Data System (ADS)

    Niu, Xiao-ling; Liu, Wei-guo; Liu, Peng; Cai, Chang-long

    2011-11-01

    Using optical rotation effect, a sensitive, simple optical analytical system is developed for determining the phase transition temperatures of liquid crystals (LCs). When a monochromatic polarized light passes through LCs sample and analyzer, the light intensity changes with temperature. Especially, during the phase transition process, the intensity varies greatly due to optical rotation effect. The variation of light intensity versus variation of temperature curve shows the phase transition temperatures of LCs clearly. The phase transition temperatures of three cholesteric liquid crystals (ChLCs) and a nematic liquid crystals (NLCs) were detected by this method, and compared with those of the differential scanning calorimetry (DSC) and polarized light microscope (PLM) methods.

  11. Optical lattice polarization effects on magnetically induced optical atomic clock transitions

    SciTech Connect

    Taichenachev, A. V.; Yudin, V. I.; Oates, C. W.

    2007-08-15

    We derive the frequency shift for a forbidden optical transition J=0{yields}J{sup '}=0 caused by the simultaneous actions of an elliptically polarized lattice field and a static magnetic field. We find that a simple configuration of lattice and magnetic fields leads to a cancellation of this shift to first order in lattice intensity and magnetic field. In this geometry, the second-order lattice intensity shift can be minimized as well by use of optimal lattice polarization. Suppression of these shifts could considerably enhance the performance of the next generation of atomic clocks.

  12. Contactless electroreflectance spectroscopy of optical transitions in low dimensional semiconductor structures

    NASA Astrophysics Data System (ADS)

    Misiewicz, J.; Kudrawiec, R.

    2012-06-01

    The authors present the application of contactless electroreflectance (CER) spectroscopy to study optical transitions in low dimensional semiconductor structures including quantum wells (QWs), step-like QWs, quantum dots (QDs), quantum dashes (QDashes), QDs and QDashes embedded in a QW, and QDashes coupled with a QW. For QWs optical transitions between the ground and excited states as well as optical transitions in QW barriers and step-like barriers have been clearly observed in CER spectra. Energies of these transitions have been compared with theoretical calculations and in this way the band structure has been determined for the investigated QWs. For QD and QDash structures optical transitions in QDs and QDashes as well as optical transitions in the wetting layer have been identified. For QDs and QDashes surrounded by a QW, in addition to energies of QD and QDash transitions, energies of optical transitions in the surrounded QW have been measured and the band structure has been determined for the surrounded QW. Finally some differences, which can be observed in CER and photo-reflectance spectra, have been presented and discussed for selected QW and QD structures.

  13. Rare earth transition metal alloys for magneto-optical recording

    NASA Astrophysics Data System (ADS)

    Daval, J.; Bechevet, B.

    1994-01-01

    Despite some drawbacks, RETM alloys in the form of amorphous thin films, have now proved their preeminence as rewritable recording media for magneto-optical data storage. Writing and read-out processes are described in terms of their magnetic, optical and structural properties. Future trends towards high storage densities are discussed through material and optics improvements and, therefrom, many possible applications for magneto-optical technology are considered.

  14. Terahertz Optical Gain Based on Intersubband Transitions in Optically-Pumped Semiconductor Quantum Wells: Coherent Pumped-Probe Interactions

    NASA Technical Reports Server (NTRS)

    Liu, Ansheng; Ning, Cun-Zheng

    1999-01-01

    Terahertz optical gain due to intersubband transitions in optically-pumped semiconductor quantum wells (QW's) is calculated nonperturbatively. We solve the pump- field-induced nonequilibrium distribution function for each subband of the QW system from a set of rate equations that include both intrasubband and intersubband relaxation processes. The gain arising from population inversion and stimulated Raman processes is calculated in a unified manner. We show that the coherent pump and signal wave interactions contribute significantly to the THz gain. Because of the optical Stark effect and pump-induced population redistribution, optical gain saturation at larger pump intensities is predicted.

  15. Theory of optical transitions in conjugated polymers. I. Ideal systems

    SciTech Connect

    Barford, William; Marcus, Max

    2014-10-28

    We describe a theory of linear optical transitions in conjugated polymers. The theory is based on three assumptions. The first is that the low-lying excited states of conjugated polymers are Frenkel excitons coupled to local normal modes, described by the Frenkel-Holstein model. Second, we assume that the relevant parameter regime is ℏω ≪ J, i.e., the adiabatic regime, and thus the Born-Oppenheimer factorization of the electronic and nuclear degrees of freedom is generally applicable. Finally, we assume that the Condon approximation is valid, i.e., the exciton-polaron wavefunction is essentially independent of the normal modes. Using these assumptions we derive an expression for an effective Huang-Rhys parameter for a chain (or chromophore) of N monomers, given by S(N) = S(1)/IPR, where S(1) is the Huang-Rhys parameter for an isolated monomer. IPR is the inverse participation ratio, defined by IPR = (∑{sub n}|Ψ{sub n}|{sup 4}){sup −1}, where Ψ{sub n} is the exciton center-of-mass wavefunction. Since the IPR is proportional to the spread of the exciton center-of-mass wavefunction, this is a key result, as it shows that S(N) decreases with chain length. As in molecules, in a polymer S(N) has two interpretations. First, ℏωS(N) is the relaxation energy of an excited state caused by its coupling to the normal modes. Second, S(N) appears in the definition of an effective Franck-Condon factor, F{sub 0v}(N) = S(N){sup v}exp ( − S(N))/v! for the vth vibronic manifold. We show that the 0 − 0 and 0 − 1 optical intensities are proportional to F{sub 00}(N) and F{sub 01}(N), respectively, and thus the ratio of the 0 − 1 to 0 − 0 absorption and emission intensities are proportional to S(N). These analytical results are checked by extensive DMRG calculations and found to be generally valid, particularly for emission. However, for large chain lengths higher-lying quasimomentum exciton states become degenerate with the lowest vibrational excitation of the

  16. Optical properties of cirrus transition zones over China detected by CALIOP

    NASA Astrophysics Data System (ADS)

    Cai, Hongke; Fu, Yunfei; Chen, Quanliang; Feng, Xiao; Tie, Xin; Tao, Ranting; Xu, Kepiao

    2017-06-01

    A transition zone near cirrus lateral boundaries can be detected by CALIOP (cloud-aerosol lidar with orthogonal polarization). In the present study, for such transition zones over China, a number of optical properties, such as the backscatter coefficient and depolarization ratio, showed transitional characteristics between cirrus and clear sky. The stepped horizontal profile showed sharp changes in particle number and morphology between cirrus clouds and clear sky. The color ratio, however, was unable to show cirrus transition features because of the low signal-to-noise ratio. Typical ice particles presented a color ratio of 0.55-1.25 and a depolarization ratio of greater than 0.12, which were significantly higher than those of clear sky. Therefore, optical properties in transition took the form of stepwise horizontal profiles. The proportion of typical-featured particles also demonstrated a stepped horizontal profile similar to the optical characteristics, but the relationship between the proportion and the optical characteristics was not uniform in the cirrus clouds, transition zone, and clear sky. Therefore, the optical changes in the transition zone were caused by not only the change in particle concentration, but also the change in the particles themselves. The probability density distribution of the transition-zone widths showed a positive skewness distribution, and transition zones with widths of 3-5 km occurred most frequently. Overall, transition-zone width decreased with increasing temperature and increased with increasing vertical and horizontal wind speeds. This trend demonstrated independence with the direction of the vertical and horizontal winds. These observations implied that the transitional features were caused by material exchange, such as entrainment and turbulent transport, near the cirrus lateral boundaries, and by the phase transformation of particles, such as sublimation.

  17. Near-UV and Optical Observations of the Transiting Extrasolar Planet Tres-3b

    NASA Astrophysics Data System (ADS)

    Smith, Carter-Thaxton W.; Smart, B.; Turner, J. D.; Walker-LaFollette, A.; Hardegree-Ullman, K. K.; Small, L. C.; McGraw, A. M.; Crawford, B. E.; Carleton, T. M.; Robertson, A. N.; Towner, A. P. M.; Daugherty, M. J.; Guvenen, B.

    2012-05-01

    Recent observations of transiting extrasolar planets in near-UV and optical bands, by Vidotto et al. 2011, suggest that asymmetries in light curve ingress times indicate the presence of a magnetic field. The University of Arizona Astronomy Club observed primary transits of extrasolar planet TrES-3b using the 1.55m Kuiper Telescope in the U, B, V, and R photometric bands in order to detect this phenomenon. We have reanalyzed transit data collected between 2009 and 2012 in order to have a consistent reduction methodology and eliminate any systematic errors. Using the Transit Analysis Package (TAP) and the JKTEBOP transit modeling code, we have modeled all of our transits to detect any light curve asymmetries between near-UV and optical bands.

  18. Delocalizing transition in one-dimensional condensates in optical lattices due to inhomogeneous interactions

    SciTech Connect

    Bludov, Yu. V.; Brazhnyi, V. A.; Konotop, V. V.

    2007-08-15

    It is shown that inhomogeneous nonlinear interactions in a Bose-Einstein condensate loaded in an optical lattice can result in a delocalizing transition in one dimension, which sharply contrasts to the known behavior of discrete and periodic systems with homogeneous nonlinearity. The transition can be originated either by decreasing the amplitude of the linear periodic potential or by the change of the mean value of the periodic nonlinearity. The dynamics of the delocalizing transition is studied.

  19. Quantum beats in transitions from levels subject to optical cascades.

    NASA Technical Reports Server (NTRS)

    Liu, C. J.; Druetta, M.; Church, D. A.

    1972-01-01

    Discussion of the g values of weakly aligned O II and O III multiplet levels subject to strong optical cascades, obtained by means of a beam-foil quantum beat method. Within the measurement precision limits of nearly plus or minus 1%, the effects of the optical cascades on the measured g values are shown to be negligible.

  20. Non-local Optical Topological Transitions and Critical States in Electromagnetic Metamaterials

    PubMed Central

    Ishii, Satoshi; Narimanov, Evgenii

    2015-01-01

    Just as the topology of the Fermi surface defines the properties of the free electrons in metals and semiconductors, the geometry of the iso-frequency surface in the phase space of the propagating electromagnetic waves, determines the optical properties of the corresponding optical materials. Furthermore, in the direct analog to the Lifshitz transition in condensed matter physics, a change in the topology of iso-frequency surface has a dramatic effect on the emission, propagation and scattering of the electromagnetic waves. Here, we uncover a new class of such optical topological transitions in metamaterials, induced by the non-locality of the electromagnetic response inherent to these composites. PMID:26670600

  1. FUNDAMENTAL AREAS OF PHENOMENOLOGY (INCLUDING APPLICATIONS): Analysis and Simulation of Adiabatic Bend Transitions in Optical Fibers

    NASA Astrophysics Data System (ADS)

    Yao, Lei; Lou, Shu-Qin; Jian, Shui-Sheng

    2009-07-01

    A low-loss criterion for bend transitions in optical fibers is proposed. An optical fiber can be tightly bent with low loss to be adiabatic for the fundamental mode, provided that an approximate upper bound on the rate of change of bend curvature for a given bend curvature is satisfied. Two typical adiabatic bend transition paths, the optimum profile and linear profile, are analyzed and studied numerically. A realizable adiabatic transition with an Archimedean spiral profile is introduced for low bend loss in tightly bent optical fibers. Design of the transitions is based on modeling of the propagation and coupling characteristics of the core and cladding modes, which clearly illustrate the physical processes involved.

  2. Energy spectrum and optical transitions in C80 fullerene isomers

    NASA Astrophysics Data System (ADS)

    Lobanov, B. V.; Murzashev, A. I.

    2013-04-01

    The energy spectra of all isomers of the C80 fullerene have been calculated in terms of the Schubin-Wonsowskii-Hubbard model. On this basis, their optical absorption spectra have also been calculated. The optical absorption spectra calculated for the endohedral Ca@C80, Ba@C80, and Sr@C80 fullerenes with the I h symmetry agree well with the experimental data. This circumstance allows us to conclude that the optical absorption spectra of other isomers (for which experimental data are unavailable) obtained in this work can be used for their identification.

  3. In-Plane Propagation of Light in Transition Metal Dichalcogenide Monolayers: Optical Selection Rules

    NASA Astrophysics Data System (ADS)

    Wang, G.; Robert, C.; Glazov, M. M.; Cadiz, F.; Courtade, E.; Amand, T.; Lagarde, D.; Taniguchi, T.; Watanabe, K.; Urbaszek, B.; Marie, X.

    2017-07-01

    The optical selection rules for interband transitions in WSe2 , WS2 , and MoSe2 transition metal dichalcogenide monolayers are investigated by polarization-resolved photoluminescence experiments with a signal collection from the sample edge. These measurements reveal a strong polarization dependence of the emission lines. We see clear signatures of the emitted light with the electric field oriented perpendicular to the monolayer plane, corresponding to an interband optical transition forbidden at normal incidence used in standard optical spectroscopy measurements. The experimental results are in agreement with the optical selection rules deduced from group theory analysis, highlighting the key role played by the different symmetries of the conduction and valence bands split by the spin-orbit interaction. These studies yield a direct determination of the bright-dark exciton splitting, for which we measure 40 ±1 meV and 55 ±2 meV in WSe2 and WS2 monolayer, respectively.

  4. Quantitative identification of dynamical transitions in a semiconductor laser with optical feedback

    NASA Astrophysics Data System (ADS)

    Quintero-Quiroz, C.; Tiana-Alsina, J.; Romà, J.; Torrent, M. C.; Masoller, C.

    2016-11-01

    Identifying transitions to complex dynamical regimes is a fundamental open problem with many practical applications. Semi- conductor lasers with optical feedback are excellent testbeds for studying such transitions, as they can generate a rich variety of output signals. Here we apply three analysis tools to quantify various aspects of the dynamical transitions that occur as the laser pump current increases. These tools allow to quantitatively detect the onset of two different regimes, low-frequency fluctuations and coherence collapse, and can be used for identifying the operating conditions that result in specific dynamical properties of the laser output. These tools can also be valuable for analyzing regime transitions in other complex systems.

  5. Feasibility study of optical boundary layer transition detection method

    NASA Technical Reports Server (NTRS)

    Azzazy, M.; Modarress, D.; Trolinger, J. D.

    1986-01-01

    A high sensitivity differential interferometer was developed to locate the region where the boundary layer flow undergoes transition from laminar to turbulent. Two laboratory experimental configurations were used to evaluate the performance of the interferometer: open shear layer, and low speed wind tunnel turbulent spot configuration. In each experiment, small temperature fluctuations were introduced as the signal source. Simultaneous cold wire measurements were compared with the interferometer data. The comparison shows that the interferometer is sensitive to very weak phase variations in the order of 0.001 the laser wavelength. An attempt to detect boundary layer transition over a flat plate at NASA-Langley Unitary Supersonic Wind Tunnel using the interferometer system was performed. The phase variations during boundary layer transition in the supersonic wind tunnel were beyond the minimum signal-to-noise level of the instrument.

  6. Sub-micrometer transverse beam size diagnostics using optical transition radiation

    NASA Astrophysics Data System (ADS)

    Kruchinin, K.; Aryshev, A.; Karataev, P.; Bolzon, B.; Lefevre, T.; Mazzoni, S.; Shevelev, M.; Boogert, S. T.; Nevay, L. J.; Terunuma, N.; Urakawa, J.

    2014-05-01

    Optical transition radiation (OTR) arising when a relativistic charged particle crosses a boundary between two media with different optical properties is widely used as a tool for diagnostics of particle beams in modern accelerator facilities. The resolution of the beam profile monitors based on OTR depends on different effects of the optical system such as spherical and chromatic aberrations and diffraction. In this paper we present a systematic study of the different optical effects influencing the OTR beam profile monitor resolution. Obtained results have shown that such monitors can be used for sub-micrometer beam profile diagnostics. Further improvements and studies of the monitor are discussed.

  7. Three-Dimensional Analysis of Optical Transition Radiation

    DTIC Science & Technology

    1988-12-01

    may be observed from the front face of the foil and is called backward transition radiation siliCe it is reflected back fLou- the foil. Transition...reflection coefficients. The Lorentz factor , aPI the velocity / are defined E -1+ KE , (2.3) and ~= - (2.4) The parallel and perpendicular reflection...Re[(-y-N2Z/ax)W(Z)+ax (2/ )l/2] , (2.8) where Z is defined as (I +i0)/a, ax as the rms beam angle of divergence projected into the observation plane

  8. Doubly Magic Optical Trapping for Cs Atom Hyperfine Clock Transitions

    NASA Astrophysics Data System (ADS)

    Carr, A. W.; Saffman, M.

    2016-10-01

    We analyze doubly magic trapping of Cs hyperfine transitions including previously neglected contributions from the ground state hyperpolarizability and the interaction of the laser light and a static magnetic field. Extensive numerical searches do not reveal any doubly magic trapping conditions for any pair of hyperfine states. However, including the hyperpolarizability reveals light intensity insensitive traps for a wide range of wavelengths at specific intensities. We then investigate the use of bichromatic trapping light fields. Deploying a bichromatic scheme, we demonstrate doubly magic red and blue detuned traps for pairs of states separated by one or two single photon transitions.

  9. Optically decomposed near-band-edge structure and excitonic transitions in Ga2S3

    PubMed Central

    Ho, Ching-Hwa; Chen, Hsin-Hung

    2014-01-01

    The band-edge structure and band gap are key parameters for a functional chalcogenide semiconductor to its applications in optoelectronics, nanoelectronics, and photonics devices. Here, we firstly demonstrate the complete study of experimental band-edge structure and excitonic transitions of monoclinic digallium trisulfide (Ga2S3) using photoluminescence (PL), thermoreflectance (TR), and optical absorption measurements at low and room temperatures. According to the experimental results of optical measurements, three band-edge transitions of EA = 3.052 eV, EB = 3.240 eV, and EC = 3.328 eV are respectively determined and they are proven to construct the main band-edge structure of Ga2S3. Distinctly optical-anisotropic behaviors by orientation- and polarization-dependent TR measurements are, respectively, relevant to distinguish the origins of the EA, EB, and EC transitions. The results indicated that the three band-edge transitions are coming from different origins. Low-temperature PL results show defect emissions, bound-exciton and free-exciton luminescences in the radiation spectra of Ga2S3. The below-band-edge transitions are respectively characterized. On the basis of experimental analyses, the optical property of near-band-edge structure and excitonic transitions in the monoclinic Ga2S3 crystal is revealed. PMID:25142550

  10. Optically pumped NMR: Revealing spin-dependent Landau level transitions in GaAs

    NASA Astrophysics Data System (ADS)

    Ramaswamy, K.; Mui, S.; Crooker, S. A.; Pan, X.; Sanders, G. D.; Stanton, C. J.; Hayes, S. E.

    2010-08-01

    We show that high-resolution optically pumped NMR (OPNMR) studies can reveal spin-dependent optical transitions between valence- and conduction-band Landau levels in bulk semiconductors such as GaAs. The OPNMR signal intensity exhibits oscillations as a function of pump photon energy that evolve with magnetic field. In contrast to standard polarized magnetoabsorption measurements, OPNMR is sensitive to the polarization of the photoexcited electron spins (i.e., the difference between spin-up and spin-down electron populations rather than the sum). This allows one to clearly resolve the spin dependence of optical transitions that might normally be obscured in conventional magnetoabsorption studies. The data are in good agreement with theoretical calculations of the transitions from the spin-split light-hole Landau levels in the valence band to the conduction-band Landau levels of GaAs.

  11. Measurement of Sub-Picosecond Electron Bunches via Electro-Optic Sampling of Coherent Transition Radiation

    SciTech Connect

    Maxwell, Timothy John

    2012-01-01

    Future collider applications as well as present high-gradient laser plasma wakefield accelerators and free-electron lasers operating with picosecond bunch durations place a higher demand on the time resolution of bunch distribution diagnostics. This demand has led to significant advancements in the field of electro-optic sampling over the past ten years. These methods allow the probing of diagnostic light such as coherent transition radiation or the bunch wakefields with sub-picosecond time resolution. We present results on the single-shot electro-optic spectral decoding of coherent transition radiation from bunches generated at the Fermilab A0 photoinjector laboratory. A longitudinal double-pulse modulation of the electron beam is also realized by transverse beam masking followed by a transverse-to-longitudinal phase-space exchange beamline. Live profile tuning is demonstrated by upstream beam focusing in conjunction with downstream monitoring of single-shot electro-optic spectral decoding of the coherent transition radiation.

  12. Extreme nonlinear response of ultranarrow optical transitions in cavity QED for laser stabilization

    SciTech Connect

    Martin, M. J.; Meiser, D.; Ye Jun; Holland, M. J.; Thomsen, J. W.

    2011-12-15

    We explore the potential of direct spectroscopy of ultranarrow optical transitions of atoms localized in an optical cavity. In contrast to stabilization against a reference cavity, which is the approach currently used for the most highly stabilized lasers, stabilization against an atomic transition does not suffer from Brownian thermal noise. Spectroscopy of ultranarrow optical transitions in a cavity operates in a very highly saturated regime in which nonlinear effects such as bistability play an important role. From the universal behavior of the Jaynes-Cummings model with dissipation, we derive the fundamental limits for laser stabilization using direct spectroscopy of ultranarrow atomic lines. We find that, with current lattice clock experiments, laser linewidths of about 1 mHz can be achieved in principle, and the ultimate limitations of this technique are at the 1 {mu}Hz level.

  13. Robust Light State by Quantum Phase Transition in Non-Hermitian Optical Materials

    NASA Astrophysics Data System (ADS)

    Zhao, Han; Longhi, Stefano; Feng, Liang

    2015-11-01

    Robust light transport is the heart of optical information processing, leading to the search for robust light states by topological engineering of material properties. Here, it is shown that quantum phase transition, rather than topology, can be strategically exploited to design a novel robust light state. We consider an interface between parity-time (PT) symmetric media with different quantum phases and use complex Berry phase to reveal the associated quantum phase transition and topological nature. While the system possesses the same topological order within different quantum phases, phase transition from PT symmetry to PT breaking across the interface in the synthetic non-Hermitian metamaterial system facilitates novel interface states, which are robust against a variety of gain/loss perturbations and topological impurities and disorder. The discovery of the robust light state by quantum phase transition may promise fault-tolerant light transport in optical communications and computing.

  14. Robust Light State by Quantum Phase Transition in Non-Hermitian Optical Materials

    PubMed Central

    Zhao, Han; Longhi, Stefano; Feng, Liang

    2015-01-01

    Robust light transport is the heart of optical information processing, leading to the search for robust light states by topological engineering of material properties. Here, it is shown that quantum phase transition, rather than topology, can be strategically exploited to design a novel robust light state. We consider an interface between parity-time (PT) symmetric media with different quantum phases and use complex Berry phase to reveal the associated quantum phase transition and topological nature. While the system possesses the same topological order within different quantum phases, phase transition from PT symmetry to PT breaking across the interface in the synthetic non-Hermitian metamaterial system facilitates novel interface states, which are robust against a variety of gain/loss perturbations and topological impurities and disorder. The discovery of the robust light state by quantum phase transition may promise fault-tolerant light transport in optical communications and computing. PMID:26592765

  15. Robust Light State by Quantum Phase Transition in Non-Hermitian Optical Materials.

    PubMed

    Zhao, Han; Longhi, Stefano; Feng, Liang

    2015-11-23

    Robust light transport is the heart of optical information processing, leading to the search for robust light states by topological engineering of material properties. Here, it is shown that quantum phase transition, rather than topology, can be strategically exploited to design a novel robust light state. We consider an interface between parity-time (PT) symmetric media with different quantum phases and use complex Berry phase to reveal the associated quantum phase transition and topological nature. While the system possesses the same topological order within different quantum phases, phase transition from PT symmetry to PT breaking across the interface in the synthetic non-Hermitian metamaterial system facilitates novel interface states, which are robust against a variety of gain/loss perturbations and topological impurities and disorder. The discovery of the robust light state by quantum phase transition may promise fault-tolerant light transport in optical communications and computing.

  16. Coherent control of a strongly driven silicon vacancy optical transition in diamond

    NASA Astrophysics Data System (ADS)

    Zhou, Yu; Rasmita, Abdullah; Li, Ke; Xiong, Qihua; Aharonovich, Igor; Gao, Wei-Bo

    2017-02-01

    The ability to prepare, optically read out and coherently control single quantum states is a key requirement for quantum information processing. Optically active solid-state emitters have emerged as promising candidates with their prospects for on-chip integration as quantum nodes and sources of coherent photons connecting these nodes. Under a strongly driving resonant laser field, such quantum emitters can exhibit quantum behaviour such as Autler-Townes splitting and the Mollow triplet spectrum. Here we demonstrate coherent control of a strongly driven optical transition in silicon vacancy centre in diamond. Rapid optical detection of photons enabled the observation of time-resolved coherent Rabi oscillations and the Mollow triplet spectrum. Detection with a probing transition further confirmed Autler-Townes splitting generated by a strong laser field. The coherence time of the emitted photons is comparable to its lifetime and robust under a very strong driving field, which is promising for the generation of indistinguishable photons.

  17. Coherent control of a strongly driven silicon vacancy optical transition in diamond

    PubMed Central

    Zhou, Yu; Rasmita, Abdullah; Li, Ke; Xiong, Qihua; Aharonovich, Igor; Gao, Wei-bo

    2017-01-01

    The ability to prepare, optically read out and coherently control single quantum states is a key requirement for quantum information processing. Optically active solid-state emitters have emerged as promising candidates with their prospects for on-chip integration as quantum nodes and sources of coherent photons connecting these nodes. Under a strongly driving resonant laser field, such quantum emitters can exhibit quantum behaviour such as Autler–Townes splitting and the Mollow triplet spectrum. Here we demonstrate coherent control of a strongly driven optical transition in silicon vacancy centre in diamond. Rapid optical detection of photons enabled the observation of time-resolved coherent Rabi oscillations and the Mollow triplet spectrum. Detection with a probing transition further confirmed Autler–Townes splitting generated by a strong laser field. The coherence time of the emitted photons is comparable to its lifetime and robust under a very strong driving field, which is promising for the generation of indistinguishable photons. PMID:28218237

  18. New trends in the optical and electronic applications of polymers containing transition-metal complexes.

    PubMed

    Liu, Shu-Juan; Chen, Yang; Xu, Wen-Juan; Zhao, Qiang; Huang, Wei

    2012-04-13

    Polymers containing transition-metal complexes exhibit excellent optical and electronic properties, which are different from those of polymers with a pure organic skeleton and combine the advantages of both polymers and metal complexes. Hence, research about this class of polymers has attracted more and more interest in recent years. Up to now, a number of novel polymers containing transition-metal complexes have been exploited, and significant advances in their optical and electronic applications have been achieved. In this article, we summarize some new research trends in the applications of this important class of optoelectronic polymers, such as chemo/biosensors, electronic memory devices and photovoltaic devices.

  19. Magneto-optical spectra of transition metal dichalcogenides: A comparative study

    SciTech Connect

    Ho, Yen-Hung; Chiu, Chih-Wei; Lin, Ming-Fa; Su, Wu-Pei

    2014-12-01

    Following our previous work [Ho et al., Phys. Rev. B 89, 155316 (2014)], we systematically calculate the magneto-optical properties of various transition metal dichalcogenide monolayers. The intrinsic spin-orbit coupling gives rise to the spin-split electronic states, while a perpendicular magnetic field further induces a valley splitting. In magneto-optical spectra with linearly polarized light, spectral features are spin and valley-polarized. Compounds are different from one another in terms of transition energies and appearance of twin peaks. Our numerical results can serve as a guide for future experimental identification.

  20. Multispectral optical metasurfaces enabled by achromatic phase transition

    PubMed Central

    Zhao, Zeyu; Pu, Mingbo; Gao, Hui; Jin, Jinjin; Li, Xiong; Ma, Xiaoliang; Wang, Yanqin; Gao, Ping; Luo, Xiangang

    2015-01-01

    The independent control of electromagnetic waves with different oscillating frequencies is critical in the modern electromagnetic techniques, such as wireless communications and multispectral imaging. To obtain complete control of different light waves with optical materials, the chromatic dispersion should be carefully controlled, which is however extremely difficult. In this paper, we propose a method to control the behaviors of different light waves through a metasurface which is able to generate achromatic geometric phase. Using this approach, a doughnut-shaped and a solid light spot were achieved at the same focal plane using two light sources with different wavelengths as used in the stimulation emission depletion (STED) microscope system. In order to reveal the full capacity of such method, tight focusing at multiple wavelengths is also represented, where the focal spots of different wavelengths are located at the same position. The results provided here may open a new door to the design of subminiature optical components and integrated optical system operating at multiple wavelengths. PMID:26503607

  1. Multispectral optical metasurfaces enabled by achromatic phase transition

    NASA Astrophysics Data System (ADS)

    Zhao, Zeyu; Pu, Mingbo; Gao, Hui; Jin, Jinjin; Li, Xiong; Ma, Xiaoliang; Wang, Yanqin; Gao, Ping; Luo, Xiangang

    2015-10-01

    The independent control of electromagnetic waves with different oscillating frequencies is critical in the modern electromagnetic techniques, such as wireless communications and multispectral imaging. To obtain complete control of different light waves with optical materials, the chromatic dispersion should be carefully controlled, which is however extremely difficult. In this paper, we propose a method to control the behaviors of different light waves through a metasurface which is able to generate achromatic geometric phase. Using this approach, a doughnut-shaped and a solid light spot were achieved at the same focal plane using two light sources with different wavelengths as used in the stimulation emission depletion (STED) microscope system. In order to reveal the full capacity of such method, tight focusing at multiple wavelengths is also represented, where the focal spots of different wavelengths are located at the same position. The results provided here may open a new door to the design of subminiature optical components and integrated optical system operating at multiple wavelengths.

  2. Intersubband optical transitions in InAs/GaSb broken-gap quantum wells

    NASA Astrophysics Data System (ADS)

    Semenikhin, I.; Zakharova, A.; Nilsson, K.; Chao, K. A.

    2008-03-01

    We investigate the intersubband optical transitions in the InAs/GaSb quantum wells using Burt's envelope function theory and the eight-band model. The self-consistent potential and the lattice-mismatched strain are taken into account to study the effects of bulk inversion asymmetry (BIA) and low interface symmetry on optical matrix elements in structures grown on the InAs substrate along the [001] direction. We have found that both BIA and low symmetry interface Hamiltonian (IH) can result in initially forbidden spin-flip optical transitions or initially forbidden spin conserved optical transitions caused by linearly polarized light. For the light polarization in the plane of the structure, the originally forbidden spin-flip processes can be induced if the light polarization is along the quasiparticle wave vector. However, if light polarization is normal to it, then the originally forbidden spin-conserved processes can be induced. If the light is polarized normally to interfaces along the growth direction [001], then the originally forbidden spin-flip transitions are activated, if in-plane wave vector of the initial quasiparticle states is along the [10] direction. We have also found a considerable lateral anisotropy of absorption caused mainly by BIA induced mechanism. The principal point of this mechanism is the interface contribution to the optical matrix elements due to the material-dependent Kane's B-parameter.

  3. Inner-shell magnetic dipole transition in Tm atoms: A candidate for optical lattice clocks

    NASA Astrophysics Data System (ADS)

    Sukachev, D.; Fedorov, S.; Tolstikhina, I.; Tregubov, D.; Kalganova, E.; Vishnyakova, G.; Golovizin, A.; Kolachevsky, N.; Khabarova, K.; Sorokin, V.

    2016-08-01

    We consider a narrow magneto-dipole transition in the 169Tm atom at the wavelength of 1.14 μ m as a candidate for a two-dimensional-optical lattice clock. Calculating dynamic polarizabilities of the two clock levels [Xe] 4 f136 s2(J =7 /2 ) and [Xe] 4 f136 s2(J =5 /2 ) in the spectral range from 250 to 1200 nm, we find a "magic" wavelength for the optical lattice at 807 nm. Frequency shifts due to black-body radiation (BBR), the van der Waals interaction, the magnetic dipole-dipole interaction, and other effects which can perturb the transition frequency are calculated. The transition at 1.14 μ m demonstrates low sensitivity to the BBR shift corresponding to 8 ×10-17 in fractional units at room temperature which makes it an interesting candidate for high-performance optical clocks. The total estimated frequency uncertainty is less than 5 ×10-18 in fractional units. By direct excitation of the 1.14 μ m transition in Tm atoms loaded into an optical dipole trap, we set the lower limit for the lifetime of the upper clock level [Xe] 4 f136 s2(J =5 /2 ) of 112 ms which corresponds to a natural spectral linewidth narrower than 1.4 Hz. The polarizability of the Tm ground state was measured by the excitation of parametric resonances in the optical dipole trap at 532 nm.

  4. Anchoring Transitions of Liquid Crystals for Optical Amplification of Phospholipid Oxidation Inhibition by Ascorbic Acid.

    PubMed

    Zhang, Minmin; Jang, Chang-Hyun

    2015-01-01

    There is considerable evidence that the antioxidant property of ascorbic acid (AH) is effective for reducing oxidative stress of phospholipids. Herein, a liquid crystals (LCs)-based method was developed for the optical amplification of resistance to phospholipid oxidation by AH. Phospholipid peroxidation initiated by free radicals was monitored from a homeotropic-to-planar anchoring transition of LCs via polarized optical microscopy. Alternatively, consistent homeotropic anchoring of LCs was observed when the oxidation caused by free radicals was blocked by AH.

  5. Superlubric-pinned Aubry transition of two dimensional monolayers in optical lattices

    NASA Astrophysics Data System (ADS)

    Mandelli, Davide; Vanossi, Andrea; Manini, Nicola; Tosatti, Erio

    Two-dimensional (2D) crystalline colloidal monolayers sliding over a laser-induced optical lattice ``corrugation'' potential emulate friction between ideal crystal surfaces. Static friction is always present when the monolayer and the optical lattices are commensurate, but when they are incommensurate the presence or absence of static friction depends upon the system parameters. In 1D, at the Aubry dynamical phase transition the static friction goes continuously from zero (superlubricity) to finite as the periodic corrugation strength is increased. We look for the Aubry-like transition in the more realistic 2D case of a monolayer in an incommensurate periodic potential using molecular dynamics simulations. Results confirm a clear and sharp 2D superlubric-pinned transition upon increasing corrugation strength. Unlike the 1D Aubry transition which is continuous, the 2D transition is first-order, with a jump of static friction. At the 2D Aubry transition there is no change of symmetry, a sudden rise of the colloid-colloid interaction energy, and a compensating drop of the colloid-corrugation energy. The observability of the superlubric-pinned colloid transition is proposed and discussed. This work has been supported by ERC Advanced Grant N. 320796 MODPHYSFRICT.

  6. Optical properties of transition metal oxide quantum wells

    NASA Astrophysics Data System (ADS)

    Demkov, Alexander; Choi, Miri; Butcher, Matthew; Rodriguez, Cesar; He, Qian; Posadas, Agham; Borisevich, Albina; Zollner, Stefan; Lin, Chungwei; Ortmann, Elliott

    2015-03-01

    We report on the investigation of SrTiO3/LaAlO3 quantum wells (QWs) grown by molecular beam epitaxy (MBE) on LaAlO3 substrate. Structures with different QW thicknesses ranging from two to ten unit cells were grown and characterized using x-ray photoemission spectroscopy, reflection high-energy electron diffraction (RHEED), scanning transmission electron microscopy (STEM). Optical properties (complex dielectric function) were measured by spectroscopic ellipsometry (SE) in the range of 1.0 eV to 6.0 eV at room temperature. We observed that the absorption edge was blue-shifted by approximately 0.39 eV as the STO quantum well thickness was reduced to two unit cells (uc). Density functional theory and tight-binding are used to model the optical response of these heterostructures. Our results demonstrate that the energy level of the first sub-band can be controlled by the QW thickness in a complex oxide material. We acknowledge support from Air Force Office of Scientific Research (FA9550-12-10494).

  7. GRIN optics with transition elements in gel-silica matrices

    NASA Astrophysics Data System (ADS)

    Kunetz, James M.; West, Jon K.; Hench, Larry L.

    1992-12-01

    Sol-gel technology is providing a viable alternative path towards developing doped optical components via impregnation of Type VI gel silica using a vapor or liquid phase. Past work presented an optical technique for determining quantitative mass transport properties of Cr3+ ions within the water filled porous phase of Type VI silica. Ion influx is measured by integrating the strong absorption bands produced by the chromium in the visible region. Diffusion coefficients are determined for an array of pore properties (radius, volume, surface area) as well as solution concentrations. Diffusion coefficients are calculated to be 2.0 X 10-8 cm2/sec for the most restricted case and approach 1.6 X 10-6 cm2/sec, the bulk liquid diffusion coefficient, as the ratio of diffusing solute diameter to the pore diameter decreases. Final chromium distributions are determined using electron microprobe x-ray. Higher chromium distributions are found on surfaces of the gels from which solvent is restricted from evaporating. Sample geometries affect the percent change of concentration across the cross-section.

  8. The Dicke Quantum Phase Transition in a Superfluid Gas Coupled to an Optical Cavity

    NASA Astrophysics Data System (ADS)

    Guerlin, Christine; Baumann, Kristian; Brennecke, Ferdinand; Esslinger, Tilman

    2010-03-01

    A fundamental approach to collective matter-light interaction is given by the Dicke model which has been predicted to show an intriguing quantum phase transition. We have realized the Dicke quantum phase transition in an open system formed by a Bose-Einstein condensate coupled to an optical cavity, and observed the emergence of a self-organized supersolid phase [1]. The phase transition is driven by infinitely long-ranged interactions between the condensed atoms. We show that the phase transition is described by the Dicke Hamiltonian, including counter-rotating coupling terms, and that the supersolid phase is associated with a spontaneously broken spatial symmetry. The boundary of the phase transition is mapped out in quantitative agreement with the Dicke model. [4pt] [1] K. Baumann, C. Guerlin, F. Brennecke, T. Esslinger, arXiv 0912.2361, 2009

  9. Direct frequency comb optical frequency standard based on two-photon transitions of thermal atoms

    PubMed Central

    Zhang, S. Y.; Wu, J. T.; Zhang, Y. L.; Leng, J. X.; Yang, W. P.; Zhang, Z. G.; Zhao, J. Y.

    2015-01-01

    Optical clocks have been the focus of science and technology research areas due to their capability to provide highest frequency accuracy and stability to date. Their superior frequency performance promises significant advances in the fields of fundamental research as well as practical applications including satellite-based navigation and ranging. In traditional optical clocks, ultrastable optical cavities, laser cooling and particle (atoms or a single ion) trapping techniques are employed to guarantee high stability and accuracy. However, on the other hand, they make optical clocks an entire optical tableful of equipment, and cannot work continuously for a long time; as a result, they restrict optical clocks used as very convenient and compact time-keeping clocks. In this article, we proposed, and experimentally demonstrated, a novel scheme of optical frequency standard based on comb-directly-excited atomic two-photon transitions. By taking advantage of the natural properties of the comb and two-photon transitions, this frequency standard achieves a simplified structure, high robustness as well as decent frequency stability, which promise widespread applications in various scenarios. PMID:26459877

  10. Optical power diodes based on phase-transition materials (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Wan, Chenghao; Horak, Erik H.; Zhou, You; Zhang, Zhen; Salman, Jad; Roney, Patrick; Rensberg, Jura; Gundlach, Bradley; Ramanathan, Shriram; Goldsmith, Randall H.; Ronning, Carsten; Kats, Mikhail A.

    2017-03-01

    We present several designs and experimental implementations of optical power diodes - devices that are designed to be transparent from one direction, but opaque from the other, when illuminated by a beam with sufficient intensity. Optical power diodes can be used to protect optical devices that both detect and transmit light. Our designs are based on phase-change material vanadium dioxide (VO2), which undergoes an insulator-to-metal transition (IMT) that can be triggered thermally or optically. Here, VO2 films serve as nonlinear elements that can be transformed from transparent to opaque by intense illumination. We build thin-film metallic structures on top of the VO2 films such that the optical absorption becomes asymmetric - light impinging from one direction is absorbed at a higher rate than from the other direction, triggering the transition, and turning the device opaque. This results in asymmetric transmission. The designs are optimized with finite-difference time-domain (FDTD) simulations, using optical constants of VO2 extracted using ellipsometry, and are shown to be scalable across the near- and mid-infrared. Our initial experimental results using a simple design comprised of metal and VO2 films on sapphire, designed for an operating wavelength of 1.35µm, show a transmission asymmetry ratio of 2, and experiments with superior designs are ongoing. Future work will include the use of defect-engineered VO2 to engineer the intensity threshold of optical power diodes.

  11. Direct frequency comb optical frequency standard based on two-photon transitions of thermal atoms.

    PubMed

    Zhang, S Y; Wu, J T; Zhang, Y L; Leng, J X; Yang, W P; Zhang, Z G; Zhao, J Y

    2015-10-13

    Optical clocks have been the focus of science and technology research areas due to their capability to provide highest frequency accuracy and stability to date. Their superior frequency performance promises significant advances in the fields of fundamental research as well as practical applications including satellite-based navigation and ranging. In traditional optical clocks, ultrastable optical cavities, laser cooling and particle (atoms or a single ion) trapping techniques are employed to guarantee high stability and accuracy. However, on the other hand, they make optical clocks an entire optical tableful of equipment, and cannot work continuously for a long time; as a result, they restrict optical clocks used as very convenient and compact time-keeping clocks. In this article, we proposed, and experimentally demonstrated, a novel scheme of optical frequency standard based on comb-directly-excited atomic two-photon transitions. By taking advantage of the natural properties of the comb and two-photon transitions, this frequency standard achieves a simplified structure, high robustness as well as decent frequency stability, which promise widespread applications in various scenarios.

  12. Very high resolution optical transition radiation imaging system: Comparison between simulation and experiment

    NASA Astrophysics Data System (ADS)

    Bolzon, B.; Aryshev, A.; Aumeyr, T.; Boogert, S.; Karataev, P.; Kruchinin, K. O.; Lefevre, T.; Mazzoni, S.; Nevay, L.; Shevelev, M.; Terunuma, N.; Urakawa, J.; Welsch, C. P.

    2015-08-01

    Optical transition radiation (OTR) has become a commonly used method for 2D beam imaging measurements. In the Accelerator Test Facility 2 (ATF2) at KEK, beam sizes smaller than the OTR point spread function have been measured. Simulations of the OTR imaging system have been performed using the ZEMAX software to study the effects of optical errors such as aberrations, diffraction, and misalignments of optical components. This paper presents a comparison of simulations of the OTR point spread function with experimental data obtained at ATF2. It shows how the quantification and control of optical errors impacts on optimizing the resolution of the system. We also show that the OTR point spread function needs to be predicted accurately to optimize any optical system and to predict the error made on measurement.

  13. First-principles characterization of native-defect-related optical transitions in ZnO

    NASA Astrophysics Data System (ADS)

    Lyons, J. L.; Varley, J. B.; Steiauf, D.; Janotti, A.; Van de Walle, C. G.

    2017-07-01

    We investigate the electrical and optical properties of oxygen vacancies (VO), zinc vacancies (VZn), hydrogenated VZn, and isolated dangling bonds in ZnO using hybrid functional calculations. While the formation energy of VO is high in n-type ZnO, indicating that this center is unlikely to form, our results for optical absorption signals associated with VO are consistent with those observed in irradiated samples, and give rise to emission with a peak at less than 1 eV. Under realistic growth conditions, we find that VZn is the lowest-energy native defect in n-type ZnO, acting as an acceptor that is likely to compensate donor doping. Turning to optical transitions, we first examine NO as a case study, since N-related transitions have been identified in experiments on ZnO. We also examine how hydrogen, often unintentionally present in ZnO, forms stable complexes with VZn and modifies its optical properties. Compared with isolated VZn, VZn-H complexes have charge-state transition levels lower in the band gap as well as have lower formation energies. These complexes also lead to characteristic vibrational frequencies which compare favorably with experiment. Oxygen dangling bonds show behavior mostly consistent with VZn, while zinc dangling bonds give rise to transition levels near the ZnO conduction-band minimum and emission peaking near 2.4 eV. We discuss our results in view of the available experimental literature.

  14. Optical properties of medium size noble and transition metal nanoparticles

    NASA Astrophysics Data System (ADS)

    Idrobo, Juan C.; Pantelides, Sokrates T.

    2009-03-01

    Using first-principles methods within time dependent density functional theory and the local density approximation (TDLDA) the absorption spectra of medium size (˜20-80 atoms) silver, gold and copper nanoparticles have been calculated. The nanoparticles are fcc fragments with different aspect ratios. We find that in the case of Ag nanoparticles is well reproduced by classical electrodynamics theory based in Mie's formalism, using the dielectric function of bulk Ag and taking into account the nanoparticle shape. For the case of Cu and Au, there is a similarity in the overall features of the quantum mechanical and classical spectra, but no detailed agreement. We will discuss the role that the d-electrons among all the different elements and the surface states play in controlling the optical properties of the nanoparticles. This work was supported by GOALI NSF grant (DMR-0513048), DOE, the Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, and Alcoa Inc.

  15. NONLINEAR-OPTICS PHENOMENA: Formation of optical pulses by modulating the resonant quantum transition frequency in a spectrally inhomogeneous medium

    NASA Astrophysics Data System (ADS)

    Polovinkin, V. A.; Radionychev, E. V.

    2010-02-01

    We consider the conversion of monochromatic radiation in the case of resonant interaction with a quantum system under the condition of harmonic modulation of the quantum transition frequency by the action of additional nonresonant radiation due to the Stark or Zeeman effect, taking into account the inhomogeneous broadening of the quantum transition line. It is shown analytically and numerically that resonant radiation can be converted in a train of ultrashort pulses with a peak intensity exceeding manifold the incident wave intensity. The possibility of the additional compression of the produced pulses is studied by compensating the inherent frequency modulation in a medium with a quadratic or programmable dispersion. The optimal values of the radiation — matter interaction parameters are found numerically. It is shown that generation of femtosecond optical pulses of radiation quasi-resonant to the δ transition of the atomic hydrogen Balmer series is possible.

  16. Simultaneous infrared and optical observations of the transiting debris cloud around WD 1145+017

    NASA Astrophysics Data System (ADS)

    Zhou, G.; Kedziora-Chudczer, L.; Bailey, J.; Marshall, J. P.; Bayliss, D. D. R.; Stockdale, C.; Nelson, P.; Tan, T. G.; Rodriguez, J. E.; Tinney, C. G.; Dragomir, D.; Colon, K.; Shporer, A.; Bento, J.; Sefako, R.; Horne, K.; Cochran, W.

    2016-12-01

    We present multiwavelength photometric monitoring of WD 1145+017, a white dwarf exhibiting periodic dimming events interpreted to be the transits of orbiting, disintegrating planetesimals. Our observations include the first set of near-infrared light curves for the object, obtained on multiple nights over the span of 1 month, and recorded multiple transit events with depths varying between ˜20 and 50 per cent. Simultaneous near-infrared and optical observations of the deepest and longest duration transit event were obtained on two epochs with the Anglo-Australian Telescope and three optical facilities, over the wavelength range of 0.5-1.2 μm. These observations revealed no measurable difference in transit depths for multiple photometric pass bands, allowing us to place a 2σ lower limit of 0.8 μm on the grain size in the putative transiting debris cloud. This conclusion is consistent with the spectral energy distribution of the system, which can be fit with an optically thin debris disc with minimum particle sizes of 10^{+5}_{-3} μm.

  17. Magnetic field-induced spectroscopy of forbidden optical transitions with application to lattice-based optical atomic clocks.

    PubMed

    Taichenachev, A V; Yudin, V I; Oates, C W; Hoyt, C W; Barber, Z W; Hollberg, L

    2006-03-03

    We develop a method of spectroscopy that uses a weak static magnetic field to enable direct optical excitation of forbidden electric-dipole transitions that are otherwise prohibitively weak. The power of this scheme is demonstrated using the important application of optical atomic clocks based on neutral atoms confined to an optical lattice. The simple experimental implementation of this method--a single clock laser combined with a dc magnetic field--relaxes stringent requirements in current lattice-based clocks (e.g., magnetic field shielding and light polarization), and could therefore expedite the realization of the extraordinary performance level predicted for these clocks. We estimate that a clock using alkaline-earth-like atoms such as Yb could achieve a fractional frequency uncertainty of well below 10(-17) for the metrologically preferred even isotopes.

  18. Magnetic-dipole transitions in highly charged ions as a basis of ultraprecise optical clocks.

    PubMed

    Yudin, V I; Taichenachev, A V; Derevianko, A

    2014-12-05

    We evaluate the feasibility of using magnetic-dipole (M1) transitions in highly charged ions as a basis of an optical atomic clockwork of exceptional accuracy. We consider a range of possibilities, including M1 transitions between clock levels of the same fine-structure and hyperfine-structure manifolds. In highly charged ions these transitions lie in the optical part of the spectra and can be probed with lasers. The most direct advantage of our proposal comes from the low degeneracy of clock levels and the simplicity of atomic structure in combination with negligible quadrupolar shift. We demonstrate that such clocks can have projected fractional accuracies below the 10^{-20}-10^{-21} level for all common systematic effects, such as blackbody radiation, Zeeman, ac-Stark, and quadrupolar shifts.

  19. Computer modelling of the optical properties of transition-metal ions in solids

    SciTech Connect

    Bartram, R.H.

    1994-12-31

    Computational methods for modeling the optical properties of substitutional transition-metal impurities in insulating solids, potentially applicable to some scintillator and phosphor materials, are reviewed. Methods considered include crystal-field and semiempirical ligand-field models; SCF-X{alpha}-SW, SCF-RHF-LCAO, SCF-UHF-LCAO and CI ab initio methods; and ICECAP and HADESR embedded-cluster methods with lattice relaxation. A detailed example of the application of the HADESR method to crystal-field spectra of Cr{sup 3+} in halide elpasolites is described. In this method, ab initio molecular-orbital calculations with effective core potentials are performed for selected ionic configurations. Simultaneous relaxation of the cluster and surrounding lattice, with mutual pair-potential interactions, is accomplished by a modified lattice statics program. properties include pressure-dependent optical transition energies, vibration frequencies and radiationless transition rates.

  20. The impact of quantum dot filling on dual-band optical transitions via intermediate quantum states

    SciTech Connect

    Wu, Jiang; Passmore, Brandon; Manasreh, M. O.

    2015-08-28

    InAs/GaAs quantum dot infrared photodetectors with different doping levels were investigated to understand the effect of quantum dot filling on both intraband and interband optical transitions. The electron filling of self-assembled InAs quantum dots was varied by direct doping of quantum dots with different concentrations. Photoresponse in the near infrared and middle wavelength infrared spectral region was observed from samples with low quantum dot filling. Although undoped quantum dots were favored for interband transitions with the absence of a second optical excitation in the near infrared region, doped quantum dots were preferred to improve intraband transitions in the middle wavelength infrared region. As a result, partial filling of quantum dot was required, to the extent of maintaining a low dark current, to enhance the dual-band photoresponse through the confined electron states.

  1. Dual-axis vapor cell for simultaneous laser frequency stabilization on disparate optical transitions

    SciTech Connect

    Jayakumar, Anupriya Plotkin-Swing, Benjamin; Jamison, Alan O.; Gupta, Subhadeep

    2015-07-15

    We have developed a dual-axis ytterbium (Yb) vapor cell and used it to simultaneously address the two laser cooling transitions in Yb at wavelengths 399 nm and 556 nm, featuring the disparate linewidths of 2π × 29 MHz and 2π × 182 KHz, respectively. By utilizing different optical paths for the two wavelengths, we simultaneously obtain comparable optical densities suitable for saturated absorption spectroscopy for both the transitions and keep both the lasers frequency stabilized over several hours. We demonstrate that by appropriate control of the cell temperature profile, two atomic transitions differing in relative strength across a large range of over three orders of magnitude can be simultaneously addressed, making the device adaptable to a variety of spectroscopic needs. We also show that our observations can be understood with a simple theoretical model of the Yb vapor.

  2. Optical frequency measurement of the 1S-3S two-photon transition in hydrogen

    NASA Astrophysics Data System (ADS)

    Arnoult, O.; Nez, F.; Julien, L.; Biraben, F.

    2010-11-01

    This article reports the first optical frequency measurement of the 1S-3S transition in hydrogen. The excitation of this transition occurs at a wavelength of 205 nm which is obtained with two frequency doubling stages of a titanium sapphire laser at 820 nm. Its frequency is measured with an optical frequency comb. The second-order Doppler effect is evaluated from the observation of the motional Stark effect due to a transverse magnetic field perpendicular to the atomic beam. The measured value of the 1S_{1/2}( F = 1)-3S1/2( F = 1) frequency splitting is 2 922 742 936.729(13) MHz with a relative uncertainty of 4.5 × 10-12. After the measurement of the 1S-2S frequency, this result is the most precise of the optical frequencies in hydrogen.

  3. Optical Strong Coupling between near-Infrared Metamaterials and Intersubband Transitions in III-Nitride Heterostructures

    SciTech Connect

    Benz, Alexander; Campione, Salvatore; Moseley, Michael W.; Wierer, Jonathan J.; Allerman, Andrew A.; Wendt, Joel R.; Brener, Igal

    2014-08-25

    We present the design, realization, and characterization of optical strong light–matter coupling between intersubband transitions within a semiconductor heterostructures and planar metamaterials in the near-infrared spectral range. The strong light–matter coupling entity consists of a III-nitride intersubband superlattice heterostructure, providing a two-level system with a transition energy of ~0.8 eV (λ ~1.55 μm) and a planar “dogbone” metamaterial structure. Furthermore, as the bare metamaterial resonance frequency is varied across the intersubband resonance, a clear anticrossing behavior is observed in the frequency domain. We found that this strongly coupled entity could enable the realization of electrically tunable optical filters, a new class of efficient nonlinear optical materials, or intersubband-based light-emitting diodes.

  4. Optical Strong Coupling between near-Infrared Metamaterials and Intersubband Transitions in III-Nitride Heterostructures

    DOE PAGES

    Benz, Alexander; Campione, Salvatore; Moseley, Michael W.; ...

    2014-08-25

    We present the design, realization, and characterization of optical strong light–matter coupling between intersubband transitions within a semiconductor heterostructures and planar metamaterials in the near-infrared spectral range. The strong light–matter coupling entity consists of a III-nitride intersubband superlattice heterostructure, providing a two-level system with a transition energy of ~0.8 eV (λ ~1.55 μm) and a planar “dogbone” metamaterial structure. Furthermore, as the bare metamaterial resonance frequency is varied across the intersubband resonance, a clear anticrossing behavior is observed in the frequency domain. We found that this strongly coupled entity could enable the realization of electrically tunable optical filters, a newmore » class of efficient nonlinear optical materials, or intersubband-based light-emitting diodes.« less

  5. Experimental analysis of Hb oxy-deoxy transition in single optically stretched red blood cells.

    PubMed

    Rusciano, G

    2010-10-01

    Raman confocal microscopy, combined with an optical stretcher, is used to study the spatial distribution and the oxidation state of hemoglobin in erythrocytes under stretching condition. In particular, a near infrared laser (λ = 1064 nm) is used to generate multiple time-sharing Optical Tweezers to trap and stretch a single erythrocyte, while a second laser (λ = 532 nm) acts as Raman probe. Our study demonstrates that stretching induces hemoglobin transition to the deoxygenated state. Moreover, by using Principal Component Analysis we prove the reversibility of the oxy ↦ deoxy hemoglobin transition after application of the optically induced mechanical stress. Copyright © 2010 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

  6. Current-modulated optical properties of vanadium dioxide thin films in the phase transition region

    SciTech Connect

    Zhang, Shuyan; Kats, Mikhail A.; Cui, Yanjie; Zhou, You; Yao, Yu; Ramanathan, Shriram; Capasso, Federico

    2014-11-24

    Vanadium dioxide (VO{sub 2}) is a correlated electron material which undergoes an insulator-metal transition proximal to room temperature. The large change of optical properties across this phase transition is promising for tunable optical and optoelectronic devices especially at infrared frequencies. We demonstrate the ability to locally tune the optical properties on the micron scale through a simple design consisting of two electrodes patterned on a VO{sub 2} thin film. By current injection between the electrodes, a localized conducting path (metallic phase) can be formed within the insulating background. The width of the conducting path can be controlled by varying the applied current. Fourier transform infrared imaging shows that this current-modulated reflectance changes significantly over a distance on the order of the wavelength in the mid-infrared spectral range.

  7. Single-shot electro-optic sampling of coherent transition radiation at the A0 Photoinjector

    SciTech Connect

    Maxwell, T.J.; Ruan, J.; Piot, P.; Thurman-Keup, R.; /Fermilab

    2011-08-01

    Future collider applications and present high-gradient laser plasma wakefield accelerators operating with picosecond bunch durations place a higher demand on the time resolution of bunch distribution diagnostics. This demand has led to significant advancements in the field of electro-optic sampling over the past ten years. These methods allow the probing of diagnostic light such as coherent transition radiation or the bunch wakefields with sub-picosecond time resolution. Potential applications in shot-to-shot, non-interceptive diagnostics continue to be pursued for live beam monitoring of collider and pump-probe experiments. Related to our developing work with electro-optic imaging, we present results on single-shot electro-optic sampling of the coherent transition radiation from bunches generated at the A0 photoinjector.

  8. Synthesis and study of optical properties of transition metals doped ZnS nanoparticles

    NASA Astrophysics Data System (ADS)

    Ramasamy, V.; Praba, K.; Murugadoss, G.

    2012-10-01

    ZnS and transition metal (Mn, Co, Ni, Cu, Ag and Cd) doped ZnS were synthesized using chemical precipitation method in an air atmosphere. The structural and optical properties were studied using various techniques. The X-ray diffraction (XRD) analysis show that the particles are in cubic structure. The mean size of the nanoparticles calculated through Scherrer equation is in the range of 4-6.1 nm. Elemental dispersive (EDX) analysis of doped samples reveals the presence of doping ions. The scanning electron microscopic (SEM) and transmission electron microscopic (TEM) studies show that the synthesized particles are in spherical shape. Optical characterization of both undoped and doped samples was carried out by ultraviolet-visible (UV-Vis) and photoluminescence (PL) spectroscopy. The absorption spectra of all the samples are blue shifted from the bulk ZnS. An optimum doping level of the transition metals for enhanced PL properties are found through optical study.

  9. Electronic and optical properties of vacancy defects in single-layer transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Khan, M. A.; Erementchouk, Mikhail; Hendrickson, Joshua; Leuenberger, Michael N.

    2017-06-01

    A detailed first-principles study has been performed to evaluate the electronic and optical properties of single-layer (SL) transition metal dichalcogenides (TMDCs) (M X 2 ; M = transition metal such as Mo, W, and X = S, Se, Te), in the presence of vacancy defects (VDs). Defects usually play an important role in tailoring electronic, optical, and magnetic properties of semiconductors. We consider three types of VDs in SL TMDCs: (i) X vacancy, (ii) X2 vacancy, and (iii) M vacancy. We show that VDs lead to localized defect states (LDS) in the band structure, which in turn gives rise to sharp transitions in in-plane and out-of-plane optical susceptibilities, χ∥ and χ⊥. The effects of spin-orbit coupling (SOC) are also considered. We find that SOC splitting in LDS is directly related to the atomic number of the transition metal atoms. Apart from electronic and optical properties we also find magnetic signatures (local magnetic moment of ˜μB ) in MoSe2 in the presence of the Mo vacancy, which breaks the time-reversal symmetry and therefore lifts the Kramers degeneracy. We show that a simple qualitative tight-binding model (TBM), involving only the hopping between atoms surrounding the vacancy with an on-site SOC term, is sufficient to capture the essential features of LDS. In addition, the existence of the LDS can be understood from the solution of the two-dimensional Dirac Hamiltonian by employing infinite mass boundary conditions. In order to provide a clear description of the optical absorption spectra, we use group theory to derive the optical selection rules between LDS for both χ∥ and χ⊥.

  10. Bias-Controlled Optical Transitions in GaN/AlN Nanowire Heterostructures.

    PubMed

    Müßener, Jan; Hille, Pascal; Grieb, Tim; Schörmann, Jörg; Teubert, Jörg; Monroy, Eva; Rosenauer, Andreas; Eickhoff, Martin

    2017-09-26

    We report on the control and modification of optical transitions in 40× GaN/AlN heterostructure superlattices embedded in GaN nanowires by an externally applied bias. The complex band profile of these multi-nanodisc heterostructures gives rise to a manifold of optical transitions, whose emission characteristic is strongly influenced by polarization-induced internal electric fields. We demonstrate that the superposition of an external axial electric field along a single contacted nanowire leads to specific modifications of each photoluminescence emission, which allows to investigate and identify their origin and to control their characteristic properties in terms of transition energy, intensity and decay time. Using this approach, direct transitions within one nanodisc, indirect transitions between adjacent nanodiscs, transitions at the top/bottom edge of the heterostructure, and the GaN near-band-edge emission can be distinguished. While the transition energy of the direct transition can be shifted by external bias over a range of 450 meV and changed in intensity by a factor of 15, the indirect transition exhibits an inverse bias dependence and is only observable and spectrally separated when external bias is applied. In addition, by tuning the band profile close to flat band conditions, the direction and magnitude of the internal electric field can be estimated, which is of high interest for the polar group III-nitrides. The direct control of emission properties over a wide range bears possible application in tunable optoelectronic devices. For more fundamental studies, single-nanowire heterostructures provide a well-defined and isolated system to investigate and control interaction processes in coupled quantum structures.

  11. High temperature phase transitions and critical exponents of Samarium orthoferrite determined by in situ optical ellipsometry

    NASA Astrophysics Data System (ADS)

    Berini, B.; Fouchet, A.; Popova, E.; Scola, J.; Dumont, Y.; Franco, N.; da Silva, R. M. C.; Keller, N.

    2012-03-01

    Determining phase transitions has always been a great challenge in material science due to their important fundamental and technological aspects. Recently, iron-based perovskites (RFeO3), exhibiting phase transitions at high temperatures, have attracted much interest for their functional properties at room temperature, such as multiferroicity (BiFeO3) and ultrafast spin dynamics (TmFeO3). In this family of materials, Samarium orthoferrite (SmFeO3) is a weak ferromagnet, ordering at high temperatures and exhibiting an intrinsic spin reorientation transition above room temperature, which is "hidden" in macroscopic magnetization measurements in polycrystalline samples. In the present article, we show that the related magnetic high temperature phase transitions can be studied through their dielectric functions by spectroscopic ellipsometry in situ and without any need for an applied external magnetic field. The presence of this intrinsic spin reorientation transition is demonstrated for textured SmFeO3 films and we have determined a critical exponent of β = 0.45 ± 0.01 for the magnetic phase transition, coherently from optical, magneto-optical, and structural investigations.

  12. Emergent Optical Phononic Modes upon Nanoscale Mesogenic Phase Transitions

    DOE PAGES

    Bolmatov, Dima; Zhernenkov, Mikhail; Sharpnack, Lewis; ...

    2017-05-26

    The investigation of phononic collective excitations in soft matter systems at the molecular scale has always been challenging due to limitations of experimental techniques in resolving low-energy modes. Recent advances in inelastic X-ray scattering (IXS) enabled the study of such systems with unprecedented spectral contrast at meV excitation energies. In particular, it has become possible to shed light on the low-energy collective motions in materials whose morphology and phase behavior can easily be manipulated, such as mesogenic systems. The understanding of collective mode behavior with a Q-dependence is the key to implement heat management based on the control of amore » sample structure. The latter has great potential for a large number of energy-inspired innovations. As a first step toward this goal, we carried out high contrast IXS measurements on a liquid crystal sample, D7AOB, which exhibits solid-like dynamic features, such as the coexistence of longitudinal and transverse phononic modes. For the first time, we found that these terahertz phononic excitations persist in the crystal, smectic A, and isotropic phases. Furthermore, the intermediate smectic A phase is shown to support a van der Waals-mediated nonhydrodynamic mode with an optical-like phononic behavior. In conclusion, the tunability of the collective excitations at nanometer–terahertz scales via selection of the sample mesogenic phase represents a new opportunity to manipulate optomechanical properties of soft metamaterials.« less

  13. Pauli Blocking Versus Electrostatic Attenuation of Optical Transition Intensities in Charged PbSe Quantum Dots

    SciTech Connect

    An, J. M.; Franceschetti, A.; Zunger, A.

    2007-01-01

    Quantum dots can be charged selectively by electrons or holes. This leads to changes in the intensity of interband and intraband optical transitions. Using atomistic pseudopotential calculations, we show that (1) when carriers are injected into dot-interior quantum-confined states, the intensity of interband transitions that have those states as their initial or final states is attenuated ('Pauli blocking') and (2) when carriers are injected into localized states near the surface of the dots, the electrostatic field set up by these charges attenuates all optically allowed interband transitions. We describe and explain these two mechanisms of intensity attenuation in the case of charged PbSe quantum dots. In addition, this study reveals a new assignment of the peaks in the absorption spectrum. The absorption spectrum of charged PbSe dots was previously interpreted assuming that all injected electrons reside in dot-interior states. This assumption has led to the suggestion that the second absorption peak originates from S{sub h}-P{sub e} and P{sub h}-S{sub e} optical transitions, despite the fact that such transitions are expected to be dipole forbidden. Our results show that the observed bleaching of absorption peaks upon electron or hole charging does not imply that the S{sub h}-P{sub e} or P{sub h}-S{sub e} transitions are allowed. Instead, the observed bleaching sequence is consistent with charging of both dot-interior and surface-localized states and with the assignment of the second absorption peak to the allowed P{sub h}-P{sub e} transition.

  14. Metal-insulator transition in epitaxial NdNiO3 thin film: A structural, electrical and optical study

    NASA Astrophysics Data System (ADS)

    Shao, Tao; Qi, Zeming; Wang, Yuyin; Li, Yuanyuan; Yang, Mei; Hu, Chuansheng

    2017-03-01

    NdNiO3 thin film has been prepared by pulsed laser deposition on LaAlO3 (001) single crystalline substrate. Temperature-dependent resistivity measurement shows a sharp metal-insulator transition in such thin film. The phase transition temperature can be tuned from 90 K to 121 K by changing the thickness of thin film. The structure evolution during phase transition is studied by Raman spectroscopy. Optical conductivity reveals that the variation carrier density in the process of phase transition. The results of structural, electrical and optical studies provide useful insights to understand the mechanism of metal-insulator transition of NdNiO3 thin film.

  15. Third-Order Nonlinear Optic and Optical Limiting Properties of a Mn(iii) Transition Metal Complex

    NASA Astrophysics Data System (ADS)

    Karakas, Asli; Elmali, Ayhan; Yahsi, Yasemin; Kara, Hulya

    N,N‧-bis(5-bromosalicylidene)propane-1,2-diamine-O,O‧,N,N‧)-manganese(III) chloride transition metal complex has been synthesized and characterized by elemental analysis and UV-vis spectroscopy. Its crystal structure has been determined using X-ray diffraction analysis. To provide an insight into the optical limiting (OL) behavior of the title compound, the third-order nonlinear optical (NLO) properties, one-photon absorption (OPA) and two-photon absorption (TPA) characterizations have been theoretically investigated by means of the time-dependent Hartree-Fock (TDHF), AM1 and configuration interaction (CI) methods, respectively. According to ab initio calculation results, the examined molecule exhibits second hyperpolarizabilities (γ) with non-zero values at the positions of TPA peaks, implying microscopic third-order optical nonlinearity. The maximum OPA wavelengths recorded by linear optical experiment and quantum mechanical computations are estimated in the UV region to be shorter than 400 nm, showing good optical transparency to the visible light. The TPA cross-sections (δ(ω)) at λ max(2) values indicate that the synthesized compound might possess OL phenomena, which are in accord with the experimental observations on the manganese complexes in the literature.

  16. Quantitative identification of dynamical transitions in a semiconductor laser with optical feedback

    PubMed Central

    Quintero-Quiroz, C.; Tiana-Alsina, J.; Romà, J.; Torrent, M. C.; Masoller, C.

    2016-01-01

    Identifying transitions to complex dynamical regimes is a fundamental open problem with many practical applications. Semi- conductor lasers with optical feedback are excellent testbeds for studying such transitions, as they can generate a rich variety of output signals. Here we apply three analysis tools to quantify various aspects of the dynamical transitions that occur as the laser pump current increases. These tools allow to quantitatively detect the onset of two different regimes, low-frequency fluctuations and coherence collapse, and can be used for identifying the operating conditions that result in specific dynamical properties of the laser output. These tools can also be valuable for analyzing regime transitions in other complex systems. PMID:27857229

  17. Band structure and optical transitions in LaFeO3: theory and experiment.

    PubMed

    Scafetta, Mark D; Cordi, Adam M; Rondinelli, James M; May, Steven J

    2014-12-17

    The optical absorption properties of LaFeO(3) (LFO) have been calculated using density functional theory and experimentally measured from several high quality epitaxial films using variable angle spectroscopic ellipsometry. We have analyzed the calculated absorption spectrum using different Tauc models and find the model based on a direct-forbidden transition gives the best agreement with the ab initio band gap energies and band dispersions. We have applied this model to the experimental data and determine the band gap of epitaxial LFO to be ∼2.34 eV, with a slight dependence on strain state. This approach has also been used to analyze the higher indirect transition at ∼3.4 eV. Temperature dependent ellipsometry measurements further confirm our theoretical analysis of the nature of the transitions. This works helps to provide a general approach for accurate determination of band gaps and transition energies in complex oxide materials.

  18. Optical and Near-UV Observations of the Transiting Extrasolar Planet TrES-4b

    NASA Astrophysics Data System (ADS)

    Smith, Carter-Thaxton; Turner, J.; Carleton, T.; Crawford, B.; Guvenen, B.; Hardegree-Ullman, K.; Small, L.; Towner, A. P.; Walker-LaFollette, A.; Henz, T.

    2013-01-01

    Using the Steward Observatory 61” Kuiper Telescope, The University of Arizona Astronomy Club conducted photometric observations of the transiting extrasolar planet TrES-4b as part of the Exoplanet Observation Project. Observations were made in the Bessell U, Harris B, and Harris R filters. Initial observations were made in 2009, with follow up observations in 2011. Basic data reduction and photometry was done using IRAF and determination of transit parameters was done using Transit Analysis Package (TAP) and JKTEBOP transit modeling code. We present an updated planetary mass, radius, density, surface gravity, Safronov number, equilibrium temperature, orbital distance, and orbital inclination for TrES-4b. In addition, we also searched for asymmetries between the near-UV and optical light curves. This project, started in spring 2009, has introduced many undergraduate students to research and given them valuable experience with data reduction and observation techniques.

  19. Quantum confinement effects on optical transitions in nanodiamonds containing nitrogen vacancies

    NASA Astrophysics Data System (ADS)

    Petrone, Alessio; Goings, Joshua J.; Li, Xiaosong

    2016-10-01

    Colored nitrogen-vacancy (NV) centers in nanosize diamonds (d ˜5 nm) are promising probe materials because their optical transitions are sensitive to mechanical, vibrational, and spin changes in the surroundings. Here, a linear response time-dependent density functional theory approach is used to describe the optical transitions in several NV-doped diamond quantum dots (QDs) in order to investigate size effects on the absorption spectra. By computing the full optical spectrum up to band-to-band transitions, we analyze both the localized "pinned" midgap and the charge-transfer excitations for an isolated reduced NV center. Subband charge-transfer excitations are shown to be size dependent, involving the excitation of the dopant s p3 electrons to the diamond conduction band. Additionally, the NV-doped systems exhibit characteristic s p3-s p3 excitations whose experimental energies are reproduced well and do not depend on QD size. However, the NV position and global cluster symmetry can affect the amount of the energy splitting of the vertical excitation energies of the midgap transitions.

  20. All-optical materials design of chiral edge modes in transition-metal dichalcogenides.

    PubMed

    Claassen, Martin; Jia, Chunjing; Moritz, Brian; Devereaux, Thomas P

    2016-10-10

    Monolayer transition-metal dichalcogenides are novel materials which at low energies constitute a condensed-matter realization of massive relativistic fermions in two dimensions. Here, we show that this picture breaks for optical pumping-instead, the added complexity of a realistic materials description leads to a new mechanism to optically induce topologically protected chiral edge modes, facilitating optically switchable conduction channels that are insensitive to disorder. In contrast to graphene and previously discussed toy models, the underlying mechanism relies on the intrinsic three-band nature of transition-metal dichalcogenide monolayers near the band edges. Photo-induced band inversions scale linearly in applied pump field and exhibit transitions from one to two chiral edge modes on sweeping from red to blue detuning. We develop an ab initio strategy to understand non-equilibrium Floquet-Bloch bands and topological transitions, and illustrate for WS2 that control of chiral edge modes can be dictated solely from symmetry principles and is not qualitatively sensitive to microscopic materials details.

  1. All-optical materials design of chiral edge modes in transition-metal dichalcogenides

    PubMed Central

    Claassen, Martin; Jia, Chunjing; Moritz, Brian; Devereaux, Thomas P.

    2016-01-01

    Monolayer transition-metal dichalcogenides are novel materials which at low energies constitute a condensed-matter realization of massive relativistic fermions in two dimensions. Here, we show that this picture breaks for optical pumping—instead, the added complexity of a realistic materials description leads to a new mechanism to optically induce topologically protected chiral edge modes, facilitating optically switchable conduction channels that are insensitive to disorder. In contrast to graphene and previously discussed toy models, the underlying mechanism relies on the intrinsic three-band nature of transition-metal dichalcogenide monolayers near the band edges. Photo-induced band inversions scale linearly in applied pump field and exhibit transitions from one to two chiral edge modes on sweeping from red to blue detuning. We develop an ab initio strategy to understand non-equilibrium Floquet–Bloch bands and topological transitions, and illustrate for WS2 that control of chiral edge modes can be dictated solely from symmetry principles and is not qualitatively sensitive to microscopic materials details. PMID:27721504

  2. All-optical materials design of chiral edge modes in transition-metal dichalcogenides

    SciTech Connect

    Claassen, Martin; Jia, Chunjing; Moritz, Brian; Devereaux, Thomas P.

    2016-10-10

    Monolayer transition-metal dichalcogenides are novel materials which at low energies constitute a condensed-matter realization of massive relativistic fermions in two dimensions. Here, we show that this picture breaks for optical pumping—instead, the added complexity of a realistic materials description leads to a new mechanism to optically induce topologically protected chiral edge modes, facilitating optically switchable conduction channels that are insensitive to disorder. In contrast to graphene and previously discussed toy models, the underlying mechanism relies on the intrinsic three-band nature of transition-metal dichalcogenide monolayers near the band edges. Photo-induced band inversions scale linearly in applied pump field and exhibit transitions from one to two chiral edge modes on sweeping from red to blue detuning. As a result, we develop an ab initio strategy to understand non-equilibrium Floquet–Bloch bands and topological transitions, and illustrate for WS2 that control of chiral edge modes can be dictated solely from symmetry principles and is not qualitatively sensitive to microscopic materials details.

  3. All-optical materials design of chiral edge modes in transition-metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Claassen, Martin; Jia, Chunjing; Moritz, Brian; Devereaux, Thomas P.

    2016-10-01

    Monolayer transition-metal dichalcogenides are novel materials which at low energies constitute a condensed-matter realization of massive relativistic fermions in two dimensions. Here, we show that this picture breaks for optical pumping--instead, the added complexity of a realistic materials description leads to a new mechanism to optically induce topologically protected chiral edge modes, facilitating optically switchable conduction channels that are insensitive to disorder. In contrast to graphene and previously discussed toy models, the underlying mechanism relies on the intrinsic three-band nature of transition-metal dichalcogenide monolayers near the band edges. Photo-induced band inversions scale linearly in applied pump field and exhibit transitions from one to two chiral edge modes on sweeping from red to blue detuning. We develop an ab initio strategy to understand non-equilibrium Floquet-Bloch bands and topological transitions, and illustrate for WS2 that control of chiral edge modes can be dictated solely from symmetry principles and is not qualitatively sensitive to microscopic materials details.

  4. Optical Limiting and Theoretical Modelling of Layered Transition Metal Dichalcogenide Nanosheets

    PubMed Central

    Dong, Ningning; Li, Yuanxin; Feng, Yanyan; Zhang, Saifeng; Zhang, Xiaoyan; Chang, Chunxia; Fan, Jintai; Zhang, Long; Wang, Jun

    2015-01-01

    Nonlinear optical property of transition metal dichalcogenide (TMDC) nanosheet dispersions, including MoS2, MoSe2, WS2, and WSe2, was performed by using Z-scan technique with ns pulsed laser at 1064 nm and 532 nm. The results demonstrate that the TMDC dispersions exhibit significant optical limiting response at 1064 nm due to nonlinear scattering, in contrast to the combined effect of both saturable absorption and nonlinear scattering at 532 nm. Selenium compounds show better optical limiting performance than that of the sulfides in the near infrared. A liquid dispersion system based theoretical modelling is proposed to estimate the number density of the nanosheet dispersions, the relationship between incident laser fluence and the size of the laser generated micro-bubbles, and hence the Mie scattering-induced broadband optical limiting behavior in the TMDC dispersions. PMID:26415562

  5. Communication: Generalization of Koopmans’ theorem to optical transitions in the Hubbard model of graphene nanodots

    SciTech Connect

    Sheng, Weidong; Luo, Kaikai; Zhou, Aiping

    2015-01-14

    Koopmans’ theorem implies that the Hartree-Fock quasiparticle gap in a closed-shell system is equal to its single-particle energy gap. In this work, the theorem is generalized to optical transitions in the Hubbard model of graphene nanodots. Based on systematic configuration interaction calculations, it is proposed that the optical gap of a closed-shell graphene system within the Hubbard model is equal to its tight-binding single-particle energy gap in the absence of electron correlation. In these systems, the quasiparticle energy gap and exciton binding energy are found to be dominated by the long-range Coulomb interaction, and thus, both become small when only on-site Hubbard interactions are present. Moreover, the contributions of the quasiparticle and excitonic effects to the optical gap are revealed to nearly cancel each other, which results in an unexpected overlap of the optical and single-particle gaps of the graphene systems.

  6. Communication: generalization of Koopmans' theorem to optical transitions in the Hubbard model of graphene nanodots.

    PubMed

    Sheng, Weidong; Luo, Kaikai; Zhou, Aiping

    2015-01-14

    Koopmans' theorem implies that the Hartree-Fock quasiparticle gap in a closed-shell system is equal to its single-particle energy gap. In this work, the theorem is generalized to optical transitions in the Hubbard model of graphene nanodots. Based on systematic configuration interaction calculations, it is proposed that the optical gap of a closed-shell graphene system within the Hubbard model is equal to its tight-binding single-particle energy gap in the absence of electron correlation. In these systems, the quasiparticle energy gap and exciton binding energy are found to be dominated by the long-range Coulomb interaction, and thus, both become small when only on-site Hubbard interactions are present. Moreover, the contributions of the quasiparticle and excitonic effects to the optical gap are revealed to nearly cancel each other, which results in an unexpected overlap of the optical and single-particle gaps of the graphene systems.

  7. Optically induced metal-to-dielectric transition in Epsilon-Near-Zero metamaterials

    PubMed Central

    Kaipurath, R. M.; Pietrzyk, M.; Caspani, L.; Roger, T.; Clerici, M.; Rizza, C.; Ciattoni, A.; Di Falco, A.; Faccio, D.

    2016-01-01

    Epsilon-Near-Zero materials exhibit a transition in the real part of the dielectric permittivity from positive to negative value as a function of wavelength. Here we study metal-dielectric layered metamaterials in the homogenised regime (each layer has strongly subwavelength thickness) with zero real part of the permittivity in the near-infrared region. By optically pumping the metamaterial we experimentally show that close to the Epsilon-Near-Zero (ENZ) wavelength the permittivity exhibits a marked transition from metallic (negative permittivity) to dielectric (positive permittivity) as a function of the optical power. Remarkably, this transition is linear as a function of pump power and occurs on time scales of the order of the 100 fs pump pulse that need not be tuned to a specific wavelength. The linearity of the permittivity increase allows us to express the response of the metamaterial in terms of a standard third order optical nonlinearity: this shows a clear inversion of the roles of the real and imaginary parts in crossing the ENZ wavelength, further supporting an optically induced change in the physical behaviour of the metamaterial. PMID:27292270

  8. Giant Zeeman shifts in the optical transitions of yttrium iron garnet thin films

    NASA Astrophysics Data System (ADS)

    Vidyasagar, R.; Alves Santos, O.; Holanda, J.; Cunha, R. O.; Machado, F. L. A.; Ribeiro, P. R. T.; Rodrigues, A. R.; Mendes, J. B. S.; Azevedo, A.; Rezende, S. M.

    2016-09-01

    We report the observation of giant Zeeman shifts in the optical transitions of high-quality very thin films of yttrium iron garnet (YIG) grown by rf sputtering on gadolinium gallium garnet substrates. The optical absorption profile measured with magneto-optical absorption spectroscopy shows dual optical transition in the UV-visible frequency region attributed to transitions from the O-2p valence band to the Fe-3d conduction band and from the O-2p valence band to Fe-2p53d6 excitonic states at the Γ-symmetry point of the YIG band structure. The application of a static magnetic field of only 0.6 kOe produces giant Zeeman shifts of ˜100 meV in the YIG band structure and ˜60 meV in the excitonic states corresponding to effective g-factors on the order of 104. The giant Zeeman effects are attributed to changes in energy levels by the large exchange fields of the Fe-3d orbitals during the magnetization process.

  9. A micromachined thermo-optical light modulator based on semiconductor-to-metal phase transition

    NASA Astrophysics Data System (ADS)

    Jiang, Lijun

    In this research, a micromachined thermo-optical light modulator was realized based on the semiconductor-to-metal phase transition of vanadium dioxide (VO2) thin film. VO2 undergoes a reversible phase transition at approximately 68°C, which is accompanied with drastic changes in its electrical and optical properties. The sharp electrical resistivity change can be as great as five orders. Optically, VO2 film will switch from a transparent semiconductor phase to a reflective metal phase upon the phase transition. The light modulator in this research exploits this phase transition related optical switching by using surface micromachined low-thermal-mass pixels to achieve good thermal isolations, which ensures that each pixel can be individually switched without cross talking. In operation, the pixel temperature was controlled by integrated resistor on each pixel or spatially addressed thermal radiation sources. Active VO2 thin film was synthesized by thermal oxidation of e-beam evaporated vanadium metal film. The oxidized film exhibits a phase transition at ˜65°C with a hysteresis of about 15°C. A transmittance switching from ˜90% to ˜30% in the near infrared and a reflectance switching from ˜50% to ˜15% in the visible have been achieved. The surface microstructure was studied and correlated to its optical properties. A study on the hysteresis loop reveals that the VO2 can be repetitively switched between the "on" and "off" states. The micromachined thermal isolation pixel was a bridge-like silicon dioxide platform suspended with narrow supporting legs. The pixel design was optimized with both thermal and optical simulations. The VO2 light modulator was fabricated by surface micromachining based on dry processing. Silicon dioxide was deposited on a polyimide sacrificial layer by PECVD and patterned to form the structural pixel. Vanadium film was e-beam evaporated and patterned with lift-off process. It was thermally oxidized into VO2 at 390°C. The thermal

  10. Evidence for microbunching "sidebands" in a saturated free-electron laser using coherent optical transition radiation.

    PubMed

    Lumpkin, A H; Dejus, R; Lewellen, J W; Berg, W; Biedron, S; Borland, M; Chae, Y C; Erdmann, M; Huang, Z; Kim, K-J; Li, Y; Milton, S V; Moog, E; Rule, D W; Sajaev, V; Yang, B X

    2002-06-10

    We report the first measurements of z-dependent coherent optical transition radiation (COTR) due to electron-beam microbunching at high gains ( >10(4)) including saturation of a self-amplified spontaneous emission free-electron laser (FEL). In these experiments the fundamental wavelength was near 530 nm, and the COTR spectra exhibit the transition from simple spectra to complex spectra ( 5% spectral width) after saturation. The COTR intensity growth and angular distribution data are reported as well as the evidence for transverse spectral dependencies and an "effective" core of the beam being involved in microbunching.

  11. Photo field-emission spectroscopy of optical transitions in the band structure of rhenium

    NASA Astrophysics Data System (ADS)

    Radoń, T.; Kleint, Ch.

    1984-09-01

    Photo field-emission (PFE) current-voltage curves of clean and barium covered rhenium have been determined with an argon ion laser and phase sensitive detection. Field strength and work function were obtained from Fowler-Nordheim plots of the field emission currents. According to a two-step PFE model the knees of the PFE characteristics are ascribed to optical transitions in the Brillouin zone near the Fermi level. Most of the observed excitations could be correlated to direct transitions in the rhenium band structure as calculated by Mattheiss including spin-orbit coupling.

  12. Coherence-enhanced optical determination of the 229Th isomeric transition.

    PubMed

    Liao, Wen-Te; Das, Sumanta; Keitel, Christoph H; Pálffy, Adriana

    2012-12-28

    The impact of coherent light propagation on the excitation and fluorescence of thorium nuclei in a crystal lattice environment is investigated theoretically. We find that in the forward direction, the fluorescence signal exhibits characteristic intensity modulations dominated by a sped-up initial decay signal that is orders of magnitude faster. This feature can be exploited for the optical determination of the isomeric transition energy. In order to obtain a unmistakable signature of the isomeric nuclear fluorescence, we put forward a novel scheme for the direct measurement of the transition energy via electromagnetically modified nuclear forward scattering involving two fields that couple to three nuclear states.

  13. Intrinsic exciton-state mixing and nonlinear optical properties in transition metal dichalcogenide monolayers

    NASA Astrophysics Data System (ADS)

    Glazov, M. M.; Golub, L. E.; Wang, G.; Marie, X.; Amand, T.; Urbaszek, B.

    2017-01-01

    Optical properties of transition metal dichalcogenides monolayers are controlled by Wannier-Mott excitons forming a series of 1 s ,2 s ,2 p ,... hydrogen-like states. We develop the theory of the excited excitonic states energy spectrum fine structure. We predict that p - and s -shell excitons are mixed due to the specific D3 h point symmetry of the transition metal dichalcogenide monolayers. Hence, both s - and p -shell excitons are active in both single- and two-photon processes, providing an efficient mechanism of second harmonic generation. The corresponding contribution to the nonlinear susceptibility is calculated.

  14. First-Principles Investigations of the Phase Transition and Optical Properties of Solid Oxygen

    NASA Astrophysics Data System (ADS)

    Liu, Yan-Hui; Duan, De-Fang; Wang, Lian-Cheng; Zhu, Chun-Ye; Cui, Tian

    2010-12-01

    Using density-functional-theory calculations, a monoclinic metallic post-ζ phase (space group C2/c) is predicted at 215 GPa. The calculated phonon dispersion curves suggest that this structure is stable at least up to 310 GPa. Oxygen remains a molecular crystal and there is no dissociation in the related pressure range. Moreover, it is found that the phase transition from ζ to post-ζ phase is attributed to phonon softening. The significant change in the optical properties can be used to identify the phase transition.

  15. Simple magneto-optic transition metal models for time-domain simulations.

    PubMed

    Wolff, Christian; Rodríguez-Oliveros, Rogelio; Busch, Kurt

    2013-05-20

    Efficient modelling of the magneto-optic effects of transition metals such as nickel, cobalt and iron is a topic of growing interest within the nano-optics community. In this paper, we present a general discussion of appropriate material models for the linear dielectric properties for such metals, provide parameter fits and formulate the anisotropic response in terms of auxiliary differential equations suitable for time-domain simulations. We validate both our material models and their implementation by comparing numerical results obtained with the Discontinuous Galerkin time-domain (DGTD) method to analytical results and previously published experimental data.

  16. Investigation of microwave transitions and nonlinear magneto-optical rotation in anti-relaxation-coated cells

    SciTech Connect

    Budker, D.; Hollberg, L.; Kimball, D.F.; Kitching, J.; Pustclny, S.; Robinson, H.G.; Yashchuk, V.V.

    2004-06-04

    Using laser optical pumping, widths and frequency shifts are determined for microwave transitions between the components of the ground-state hyperfine structure for {sup 85}Rb and {sup 87}Rb atoms contained in vapor cells with alkane anti-relaxation coatings. The results are compared with data on Zeeman relaxation obtained in nonlinear magneto-optical rotation (NMOR) experiments, a comparison important for quantitative understanding of spin-relaxation mechanisms in coated cells. By comparing cells manufactured over a forty-year period we demonstrate the long-term stability of coated cells, which may be useful for atomic clocks and magnetometers.

  17. Microwave transitions and nonlinear magneto-optical rotation in anti-relaxation-coated cells

    SciTech Connect

    Budker, Dmitry; Hollberg. Leo; Kimball, Derek F.; Kitching J.; Pustelny Szymon; Yashchuk, Valeriy V.

    2004-08-12

    Using laser optical pumping, widths and frequency shifts are determined for microwave transitions between ground-state hyperfine components of {sup 85}Rb and {sup 87}Rb atoms contained in vapor cells with alkane anti-relaxation coatings. The results are compared with data on Zeeman relaxation obtained in nonlinear magneto-optical rotation (NMOR) experiments, a comparison important for quantitative understanding of spin-relaxation mechanisms in coated cells. By comparing cells manufactured over a forty-year period we demonstrate the long-term stability of coated cells, an important property for atomic clocks and magnetometers.

  18. A novel method for sub-micrometer transverse electron beam size measurements using optical transition radiation

    NASA Astrophysics Data System (ADS)

    Aryshev, A.; Boogert, S. T.; Howell, D.; Karataev, P.; Terunuma, N.; Urakawa, J.

    2010-06-01

    Optical Transition Radiation (OTR) appearing when a charged particle crosses a boundary between two media with different dielectric properties has widely been used as a tool for transverse profile measurements of charged particle beams in various facilities worldwide. The resolution of the monitor is defined by so-called Point Spread Function (PSF), source distribution generated by a single electron and projected by an optical system onto a screen. In this paper we represent the development of a novel sub-micrometre electron beam profile monitor based on the measurements of the PSF structure. The first experimental results are presented and future plans on the optimization of the monitor are discussed

  19. Microwave transitions and nonlinear magneto-optical rotation in anti-relaxation-coated cells

    SciTech Connect

    Budker, D.; Hollberg, L.; Kitching, J.; Kimball, D.F.; Pustelny, S.; Yashchuk, V.V.

    2005-01-01

    Using laser optical pumping, widths and frequency shifts are determined for microwave transitions between ground-state hyperfine components of {sup 85}Rb and {sup 87}Rb atoms contained in vapor cells with alkane antirelaxation coatings. The results are compared with data on Zeeman relaxation obtained in nonlinear magneto-optical rotation experiments, a comparison important for quantitative understanding of spin-relaxation mechanisms in coated cells. By comparing cells manufactured over a 40-year period we demonstrate the long-term stability of coated cells, an important property for atomic clocks and magnetometers.

  20. Optically controlled polarizer using a ladder transition for high speed Stokesmetric Imaging and Quantum Zeno Effect based optical logic.

    PubMed

    Krishnamurthy, Subramanian; Wang, Y; Tu, Y; Tseng, S; Shahriar, M S

    2013-10-21

    We demonstrate an optically controlled polarizer at ~1323 nm using a ladder transition in a Rb vapor cell. The lower leg of the 5S(1/2),F = 1->5P(1/2),F = 1,2->6S(1/2),F = 1,2 transitions is excited by a Ti:Sapphire laser locked to a saturated absorption signal, representing the control beam. A tunable fiber laser at ~1323 nm is used to excite the upper leg of the transitions, representing the signal beam. When the control beam is linearly polarized, it produces an excitation of the intermediate level with a particular orientation of the angular momentum. Under ideal conditions, this orientation is transparent to the signal beam if it has the same polarization as the control beam and is absorbed when it is polarized orthogonally. We also present numerical simulations of the system using a comprehensive model which incorporates all the relevant Zeeman sub-levels in the system, and identify means to improve the performance of the polarizer. A novel algorithm to compute the evolution of large scale quantum system enabled us to perform this computation, which may have been considered too cumbersome to carry out previously. We describe how such a polarizer may serve as a key component for high-speed Stokesmetric imaging. We also show how such a polarizer, combined with an optically controlled waveplate, recently demonstrated by us, can be used to realize a high speed optical logic gate by making use of the Quantum Zeno Effect. Finally, we describe how such a logic gate can be realized at an ultra-low power level using a tapered nanofiber embedded in a vapor cell.

  1. Bending light via adiabatic optical transition in longitudinally modulated photonic lattices.

    PubMed

    Han, Bin; Xu, Lei; Dou, Yiling; Xu, Jingjun; Zhang, Guoquan

    2015-10-29

    Bending light in a controllable way is desired in various applications such as beam steering, navigating and cloaking. Different from the conventional way to bend light by refractive index gradient, transformation optics or special beams through wavefront design such as Airy beams and surface plasmons, we proposed a mechanism to bend light via resonant adiabatic optical transition between Floquet-Bloch (FB) modes from different FB bands in longitudinally modulated photonic lattices. The band structure of longitudinally modulated photonic lattices was calculated by employing the concept of quasi-energy based on the Floquet-Bloch theory, showing the existence of band discontinuities at specific resonant points which cannot be revealed by the coupled-mode theory. Interestingly, different FB bands can be seamlessly connected at these resonant points in longitudinally modulated photonic lattices driven by adiabatically varying the longitudinal modulation period along the propagation direction, which stimulates the adiabatic FB mode transition between different FB bands.

  2. Anisotropy in the optical properties of bulk and layered transition metal dichalcogenide ReS2

    NASA Astrophysics Data System (ADS)

    Das, Suvadip; Pradhan, Nihar; Garcia, Carlos; Rhodes, Daniel; McGill, Stephen; Balicas, Luis; Manousakis, Efstratios

    Unlike most transition metal dichalcogenides, ReS2 in the distorted 1T' phase, is a direct gap semiconductor. We measured the temperature dependent photoluminescence in both bulk and layered ReS2 and examined the evolution of the peaks with the number of layers. We obtained strong signatures of optical anisotropy in the absorption spectroscopy and photocurrent response which makes this material a potential candidate for optoelectronic applications. Many body calculations including electron-hole interactions as implemented in the GW+BSE approach, agrees with the strong anisotropy in the optical properties of bulk and monolayer ReS2. A shift in the excitonic peaks by about 0.8 eV introduced by solving the Bethe-Salpeter equation indicates strong contribution from excitonic bound states in this transition metal dichalcogenide.

  3. Tunable optical transition in polymeric carbon nitrides synthesized via bulk thermal condensation

    NASA Astrophysics Data System (ADS)

    Tyborski, T.; Merschjann, C.; Orthmann, S.; Yang, F.; Lux-Steiner, M.-Ch; Schedel-Niedrig, Th

    2012-04-01

    Polymeric derivatives of dicyandiamide were synthesized via a bulk thermal condensation method, using a range of process temperatures between 400 and 610 °C. The obtained carbon nitride powders exhibit an optical transition in the UV-green range that has been assigned to the direct bandgap of a semiconductor-like material. Within this context, the apparent bandgap is linearly tunable with increasing process temperatures, showing a temperature coefficient of - 1.7(1) meV K-1 between 2.5 and 3.0 eV. The obtained results show a predominant optical transition within the tri-s-triazine unit of the polymer, with a bathochromic shift originating from a gradually increasing degree of polymerization.

  4. Theory of edge-state optical absorption in two-dimensional transition metal dichalcogenide flakes

    NASA Astrophysics Data System (ADS)

    Trushin, Maxim; Kelleher, Edmund J. R.; Hasan, Tawfique

    2016-10-01

    We develop an analytical model to describe sub-band-gap optical absorption in two-dimensional semiconducting transition metal dichalcogenide (s-TMD) nanoflakes. The material system represents an array of few-layer molybdenum disulfide crystals, randomly orientated in a polymer matrix. We propose that optical absorption involves direct transitions between electronic edge states and bulk bands, depends strongly on the carrier population, and is saturable with sufficient fluence. For excitation energies above half the band gap, the excess energy is absorbed by the edge-state electrons, elevating their effective temperature. Our analytical expressions for the linear and nonlinear absorption could prove useful tools in the design of practical photonic devices based on s-TMDs.

  5. Electronic wave functions and optical transitions in (In,Ga)As/GaP quantum dots

    NASA Astrophysics Data System (ADS)

    Robert, C.; Pereira Da Silva, K.; Nestoklon, M. O.; Alonso, M. I.; Turban, P.; Jancu, J.-M.; Even, J.; Carrère, H.; Balocchi, A.; Koenraad, P. M.; Marie, X.; Durand, O.; Goñi, A. R.; Cornet, C.

    2016-08-01

    We study the complex electronic band structure of low In content InGaAs/GaP quantum dots. A supercell extended-basis tight-binding model is used to simulate the electronic and the optical properties of a pure GaAs/GaP quantum dot modeled at the atomic level. Transitions between hole states confined into the dots and several XZ-like electronic states confined by the strain field in the GaP barrier are found to play the main role on the optical properties. Especially, the calculated radiative lifetime for such indirect transitions is in good agreement with the photoluminescence decay time measured in time-resolved photoluminescence in the µs range. Photoluminescence experiments under hydrostatic pressure are also presented. The redshift of the photoluminescence spectrum with pressure is also in good agreement with the nature of the electronic confined states simulated with the tight-binding model.

  6. Effective optical Faraday rotations of semiconductor EuS nanocrystals with paramagnetic transition-metal ions.

    PubMed

    Hasegawa, Yasuchika; Maeda, Masashi; Nakanishi, Takayuki; Doi, Yoshihiro; Hinatsu, Yukio; Fujita, Koji; Tanaka, Katsuhisa; Koizumi, Hitoshi; Fushimi, Koji

    2013-02-20

    Novel EuS nanocrystals containing paramagnetic Mn(II), Co(II), or Fe(II) ions have been reported as advanced semiconductor materials with effective optical rotation under a magnetic field, Faraday rotation. EuS nanocrystals with transition-metal ions, EuS:M nanocrystals, were prepared by the reduction of the Eu(III) dithiocarbamate complex tetraphenylphosphonium tetrakis(diethyldithiocarbamate)europium(III) with transition-metal complexes at 300 °C. The EuS:M nanocrystals thus prepared were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma atomic emission spectroanalysis (ICP-AES), and a superconducting quantum interference device (SQUID) magnetometer. Enhanced Faraday rotations of the EuS:M nanocrystals were observed around 550 nm, and their enhanced spin polarization was estimated using electron paramagnetic resonance (EPR) measurements. In this report, the magneto-optical relationship between the Faraday rotation efficiency and spin polarization is discussed.

  7. Optical and magnetic properties of transition-metal ions in tetrahedral and octahedral compounds

    NASA Astrophysics Data System (ADS)

    Li, Huifang; Wang, Huaiqian; Kuang, Xiaoyu

    2011-10-01

    This paper presents the complete energy matrix of the 3d2 system containing the electron-electron interaction, the ligand-field interaction, the spin-orbit coupling interaction, and the Zeeman interaction, in which the optical spectra and g-factor of V3+and Ti2+ ions in the series of tetrahedral AIIBVI (AII=Zn, Cd, BVI=S, Se, Te) semiconductor materials are determined. In the investigation of the optical and magnetic properties of these transition-metal ions in the tetrahedral coordination complexes, we compared the data obtained from the transition-metal ions in the tetrahedral coordination complexes with those obtained from the corresponding ions in the octahedral ones, and found that the tetrahedral complexes have weaker crystal-field strength, inverse energy level ordering and stronger covalence effect.

  8. Magnetically Induced Optical Transparency on a Forbidden Transition in Strontium for Cavity-Enhanced Spectroscopy

    NASA Astrophysics Data System (ADS)

    Winchester, Matthew N.; Norcia, Matthew A.; Cline, Julia R. K.; Thompson, James K.

    2017-06-01

    In this Letter we realize a narrow spectroscopic feature using a technique that we refer to as magnetically induced optical transparency. A cold ensemble of 88Sr atoms interacts with a single mode of a high-finesse optical cavity via the 7.5 kHz linewidth, spin forbidden 1S0 to 3P1 transition. By applying a magnetic field that shifts two excited state Zeeman levels, we open a transmission window through the cavity where the collective vacuum Rabi splitting due to a single level would create destructive interference for probe transmission. The spectroscopic feature approaches the atomic transition linewidth, which is much narrower than the cavity linewidth, and is highly immune to the reference cavity length fluctuations that limit current state-of-the-art laser frequency stability.

  9. Length optimization of an S-shaped transition between offset optical waveguides.

    PubMed

    Marcuse, D

    1978-03-01

    We derive expressions for the radiation loss of an S-shaped waveguide transition used to connect two straight integrated optics waveguides that are offset with respect to each other. It is assumed that the diffused integrated optics waveguides are produced with the help of an electron beam machine that allows beam positioning in the y direction only in discrete steps. We thus must consider staircase approximations to the desired smooth S-shaped curves. A waveguide whose axis consists of a staircase suffers radiation losses due to the quasi-periodic deformation of its axis. A second loss contribution comes from the S-shape of the waveguide axis. The sum of these loss contributions assumes a minimum that defines the optimum length of the transition waveguide.

  10. Bending light via adiabatic optical transition in longitudinally modulated photonic lattices

    PubMed Central

    Han, Bin; Xu, Lei; Dou, Yiling; Xu, Jingjun; Zhang, Guoquan

    2015-01-01

    Bending light in a controllable way is desired in various applications such as beam steering, navigating and cloaking. Different from the conventional way to bend light by refractive index gradient, transformation optics or special beams through wavefront design such as Airy beams and surface plasmons, we proposed a mechanism to bend light via resonant adiabatic optical transition between Floquet-Bloch (FB) modes from different FB bands in longitudinally modulated photonic lattices. The band structure of longitudinally modulated photonic lattices was calculated by employing the concept of quasi-energy based on the Floquet-Bloch theory, showing the existence of band discontinuities at specific resonant points which cannot be revealed by the coupled-mode theory. Interestingly, different FB bands can be seamlessly connected at these resonant points in longitudinally modulated photonic lattices driven by adiabatically varying the longitudinal modulation period along the propagation direction, which stimulates the adiabatic FB mode transition between different FB bands. PMID:26511890

  11. Effect of an excited-state optical transition on the linewidth enhancement factor of quantum dot lasers

    SciTech Connect

    Zhukov, A. E. Savelyev, A. V.; Maximov, M. V.; Shernyakov, Yu. M.; Arakcheeva, E. M.; Zubov, F. I.; Krasivichev, A. A.; Kryzhanovskaya, N. V.

    2012-02-15

    An analytical expression is derived for the linewidth enhancement factor of a quantum-dot laser, which makes it possible to describe its dependence on optical loss and photon density in an explicit form. The model accounts for refractive index variations at the ground-state optical transition due to gain/absorption variations upon the first excited-state transition in quantum dots. It is shown that a decrease in optical loss, an increase in saturated gain, and an increase in the energy separation between the excited-state and ground-state transitions results in a decrease in the {alpha} factor both at and above the lasing threshold.

  12. Observation of the structural phase transition in manganite films by magneto-optical imaging.

    SciTech Connect

    Crabtree, G. W.; Lin, Y.; Miller, D. J.; Nikitenko, V. I.; Vlasko-Vlasov, V. K.; Welp, U.

    1999-08-31

    A high-resolution magneto-optical imaging technique is used to reveal the formation of twins occurring during a martensitic phase transition at {approximately}105K in LCMO films grown on STO substrates. The magnetic contrast arises due to the magneto-elastic tilts of the Mn - magnetic moments in the twins. Different magnetic structures are found in LCMO films grown on MgO, NGO, and LAO substrates showing the importance of the substrate material for the manganite film properties.

  13. Fine tuning of optical transition energy of twisted bilayer graphene via interlayer distance modulation

    NASA Astrophysics Data System (ADS)

    del Corro, Elena; Peña-Alvarez, Miriam; Sato, Kentaro; Morales-Garcia, Angel; Bousa, Milan; Mračko, Michal; Kolman, Radek; Pacakova, Barbara; Kavan, Ladislav; Kalbac, Martin; Frank, Otakar

    2017-02-01

    Twisted bilayer graphene (tBLG) represents a family of unique materials with optoelectronic properties tuned by the rotation angle between the two layers. The presented work shows an additional way of tweaking the electronic structure of tBLG by modifying the interlayer distance, for example by a small uniaxial out-of-plane compression. We have focused on the optical transition energy, which shows a clear dependence on the interlayer distance, both experimentally and theoretically.

  14. All-optical materials design of chiral edge modes in transition-metal dichalcogenides

    DOE PAGES

    Claassen, Martin; Jia, Chunjing; Moritz, Brian; ...

    2016-10-10

    Monolayer transition-metal dichalcogenides are novel materials which at low energies constitute a condensed-matter realization of massive relativistic fermions in two dimensions. Here, we show that this picture breaks for optical pumping—instead, the added complexity of a realistic materials description leads to a new mechanism to optically induce topologically protected chiral edge modes, facilitating optically switchable conduction channels that are insensitive to disorder. In contrast to graphene and previously discussed toy models, the underlying mechanism relies on the intrinsic three-band nature of transition-metal dichalcogenide monolayers near the band edges. Photo-induced band inversions scale linearly in applied pump field and exhibit transitionsmore » from one to two chiral edge modes on sweeping from red to blue detuning. As a result, we develop an ab initio strategy to understand non-equilibrium Floquet–Bloch bands and topological transitions, and illustrate for WS2 that control of chiral edge modes can be dictated solely from symmetry principles and is not qualitatively sensitive to microscopic materials details.« less

  15. Spectrophotometric method for optical band gap and electronic transitions determination of semiconductor materials

    NASA Astrophysics Data System (ADS)

    Sangiorgi, Nicola; Aversa, Lucrezia; Tatti, Roberta; Verucchi, Roberto; Sanson, Alessandra

    2017-02-01

    The optical band gap energy and the electronic processes involved are important parameters of a semiconductor material and it is therefore important to determine their correct values. Among the possible methods, the spectrophotometric is one of the most common. Several methods can be applied to determine the optical band gap energy and still now a defined consensus on the most suitable one has not been established. A highly diffused and accurate optical method is based on Tauc relationship, however to apply this equation is necessary to know the nature of the electronic transitions involved commonly related to the coefficient n. For this purpose, a spectrophotometric technique was used and we developed a graphical method for electronic transitions and band gap energy determination for samples in powder form. In particular, the n coefficient of Tauc equation was determined thorough mathematical elaboration of experimental results on TiO2 (anatase), ZnO, and SnO2. The results were used to calculate the band gap energy values and then compared with the information obtained by Ultraviolet Photoelectron Spectroscopy (UPS). This approach provides a quick and accurate method for band gap determination through n coefficient calculation. Moreover, this simple but reliable method can be used to evaluate the nature of electronic transition that occurs in a semiconductor material in powder form.

  16. Using a Semiconductor-to-Metal Transition to Control Optical Transmission through Subwavelength Hole Arrays

    DOE PAGES

    Donev, E. U.; Suh, J. Y.; Lopez, R.; ...

    2008-01-01

    We describe a simple configuration in which the extraordinary optical transmission effect through subwavelength hole arrays in noble-metal films can be switched by the semiconductor-to-metal transition in an underlying thin film of vanadium dioxide. In these experiments, the transition is brought about by thermal heating of the bilayer film. The surprising reverse hysteretic behavior of the transmission through the subwavelength holes in the vanadium oxide suggest that this modulation is accomplished by a dielectric-matching condition rather than plasmon coupling through the bilayer film. The results of this switching, including the wavelength dependence, are qualitatively reproduced by a transfer matrix model.more » The prospects for effecting a similar modulation on a much faster time scale by using ultrafast laser pulses to trigger the semiconductor-to-metal transition are also discussed.« less

  17. Ultra-compact silicon photonic devices reconfigured by an optically induced semiconductor-to-metal transition.

    PubMed

    Ryckman, Judson D; Hallman, Kent A; Marvel, Robert E; Haglund, Richard F; Weiss, Sharon M

    2013-05-06

    Vanadium dioxide (VO(2)) is a promising reconfigurable optical material and has long been a focus of condensed matter research owing to its distinctive semiconductor-to-metal phase transition (SMT), a feature that has stimulated recent development of thermally reconfigurable photonic, plasmonic, and metamaterial structures. Here, we integrate VO(2) onto silicon photonic devices and demonstrate all-optical switching and reconfiguration of ultra-compact broadband Si-VO(2) absorption modulators (L < 1 μm) and ring-resonators (R ~ λ(0)). Optically inducing the SMT in a small, ~0.275 μm(2), active area of polycrystalline VO(2) enables Si-VO(2) structures to achieve record values of absorption modulation, ~4 dB μm(-1), and intracavity phase modulation, ~π/5 rad μm(-1). This in turn yields large, tunable changes to resonant wavelength, |Δλ(SMT)| ~ 3 nm, approximately 60 times larger than Si-only control devices, and enables reconfigurable filtering and optical modulation in excess of 7 dB from modest Q-factor (~10(3)), high-bandwidth ring resonators (>100 GHz). All-optical integrated Si-VO(2) devices thus constitute platforms for reconfigurable photonics, bringing new opportunities to realize dynamic on-chip networks and ultrafast optical shutters and modulators.

  18. Excitation rate coefficients and line ratios for the optical and ultraviolet transitions in S II

    NASA Technical Reports Server (NTRS)

    Cai, Wei; Pradhan, Anil K.

    1993-01-01

    New calculations are reported for electron excitation collision strengths, rate coefficients, transition probabilities, and line ratios for the astrophysically important optical and UV lines in S II. The collision strengths are calculated in the close coupling approximation using the R-matrix method. The present calculations are more extensive than previous ones, including all transitions among the 12 lowest LS terms and the corresponding 28 fine-structure levels in the collisional-radiative model for S II. While the present rate coefficients for electron impact excitation are within 10-30 percent of the previous values for the low-lying optical transitions employed as density diagnostics of H II regions and nebulae, the excitation rates for the UV transitions 4S super 0 sub 3/2 - 4Psub 1/2,3/2,5/2 differ significantly from earlier calculations, by up to factor of 2. We describe temperature and density sensitive flux ratios for a number of UV lines. The present UV results are likely to be of interest in a more accurate interpretation of S II emission from the Io plasma torus in the magnetosphere of Jupiter, as well as other UV sources observed from the IUE, ASTRO 1, and the HST.

  19. Phase transitions in ensembles of solitons induced by an optical pumping or a strong electric field

    NASA Astrophysics Data System (ADS)

    Karpov, P.; Brazovskii, S.

    2016-09-01

    The latest trend in studies of modern electronically and/or optically active materials is to provoke phase transformations induced by high electric fields or by short (femtosecond) powerful optical pulses. The systems of choice are cooperative electronic states whose broken symmetries give rise to topological defects. For typical quasi-one-dimensional architectures, those are the microscopic solitons taking from electrons the major roles as carriers of charge or spin. Because of the long-range ordering, the solitons experience unusual super-long-range forces leading to a sequence of phase transitions in their ensembles: the higher-temperature transition of the confinement and the lower one of aggregation into macroscopic walls. Here we present results of an extensive numerical modeling for ensembles of both neutral and charged solitons in both two- and three-dimensional systems. We suggest a specific Monte Carlo algorithm preserving the number of solitons, which substantially facilitates the calculations, allows to extend them to the three-dimensional case and to include the important long-range Coulomb interactions. The results confirm the first confinement transition, except for a very strong Coulomb repulsion, and demonstrate a pattern formation at the second transition of aggregation.

  20. The excitonic insulator route through a dynamical phase transition induced by an optical pulse

    SciTech Connect

    Brazovskii, S.; Kirova, N.

    2016-03-15

    We consider a dynamical phase transition induced by a short optical pulse in a system prone to thermodynamical instability. We address the case of pumping to excitons whose density contributes directly to the order parameter. To describe both thermodynamic and dynamic effects on equal footing, we adopt a view of the excitonic insulator for the phase transition and suggest a formation of the Bose condensate for the pumped excitons. The work is motivated by experiments in donor–acceptor organic compounds with a neutral- ionic phase transition coupled to the spontaneous lattice dimerization and to charge transfer excitons. The double nature of the ensemble of excitons leads to an intricate time evolution, in particular, to macroscopic quantum oscillations from the interference between the Bose condensate of excitons and the ground state of the excitonic insulator. The coupling of excitons and the order parameter also leads to self-trapping of their wave function, akin to self-focusing in optics. The locally enhanced density of excitons can surpass a critical value to trigger the phase transformation, even if the mean density is below the required threshold. The system is stratified in domains that evolve through dynamical phase transitions and sequences of merging. The new circumstances in experiments and theory bring to life, once again, some remarkable inventions made by L.V. Keldysh.

  1. Ab initio theory of optical transitions of point defects in SiO2

    NASA Astrophysics Data System (ADS)

    Pacchioni, Gianfranco; Ierańo, Gianluigi

    1998-01-01

    We report the results of high-level quantum-mechanical calculations on the optical transitions of a series of point defects in α quartz. We determined all electron-configuration-interaction wave functions for cluster models of the following bulk defects: neutral oxygen vacancy, ≡Si-Si≡, oxygen divacancy, ≡Si-Si-Si≡, dicoordinated Si, =Si:, E' center, ≡Si• +Si≡, hydride group, ≡Si-H, peroxyl linkage, ≡Si-O-O-Si≡, peroxyl radical, ≡Si-O-O•, nonbridging oxygen hole center, ≡Si-O•, and silanol group ≡Si-OH. The computed transition energies and intensities have been compared with the observed absorption bands of defective silica and with the electronic transitions of molecular analogs when available. When a direct comparison of computed and experimental data is possible, a very good agreement is found. The results form the basis for a well-grounded assignment of the optical transitions of point defects in α quartz and amorphous silica.

  2. Emittance Measurements of the Jefferson Lab Free Electron Laser using optical transition radiation

    SciTech Connect

    Holloway, Michael Andrew

    2007-05-01

    Charged particle accelerators, such as the ones that power Free Electron Lasers (FEL), require high quality (low emittance) beams for efficient operation. Accurate and reliable beam diagnostics are essential to monitoring beam parameters in order to maintain a high quality beam. Optical Transition Radiation Interferometry (OTRI) has shown potential to be a quality diagnostic that is especially useful for high brightness electron beams such as Jefferson Labs FEL energy recovery linac. The purpose of this project is to further develop OTRI beam diagnostic techniques. An optical system was designed to make beam size and divergence measurements as well as to prepare for experiments in optical phase space mapping. Beam size and beam divergence measurements were taken to calculate the emittance of the Jefferson Lab FEL. OTRI is also used to separate core and halo beam divergences in order to estimate core and halo emittance separately.

  3. Method of synthesizing a plurality of reactants and producing thin films of electro-optically active transition metal oxides

    DOEpatents

    Tracy, C.E.; Benson, D.K.; Ruth, M.R.

    1985-08-16

    A method of synthesizing a plurality of reactants by inducing a reaction by plasma deposition among the reactants. The plasma reaction is effective for consolidating the reactants and producing thin films of electro-optically active transition metal oxides.

  4. Transitions.

    ERIC Educational Resources Information Center

    Agnew, Jeanne L.; Choike, James R.

    1987-01-01

    Mathematical observations are made about some continuous curves, called transitions, encountered in well-known experiences. The transition parabola, the transition spiral, and the sidestep maneuver are presented. (MNS)

  5. Photocurrent spectroscopy of exciton and free particle optical transitions in suspended carbon nanotube pn-junctions

    SciTech Connect

    Chang, Shun-Wen; Theiss, Jesse; Hazra, Jubin; Aykol, Mehmet; Kapadia, Rehan; Cronin, Stephen B.

    2015-08-03

    We study photocurrent generation in individual, suspended carbon nanotube pn-junction diodes formed by electrostatic doping using two gate electrodes. Photocurrent spectra collected under various electrostatic doping concentrations reveal distinctive behaviors for free particle optical transitions and excitonic transitions. In particular, the photocurrent generated by excitonic transitions exhibits a strong gate doping dependence, while that of the free particle transitions is gate independent. Here, the built-in potential of the pn-junction is required to separate the strongly bound electron-hole pairs of the excitons, while free particle excitations do not require this field-assisted charge separation. We observe a sharp, well defined E{sub 11} free particle interband transition in contrast with previous photocurrent studies. Several steps are taken to ensure that the active charge separating region of these pn-junctions is suspended off the substrate in a suspended region that is substantially longer than the exciton diffusion length and, therefore, the photocurrent does not originate from a Schottky junction. We present a detailed model of the built-in fields in these pn-junctions, which, together with phonon-assistant exciton dissociation, predicts photocurrents on the same order of those observed experimentally.

  6. Optically induced indirect photonic transitions in a slow light photonic crystal waveguide.

    PubMed

    Castellanos Muñoz, Michel; Petrov, Alexander Yu; O'Faolain, Liam; Li, Juntao; Krauss, Thomas F; Eich, Manfred

    2014-02-07

    We demonstrate indirect photonic transitions in a silicon slow light photonic crystal waveguide. The transitions are driven by an optically generated refractive index front that moves along the waveguide and interacts with a signal pulse copropagating in the structure. We experimentally confirm a theoretical model which indicates that the ratio of the frequency and wave vector shifts associated with the indirect photonic transition is identical to the propagation velocity of the refractive index front. The physical origin of the transitions achieved here is fundamentally different than in previously proposed refractive index modulation concepts with fixed temporal and spatial modulation frequencies; as here, the interaction with the refractive index front results in a Doppler-like signal frequency and wave vector shift. Consequently, the bandwidth over which perfect mode frequency and wave vector matching is achieved is not intrinsically limited by the shape of the photonic bands, and tuning of the indirect photonic transitions is possible without any need for geometrical modifications of the structure. Our device is genuinely nonreciprocal, as it provides different frequency shifts for co- and counterpropagating signal and index fronts.

  7. Bose–Einstein condensation versus Dicke–Hepp–Lieb transition in an optical cavity

    SciTech Connect

    Piazza, Francesco; Strack, Philipp; Zwerger, Wilhelm

    2013-12-15

    We provide an exact solution for the interplay between Bose–Einstein condensation and the Dicke–Hepp–Lieb self-organization transition of an ideal Bose gas trapped inside a single-mode optical cavity and subject to a transverse laser drive. Based on an effective action approach, we determine the full phase diagram at arbitrary temperature, which features a bi-critical point where the transitions cross. We calculate the dynamically generated band structure of the atoms and the associated suppression of the critical temperature for Bose–Einstein condensation in the phase with a spontaneous periodic density modulation. Moreover, we determine the evolution of the polariton spectrum due to the coupling of the cavity photons and the atomic field near the self-organization transition, which is quite different above or below the Bose–Einstein condensation temperature. At low temperatures, the critical value of the Dicke–Hepp–Lieb transition decreases with temperature and thus thermal fluctuations can enhance the tendency to a periodic arrangement of the atoms. -- Highlights: •Atoms inside a driven cavity can undergo two transitions: self-organization and BEC. •The phase diagram has four phases which coexist at a bi-critical point. •Atom–cavity coupling creates a dynamical lattice for the atoms. •Finite temperature can enhance the tendency towards self-organization. •We calculate the detailed spectrum of the polaritonic excitations.

  8. Impact of strain on the optical fingerprint of monolayer transition-metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Feierabend, Maja; Morlet, Alexandre; Berghäuser, Gunnar; Malic, Ermin

    2017-07-01

    Strain presents a straightforward tool to tune electronic properties of atomically thin nanomaterials that are highly sensitive to lattice deformations. While the influence of strain on the electronic band structure has been intensively studied, there are only a few works on its impact on optical properties of monolayer transition-metal dichalcogenides (TMDs). Combining microscopic theory based on Wannier and Bloch equations with nearest-neighbor tight-binding approximation, we present an analytical view on how uni- and biaxial strain influences the optical fingerprint of TMDs, including their excitonic binding energy, oscillator strength, optical selection rules, and the radiative broadening of excitonic resonances. We show that the impact of strain can be reduced to changes in the lattice structure (geometric effect) and in the orbital functions (overlap effect). In particular, we demonstrate that the valley-selective optical selection rule is softened in the case of uniaxial strain due to the introduced asymmetry in the lattice structure. Furthermore, we reveal a considerable increase of the radiative dephasing due to strain-induced changes in the optical matrix element and the excitonic wave functions.

  9. The GTC exoplanet transit spectroscopy survey . VII. An optical transmission spectrum of WASP-48b

    NASA Astrophysics Data System (ADS)

    Murgas, F.; Pallé, E.; Parviainen, H.; Chen, G.; Nortmann, L.; Nowak, G.; Cabrera-Lavers, A.; Iro, N.

    2017-09-01

    Context. Transiting planets offer an excellent opportunity for characterizing the atmospheres of extrasolar planets under very different conditions from those found in our solar system. Aims: We are currently carrying out a ground-based survey to obtain the transmission spectra of several extrasolar planets using the 10 m Gran Telescopio Canarias. In this paper we investigate the extrasolar planet WASP-48b, a hot Jupiter orbiting around an F-type star with a period of 2.14 days. Methods: We obtained long-slit optical spectroscopy of one transit of WASP-48b with the Optical System for Imaging and low-Intermediate-Resolution Integrated Spectroscopy (OSIRIS) spectrograph. We integrated the spectrum of WASP-48 and one reference star in several channels with different wavelength ranges, creating numerous color light curves of the transit. We fit analytic transit curves to the data taking into account the systematic effects present in the time series in an effort to measure the change of the planet-to-star radius ratio (Rp/Rs) across wavelength. The change in transit depth can be compared with atmosphere models to infer the presence of particular atomic or molecular compounds in the atmosphere of WASP-48b. Results: After removing the transit model and systematic trends to the curves we reached precisions between 261 ppm and 455-755 ppm for the white and spectroscopic light curves, respectively. We obtained Rp/Rs uncertainty values between 0.8 × 10-3 and 1.5 × 10-3 for all the curves analyzed in this work. The measured transit depth for the curves made by integrating the wavelength range between 530 nm and 905 nm is in agreement with previous studies. We report a relatively flat transmission spectrum for WASP-48b with no statistical significant detection of atmospheric species, although the theoretical models that fit the data more closely include TiO and VO. The transit light curves are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http

  10. Optical transitions from the lowest to higher exciton and biexciton Rydberg states in CuCl

    NASA Astrophysics Data System (ADS)

    Miyajima, K.; Sakaniwa, K.; Sugawara, M.

    2016-11-01

    We measured the optical transitions due to the internal energy levels of an exciton and biexciton in a CuCl single crystal using pump-probe spectroscopy. The transient absorption bands due to the transitions from the 1 s to 2 p and from the 1 s to 3 p exciton states were observed at 3 K, which is consistent with their reported energies. Simultaneously, the transient absorption peak due to the biexciton was observed, which corresponds to a transition from the lowest state (composed of two 1 s excitons) to higher states (composed of 1 s and 2 p excitons). The value of the observed biexciton peak energy was reasonable considering the hydrogen molecule orbitals and the electron-to-hole effective mass ratio. In addition, the transient absorption peaks were broadened at 77 K, because of the increase in the homogeneous width of the 2 p exciton state. The transient absorption spectrum was almost completely determined by this width. Our findings are of importance with regard to the optical phenomena in the infrared region related to the quantum coherence of excitons and biexcitons in semiconductors.

  11. Observation of Spin Polarized Clock Transition in 87Sr Optical Lattice Clock

    NASA Astrophysics Data System (ADS)

    Wang, Qiang; Lin, Yi-Ge; Li, Ye; Lin, Bai-Ke; Meng, Fei; Zang, Er-Jun; Li, Tian-Chu; Fang, Zhan-Jun

    2014-12-01

    We report our observation of the spin polarized 1S0 → 3P0 clock transition spectrum in an optical lattice clock based on fermionic 87Sr. The atoms are trapped and pre-cooled to about 2 μK with two stages of laser cooling at 461 nm and 689 nm, respectively. Then the atoms are loaded into an optical lattice formed by the interference of counter-propagating laser beams at 813 nm. An external cavity diode laser at 698 nm, which is stabilized to a high finesse cavity with a linewidth of about 5 Hz and a drift rate of less than 0.2 Hz/s, is used to excite the atoms to the 3P0 state. The π-polarized clock transition spectrum of resolvable mF states is obtained by applying a small bias magnetic field along the polarization axis of the probe beam. A spin polarized clock transition spectrum as narrow as 10 Hz with an 80 ms probe pulse is obtained.

  12. Effect of Doped Transition Metal Atoms on Structure and Nonlinear Optical Properties of Decaborane

    NASA Astrophysics Data System (ADS)

    Beigi, Motahareh Noormohammad; Shamlouei, Hamid Reza; Omidi, Masoome; Jalalvandi, Esmat

    2017-07-01

    In this study, electrical and nonlinear optical properties of decaborane (B10H14) were investigated using the density functional theory method when transition metal atoms (scandium, titanium and vanadium) were doped on the structure. Hydrogen and boron atoms in B10H14 were substituted by the transition metals. This doping process resulted in a drastic reduction in the energy gap of decaborane. First, the hyperpolarizability (β 0) of B10H14 dramatically increased in the presence of titanium (Ti) in the place of hydrogen atoms. The highest value of β 0 (≈ 98,387.90 a.u.) was obtained for B10TiH13 (in the S3 position) and calculated to be 1700 times larger than the β 0 value for B10H14 (≈57.82 a.u.). Therefore, the Ti-doped systems showed a significantly larger non-linear optical (NLO) response than the other studied transition metals, suggesting that its system might be useful as a promising NLO material.

  13. Near-uv and optical observations of the transiting hot Jupiter WASP-1b

    NASA Astrophysics Data System (ADS)

    Pearson, K. A.; Zellem, R.; Biddle, L. I.; Amaya, H.; Watson, Z.; Griffith, C.; Small, L.; Hume, J.

    2014-03-01

    We present simultaneous near-UV (U-band) and optical (B-band) photometric observations of the primary transit of the highly irradiated, hot-Jupiter WASP-1b on the Kuiper 61" telescope. We use our results to search for timing transit variations, which would indicate additional planets, and provide new constraints on WASP-1b's physical parameters. Assuming the opacity at these two photometric bands is dominated by Rayleigh scattering by molecular hydrogen, we can place strong upper limits on its radius. Such constraints can limit the degeneracy between an exoplanet's physical radius and atmospheric composition in radiative transfer retrievals. Additionally its host star is chromospherically active and WASP-1b orbits within in the co-rotation radius of the star making it likely that WASP-1b has a bowshock. Therefore, we will search for a planetary magnetic field as indicated by an early ingress in the near-UV light curve compared to the optical due to the bowshock itself. Such measurements would confirm the observational methodology of detecting magnetic fields around transiting exoplanets, place an upper limit on WASP-1b's magnetic field strength, and confirm previous theoretical estimations of hot Jupiter magnetic fields.

  14. Chemical Stabilization of 1T' Phase Transition Metal Dichalcogenides with Giant Optical Kerr Nonlinearity.

    PubMed

    Tan, Sherman J R; Abdelwahab, Ibrahim; Ding, Zijing; Zhao, Xiaoxu; Yang, Tieshan; Loke, Gabriel Z J; Lin, Han; Verzhbitskiy, Ivan; Poh, Sock Mui; Xu, Hai; Nai, Chang Tai; Zhou, Wu; Eda, Goki; Jia, Baohua; Loh, Kian Ping

    2017-02-15

    The 2H-to-1T' phase transition in transition metal dichalcogenides (TMDs) has been exploited to phase-engineer TMDs for applications in which the metallicity of the 1T' phase is beneficial. However, phase-engineered 1T'-TMDs are metastable; thus, stabilization of the 1T' phase remains an important challenge to overcome before its properties can be exploited. Herein, we performed a systematic study of the 2H-to-1T' phase evolution by lithiation in ultrahigh vacuum. We discovered that by hydrogenating the intercalated Li to form lithium hydride (LiH), unprecedented long-term (>3 months) air stability of the 1T' phase can be achieved. Most importantly, this passivation method has wide applicability for other alkali metals and TMDs. Density functional theory calculations reveal that LiH is a good electron donor and stabilizes the 1T' phase against 2H conversion, aided by the formation of a greatly enhanced interlayer dipole-dipole interaction. Nonlinear optical studies reveal that air-stable 1T'-TMDs exhibit much stronger optical Kerr nonlinearity and higher optical transparency than the 2H phase, which is promising for nonlinear photonic applications.

  15. Electronic and Optical properties of Vacancy Defects in two dimensional monolayer Transition metal Dichalcogenides

    NASA Astrophysics Data System (ADS)

    Khan, Mahtab; Erementchouk, Mikhail; Leuenberger, Michael

    Defects play an important role in tailoring electronic and optical properties of two-dimensional monolayer transition metal dichalcogenides (TMDCs). Recently it has been shown that the presence of vacancy defects (VDs) in two-dimensional monolayer MoS_2 induces localized states which give rise to extra resonance peaks in both in-plane χ∥ and out-of-plane χ⊥ susceptibilities.1 In-plane χ∥ and out-of-plane χ⊥ susceptibilities are related to the presence of even and odd states with respect to the Mo plane, respectively1. Moreover, monolayer TMDCs have a large spin orbit coupling (SOC), originating from d-orbitals of heavy transition metals and being of the order of a few 100 meV. We present a more general picture of the electronic and optical properties of defected monolayer TMDCs. In particular, we consider MoS2, MoSe2, WS2 and WSe2 with three types of VDs (i) Mo, W vacancy, (ii) S2, Se2 vacancy, and (iii) S, Se vacancy. In addition, we investigate the effects of SOC on the band structures and the optical susceptibilities of VDs in TMDCs. 1. Mikhail Erementchouk, M. A. Khan, and Michael N. Leuenberger, Phys. Rev. B 92, 121401(R) (2015).

  16. Method of synthesizing a plurality of reactants and producing thin films of electro-optically active transition metal oxides

    DOEpatents

    Tracy, C. Edwin; Benson, David K.; Ruth, Marta R.

    1987-01-01

    A method of synthesizing electro-optically active reaction products from a plurality of reactants by inducing a reaction by plasma deposition among the reactants. The plasma reaction is effective for consolidating the reactants and producing thin films of electro-optically active transition metal oxides.

  17. Observation of the 1S0-3P0 transition in atomic ytterbium for optical clocks and qubit arrays.

    PubMed

    Hong, Tao; Cramer, Claire; Cook, Eryn; Nagourney, Warren; Fortson, E N

    2005-10-01

    We report an observation of the weak 6 1S0-6 3P0 transition in (171,173)Yb as an important step to establishing Yb as a primary candidate for future optical frequency standards, and to open up a new approach for qubits using the 1S0 and 3P0 states of Yb atoms in an optical lattice.

  18. Transitions.

    ERIC Educational Resources Information Center

    Nathanson, Jeanne H., Ed.

    1993-01-01

    This theme issue on transitions for individuals with disabilities contains nine papers discussing transition programs and issues. "Transition Issues for the 1990s," by Michael J. Ward and William D. Halloran, discusses self-determination, school responsibility for transition, continued educational engagement of at-risk students, and service…

  19. Acoustical and optical investigations of the size effect in nematic-isotropic phase transition in liquid crystal microemulsions

    NASA Astrophysics Data System (ADS)

    Maksimochkin, G. I.; Pasechnik, S. V.; Lukin, A. V.

    2015-07-01

    The absorption of ultrasound (at a frequency of 2.7 MHz) and the depolarized light transmission and scattering (at a wavelength of 630 nm) in liquid crystal (LC) emulsions have been studied during the nematic-isotropic (N-I) phase transition in LC droplets with radii ranging from 150 to 2300 nm. The obtained acoustical and optical data are used to determine the influence of the droplet size on characteristics of the N-I phase transition. It is shown that the acoustical and optical characteristics of LC emulsions have good prospects to be used for the investigation of phase transitions in submicron samples.

  20. Multimodal coupling of optical transitions and plasmonic oscillations in rhodamine B modified gold nanoparticles.

    PubMed

    Stobiecka, Magdalena; Hepel, Maria

    2011-01-21

    The optical properties of a photoluminescent dye rhodamine B (RhB) interacting with gold nanoparticles (AuNP) have been investigated using plasmonic absorbance, fluorescence, and resonance elastic light scattering (RELS) spectroscopy. We have found that these interactions result in a multimodal coupling that influence optical transitions in RhB. In absorbance measurements, we have observed for the first time the coupling resulting in strong screening of RhB π-π* transitions, likely caused by a contact adsorption of RhB on a conductive surface of AuNP. The nanoparticles quench also very efficiently the RhB fluorescence. We have determined that the static quenching mechanism with a non-Förster fluorescence resonance energy transfer (FRET) from RhB molecules to AuNP is involved. The Stern-Volmer dependence F(0)/F = f(Q) shows an upward deviation from linearity, attributed to the ultra-high quenching efficiency of AuNP leading to the new extended Stern-Volmer model. A sharp RELS peak of RhB alone (λ(max) = 566 nm) has been observed for the first time and attributed to the resonance fluorescence and enhanced scattering. This peak is completely quenched in the presence of AuNP(22nm). Our quantum mechanical calculations confirm that the distance between AuNP surface and conjugated π-electron system in RhB is well within the range of plasmonic fields extending from AuNP. The optical transition coupling to plasmonic oscillations and the efficient energy transfer due to the interactions of fluorescent dyes with nanoparticles are important for biophysical studies of life processes and applications in nanomedicine.

  1. Nonequilibrium phase transition of interacting bosons in an intra-cavity optical lattice.

    PubMed

    Bakhtiari, M Reza; Hemmerich, A; Ritsch, H; Thorwart, M

    2015-03-27

    We investigate the nonlinear light-matter interaction of a Bose-Einstein condensate trapped in an external periodic potential inside an optical cavity which is weakly coupled to vacuum radiation modes and driven by a transverse pump field. Based on a generalized Bose-Hubbard model which incorporates a single cavity mode, we include the collective backaction of the atoms on the cavity light field and determine the nonequilibrium quantum phases within the nonperturbative bosonic dynamical mean-field theory. With the system parameters adapted to recent experiments, we find a quantum phase transition from a normal phase to a self-organized superfluid phase, which is related to the Hepp-Lieb-Dicke superradiance phase transition. For even stronger pumping, a self-organized Mott insulator phase arises.

  2. First observation of the point spread function of optical transition radiation.

    PubMed

    Karataev, Pavel; Aryshev, Alexander; Boogert, Stewart; Howell, David; Terunuma, Nobuhiro; Urakawa, Junji

    2011-10-21

    We represent the first experimental observation of the point spread function (PSF) of optical transition radiation (OTR) performed at KEK-Accelerator Test Facility extraction line. We have demonstrated that the PSF vertical polarization component has a central minimum with a two lobe distribution. However, the distribution width varied significantly with wavelength. We assume that we observed a severe effect from spherical or chromatic aberrations which are not taken into account in any existing theoretical model. We believe that the result of this work will encourage theoreticians to continue developing the theory as it is important for various transition radiation applications. Nonuniform distribution of the OTR PSF creates an opportunity for developing a submicrometer transverse beam size monitor.

  3. Electronic and optical properties of monolayer and few-layer of distorted transition-metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Darancet, Pierre; Millis, Andrew J.; Marianetti, Chris A.

    2014-03-01

    Groups IV, V, and VI- transition-metal dichalcogenides (TMDC) are layered compounds exhibiting a wealth of competing phenomena, ranging from charge density waves (CDW) to Mott transitions. We present investigations using density functional theory (DFT) and DFT+U regarding the electronic structure and electronic correlations arising in distorted tantalum disulfide (TaS2). We show that the monolayer material is a Mott insulator while the bulk is a metal, in contradiction with much of the existing literature, which argues that the bulk material is a Mott insulator. Properties of the few layer system will also be presented.Finally, we will discuss the influence of these competing energy scales on the transport and optical properties of these materials. This work is funded by NSF under contract DMR-1122594. Computation time is provided by NERSC and NY Blue Gene.

  4. Observation of optical transition radiation from electron beams generated by laser plasma accelerator

    NASA Astrophysics Data System (ADS)

    Lin, Chen; Nakamura, K.; Van, Tilborg J.; Gonsalves, A. J.; Sokollik, T.; Shiraishi, S.; Leemans, W. P.; Guo, Zhi-Yu

    2013-02-01

    Laser plasma accelerators (LPAs) have made great progress, achieving electron beam with energy up to 1 GeV from a centimeter scale capillary plasma waveguide. Here, we report the measurement of optical transition radiation (OTR) from the capillary-based LPA electron beams. Transition radiation images, produced by electrons passing through two separate foils (located at 2.3 m and 3.8 m away from the exit of the LPA) were recorded with a high resolution imaging system, respectively. Two magnetic quadrupole lenses were placed right after the capillary to focus and collimate the electron beams. Significant localized spikes appeared in the OTR images when the electron beam was focused by the magnetic quadrupole lenses, indicating the coherence of the radiation and the existence of ultrashort longitudinal structures inside the electron beam.

  5. First Observation of the Point Spread Function of Optical Transition Radiation

    NASA Astrophysics Data System (ADS)

    Karataev, Pavel; Aryshev, Alexander; Boogert, Stewart; Howell, David; Terunuma, Nobuhiro; Urakawa, Junji

    2011-10-01

    We represent the first experimental observation of the point spread function (PSF) of optical transition radiation (OTR) performed at KEK-Accelerator Test Facility extraction line. We have demonstrated that the PSF vertical polarization component has a central minimum with a two lobe distribution. However, the distribution width varied significantly with wavelength. We assume that we observed a severe effect from spherical or chromatic aberrations which are not taken into account in any existing theoretical model. We believe that the result of this work will encourage theoreticians to continue developing the theory as it is important for various transition radiation applications. Nonuniform distribution of the OTR PSF creates an opportunity for developing a submicrometer transverse beam size monitor.

  6. Electronic properties of [core+exo]-type gold clusters: factors affecting the unique optical transitions.

    PubMed

    Shichibu, Yukatsu; Konishi, Katsuaki

    2013-06-03

    Unusual visible absorption properties of [core+exo]-type Au6 (1), Au8 (2), and Au11 (3) clusters were studied from experimental and theoretical aspects, based on previously determined crystal structures. Unlike conventional core-only clusters having no exo gold atoms, these nonspherical clusters all showed an isolated visible absorption band in solution. Density functional theory (DFT) studies on corresponding nonphenyl models (1'-3') revealed that they had similar electronic structures with discrete highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) bands. The theoretical spectra generated by time-dependent DFT (TD-DFT) calculations agreed well with the experimentally measured properties of 1-3, allowing assignment of the characteristic visible bands to HOMO-LUMO transitions. The calculated HOMO-LUMO transition energies increased in the order Au11 < Au6 < Au8, as was found experimentally. Frontier orbital analyses indicated that the HOMO and LUMO were both found in proximity to the terminal Au3 triangles containing the exo gold atom, with the HOMO → LUMO transition occurring in the core → exo direction. The HOMO/LUMO distribution patterns of 1' and 3' were similar to each other but were markedly different from that of 2', which has longer core-to-exo distances. These findings showed that not only nuclearity (size) but also geometric structures have profound effects on electronic properties and optical transitions of the [core+exo]-type clusters.

  7. High-accuracy optical clock based on the octupole transition in 171Yb+.

    PubMed

    Huntemann, N; Okhapkin, M; Lipphardt, B; Weyers, S; Tamm, Chr; Peik, E

    2012-03-02

    We experimentally investigate an optical frequency standard based on the 467 nm (642 THz) electric-octupole reference transition (2)S(1/2)(F=0)→(2)F(7/2)(F=3) in a single trapped (171)Yb(+) ion. The extraordinary features of this transition result from the long natural lifetime and from the 4f(13)6s(2) configuration of the upper state. The electric-quadrupole moment of the (2)F(7/2) state is measured as -0.041(5)ea(0)(2), where e is the elementary charge and a(0) the Bohr radius. We also obtain information on the differential scalar and tensorial components of the static polarizability and of the probe-light-induced ac Stark shift of the octupole transition. With a real-time extrapolation scheme that eliminates this shift, the unperturbed transition frequency is realized with a fractional uncertainty of 7.1×10(-17). The frequency is measured as 642 121 496 772 645.15(52) Hz.

  8. Magneto-optical Phase Transition in a Nanostructured Co/Pd Thin Film

    NASA Astrophysics Data System (ADS)

    Nwokoye, Chidubem; Bennett, Lawrence; Della Torre, Edward; Siddique, Abid; Zhang, Ming; Wagner, Michael; Narducci, Frank

    Interest in the study of magnetism in nanostructures at low temperatures is growing. We report work that extends the magnetics experiments in that studied Bose-Einstein Condensation (BEC) of magnons in confined nanostructures. We report experimental investigation of the magneto-optical properties, influenced by photon-magnon interactions, of a Co/Pd thin film below and above the magnon BEC temperature. Comparison of results from SQUID and MOKE experiments revealed a phase transition temperature in both magnetic and magneto-optical properties of the material that is attributed to the magnon BEC. Recent research in magnonics has provided a realization scheme for developing magnon BEC qubit gates for a quantum computing processor. Future research work will explore this technology and find ways to apply quantum computing to address some computational challenges in communication systems. We recognize financial support from the Naval Air Systems Command Section 219 grant.

  9. Time-Resolved Emittance Characterization of an Induction Linac Beam using Optical Transition Radiation

    SciTech Connect

    Le Sage, G P

    2002-11-05

    An induction linac is used by Lawrence Livermore National Laboratory to perform radiographic testing at the Flash X-ray Radiography facility. Emittance characterization is important since x-ray spot size impacts the resolution of shadow-graphs. Due to the long pulse length, high current, and beam energy, emittance measurement using Optical Transition Radiation is an attractive alternative for reasons that will be described in the text. The utility of OTR-based emittance measurement has been well demonstrated for both RF and induction linacs. We describe the time-resolved emittance characterization of an induction linac electron beam. We have refined the optical collection system for the induction linac application, and have demonstrated a new technique for probing the divergence of a subset of the beam profile. The experimental apparatus, data reduction, and conclusions will be presented. Additionally, a new scheme for characterizing the correlation between beam divergence and spatial coordinates within the beam profile will be described.

  10. Identification of volume phase transition of a single microgel particle using optical tweezers

    NASA Astrophysics Data System (ADS)

    Karthickeyan, D.; Gupta, Deepak K.; Tata, B. V. R.

    2016-10-01

    Poly (N-isopropyl acrylamide-co-acrylic acid) (PNIPAM-co-Aac) microgel particles are pH responsive and exhibit volume phase transition (VPT) upon variation of pH. Dynamic light scattering (DLS) is used conventionally to identify VPT and requires a dilute suspension with particle concentration ˜107 particles cm-3 and if particles are polydisperse in nature, DLS data interpretation is relatively difficult. Here we show that optical tweezers allow one to measure the VPT of a single microgel particle by measuring the optical trap stiffness, κ of trapped particle as a function of pH. We report here a sudden change in κ at VPT, which is shown to arise from a sudden decrease in particle diameter with a concomitant increase in the refractive index of the particle at VPT.

  11. Flow restrictor silicon membrane microvalve actuated by optically controlled paraffin phase transition

    NASA Astrophysics Data System (ADS)

    Kolari, K.; Havia, T.; Stuns, I.; Hjort, K.

    2014-08-01

    Restrictor valves allow proportional control of fluid flow but are rarely integrated in microfluidic systems. In this study, an optically actuated silicon membrane restrictor microvalve is demonstrated. Its actuation is based on the phase transition of paraffin, using a paraffin wax mixed with a suitable concentration of optically absorbing nanographite particles. Backing up the membrane with oil (the melted paraffin) allows for a compliant yet strong contact to the valve seat, which enables handling of high pressures. At flow rates up to 30 µL min-1 and at a pressure of 2 bars, the valve can successfully be closed and control the flow level by restriction. The use of this paraffin composite as an adhesive layer sandwiched between the silicon valve and glass eases fabrication. This type of restrictor valve is best suited for high pressure, low volume flow silicon-based nanofluidic systems.

  12. Bose-Einstein quantum phase transition in an optical lattice model

    SciTech Connect

    Aizenman, Michael; Lieb, Elliott H.; Seiringer, Robert; Solovej, Jan Philip; Yngvason, Jakob

    2004-08-01

    Bose-Einstein condensation (BEC) in cold gases can be turned on and off by an external potential, such as that presented by an optical lattice. We present a model of this phenomenon which we are able to analyze rigorously. The system is a hard core lattice gas at half of the maximum density and the optical lattice is modeled by a periodic potential of strength {lambda}. For small {lambda} and temperature, BEC is proved to occur, while at large {lambda} or temperature there is no BEC. At large {lambda} the low-temperature states are in a Mott insulator phase with a characteristic gap that is absent in the BEC phase. The interparticle interaction is essential for this transition, which occurs even in the ground state. Surprisingly, the condensation is always into the p=0 mode in this model, although the density itself has the periodicity of the imposed potential.

  13. Magneto-optical activity at the structural phase transition in paramagnetic KMnF 3

    NASA Astrophysics Data System (ADS)

    Pezzoni, R.; Rigamonti, A.; Torre, S.

    1985-09-01

    The magneto-optical Verdet constant ø has been measured in the paramagnetic phase of KMnF 3 and particularly in the neighbourhood of the cubic-tetragonal phase transition driven by the softening of zone boundary modes. ø is positive and displays a sizeable decrease on cooling, thus indicating the presence of a temperature dependent paramagnetic contribution that, in view of the 6S ground state of the Mn 2+ ion, is attributed to the role of spin-orbit interaction. In a temperature range of about 20K around Tc = 186K, a cusp-shaped anomaly of ø is observed. From the dependence on the wavelength, and by taking into account also EPR linewidth and g measurements and optical absorption spectra, an analysis of the possible mechanisms for the cusp-shaped anomaly is given. It is argued that the enhancement of the critical rotational fluctuations of the MnF 6 octahedra can be responsible for this effect.

  14. Synthesis and Characterization of Layered Double Hydroxides Containing Optically Active Transition Metal Ion

    NASA Astrophysics Data System (ADS)

    Tyagi, S. B.; Kharkwal, Aneeta; Nitu; Kharkwal, Mamta; Sharma, Raghunandan

    2017-01-01

    The acetate intercalated layered double hydroxides of Zn and Mn, have been synthesized by chimie douce method. The materials were characterized by XRD, TGA, CHN, IR, XPS, SEM-EDX and UV-visible spectroscopy. The photoluminescence properties was also studied. The optical properties of layered hydroxides are active transition metal ion dependent, particularly d1-10 system plays an important role. Simultaneously the role of host - guest orientation has been considered the basis of photoluminescence. Acetate ion can be exchanged with iodide and sulphate ions. The decomposed product resulted the pure phase Mn doped zinc oxide are also reported.

  15. Transverse beam shape measurements of intense proton beams using optical transition radiation

    SciTech Connect

    Scarpine, Victor E.; /Fermilab

    2012-03-01

    A number of particle physics experiments are being proposed as part of the Department of Energy HEP Intensity Frontier. Many of these experiments will utilize megawatt level proton beams onto targets to form secondary beams of muons, kaons and neutrinos. These experiments require transverse size measurements of the incident proton beam onto target for each beam spill. Because of the high power levels, most beam intercepting profiling techniques will not work at full beam intensity. The possibility of utilizing optical transition radiation (OTR) for high intensity proton beam profiling is discussed. In addition, previous measurements of OTR beam profiles from the NuMI beamline are presented.

  16. Theory of magic optical traps for Zeeman-insensitive clock transitions in alkali-metal atoms

    SciTech Connect

    Derevianko, Andrei

    2010-05-15

    Precision measurements and quantum-information processing with cold atoms may benefit from trapping atoms with specially engineered, 'magic' optical fields. At the magic trapping conditions, the relevant atomic properties remain immune to strong perturbations by the trapping fields. Here we develop a theoretical analysis of magic trapping for especially valuable Zeeman-insensitive clock transitions in alkali-metal atoms. The involved mechanism relies on applying a magic bias B field along a circularly polarized trapping laser field. We map out these B fields as a function of trapping laser wavelength for all commonly used alkalis. We also highlight a common error in evaluating Stark shifts of hyperfine manifolds.

  17. Phase Transition of Bosons Driven by a Staggered Gauge Field in AN Optical Lattice

    NASA Astrophysics Data System (ADS)

    Cha, Min-Chul

    2013-06-01

    We have studied the ground state properties of hard-core bosons in a two-leg optical ladder in the presence of uniform and staggered frustrations due to an artificial gauge field. By calculating the ground state via the Lanczos method, we find first-order phase transitions tuned by the staggered gauge field between the Meissner and the vortex states. The momentum distributions show that the Meissner state has edge and staggered currents, while the vortex states have vortex-solid or vortex-glass phases in the presence of a staggered field.

  18. Strain-induced fundamental optical transition in (In,Ga)As/GaP quantum dots

    SciTech Connect

    Robert, C. E-mail: cedric.robert@tyndall.ie; Pedesseau, L.; Cornet, C.; Jancu, J.-M.; Even, J.; Durand, O.; Nestoklon, M. O.; Pereira da Silva, K.; Alonso, M. I.; Goñi, A. R.; Turban, P.

    2014-01-06

    The nature of the ground optical transition in an (In,Ga)As/GaP quantum dot is thoroughly investigated through a million atoms supercell tight-binding simulation. Precise quantum dot morphology is deduced from previously reported scanning-tunneling-microscopy images. The strain field is calculated with the valence force field method and has a strong influence on the confinement potentials, principally, for the conduction band states. Indeed, the wavefunction of the ground electron state is spatially confined in the GaP matrix, close to the dot apex, in a large tensile strain region, having mainly Xz character. Photoluminescence experiments under hydrostatic pressure strongly support the theoretical conclusions.

  19. Progress on the Flash X-Ray Optical Transition Radiation Diagnostic

    SciTech Connect

    Tang, V; Houck, T; Brown, C

    2008-03-30

    This document summarizes the Flash X-Ray accelerator (FXR) optical transition radiation (OTR) spot-size diagnostics efforts in FY07. During this year, new analysis, simulation, and experimental approaches were utilized to interpret OTR spot data from both dielectric foils such as Kapton (VN type) and metal coated foils. Significant new findings of the intricacies involved in the diagnostic and of FXR operational issues were achieved. Geometry and temperature based effects were found to affect the beam image profiles from the OTR foils. These effects must be taken into account in order to deduce accurately the beam current density profile.

  20. Quantum phase transition of alkaline-earth fermionic atoms confined in an optical superlattice

    NASA Astrophysics Data System (ADS)

    Silva-Valencia, J.; Franco, R.; Figueira, M. S.

    2013-03-01

    Using the density matrix renormalization group method, we evaluate the spin and charge gaps of alkaline-earth fermionic atoms in a periodic one-dimensional optical superlattice. The number of delocalized atoms is equal to the lattice size and we consider an antiferromagnetic coupling between delocalized and localized atoms. We found a quantum phase transition from a Kondo insulator spin liquid state without confining potential to a charge-gapped antiferromagnetic state with nonzero potential. For each on-site coupling, there is a critical potential point for which the spin gap vanishes and its value increases linearly with the local interaction.

  1. RMS Emittance Measurements Using Optical Transition Radiation Interferometry at the Jefferson Lab FEL

    SciTech Connect

    M. A. Holloway; S. V. Benson; W. Brock; J. L. Coleman; D. Douglas; R. Evans; P. Evtushenko; K. Jordan; D. W. Sexton; R. B. Fiorito; P. G. O'Shea; A. G. Shkvarunets

    2007-08-01

    Optical Transition Radiation Interferometry (OTRI) has proven to be effective tool for measuring rms beam divergence. We present rms emittance measurement results of the 115 MeV energy recovery linac at the Thomas Jefferson National Laboratories Free electron Laser using OTRI. OTRI data from both near field beam images and far field angular distribution images give evidence of two spatial and angular distributions within the beam. Using the unique features of OTRI we segregate the two distributions of the beam and estimate separate rms emittance values for each component.

  2. Ellipsometric method for the measurement of temperature and optical constants of incandescent transition metals

    NASA Technical Reports Server (NTRS)

    Hansen, George P.; Krishnan, Shankar; Hauge, Robert H.; Margrave, John L.

    1989-01-01

    The development of a unique noncontact temperature measurement device utilizing rotating analyzer ellipsometry is described. The technique circumvents the necessity of spectral emissivity estimation by direct measurement concomitant with radiance brightness. Simultaneous determinations of dielectric constants and refractive indices allow changes in the physical and chemical state of a heated surface to be monitored. The results of optical property measurements at 633 nm as functions of temperature between 1000 and 2500 K for eight transition metals including Hf, Ir, Mo, Nb, Pd, Pt, Ta, and V are presented together with preliminary results of oxidation studies on iridium.

  3. Transverse Beam Shape Measurements of Intense Proton Beams Using Optical Transition Radiation

    NASA Astrophysics Data System (ADS)

    Scarpine, Victor E.

    A number of particle physics experiments are being proposed as part of the Department of Energy HEP Intensity Frontier. Many of these experiments will utilize megawatt level proton beams onto targets to form secondary beams of muons, kaons and neutrinos. These experiments require transverse size measurements of the incident proton beam onto target for each beam spill. Because of the high power levels, most beam intercepting profiling techniques will not work at full beam intensity. The possibility of utilizing optical transition radiation (OTR) for high intensity proton beam profiling is discussed. In addition, previous measurements of OTR beam profiles from the NuMI beamline are presented.

  4. Ellipsometric method for the measurement of temperature and optical constants of incandescent transition metals

    NASA Technical Reports Server (NTRS)

    Hansen, George P.; Krishnan, Shankar; Hauge, Robert H.; Margrave, John L.

    1989-01-01

    The development of a unique noncontact temperature measurement device utilizing rotating analyzer ellipsometry is described. The technique circumvents the necessity of spectral emissivity estimation by direct measurement concomitant with radiance brightness. Simultaneous determinations of dielectric constants and refractive indices allow changes in the physical and chemical state of a heated surface to be monitored. The results of optical property measurements at 633 nm as functions of temperature between 1000 and 2500 K for eight transition metals including Hf, Ir, Mo, Nb, Pd, Pt, Ta, and V are presented together with preliminary results of oxidation studies on iridium.

  5. Optical fingerprint of dark 2p-states in transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Berghäuser, Gunnar; Knorr, Andreas; Malic, Ermin

    2017-03-01

    Atomically thin transition metal dichalcogenides exhibit a remarkably strong Coulomb interaction. This results in a fascinating many-particle physics including a variety of bright and dark excitonic states that determine optical and electronic properties of these materials. So far, the impact of dark states has remained literally in the dark to a large extent, since a measurement of these optically forbidden states is very challenging. Here we demonstrate a strategy to measure a direct fingerprint of dark states even in standard linear absorption spectroscopy. We present a microscopic study on bright and dark higher excitonic states in the presence of disorder for the exemplary material of tungsten disulfide (WS2). We show that the geometric phase cancels the degeneration of 2s and 2p states and that a significant disorder-induced coupling of these bright and dark states offers a strategy to circumvent optical selection rules. As a proof, we show a clear fingerprint of dark 2p states in the absorption spectrum of WS2. The predicted softening of optical selection rules through exciton-disorder coupling is of general nature and therefore applicable to related two-dimensional semiconductors.

  6. One-way optical modal transition based on causality in momentum space.

    PubMed

    Yu, Sunkyu; Piao, Xianji; Yoo, KyungWan; Shin, Jonghwa; Park, Namkyoo

    2015-09-21

    The concept of parity-time (PT) symmetry has been used to identify a route toward unidirectional dynamics in optical k-space: imposing asymmetry on the flow of light. Although PT-symmetric potentials have been implemented under the requirement of V(x) = V*(-x), this precondition has only been interpreted within the mathematical framework for the symmetry of Hamiltonians and has not been directly linked to unidirectionality induced by PT symmetry. In this paper, within the context of light-matter interactions, we develop an alternative route toward unidirectionality in k-space by employing the concept of causality. We demonstrate that potentials with real and causal momentum spectra produce unidirectional transitions of optical modes inside the k-continuum, which corresponds to an exceptional point on the degree of PT symmetry. Our analysis reveals a critical link between non-Hermitian problems and spectral theory and also enables multi-dimensional designer manipulation of optical modes, in contrast to the one-dimensional approach that used a Schrödinger-like equation in previous PT-symmetric optics.

  7. Spectroscopy of the helium 2 3S 2 3P transition above 0.01 Tesla application to optical pumping studies

    NASA Astrophysics Data System (ADS)

    Courtade, E.; Marion, F.; Nacher, P. J.; Tastevin, G.; Dohnalik, T.; Kiersnowski, K.

    2000-08-01

    Optical pumping of helium makes use of the 2 3S-2 3P transition at 1083 nm. We report on a study of this transition in magnetic fields up to 1.5 T. Based on these results, an optical method to measure nuclear polarisation in arbitrary field has been developed. Preliminary results on optical pumping at 0.1 T are presented.

  8. Transitions.

    ERIC Educational Resources Information Center

    Field, David; And Others

    1992-01-01

    Includes four articles: "Career Aspirations" (Field); "Making the Transition to a New Curriculum" (Baker, Householder); "How about a 'Work to School' Transition?" (Glasberg); and "Technological Improvisation: Bringing CNC to Woodworking" (Charles, McDuffie). (SK)

  9. ADAPTIVE OPTICS IMAGES. II. 12 KEPLER OBJECTS OF INTEREST AND 15 CONFIRMED TRANSITING PLANETS

    SciTech Connect

    Adams, E. R.; Dupree, A. K.; Kulesa, C.; McCarthy, D.

    2013-07-01

    All transiting planet observations are at risk of contamination from nearby, unresolved stars. Blends dilute the transit signal, causing the planet to appear smaller than it really is, or producing a false positive detection when the target star is blended with an eclipsing binary. High spatial resolution adaptive optics images are an effective way of resolving most blends. Here we present visual companions and detection limits for 12 Kepler planet candidate host stars, of which 4 have companions within 4''. One system (KOI 1537) consists of two similar-magnitude stars separated by 0.''1, while KOI 174 has a companion at 0.''5. In addition, observations were made of 15 transiting planets that were previously discovered by other surveys. The only companion found within 1'' of a known planet is the previously identified companion to WASP-2b. An additional four systems have companions between 1'' and 4'': HAT-P-30b (3.''7, {Delta}Ks = 2.9), HAT-P-32b (2.''9, {Delta}Ks = 3.4), TrES-1b (2.''3, {Delta}Ks = 7.7), and WASP-P-33b (1.''9, {Delta}Ks = 5.5), some of which have not been reported previously. Depending on the spatial resolution of the transit photometry for these systems, these companion stars may require a reassessment of the planetary parameters derived from transit light curves. For all systems observed, we report the limiting magnitudes beyond which additional fainter objects located 0.''1-4'' from the target may still exist.

  10. Optical gain for the interband optical transition in InAsP/InP quantum well wire in the influence of laser field intensity

    SciTech Connect

    Saravanan, S.; Peter, A. John

    2016-05-23

    Intense high frequency laser field induced electronic and optical properties of heavy hole exciton in the InAs{sub 0.8}P{sub 0.2}/InP quantum wire is studied taking into account the geometrical confinement effect. Laser field related exciton binding energies and the optical band gap in the InAs{sub 0.8}P{sub 0.2}/InP quantum well wire are investigated. The optical gain, for the interband optical transition, as a function of photon energy, in the InAs{sub 0.8}P{sub 0.2}/InP quantum wire, is obtained in the presence of intense laser field. The compact density matrix method is employed to obtain the optical gain. The obtained optical gain in group III-V narrow quantum wire can be applied for achieving the preferred telecommunication wavelength.

  11. Energy band gap and optical transition of metal ion modified double crossover DNA lattices.

    PubMed

    Dugasani, Sreekantha Reddy; Ha, Taewoo; Gnapareddy, Bramaramba; Choi, Kyujin; Lee, Junwye; Kim, Byeonghoon; Kim, Jae Hoon; Park, Sung Ha

    2014-10-22

    We report on the energy band gap and optical transition of a series of divalent metal ion (Cu(2+), Ni(2+), Zn(2+), and Co(2+)) modified DNA (M-DNA) double crossover (DX) lattices fabricated on fused silica by the substrate-assisted growth (SAG) method. We demonstrate how the degree of coverage of the DX lattices is influenced by the DX monomer concentration and also analyze the band gaps of the M-DNA lattices. The energy band gap of the M-DNA, between the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO), ranges from 4.67 to 4.98 eV as judged by optical transitions. Relative to the band gap of a pristine DNA molecule (4.69 eV), the band gap of the M-DNA lattices increases with metal ion doping up to a critical concentration and then decreases with further doping. Interestingly, except for the case of Ni(2+), the onset of the second absorption band shifts to a lower energy until a critical concentration and then shifts to a higher energy with further increasing the metal ion concentration, which is consistent with the evolution of electrical transport characteristics. Our results show that controllable metal ion doping is an effective method to tune the band gap energy of DNA-based nanostructures.

  12. All-Optical Materials Design of Dissipationless Chiral Edge Modes in Transition-Metal Dichalcogenides

    NASA Astrophysics Data System (ADS)

    Claassen, Martin; Jia, Chunjing; Moritz, Brian; Devereaux, Thomas

    Spurred by the recent progress in transient melting, enhancement and induction of electronic order, a particularly tantalizing prospect concerns the possibility to instead access dynamical steady states with distinct non-equilibrium phase transitions, to affect electronic transport. Here, we show that the interplay of crystal symmetry and optical pumping of monolayer transition-metal dichalcogenides (TMDCs) provides a novel avenue to engineer topologically-protected chiral edge modes, facilitating optically-switchable conduction channels that are insensitive to disorder. Intriguingly, while TMDCs are canonically described as condensed-matter realizations of massive relativistic fermions, here we predict from first principles that circularly-polarized pumping instead accesses the intrinsic three-band nature near the band edges to selectively photo-induce topological band inversions at low pump intensities, while simultaneously limiting absorption for sub-gap pump frequencies. The results presented provide a new strategy to predict and design topological materials out of equilibrium, and should be readily applicable to other classes of semiconductors.

  13. Optical transitions and point defects in F:SnO2 films: Effect of annealing

    NASA Astrophysics Data System (ADS)

    El Akkad, Fikry; Paulose, Tressia A. P.

    2014-03-01

    FTO films were deposited on borosilicate glass using chemical spray pyrolysis at 450 °C then subjected to post deposition annealing in air at 500, 550 and 600 °C. The films are characterized using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy (AFM), optical and electrical measurements. They are found to have the Rutile structure with strong orientation along the (1 1 0) and (2 0 0) planes and with grain size varying with annealing temperature in the range 20-100 nm. Electron concentration and oxygen vacancy concentration in the range (2.61-7.07) × 1020 cm-3 and (1.49-2.41) × 1022 cm-3 were determined using Hall and XPS measurements respectively. The analysis of optical absorption spectra revealed the presence of three direct optical transitions of energies E1 = 3.78 ± 0.07 eV, E2 = 4.39 ± 0.07 eV and E3 = 4.81 ± 0.08 eV. Taking into account the Moss-Burstein and the Urbach tailing effects, E2 was identified as being due to a direct optical transition across the Γ3v+-Γ1c+ gap. The mean value of the width of this gap is determined to be 3.86 ± 0.14 eV. The two other energies E1 and E3 are assigned to electronic transitions originating from the lower valence bands Γ5v- and Γ1v+ respectively to a defect level at Ec -0.61 ± 0.02 eV attributed to the second ionization state of the oxygen vacancy. On the other hand, the analysis of the Hall mobility results on the basis of current theories provides evidence that fluorine is at the origin of a double donor which, according to XPS measurements, must contain FSn bonds. This double donor, suggested to be the complex center [F-Sn-F]++, dominates the electrical properties of as-deposited films and creates isolated substitutional fluorine FO at higher annealing temperatures possibly by thermal dissociation.

  14. Hard-templating of chiral TiO2 nanofibres with electron transition-based optical activity

    PubMed Central

    Wang, Cui; Liu, Shaohua; Duan, Yingying; Huang, Zhehao; Che, Shunai

    2015-01-01

    The fabrication of optically active inorganic nanomaterials with chiral superstructures attracts attention because of their potential applications in chemical sensing and non-linear optics. Here, we present a facile way to prepare TiO2 nanofibres, in which the nanocrystals are helically arranged into a chiral superstructure. Notably, the chiral superstructure shows strong optical activity due to the difference of absorbing left- and right-handed circularly polarized light. This special optical activity resulted from electron transition from the valence band to the conduction band of TiO2 through a vicinal effect of helically arranged TiO2 nanocrystals. PMID:27877835

  15. Indirect interband transition induced by optical near fields with large wave numbers

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Maiku; Nobusada, Katsuyuki

    2016-05-01

    Optical near fields (ONFs) have Fourier components with large wave numbers that are two or three orders of magnitude larger than those of far-field propagating light owing to their nonuniformity in space. By utilizing these large wave numbers, the ONF is expected to induce an indirect interband transition between Bloch states having different wave numbers and directly generate an electron-hole pair without electron-phonon coupling. We perform time-dependent dynamics calculations of a one-dimensional periodic potential with an indirect band-gap structure and demonstrate that the ONF definitely induces an indirect interband transition. Instead of using the general Bloch boundary condition, which is usually imposed in conventional band structure calculations, we adopt an alternative boundary condition, the Born-von Kármán boundary condition, to appropriately treat indirect interband transitions. The calculated absorption spectra for the far-field and ONF excitations show different absorption edges and spectral patterns. We argue that this difference can be experimentally measured as evidence of the effects of the large wave numbers of the ONF.

  16. Potential of electric quadrupole transitions in radium isotopes for single-ion optical frequency standards

    SciTech Connect

    Versolato, O. O.; Wansbeek, L. W.; Jungmann, K.; Timmermans, R. G. E.; Willmann, L.; Wilschut, H. W.

    2011-04-15

    We explore the potential of the electric quadrupole transitions 7s {sup 2}S{sub 1/2}-6d {sup 2}D{sub 3/2}, 6d {sup 2}D{sub 5/2} in radium isotopes as single-ion optical frequency standards. The frequency shifts of the clock transitions due to external fields and the corresponding uncertainties are calculated. Several competitive {sup A}Ra{sup +} candidates, with A= 223-229, are identified. In particular, we show that the transition 7s {sup 2}S{sub 1/2} (F=2,m{sub F}=0)-6d {sup 2}D{sub 3/2} (F=0,m{sub F}=0) at 828 nm in {sup 223}Ra{sup +}, with no linear Zeeman and electric quadrupole shifts, stands out as a relatively simple case, which could be exploited as a compact, robust, and low-cost atomic clock operating at a fractional frequency uncertainty of 10{sup -17}. With more experimental effort, the {sup 223,225,226}Ra{sup +} clocks could be pushed to a projected performance reaching the 10{sup -18} level.

  17. Stochastic dynamic study of optical transition properties of single GFP-like molecules.

    PubMed

    Lin, Hanbing; Yuan, Jian-Min

    2016-03-01

    Due to high fluctuations and quantum uncertainty, the processes of single-molecules should be treated by stochastic methods. To study fluorescence time series and their statistical properties, we have applied two stochastic methods, one of which is an analytic method to study the off-time distributions of certain fluorescence transitions and the other is Gillespie's method of stochastic simulations. These methods have been applied to study the optical transition properties of two single-molecule systems, GFPmut2 and a Dronpa-like molecule, to yield results in approximate agreement with experimental observations on these systems. Rigorous oscillatory time series of GFPmut2 before it unfolds in the presence of denaturants have not been obtained based on the stochastic method used, but, on the other hand, the stochastic treatment puts constraints on the conditions under which such oscillatory behavior is possible. Furthermore, a sensitivity analysis is carried out on GFPmut2 to assess the effects of transition rates on the observables, such as fluorescence intensities.

  18. Giant anisotropic nonlinear optical response in transition metal monopnictide Weyl semimetals

    NASA Astrophysics Data System (ADS)

    Wu, Liang; Patankar, S.; Morimoto, T.; Nair, N. L.; Thewalt, E.; Little, A.; Analytis, J. G.; Moore, J. E.; Orenstein, J.

    2017-04-01

    Although Weyl fermions have proven elusive in high-energy physics, their existence as emergent quasiparticles has been predicted in certain crystalline solids in which either inversion or time-reversal symmetry is broken. Recently they have been observed in transition metal monopnictides (TMMPs) such as TaAs, a class of noncentrosymmetric materials that heretofore received only limited attention. The question that arises now is whether these materials will exhibit novel, enhanced, or technologically applicable electronic properties. The TMMPs are polar metals, a rare subset of inversion-breaking crystals that would allow spontaneous polarization, were it not screened by conduction electrons. Despite the absence of spontaneous polarization, polar metals can exhibit other signatures of inversion-symmetry breaking, most notably second-order nonlinear optical polarizability, χ(2), leading to phenomena such as optical rectification and second-harmonic generation (SHG). Here we report measurements of SHG that reveal a giant, anisotropic χ(2) in the TMMPs TaAs, TaP and NbAs. With the fundamental and second-harmonic fields oriented parallel to the polar axis, the value of χ(2) is larger by almost one order of magnitude than its value in the archetypal electro-optic materials GaAs and ZnTe, and in fact larger than reported in any crystal to date.

  19. Prediction of direct band gap silicon superlattices with dipole-allowed optical transition

    NASA Astrophysics Data System (ADS)

    Kim, Sunghyun; Oh, Young Jun; Lee, In-Ho; Lee, Jooyoung; Chang, K. J.

    While cubic diamond silicon (c-Si) is an important element in electronic devices, it has poor optical properties owing to its indirect gap nature, thereby limiting its applications to optoelectronic devices. Here, we report Si superlattice structures which are computationally designed to possess direct band gaps and excellent optical properties. The computational approach adopts density functional calculations and conformational space annealing for global optimization. The Si superlattices, which consist of alternating stacks of Si(111) layers and a defective layer with Seiwatz chains, have either direct or quasi-direct band gaps depending on the details of attacking layers. The photovoltaic efficiencies are calculated by solving Bethe-Salpeter equation together with quasiparticle G0W0 calculations. The strong direct optical transition is attributed to the overlap of the valence and conduction band edge states in the interface region. Our Si superlattices exhibit high thermal stability, with the energies lower by an order of magnitude than those of the previously reported Si allotropes. We discuss a possible route to the synthesis of the superlattices through wafer bonding. This work is supported by Samsung Science and Technology Foundation under Grant No. SSTF-BA1401-08.

  20. Size-dependent nonlinear optical properties of atomically thin transition metal dichalcogenide nanosheets.

    PubMed

    Zhou, Kai-Ge; Zhao, Min; Chang, Meng-Jie; Wang, Qiang; Wu, Xin-Zhi; Song, Yinglin; Zhang, Hao-Li

    2015-02-11

    Size-dependent nonlinear optical properties of modification-free transition metal dichalcogenide (TMD) nanosheets are reported, including MoS2 , WS2 , and NbSe2 . Firstly, a gradient centrifugation method is demonstrated to separate the TMD nanosheets into different sizes. The successful size separation allows the study of size-dependent nonlinear optical properties of nanoscale TMD materials for the first time. Z-scan measurements indicate that the dispersion of MoS2 and WS2 nanosheets that are 50-60 nm thick leads to reverse saturable absorption (RSA), which is in contrast to the saturable absorption (SA) seen in the thicker samples. Moreover, the NbSe2 nanosheets show no size-dependent effects because of their metallic nature. The mechanism behind the size-dependent nonlinear optical properties of the semiconductive TMD nanosheets is revealed by transient transmission spectra measurements. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. A Design Report for the Optical Transition Radiation Imager for the LCLS Undulator

    SciTech Connect

    Yang, Bingxin

    2010-12-13

    The Linac Coherent Light Source (LCLS), a free-electron x-ray laser, is under design and construction. Its high-intensity electron beam, 3400 A in peak current and 46 TW in peak power, is concentrated in a small area (37 micrometer in rms radius) inside its undulator. Ten optical transition radiation (OTR) imagers are planned between the undulator segments for characterizing the transverse profiles of the electron beam. In this note, we report on the optical and mechanical design of the OTR imager. Through a unique optical arrangement, using a near-normal-incidence screen and a multi-layer coated mirror, this imager will achieve a fine resolution (12 micrometer or better) over the entire field of view (8 mm x 5 mm), with a high efficiency for single-shot imaging. A digital camera will be used to read out the beam images in a programmable region (5 mm x 0.5 mm) at the full beam repetition rate (120 Hz), or over the entire field at a lower rate (10 Hz). Its built-in programmable amplifier will be used as an electronic intensity control.

  2. Molecular-Based Optical Measurement Techniques for Transition and Turbulence in High-Speed Flow

    NASA Technical Reports Server (NTRS)

    Bathel, Brett F.; Danehy, Paul M.; Cutler, Andrew D.

    2013-01-01

    photogrammetry (for model attitude and deformation measurement) are excluded to limit the scope of this report. Other physical probes such as heat flux gauges, total temperature probes are also excluded. We further exclude measurement techniques that require particle seeding though particle based methods may still be useful in many high speed flow applications. This manuscript details some of the more widely used molecular-based measurement techniques for studying transition and turbulence: laser-induced fluorescence (LIF), Rayleigh and Raman Scattering and coherent anti-Stokes Raman scattering (CARS). These techniques are emphasized, in part, because of the prior experience of the authors. Additional molecular based techniques are described, albeit in less detail. Where possible, an effort is made to compare the relative advantages and disadvantages of the various measurement techniques, although these comparisons can be subjective views of the authors. Finally, the manuscript concludes by evaluating the different measurement techniques in view of the precision requirements described in this chapter. Additional requirements and considerations are discussed to assist with choosing an optical measurement technique for a given application.

  3. Multicomponent measurements of the Jefferson Lab energy recovery linac electron beam using optical transition and diffraction radiation

    NASA Astrophysics Data System (ADS)

    Holloway, M. A.; Fiorito, R. B.; Shkvarunets, A. G.; O'Shea, P. G.; Benson, S. V.; Douglas, D.; Evtushenko, P.; Jordan, K.

    2008-08-01

    High brightness electron accelerators, such as energy recovery linacs (ERL), often have complex particle distributions that can create difficulties in beam transport as well as matching to devices such as wigglers used to generate radiation from the beam. Optical transition radiation (OTR), OTR interferometry (OTRI), and optical diffraction-transition radiation interferometry (ODTRI) have proven to be effective tools for diagnosing both the spatial and angular distributions of charged particle beams. OTRI and ODTRI have been used to measure rms divergences, and optical transverse phase space mapping has been demonstrated using OTRI. In this work we present the results of diagnostic experiments using OTR and optical diffraction radiation conducted at the Jefferson Laboratory’s 115 MeV ERL which show the presence of two separate components within the beam’s spatial and angular distributions. By assuming a correlation between the spatial and angular features, we estimate an rms emittance value for each of the two components.

  4. Interplay of Cu and oxygen vacancy in optical transitions and screening of excitons in ZnO:Cu films

    SciTech Connect

    Darma, Yudi; Rusydi, Andrivo; Seng Herng, Tun; Marlina, Resti; Fauziah, Resti; Ding, Jun

    2014-02-24

    We study room temperature optics and electronic structures of ZnO:Cu films as a function of Cu concentration using a combination of spectroscopic ellipsometry, photoluminescence, and ultraviolet-visible absorption spectroscopy. Mid-gap optical states, interband transitions, and excitons are observed and distinguishable. We argue that the mid-gap states are originated from interactions of Cu and oxygen vacancy (Vo). They are located below conduction band (Zn4s) and above valence band (O2p) promoting strong green emission and narrowing optical band gap. Excitonic states are screened and its intensities decrease upon Cu doping. Our results show the importance of Cu and Vo driving the electronic structures and optical transitions in ZnO:Cu films.

  5. Optical transitions in highly charged californium ions with high sensitivity to variation of the fine-structure constant.

    PubMed

    Berengut, J C; Dzuba, V A; Flambaum, V V; Ong, A

    2012-08-17

    We study electronic transitions in highly charged Cf ions that are within the frequency range of optical lasers and have very high sensitivity to potential variations in the fine-structure constant, α. The transitions are in the optical range despite the large ionization energies because they lie on the level crossing of the 5f and 6p valence orbitals in the thallium isoelectronic sequence. Cf(16+) is a particularly rich ion, having several narrow lines with properties that minimize certain systematic effects. Cf(16+) has very large nuclear charge and large ionization energy, resulting in the largest α sensitivity seen in atomic systems. The lines include positive and negative shifters.

  6. Optical Transitions in Highly Charged Californium Ions with High Sensitivity to Variation of the Fine-Structure Constant

    NASA Astrophysics Data System (ADS)

    Berengut, J. C.; Dzuba, V. A.; Flambaum, V. V.; Ong, A.

    2012-08-01

    We study electronic transitions in highly charged Cf ions that are within the frequency range of optical lasers and have very high sensitivity to potential variations in the fine-structure constant, α. The transitions are in the optical range despite the large ionization energies because they lie on the level crossing of the 5f and 6p valence orbitals in the thallium isoelectronic sequence. Cf16+ is a particularly rich ion, having several narrow lines with properties that minimize certain systematic effects. Cf16+ has very large nuclear charge and large ionization energy, resulting in the largest α sensitivity seen in atomic systems. The lines include positive and negative shifters.

  7. Structural, optical and photocatalytic studies on pure and transition metal ion doped ZnO-graphene nanocomposites

    NASA Astrophysics Data System (ADS)

    Beura, Rosalin; Thangadurai, P.

    2017-05-01

    This work reports the structural, optical and photocatalytic properties of nanocomposites made with graphene and transition metal ion doped ZnO, the graphene-ZnO nanocomposite. The doped and the un-doped ZnO were prepared by chemical method and then the nanocomposites were made. Structural confirmation was done by XRD and Raman spectroscopy. Optical properties were studied by UV-Vis and PL spectroscopies. Photocatalytic activity on the degradation of an industrial dye was studied. It was observed that the nanocomposite with transition metal ion doped ZnO have a higher degradation efficiency compared to the same with un-doped ZnO.

  8. Distinct Length Scales in the VO{sub 2} Metal–Insulator Transition Revealed by Bi-chromatic Optical Probing

    SciTech Connect

    Wang, Lei; Novikova, Irina B.; Klopf, John M.; Madaras, Scott E.; Williams, Gwyn P.; Madaras, Eric; Lu, Liwei; Wolf, Stuart A.; Lukaszew, Rosa A.

    2014-01-01

    Upon a heating-induced metal–instulator transition (MIT) in VO{sub 2}, microscopic metallic VO{sub 2} puddles nucleate and coarsen within the insulating matrix. This coexistence of the two phases across the transition spans distinct length scales as their relative domain sizes change. Far-field optical probing is applied to follow the dynamic evolution of the highly correlated metallic domains as the MIT progresses.

  9. Transition.

    ERIC Educational Resources Information Center

    Thompson, Sandy, Ed.; And Others

    1990-01-01

    This "feature issue" focuses on transition from school to adult life for persons with disabilities. Included are "success stories," brief program descriptions, and a list of resources. Individual articles include the following titles and authors: "Transition: An Energizing Concept" (Paul Bates); "Transition…

  10. Further time-resolved electron-beam characterizations with optical transition radiation

    SciTech Connect

    Lumpkin, A.H. . Advanced Photon Source Accelerator Systems Div.); Wilke, M.D. )

    1992-01-01

    Time-resolved characterizations of electron beams using optical transition radiation (OTR) as a prompt conversion mechanism have recently been extended on the Los Alamos Free-electron Laser (FEL) facility 40-MeV linac. Two key timescales for rf-linac driven FELs are the micropulse (10 ps) and the macropulse (5 [mu]s to 1 ms). In the past we have used gated, intensified cameras to select a single or few micropulses (25 to 400 ns gate width) out of the pulse train to evaluate submacropulse effects. Recently, we have obtained some of the first measurements of micropulse bunch length (7 to 10 ps) and submacropulse spatialposition and profile using OTR and a Hamamatsu streak camera. Additionally, micropulse elongation effects and head-to-tail transverse kick effects are reported as a function of charge.

  11. Time-resolved electron-beam characterizations with optical transition radiation

    SciTech Connect

    Lumpkin, A.H. ); Wilke, M.D. )

    1992-01-01

    Time-resolved characterizations of electron beams using optical transition radiation (OTR) as a prompt conversion mechanism have recently been extended on the Los Alamos Free-electron Laser (FEL) facility 40-MeV linac. Two key timescales for rf-linac driven FELs are the micropulse (10 ps) and the macropulse (5 {mu}s to 1 ms). In the past we have used gated, intensified cameras to select a single or few micropulses (25 to 400 ns gate width) out of the pulse train to evaluate submacropulse effects. Recently, we have obtained some of the first measurements of micropulse bunch length (7 to 10 ps) and submacropulse spatial position and profile using OTR and a Hamamatsu streak camera. Additionally, micropulse elongation effects and head-to-tail transverse kicks are reported as a function of charge.

  12. Time-resolved electron-beam characterizations with optical transition radiation

    SciTech Connect

    Lumpkin, A.H.; Wilke, M.D.

    1992-09-01

    Time-resolved characterizations of electron beams using optical transition radiation (OTR) as a prompt conversion mechanism have recently been extended on the Los Alamos Free-electron Laser (FEL) facility 40-MeV linac. Two key timescales for rf-linac driven FELs are the micropulse (10 ps) and the macropulse (5 {mu}s to 1 ms). In the past we have used gated, intensified cameras to select a single or few micropulses (25 to 400 ns gate width) out of the pulse train to evaluate submacropulse effects. Recently, we have obtained some of the first measurements of micropulse bunch length (7 to 10 ps) and submacropulse spatial position and profile using OTR and a Hamamatsu streak camera. Additionally, micropulse elongation effects and head-to-tail transverse kicks are reported as a function of charge.

  13. Further time-resolved electron-beam characterizations with optical transition radiation

    SciTech Connect

    Lumpkin, A.H.; Wilke, M.D.

    1992-12-31

    Time-resolved characterizations of electron beams using optical transition radiation (OTR) as a prompt conversion mechanism have recently been extended on the Los Alamos Free-electron Laser (FEL) facility 40-MeV linac. Two key timescales for rf-linac driven FELs are the micropulse (10 ps) and the macropulse (5 {mu}s to 1 ms). In the past we have used gated, intensified cameras to select a single or few micropulses (25 to 400 ns gate width) out of the pulse train to evaluate submacropulse effects. Recently, we have obtained some of the first measurements of micropulse bunch length (7 to 10 ps) and submacropulse spatialposition and profile using OTR and a Hamamatsu streak camera. Additionally, micropulse elongation effects and head-to-tail transverse kick effects are reported as a function of charge.

  14. Extended Coherence Time on the Clock Transition of Optically Trapped Rubidium

    SciTech Connect

    Kleine Buening, G.; Will, J.; Ertmer, W.; Rasel, E.; Klempt, C.; Arlt, J.; Ramirez-Martinez, F.; Rosenbusch, P.; Piechon, F.

    2011-06-17

    Optically trapped ensembles are of crucial importance for frequency measurements and quantum memories but generally suffer from strong dephasing due to inhomogeneous density and light shifts. We demonstrate a drastic increase of the coherence time to 21 s on the magnetic field insensitive clock transition of {sup 87}Rb by applying the recently discovered spin self-rephasing [C. Deutsch et al., Phys. Rev. Lett. 105, 020401 (2010)]. This result confirms the general nature of this new mechanism and thus shows its applicability in atom clocks and quantum memories. A systematic investigation of all relevant frequency shifts and noise contributions yields a stability of 2.4x10{sup -11{tau}-1/2}, where {tau} is the integration time in seconds. Based on a set of technical improvements, the presented frequency standard is predicted to rival the stability of microwave fountain clocks in a potentially much more compact setup.

  15. Extended Coherence Time on the Clock Transition of Optically Trapped Rubidium

    NASA Astrophysics Data System (ADS)

    Kleine Büning, G.; Will, J.; Ertmer, W.; Rasel, E.; Arlt, J.; Klempt, C.; Ramirez-Martinez, F.; Piéchon, F.; Rosenbusch, P.

    2011-06-01

    Optically trapped ensembles are of crucial importance for frequency measurements and quantum memories but generally suffer from strong dephasing due to inhomogeneous density and light shifts. We demonstrate a drastic increase of the coherence time to 21 s on the magnetic field insensitive clock transition of Rb87 by applying the recently discovered spin self-rephasing [C. Deutsch , Phys. Rev. Lett. 105, 020401 (2010)PRLTAO0031-900710.1103/PhysRevLett.105.020401]. This result confirms the general nature of this new mechanism and thus shows its applicability in atom clocks and quantum memories. A systematic investigation of all relevant frequency shifts and noise contributions yields a stability of 2.4×10-11τ-1/2, where τ is the integration time in seconds. Based on a set of technical improvements, the presented frequency standard is predicted to rival the stability of microwave fountain clocks in a potentially much more compact setup.

  16. Low-frequency optical dielectric response and rigidity transitions in network glasses

    SciTech Connect

    Gonzalez-Leal, J. M.; Angel, J. A.; Marquez, E.; Jimenez-Garay, R.; Krecmer, P.

    2006-11-15

    Self-organization occurring in As{sub x}S{sub 1-x} and As{sub x}Se{sub 1-x} glass alloy films reflects in their low-frequency optical dielectric response, and valuable information about the building blocks conforming their structure, can be derived from the analysis of the refractive-index dispersion data. The experimental results are discussed in the framework of the single-oscillator approach proposed by Wemple and DiDomenico, which provides a meaningful parametrization of the phenomena ruling the coupling between the photon-probe and the electron plasma in the near-infrared spectral region. Rigidity transitions occurring in both binary glassy systems are discussed in terms of the differences observed in the oscillator parameters, and these electronic evidences are linked to those arguments found in the literature, based on calorimetric and Raman measurements, that point to a segregated-phase view of glass materials.

  17. Extended coherence time on the clock transition of optically trapped rubidium.

    PubMed

    Büning, G Kleine; Will, J; Ertmer, W; Rasel, E; Arlt, J; Klempt, C; Ramirez-Martinez, F; Piéchon, F; Rosenbusch, P

    2011-06-17

    Optically trapped ensembles are of crucial importance for frequency measurements and quantum memories but generally suffer from strong dephasing due to inhomogeneous density and light shifts. We demonstrate a drastic increase of the coherence time to 21 s on the magnetic field insensitive clock transition of (87)Rb by applying the recently discovered spin self-rephasing [C. Deutsch et al., Phys. Rev. Lett. 105, 020401 (2010)]. This result confirms the general nature of this new mechanism and thus shows its applicability in atom clocks and quantum memories. A systematic investigation of all relevant frequency shifts and noise contributions yields a stability of 2.4×10(-11)τ(-1/2), where τ is the integration time in seconds. Based on a set of technical improvements, the presented frequency standard is predicted to rival the stability of microwave fountain clocks in a potentially much more compact setup.

  18. Bound-Free Transitions to GeV Energy via Optical Tunneling

    NASA Astrophysics Data System (ADS)

    Gordon, Daniel

    2015-11-01

    Many laser plasmas are created through the mechanism of tunneling ionization. For weakly to moderately relativistic laser amplitudes (a = eA / mc ~ 1), the photoelectron spectrum can extend to the MeV range, with the electron gaining approximately the ponderomotive potential at the position where the bound-free transition occurred. When a ~ 100 , a new regime of acceleration appears, in which ultrarelativistic energy is obtained in a fraction of an optical cycle. We compute photoelectron characteristics based on relativistic tunneling ionization rates, and advanced particle tracking simulations, utilizing state-of-the art computer hardware. It is found that using near-term multi-petawatt lasers, free space acceleration from rest to GeV energy is possible. The effect of radiation reaction is also examined.

  19. Emittance and Energy Measurements of Low-Energy Electron Beam Using Optical Transition Radiation Techniques

    NASA Astrophysics Data System (ADS)

    Sakamoto, Fumito; Iijima, Hokuto; Dobashi, Katsuhiro; Imai, Takayuki; Ueda, Toru; Watanabe, Takahiro; Uesaka, Mitsuru

    2005-03-01

    Emittance and energy of an electron beam in the range of 8 to 22 MeV were measured via optical transition radiation (OTR) techniques. The beam divergence effect on observations of the far-field OTR image at low energies was studied by means of numerical analysis. The numerical analysis indicates that if the beam divergence is under 1.5 mrad, a simultaneous single-shot measurement of emittance and energy is possible. The results of the single-shot experiment agree with independent measurements conducted using the quadrupole scan method and an electron spectrometer. The experiments were performed with an S-band linac at the Nuclear Engineering Research Laboratory, The University of Tokyo (UTNL).

  20. Evidence for anomalous optical transition radiation linear polarization effects in beam-profile monitors

    NASA Astrophysics Data System (ADS)

    Lumpkin, A. H.; Johnson, A. S.; Ruan, J.; Thurman-Keup, R. M.; Yao, C.-Y.; Evtushenko, P.

    2013-10-01

    Investigations of the effects of optical transition radiation (OTR) polarization components on beam profiles are presented. The transverse profiles are examined using the OTR perpendicular and parallel polarization components with respect to the dimension of interest. We observed ˜15% projected profile size reductions with the perpendicularly polarized components on a 65-μm beam image size case at 14 MeV, a 150-μm beam image size at 4.5 GeV, and a 1100-μm beam image size at 7 GeV. These effects are all several times larger than expected (and anomalous in this sense) when compared to the standard OTR point-spread function calculations. We propose the time-averaged induced-current distribution which generates the OTR represents the actual beam size more faithfully with the perpendicular polarization component and recommend its routine use and subsequent deconvolution.

  1. Optical transitions and nature of Stokes shift in spherical CdSquantum dots

    SciTech Connect

    Demchenko, Denis O.; Wang, Lin-Wang

    2005-12-16

    We study the structure of the energy spectra along with the character of the states participating in optical transitions in colloidal CdS quantum dots (QDs) using the ab initio accuracy charge patching method combined with the folded spectrum calculations of electronic structure of thousand-atom nanostructures. In particular, attention is paid to the nature of the large resonant Stokes shift observed in CdS quantum dots. We find that the top of the valence band state is bright, in contrast with the results of numerous k {center_dot} p calculations, and determine the limits of applicability of the k {center_dot} p approach. The calculated electron-hole exchange splitting suggests the spin-forbidden valence state may explain the nature of the ''dark exciton'' in CdS quantum dots.

  2. Optical study of the multiple charge-density-wave transitions in ErTe3

    NASA Astrophysics Data System (ADS)

    Hu, B. F.; Cheng, B.; Yuan, R. H.; Dong, T.; Fang, A. F.; Guo, W. T.; Chen, Z. G.; Zheng, P.; Shi, Y. G.; Wang, N. L.

    2011-10-01

    We present an optical spectroscopy study on singe crystalline ErTe3, a rare-earth-element tritelluride, which experiences two successive charge-density wave (CDW) transitions at Tc1=267 K and Tc2=150 K. Two corresponding gap features, centered at 2770 cm-1 (˜343 meV) and 890 cm-1 (˜110 meV), respectively, are clearly seen in ordered state. A pronounced Drude component, which exists at all measurement temperatures, demonstrates the partial gap character of both CDW orders. About half of the unmodulated Fermi surface (FS) remains in the CDW state at the lowest measurement temperature. The study also indicates that fluctuation effect may be still prominent in this two-dimensional material.

  3. Synthetic Dimensions and Spin-Orbit Coupling with an Optical Clock Transition

    NASA Astrophysics Data System (ADS)

    Livi, L. F.; Cappellini, G.; Diem, M.; Franchi, L.; Clivati, C.; Frittelli, M.; Levi, F.; Calonico, D.; Catani, J.; Inguscio, M.; Fallani, L.

    2016-11-01

    We demonstrate a novel way of synthesizing spin-orbit interactions in ultracold quantum gases, based on a single-photon optical clock transition coupling two long-lived electronic states of two-electron 173Yb atoms. By mapping the electronic states onto effective sites along a synthetic "electronic" dimension, we have engineered fermionic ladders with synthetic magnetic flux in an experimental configuration that has allowed us to achieve uniform fluxes on a lattice with minimal requirements and unprecedented tunability. We have detected the spin-orbit coupling with fiber-link-enhanced clock spectroscopy and directly measured the emergence of chiral edge currents, probing them as a function of the flux. These results open new directions for the investigation of topological states of matter with ultracold atomic gases.

  4. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Phase Transition and Optical Properties of Solid Oxygen under High Pressure: A Density Functional Theory Study

    NASA Astrophysics Data System (ADS)

    Liu, Yan-Hui; Tian, Fu-Bo; Ma, Yan-Ming; He, Zhi; Cui, Tian; Liu, Bing-Bing; Zou, Guang-Tian

    2008-07-01

    Crystal structures and optical properties of the δ-O2 phase and the ∈-O8 phase have been investigated by using the ab initio pseudopotential plane-wave method. It is found that the phase transition is of the first order with a discontinuous volumetric change from the antiferromagnetic δ-O2 phase to the nonmagnetic ∈-O8 phase, consistent with the experimental findings. The energy band calculations show that the direct band gap changes into an indirect band gap after the phase transition. The apparent change in the optical properties can be used for identifying the phase transition from δ-O2 to ∈-O8.

  5. Optically excited structural transition in atomic wires on surfaces at the quantum limit

    NASA Astrophysics Data System (ADS)

    Frigge, T.; Hafke, B.; Witte, T.; Krenzer, B.; Streubühr, C.; Samad Syed, A.; Mikšić Trontl, V.; Avigo, I.; Zhou, P.; Ligges, M.; von der Linde, D.; Bovensiepen, U.; Horn-von Hoegen, M.; Wippermann, S.; Lücke, A.; Sanna, S.; Gerstmann, U.; Schmidt, W. G.

    2017-03-01

    Transient control over the atomic potential-energy landscapes of solids could lead to new states of matter and to quantum control of nuclear motion on the timescale of lattice vibrations. Recently developed ultrafast time-resolved diffraction techniques combine ultrafast temporal manipulation with atomic-scale spatial resolution and femtosecond temporal resolution. These advances have enabled investigations of photo-induced structural changes in bulk solids that often occur on timescales as short as a few hundred femtoseconds. In contrast, experiments at surfaces and on single atomic layers such as graphene report timescales of structural changes that are orders of magnitude longer. This raises the question of whether the structural response of low-dimensional materials to femtosecond laser excitation is, in general, limited. Here we show that a photo-induced transition from the low- to high-symmetry state of a charge density wave in atomic indium (In) wires supported by a silicon (Si) surface takes place within 350 femtoseconds. The optical excitation breaks and creates In-In bonds, leading to the non-thermal excitation of soft phonon modes, and drives the structural transition in the limit of critically damped nuclear motion through coupling of these soft phonon modes to a manifold of surface and interface phonons that arise from the symmetry breaking at the silicon surface. This finding demonstrates that carefully tuned electronic excitations can create non-equilibrium potential energy surfaces that drive structural dynamics at interfaces in the quantum limit (that is, in a regime in which the nuclear motion is directed and deterministic). This technique could potentially be used to tune the dynamic response of a solid to optical excitation, and has widespread potential application, for example in ultrafast detectors.

  6. Optically excited structural transition in atomic wires on surfaces at the quantum limit.

    PubMed

    Frigge, T; Hafke, B; Witte, T; Krenzer, B; Streubühr, C; Samad Syed, A; Mikšić Trontl, V; Avigo, I; Zhou, P; Ligges, M; von der Linde, D; Bovensiepen, U; Horn-von Hoegen, M; Wippermann, S; Lücke, A; Sanna, S; Gerstmann, U; Schmidt, W G

    2017-03-29

    Transient control over the atomic potential-energy landscapes of solids could lead to new states of matter and to quantum control of nuclear motion on the timescale of lattice vibrations. Recently developed ultrafast time-resolved diffraction techniques combine ultrafast temporal manipulation with atomic-scale spatial resolution and femtosecond temporal resolution. These advances have enabled investigations of photo-induced structural changes in bulk solids that often occur on timescales as short as a few hundred femtoseconds. In contrast, experiments at surfaces and on single atomic layers such as graphene report timescales of structural changes that are orders of magnitude longer. This raises the question of whether the structural response of low-dimensional materials to femtosecond laser excitation is, in general, limited. Here we show that a photo-induced transition from the low- to high-symmetry state of a charge density wave in atomic indium (In) wires supported by a silicon (Si) surface takes place within 350 femtoseconds. The optical excitation breaks and creates In-In bonds, leading to the non-thermal excitation of soft phonon modes, and drives the structural transition in the limit of critically damped nuclear motion through coupling of these soft phonon modes to a manifold of surface and interface phonons that arise from the symmetry breaking at the silicon surface. This finding demonstrates that carefully tuned electronic excitations can create non-equilibrium potential energy surfaces that drive structural dynamics at interfaces in the quantum limit (that is, in a regime in which the nuclear motion is directed and deterministic). This technique could potentially be used to tune the dynamic response of a solid to optical excitation, and has widespread potential application, for example in ultrafast detectors.

  7. Observation of the 5 p3 /2→6 p3 /2 electric-dipole-forbidden transition in atomic rubidium using optical-optical double-resonance spectroscopy

    NASA Astrophysics Data System (ADS)

    Ponciano-Ojeda, F.; Hernández-Gómez, S.; López-Hernández, O.; Mojica-Casique, C.; Colín-Rodríguez, R.; Ramírez-Martínez, F.; Flores-Mijangos, J.; Sahagún, D.; Jáuregui, R.; Jiménez-Mier, J.

    2015-10-01

    Direct evidence of excitation of the 5 p3 /2→6 p3 /2 electric-dipole-forbidden transition in atomic rubidium is presented. The experiments were performed in a room-temperature rubidium cell with continuous-wave external cavity diode lasers. Optical-optical double-resonance spectroscopy with counterpropagating beams allows the detection of the nondipole transition free of Doppler broadening. The 5 p3 /2 state is prepared by excitation with a laser locked to the maximum F cyclic transition of the D2 line, and the forbidden transition is produced by excitation with a 911 nm laser. Production of the forbidden transition is monitored by detection of the 420 nm fluorescence that results from decay of the 6 p3 /2 state. Spectra with three narrow lines (≈13 MHz FWHM) with the characteristic F -1 , F , and F +1 splitting of the 6 p3 /2 hyperfine structure in both rubidium isotopes were obtained. The results are in very good agreement with a direct calculation that takes into account the 5 s →5 p3 /2 preparation dynamics, the 5 p3 /2→6 p3 /2 nondipole excitation geometry, and the 6 p3 /2→5 s1 /2 decay. The comparison also shows that the electric-dipole-forbidden transition is a very sensitive probe of the preparation dynamics.

  8. On the determination of the position of laminar-turbulent transition in boundary layer by optical methods

    NASA Astrophysics Data System (ADS)

    Bountin, D. A.; Gromyko, Yu. V.; Maslov, A. A.; Polivanov, P. A.; Sidorenko, A. A.

    2015-11-01

    As a rule, aerodynamic studies at hypersonic flow velocities are carried out in short-duration wind-tunnel facilities. For such facilities, optical diagnostic methods are most preferable. In the present study, we give for the first time a comparison of two methods for determining the end of laminar-turbulent transition: from the distribution of heat fluxes and from schlieren visualization data for the boundary-layer flow. Parametric data on the position of the transition are obtained. These data can be used in the future as reference ones while calibrating semi-empirical calculation models for the transition.

  9. High-temperature phase transition in the coupled atom-light system in the presence of optical collisions

    NASA Astrophysics Data System (ADS)

    Alodjants, A. P.; Chestnov, I. Yu.; Arakelian, S. M.

    2011-05-01

    The problem of photonic phase transition for the system of a two-level atomic ensemble interacting with a quantized single-mode electromagnetic field in the presence of optical collisions (OCs) is considered. We have shown that for large and negative atom-field detuning a photonic field exhibits high-temperature second-order phase transition to superradiant state under thermalization condition for coupled atom-light states. Such a transition can be connected with superfluid (coherent) properties of photonlike low branch (LB) polaritons. We discuss the application of metallic cylindrical waveguide for observing predicted effects.

  10. Intrinsic evolutions of optical functions, band gap, and higher-energy electronic transitions in VO2 film near the metal-insulator transition region

    NASA Astrophysics Data System (ADS)

    Li, W. W.; Yu, Q.; Liang, J. R.; Jiang, K.; Hu, Z. G.; Liu, J.; Chen, H. D.; Chu, J. H.

    2011-12-01

    Transmittance spectra of (011) vanadium dioxide (VO2) film have been studied in the temperature range of 45-80 °C. Owing to increasing carrier concentration, the near-infrared extinction coefficient and optical conductivity around metal-insulator transition (MIT) rapidly increase with the temperature. Moreover, three electronic transitions can be uniquely assigned and show the hysteresis behavior near the MIT region. It was found that the optical band gap decreases from 0.457 to 0.042 eV before the MIT, then reduces to zero for the metal state. This confirms the fact that the a1g and egπ bands are moved close and finally overlap with the temperature.

  11. Band gap energy and optical transitions in polyenes formed by thermal decomposition of polyvinyl alcohol

    NASA Astrophysics Data System (ADS)

    Kulak, A. I.; Bondarava, G. V.; Shchurevich, O. A.

    2013-07-01

    The band gap of the ensemble of oligoene clusters formed by thermocatalytic decomposition of polyvinyl alcohol is parametrized using optical absorption spectra. A band gap energy of E gm =1.53 ± 0.02 eV at the end of an infinite polyene chain is found by extrapolating the energies of π → π* transitions in clusters with a number of double bonds varying from 4 to 12. This value is close to the band gap of trans-polyacetylene and the lower bound for the Tauc energy E gT =1.50 eV, which characterizes the minimum interband transition energy. E gT is essentially independent of the concentration of oligoene clusters, which is determined by the concentration of the AlCl3 thermal decomposition catalyst. The Urbach energy determined from the long wavelength edge of the spectrum falls from 2.21 to 0.66 eV as the AlCl3 concentration is raised from 11.1 to 41.7 mmol per mol of polyvinyl alcohol structural units.

  12. Symmetry of electron states and optical transitions in GaN/AlN hexagonal quantum dots

    NASA Astrophysics Data System (ADS)

    Tronc, P.; Smirnov, V. P.; Zhuravlev, K. S.

    2004-11-01

    The exact symmetry of hexagonal quantum dots (QDs) made of materials with the wurtzite structure such as GaN/AlN QDs for example, is described by the C3v point group and does not depend on the existence of a wetting layer. We have determined the possible exact symmetries of electron states and vibration modes in the dots and derived the optical selection rules. The vibration modes involved in the Frölich interaction are totally symmetric with respect to the C3v group and can induce transitions only between states with the same symmetry. The not totally symmetric modes provide other channels for lowering the energy of excited carriers and excitons by connecting states with symmetries different one from another. The rapid decay of created polarons, due to the short lifetime of vibration modes, releases the carriers and excitons into ground levels. In the envelope function approximation (EFA), the symmetry of the dots is represented by the C6v point group. Interband transitions are allowed only between states whose envelope functions have the same symmetry. EFA artificially increases the number of dark exciton symmetries.

  13. Characterization and mitigation of coherent-optical-transition-radiation signals from a compressed electron beam

    NASA Astrophysics Data System (ADS)

    Lumpkin, A. H.; Sereno, N. S.; Berg, W. J.; Borland, M.; Li, Y.; Pasky, S. J.

    2009-08-01

    The Advanced Photon Source (APS) injector complex includes an option for rf photocathode (PC) gun beam injection into the 450-MeV S-band linac. At the 150-MeV point, a four-dipole chicane was used to compress the micropulse bunch length from a few ps to sub-0.5 ps (FWHM). Noticeable enhancements of the optical transition radiation (OTR) signal sampled after the APS chicane were then observed as has been reported in the Linac Coherent Light Source (LCLS) injector commissioning. A far-infrared (FIR) coherent transition radiation detector and interferometer were used to monitor the bunch compression process and correlate the appearance of localized spikes of OTR signal (5 to 10 times brighter than adjacent areas) within the beam-image footprint. We have performed spectral-dependency measurements at 375 MeV with a series of bandpass filters centered in 50-nm increments from 400 to 700 nm and with an imaging spectrometer and observed a broadband enhancement in these spikes. Mitigation concepts of the observed coherent OTR, which exhibits an intensity enhancement in the red part of the visible spectrum as compared to incoherent OTR, are described.

  14. Theoretical calculations of phase transitions and optical properties of solid iodine under high pressures

    NASA Astrophysics Data System (ADS)

    San, Xiaojiao; Wang, Liancheng; Ma, Yanming; Liu, Zhiming; Cui, Tian; Liu, Bingbing; Zou, Guangtian

    2008-04-01

    The structural stability and optical properties of solid iodine under pressure have been studied using the ab initio pseudopotential plane-wave method. The dependence of lattice parameters on pressure indicates that the first structural phase transition from phase I to phase V occurs at about 20 GPa. From the pressure dependence of our elastic constants for solid iodine in phase I, it is found that the first structural transformation from molecular phase I to the intermediate phase V occurs at about 20 GPa due to the softening of the elastic constant C44, which is very close to the transition pressure of 20 GPa obtained by geometry optimizations and 23.2 GPa obtained by experimental measurements. The optimized structure for phase V is a face-centered orthorhombic (fco) phase with equal interatomic distances d1 = d2 = d3, but this fco structure is mechanically unstable, with shear elastic stiffness coefficient C44<0. To understand the modulated phase V, we use a periodic crystal structure to mimic the incommensurate phase V and obtain some quantitative information. In our calculation, the modulated phase is thermodynamically and mechanically stable. It is believed that phase V is not a monatomic phase but an intermediate state between a molecular and a monatomic state.

  15. Characterization and mitigation of coherent optical transition radiation signal from a compressed electron beam.

    SciTech Connect

    Lumpkin, A. H.; Sereno, N. S.; Berg, W.; Borland, M.; Li, Y.; Pasky, S. )

    2009-01-01

    The Advanced Photon Source (APS) injector complex includes an option for rf photocathode (PC) gun beam injection into the 450-MeV S-band linac. At the 150-MeV point, a four-dipole chicane was used to compress the micropulse bunch length from a few ps to sub-0.5 ps (FWHM). Noticeable enhancements of the optical transition radiation (OTR) signal sampled after the APS chicane were then observed as has been reported in the Linac Coherent Light Source (LCLS) injector commissioning. A far-infrared (FIR) coherent transition radiation detector and interferometer were used to monitor the bunch compression process and correlate the appearance of localized spikes of OTR signal (5 to 10 times brighter than adjacent areas) within the beam-image footprint. We have performed spectral-dependency measurements at 375 MeV with a series of bandpass filters centered in 50-nm increments from 400 to 700 nm and with an imaging spectrometer and observed a broadband enhancement in these spikes. Mitigation concepts of the observed coherent OTR, which exhibits an intensity enhancement in the red part of the visible spectrum as compared to incoherent OTR, are described.

  16. Dephasing mechanisms of optical transitions in rare-earth-doped transparent ceramics

    NASA Astrophysics Data System (ADS)

    Kunkel, Nathalie; Bartholomew, John; Welinski, Sacha; Ferrier, Alban; Ikesue, Akio; Goldner, Philippe

    2016-11-01

    We identify and analyze dephasing mechanisms that broaden the optical transitions of rare-earth ions in randomly oriented transparent ceramics. The study examines the narrow F70↔D50 transition of Eu3 + dopants in a series of Y2O3 ceramic samples prepared under varying conditions. We characterize the temperature and magnetic field dependence of the homogeneous linewidth, as well as long-term spectral diffusion on time scales up to 1 s. The results highlight significant differences between samples with differing thermal treatments and Zr4 + additive concentrations. In particular, several distinct magnetic interactions from defect centers are observed, which are clearly distinguished from the broadening due to interactions with two-level systems and phonons. By minimizing the broadening due to the different defect centers, linewidths of the order of 4 kHz are achieved for all samples. The linewidths are limited by temperature-dependent interactions and by an interaction that is yet to be identified. Although the homogeneous linewidth can be narrowed further in these ceramic samples, the broadening is now comparable to the linewidths achieved in rare-earth-ion-doped single crystals. Thus, this work emphasizes the usefulness of studying ceramics to gain insights into dephasing mechanisms relevant to single crystals and suggests that ceramics may be an interesting alternative for applications in classical and quantum information processing.

  17. Exciton formation assisted by longitudinal optical phonons in monolayer transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Thilagam, A.

    2016-09-01

    We examine a mechanism by which excitons are generated via the longitudinal optical (LO) phonon-assisted scattering process after optical excitation of monolayer transition metal dichalcogenides. The exciton formation time is computed as a function of the exciton center-of-mass wavevector, electron and hole temperatures, and carrier densities for known values of the Fröhlich coupling constant, LO phonon energy, lattice temperature, and the exciton binding energy in layered structures. For the monolayer MoS2, we obtain ultrafast exciton formation times on the sub-picosecond time scale at charge densities of 5 × 1011 cm-2 and carrier temperatures less than 300 K, in good agreement with recent experimental findings ( ≈0.3 ps). While excitons are dominantly created at zero center-of-mass wavevectors at low charge carrier temperatures ( ≈30 K), the exciton formation time is most rapid at non-zero wavevectors at higher temperatures ( ≥120 K) of charge carriers. The results show the inverse square-law dependence of the exciton formation times on the carrier density, consistent with a square-law dependence of photoluminescence on the excitation density. Our results show that excitons are formed more rapidly in exemplary monolayer selenide-based dichalcogenides (MoSe2 and WSe2) than sulphide-based dichalcogenides (MoS2 and WS2).

  18. Rapid, all-optical crystal orientation imaging of two-dimensional transition metal dichalcogenide monolayers

    SciTech Connect

    David, Sabrina N.; Zhai, Yao; Zande, Arend M. van der; O'Brien, Kevin; Huang, Pinshane Y.; Chenet, Daniel A.; Hone, James C.; Zhang, Xiang; Yin, Xiaobo

    2015-09-14

    Two-dimensional (2D) atomic materials such as graphene and transition metal dichalcogenides (TMDCs) have attracted significant research and industrial interest for their electronic, optical, mechanical, and thermal properties. While large-area crystal growth techniques such as chemical vapor deposition have been demonstrated, the presence of grain boundaries and orientation of grains arising in such growths substantially affect the physical properties of the materials. There is currently no scalable characterization method for determining these boundaries and orientations over a large sample area. We here present a second-harmonic generation based microscopy technique for rapidly mapping grain orientations and boundaries of 2D TMDCs. We experimentally demonstrate the capability to map large samples to an angular resolution of ±1° with minimal sample preparation and without involved analysis. A direct comparison of the all-optical grain orientation maps against results obtained by diffraction-filtered dark-field transmission electron microscopy plus selected-area electron diffraction on identical TMDC samples is provided. This rapid and accurate tool should enable large-area characterization of TMDC samples for expedited studies of grain boundary effects and the efficient characterization of industrial-scale production techniques.

  19. Optically trapped atom interferometry using the clock transition of large 87Rb Bose-Einstein condensates

    NASA Astrophysics Data System (ADS)

    Altin, P. A.; McDonald, G.; Döring, D.; Debs, J. E.; Barter, T. H.; Close, J. D.; Robins, N. P.; Haine, S. A.; Hanna, T. M.; Anderson, R. P.

    2011-06-01

    We present a Ramsey-type atom interferometer operating with an optically trapped sample of 106 Bose-condensed 87Rb atoms. We investigate this interferometer experimentally and theoretically with an eye to the construction of future high precision atomic sensors. Our results indicate that, with further experimental refinements, it will be possible to produce and measure the output of a sub-shot-noise-limited, large atom number BEC-based interferometer. The optical trap allows us to couple the |F=1, mF=0rang→|F=2, mF=0rang clock states using a single photon 6.8 GHz microwave transition, while state selective readout is achieved with absorption imaging. We analyse the process of absorption imaging and show that it is possible to observe atom number variance directly, with a signal-to-noise ratio ten times better than the atomic projection noise limit on 106 condensate atoms. We discuss the technical and fundamental noise sources that limit our current system, and present theoretical and experimental results on interferometer contrast, de-phasing and miscibility.

  20. Optical studies of phase transitions in oxyfluoride (NH4)2NbOF5

    NASA Astrophysics Data System (ADS)

    Mel'Nikova, S. V.; Laptash, N. M.; Aleksandrov, K. S.

    2010-10-01

    Polarization-optical studies and measurements of the birefringence Δ n and the angle of rotation of the optical indicatrix for the (NH4)2NbOF5 crystal have been carried out in the temperature range 100-350 K. Two anomalies of the birefringence have been revealed at the temperatures T 01 = 258 K and T 02 ≈ 219 K. According to the twinning pattern, the crystal undergoes successive changes in symmetry: orthorhombic ↔ monoclinic 1 ↔ monoclinic 2. The twofold axis of the monoclinic phases (or the normal to the plane) is directed along [001]or. The effect of the uniaxial compression along [011]or and the electric field E ≈ 25 kV/cm along [100]or on the twin structure has been studied. The ferroelastic phase transition at T 01 is due to the appearance of the shear deformation x 4( T) and is accompanied by significant anomalies of the birefringence. Strong pretransition phenomena mask the jumps in the birefringence Δ n( T) and in the angle of rotation of the indicatrix φ( T) at T 01.

  1. Instantaneous electron beam emittance measurement system based on the optical transition radiation principle

    NASA Astrophysics Data System (ADS)

    Jiang, Xiao-Guo; Wang, Yuan; Zhang, Kai-Zhi; Yang, Guo-Jun; Shi, Jin-Shui; Deng, Jian-Jun; Li, Jin

    2014-01-01

    One kind of instantaneous electron beam emittance measurement system based on the optical transition radiation principle and double imaging optical method has been set up. It is mainly adopted in the test for the intense electron-beam produced by a linear induction accelerator. The system features two characteristics. The first one concerns the system synchronization signal triggered by the following edge of the main output waveform from a Blumlein switch. The synchronous precision of about 1 ns between the electron beam and the image capture time can be reached in this way so that the electron beam emittance at the desired time point can be obtained. The other advantage of the system is the ability to obtain the beam spot and beam divergence in one measurement so that the calculated result is the true beam emittance at that time, which can explain the electron beam condition. It provides to be a powerful beam diagnostic method for a 2.5 kA, 18.5 MeV, 90 ns (FWHM) electron beam pulse produced by Dragon I. The ability of the instantaneous measurement is about 3 ns and it can measure the beam emittance at any time point during one beam pulse. A series of beam emittances have been obtained for Dragon I. The typical beam spot is 9.0 mm (FWHM) in diameter and the corresponding beam divergence is about 10.5 mrad.

  2. Robotic Transit Follow-up: Adaptive Optics Imaging of Thousands of Stars

    NASA Astrophysics Data System (ADS)

    Law, Nicholas M.; Morton, T.; Baranec, C.; Riddle, R. L.; Tendulkar, S. P.; Johnson, J. A.; Bui, K.; Burse, M.; Chordia, P.; Das, H.; Dekany, R.; Kulkarni, S. R.; Punnadi, S.; Ramaprakash, A. N.; Robo-AO Collaboration

    2013-01-01

    Stars that host transiting exoplanet candidates may have close companions. If undetected, these companions can produce false-positive planets or affect the measured exoplanet characteristics. High-angular-resolution imaging is required to resolve these systems. Up to now, it has been impossible to obtain adaptive optics images of all the thousands of candidates generated by large surveys like Kepler because of the faintness of the targets and the excessive observing time required. The Robo-AO robotic laser adaptive optics system, newly-commissioned on the Palomar 60-inch telescope, is the first system capable of rapidly observing thousands of targets at high resolution. Robo-AO routinely images 200+ targets per night and produces 0.1" FWHM images in visible wavelengths similar to the Kepler passband. We are using Robo-AO to perform a stellar companion search of unprecedented size, including every Kepler planet candidate and 3,000 nearby planet-search stars. In our first observing season we have imaged over 1,000 Kepler objects of interest and 75% of the Northern stars within 25pc. We will describe the system and discuss its use for future exoplanet surveys such as TESS. We will also present the first results from the survey: a comprehensive assessment of stellar multiplicity among Kepler exoplanet hosts and the discovery of new close stellar companions around Kepler objects of interest.

  3. Tolerancing, alignment and test of the Transiting Exoplanet Survey Satellite (TESS) optical assembly

    NASA Astrophysics Data System (ADS)

    Primeau, Brian; Balonek, Gregory; MacDonald, Robert; Chrisp, Michael; Chesbrough, Christian; Andre, James; Clark, Kristin

    2016-09-01

    The Transiting Exoplanet Survey Satellite (TESS) will carry four visible waveband seven-element refractive f/1.4 lenses, each with a 34 degree diagonal field of view. This paper describes the tolerancing, assembly and alignment methods developed during the build of the TESS Risk Reduction Unit optical system. Lens assembly tolerances were derived from a sensitivity analysis using an image quality metric customized for mission performance. The optomechanical design consists of a two-stage lens housing that provides access for active alignment of each lens using a Trioptics OptiCentric measurement system. Thermal stresses and alignment shifts are mitigated by mounting the optics with cast RTV silicone spacers into individually aligned bezels, and custom fixtures were developed to aid in RTV bonding with reduced alignment error. The lens assembly was tested interferometrically over the field of view at room temperature and results were used to successfully predict lens performance and compensator adjustments and detector shim thickness for the -75C operational temperature and pressure.

  4. Multisectional linear ion trap and novel loading method for optical spectroscopy of electron and nuclear transitions.

    PubMed

    Sysoev, Alexey A; Troyan, Victor I; Borisyuk, Peter V; Krasavin, Andrey V; Vasiliev, Oleg S; Palchikov, Vitaly G; Avdeev, Ivan A; Chernyshev, Denis M; Poteshin, Sergey S

    2015-01-01

    There is a growing need for the development of atomic and nuclear frequency standards because of the important contribution of methods for precision time and frequency measurements to the development of fundamental science, technology, and the economy. It is also conditioned by their potential use in optical clocks and quantum logic applications. It is especially important to develop a universal method that could allow one to use ions of most elements effectively (including ones that are not easily evaporated) proposed for the above-mentioned applications. A linear quadrupole ion trap for the optical spectroscopy of electron and nuclear transitions has been developed and evaluated experimentally. An ion source construction is based on an ultra-high vacuum evaporator in which a metal sample is subjected to an electron beam of energy up to 1 keV, resulting in the appearance of gaseous atoms and ions of various charge state. The linear ion trap consists of five successive quadrupole sections including an entrance quadrupole section, quadrupole mass filter, quadrupole ion guide, ion-trap section, and exit quadrupole section. The same radiofrequency but a different direct current voltage feeds the quadrupole sections. The instrument allows the mass and energy selected trapping of ions from ion beams of various intensities and their localization in the area of laser irradiation. The preliminary results presented show that the proposed instrument and methods allow one to produce effectively up to triply charged thorium ions as well as to trap ions for future spectroscopic study. The instrument is proposed for future use in optical clocks and quantum logic application development.

  5. Near-UV and optical observations of the transiting exoplanet TrES-3b

    NASA Astrophysics Data System (ADS)

    Turner, Jake D.; Smart, Brianna M.; Hardegree-Ullman, Kevin K.; Carleton, Timothy M.; Walker-LaFollette, Amanda M.; Crawford, Benjamin E.; Smith, Carter-Thaxton W.; McGraw, Allison M.; Small, Lindsay C.; Rocchetto, Marco; Cunningham, Kathryn I.; Towner, Allison P. M.; Zellem, Robert; Robertson, Amy N.; Guvenen, Blythe C.; Schwarz, Kamber R.; Hardegree-Ullman, Emily E.; Collura, Daniel; Henz, Triana N.; Lejoly, Cassandra; Richardson, Logan L.; Weinand, Michael A.; Taylor, Joanna M.; Daugherty, Michael J.; Wilson, Ashley A.; Austin, Carmen L.

    2013-01-01

    We observed nine primary transits of the hot Jpiter TrES-3b in several optical and near-UV photometric bands from 2009 June to 2012 April in an attempt to detect its magnetic field. Vidotto, Jardine and Helling suggest that the magnetic field of TrES-3b can be constrained if its near-UV light curve shows an early ingress compared to its optical light curve, while its egress remains unaffected. Predicted magnetic field strengths of Jpiter-like planets should range between 8 G and 30 G. Using these magnetic field values and an assumed B* of 100 G, the Vidotto et al. method predicts a timing difference of 5-11 min. We did not detect an early ingress in our three nights of near-UV observations, despite an average cadence of 68 s and an average photometric precision of 3.7 mmag. However, we determined an upper limit of TrES-3b's magnetic field strength to range between 0.013 and 1.3 G (for a 1-100 G magnetic field strength range for the host star, TrES-3) using a timing difference of 138 s derived from the Nyquist-Shannon sampling theorem. To verify our results of an abnormally small magnetic field strength for TrES-3b and to further constrain the techniques of Vidotto et al., we propose future observations of TrES-3b with other platforms capable of achieving a shorter near-UV cadence. We also present a refinement of the physical parameters of TrES-3b, an updated ephemeris and its first published near-UV light curve. We find that the near-UV planetary radius of Rp = 1.386+ 0.248- 0.144 RJup is consistent with the planet's optical radius.

  6. Dependence of energy levels and optical transitions on layer thicknesses in InSe/GaSe superlattices

    NASA Astrophysics Data System (ADS)

    Erkoç, Şakir; Katırcıoğlu, Şenay

    1998-01-01

    We have investigated the dependence of energy levels and optical transition matrix elements in InSe/GaSe superlattices on well and/or barrier widths. Self-consistent-field calculations have been performed within the effective-mass theory approximation.

  7. Optical and structural study of the pressure-induced phase transition of CdWO4

    NASA Astrophysics Data System (ADS)

    Ruiz-Fuertes, J.; Friedrich, A.; Errandonea, D.; Segura, A.; Morgenroth, W.; Rodríguez-Hernández, P.; Muñoz, A.; Meng, Y.

    2017-05-01

    The optical absorption of CdWO4 is reported at high pressures up to 23 GPa. The onset of a phase transition was detected at 19.5 GPa, in good agreement with a previous Raman spectroscopy study. The crystal structure of the high-pressure phase of CdWO4 was solved at 22 GPa, employing single-crystal synchrotron x-ray diffraction. The symmetry changes from space group P 2 /c in the low-pressure wolframite phase to P 21/c in the high-pressure postwolframite phase accompanied by a doubling of the unit-cell volume. The octahedral oxygen coordination of the tungsten and cadmium ions is increased to [7]-fold and [6+1]-fold, respectively, at the phase transition. The compressibility of the low-pressure phase of CdWO4 has been reevaluated with powder x-ray diffraction up to 15 GPa, finding a bulk modulus of B0=123 GPa. The direct band gap of the low-pressure phase increases with compression up to 16.9 GPa at 12 meV/GPa. At this point an indirect band gap crosses the direct band gap and decreases at -2 meV/GPa up to 19.5 GPa where the phase transition starts. At the phase transition the band gap collapses by 0.7 eV and another direct band gap decreases at -50 meV/GPa up to the maximum measured pressure. The structural stability of the postwolframite structure is confirmed by ab initio calculations, finding the postwolframite-type phase to be more stable than the wolframite at 18 GPa. Lattice dynamic calculations based on space group P 21/c explain well the Raman-active modes previously measured in the high-pressure postwolframite phase. The pressure-induced band gap crossing in the wolframite phase as well as the pressure dependence of the direct band gap in the high-pressure phase are further discussed with respect to the calculations.

  8. Measurement of the Yb I S10-P11 transition frequency at 399 nm using an optical frequency comb

    NASA Astrophysics Data System (ADS)

    Kleinert, Michaela; Gold Dahl, M. E.; Bergeson, Scott

    2016-11-01

    We determine the frequency of the Yb I S10-P11 transition at 399 nm using an optical frequency comb. Although this transition was measured previously using an optical transfer cavity [D. Das et al., Phys. Rev. A 72, 032506 (2005), 10.1103/PhysRevA.72.032506], recent work has uncovered significant errors in that method. We compare our result of 751 526 533.49 ± 0.33 MHz for the 174Yb isotope with those from the literature and discuss observed differences. We verify the correctness of our method by measuring the frequencies of well-known transitions in Rb and Cs, and by demonstrating proper control of systematic errors in both laser metrology and atomic spectroscopy. We also demonstrate the effect of quantum interference due to hyperfine structure in a divalent atomic system and present isotope shift measurements for all stable isotopes.

  9. Laminar microvascular transit time distribution in the mouse somatosensory cortex revealed by Dynamic Contrast Optical Coherence Tomography.

    PubMed

    Merkle, Conrad W; Srinivasan, Vivek J

    2016-01-15

    The transit time distribution of blood through the cerebral microvasculature both constrains oxygen delivery and governs the kinetics of neuroimaging signals such as blood-oxygen-level-dependent functional Magnetic Resonance Imaging (BOLD fMRI). However, in spite of its importance, capillary transit time distribution has been challenging to quantify comprehensively and efficiently at the microscopic level. Here, we introduce a method, called Dynamic Contrast Optical Coherence Tomography (DyC-OCT), based on dynamic cross-sectional OCT imaging of an intravascular tracer as it passes through the field-of-view. Quantitative transit time metrics are derived from temporal analysis of the dynamic scattering signal, closely related to tracer concentration. Since DyC-OCT does not require calibration of the optical focus, quantitative accuracy is achieved even deep in highly scattering brain tissue where the focal spot degrades. After direct validation of DyC-OCT against dilution curves measured using a fluorescent plasma label in surface pial vessels, we used DyC-OCT to investigate the transit time distribution in microvasculature across the entire depth of the mouse somatosensory cortex. Laminar trends were identified, with earlier transit times and less heterogeneity in the middle cortical layers. The early transit times in the middle cortical layers may explain, at least in part, the early BOLD fMRI onset times observed in these layers. The layer-dependencies in heterogeneity may help explain how a single vascular supply manages to deliver oxygen to individual cortical layers with diverse metabolic needs.

  10. The Influence of the Aspheric Profiles for Transition Zone on Optical Performance of Human Eye After Conventional Ablation

    NASA Astrophysics Data System (ADS)

    Fang, L.

    2014-12-01

    The analysis in the impact of transition zone on the optical performance of human eye after laser refractive surgery is important for improving visual correction technology. By designing the ablation profiles of aspheric transition zone and creating the ablation profile for conventional refractive surgery in optical zone, the influence of aspheric transition zone on residual aberrations was studied. The results indicated that the ablation profiles of transition zone had a significant influence on the residual wavefront aberrations. For a hyperopia correction, the profile #9 shows a larger induced coma and spherical aberration when the translation of the centre of pupil remains constant. However, for a myopia astigmatism correction, the induced coma and spherical aberration in profile #1 shows relatively larger RMS values than those in other profiles. Therefore, the residual higher order aberrations may be decreased by optimizing ablation profiles of transition zone, but they cannot be eliminated. In order to achieve the best visual performance, the design of ablation pattern of transition zone played a crucial role.

  11. Optically controlled waveplate at a telecom wavelength using a ladder transition in Rb atoms for all-optical switching and high speed Stokesmetric imaging.

    PubMed

    Krishnamurthy, Subramanian; Tu, Y; Wang, Y; Tseng, S; Shahriar, M S

    2014-11-17

    We demonstrate an optically controlled waveplate at ~1323 nm using the 5S(1/2)-5P(1/2)-6S(1/2) ladder transition in a Rb vapor cell. The lower leg of the transitions represents the control beam, while the upper leg represents the signal beam. We show that we can place the signal beam in any arbitrary polarization state with a suitable choice of polarization of the control beam. Specifically, we demonstrate a differential phase retardance of ~180 degrees between the two circularly polarized components of a linearly polarized signal beam. We also demonstrate that the system can act as a Quarter Wave plate. The optical activity responsible for the phase retardation process is explained in terms of selection rules involving the Zeeman sublevels. As such, the system can be used to realize a fast Stokesmetric imaging system with a speed of ~3 MHz. When implemented using a tapered nano fiber embedded in a vapor cell, this system can be used to realize an ultra-low power all-optical switch as well as a Quantum Zeno Effect based all-optical logic gate by combining it with an optically controlled polarizer, previously demonstrated by us. We present numerical simulations of the system using a comprehensive model which incorporates all the relevant Zeeman sub-levels in the system, using a novel algorithm recently developed by us for efficient computation of the evolution of an arbitrary large scale quantum system.

  12. Modelling for Transient Optically Induced Metal - Transitions in Narrow-Gap Semiconductors and Semimetals.

    NASA Astrophysics Data System (ADS)

    Vidal, Jordina

    1994-01-01

    The theoretical work presented in this thesis is based on models developed to interpret a series of optical experiments with short-pulse lasers, which allow a time -domain study of phenomena on a sub-picosecond timescale. By means of a pump-probe technique, we observe large amplitude oscillations in the time domain reflectivity response of a series of narrow-gap semiconductors and semimetals. The oscillations have the frequency of the fully-symmetric optical phonon mode of the system, and are maximally displaced from their midpoint value at zero time delay between pump and probe. These features indicate that a coherent phonon vibration is generated in these materials via an electronic excitation at different points of the Brillouin zone, which displaces instantaneously the equilibrium positions of the atoms. It is precisely this generation of coherent phonons that makes the time-domain technique distinct from conventional frequency domain techniques, such as Raman and neutron scattering. Using a range of theoretical techniques, from nearly free electron models to state-of-the art ab initio calculations, I have made quantitative microscopic evaluations of the coherent phonon phenomenon. The studies focus on two unique aspects of having such coherent atomic vibrations in a narrow gap material, with special emphasis on the group V semimetals Sb and Bi. First of all, I have performed dynamical band structure calculations, as a function of the coherent atomic motion, in order to inspect the possibility of a transient metal-insulator transition at a terahertz frequency. Secondly, I have calculated the evolution of the displaced atoms in quasi-equilibrium with the laser -excited carriers, as the electron-ion coupled system returns to its ground state equilibrium. These calculations are fundamental, insofar they provide a quantitative microscopic description of the coherent phonon phenomenon. Moreover, the predicted magnitude of the atomic displacements, and the resulting

  13. Colonic motor abnormalities in slow transit constipation defined by high resolution, fibre-optic manometry.

    PubMed

    Dinning, P G; Wiklendt, L; Maslen, L; Patton, V; Lewis, H; Arkwright, J W; Wattchow, D A; Lubowski, D Z; Costa, M; Bampton, P A

    2015-03-01

    Slow transit constipation (STC) is associated with colonic motor abnormalities. The underlying cause(s) of the abnormalities remain poorly defined. In health, utilizing high resolution fiber-optic manometry, we have described a distal colonic propagating motor pattern with a slow wave frequency of 2-6 cycles per minute (cpm). A high calorie meal caused a rapid and significant increase in this activity, suggesting the intrinsic slow wave activity could be mediated by extrinsic neural input. Utilizing the same protocol our aim was to characterize colonic meal response STC patients. A fiber-optic manometry catheter (72 sensors at 1 cm intervals) was colonoscopically placed with the tip clipped at the ascending or transverse colon, in 14 patients with scintigraphically confirmed STC. Manometric recordings were taken, for 2 h pre and post a 700 kCal meal. Data were compared to 12 healthy adults. Prior to and/or after the meal the cyclic propagating motor pattern was identified in 13 of 14 patients. However, the meal, did not increase the cyclic motor pattern (preprandial 7.4 ± 7.6 vs postprandial 8.3 ± 4.5 per/2 h), this is in contrast to the dramatic increase observed in health (8.3 ± 13.3 vs 59.1 ± 89.0 per/2 h; p < 0.001). In patients with STC a meal fails to induce the normal increase in the distal colonic cyclic propagating motor patterns. We propose that these data may indicate that the normal extrinsic parasympathetic inputs to the colon are attenuated in these patients. © 2015 John Wiley & Sons Ltd.

  14. Dynamic contrast optical coherence tomography: quantitative measurement of microvascular transit-time distributions in vivo (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Merkle, Conrad W.; Srinivasan, Vivek J.

    2016-03-01

    Transit time is a fundamental microcirculatory parameter that is critical in determining oxygen delivery from capillaries to surrounding tissue. Recently, it was demonstrated theoretically that capillary transit-time heterogeneity potentially leads to non-uniform oxygen extraction in micro-domains. However, in spite of its importance, capillary transit-time distribution has been challenging to quantify comprehensively and efficiently at the microscopic level. Here, we introduce a method, called Dynamic Contrast Optical Coherence Tomography (DyC-OCT), based on dynamic cross-sectional OCT imaging of the kinetics of an intravascular tracer during its passage through the field-of-view. DyC-OCT is used to quantitatively measure the transit-time distribution in microvascular networks in cross-section at the single-capillary level. Transit-time metrics are derived from analysis of the temporal characteristics of the dynamic scattering signal, related to tracer concentration, using indicator-dilution theory. Since DyC-OCT does not require calibration of the optical focus, quantitative accuracy is achieved even deep in highly scattering brain tissue where the focal spot degrades. After direct validation of DyC-OCT against the dilution curves measured using a fluorescent plasma label in the surface pial vessels of a mouse brain, imaged through a thinned-skull, glass coverslip-reinforced cranial window, the laminar transit-time distribution was investigated in microvasculature across the entire depth of the mouse somatosensory cortex. Laminar trends were identified, with the earliest transit times in the middle cortical layers, and the lowest heterogeneity in cortical layer 4. The new DyC-OCT technique affords a novel perspective of microvascular networks, with the unique capability of performing simultaneous measurements of transit-time distributions across cortical laminae.

  15. Frequency stabilization of a 1083 nm fiber laser to {sup 4}He transition lines with optical heterodyne saturation spectroscopies

    SciTech Connect

    Gong, W.; Peng, X. Li, W.; Guo, H.

    2014-07-15

    Two kinds of optical heterodyne saturation spectroscopies, namely, frequency modulation spectroscopy (FMS) and modulation transfer spectroscopy (MTS), are demonstrated for locking a fiber laser to the transition lines of metastable {sup 4}He atoms around 1083 nm. The servo-loop error signals of FMS and MTS for stabilizing laser frequency are optimized by studying the dependence of the peak-to-peak amplitude and slope on the optical power of pump and probe beams. A comparison of the stabilization performances of FMS/MTS and polarization spectroscopy (PS) is presented, which shows that MTS exhibits relatively superior performance with the least laser frequency fluctuation due to its flat-background dispersive signal, originated from the four-wave mixing process. The Allan deviation of the stabilized laser frequency is 5.4 × 10{sup −12}@100 s with MTS for data acquired in 1000 s, which is sufficiently applicable for fields like laser cooling, optical pumping, and optical magnetometry.

  16. Frequency stabilization of a 1083 nm fiber laser to 4He transition lines with optical heterodyne saturation spectroscopies

    NASA Astrophysics Data System (ADS)

    Gong, W.; Peng, X.; Li, W.; Guo, H.

    2014-07-01

    Two kinds of optical heterodyne saturation spectroscopies, namely, frequency modulation spectroscopy (FMS) and modulation transfer spectroscopy (MTS), are demonstrated for locking a fiber laser to the transition lines of metastable 4He atoms around 1083 nm. The servo-loop error signals of FMS and MTS for stabilizing laser frequency are optimized by studying the dependence of the peak-to-peak amplitude and slope on the optical power of pump and probe beams. A comparison of the stabilization performances of FMS/MTS and polarization spectroscopy (PS) is presented, which shows that MTS exhibits relatively superior performance with the least laser frequency fluctuation due to its flat-background dispersive signal, originated from the four-wave mixing process. The Allan deviation of the stabilized laser frequency is 5.4 × 10-12@100 s with MTS for data acquired in 1000 s, which is sufficiently applicable for fields like laser cooling, optical pumping, and optical magnetometry.

  17. Effect of MWCNTs on the electro-optic properties of 5CB LC cells during the Freedericksz Transition

    NASA Astrophysics Data System (ADS)

    Eakle, Matthew; Georgiev, Georgi; Atherton, Timothy; Cebe, Peggy

    2014-03-01

    Multi-walled carbon nanotubes (MWCNTs) affect the electro-optic properties of liquid crystals, but the mechanisms of interaction between the two remain not well understood. To address this, we are investigating the effect of alternating electric fields on the optical properties and Freedericksz Transition of 5CB liquid crystal with different concentrations of MWCNTs. 5CB cells with ITO electrodes were made using spin-coated PVA for sample alignment and MylarTM spacer films to control the thickness, which ranged from 12 to 23 microns. Transmission optical ellipsometry was used to measure the optical retardance (phase delay) and uniaxial director angle of 5CB liquid crystals as the peak voltage of a high-frequency (1 kHz - 1 MHz) AC electric field was varied from 0 to 10 V. For constant frequency, the Freedericksz Transition was noted by a sharp decrease in retardance from an initial plateau, which gradually decreased toward zero as the voltage increased. With increasing frequency, the decay broadened and the Freedericksz Transition occurred at higher voltage. Numerical simulations of CNT-facilitated switching are also presented. Research was funded by the National Science Foundation, Polymers Program of the Division of Materials Research, through DMR-12061010.

  18. Optical response from terahertz to visible light of electronuclear transitions in LiYF4:Ho3 +

    NASA Astrophysics Data System (ADS)

    Matmon, G.; Lynch, S. A.; Rosenbaum, T. F.; Fisher, A. J.; Aeppli, G.

    2016-11-01

    Because of its role as a model system with tunable quantum fluctuations and quenched disorder, and the desire for optical control and readout of its states, we have used high-resolution optical absorption spectroscopy to measure the crystal-field excitations for Ho3 + ions in LiHoxY1 -xF4 from the terahertz to visible regimes. We show that many of the excitations yield very narrow lines visibly split even by the nuclear hyperfine interaction, making Ho3 + in LiHoxY1 -xF4 a candidate host for optically addressable electronuclear qubits with quality factors as high as Q =4.7 ×105 , where the higher-lying levels are electronic singlets. Optical transitions in the easily accessible near- and mid-infrared are narrow enough to allow readout of the ground-state electronuclear qubits responsible for the interesting magnetism of LiHoxY1 -xF4 . While many of the higher-lying states have been observed previously, we also report here detailed spectra of terahertz excitations. The strengths of the electric and magnetic dipole crystal-field transition lines of five of the lowest excited spin-orbit manifolds of dilute LiYF4:Ho3 + were calculated and compared with measurement. The magnitude of the nuclear hyperfine coupling was used to assign the correct upper and lower states to transition lines.

  19. Optical signatures of electric-field-driven magnetic phase transitions in graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Basak, Tista; Shukla, Alok

    2016-06-01

    Experimental challenges in identifying various types of magnetic ordering in graphene quantum dots (QDs) pose a major hurdle in the application of these nanostructures for spintronic devices. Based upon phase diagrams obtained by employing the π -electron Pariser-Parr-Pople (PPP) model Hamiltonian, we demonstrate that the magnetic states undergo phase transition under the influence of an external electric field. Our calculations of the electroabsorption spectra of these QDs indicate that the spectrum in question carries strong signatures of their magnetic state (FM vs AFM), thus suggesting the possibility of an all-optical characterization of their magnetic nature. Further, the gaps for the up and the down spins are the same in the absence of an external electric field, both for the antiferromagnetic (AFM) and the ferromagnetic (FM) states of QDs. But, once the QDs are exposed to a suitably directed external electric field, gaps for different spins split and exhibit distinct variations with respect to the strength of the field. The nature of variation exhibited by the energy gaps corresponding to the up and down spins is different for the AFM and FM configurations of QDs. This selective manipulation of the spin-polarized gap splitting by an electric field in finite graphene nanostructures can open up new frontiers in the design of graphene-based spintronic devices.

  20. Laser driven intraband optical transitions in two-dimensional quantum dots and quantum rings

    NASA Astrophysics Data System (ADS)

    Barseghyan, M. G.; Kirakosyan, A. A.; Laroze, D.

    2017-01-01

    The intraband optical absorption have been investigated in the presence of hydrogenic donor impurity in GaAs/GaAlAs quantum dot and quantum ring in the intense laser field. The single electron energy spectrum and wave functions have been found using the effective mass approximation and exact diagonalization technique. Different selection rules are obtained for intraband transitions depending on the direction of incident light polarization. Due to the accidental degeneracy of the laser dressed impurity states the crossings of the curves of the threshold energies and the dipole matrix elements on laser field parameter have been observed. The intraband absorption coefficient is calculated for different locations of hydrogenic donor impurity and different values of intense laser field parameter. The obtained results show that the absorption spectrum can exhibit either a blue- or redshift depending on the impurity location, values of the laser field parameter and direction of incident light polarization. The obtained theoretical results indicate a novel opportunity to tune the performance of new devices, based on the quantum dots and quantum rings and to control their specific properties by means of intense laser and hydrogenic donor impurity.

  1. Phase controlled metal-insulator transition in multi-leg quasiperiodic optical lattices

    NASA Astrophysics Data System (ADS)

    Maiti, Santanu K.; Sil, Shreekantha; Chakrabarti, Arunava

    2017-07-01

    A tight-binding model of a multi-leg ladder network with a continuous quasiperiodic modulation in both the site potential and the inter-arm hopping integral is considered. The model mimics optical lattices where ultra-cold fermionic or bosonic atoms are trapped in double well potentials. It is observed that, the relative phase difference between the on-site potential and the inter-arm hopping integral, which can be controlled by the tuning of the interfering laser beams trapping the cold atoms, can result in a mixed spectrum of one or more absolutely continuous subband(s) and point like spectral measures. This opens up the possibility of a re-entrant metal-insulator transition. The subtle role played by the relative phase difference mentioned above is revealed, and we corroborate it numerically by working out the multi-channel electronic transmission for finite two-, and three-leg ladder networks. The extension of the calculation beyond the two-leg case is trivial, and is discussed in the work.

  2. Theoretical considerations on imaging of micron size electron beam with optical transition radiation

    NASA Astrophysics Data System (ADS)

    Xiang, Dao; Huang, Wen-Hui

    2007-01-01

    Optical transition radiation (OTR) has been widely used to image electron beam profile. In this paper, we systematically investigated the issues related to imaging of electron beam with OTR. It is found that the point-spread function (PSF) largely depends on the acceptance angle of the lens and is only very weakly dependent on beam energy and the distance from the OTR target to the lens. This excludes the potential obstacles to imaging of high-energy electron beam for which, the photons are emitted in a relatively small cone and the far field condition is hard to fulfill. The image of a whole beam is found by convoluting the real beam distribution with the PSF. It is shown that for micron size beam, the image formed with OTR largely deviates from the real beam distribution. And the real beam distribution could be restored from deconvoluting the image with the PSF. The effectiveness of the restoration is demonstrated, which opens up the possibility of measuring micron size beam profile with OTR.

  3. Characterization of Fast-Electron Beam Propagation Through Solid-Density Matter by Optical Transition Radiation

    NASA Astrophysics Data System (ADS)

    Storm, M.; Myatt, J.; Stoeckl, C.

    2006-10-01

    A diagnostic has been developed to measure the emission of optical transition radiation (OTR) produced by relativistic electrons emerging at the rear side of laser-illuminated targets. The device will be deployed in the newly completed multiterawatt (MTW) experimental facility at the University of Rochester's Laboratory for Laser Energetics. The MTW laser is capable of producing 10-J, 600-fs pulses of 1053-nm-wavelength radiation, which are focused using an f/2 off-axis parabolic mirror to intensities in excess of 10^19 Wcm-2. A 20x microscope objective with a resolution of better than 1 μm will image the OTR signal onto a CCD camera. A postprocessor to the particle-in-cell code LSP will be used to generate a simulated OTR signal from the calculated fast-electron distributions at the rear side of the target for comparison with experimental data. This talk will present the characteristics and capabilities of the OTR device along with the most recently acquired data. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-92SF19460.

  4. Optical spectroscopy in turbid media utilizing an integrating sphere: mitochondrial chromophore analysis during metabolic transitions

    PubMed Central

    Chess, David J.; Billings, Eric; Covian, Raúl; Glancy, Brian; French, Stephanie; Taylor, Joni; de Bari, Heather; Murphy, Elizabeth; Balaban, Robert S.

    2013-01-01

    Recent evidence suggests that the activity of mitochondrial oxidative phosphorylation Complexes (MOPC) is modulated at multiple sites. Herein, a method of optically monitoring electron distribution within and between MOPC is described using a center-mounted sample in an integrating sphere (to minimize scattering effects) with a rapid-scanning spectrometer. The redox-sensitive MOPC absorbances (~465 to 630 nm) were modeled using linear least squares analysis with individual chromophore spectra. Classical mitochondrial activity transitions (e.g., ADP-induced increase in oxygen consumption) were used to characterize this approach. Most notable in these studies was the observation that intermediates of the catalytic cycle of cytochrome oxidase are dynamically modulated with metabolic state. The MOPC redox state, along with measurements of oxygen consumption and mitochondrial membrane potential, was used to evaluate the conductances of different sections of the electron transport chain. This analysis then was applied to mitochondria isolated from rabbit hearts subjected to ischemia-reperfusion (I/R). Surprisingly, I/R resulted in an inhibition of all measured MOPC conductances, suggesting a coordinated down-regulation of mitochondrial activity with this well-established cardiac perturbation. PMID:23665273

  5. Ionic and Optical Properties of Methylammonium Lead Iodide Perovskite across the Tetragonal-Cubic Structural Phase Transition.

    PubMed

    Hoque, Md Nadim Ferdous; Islam, Nazifah; Li, Zhen; Ren, Guofeng; Zhu, Kai; Fan, Zhaoyang

    2016-09-22

    Practical hybrid perovskite solar cells (PSCs) must endure temperatures above the tetragonal-cubic structural phase transition of methylammonium lead iodide (MAPbI3 ). However, the ionic and optical properties of MAPbI3 in such a temperature range, and particularly, dramatic changes in these properties resulting from a structural phase transition, are not well studied. Herein, we report a striking contrast at approximately 45 °C in the ionic/electrical properties of MAPbI3 owing to a change of the ion activation energy from 0.7 to 0.5 eV, whereas the optical properties exhibit no particular transition except for the steady increase of the bandgap with temperature. These observations can be explained by the "continuous" nature of perovskite phase transition. We speculate that the critical temperature at which the ionic/electrical properties change, although related to crystal symmetry variation, is not necessarily the same temperature as when tetragonal-cubic structural phase transition occurs. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Ionic and Optical Properties of Methylammonium Lead Iodide Perovskite across the Tetragonal-Cubic Structural Phase Transition

    SciTech Connect

    Hoque, Md Nadim Ferdous; Islam, Nazifah; Li, Zhen; Ren, Guofeng; Zhu, Kai; Fan, Zhaoyang

    2016-09-01

    Practical hybrid perovskite solar cells (PSCs) must endure temperatures above the tetragonal-cubic structural phase transition of methylammonium lead iodide (MAPbI3). However, the ionic and optical properties of MAPbI3 in such a temperature range, and particularly, dramatic changes in these properties resulting from a structural phase transition, are not well studied. Herein, we report a striking contrast at approximately 45 degrees C in the ionic/electrical properties of MAPbl3 owing to a change of the ion activation energy from 0.7 to 0.5 eV, whereas the optical properties exhibit no particular transition except for the steady increase of the bandgap with temperature. These observations can be explained by the 'continuous' nature of perovskite phase transition. We speculate that the critical temperature at which the ionic/electrical properties change, although related to crystal symmetry variation, is not necessarily the same temperature as when tetragonal-cubic structural phase transition occurs.

  7. Multiphonon scattering of light with direct transitions between optical modes in uniaxial single crystals and its application to an all-optical computing

    NASA Astrophysics Data System (ADS)

    Shcherbakov, Alexandre S.; Tepichin Rodriguez, Eduardo; Aguirre Lopez, Arturo

    2004-11-01

    A specific case of a multi-phonon non-collinear light scattering in optically uniaxial media is presented. Compared to our previous studies, an innovation lies in the fact that now we consider passing just the quartet of incident light beams through a single crystal that is perturbed by the triplet of coherent acoustic waves. The exact and closed analytical model for describing this strongly nonlinear phenomenon is developed. In fact, specially designed regime of a four-order light scattering whit direct coupling of all the light modes, when transitions of four input light beams into four output light modes are allowed and electronically controlled, is examined. The feasibility of applying such an effect to an all-optical computing and performing an all-optical adder is analyzed.

  8. Dynamical quantum phase transition of a two-component Bose-Einstein condensate in an optical lattice

    SciTech Connect

    Collin, Anssi; Martikainen, Jani-Petri; Larson, Jonas

    2010-01-15

    We study the dynamics of a two-component Bose-Einstein condensate where the two components are coupled via an optical lattice. In particular, we focus on the dynamics as one drives the system through a critical point of a first-order phase transition characterized by a jump in the internal populations. Solving the time-dependent Gross-Pitaevskii equation, we analyze the breakdown of adiabaticity, impact of nonlinear atom-atom scattering, and role of a harmonic trapping potential. Our findings demonstrate that the phase transition is resilient to both contact interaction between atoms and external trapping confinement.

  9. Sub-Doppler spectroscopy based on optical pumping and transit relaxation of atoms in a thin gas cell

    NASA Astrophysics Data System (ADS)

    Izmailov, Azad Ch.

    2007-06-01

    The paper is the review of methods, achievements, and possibilities of the recently elaborated and well tested high-resolution laser spectroscopy based on sub-Doppler absorption and polarization resonances (on centers of quantum transitions), which arise because of the optical pumping and specific transit relaxation of atoms (molecules) in a thin cell with a rarefied gas. Theoretical basis of this spectroscopy is presented. Experimental technique and results on the record of the sub-Doppler spectral structure of Cs and Rb atoms and on the frequency stabilization of diode lasers by given spectroscopy methods are discussed.

  10. Interband optical transition energy and oscillator strength in a lead based CdSe quantum dot quantum well heterostructure

    SciTech Connect

    Saravanamoorthy, S. N.; Peter, A. John

    2015-06-24

    Binding energies of the exciton and the interband optical transition energies are studied in a CdSe/Pb{sub 1-x}Cd{sub x}Se/CdSe spherical quantum dot-quantum well nanostructure taking into account the geometrical confinement effect. The core and shell are taken as the same material. The initial and final states of energy and the overlap integrals of electron and hole wave functions are determined by the oscillator strength. The oscillator strength and the radiative transition life time with the dot radius are investigated for various Cd alloy content in the core and shell materials.

  11. Identifying and discriminating phase transitions along decaying shocks with line imaging Doppler interferometric velocimetry and streaked optical pyrometry

    SciTech Connect

    Millot, Marius

    2016-01-15

    Ultrafast line-imaging velocity interferometer system for any reflector and streaked optical pyrometry are now commonly used to obtain high precision equation of state and electronic transport data under dynamic compression at major high energy density science facilities. We describe a simple way to improve distinguishing phase transformation signatures from other signals when monitoring decaying shock waves. The line-imaging capability of these optical diagnostics offers additional supporting evidence to the assignment of particular anomalies—such as plateaus or reversals—to the occurrence of a phase transition along the Hugoniot. We illustrate the discussion with two example datasets collected during laser driven shock compression of quartz and stishovite.

  12. Identifying and discriminating phase transitions along decaying shocks with line imaging Doppler interferometric velocimetry and streaked optical pyrometry

    NASA Astrophysics Data System (ADS)

    Millot, Marius

    2016-01-01

    Ultrafast line-imaging velocity interferometer system for any reflector and streaked optical pyrometry are now commonly used to obtain high precision equation of state and electronic transport data under dynamic compression at major high energy density science facilities. We describe a simple way to improve distinguishing phase transformation signatures from other signals when monitoring decaying shock waves. The line-imaging capability of these optical diagnostics offers additional supporting evidence to the assignment of particular anomalies—such as plateaus or reversals—to the occurrence of a phase transition along the Hugoniot. We illustrate the discussion with two example datasets collected during laser driven shock compression of quartz and stishovite.

  13. Structural phase transition, electronic structure and optical properties of half Heusler alloys LiBeZ (Z = As, Sb)

    SciTech Connect

    Amudhavalli, A.; Rajeswarapalanichamy, R.

    2016-05-23

    Ab initio calculations are performed to investigate the structural stability, electronic structure, mechanical properties and optical properties of half Heusler alloys (LiBeAs and LiBeSb) for three different phases of zinc blende crystal structure. Among the considered phases, α- phase is found to be the most stable phase for these alloys at normal pressure. A pressure induced structural phase transition from α-phase to β- phase is observed for LiBeAs. The electronic structure reveals that these alloys are semiconductors. The optical properties confirm that these alloys are semiconductor in nature.

  14. Dynamic contrast optical coherence tomography images transit time and quantifies microvascular plasma volume and flow in the retina and choriocapillaris

    PubMed Central

    Merkle, Conrad W.; Leahy, Conor; Srinivasan, Vivek J.

    2016-01-01

    Despite the prevalence of optical imaging techniques to measure hemodynamics in large retinal vessels, quantitative measurements of retinal capillary and choroidal hemodynamics have traditionally been challenging. Here, a new imaging technique called dynamic contrast optical coherence tomography (DyC-OCT) is applied in the rat eye to study microvascular blood flow in individual retinal and choroidal layers in vivo. DyC-OCT is based on imaging the transit of an intravascular tracer dynamically as it passes through the field-of-view. Hemodynamic parameters can be determined through quantitative analysis of tracer kinetics. In addition to enabling depth-resolved transit time, volume, and flow measurements, the injected tracer also enhances OCT angiograms and enables clear visualization of the choriocapillaris, particularly when combined with a post-processing method for vessel enhancement. DyC-OCT complements conventional OCT angiography through quantification of tracer dynamics, similar to fluorescence angiography, but with the important added benefit of laminar resolution. PMID:27867732

  15. Glass Former Effects on Photoluminescence and Optical Properties of Some Heavy Metal Oxide Glasses Doped with Transition Metal Ions

    NASA Astrophysics Data System (ADS)

    Marzouk, M. A.; Abo-Naf, S. M.; Zayed, H. A.; Hassan, N. S.

    2017-03-01

    Heavy metal oxide (PbO and Bi2O3) glasses doped with transition metal (TM) ions (TiO2, V2O5, Cr2O3, and MnO2) and having low content of common glass formers (B2O3, SiO2, or P2O5) were prepared by the conventional melt annealing method. Ultraviolet, visible absorption, and photoluminescence properties of these glasses were measured, and the data were employed to investigate the prepared glassy samples. The optical absorption spectra of TiO2 and V2O5 exhibited three bands centered at about 240, 305, and 380 nm, followed by a broad asymmetrical near-visible band centered at 425-432 nm, while Cr2O3 and MnO2 exhibited an extended visible peak at 517-548 nm. Results showed that the luminescence intensity changed with different transition metal oxides. From the absorption edge data, the values of the optical band gap Eopt and Urbach energy (ΔE) were calculated. The calculated values of the optical energy gap were found to be dependent on the glass composition. The changing values of optical band gap and band tail can be related to the structural changes that are taking place in the glass samples. The variations of the luminescence intensity, values of optical band gap, band tail, and refractive index gave an indication of the potential use of the prepared glasses to design novel optical functional materials with higher optical performance.

  16. Bio-optical profile data report coastal transition zone program, R/V Point Sur, June 15-28, 1987

    NASA Technical Reports Server (NTRS)

    Davis, Curtiss O.; Rhea, W. Joseph

    1990-01-01

    Twenty vertical profiles of the bio-optical properties of the ocean were made during a research cruise on the R/V Point Sur, June 15 to 28, 1987, as part of the Coastal Transition Zone Program off Point Arena, California. Extracted chlorophyll values were also measured at some stations to provide calibration data for the in situ fluorometer. This summary provides investigators with an overview of the data collected. The entire data set is available in digital form.

  17. On the size-dependent magnetism and all-optical magnetization switching of transition-metal silicide nanostructures

    SciTech Connect

    Glushkov, G. I.; Tuchin, A. V.; Popov, S. V.; Bityutskaya, L. A.

    2015-12-15

    Theoretical investigations of the electronic structure, synthesis, and all-optical magnetization switching of transition-metal silicide nanostructures are reported. The magnetic moment of the nanostructures is studied as a function of the silicide cluster size and configuration. The experimentally demonstrated magnetization switching of nanostructured nickel silicide by circularly polarized light makes it possible to create high-speed storage devices with high density data recording.

  18. Bio-optical profile data report coastal transition zone program, R/V Thomas Washington, June 24 - July 21, 1988

    NASA Technical Reports Server (NTRS)

    Davis, Curtiss O.; Rhea, W. Joseph

    1990-01-01

    Twenty-three vertical profiles of the bio-optical properties of the ocean were made during a research cruise on the R/V Thomas Washington, June 24 to July 21, 1988, as part of the Coastal Transition Zone Program off Point Arena, California. A summary is given, to provide investigators with an overview of the data collected. The entire data set is available in digital form for interested researchers.

  19. Mg doping of thermochromic VO2 films enhances the optical transmittance and decreases the metal-insulator transition temperature

    NASA Astrophysics Data System (ADS)

    Mlyuka, N. R.; Niklasson, G. A.; Granqvist, C. G.

    2009-10-01

    Thermochromic films of MgxV1-xO2 were made by reactive dc magnetron sputtering onto heated glass. The metal-insulator transition temperature decreased by ˜3 K/at. %Mg, while the optical transmittance increased concomitantly. Specifically, the transmittance of visible light and of solar radiation was enhanced by ˜10% when the Mg content was ˜7 at. %. Our results point at the usefulness of these films for energy efficient fenestration.

  20. Thermophysical, Electrical, and Optical Properties of Selected Metal-Nonmetal Transition Materials: Comprehensive Bibliography with Typical Data.

    DTIC Science & Technology

    1978-02-01

    ELECTRICAL, AND OPTICAL PROPERTIES OF SELECTED METAL-NONMETAL TRANSITION MATERIALS Comprehensive Bibliography with Typical Data Y. S. TOULOUKIAN , C. Y. HO, and...volume entitled "Thermo-Iphysical Properties of Selected Aerospace Materials. Part II: Thermophysical Properties of Seven Materials." Y. S. TOULOUKIAN ...Kolomoets, N.V., and Ovechkina, V.N., "Preparation and Study of the Properties of Samarium(II) Sulfide-Based Alloys ," Izv. Akad. Nauk SSSR, Neorg

  1. Optical transitions in semiconductor nanospherical core/shell/shell heterostructure in the presence of radial electrostatic field

    NASA Astrophysics Data System (ADS)

    Baghdasaryan, D. A.; Hayrapetyan, D. B.; Harutyunyan, V. A.

    2017-04-01

    The electronic states and optical properties of spherical nanolayer in the presence of the electrostatic radial field in the strong size quantization regime have been considered. Both analytical and numerical methods have been applied to the problem of one-electron states in the system. According to the intensity of the external electrostatic field, three regimes have been distinguished: week, intermediate and strong. Perturbative approach have been applied to the case of week, WKB to the case of intermediate and variation approach to the case of strong field intensities. The analytical dependencies of the one electron energy and wave function on the electric field value and geometrical parameters of the nanolayer have been achieved. The comparison of the results obtained by the analytical method with the results of the numerical method have been made. The interband and intraband optical transitions caused by incident optical light polarized in z direction have been considered in this system. The selection rules for this transitions have been obtained. The dependence of the absorption coefficient on the energy of incident light for both cases of interband and intraband transitions for every regime of the electrostatic field value have been received.

  2. Native defects as sources of optical transitions in MgAl2O4 spinel

    NASA Astrophysics Data System (ADS)

    Borges, P. D.; Cott, J.; Pinto, F. G.; Tronto, J.; Scolfaro, L.

    2016-07-01

    The outstanding physical and chemical properties of the magnesium aluminate (MgAl2O4) spinel makes it an important material for novel technological applications. Considering that a presence of native defects can promote important changes in those properties, in this work we present a study of the structural, electronic and thermodynamic properties of the MgAl2O4 spinel. The calculated formation energy for isolated defects, such as the vacancies of magnesium (V Mg), aluminum (V Al) and oxygen (V O), oxygen interstitial (Oi), magnesium and aluminum antisites (MgAl, AlMg), as well as some complex defects (V O + Oi, V O + AlMg, V O + MgAl, MgAl + AlMg) in the most stable charge states are shown. Through experimental data, we obtained that complex defects centers, such as V O , V O + Oi, V O + AlMg and VO + MgAl at different charge states are good candidates for the observed optical transitions at 4.75, 5.3, and 6.4 eV. Our findings were obtained from ab initio electronic structure calculations performed by using density functional theory. The Perdew-Burke-Ernzerhof generalized gradient approximation was used for the exchange-correlation potential. Furthermore, a modified Becke-Johnson exchange potential (GGA-mBJ) correction to the exchange potential were used to obtain a suitable value for the band gap energy, 7.40 eV, in accordance with the experimental one of 7.8 eV.

  3. Optical-lattice-assisted magnetic phase transition in a spin-orbit-coupled Bose-Einstein condensate

    NASA Astrophysics Data System (ADS)

    Martone, Giovanni I.; Ozawa, Tomoki; Qu, Chunlei; Stringari, Sandro

    2016-10-01

    We investigate the effect of a periodic potential generated by a one-dimensional optical lattice on the magnetic properties of an S =1 /2 spin-orbit-coupled Bose gas. By increasing the lattice strength one can achieve a magnetic phase transition between a polarized and an unpolarized Bloch wave phase, characterized by a significant enhancement of the contrast of the density fringes. If the wave vector of the periodic potential is chosen close to the roton momentum, the transition could take place at very small lattice intensities, revealing the strong enhancement of the response of the system to a weak density perturbation. By solving the Gross-Pitaevskii equation in the presence of a three-dimensional trapping potential, we shed light on the possibility of observing the magnetic phase transition in currently available experimental conditions.

  4. Optical conductivity of visons in Z2 spin liquids close to a valence bond solid transition on the kagome lattice

    NASA Astrophysics Data System (ADS)

    Huh, Yejin; Punk, Matthias; Sachdev, Subir

    2013-06-01

    We consider Z2 spin liquids on the kagome lattice on the verge of a valence bond solid (VBS) transition, where vortex excitations carrying Z2 magnetic flux—so-called visons—condense. We show that these vison excitations can couple directly to the external electromagnetic field, even though they carry neither spin nor charge. This is possible via a magnetoelastic coupling mechanism recently identified. [Potter, Senthil, and Lee, arXiv:1301.3495; Hao, Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.85.174432 85, 174432 (2012)] For the case of transitions to a 36-site unit cell VBS state, the corresponding finite ac conductivity has a specific power-law frequency dependence, which is related to the crossover exponent of the quantum critical point. The visons’ contribution to the optical conductivity at transitions to VBS states with a 12-site unit cell vanishes, however.

  5. Natural optical activity of f-f transitions in ErAl3(BO3)4 single crystal

    NASA Astrophysics Data System (ADS)

    Malakhovskii, A. V.; Sokolov, V. V.; Gudim, I. A.

    2017-08-01

    Absorption and natural circular dichroism (NCD) spectra of ErAl3(BO3)4 single crystal were measured at 90 K in the range of 10,000-28,200 cm-1. The spectra were decomposed on the Lorentz shape components and the natural optical activities (NOA) of f-f transitions between Stark components of the ground and excited multiplets were found. The NCD spectra permitted us to find out existence of two non equivalent positions of Er3+ ion in one of its excited states, which are due to the local decrease of the crystal symmetry in this state. Very large NOA of a vibronic line was revealed. This phenomenon was accounted for basing on the new quantum mechanical formula for the NOA of electron transitions. The principle difference of the NOA properties of electric dipole allowed and parity forbidden transitions is discussed.

  6. Optical properties of VO{sub 2} films at the phase transition: Influence of substrate and electronic correlations

    SciTech Connect

    Peterseim, Tobias; Dressel, Martin; Dietrich, Marc; Polity, Angelika

    2016-08-21

    Thin films of VO{sub 2} on different substrates, Al{sub 2}O{sub 3} and SiO{sub 2}/Si, have been prepared and characterized from room temperature up to 360 K. From the band structure in the rutile metallic phase and in the monoclinic insulating phase, the optical properties are calculated and compared with reflection measurements performed as a function of temperatures. Various interband transitions can be assigned and compared with previous speculations. We extract the parameters of the metallic charge carriers that evolve upon crossing the insulator-to-metal phase transition and find effects by the substrate. The influence of electronic correlations becomes obvious at the phase transition.

  7. Structural phase transition in IrTe2: A combined study of optical spectroscopy and band structure calculations

    PubMed Central

    Fang, A. F.; Xu, G.; Dong, T.; Zheng, P.; Wang, N. L.

    2013-01-01

    Ir1−xPtxTe2 is an interesting system showing competing phenomenon between structural instability and superconductivity. Due to the large atomic numbers of Ir and Te, the spin-orbital coupling is expected to be strong in the system which may lead to nonconventional superconductivity. We grew single crystal samples of this system and investigated their electronic properties. In particular, we performed optical spectroscopic measurements, in combination with density function calculations, on the undoped compound IrTe2 in an effort to elucidate the origin of the structural phase transition at 280 K. The measurement revealed a dramatic reconstruction of band structure and a significant reduction of conducting carriers below the phase transition. We elaborate that the transition is not driven by the density wave type instability but caused by the crystal field effect which further splits/separates the energy levels of Te (px, py) and Te pz bands. PMID:23362455

  8. Performance of horn-coupled transition edge sensors for L- and S-band optical detection on the SAFARI instrument

    NASA Astrophysics Data System (ADS)

    Goldie, D. J.; Glowacka, D. M.; Withington, S.; Chen, Jiajun; Ade, P. A. R.; Morozov, D.; Sudiwala, R.; Trappe, N. A.; Quaranta, O.

    2016-07-01

    We describe the geometry, architecture, dark- and optical performance of ultra-low-noise transition edge sensors as THz detectors for the SAFARI instrument. The TESs are fabricated from superconducting Mo/Au bilayers coupled to impedance-matched superconducting β-phase Ta thin-film absorbers. The detectors have phonon-limited dark noise equivalent powers of order 0.5 - 1.0 aW/ √ Hz and saturation powers of order 20 - 40 fW. The low temperature test configuration incorporating micro-machined backshorts is also described, and construction and typical performance characteristics for the optical load are shown. We report preliminary measurements of the optical performance of these TESs for two SAFARI bands; L-band at 110 - 210 μm and S-band 34 - 60 μm .

  9. Laminar microvascular transit time distribution in the mouse somatosensory cortex revealed by Dynamic Contrast Optical Coherence Tomography

    PubMed Central

    Merkle, Conrad W.; Srinivasan, Vivek J.

    2015-01-01

    The transit time distribution of blood through the cerebral microvasculature both constrains oxygen delivery and governs the kinetics of neuroimaging signals such as blood-oxygen-level-dependent functional Magnetic Resonance Imaging (BOLD fMRI). However, in spite of its importance, capillary transit time distribution has been challenging to quantify comprehensively and efficiently at the microscopic level. Here, we introduce a method, called Dynamic Contrast Optical Coherence Tomography (DyC-OCT), based on dynamic cross-sectional OCT imaging of an intravascular tracer as it passes through the field-of-view. Quantitative transit time metrics are derived from temporal analysis of the dynamic scattering signal, closely related to tracer concentration. Since DyC-OCT does not require calibration of the optical focus, quantitative accuracy is achieved even deep in highly scattering brain tissue where the focal spot degrades. After direct validation of DyC-OCT against dilution curves measured using a fluorescent plasma label in surface pial vessels, we used DyC-OCT to investigate the transit time distribution in microvasculature across the entire depth of the mouse somatosensory cortex. Laminar trends were identified, with earlier transit times and less heterogeneity in the middle cortical layers. The early transit times in the middle cortical layers may explain, at least in part, the early BOLD fMRI onset times observed in these layers. The layer-dependencies in heterogeneity may help explain how a single vascular supply manages to deliver oxygen to individual cortical layers with diverse metabolic needs. PMID:26477654

  10. Variation of optical conductivity spectra in the course of bandwidth-controlled metal-insulator transitions in pyrochlore iridates

    NASA Astrophysics Data System (ADS)

    Ueda, K.; Fujioka, J.; Tokura, Y.

    2016-06-01

    We spectroscopically investigate a series of pyrochlore iridates R2Ir2O7 (R : rare-earth and Y ions) where the metal-insulator transitions are induced by systematic bandwidth control via chemical substitutions of R ions. We establish the phase diagram of R2Ir2O7 , as endorsed by the variation of the optical conductivity spectra, in which the competing phases including paramagnetic insulator (PI), paramagnetic metal (PM), and antiferromagnetic insulator (AFI) show up as a function of bandwidth and temperature. For small R -ionic radius (R = Y-Sm), i.e., strongly correlated region, pronounced peaks on the edge of the optical gap are discerned below the magnetic transition temperature TN, which is attributable to exciton and magnon sideband absorptions. It turns out that the estimated nearest-neighbor exchange interaction increases as R -ionic radius increases, whereas TN monotonically decreases, indicating that the all-in all-out magnetic order arises from the interplay among several exchange interactions inherent to extended 5 d orbitals on the frustrated lattice. For larger R -ionic radius (R = Sm-Pr), i.e., relatively weakly correlated region, the optical conductivity spectra markedly change below 0.3 eV in the course of PM-AFI transition, implying that the magnetic order induces the insulating state. In particular, we have found distinct electrodynamics in the composition of R =Nd0.5Pr0.5 which is located on the boundary of the quantum PM-AFI transition, pointing to the possible emergence of unconventional topological electronic phases related possibly to the correlated Weyl electrons.

  11. Steady-state linear optical properties and Kerr nonlinear optical response of a four-level quantum dot with phonon-assisted transition

    NASA Astrophysics Data System (ADS)

    Yan-Chao, She; Ting-Ting, Luo; Wei-Xi, Zhang; Mao-Wu, Ran; Deng-Long, Wang

    2016-01-01

    The linear optical properties and Kerr nonlinear optical response in a four-level loop configuration GaAs/AlGaAs semiconductor quantum dot are analytically studied with the phonon-assisted transition (PAT). It is shown that the changes among a single electromagnetically induced transparency (EIT) window, a double EIT window and the amplification of the probe field in the absorption curves can be controlled by varying the strength of PAT κ. Meanwhile, double switching from the anomalous dispersion regime to the normal dispersion regime can likely be achieved by increasing the Rabi energy of the external optical control field. Furthermore, we demonstrate that the group velocity of the probe field can be practically regulated by varying the PAT and the intensity of the optical control field. In the nonlinear case, it is shown that the large SPM and XPM can be achieved as linear absorption vanishes simultaneously, and the PAT can suppress both third-order self-Kerr and the cross-Kerr nonlinear effect of the QD. Our study is much more practical than its atomic counterpart due to its flexible design and the controllable interference strength, and may provide some new possibilities for technological applications. Project supported by the National Natural Science Foundation of China (Grant No. 61367003), the Scientific Research Fund of Hunan Provincial Education Department, China (Grant No. 12A140), and the Scientific Research Fund of Guizhou Provincial Education Department, China (Grant Nos. KY[2015]384 and KY[2015]446).

  12. Empirical one-electron model of optical transitions in Cu-doped ZnS and CdS

    NASA Astrophysics Data System (ADS)

    Peka, P.; Schulz, H.-J.

    1994-01-01

    Optical absorption and emission processes in the paradigmatic wide-gap II-VI compounds ZnS: Cu and CdS: Cu find an unconstrained interpretation in a plain strong-field model of light-induced electronic processes which depicts the charge states Cu 2+ (d 9) and Cu + (d 10), viz. their internal and charge transfer transitions. A variety of observed spectroscopic features between the UV and the IR regions are included, supplemented by some tentative assignments and/or predictions. Among the phenomena covered are the blue (B-Cu), green (G-Cu) and orange-red (R-Cu) emission bands of ZnS and their homologues in CdS. Novel near-infrared luminescence bands in ZnS peaking near 7200 and 9200 cm -1 are tentatively assigned to radiative hole-recombination at a Cu acceptor state and to the t 52e 3 → t 42e 4 internal transitions of Cu 3+ (d 8), respectively. Participation of a native donor turns out to be essential for some of the processes covered. Formation of deep-acceptor-bound excitons is demonstrated for several absorptive and emissive optical transitions.

  13. Direct optical transitions at K- and H-point of Brillouin zone in bulk MoS2, MoSe2, WS2, and WSe2

    NASA Astrophysics Data System (ADS)

    Kopaczek, J.; Polak, M. P.; Scharoch, P.; Wu, K.; Chen, B.; Tongay, S.; Kudrawiec, R.

    2016-06-01

    Modulated reflectance (contactless electroreflectance (CER), photoreflectance (PR), and piezoreflectance (PzR)) has been applied to study direct optical transitions in bulk MoS2, MoSe2, WS2, and WSe2. In order to interpret optical transitions observed in CER, PR, and PzR spectra, the electronic band structure for the four crystals has been calculated from the first principles within the density functional theory for various points of Brillouin zone including K and H points. It is clearly shown that the electronic band structure at H point of Brillouin zone is very symmetric and similar to the electronic band structure at K point, and therefore, direct optical transitions at H point should be expected in modulated reflectance spectra besides the direct optical transitions at the K point of Brillouin zone. This prediction is confirmed by experimental studies of the electronic band structure of MoS2, MoSe2, WS2, and WSe2 crystals by CER, PR, and PzR spectroscopy, i.e., techniques which are very sensitive to critical points of Brillouin zone. For the four crystals besides the A transition at K point, an AH transition at H point has been observed in CER, PR, and PzR spectra a few tens of meV above the A transition. The spectral difference between A and AH transition has been found to be in a very good agreement with theoretical predictions. The second transition at the H point of Brillouin zone (BH transition) overlaps spectrally with the B transition at K point because of small energy differences in the valence (conduction) band positions at H and K points. Therefore, an extra resonance which could be related to the BH transition is not resolved in modulated reflectance spectra at room temperature for the four crystals.

  14. Ultra-narrow linewidth optical filter based on Faraday effect at isotope 87Rb 420 nm transitions

    NASA Astrophysics Data System (ADS)

    Bi, Gang; Kang, Jia; Fu, Jun; Ling, Li; Chen, Jingbiao

    2016-12-01

    An ultra-narrow linewidth optical filter with isotope 87Rb vapor at 420 nm, within the best waveband 400-500 nm for deep sea communication is achieved for the first time. The Faraday effect, circular dichroism, and nonlinear saturation techniques are utilized to narrow the bandwidth from previous 2.5 GHz to about 15 MHz level on the energy transition 5S1/2 → 6P3/2. By changing the temperature and magnetic field, the maximum transmission is obtained when the temperature and the magnetic field of the 87Rb cell are at 100 °C and 12 G. We discuss the varying influences of temperature, magnetic field, and pump power on the transmission of the atomic filter. The maximum single peak transmission at 5S1/2, F = 2 → 6P3/2, F‧ = 3 transition is 2.1% with a bandwidth of 17.8 MHz, and 1.9% at the 5S1/2, F = 2 → 6P3/2, F‧ = 2 , 3 (cross-over) transition with that of 14.2 MHz. The calculated equivalent noise bandwidth of this system is 32.5 MHz. Compared with the conventional Faraday anomalous dispersion optical filter, the bandwidth of our system is narrowed at least two orders of magnitude and is closer to the natural linewidth. This ultra-narrow linewidth filter has the potential to be applied to submarine communication or the pump laser in a four-level Rb-based active optical clock.

  15. Metal-Insulator Transition of strained SmNiO3 Thin Films: Structural, Electrical and Optical Properties

    NASA Astrophysics Data System (ADS)

    Torriss, B.; Margot, J.; Chaker, M.

    2017-01-01

    Samarium nickelate (SmNiO3) thin films were successfully synthesized on LaAlO3 and SrTiO3 substrates using pulsed-laser deposition. The Mott metal-insulator (MI) transition of the thin films is sensitive to epitaxial strain and strain relaxation. Once the strain changes from compressive to tensile, the transition temperature of the SmNiO3 samples shifts to slightly higher values. The optical conductivity reveals the strong dependence of the Drude spectral weight on the strain relaxation. Actually, compressive strain broadens the bandwidth. In contrast, tensile strain causes the effective number of free carriers to reduce which is consistent with the d-band narrowing.

  16. Metal-Insulator Transition of strained SmNiO3 Thin Films: Structural, Electrical and Optical Properties

    PubMed Central

    Torriss, B.; Margot, J.; Chaker, M.

    2017-01-01

    Samarium nickelate (SmNiO3) thin films were successfully synthesized on LaAlO3 and SrTiO3 substrates using pulsed-laser deposition. The Mott metal-insulator (MI) transition of the thin films is sensitive to epitaxial strain and strain relaxation. Once the strain changes from compressive to tensile, the transition temperature of the SmNiO3 samples shifts to slightly higher values. The optical conductivity reveals the strong dependence of the Drude spectral weight on the strain relaxation. Actually, compressive strain broadens the bandwidth. In contrast, tensile strain causes the effective number of free carriers to reduce which is consistent with the d-band narrowing. PMID:28098240

  17. Multicriticality and interaction-induced first-order phase transitions in mixtures of ultracold bosons in an optical lattice

    NASA Astrophysics Data System (ADS)

    Anufriiev, S.; Zaleski, T. A.

    2016-10-01

    We study a critical behavior of mixtures of two species of ultracold bosons trapped in an optical lattice. Using mean-field approximation, we determine the ground-state phase diagram of the system for a wide range of parameters. The introduction of interactions between different species of atoms strongly renormalizes the phase diagram. It can alter the critical behavior modifying multicriticality of crossing points and order of phase transitions in their vicinity between mixed and superfluid states. For selected values of model parameters, the behavior of the system falls out of the X Y model universality class, which usually is a hallmark of superfluid phase transition. We supplement our analysis with analytical calculations to explain the observed scenario.

  18. Molecular Dynamics at Electrical- and Optical-Driven Phase Transitions: Time-Resolved Infrared Studies Using Fourier-Transform Spectrometers

    NASA Astrophysics Data System (ADS)

    Peterseim, Tobias; Dressel, Martin

    2017-01-01

    The time-dependent optical properties of molecular systems are investigated by step-scan Fourier-transform spectroscopy in order to explore the dynamics at phase transitions and molecular orientation in the milli- and microsecond range. The electrical switching of liquid crystals traced by vibrational spectroscopy reveals a rotation of the molecules with a relaxation time of 2 ms. The photo-induced neutral-ionic transition in TTF-CA takes place by a suppression of the dimerization in the ionic phase and creation of neutral domains. The time-dependent infrared spectra, employed to investigate the domain-wall dynamics, depend on temperature and laser pulse intensity; the relaxation of the spectra follows a stretched-exponential decay with relaxation times in the microsecond range strongly dependent on temperature and laser intensity. We present all details of the experimental setups and thoroughly discuss the technical challenges.

  19. Evolution of Extended JC-Dicke Quantum Phase Transition with a Coupled Optical Cavity in Bose-Einstein Condensate System

    NASA Astrophysics Data System (ADS)

    Abdel-Rady, A. S.; Hassan, Samia S. A.; Osman, Abdel-Nasser A.; Salah, Ahmed

    2017-09-01

    In this paper, the extended Jaynes-Cummings-Dicke (JC-Dicke) model which describes a two-level atomic Bose-Einstein condensate (BEC) dispersive coupled to a high-finesse optical cavity is considered. The theoretical description of an effective Hamiltonian for BEC is introduced. The potential energy surface of the system is obtained from the direct product Heisenberg-Weyl (HW1) coherent states for the field and U(2) coherent states for the matter. Also, the variational energy is evaluated as the expectation value of the Hamiltonian for this state in the framework of mean-field approach. The quantum phase transitions (QPTs) and the Berry phase for this model are investigated numerically. We observed that the atom-atom interactions can strongly affect the quantum phase transition point. Furthermore, we noticed that the coherent atoms not only shift the phase transition point but also affect the macroscopic excitations in the superradiant phase. Moreover, it is found that the new phase transition occurs when the microwave amplitude changes. Some of the numerical results in this paper are agreement precisely with the results of our paper which has published in Int. J. Mod. Phys. B when we studied the same model using a different coherent state.

  20. High efficiency optical modulation at a telecom wavelength using the quantum Zeno effect in a ladder transition in Rb atoms.

    PubMed

    Krishnamurthy, Subramanian; Wang, Y; Tu, Y; Tseng, S; Shahriar, M S

    2012-06-18

    We demonstrate a high-efficiency optical modulator at ~1323 nm using the quantum Zeno effect in a ladder transition in a Rb vapor cell. The lower leg of the transitions represents the control beam while the upper leg of the transitions represents the signal beam. The cross-modulation of the signal beam transmission is observed as the control beam is intensity modulated, and is explained in terms of the quantum Zeno effect. We observe a modulation depth of near 100% at frequencies up to 1 MHz and demonstrate modulation at speeds up to 75 MHz, with a 3 dB bandwidth of about 5 MHz, limited by the homogeneous linewidth of the intermediate state. We also describe how much higher modulation speeds could be realized by using a buffer gas to broaden the transitions. We identify and explain the special conditions needed for optimizing the modulation efficiency. Numerical simulations of modulation at ~1 GHz are presented. The maximum modulation speed is found to scale with the pressure-broadened linewidth of the intermediate state, so that much higher speeds should be attainable.

  1. Anisotropy of optical transitions in ordered ensemble of CdSe quantum rods.

    PubMed

    Mukhina, Maria V; Maslov, Vladimir G; Baranov, Alexander V; Artemyev, Mikhail V; Orlova, Anna O; Fedorov, Anatoly V

    2013-09-01

    We report on the observation of spectral dependence of absorption anisotropy in a CdSe quantum rod (QR) ensemble, which is aligned in a polymer film with a nanocrystal concentration of 2×10(-5) M. The experimental data on the polarization direction and anisotropy factor were obtained for the lowest excitonic transition and the second group of transitions in the QR. The nonzero constant value of anisotropy was investigated for the high-energy transitions, and is evidence of the one-dimensional confinement in the QR.

  2. Ultra-thin and flexible endoscopy probe for optical coherence tomography based on stepwise transitional core fiber

    PubMed Central

    Lee, Jangbeom; Chae, Yugyeong; Ahn, Yeh-Chan; Moon, Sucbei

    2015-01-01

    We present an ultra-thin fiber-body endoscopy probe for optical coherence tomography (OCT) which is based on a stepwise transitional core (STC) fiber. In a minimalistic design, our probe was made of spliced specialty fibers that could be directly used for beam probing optics without using a lens. In our probe, the OCT light delivered through a single-mode fiber was efficiently expanded to a large mode field of 24 μm diameter for a low beam divergence. The size of our probe was 85 μm in the probe’s diameter while operated in a 160-μm thick protective tubing. Through theoretical and experimental analyses, our probe was found to exhibit various attractive features in terms of compactness, flexibility and reliability along with its excellent fabrication simplicity. PMID:26137380

  3. Electron and lattice dynamics of transition metal thin films observed by ultrafast electron diffraction and transient optical measurements

    PubMed Central

    Nakamura, A.; Shimojima, T.; Nakano, M.; Iwasa, Y.; Ishizaka, K.

    2016-01-01

    We report the ultrafast dynamics of electrons and lattice in transition metal thin films (Au, Cu, and Mo) investigated by a combination of ultrafast electron diffraction (UED) and pump-probe optical methods. For a single-crystalline Au thin film, we observe the suppression of the diffraction intensity occuring in 10 ps, which direcly reflects the lattice thermalization via the electron-phonon interaction. By using the two-temperature model, the electron-phonon coupling constant (g) and the electron and lattice temperatures (Te, Tl) are evaluated from UED, with which we simulate the transient optical transmittance. The simulation well agrees with the experimentally obtained transmittance data, except for the slight deviations at the initial photoexcitation and the relaxed quasi-equilibrium state. We also present the results similarly obtained for polycrystalline Au, Cu, and Mo thin films and demonstrate the electron and lattice dynamics occurring in metals with different electron-phonon coupling strengths. PMID:28004010

  4. Transition from two-dimensional photonic crystals to dielectric metasurfaces in the optical diffraction with a fine structure.

    PubMed

    Rybin, Mikhail V; Samusev, Kirill B; Lukashenko, Stanislav Yu; Kivshar, Yuri S; Limonov, Mikhail F

    2016-08-05

    We study experimentally a fine structure of the optical Laue diffraction from two-dimensional periodic photonic lattices. The periodic photonic lattices with the C4v square symmetry, orthogonal C2v symmetry, and hexagonal C6v symmetry are composed of submicron dielectric elements fabricated by the direct laser writing technique. We observe surprisingly strong optical diffraction from a finite number of elements that provides an excellent tool to determine not only the symmetry but also exact number of particles in the finite-length structure and the sample shape. Using different samples with orthogonal C2v symmetry and varying the lattice spacing, we observe experimentally a transition between the regime of multi-order diffraction, being typical for photonic crystals to the regime where only the zero-order diffraction can be observed, being is a clear fingerprint of dielectric metasurfaces characterized by effective parameters.

  5. Transition from two-dimensional photonic crystals to dielectric metasurfaces in the optical diffraction with a fine structure

    NASA Astrophysics Data System (ADS)

    Rybin, Mikhail V.; Samusev, Kirill B.; Lukashenko, Stanislav Yu.; Kivshar, Yuri S.; Limonov, Mikhail F.

    2016-08-01

    We study experimentally a fine structure of the optical Laue diffraction from two-dimensional periodic photonic lattices. The periodic photonic lattices with the C4v square symmetry, orthogonal C2v symmetry, and hexagonal C6v symmetry are composed of submicron dielectric elements fabricated by the direct laser writing technique. We observe surprisingly strong optical diffraction from a finite number of elements that provides an excellent tool to determine not only the symmetry but also exact number of particles in the finite-length structure and the sample shape. Using different samples with orthogonal C2v symmetry and varying the lattice spacing, we observe experimentally a transition between the regime of multi-order diffraction, being typical for photonic crystals to the regime where only the zero-order diffraction can be observed, being is a clear fingerprint of dielectric metasurfaces characterized by effective parameters.

  6. Investigation of optical transitions in InAs/GaAs(Sb)/AlAsSb quantum dots using modulation spectroscopy

    SciTech Connect

    Bittner, Zachary S. Hellstroem, Staffan; Polly, Stephen J.; Hubbard, Seth M.; Laghumavarapu, Ramesh B.; Liang, Baolai; Huffaker, Diana L.

    2014-12-22

    InAs quantum dots (QDs) were grown in an AlAs{sub 0.56}Sb{sub 0.44}/GaAs matrix in the unintentionally doped (uid) region of an In{sub 0.52}Al{sub 0.48}As solar cell, establishing a variety of optical transitions both into and out of the QDs. The ultimate goal is to demonstrate sequential absorption, where one photon is absorbed, promoting an electron from the valence band into the QD, and a second photon is absorbed in order to promote the trapped electron from a QD state into the host conduction band. In this study, we directly investigate the optical properties of the solar cell using photoreflectance and evaluate the possibility of sequential absorption by measuring spectral responsivity with broadband infrared illumination.

  7. Transition from two-dimensional photonic crystals to dielectric metasurfaces in the optical diffraction with a fine structure

    PubMed Central

    Rybin, Mikhail V.; Samusev, Kirill B.; Lukashenko, Stanislav Yu.; Kivshar, Yuri S.; Limonov, Mikhail F.

    2016-01-01

    We study experimentally a fine structure of the optical Laue diffraction from two-dimensional periodic photonic lattices. The periodic photonic lattices with the C4v square symmetry, orthogonal C2v symmetry, and hexagonal C6v symmetry are composed of submicron dielectric elements fabricated by the direct laser writing technique. We observe surprisingly strong optical diffraction from a finite number of elements that provides an excellent tool to determine not only the symmetry but also exact number of particles in the finite-length structure and the sample shape. Using different samples with orthogonal C2v symmetry and varying the lattice spacing, we observe experimentally a transition between the regime of multi-order diffraction, being typical for photonic crystals to the regime where only the zero-order diffraction can be observed, being is a clear fingerprint of dielectric metasurfaces characterized by effective parameters. PMID:27491952

  8. Ultra-thin and flexible endoscopy probe for optical coherence tomography based on stepwise transitional core fiber.

    PubMed

    Lee, Jangbeom; Chae, Yugyeong; Ahn, Yeh-Chan; Moon, Sucbei

    2015-05-01

    We present an ultra-thin fiber-body endoscopy probe for optical coherence tomography (OCT) which is based on a stepwise transitional core (STC) fiber. In a minimalistic design, our probe was made of spliced specialty fibers that could be directly used for beam probing optics without using a lens. In our probe, the OCT light delivered through a single-mode fiber was efficiently expanded to a large mode field of 24 μm diameter for a low beam divergence. The size of our probe was 85 μm in the probe's diameter while operated in a 160-μm thick protective tubing. Through theoretical and experimental analyses, our probe was found to exhibit various attractive features in terms of compactness, flexibility and reliability along with its excellent fabrication simplicity.

  9. Multimode mean-field model for the quantum phase transition of a Bose-Einstein condensate in an optical resonator

    NASA Astrophysics Data System (ADS)

    Kónya, G.; Szirmai, G.; Domokos, P.

    2011-11-01

    We develop a mean-field model describing the Hamiltonian interaction of ultracold atoms and the optical field in a cavity. The Bose-Einstein condensate is properly defined by means of a grand-canonical approach. The model is efficient because only the relevant excitation modes are taken into account. However, the model goes beyond the two-mode subspace necessary to describe the self-organization quantum phase transition observed recently. We calculate all the second-order correlations of the coupled atom field and radiation field hybrid bosonic system, including the entanglement between the two types of fields.

  10. Mid-infrared fiber-optic attenuated total reflection spectroscopy of the solid-liquid phase transition of water.

    PubMed

    Millo, Arnon; Raichlin, Yosef; Katzir, Abraham

    2005-04-01

    Measurements of mid-infrared (MIR) absorption spectra of water and heavy water were carried out by fiber-optic evanescent wave spectroscopy, using silver halide (AgClBr) infrared fibers. Such measurements were performed for the first time on one sample, during the solid-liquid phase transition. From the variation of the spectra with temperature we found a new isosbestic point (at 3280 cm(-1) for H(2)O or at 2475 cm(-1) for D(2)O) and we identified five components of the O-H (O-D) stretch band. These phenomena have provided new information about the molecular structure of water.

  11. Absolute frequency measurement of the 674-nm {sup 88}Sr{sup +} clock transition using a femtosecond optical frequency comb

    SciTech Connect

    Margolis, H.S.; Huang, G.; Barwood, G.P.; Lea, S.N.; Klein, H.A.; Rowley, W.R.C.; Gill, P.; Windeler, R.S.

    2003-03-01

    The frequency of the 5s {sup 2}S{sub 1/2}-4d {sup 2}D{sub 5/2} electric quadrupole transition at 674 nm in a single, trapped, laser-cooled {sup 88}Sr{sup +} ion has been measured with respect to the Systeme International (SI) second using a femtosecond laser optical frequency comb. The measured frequency of 444 779 044 095.52 kHz, with an estimated standard uncertainty of 0.10 kHz, is more accurate than, and in agreement with, the value previously measured using a conventional frequency chain.

  12. Simultaneous subsecond hyperpolarization of the nuclear and electron spins of phosphorus in silicon by optical pumping of exciton transitions.

    PubMed

    Yang, A; Steger, M; Sekiguchi, T; Thewalt, M L W; Ladd, T D; Itoh, K M; Riemann, H; Abrosimov, N V; Becker, P; Pohl, H-J

    2009-06-26

    We demonstrate a method which can hyperpolarize both the electron and nuclear spins of 31P donors in Si at low field, where both would be essentially unpolarized in equilibrium. It is based on the selective ionization of donors in a specific hyperfine state by optically pumping donor bound exciton hyperfine transitions, which can be spectrally resolved in 28Si. Electron and nuclear polarizations of 90% and 76%, respectively, are obtained in less than a second, providing an initialization mechanism for qubits based on these spins, and enabling further ESR and NMR studies on dilute 31P in 28Si.

  13. Time-domain separation of optical properties from structural transitions in resonantly bonded materials.

    PubMed

    Waldecker, Lutz; Miller, Timothy A; Rudé, Miquel; Bertoni, Roman; Osmond, Johann; Pruneri, Valerio; Simpson, Robert E; Ernstorfer, Ralph; Wall, Simon

    2015-10-01

    The extreme electro-optical contrast between crystalline and amorphous states in phase-change materials is routinely exploited in optical data storage and future applications include universal memories, flexible displays, reconfigurable optical circuits, and logic devices. Optical contrast is believed to arise owing to a change in crystallinity. Here we show that the connection between optical properties and structure can be broken. Using a combination of single-shot femtosecond electron diffraction and optical spectroscopy, we simultaneously follow the lattice dynamics and dielectric function in the phase-change material Ge2Sb2Te5 during an irreversible state transformation. The dielectric function changes by 30% within 100 fs owing to a rapid depletion of electrons from resonantly bonded states. This occurs without perturbing the crystallinity of the lattice, which heats with a 2-ps time constant. The optical changes are an order of magnitude larger than those achievable with silicon and present new routes to manipulate light on an ultrafast timescale without structural changes.

  14. Correcting artifacts in transition to a wound optic fiber: Example from high-resolution temperature profiling in the Dead Sea

    NASA Astrophysics Data System (ADS)

    Arnon, Ali; Selker, John; Lensky, Nadav

    2014-06-01

    Spatial resolution fiber-optic cables allow for detailed observation of thermally complex heterogeneous hydrologic systems. A commercially produced high spatial resolution helically wound optic fiber sensing cable is employed in the Dead Sea, in order to study the dynamics of thermal stratification of the hypersaline lake. Structured spatial artifacts were found in the data from the first 10 m of cable (110 m of fiber length) following the transition from straight fiber optic. The Stokes and Anti-Stokes signals indicate that this is the result of differential attenuation, thought to be due to cladding losses. Though the overall spatial form of the loss was consistent, the fine structure of the loss changed significantly in time, and was strongly asymmetrical, and thus was not amenable to standard calibration methods. Employing the fact that the cable was built with a duplex construction, and using high-precision sensors mounted along the cable, it was possible to correct the artifact in space and time, while retaining the high-quality of data obtained in the early part of the cable (prior to significant optical attenuation). The defect could easily be overlooked; however, reanalyzing earlier experiments, we have observed the same issue with installations employing similar cables in Oregon and France, so with this note we both alert the community to this persistent concern and provide an approach to correct the data in case of similar problems.

  15. Quantum and thermal phase transitions in a bosonic atom-molecule mixture in a two-dimensional optical lattice

    NASA Astrophysics Data System (ADS)

    de Forges de Parny, L.; Rousseau, V. G.

    2017-01-01

    We study the ground state and the thermal phase diagram of a two-species Bose-Hubbard model, with U(1 ) ×Z2 symmetry, describing atoms and molecules on a two-dimensional optical lattice interacting via a Feshbach resonance. Using quantum Monte Carlo simulations and mean-field theory, we show that the conversion between the two species, coherently coupling the atomic and molecular states, has a crucial impact on the Mott-superfluid transition and stabilizes an insulating phase with a gap controlled by the conversion term—the Feshbach insulator—instead of a standard Mott-insulating phase. Depending on the detuning between atoms and molecules, this model exhibits three phases: the Feshbach insulator, a molecular condensate coexisting with noncondensed atoms, and a mixed atomic-molecular condensate. Employing finite-size scaling analysis, we observe three-dimensional (3D) X Y (3D Ising) transition when U(1 ) (Z2) symmetry is broken, whereas the transition is first order when both U(1 ) and Z2 symmetries are spontaneously broken. The finite-temperature phase diagram is also discussed. The thermal disappearance of the molecular superfluid leads to a Berezinskii-Kosterlitz-Thouless transition with unusual universal jump in the superfluid density. The loss of the quasi-long-range coherence of the mixed atomic and molecular superfluid is more subtle since only atoms exhibit conventional Berezinskii-Kosterlitz-Thouless criticality. We also observe a signal compatible with a classical first-order transition between the mixed superfluid and the normal Bose liquid at low temperature.

  16. Nonadiabatic optical transitions as a turn-on switch for pulse shaping

    SciTech Connect

    Hashmi, F. A.; Bouchene, M. A.

    2010-10-15

    A strong nonresonant, asymmetric ultrashort pulse drives an atomic transition and causes a complete population inversion because of a sudden nonadiabatic jump. This jump is probed in real time by propagating a weak ultrashort pulse in the system which is resonant on an adjacent transition. The probe at the exit of the medium presents an oscillatory structure with the nonadiabatic jump marked in time by the onset of oscillations. The nonadiabatic jump thus acts as a 'turn-on' switch for the shaping of the probe.

  17. Optical transitions and frequency upconversion emission of Er 3+ions in novel lead-bismuthate glass

    NASA Astrophysics Data System (ADS)

    Sun, Hongtao; Dai, Shixun; Zhang, Debao; Xu, Shiqing; Zhang, Junjie; Hu, Lili; Jiang, Zhonghong

    2004-12-01

    Er 3+-doped strontiam lead bismuth glass for developing upconversion lasers has been fabricated and characterized. The Judd-Ofelt analysis was performed on the absorption spectrum and the transition probabilities, excited state lifetimes, and the fluorescence branching ratios were calculated and discussed. Under 975 nm excitation, intense green and red emissions centered at 525, 546, and 657 nm, corresponding to the transitions 2H→4I, 4S→4I, and 4F→4I, respectively, were observed. The upconversion mechanisms are discussed based on the energy matching and quadratic dependence on excitation power, and the dominant mechanisms are excited state absorption and energy transfer upconversion for the green and red emissions.

  18. Giant magneto-optical Raman effect in a layered transition metal compound

    DOE PAGES

    Ji, Jianting; Zhang, Anmin; Fan, Jiahe; ...

    2016-02-16

    Here, we report a dramatic change in the intensity of a Raman mode with applied magnetic field, displaying a gigantic magneto-optical effect. Using the nonmagnetic layered material MoS2 as a prototype system, we demonstrate that the application of a magnetic field perpendicular to the layers produces a dramatic change in intensity for the out-of-plane vibrations of S atoms, but no change for the in-plane breathing mode. The distinct intensity variation between these two modes results from the effect of field-induced broken symmetry on Raman scattering cross-section. A quantitative analysis on the field-dependent integrated Raman intensity provides a unique method tomore » precisely determine optical mobility. Our analysis is symmetry-based and material-independent, and thus the observations should be general and inspire a new branch of inelastic light scattering and magneto-optical applications.« less

  19. Giant magneto-optical Raman effect in a layered transition metal compound

    PubMed Central

    Ji, Jianting; Zhang, Anmin; Fan, Jiahe; Li, Yuesheng; Wang, Xiaoqun; Zhang, Jiandi; Plummer, E. W.; Zhang, Qingming

    2016-01-01

    We report a dramatic change in the intensity of a Raman mode with applied magnetic field, displaying a gigantic magneto-optical effect. Using the nonmagnetic layered material MoS2 as a prototype system, we demonstrate that the application of a magnetic field perpendicular to the layers produces a dramatic change in intensity for the out-of-plane vibrations of S atoms, but no change for the in-plane breathing mode. The distinct intensity variation between these two modes results from the effect of field-induced broken symmetry on Raman scattering cross-section. A quantitative analysis on the field-dependent integrated Raman intensity provides a unique method to precisely determine optical mobility. Our analysis is symmetry-based and material-independent, and thus the observations should be general and inspire a new branch of inelastic light scattering and magneto-optical applications. PMID:26884198

  20. Optical properties of TiN thin films close to the superconductor-insulator transition.

    SciTech Connect

    Pfuner, F.; Degiorgi, L.; Baturina, T. I.; Vinokur, V. M.; Baklanov, M. R.; Materials Science Division; ETH Zurich; Inst. Semiconductor Physics; IMEC Kapeldreef

    2009-11-10

    We present the intrinsic optical properties over a broad spectral range of TiN thin films deposited on an Si/SiO{sub 2} substrate. We analyze the measured reflectivity spectra of the film-substrate multilayer structure within a well-establish procedure based on the Fresnel equation and extract the real part of the optical conductivity of TiN. We identify the metallic contribution as well as the finite energy excitations and disentangle the spectral weight distribution among them. The absorption spectrum of TiN bears some similarities with the electrodynamic response observed in the normal state of the high-temperature superconductors. Particularly, a mid-infrared feature in the optical conductivity is quite reminiscent of a pseudogap-like excitation.

  1. ZnO:Mo:In nanofilms on SiO2 substrate under investigation framework of the second optical transition

    NASA Astrophysics Data System (ADS)

    Souissi, A.; Amlouk, M.; Guermazi, S.

    2017-02-01

    ZnO and ZnO:Mo:In nanofilms were deposited on SiO2 substrate at 460 °C by the spray pyrolysis method with the molar ratio (Mo/Zn) set at 1% and (In/Zn) dosed at 1%, 2%, 3% and 10%. The optical, dielectric and photonic characteristics of these samples were analyzed from the optical spectra of transmission and reflection, which revealed the presence of two absorption edges. The first one was related to the ZnO:Mo:In typical transition and the second edge originated from the ZnO:Mo:In/SiO2 interface transition by the probable formation of an ultrafine layer identified as SiOx and/or ZnO(1-x)SiO2(x). The optical gap and Urbach energies of ZnO:Mo:In nanofilms varied almost uniformly and in a complementary manner depending on the co-doping of ∼3.28-3.24 eV and ∼82-136 meV. These energies associated with the interface varied randomly from 3.93 to 4.18 eV and ∼263 to 408 meV, and showed strong dependencies with the structural, crystalline and vibrational properties previously studied. They also displayed possible correlations with electron scattering time and the dc photoconductivity which reaches high value for film prepared using In = 2%. AFM study showed variable morphologies of the surfaces that are responsive to codoping elements, therefore at the interface, wherein the film growth began. All these factors influenced the results described above. The study also showed good agreement between rms roughness and TC texture coefficient of the studied films, of high transparency ∼89-92%. The films prepared with In = 2% revealed a high photoconductivity and could be used in photocatalytic and photonic applications.

  2. Optoelectronic properties of transition metal and rare earth doped epitaxial layers on InP for magneto-optics

    NASA Astrophysics Data System (ADS)

    Stadler, B. J. H.; Vaccaro, K.; Davis, A.; Ramseyer, G. O.; Martin, E. A.; Dauplaise, H. M.; Theodore, L. M.; Lorenzo, J. P.

    1996-05-01

    Rare earth-and transition metal-doped thin films of InP, In0.53Ga0.47As, and In0.71Ga0.29As0.58P0.42 were grown by liquid phase epitaxy and evaluated for use in integrated electro-optical and magneto-optical applications, such as waveguides and Faraday rotators. The films were lattice matched to (100) InP substrates, and the transition metal (Mn) and rare earth (Gd, Eu, and Er) doping concentra-tions were between 2.6 × 1018 and 1.5 × 1020 cm-3. The chemical profiles were generally found to be homogeneous by SIMS, although in more highly doped films the rare earths were observed to segregate toward the interfaces. The undoped films were n-type, and the net carrier concentrations in the rare earth-doped (Gd, Eu, Er) films were decreased by an order of magnitude. The Mn-doped films were p-type. Optically, the rare earth dopants were observed to raise the refractive index of the layers at 632.8 nm, and subsequent waveguiding in doped InP layers was observed at 1.3 μm. Although the Faraday rotations of our materials were much less than that of well known oxides, such as yttrium iron garnet, they were sufficient for device applications, and our materials can be much more easily integrated with InP OEIC devices. For example, a 1 cm waveguide would provide the large rotation (45°) required in isolator applica-tions.

  3. LINKING Lyα AND LOW-IONIZATION TRANSITIONS AT LOW OPTICAL DEPTH

    SciTech Connect

    Jaskot, A. E.; Oey, M. S.

    2014-08-20

    We suggest that low optical depth in the Lyman continuum (LyC) may relate the Lyα emission, C II and Si II absorption, and C II* and Si II* emission seen in high-redshift galaxies. We base this analysis on Hubble Space Telescope Cosmic Origins Spectrograph spectra of four Green Pea (GP) galaxies, which may be analogs of z > 2 Lyα emitters (LAEs). In the two GPs with the strongest Lyα emission, the Lyα line profiles show reduced signs of resonant scattering. Instead, the Lyα profiles resemble the Hα line profiles of evolved star ejecta, suggesting that the Lyα emission originates from a low column density and similar outflow geometry. The weak C II absorption and presence of non-resonant C II* emission in these GPs support this interpretation and imply a low LyC optical depth along the line of sight. In two additional GPs, weak Lyα emission and strong C II absorption suggest a higher optical depth. These two GPs differ in their Lyα profile shapes and C II* emission strengths, however, indicating different inclinations of the outflows to our line of sight. With these four GPs as examples, we explain the observed trends linking Lyα, C II, and C II* in stacked LAE spectra, in the context of optical depth and geometric effects. Specifically, in some galaxies with strong Lyα emission, a low LyC optical depth may allow Lyα to escape with reduced scattering. Furthermore, C II absorption, C II* emission, and Lyα profile shape can reveal the optical depth, constrain the orientation of neutral outflows in LAEs, and identify candidate LyC emitters.

  4. Optical transitions in GaNAs quantum wells with variable nitrogen content embedded in AlGaAs

    SciTech Connect

    Elborg, M.; Noda, T.; Mano, T.; Sakuma, Y.

    2016-06-15

    We investigate the optical transitions of GaN{sub x}As{sub 1−x} quantum wells (QWs) embedded in wider band gap AlGaAs. A combination of absorption and emission spectroscopic techniques is employed to systematically investigate the properties of GaNAs QWs with N concentrations ranging from 0 – 3%. From measurement of the photocurrent spectra, we find that besides QW ground state and first excited transition, distinct increases in photocurrent generation are observed. Their origin can be explained by N-induced modifications in the density of states at higher energies above the QW ground state. Photoluminescence experiments reveal that peak position dependence with temperature changes with N concentration. The characteristic S-shaped dependence for low N concentrations of 0.5% changes with increasing N concentration where the low temperature red-shift of the S-shape gradually disappears. This change indicates a gradual transition from impurity picture, where localized N induced energy states are present, to alloying picture, where an impurity-band is formed. In the highest-N sample, photoluminescence emission shows remarkable temperature stability. This phenomenon is explained by the interplay of N-induced energy states and QW confined states.

  5. Optical absorption and heating rate dependent glass transition in vanadyl doped calcium oxy-chloride borate glasses

    NASA Astrophysics Data System (ADS)

    Dahiya, M. S.; Khasa, S.; Agarwal, A.

    2015-04-01

    Some important results pertaining to optical and thermal properties of vanadyl doped oxy-halide glasses in the chemical composition CaCl2-CaO-B2O3 are discussed. These glasses have been prepared by conventional melt quench technique. From X-ray diffraction (XRD) profiles the amorphous nature of the doped glasses has been confirmed. The electronic polarizability is calculated and found to increase with increase in chloride content. The optical absorption spectra have been recorded in the frequency range of 200-3200 nm. Recorded spectra are analyzed to evaluate cut-off wavelength (λcut-off), optical band gap (Eg), band tailing (B), Urbach energy (ΔE) and refractive index (n). Thermal analysis has been carried out for the prepared glasses at three different heating rates viz. 5, 10 and 20 °C/min. The glass transition temperature (Tg) along with thermal activation energy (Ea) corresponding to each heating rate are evaluated from differential scanning calorimetry (DSC) thermographs. It is found that Ea decrease and Tg increase with increase in heating rate. The variation in Tg is also observed with the substitution of calcium chloride in place of calcium oxide. The increasing and higher values of Ea suggest that prepared glasses have good thermal stability. Variation in Tg and Eg suggests that Cl- anions enter into the voids of borate network at low concentrations (<5.0%) and contribute to the network formation at high concentration (>5.0%).

  6. Probe spectroscopy in an operating magneto-optical trap: The role of Raman transitions between discrete and continuum atomic states

    SciTech Connect

    Brzozowski, Tomasz M.; Brzozowska, Maria; Zachorowski, Jerzy; Zawada, Michal; Gawlik, Wojciech

    2005-01-01

    We report on cw measurements of probe beam absorption and four-wave-mixing spectra in a {sup 85}Rb magneto-optical trap taken while the trap is in operation. The trapping beams are used as pump light. We concentrate on the central feature of the spectra at small pump-probe detuning and attribute its narrow resonant structures to the superposition of Raman transitions between light-shifted sublevels of the ground atomic state and to atomic recoil processes. These two contributions have different dependencies on trap parameters and we show that the former is inhomogeneously broadened. The strong dependence of the spectra on the probe-beam polarization indicates the existence of large optical anisotropy of the cold-atom sample, which is attributed to the recoil effects. We point out that the recoil-induced resonances can be isolated from other contributions, making pump-probe spectroscopy a highly sensitive diagnostic tool for atoms in a working magneto-optical trap.

  7. Investigation of high-contrast velocity selective optical pumping resonance at the cycling transition of Cs using fluorescence technique

    NASA Astrophysics Data System (ADS)

    Dey, Saswati; Ray, Biswajit; Ghosh, Pradip Narayan; Cartaleva, Stefka; Slavov, Dimitar

    2015-12-01

    A high contrast (∼48%) Velocity Selective Optical Pumping (VSOP) resonance at the closed transition Fg=4→Fe=5 of Cs-D2 line is obtained in the fluorescence signal under co-propagating pump-probe configuration. We use a 5.2 μm cell operating at reduced temperature (∼55 °C) and the intensity of the pump-laser is kept lower than that of the probe-laser. The observed sharp narrow structure is suitable for side-arms frequency-locking of the cooling- (i.e. probe-) laser in a cold atom experiment, with possibility for "-Γ" to "-4Γ" red-detuning and "+Γ" to "+10Γ" blue-detuning using the standard properties of the commercially available electronics. We have developed a theoretical model corresponding to the thin cell, incorporating the atomic time-of-flight dependent optical pumping decay rate to describe the dimensional anisotropy of the thin cell. The model shows good qualitative agreement with the observation and simulates as well the cases of cells with smaller thickness. It also describes correctly the temperature dependence of the line broadening and shows the potential for further optimization and red-shift detuning above "-4Γ". It may be of interest for further development of miniaturized modules, like the recently developed portable small magneto-optical traps.

  8. The second- and third- order nonlinear optical properties and electronic transition of a NLO chromophore: A DFT study

    NASA Astrophysics Data System (ADS)

    Altürk, Sümeyye; Avci, Davut; Tamer, Ömer; Atalay, Yusuf

    2016-03-01

    It is well known that the practical applications of second-order and third-order nonlinear optical (NLO) materials have been reported in modern technology, such as optical data processing, transmission and storage, etc. In this respect, the linear and nonlinear optical parameters (the molecular static polarizability (α), and the first-order static hyperpolarizability (β0), the second-order static hyperpolarizability (γ)), UV-vis spectra and HOMO and LUMO energies of 2-(1'-(4'''-Methoxyphenyl)-5'-(thien-2″-yl)pyrrol-2'-yl)-1,3-benzothiazole were investigated by using the HSEh1PBE/6-311G(d,p) level of density functional theory. The UV-vis spectra were simulated using TD/HSEh1PBE/6- 311G(d,p) level, and the major contributions to the electronic transitions were obtained. The molecular hardness (η) and electronegativity (χ) parameters were also obtained by using molecular frontier orbital energies. The NLO parameters of the title compound were calculated, and obtained data were compared with that of para-Nitroaniline (pNA) which is a typical NLO material and the corresponding experimental data. Obtained data of the chromosphere display significant molecular second-and third-nonlinearity.

  9. The second– and third– order nonlinear optical properties and electronic transition of a NLO chromophore: A DFT study

    SciTech Connect

    Altürk, Sümeyye Avci, Davut Tamer, Ömer Atalay, Yusuf

    2016-03-25

    It is well known that the practical applications of second-order and third-order nonlinear optical (NLO) materials have been reported in modern technology, such as optical data processing, transmission and storage, etc. In this respect, the linear and nonlinear optical parameters (the molecular static polarizability (α), and the first–order static hyperpolarizability (β{sub 0}), the second–order static hyperpolarizability (γ)), UV-vis spectra and HOMO and LUMO energies of 2-(1′-(4’’’-Methoxyphenyl)-5′-(thien-2″-yl)pyrrol-2′-yl)-1,3-benzothiazole were investigated by using the HSEh1PBE/6–311G(d,p) level of density functional theory. The UV–vis spectra were simulated using TD/HSEh1PBE/6– 311G(d,p) level, and the major contributions to the electronic transitions were obtained. The molecular hardness (η) and electronegativity (χ) parameters were also obtained by using molecular frontier orbital energies. The NLO parameters of the title compound were calculated, and obtained data were compared with that of para-Nitroaniline (pNA) which is a typical NLO material and the corresponding experimental data. Obtained data of the chromosphere display significant molecular second-and third-nonlinearity.

  10. Optically allowed transitions among Fe IV levels belonging to lowest three configurations

    NASA Astrophysics Data System (ADS)

    Deb, Narayan C.; Hibbert, Alan

    2008-05-01

    Oscillator strengths and transition rates for the dipole allowed transitions among 3d^5, 3d^44s and 3d^44p levels of Fe IV are calculated with the CIV3 program of Hibbert [1]. Using Hartree-Fock functions up to 3d orbitals we have optimised 4s, 4p, 4d, 4f, 5s, 5p and 5d orbitals of which 4s and 4p are taken to be the spectroscopic and the remaining orbitals representing corrections to the spectroscopic orbitals or the correlation effects. The J-dependent levels of all 108 LS states are included in the calculation and relativistic effects are accounted for via the Breit-Pauli operator. Configurations are chosen in two steps: (a) two promotions were allowed from the 3p, 3d and 4l subshells, using all the above orbitals; (b) selective promotions from the 3s subshell are included, but only to the 3d, 4s and 4p orbitals. The ab initio fine-structure levels were then fine-tuned to reproduce the observed energy levels as closely as possible, and the wavefunctions used to calculate oscillator strengths for all possible E1 transitions. For many of these transitions, the present results show agreement between length and velocity forms to within 5%.[1] A.Hibbert, Comput. Phys. Commun. 9 (1975) 141

  11. Atomic loss and gain as a resource for nonequilibrium phase transitions in optical lattices

    NASA Astrophysics Data System (ADS)

    Everest, B.; Marcuzzi, M.; Lesanovsky, I.

    2016-02-01

    Recent breakthroughs in the experimental manipulation of strongly interacting atomic Rydberg gases in lattice potentials have opened an avenue for the study of many-body phenomena. Considerable efforts are currently being undertaken to achieve clean experimental settings that show a minimal amount of noise and disorder and are close to zero temperature. A complementary direction investigates the interplay between coherent and dissipative processes. Recent experiments have revealed a glimpse into the emergence of a rich nonequilibrium behavior stemming from the competition of laser excitation, strong interactions, and radiative decay of Rydberg atoms. The aim of the present theoretical work is to show that local incoherent loss and gain of atoms can in fact be the source of interesting out-of-equilibrium dynamics. This perspective opens up paths for the exploration of nonequilibrium critical phenomena and, more generally, phase transitions, some of which so far have been rather difficult to study. To demonstrate the richness of the encountered dynamical behavior we consider here three examples. The first two feature local atom loss and gain together with an incoherent excitation of Rydberg states. In this setting either a continuous or a discontinuous phase transition emerges with the former being reminiscent of genuine nonequilibrium transitions of stochastic processes with multiple absorbing states. The third example considers the regime of coherent laser excitation. Here the many-body dynamics is dominated by an equilibrium transition of the "model A" universality class.

  12. Mean-field analysis of quantum phase transitions in a periodic optical superlattice

    SciTech Connect

    Dhar, Arya; Singh, Manpreet; Pai, Ramesh V.; Das, B. P.

    2011-09-15

    We analyze the various phases exhibited by a system of ultracold bosons in a periodic optical superlattice using the mean-field decoupling approximation. We investigate for a wide range of commensurate and incommensurate densities. We find the gapless superfluid phase, the gapped Mott insulator phase, and gapped insulator phases with distinct density wave orders.

  13. Charge-transfer states and optical transitions at the pentacene-TiO2 interface

    NASA Astrophysics Data System (ADS)

    Ljungberg, M. P.; Vänskä, O.; Koval, P.; Koch, S. W.; Kira, M.; Sánchez-Portal, D.

    2017-03-01

    Pentacene molecules have recently been observed to form a well-ordered monolayer on the (110) surface of rutile TiO2, with the molecules adsorbed lying flat, head to tail. With the geometry favorable for direct optical excitation and given its ordered character, this interface seems to provide an intriguing model to study charge-transfer excitations where the optically excited electrons and holes reside on different sides of the organic-inorganic interface. In this work, we theoretically investigate the structural and electronic properties of this system by means of ab initio calculations and compute its excitonic absorption spectrum. Molecular states appear in the band gap of the clean TiO2 surface, which enables charge-transfer excitations directly from the molecular HOMO to the TiO2 conduction band. The calculated optical spectrum shows a strong polarization dependence and displays excitonic resonances corresponding to the charge-transfer states, which could stimulate new experimental work on the optical response of this interface.

  14. Anisotropic optical properties of few-layer transition metal dichalcogenide ReS2

    NASA Astrophysics Data System (ADS)

    Li, Zhenglu; Cao, Ting; da Jornada, Felipe H.; Wu, Meng; Louie, Steven G.

    We present first-principles (DFT, GW and GW-BSE) calculations of the electronic and optical properties of few-layer rhenium disulfide (ReS2). Monolayer ReS2 shows strong many-electron effects with a fundamental quasiparticle band gap of 2.38 eV based on G0W0 calculation and a large exciton binding energy of 690 meV based on solving the Bethe-Salpeter equation. Highly anisotropic linear-polarized optical absorptions are revealed for few-layer and bulk ReS2. The band gap shows a decreasing trend with the optical polarization direction near the absorption edge gradually rotating from around 67 degree in the monolayer to 85 degree in the bulk, referencing to the Re-chain. Our calculations are consistent with recent experimental data and theoretical studies, and provide a systematic understanding of the electronic and optical properties in few-layer ReS2. This work was supported by National Science Foundation Grant No. DMR15-1508412 and the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Computational resources have been provided by DOE at Lawrence Berkeley National Laboratory's NERSC facility.

  15. Electron-impact Excitation of Ni II: Effective Collision Strengths for Optically Allowed Fine-structure Transitions

    NASA Astrophysics Data System (ADS)

    Cassidy, C. M.; Ramsbottom, C. A.; Scott, M. P.

    2011-09-01

    In this paper, we present collision strengths and Maxwellian averaged effective collision strengths for the electron-impact excitation of Ni II. Attention is expressly concentrated on the optically allowed fine-structure transitions between the 3d 9, 3d 84s, and 3d 74s 2 even parity levels and the 3d 84p and 3d 74s 4p odd parity levels. The parallel RMATRXII R-matrix package has been recently extended to allow for the inclusion of relativistic fine-structure effects. This suite of codes has been utilized in conjunction with the parallel PSTGF and PSTGICF programs in order to compute converged total collision strengths for the allowed transitions with which this study is concerned. All 113 LS terms identified with the 3d 9, 3d 84s, 3d 74s 2, 3d 84p, and 3d 74s 4p basis configurations were included in the target wavefunction representation, giving rise to a sophisticated 295 jj-level, 1930 coupled channel scattering complex. Maxwellian averaged effective collision strengths have been computed at 30 individual electron temperatures ranging from 30 to 1,000,000 K. This range comfortably encompasses all temperatures significant to astrophysical and plasma applications. The convergence of the collision strengths is exhaustively investigated and comparisons are made with previous theoretical works, where significant discrepancies exist for the majority of transitions. We conclude that intrinsic in achieving converged collision strengths and thus effective collision strengths for the allowed transitions is the combined inclusion of contributions from the (N + 1) partial waves extending to a total angular momentum value of L = 50 and further contributions from even higher partial waves accomplished by employing a "top-up" procedure.

  16. Simultaneous effects of pressure and temperature on the optical transition energies in a Ga0.7In0.3N/GaN quantum ring

    NASA Astrophysics Data System (ADS)

    Bala, K. Jaya; Peter, A. John; Lee, Chang Woo

    2017-09-01

    Simultaneous effects of pressure and temperature on electronic and optical properties are studied in a Ga0.7In0.3N/GaN quantum ring using variational formulism. The changes in exciton binding energy due to the applications of hydrostatic pressure and temperature are obtained taking into account the geometrical confinement. The transition energies of interband and intersubband as a function of hydrostatic pressure, at a constant temperature, are obtained. The oscillator strength due to interband and intersubband optical transitions with the combined effects of hydrostatic pressure and temperature is found. The pressure and temperature induced absorption coefficients as a function of photon energy are investigated in a Ga0.7In0.3N/GaN quantum ring. The results show that the application of pressure leads to blue shift of the resonant peaks of the optical transition whereas the effect of temperature suffers red shift of the resonant peaks.

  17. Pressure coefficients for direct optical transitions in MoS2, MoSe2, WS2, and WSe2 crystals and semiconductor to metal transitions

    PubMed Central

    Dybała, F.; Polak, M. P.; Kopaczek, J.; Scharoch, P.; Wu, K.; Tongay, S.; Kudrawiec, R.

    2016-01-01

    The electronic band structure of MoS2, MoSe2, WS2, and WSe2, crystals has been studied at various hydrostatic pressures experimentally by photoreflectance (PR) spectroscopy and theoretically within the density functional theory (DFT). In the PR spectra direct optical transitions (A and B) have been clearly observed and pressure coefficients have been determined for these transitions to be: αA = 2.0 ± 0.1 and αB = 3.6 ± 0.1 meV/kbar for MoS2, αA = 2.3 ± 0.1 and αB = 4.0 ± 0.1 meV/kbar for MoSe2, αA = 2.6 ± 0.1 and αB = 4.1 ± 0.1 meV/kbar for WS2, αA = 3.4 ± 0.1 and αB = 5.0 ± 0.5 meV/kbar for WSe2. It has been found that these coefficients are in an excellent agreement with theoretical predictions. In addition, a comparative study of different computational DFT approaches has been performed and analyzed. For indirect gap the pressure coefficient have been determined theoretically to be −7.9, −5.51, −6.11, and −3.79, meV/kbar for MoS2, MoSe2, WS2, and WSe2, respectively. The negative values of this coefficients imply a narrowing of the fundamental band gap with the increase in hydrostatic pressure and a semiconductor to metal transition for MoS2, MoSe2, WS2, and WSe2, crystals at around 140, 180, 190, and 240 kbar, respectively. PMID:27215469

  18. Pressure coefficients for direct optical transitions in MoS2, MoSe2, WS2, and WSe2 crystals and semiconductor to metal transitions

    NASA Astrophysics Data System (ADS)

    Dybała, F.; Polak, M. P.; Kopaczek, J.; Scharoch, P.; Wu, K.; Tongay, S.; Kudrawiec, R.

    2016-05-01

    The electronic band structure of MoS2, MoSe2, WS2, and WSe2, crystals has been studied at various hydrostatic pressures experimentally by photoreflectance (PR) spectroscopy and theoretically within the density functional theory (DFT). In the PR spectra direct optical transitions (A and B) have been clearly observed and pressure coefficients have been determined for these transitions to be: αA = 2.0 ± 0.1 and αB = 3.6 ± 0.1 meV/kbar for MoS2, αA = 2.3 ± 0.1 and αB = 4.0 ± 0.1 meV/kbar for MoSe2, αA = 2.6 ± 0.1 and αB = 4.1 ± 0.1 meV/kbar for WS2, αA = 3.4 ± 0.1 and αB = 5.0 ± 0.5 meV/kbar for WSe2. It has been found that these coefficients are in an excellent agreement with theoretical predictions. In addition, a comparative study of different computational DFT approaches has been performed and analyzed. For indirect gap the pressure coefficient have been determined theoretically to be -7.9, -5.51, -6.11, and -3.79, meV/kbar for MoS2, MoSe2, WS2, and WSe2, respectively. The negative values of this coefficients imply a narrowing of the fundamental band gap with the increase in hydrostatic pressure and a semiconductor to metal transition for MoS2, MoSe2, WS2, and WSe2, crystals at around 140, 180, 190, and 240 kbar, respectively.

  19. Exploring the optical contrast effect in strong atomic lines for exoplanets transiting active stars

    NASA Astrophysics Data System (ADS)

    Cauley, Paul W.; Redfield, Seth

    2017-01-01

    Transmission spectroscopy is a powerful tool for detecting and characterizing planetary atmospheres. Non-photospheric features on the stellar disk, however, can contaminate the planetary signal: during transit the observed spectrum is weighted towards the features not currently being occulted by the planet. This contrast effect can mimic absorption in the planetary atmosphere for strong atomic lines such as Na I, Ca II, and the hydrogen Balmer lines. While the contrast effect is negligible for quiet stars, contributions to the transmission signal from active stellar surfaces can produce ~1% changes in the line core. It is therefore critical that these contrast signals be differentiated from true absorption features in the planetary atmosphere. Here we present our work on simulating the contrast effect for an active stellar surface. We discuss the particular case of HD 189733 b, a well-studied hot Jupiter orbiting an active K-dwarf, due to the plethora of atomic absorption signals reported in its atmosphere.Specifically, we focus on Hα to address recent suggestions that the measured in-transit signals are a result of stellar activity. In the contrast model we include center-to-limb variations and calculate limb darkening parameters as a function of wavelength across the line of interest. The model includes contributions to the spectrum from spots, faculae and plages, filaments, and the bare stellar photosphere. Stellar rotation is also included. We find that it is very difficult to reproduce the measured in-transit Hα signals for reasonable active region parameters. In addition, it is difficult to create an in-transit contrast signature that lasts for the duration of the transit unless the planet is crossing an active latitudinal belt and is always obscuring active regions. This suggests that the Hα measurements arise predominantly in the planetary atmosphere. However, the contrast effect likely contributes to these signals. Furthermore, our results could be

  20. Forbidden optical transition in Ti-like Xe, Ba, and Ir

    SciTech Connect

    Bekker, H.; Windberger, A.; Binder, M.; López-Urrutia, J. R. Crespo; Versolato, O. O.; Klawitter, R.

    2015-01-09

    We present measurements of the (3d{sup 4}){sup 5}D{sub 2}−{sup 5}D{sub 3} transitions in the Ti-like ions Xe{sup 32+}, Ba{sup 34+}, and Ir{sup 55+} produced and trapped in the Heidelberg electron beam ion trap. The obtained wavelengths have a precision at the few ppm-level and are thereby the most precise measurements of these transitions up to date. For Z=60−75 semi-empirical calculations have shown excellent agreement, however our measurements combined with data from other works shows that outside this range predictions quickly deviate. The value obtained for Ir{sup 55+} 357.434(2) nm confirms the linear mismatch to ab initio calculations for Z > 70, as hypothesized in Utter et al., Phys. Rev. A 67, 012508 (2003)

  1. Chirping of an optical transition by an ultrafast acoustic soliton train in a semiconductor quantum well.

    PubMed

    Scherbakov, A V; van Capel, P J S; Akimov, A V; Dijkhuis, J I; Yakovlev, D R; Berstermann, T; Bayer, M

    2007-08-03

    Acoustic solitons formed during the propagation of a picosecond strain pulse in a GaAs crystal with a ZnSe/ZnMgSSe quantum well on top lead to exciton resonance energy shifts of up to 10 meV, and ultrafast frequency modulation, i.e., chirping, of the exciton transition. The effects are well described by a theoretical analysis based on the Korteweg-de Vries equation and accounting for the properties of the excitons in the quantum well.

  2. Population inversion on vibrational transitions of molecules under nonresonant optical excitation

    SciTech Connect

    Parkhomenko, A. I. Shalagin, A. M.

    2010-09-15

    The possibility of obtaining a population inversion on vibrational transitions of molecules through nonlinear effects when the pump radiation is absorbed in the wings of spectral lines is investigated theoretically. We show that a population inversion can be produced in molecules on vibrational transitions when intense pump radiation is absorbed in the blue wing of the R branch of the vibrational-rotational molecular spectrum. This effect is related to inequality of the probabilities of the absorption and stimulated emission of radiation and is attributable to collisional transitions between rotational levels. We have ascertained that the larger the rotational constant of the molecule and the higher the pump radiation intensity, the higher the effective frequency of the collisions that give rise to a population inversion. Using the carbon monoxide (CO) molecule as an example, we show that when intense ({approx}1010 W cm{sup -2}) pump radiation is absorbed in the blue wing of the R branch, a noticeable population inversion can be produced and the gain at the center of the R and P branches of the molecular spectrum can reach 0.011 and 0.250 cm{sup -1} at temperatures T = 300 and 100 K, respectively.

  3. Optical stability of 3d transition metal ions doped-cadmium borate glasses towards γ-rays interaction

    NASA Astrophysics Data System (ADS)

    Marzouk, M.; ElBatal, H.; Eisa, W.

    2016-07-01

    This work reports the preparation of glasses of binary cadmium borate with the basic composition (mol% 45 CdO 55 B2O3) and samples of the same composition containing 0.2 wt% dopants of 3d transition metal (TM) oxides (TiO2 → CuO). The glasses have been investigated by combined optical and Fourier Transform infrared spectroscopic measurements before and after being subjected to gamma irradiation with a dose of 8 Mrad (8 × 104 Gy). Optical absorption of the undoped glass before irradiation reveals strong charge transfer UV absorption which is related to the presence of unavoidable contaminated trace iron impurities (mainly Fe3+) within the raw materials used for the preparation of the base cadmium borate glass. The optical spectra of the 3d TM ions exhibit characteristic bands which are related the stable oxidation state of the 3d TM ions within the host glass. Gamma irradiation produces some limited variations in the optical spectra due to the stability of the host glass containing high percent 45 mol% of heavy metal oxide (CdO) which causes some shielding effects towards irradiation. From the absorption edge data, the values of the optical band gap Eopt and Urbach energy (∆E) have been calculated. The values of the optical energy gap are found to be dependent on the glass composition. Infrared absorption spectral measurements reveal characteristic absorption bands due to both triangular and tetrahedral borate groups with the BO3 units vibrations more intense than BO4 units due to the known limit value for the change of BO3 to BO4 groups. The introduction of 3d TM ions with the doping level (0.2 wt%) causes no changes in the number or position of the IR bands because of the presence of TM ions in modifying sites in the glass network. It is observed that gamma irradiation causes some limited changes in the FT-IR spectral bands due to the stability of the host heavy cadmium borate glass.

  4. Optical Design of the Camera for Transiting Exoplanet Survey Satellite (TESS)

    NASA Technical Reports Server (NTRS)

    Chrisp, Michael; Clark, Kristin; Primeau, Brian; Dalpiaz, Michael; Lennon, Joseph

    2015-01-01

    The optical design of the wide field of view refractive camera, 34 degrees diagonal field, for the TESS payload is described. This fast f/1.4 cryogenic camera, operating at -75 C, has no vignetting for maximum light gathering within the size and weight constraints. Four of these cameras capture full frames of star images for photometric searches of planet crossings. The optical design evolution, from the initial Petzval design, took advantage of Forbes aspheres to develop a hybrid design form. This maximized the correction from the two aspherics resulting in a reduction of average spot size by sixty percent in the final design. An external long wavelength pass filter was replaced by an internal filter coating on a lens to save weight, and has been fabricated to meet the specifications. The stray light requirements were met by an extended lens hood baffle design, giving the necessary off-axis attenuation.

  5. Report on the Radiation Effects Testing of the Infrared and Optical Transition Radiation Camera Systems

    SciTech Connect

    Holloway, Michael Andrew

    2016-04-20

    Presented in this report are the results tests performed at Argonne National Lab in collaboration with Los Alamos National Lab to assess the reliability of the critical 99Mo production facility beam monitoring diagnostics. The main components of the beam monitoring systems are two cameras that will be exposed to radiation during accelerator operation. The purpose of this test is to assess the reliability of the cameras and related optical components when exposed to operational radiation levels. Both X-ray and neutron radiation could potentially damage camera electronics as well as the optical components such as lenses and windows. This report covers results of the testing of component reliability when exposed to X-ray radiation. With the information from this study we provide recommendations for implementing protective measures for the camera systems in order to minimize the occurrence of radiation-induced failure within a ten month production run cycle.

  6. Transition operators in electromagnetic-wave diffraction theory. II - Applications to optics

    NASA Technical Reports Server (NTRS)

    Hahne, G. E.

    1993-01-01

    The theory developed by Hahne (1992) for the diffraction of time-harmonic electromagnetic waves from fixed obstacles is briefly summarized and extended. Applications of the theory are considered which comprise, first, a spherical harmonic expansion of the so-called radiation impedance operator in the theory, for a spherical surface, and second, a reconsideration of familiar short-wavelength approximation from the new standpoint, including a derivation of the so-called physical optics method on the basis of quasi-planar approximation to the radiation impedance operator, augmented by the method of stationary phase. The latter includes a rederivation of the geometrical optics approximation for the complete Green's function for the electromagnetic field in the presence of a smooth- and a convex-surfaced perfectly electrically conductive obstacle.

  7. Single-Slit Diffraction: Transitioning from Geometric Optics to the Fraunhofer Regime

    ERIC Educational Resources Information Center

    Panuski, Christopher L.; Mungan, Carl E.

    2016-01-01

    Suppose a red laser beam (of wavelength ? equal to 0.660 µm) is expanded using an optical telescope into a collimated, approximately plane wave that is 5.68 mm in diameter. Pass that beam through a tall rectangular slit whose width "a" is gradually reduced from 3.30 to 0.100 mm. Look at its image on a screen located at a distance…

  8. Quadrupole Transition Spectrum Measurement of Single Ca+ Ions Toward Optical Frequency Standards

    DTIC Science & Technology

    2007-01-01

    following subsections. The 854-nm one is a Littman-type extended-cavity diode laser ( ECDL ) frequency-stabilized with a confocal optical resonant...frequency-stabilized He-Ne laser, and a function generator. Details of this light source system are reported in [6]. The Littrow-type ECDLs at 866 nm...from the ECDL and the He-Ne laser are coupled to a single scanning transfer cavity. The cavity is placed in an airtight container made of an

  9. Single-Slit Diffraction: Transitioning from Geometric Optics to the Fraunhofer Regime

    ERIC Educational Resources Information Center

    Panuski, Christopher L.; Mungan, Carl E.

    2016-01-01

    Suppose a red laser beam (of wavelength ? equal to 0.660 µm) is expanded using an optical telescope into a collimated, approximately plane wave that is 5.68 mm in diameter. Pass that beam through a tall rectangular slit whose width "a" is gradually reduced from 3.30 to 0.100 mm. Look at its image on a screen located at a distance…

  10. Optical thickness identification of transition metal dichalcogenide nanosheets on transparent substrates

    NASA Astrophysics Data System (ADS)

    Zhang, Hao; Ran, Feirong; Shi, Xiaotong; Fang, Xiangru; Wu, Shiyu; Liu, Yue; Zheng, Xianqiang; Yang, Peng; Liu, Yang; Wang, Lin; Huang, Xiao; Li, Hai; Huang, Wei

    2017-04-01

    Transparent and flexible devices based on two-dimensional (2D) materials hold great potential for many electronic/optoelectronic applications. The direct and fast thickness identification of 2D materials on transparent substrates is therefore an essential step in such applications, but remains challenging. Here, we present a simple, rapid and reliable optical method to identify the thickness of 2D nanosheets on transparent substrates, such as polydimethylsiloxane, glass, and coverslip. Under reflection and transmission light, 1-20L MoS2 and 1-14L WSe2 nanosheets can be reliably identified by measuring the optical contrast difference between the 2D nanosheets and substrates in color, red, green or blue channels. Meanwhile, the values of all the measured contrast differences as a function of layer number can be well fitted with the Boltzmann function, indicating the generalizability and reliability of our optical method. Our method will not only facilitate the fundamental study of the thickness-dependent properties of 2D nanosheets, but will also expand their potential applications in the field of flexible/transparent electronics and optoelectronics.

  11. Optical thickness identification of transition metal dichalcogenide nanosheets on transparent substrates.

    PubMed

    Zhang, Hao; Ran, Feirong; Shi, Xiaotong; Fang, Xiangru; Wu, Shiyu; Liu, Yue; Zheng, Xianqiang; Yang, Peng; Liu, Yang; Wang, Lin; Huang, Xiao; Li, Hai; Huang, Wei

    2017-04-21

    Transparent and flexible devices based on two-dimensional (2D) materials hold great potential for many electronic/optoelectronic applications. The direct and fast thickness identification of 2D materials on transparent substrates is therefore an essential step in such applications, but remains challenging. Here, we present a simple, rapid and reliable optical method to identify the thickness of 2D nanosheets on transparent substrates, such as polydimethylsiloxane, glass, and coverslip. Under reflection and transmission light, 1-20L MoS2 and 1-14L WSe2 nanosheets can be reliably identified by measuring the optical contrast difference between the 2D nanosheets and substrates in color, red, green or blue channels. Meanwhile, the values of all the measured contrast differences as a function of layer number can be well fitted with the Boltzmann function, indicating the generalizability and reliability of our optical method. Our method will not only facilitate the fundamental study of the thickness-dependent properties of 2D nanosheets, but will also expand their potential applications in the field of flexible/transparent electronics and optoelectronics.

  12. Adsorption-induced changes of intramolecular optical transitions: PTCDA/NaCl and PTCDA/KCl.

    PubMed

    Hochheim, Manuel; Bredow, Thomas

    2015-09-15

    Structural and optical properties of isolated perylene-3,4,9,10-tetracarboxylic acid dianhydride molecules adsorbed on (100) oriented NaCl and KCl surfaces were studied theoretically to analyze the recently observed red-shift of the optical excitation spectrum after adsorption (Müller et al., Phys. Rev. B, 2011, 83, 241203; Paulheim et al. Phys. Chem. Chem. Phys., 2013, 15, 4906). The ground-state structures were obtained by periodic dispersion-corrected density functional theory (DFT) calculations. For the excited-state calculations, nonperiodic time-dependent DFT methods were applied for a cluster model embedded in point charges. The range-separated hybrid functional CAM-B3LYP was used. Correlation-consistent basis sets were used and the calculated excitation energies were extrapolated to the complete basis set limit. The shift of the first optical excitation energy was analyzed in terms of electronic and geometric contributions. It was found that both the distortion of the molecule due to the interaction with the surface and the electrostatic potential of the surface play an important role.

  13. Mean-Field Scaling of the Superfluid to Mott Insulator Transition in a 2D Optical Superlattice

    NASA Astrophysics Data System (ADS)

    Thomas, Claire K.; Barter, Thomas H.; Leung, Tsz-Him; Okano, Masayuki; Jo, Gyu-Boong; Guzman, Jennie; Kimchi, Itamar; Vishwanath, Ashvin; Stamper-Kurn, Dan M.

    2017-09-01

    The mean-field treatment of the Bose-Hubbard model predicts properties of lattice-trapped gases to be insensitive to the specific lattice geometry once system energies are scaled by the lattice coordination number z . We test this scaling directly by comparing coherence properties of 87Rb gases that are driven across the superfluid to Mott insulator transition within optical lattices of either the kagome (z =4 ) or the triangular (z =6 ) geometries. The coherent fraction measured for atoms in the kagome lattice is lower than for those in a triangular lattice with the same interaction and tunneling energies. A comparison of measurements from both lattices agrees quantitatively with the scaling prediction. We also study the response of the gas to a change in lattice geometry, and observe the dynamics as a strongly interacting kagome-lattice gas is suddenly "hole doped" by introducing the additional sites of the triangular lattice.

  14. Optical transitions of Er3+/Yb3+ codoped TeO2-WO3-Bi2O3 glass.

    PubMed

    Shen, Xiang; Nie, Qiuhua; Xu, Tiefeng; Gao, Yuan

    2005-10-01

    Optical absorption and emission properties of the Er3+/Yb3+ codoped TeO2-WO3-Bi2O3 (TWB) glass has been investigated. The transition probabilities, excited state lifetimes, and the branching ratios have been predicted for Er3+ based on the Judd-Ofelt theory. The broad 1.5 microm fluorescence was observed under 970 nm excitation, and its full width at half maximum (FWHM) is 77 nm. The emission cross-section is calculated using the McCumber theory, and the peak emission cross-section is 1.03 x 10(-21) cm2 at 1.531 microm. This value is much larger than those of the silicate and phosphate glasses. Efficient green and weak red upconversion luminescence from Er3+ centers in the glass sample was observed at room temperature, and the upconversion excitation processes have been analyzed.

  15. Cloud droplets to drizzle: Contribution of transition drops to microphysical and optical properties of marine stratocumulus clouds

    NASA Astrophysics Data System (ADS)

    Glienke, S.; Kostinski, A.; Fugal, J.; Shaw, R. A.; Borrmann, S.; Stith, J.

    2017-08-01

    Aircraft measurements of the ubiquitous marine stratocumulus cloud type, with over 3000 km of in situ data from the Pacific during the Cloud System Evolution in the Trades experiment, show the ability of the Holographic Detector for Clouds (HOLODEC) instrument to smoothly interpolate the small and large droplet data collected with Cloud Droplet Probe and 2DC instruments. The combined, comprehensive instrument suite reveals a surprisingly large contribution in the predrizzle size range of 40-80 μm (transition droplets, or drizzlets), a range typically not measured and assumed to reside in a condensation-to-collision minimum between cloud droplet and drizzle modes. Besides shedding light on the onset of collision coalescence, drizzlets are essential contributors to optical and chemical properties because of a substantial contribution to the total surface area. When adjusted to match spatial resolution of spaceborne remote sensing, the missing drizzlets bring in situ measurements to closer agreement with satellite observations.

  16. Observations of a mode transition in a hydrogen hollow cathode discharge using phase resolved optical emission spectroscopy

    SciTech Connect

    Dixon, Sam Charles, Christine; Dedrick, James; Boswell, Rod; Gans, Timo; O'Connell, Deborah

    2014-07-07

    Two distinct operational modes are observed in a radio frequency (rf) low pressure hydrogen hollow cathode discharge. The mode transition is characterised by a change in total light emission and differing expansion structures. An intensified CCD camera is used to make phase resolved images of Balmer α emission from the discharge. The low emission mode is consistent with a typical γ discharge, and appears to be driven by secondary electrons ejected from the cathode surface. The bright mode displays characteristics common to an inductive discharge, including increased optical emission, power factor, and temperature of the H{sub 2} gas. The bright mode precipitates the formation of a stationary shock in the expansion, observed as a dark region adjacent to the source-chamber interface.

  17. Plasmonic phase transition and phase retardation: essential optical characteristics of localized surface plasmon resonance

    NASA Astrophysics Data System (ADS)

    Chen, Wen-Yu; Lin, Chun-Hung; Chen, Wei-Ting

    2013-09-01

    Phase transition that occurs around the spectral position of localized surface plasmon resonance (LSPR) has various applications for light manipulation and refractive index sensing. Previous studies focused on phase responses of specific plasmonic structures, whereas the general theoretical analysis remains inadequate. In this study, we analytically modeled the phase spectra and the intensity spectra of silver nanodots with temporal coupled-mode theory. The phase transition occurs at the transmission dip, whereas the phase of reflection varies much more gradually. We further derived the equation for the slope of the phase at the transmission dip, which is a function of the rates of Ohmic dissipation and emission. The theoretical analysis is also applicable for wide varieties of LSPR systems and provides an intuitive physical mechanism for phase properties. Then, based on the fundamental discussion, we further investigated plasmonic phase retardation in anisotropic nanodots for the application of boosting the figure of merit (FOM) of refractive index sensing. The anisotropic nanodots induce plasmonic phase transitions, which spectrally split, for transmission waves polarized along the symmetric axes. Thus, anisotropy induces relative phase retardation in the narrow spectral region between the wavelengths of the LSPRs. We numerically manipulated the full width at half maximum of the ellipsometric spectra by adjusting the aspect ratio of the nanodots and observed an FOM of 24.3. In addition, experiments were performed to demonstrate the feasibility of this arrangement.Phase transition that occurs around the spectral position of localized surface plasmon resonance (LSPR) has various applications for light manipulation and refractive index sensing. Previous studies focused on phase responses of specific plasmonic structures, whereas the general theoretical analysis remains inadequate. In this study, we analytically modeled the phase spectra and the intensity spectra of

  18. Transition from unidirectional to delayed bidirectional coupling in optically coupled semiconductor lasers.

    PubMed

    Bonatto, Cristian; Kelleher, Bryan; Huyet, Guillaume; Hegarty, Stephen P

    2012-02-01

    We investigate the transition from unidirectional to delayed bidirectional coupling of semiconductor lasers. By tuning the coupling strength in one direction we show how the locking region evolves as a function of the detuning and coupling strength. We consider two representative values of the relaxation oscillation damping: one where the relaxation oscillations are very underdamped and one where they are very overdamped. Qualitatively different dynamical scenarios are shown to emerge for each case. Several features of the delayed bidirectional system can be seen as remaining from the unidirectional system while others clearly arise due to the delayed coupling and are similar to effects seen in delayed feedback configurations.

  19. Temperature dependence of terahertz optical transitions from boron and phosphorus dopant impurities in silicon

    NASA Astrophysics Data System (ADS)

    Lynch, S. A.; Townsend, P.; Matmon, G.; Paul, D. J.; Bain, M.; Gamble, H. S.; Zhang, J.; Ikonic, Z.; Kelsall, R. W.; Harrison, P.

    2005-09-01

    There has been considerable interest in using impurity dopants in silicon, such as boron and phosphorus, since it was demonstrated that such materials can show emission in the THz region of the electromagnetic spectrum. The measured temperature dependence of these transitions in this letter shows that the most optimistic maximum operating temperature of such an impurity-based laser is 90 K. In a real device with current flowing and associated Joule heating, the actual operating range is likely to be much narrower and it is therefore unlikely that such a device would have a maximum operating temperature above 40 K.

  20. Singlet biradical{yields}singlet zwitterion optical transition in a twisted olefin

    SciTech Connect

    Piotrowiak, P.; Strati, G.; Smirnov, S.N.; Warman, J.M.; Schuddeboom, W.

    1996-09-18

    We report the first direct observation of the singlet biradical $YLD singlet zwitterion transition in a twisted olefin, biphenanthrenylidene. Biphenanthrenylidene (full name, bi-4H-cyclopenta[def]phenanthren-4-ylidene, abbreviated as BPH) is an analogue of tetraphenylethylene (TPE) and stilbene, both of which are the favorite models of photoisomerization reactions. The investigations have been focusing on the dynamics of the twisting motion of the double bond which leads to decoupling of the two halves of the olefin and results in the formation of the D{sub 2d} 90{degree}-twisted zwitterionic or biradical excited state. 13 refs., 2 figs., 1 tab.

  1. Single-Slit Diffraction: Transitioning from Geometric Optics to the Fraunhofer Regime

    NASA Astrophysics Data System (ADS)

    Panuski, Christopher L.; Mungan, Carl E.

    2016-09-01

    Suppose a red laser beam (of wavelength λ equal to 0.660 μm) is expanded using an optical telescope into a collimated, approximately plane wave that is 5.68 mm in diameter. Pass that beam through a tall rectangular slit whose width a is gradually reduced from 3.30 to 0.100 mm. Look at its image on a screen located at a distance L from the slit equal to 0.656 m. As the slit is narrowed, you predict that the width of the pattern will: (A) smoothly increase, (B) smoothly decrease, (C)increase and then decrease, or (D) decrease and then increase.

  2. Surface plasmon optical study of the interfacial phase transition of elastinlike polypeptide grafted on gold.

    PubMed

    Xu, Fei; Joon, Huang Min; Trabbic-Carlson, Kimberly; Chilkoti, Ashutosh; Knoll, Wolfgang

    2008-09-01

    The conformational changes in elastinlike polypeptides (ELPs) grafted to a solid/solution interface via different architectures were studied using surface plasmon resonance spectroscopy and surface plasmon field-enhanced fluorescence spectroscopy (SPFS). SPFS provides a simple and convenient optical method to study the influence of the grafting method and the graft density on the conformational changes in ELPs at the solid-solution interface as a function of environmental variables. A typical response of the ELP, consistent with its stimuli responsiveness, was a gradual collapse upon increasing the ionic strength; this effect was inversely correlated with the surface graft density of the ELP.

  3. Effect of the order-disorder transition on the optical properties of Cu2ZnSnS4

    NASA Astrophysics Data System (ADS)

    Valentini, M.; Malerba, C.; Menchini, F.; Tedeschi, D.; Polimeni, A.; Capizzi, M.; Mittiga, A.

    2016-05-01

    The effect of the order-disorder transition on the band gap of kesterite Cu2ZnSnS4, an interesting material for solar cells, has been investigated by optical spectroscopy. The band gap energy (Eg) decreases continuously with increasing annealing temperature, Ta, and reaches its minimum at Ta ˜ 273 °C. Eg is about 200 meV higher in the most ordered state, than in the fully disordered state. Its value and the transition kinetic depend on the sample stoichiometry. A simplified model able to explain the order degree and stoichiometry effects on the Eg value is developed. Ordering results in narrower Raman peaks without affecting the shape of the photoluminescence spectrum—except for the change in Eg—or the characteristic energy of the exponential tail below the fundamental absorption edge. Although a prolonged annealing increases the order degree, the material properties are still influenced by residual disorder as well as by defects related to the off-stoichiometry composition.

  4. Experimental study for the detection of the laminar/turbulent aerodynamic transition on a wing aircraft, using fiber optic sensors

    NASA Astrophysics Data System (ADS)

    Molin, S.; Dolfi, D.; Doisy, M.; Seraudie, A.; Arnal, D.; Coustols, E.; Mandle, J.

    2010-09-01

    We demonstrate the feasibility of detection of the nature (laminar/turbulent/transitional) of the aerodynamic boundary layer of a profile of a wing aircraft model, using a Distributed FeedBack (DFB) Fiber Laser as optical fiber sensor. Signals to be measured are pressure variations : ΔP~1Pa at few 100Hz in the laminar region and ΔP~10Pa at few kHz in the turbulent region. Intermittent regime occurring in-between these two regions (transition) is characterized by turbulent bursts in laminar flow. Relevant pressure variations have been obtained in a low-speed research-type wind tunnel of ONERA Centre of Toulouse. In order to validate the measurements, a "classical" hot film sensor, the application and use of which have been formerly developed and validated by ONERA, has been placed at the neighborhood of the fiber sensor. The hot film allows measurement of the boundary layer wall shear stress whose characteristics are a well known signature of the boundary layer nature (laminar, intermittent or turbulent) [1]. In the three regimes, signals from the fiber sensor and the hot film sensor are strongly correlated, which allows us to conclude that a DFB fiber laser sensor is a good candidate for detecting the boundary layer nature, and thus for future integration in an aircraft wing. The work presented here has been realized within the framework of "Clean Sky", a Joint Technology Initiative of the European Union.

  5. Optical properties, lattice dynamics, and structural phase transition in hexagonal 2 H -BaMn O3 single crystals

    NASA Astrophysics Data System (ADS)

    Stanislavchuk, T. N.; Litvinchuk, A. P.; Hu, Rongwei; Jeon, Young Hun; Ji, Sung Dae; Cheong, S.-W.; Sirenko, A. A.

    2015-10-01

    Optical properties and lattice dynamics of hexagonal 2 H -BaMn O3 single crystals are studied experimentally in a wide temperature range by means of rotating analyzer ellipsometry and Raman scattering. The magnitude of the direct electronic band gap is found to be Eg=3.2 eV . At room temperature the far-infrared (IR) ellipsometry spectra reveal six IR-active phonons; two of them are polarized along the c axis and four are polarized within the a-b plane. Seven phonon modes are identified in the Raman scattering experiments. Group theoretical mode analysis and complementary density functional theory lattice dynamics calculations are consistent with the 2 H -BaMn O3 structure belonging to the polar P 63m c space group at room temperature. All observed vibrational modes are assigned to specific eigenmodes of the lattice. The neutron diffraction measurements reveal a structural phase transition upon cooling below TC=130 ±5 K , which is accompanied by a lattice symmetry change from P 63m c to P 63c m . Simultaneously, at temperatures below TC several additional IR- and Raman-active modes are detected in experimental spectra. This confirms the occurrence of a structural transition, which is possibly associated with the appearance of electrical polarization along the c axis and a previously known tripling of the primitive cell volume at low temperatures.

  6. Fractional Mott insulator-to-superfluid transition of Bose-Hubbard model in a trimerized Kagomé optical lattice.

    PubMed

    Chen, Qi-Hui; Li, Peng; Su, Haibin

    2016-06-29

    By generalizing the traditional single-site strong coupling expansion approach to a cluster one, we study the zero-temperature phase diagram of bosonic atoms in a trimerized Kagomé optical lattice. Some new features are present in this system. Due to the strong intra-trimer hopping interaction, there will be a new Mott insulator (MI), which is by definition incompressible but with a fractional filling per trimer. This is different from the traditional MI, which has an integral filling and originates only from the repulsive interaction between particles. We investigate the MI-to-superfluid transition and the nature of the fractional MI by calculating the critical exponents of phase transitions and the low-lying energy excitation spectra of quasiparticles (quasihole). We will show how the low-energy properties of this system can be understood qualitatively as a Bose-Hubbard model in triangular lattice from the point of view of the cluster strong coupling expansion. We also discuss how our results are related to experiment by studying the Bragg spectroscopy.

  7. Fractional Mott insulator-to-superfluid transition of Bose-Hubbard model in a trimerized Kagomé optical lattice

    NASA Astrophysics Data System (ADS)

    Chen, Qi-Hui; Li, Peng; Su, Haibin

    2016-06-01

    By generalizing the traditional single-site strong coupling expansion approach to a cluster one, we study the zero-temperature phase diagram of bosonic atoms in a trimerized Kagomé optical lattice. Some new features are present in this system. Due to the strong intra-trimer hopping interaction, there will be a new Mott insulator (MI), which is by definition incompressible but with a fractional filling per trimer. This is different from the traditional MI, which has an integral filling and originates only from the repulsive interaction between particles. We investigate the MI-to-superfluid transition and the nature of the fractional MI by calculating the critical exponents of phase transitions and the low-lying energy excitation spectra of quasiparticles (quasihole). We will show how the low-energy properties of this system can be understood qualitatively as a Bose-Hubbard model in triangular lattice from the point of view of the cluster strong coupling expansion. We also discuss how our results are related to experiment by studying the Bragg spectroscopy.

  8. Synthetic Mimics of Bacterial Lipid A Trigger Optical Transitions in Liquid Crystal Microdroplets at Ultralow Picogram-per-Milliliter Concentrations

    PubMed Central

    2016-01-01

    We report synthetic six-tailed mimics of the bacterial glycolipid Lipid A that trigger changes in the internal ordering of water-dispersed liquid crystal (LC) microdroplets at ultralow (picogram-per-milliliter) concentrations. These molecules represent the first class of synthetic amphiphiles to mimic the ability of Lipid A and bacterial endotoxins to trigger optical responses in LC droplets at these ultralow concentrations. This behavior stands in contrast to all previously reported synthetic surfactants and lipids, which require near-complete monolayer coverage at the LC droplet surface to trigger ordering transitions. Surface-pressure measurements and SAXS experiments reveal these six-tailed synthetic amphiphiles to mimic key aspects of the self-assembly of Lipid A at aqueous interfaces and in solution. These and other results suggest that these amphiphiles trigger orientational transitions at ultralow concentrations through a unique mechanism that is similar to that of Lipid A and involves formation of inverted self-associated nanostructures at topological defects in the LC droplets. PMID:26562069

  9. Direct Excitation of the Forbidden Clock Transition in Neutral {sup 174}Yb Atoms Confined to an Optical Lattice

    SciTech Connect

    Barber, Z.W.; Hoyt, C.W.; Oates, C.W.; Hollberg, L.; Taichenachev, A.V.; Yudin, V.I.

    2006-03-03

    We report direct single-laser excitation of the strictly forbidden (6s{sup 2}){sup 1}S{sub 0}{r_reversible}(6s6p){sup 3}P{sub 0} clock transition in {sup 174}Yb atoms confined to a 1D optical lattice. A small ({approx}1.2 mT) static magnetic field was used to induce a nonzero electric dipole transition probability between the clock states at 578.42 nm. Narrow resonance linewidths of 20 Hz (FWHM) with high contrast were observed, demonstrating a resonance quality factor of 2.6x10{sup 13}. The previously unknown ac Stark shift-canceling (magic) wavelength was determined to be 759.35{+-}0.02 nm. This method for using the metrologically superior even isotope can be easily implemented in current Yb and Sr lattice clocks and can create new clock possibilities in other alkaline-earth-like atoms such as Mg and Ca.

  10. Optical transitions of Er3+ ions in RbMgF3 and RbMgF3: Mn

    NASA Astrophysics Data System (ADS)

    Shinn, M. D.; Windscheif, J. C.; Sardar, D. K.; Sibley, W. A.

    1982-09-01

    Optical absorption, emission, and excitation spectra, as well as lifetime values, are presented for Er3+ ions in RbMgF3. Previous workers have demonstrated that Er3+ ions can reside in a number of different site symmetries in crystalline hosts such as CaF2 and CdF2. The numerous sites in this type lattice are most likely due to compensating fluorine interstitials which are necessarily present for charge compensation. In a unit cell of RbMgF3 there are two nonequivalent Mg2+ sites with C3v symmetry. Evidence is presented in this paper that Er3+ ions in RbMgF3 substitute for Mg2+ ions in both types of sites. The charge compensation is not local, which leaves the symmetry of the Er3+ sites unchanged. Absorption data for Er3+-ion transitions in both sites are shown. Emission from Er3+ ions is observed from one type of site in RbMgF3 and from both types of sites in RbMgF3: Mn. Lifetime values for the 4S32 and 4F92 transitions are shorter than those normally measured in fluoride host lattices, and the emissions are quenched above 200 K. Energy migration among Er3+ ions and subsequent energy transfer to Mn2+-ion impurities are responsible for the steady-state and transient-emission behavior.

  11. Optically induced reversible wettability transition on single crystal lithium niobate surfaces

    NASA Astrophysics Data System (ADS)

    Yan, Weishan; Zhao, Dongfang; Zhang, Ling; Jia, Ran; Gao, Naikun; Zhang, Dongdong; Luo, Wenyao; Li, Yanlu; Liu, Duo

    2017-08-01

    Solid surfaces with controllable and reversible wettability are scientifically and technologically important. Here, we report on the reversible wettability transitions of single crystal (0001) lithium niobate (LiNbO3) surfaces by alternate ultraviolet (UV) and infrared (IR) light irradiation. The UV irradiation (170 mW/cm2) could markedly reduce the contact angle of LiNbO3 over 30 min from 55.3° to 10.7°. IR irradiation (200 mW/cm2) recovered the water contact angle from 10.7° to 55.1° over 1 h. First-principles calculations showed that under both O-poor and O-rich conditions, oxygen vacancies preferred to form at the Li-terminal (0001) surface rather than at the Nb-terminal surface and the O-terminal surface or in the bulk. We further show that this light induced wettability transition has a dependence on the light wavelength. The influences of relative humidity and oxygen concentration were also investigated.

  12. Electronic structures and enhanced optical properties of blue phosphorene/transition metal dichalcogenides van der Waals heterostructures

    NASA Astrophysics Data System (ADS)

    Peng, Qiong; Wang, Zhenyu; Sa, Baisheng; Wu, Bo; Sun, Zhimei

    2016-08-01

    As a fast emerging topic, van der Waals (vdW) heterostructures have been proposed to modify two-dimensional layered materials with desired properties, thus greatly extending the applications of these materials. In this work, the stacking characteristics, electronic structures, band edge alignments, charge density distributions and optical properties of blue phosphorene/transition metal dichalcogenides (BlueP/TMDs) vdW heterostructures were systematically studied based on vdW corrected density functional theory. Interestingly, the valence band maximum and conduction band minimum are located in different parts of BlueP/MoSe2, BlueP/WS2 and BlueP/WSe2 heterostructures. The MoSe2, WS2 or WSe2 layer can be used as the electron donor and the BlueP layer can be used as the electron acceptor. We further found that the optical properties under visible-light irradiation of BlueP/TMDs vdW heterostructures are significantly improved. In particular, the predicted upper limit energy conversion efficiencies of BlueP/MoS2 and BlueP/MoSe2 heterostructures reach as large as 1.16% and 0.98%, respectively, suggesting their potential applications in efficient thin-film solar cells and optoelectronic devices.

  13. Phase transition from BCT to spinel structure in CdAl2Se4 and its optical properties

    NASA Astrophysics Data System (ADS)

    Singh, Poonam; Verma, U. P.; Jensen, Per

    2013-10-01

    We present a detailed first principle investigation on CdAl2Se4 both at ambient and the high pressure conditions. At ambient condition CdAl2Se4 exists in body centered tetragonal (BCT) phase and at high pressure in spinel phase. Corresponding to different volume the total energy has been optimized using three functional, viz., the local density approximation (LDA), the generalized gradient approximation (GGA) and the Engel-Vosko generalised gradient approximation (EV-GGA). In all the cases phase transition from the BCT to the spinel phase has been observed. The equilibrium lattice constants, energy band gaps, bulk modulus have been reported at ambient conditions in both the phases. According to our prediction CdAl2Se4 is a direct band gap material in both the studied phases, contrary to the earlier results reported by Funetes-cabrea and Sankey for spinel phase. Among optical constants index of refraction, absorption coefficient and optical conductivity are calculated and compared with the existing results in both the phases within the energy range of 0-25 eV.

  14. Electronic structures and enhanced optical properties of blue phosphorene/transition metal dichalcogenides van der Waals heterostructures.

    PubMed

    Peng, Qiong; Wang, Zhenyu; Sa, Baisheng; Wu, Bo; Sun, Zhimei

    2016-08-24

    As a fast emerging topic, van der Waals (vdW) heterostructures have been proposed to modify two-dimensional layered materials with desired properties, thus greatly extending the applications of these materials. In this work, the stacking characteristics, electronic structures, band edge alignments, charge density distributions and optical properties of blue phosphorene/transition metal dichalcogenides (BlueP/TMDs) vdW heterostructures were systematically studied based on vdW corrected density functional theory. Interestingly, the valence band maximum and conduction band minimum are located in different parts of BlueP/MoSe2, BlueP/WS2 and BlueP/WSe2 heterostructures. The MoSe2, WS2 or WSe2 layer can be used as the electron donor and the BlueP layer can be used as the electron acceptor. We further found that the optical properties under visible-light irradiation of BlueP/TMDs vdW heterostructures are significantly improved. In particular, the predicted upper limit energy conversion efficiencies of BlueP/MoS2 and BlueP/MoSe2 heterostructures reach as large as 1.16% and 0.98%, respectively, suggesting their potential applications in efficient thin-film solar cells and optoelectronic devices.

  15. Constraining The Magnetic Fields Of Transiting Exoplanets Through Ground-based Near-UV And Optical Observations

    NASA Astrophysics Data System (ADS)

    Turner, Jake; Smart, B.; Hardegree-Ullman, K.; Griffith, C. A.; Biddle, L.; Carleton, T.; Crawford, B.; De La Rosa, R.; Donnels, M.; Guvenen, B.; Guvenen, B.; Hofmann, R.; McGraw, A. M.; Nieberding, M.; Robertson, A.; Scott, A.; Small, L.; Smith, C.; Teske, J.; Towner, A. P.; Walker-LaFollette, A.; Zellem, R.

    2013-01-01

    Studying the magnetic fields of exoplanets allow for the investigation of their interior structure and rotation period, the presence of extrasolar moons, atmospheric retention, and potential habitability. We observed the primary transits of the hot Jupiters TrES-3b, WASP-12b, TrES-4b, WASP-26b, WASP-33b, HAT-P-1b, WASP-14b, HAT-P-6b, XO-2b, CoRoT-9b, and CoRoT-1b, the hot Neptune GJ 436b, and the super Earth GJ 1214b with the Steward Observatory 1.55 meter Kuiper Telescope using near-UV and optical filters in an attempt to constrain their magnetic fields. Vidotto et al. (2011) suggest that the magnetic field of these planets can be constrained if their near-UV light curve shows an early ingress compared to its optical light curve, while their egress remains unaffected. Our study provides the first constraints on the effect proposed by Vidotto et al. (2011) and the magnetic field strengths for many of our targets.

  16. Electronic structures and enhanced optical properties of blue phosphorene/transition metal dichalcogenides van der Waals heterostructures

    PubMed Central

    Peng, Qiong; Wang, Zhenyu; Sa, Baisheng; Wu, Bo; Sun, Zhimei

    2016-01-01

    As a fast emerging topic, van der Waals (vdW) heterostructures have been proposed to modify two-dimensional layered materials with desired properties, thus greatly extending the applications of these materials. In this work, the stacking characteristics, electronic structures, band edge alignments, charge density distributions and optical properties of blue phosphorene/transition metal dichalcogenides (BlueP/TMDs) vdW heterostructures were systematically studied based on vdW corrected density functional theory. Interestingly, the valence band maximum and conduction band minimum are located in different parts of BlueP/MoSe2, BlueP/WS2 and BlueP/WSe2 heterostructures. The MoSe2, WS2 or WSe2 layer can be used as the electron donor and the BlueP layer can be used as the electron acceptor. We further found that the optical properties under visible-light irradiation of BlueP/TMDs vdW heterostructures are significantly improved. In particular, the predicted upper limit energy conversion efficiencies of BlueP/MoS2 and BlueP/MoSe2 heterostructures reach as large as 1.16% and 0.98%, respectively, suggesting their potential applications in efficient thin-film solar cells and optoelectronic devices. PMID:27553787

  17. Metal-insulator transition and nonlinear optical responseof sputter-deposited V3O5 thin films

    NASA Astrophysics Data System (ADS)

    Rúa, Armando; Díaz, Ramón D.; Kumar, Nardeep; Lysenko, Sergiy; Fernández, Félix E.

    2017-06-01

    The compound V3O5, a member of the vanadium oxide Magnéli series, exhibits a metal-insulator transition near 430 K, the highest known temperature value among all vanadium oxides. It has been studied before mainly in single-crystal form, and for the very few cases in which thin films have been fabricated before, the procedure has required extensive post-deposition annealing of other oxides or vanadium metal at high temperatures in tightly controlled atmospheres. For the present work, V3O5 films were deposited directly on SiO2 glass substrates, without subsequent annealing, by DC magnetron sputtering. X-ray diffraction study of the samples evidenced oxygen deficiency, accommodated by oxygen vacancies. Resistivity measurements from 300 to 500 K revealed the metal-insulator transition by Tc ˜ 430 K, with an associated resistivity change by a factor of 20, and no detectable hysteresis in heating-cooling cycles, in agreement with most single-crystal studies. Resistivity values obtained were, however, lower than published results for bulk crystal values, particularly at temperatures below Tc. This was attributed to conduction electrons generated by the oxygen vacancies. Gradual resistivity increase in a very thin sample, through heating in air at temperatures up to 500 K, lends support to this argument. Using a pump-probe scattering technique, the V3O5 films were also probed for ultrafast nonlinear optical response. A reduction in the transient relative scattered light signal was recorded, which reached -10% within ˜800 fs. This observed response, likely related to the photoinduced insulator-to-metal phase transition, should stimulate additional interest in this material.

  18. Magnetic and natural optical activity of f- f transitions in multiferroic Nd0.5Gd0.5Fe3(BO3)4

    NASA Astrophysics Data System (ADS)

    Malakhovskii, A. V.; Sukhachev, A. L.; Leont'ev, A. A.; Temerov, V. L.

    2016-05-01

    Spectra of absorption, magnetic circular dichroism, and natural circular dichroism of the f-f transitions 4 I 9/2 → 4 F 3/2, 2 H 9/2 + 4 F 5/2, 4 S 3/2 + 4 F 7/2, 2 G 7/2 + 4 G 5/2, 2 K 13/2 + 4 G 7/2, and 4 G 9/2 in the Nd3+ ions in the Nd0.5Gd0.5Fe3(BO3)4 crystal have been measured as a function of the temperature in the interval of 90-300 K. Temperature dependences of the magneto-optical activity (MOA) and natural optical activity (NOA) of the transitions have been obtained. It has been found that, in contrast to allowed transitions, the temperature dependence of the MOA of the f-f transitions does not obey the Curie-Weiss law and the NOA depends on temperature. The NOA of some transitions changes the sign with variation in temperature. These phenomena have been explained by the presence of three contributions to the allowance of the f-f transitions, which lead to three contributions of different signs to the MOA and NOA. The range of the MOA of the f-f transitions in the Nd3+ ion has been predicted theoretically and confirmed experimentally.

  19. Optical conductivity of Weyl semimetals and signatures of the gapped semimetal phase transition

    NASA Astrophysics Data System (ADS)

    Tabert, C. J.; Carbotte, J. P.

    2016-02-01

    The interband optical response of a three-dimensional Dirac cone is linear in photon energy (Ω ) . Here, we study the evolution of the interband response within a model Hamiltonian which contains Dirac, Weyl, and gapped semimetal phases. In the pure Dirac case, a single linear dependence is observed, while in the Weyl phase, we find two quasilinear regions with different slopes. These regions are also distinct from the large-Ω dependence. As the boundary between the Weyl (WSM) and gapped phases is approached, the slope of the low-Ω response increases, while the photon-energy range over which it applies decreases. At the phase boundary, a square root behavior is obtained which is followed by a gapped response in the gapped semimetal phase. The density of states parallels these behaviors with the linear law replaced by quadratic behavior in the WSM phase and the square root dependence at the phase boundary changed to |ω| 3 /2. The optical spectral weight under the intraband (Drude) response at low temperature (T ) and/or small chemical potential (μ ) is found to change from T2 (μ2) in the WSM phase to T3 /2 (|μ |3/2) at the phase boundary.

  20. Exploring the quantum-classical transition in an optical Bose-Einstein condensate

    NASA Astrophysics Data System (ADS)

    Zhang, Keye; Meystre, Pierre; Zhang, Weiping

    2014-05-01

    Recent experiments have demonstrated the Bose-Einstein condensation of photons in a dye microcavity. A remarkable feature is that it behaves as a condensate of massive particles essentially at room temperature and is coupled to the heat reservoir that realizes grand-canonical conditions. We analyze theoretically the control of that system by a secondary coherent cavity field that produces an optomechanical-like coupling between the probe and the condensate. We find that the controllable quantum statistics associated with the size of the reservoir allow one to prepare the photon condensate in a variety of nonclassical states, carry out quantum nondemolition measurements of its number fluctuations, and provide an effective tool to explore the physics of the quantum-classical transition regime.

  1. Band structure and optical transitions in the Hg3Se2Cl2 crystals

    NASA Astrophysics Data System (ADS)

    Bokotey, O. V.; Vakulchak, V. V.; Nebola, I. I.; Bokotey, A. A.

    2016-12-01

    First-principles calculations of the band structure for Hg3Se2Cl2 crystal were performed by means of density functional theory (DFT). The exchange and correlation potential was described within a framework of the local density approximation based on exchange-correlation energy optimization to calculate the total energy. DOS/PDOS and valence charge distribution were studied in details. Absorption near the fundamental edge was found to be due to indirect and direct allowed transitions. For device applications based on Hg3Se2Cl2 crystal, understanding these fundamental issues is highly important and essential. It should be noted that optoelectronic applications of Hg3Se2Cl2 are caused by coexistence of the large polarized Hg cations and a huge contribution of an harmonic phonon subsystem caused by anions.

  2. Optically trapped atom interferometry using the clock transition of large 87Rb Bose-Einstein condensates

    NASA Astrophysics Data System (ADS)

    Altin, P. A.; McDonald, G.; Döring, D.; Debs, J. E.; Barter, T. H.; Robins, N. P.; Close, J. D.; Haine, S. A.; Hanna, T. M.; Anderson, R. P.

    2011-11-01

    In our original paper (Altin et al 2011 New J. Phys. 13 065020), we presented the results from a Ramsey atom interferometer operating with an optically trapped sample of up to 106 Bose-condensed 87Rb atoms in the mF = 0 clock states. We were unable to observe projection noise fluctuations on the interferometer output, which we attribute to the stability of our microwave oscillator and background magnetic field. Numerical simulations of the Gross-Pitaevskii equations for our system show that dephasing due to spatial dynamics driven by interparticle interactions accounts for much of the observed decay in fringe visibility at long interrogation times. The simulations show good agreement with the experimental data when additional technical decoherence is accounted for, and suggest that the clock states are indeed immiscible. With smaller samples of 5 × 104 atoms, we observe a coherence time of τ = 1.0+0.5-0.3 s.

  3. Probing the Spin-Polarized Electronic Band Structure in Monolayer Transition Metal Dichalcogenides by Optical Spectroscopy

    NASA Astrophysics Data System (ADS)

    Wang, Zefang; Zhao, Liang; Mak, Kin Fai; Shan, Jie

    2017-02-01

    We study the electronic band structure in the K/K' valleys of the Brillouin zone of monolayer WSe2 and MoSe2 by optical reflection and photoluminescence spectroscopy on dual-gated field-effect devices. Our experiment reveals the distinct spin polarization in the conduction bands of these compounds by a systematic study of the doping dependence of the A and B excitonic resonances. Electrons in the highest-energy valence band and the lowest-energy conduction band have antiparallel spins in monolayer WSe2, and parallel spins in monolayer MoSe2. The spin splitting is determined to be hundreds of meV for the valence bands and tens of meV for the conduction bands, which are in good agreement with first principles calculations. These values also suggest that both n- and p-type WSe2 and MoSe2 can be relevant for spin- and valley-based applications

  4. Theoretical study of intraband optical transitions in conduction band of dot-in-a-well system

    SciTech Connect

    Chaganti, Venkata R.; Apalkov, Vadym

    2014-02-15

    We study numerically absorption optical spectra of n-doped InAs/In{sub 015}Ga{sub 085}As/GaAs quantum dot-in-a-well systems. The absorption spectra are mainly determined by the size of a quantum dot and have weak dependence on the thickness of quantum well and position of the dot in a well. The dot-in-a-well system is sensitive to both in-plane and out-of-plane polarizations of the incident light with much stronger absorption intensities for the in-plane-polarized light. The absorption spectrum of in-plane-polarized light has also a multi-peak structure with two or three peaks of comparable intensities, while the absorption spectrum of out-of-plane polarized light has a single well-pronounced peak.

  5. Spin Flips versus Spin Transport in Nonthermal Electrons Excited by Ultrashort Optical Pulses in Transition Metals

    NASA Astrophysics Data System (ADS)

    Shokeen, V.; Sanchez Piaia, M.; Bigot, J.-Y.; Müller, T.; Elliott, P.; Dewhurst, J. K.; Sharma, S.; Gross, E. K. U.

    2017-09-01

    A joint theoretical and experimental investigation is performed to understand the underlying physics of laser-induced demagnetization in Ni and Co films with varying thicknesses excited by 10 fs optical pulses. Experimentally, the dynamics of spins is studied by determining the time-dependent amplitude of the Voigt vector, retrieved from a full set of magnetic and nonmagnetic quantities performed on both sides of films, with absolute time reference. Theoretically, ab initio calculations are performed using time-dependent density functional theory. Overall, we demonstrate that spin-orbit induced spin flips are the most significant contributors with superdiffusive spin transport, which assumes only that the transport of majority spins without spin flips induced by scattering does not apply in Ni. In Co it plays a significant role during the first ˜20 fs only. Our study highlights the material dependent nature of the demagnetization during the process of thermalization of nonequilibrium spins.

  6. Probing the Spin-Polarized Electronic Band Structure in Monolayer Transition Metal Dichalcogenides by Optical Spectroscopy.

    PubMed

    Wang, Zefang; Zhao, Liang; Mak, Kin Fai; Shan, Jie

    2017-02-08

    We study the electronic band structure in the K/K' valleys of the Brillouin zone of monolayer WSe2 and MoSe2 by optical reflection and photoluminescence spectroscopy on dual-gated field-effect devices. Our experiment reveals the distinct spin polarization in the conduction bands of these compounds by a systematic study of the doping dependence of the A and B excitonic resonances. Electrons in the highest-energy valence band and the lowest-energy conduction band have antiparallel spins in monolayer WSe2 and parallel spins in monolayer MoSe2. The spin splitting is determined to be hundreds of meV for the valence bands and tens of meV for the conduction bands, which are in good agreement with first-principles calculations. These values also suggest that both n- and p-type WSe2 and MoSe2 can be relevant for spin- and valley-based applications.

  7. Pressure sensor via optical detection based on a 1D spin transition coordination polymer.

    PubMed

    Jureschi, Cătălin M; Linares, Jorge; Rotaru, Aurelian; Ritti, Marie Hélène; Parlier, Michel; Dîrtu, Marinela M; Wolff, Mariusz; Garcia, Yann

    2015-01-22

    We have investigated the suitability of using the 1D spin crossover coordination polymer [Fe(4-(2'-hydroxyethyl)-1,2,4-triazole)3]I2∙H2O, known to crossover around room temperature, as a pressure sensor via optical detection using various contact pressures up to 250 MPa. A dramatic persistent colour change is observed. The experimental data, obtained by calorimetric and Mössbauer measurements, have been used for a theoretical analysis, in the framework of the Ising-like model, of the thermal and pressure induced spin state switching. The pressure (P)-temperature (T) phase diagram calculated for this compound has been used to obtain the P-T bistability region.

  8. Pressure Sensor via Optical Detection Based on a 1D Spin Transition Coordination Polymer

    PubMed Central

    Jureschi, Cătălin M.; Linares, Jorge; Rotaru, Aurelian; Ritti, Marie Hélène; Parlier, Michel; Dîrtu, Marinela M.; Wolff, Mariusz; Garcia, Yann

    2015-01-01

    We have investigated the suitability of using the 1D spin crossover coordination polymer [Fe(4-(2′-hydroxyethyl)-1,2,4-triazole)3]I2·H2O, known to crossover around room temperature, as a pressure sensor via optical detection using various contact pressures up to 250 MPa. A dramatic persistent colour change is observed. The experimental data, obtained by calorimetric and Mössbauer measurements, have been used for a theoretical analysis, in the framework of the Ising-like model, of the thermal and pressure induced spin state switching. The pressure (P)-temperature (T) phase diagram calculated for this compound has been used to obtain the P-T bistability region. PMID:25621610

  9. Optical Transients Powered by Magnetars: Dynamics, Light Curves, and Transition to the Nebular Phase

    NASA Astrophysics Data System (ADS)

    Wang, Ling-Jun; Wang, S. Q.; Dai, Z. G.; Xu, Dong; Han, Yan-Hui; Wu, X. F.; Wei, Jian-Yan

    2016-04-01

    Millisecond magnetars can be formed via several channels: core collapse of massive stars, accretion-induced collapse of white dwarfs (WDs), double WD mergers, double neutron star (NS) mergers, and WD-NS mergers. Because the mass of ejecta from these channels could be quite different, their light curves are also expected to be diverse. We evaluate the dynamic evolution of optical transients powered by millisecond magnetars. We find that the magnetar with a short spin-down timescale converts its rotational energy mostly into the kinetic energy of the transient, while the energy of a magnetar with a long spin-down timescale goes into radiation of the transient. This leads us to speculate that hypernovae could be powered by magnetars with short spin-down timescales. At late times the optical transients will gradually evolve into a nebular phase because of the photospheric recession. We treat the photosphere and nebula separately because their radiation mechanisms are different. In some cases the ejecta could be light enough that the magnetar can accelerate it to a relativistic speed. It is well known that the peak luminosity of a supernova (SN) occurs when the luminosity is equal to the instantaneous energy input rate, as shown by Arnett. We show that photospheric recession and relativistic motion can modify this law. The photospheric recession always leads to a delay of the peak time {t}{pk} relative to the time {t}× at which the SN luminosity equals the instantaneous energy input rate. Relativistic motion, however, may change this result significantly.

  10. SEEDS ADAPTIVE OPTICS IMAGING OF THE ASYMMETRIC TRANSITION DISK OPH IRS 48 IN SCATTERED LIGHT

    SciTech Connect

    Follette, Katherine B.; Close, Laird M.; Grady, Carol A.; Swearingen, Jeremy R.; Sitko, Michael L.; Champney, Elizabeth H.; Van der Marel, Nienke; Maaskant, Koen; Min, Michiel; Takami, Michihiro; Kuchner, Marc J; McElwain, Michael W.; Muto, Takayuki; Mayama, Satoshi; Fukagawa, Misato; Russell, Ray W.; Kudo, Tomoyuki; Kusakabe, Nobuhiko; Hashimoto, Jun; Abe, Lyu; and others

    2015-01-10

    We present the first resolved near-infrared imagery of the transition disk Oph IRS 48 (WLY 2-48), which was recently observed with ALMA to have a strongly asymmetric submillimeter flux distribution. H-band polarized intensity images show a ∼60 AU radius scattered light cavity with two pronounced arcs of emission, one from northeast to southeast and one smaller, fainter, and more distant arc in the northwest. K-band scattered light imagery reveals a similar morphology, but with a clear third arc along the southwestern rim of the disk cavity. This arc meets the northwestern arc at nearly a right angle, revealing the presence of a spiral arm or local surface brightness deficit in the disk, and explaining the east-west brightness asymmetry in the H-band data. We also present 0.8-5.4 μm IRTF SpeX spectra of this object, which allow us to constrain the spectral class to A0 ± 1 and measure a low mass accretion rate of 10{sup –8.5} M {sub ☉} yr{sup –1}, both consistent with previous estimates. We investigate a variety of reddening laws in order to fit the multiwavelength spectral energy distribution of Oph IRS 48 and find a best fit consistent with a younger, higher luminosity star than previous estimates.

  11. Nonequilibrium quantum phase transition of Bose-Einstein condensates in an optical cavity

    NASA Astrophysics Data System (ADS)

    Liu, Ni; Li, Jiangdan; Liang, J.-Q.

    2013-05-01

    A link to the Dicke-model type quantum phase transition (QPT) is established by considering a time-dependent driving of the atom-field coupling and nonlinear atom-photon interaction as well, which make a notable impact on the ground-state properties. Motivated by the recent pioneer experiment [K. Baumann, C. Guerlin, F. Brennecke, and T. Esslinger, Nature (London)10.1038/nature09009 464, 1301 (2010)], in this paper we demonstrate theoretically a rich multistable structure and nonequilibrium QPTs in terms of the Floquet theory and generalized rotating wave approximation. The positive nonlinear interaction does not lead to the change of the order-parameter curve except for a slight shift of the critical point. However, an additional full atomic population of the excited state is generated by the negative interaction resulting in the coexistence region of normal and superradiant phases. When both driving and nonlinear interaction exist the single order-parameter curve of the superradiant phase spreads out and a wide area of multiple local minima emerges in addition.

  12. Finite-temperature Dicke phase transition of a Bose-Einstein condensate in an optical cavity

    NASA Astrophysics Data System (ADS)

    Zhang, Yuanwei; Lian, Jinling; Liang, J.-Q.; Chen, Gang; Zhang, Chuanwei; Jia, Suotang

    2013-01-01

    In this paper we investigate the finite-temperature properties of a Bose-Einstein condensate (BEC)-cavity system with a strong nonlinear atom-photon interaction by means of a functional path-integral approach. It is shown that the experimentally observed phase diagram [Baumann, Guerlin, Brennecke, and Esslinger, Nature (London)NATUAS0028-083610.1038/nature09009 464, 1301 (2010)] can be better explained in our finite-temperature theory. More importantly, we identify a new dynamical unstable phase in this experiment. By tuning various experimental parameters, we reveal some rich temperature-driven phase diagrams and, in particular, predict a four-phase coexistence point. Finally, we find analytically that the specific heat in the superradiant phase increases exponentially at lower temperatures. Moreover, it has a large jump at the temperature-driven critical point where the superradiant-normal phase transition occurs. As a result, we argue that the specific heat can serve as a powerful tool to probe the thermodynamic properties of the BEC-cavity system.

  13. Electrical and optical properties of p-GaN films implanted with transition metal impurities

    NASA Astrophysics Data System (ADS)

    Polyakov, A. Y.; Smirnov, N. B.; Govorkov, A. V.; Khanna, Rohit; Pearton, S. J.

    2005-05-01

    The electrical and optical properties and the spectra of deep hole traps in p-GaN films implanted with Co, Mn, Fe and Cr and annealed at 700 °C were studied. The amount of increase in the series resistance of TM implanted and annealed p-GaN films can be reduced for samples with higher Mg doping and higher Mg acceptor activation efficiency. This is of primary importance for practical use in fabricating GaN spin-LEDs by TM ion implantation into the top p-GaN layer of a spin-LED structure involving injection from GaMnN into a InGaN MQW structure. The Fermi level after the implantation of these TM elements into p-GaN is found not to be shifted far away from the Mg acceptors band where it is pinned in the virgin samples. The main deep defects generated by implantation are found to be the 0.3 eV hole traps and the 0.9 eV hole traps as in the case of p-GaN samples heavily implanted with protons.In practical terms it is found that for fabricating GaN-based spin-LEDs by implantation of TM ions the best results should be expected for the Cr implantation which has also been shown to produce the highest Curie temperature (>350 K in p-GaN,by both implantation or MBE growth).

  14. Independent Control of Optical and Explosive Properties: Pyrazole-Tetrazine Complexes of First Row Transition Metals.

    PubMed

    Myers, Thomas W; Chavez, David E; Hanson, Susan K; Scharff, R Jason; Scott, Brian L; Veauthier, Jacqueline M; Wu, Ruilian

    2015-08-17

    Complexes of 3-amino-6-(3,5-dimethylpyrazole)tetrazine) (NH2TzDMP, 1) and 3-(3,3'-dinitroazetidine)-6-(3,5-dimethylpyrazole)tetrazine) (DNAZTzDMP, 2) with first row transition metal centers were synthesized. Reactions of Fe(II)(H2O)6(BF4)2 and Fe(NO3)3·9H2O with 1 and 2 both led to complexes of the form [(RTzDMP)3Fe]X2 (X = BF4, R = NH2 (3), DNAZ (4); X = NO3, R = NH2 (5), DNAZ (6)), which showed intense MLCT bands in the visible region of the spectrum. Ligands 1 and 2 also reacted with Cu(II)(NO3)2·5/2H2O to form [(RTzDMP)2Cu(NO3)][NO3] (R = NH2 (7), DNAZ (8)) in addition to reacting with Cu(I)(CH3CN)4(PF6) to form [(RTzDMP)2Cu][PF6] (R = NH2 (9), DNAZ (10)). Lastly reactions of 1 and 2 with Co(NO3)2·6H2O and Ni(NO3)2·6H2O led to [(NH2TzDMP)2Co(H2O) (NO3)][NO3] (11), [(DNAZTzDMP)2Co(H2O)2][NO3]2 (12), [(NH2TzDMP)3Ni][NO3]2 (13), and [(DNAZTzDMP)2Ni(H2O)2][NO3]2 (14). The complexes display rich electrochemical and photophysical properties that are unaffected by derivation with explosive groups.

  15. Renormalization of optical transition strengths in semiconductor nanoparticles due to band mixing

    DOE PAGES

    Velizhanin, Kirill A.

    2016-05-25

    We report that unique optical properties of semiconductor nanoparticles (SN) make them very promising in the multitude of applications including lasing, light emission and photovoltaics. In many of these applications it is imperative to understand the physics of interaction of electrons in a SN with external electromagnetic fields on the quantitative level. In particular, the strength of electron–photon coupling determines such important SN parameters as the radiative lifetime and absorption cross section. This strength is often assumed to be fully encoded by the so called Kane momentum matrix element. This parameter, however, pertains to a bulk semiconductor material and, asmore » such, is not sensitive to the quantum confinement effects in SNs. In this work we demonstrate that the quantum confinement, via the so called band mixing, can result in a significant suppression of the strength of electron interaction with electromagnetic field. Within the envelope function formalism we show how this suppression can be described by introducing an effective energy-dependent Kane momentum. Then, the effect of band mixing on the efficiencies of various photoinduced processes can be fully captured by the conventional formulae (e.g., spontaneous emission rate), once the conventional Kane momentum is substituted with the renormalized energy-dependent Kane momentum introduced in here. Lastly, as an example, we evaluate the energy-dependent Kane momentum for spherical PbSe and PbS SNs (i.e., quantum dots) and show that neglecting band mixing in these systems can result in the overestimation of absorption cross sections and emission rates by a factor of ~2.« less

  16. Renormalization of optical transition strengths in semiconductor nanoparticles due to band mixing

    SciTech Connect

    Velizhanin, Kirill A.

    2016-05-25

    We report that unique optical properties of semiconductor nanoparticles (SN) make them very promising in the multitude of applications including lasing, light emission and photovoltaics. In many of these applications it is imperative to understand the physics of interaction of electrons in a SN with external electromagnetic fields on the quantitative level. In particular, the strength of electron–photon coupling determines such important SN parameters as the radiative lifetime and absorption cross section. This strength is often assumed to be fully encoded by the so called Kane momentum matrix element. This parameter, however, pertains to a bulk semiconductor material and, as such, is not sensitive to the quantum confinement effects in SNs. In this work we demonstrate that the quantum confinement, via the so called band mixing, can result in a significant suppression of the strength of electron interaction with electromagnetic field. Within the envelope function formalism we show how this suppression can be described by introducing an effective energy-dependent Kane momentum. Then, the effect of band mixing on the efficiencies of various photoinduced processes can be fully captured by the conventional formulae (e.g., spontaneous emission rate), once the conventional Kane momentum is substituted with the renormalized energy-dependent Kane momentum introduced in here. Lastly, as an example, we evaluate the energy-dependent Kane momentum for spherical PbSe and PbS SNs (i.e., quantum dots) and show that neglecting band mixing in these systems can result in the overestimation of absorption cross sections and emission rates by a factor of ~2.

  17. Optical properties and temperature dependence of the interband transitions of cubic and hexagonal GaN

    NASA Astrophysics Data System (ADS)

    Logothetidis, S.; Petalas, J.; Cardona, M.; Moustakas, T. D.

    1994-12-01

    The optical properties of cubic and hexagonal GaN thin films, grown by electron-cyclotron resonance microwave plasma-assisted molecular-beam epitaxy on silicon and sapphire substrates, respectively, have been studied at photon energies up to 25 eV with conventional and synchrotron-radiation spectroscopic ellipsometry. The fundamental gaps of the two polytypes are located at different energies, namely at 3.25 and 3.43 eV for cubic and hexagonal GaN. Analysis of the dielectric function of the two phases in the region 4.5-9.5 eV with appropriate models yields the energy location and broadening of the observed critical points. These critical points are assigned to specific points in the zinc-blende and wurtzite Brillouin zones, respectively, making use of the latest published band-structure studies and a comparison is made between the corresponding results for GaN, GaAs, and GaP. Measurements in the temperature range from 80 to 650 K provide the temperature dependence of these parameters. The features observed in the reflectivity spectra of hexagonal GaN are discussed in relation to other works. Kramers-Kronig analysis of the reflectivity between 0 and 33 eV of the hexagonal polytype verifies the existence of a broad feature centered at 14 eV. Finally, average properties, such as the effective ir dielectric constant and the effective number of valence electrons per atom are calculated for the two polytypes and compared to GaAs and GaP.

  18. Renormalization of optical transition strengths in semiconductor nanoparticles due to band mixing

    NASA Astrophysics Data System (ADS)

    Velizhanin, Kirill A.

    2016-12-01

    Unique optical properties of semiconductor nanoparticles (SN) make them very promising in the multitude of applications including lasing, light emission and photovoltaics. In many of these applications it is imperative to understand the physics of interaction of electrons in a SN with external electromagnetic fields on the quantitative level. In particular, the strength of electron-photon coupling determines such important SN parameters as the radiative lifetime and absorption cross section. This strength is often assumed to be fully encoded by the so called Kane momentum matrix element. This parameter, however, pertains to a bulk semiconductor material and, as such, is not sensitive to the quantum confinement effects in SNs. In this work we demonstrate that the quantum confinement, via the so called band mixing, can result in a significant suppression of the strength of electron interaction with electromagnetic field. Within the envelope function formalism we show how this suppression can be described by introducing an effective energy-dependent Kane momentum. Then, the effect of band mixing on the efficiencies of various photoinduced processes can be fully captured by the conventional formulae (e.g., spontaneous emission rate), once the conventional Kane momentum is substituted with the renormalized energy-dependent Kane momentum introduced in here. As an example, we evaluate the energy-dependent Kane momentum for spherical PbSe and PbS SNs (i.e., quantum dots) and show that neglecting band mixing in these systems can result in the overestimation of absorption cross sections and emission rates by a factor of ∼ 2.

  19. Renormalization of optical transition strengths in semiconductor nanoparticles due to band mixing

    SciTech Connect

    Velizhanin, Kirill A.

    2016-05-25

    We report that unique optical properties of semiconductor nanoparticles (SN) make them very promising in the multitude of applications including lasing, light emission and photovoltaics. In many of these applications it is imperative to understand the physics of interaction of electrons in a SN with external electromagnetic fields on the quantitative level. In particular, the strength of electron–photon coupling determines such important SN parameters as the radiative lifetime and absorption cross section. This strength is often assumed to be fully encoded by the so called Kane momentum matrix element. This parameter, however, pertains to a bulk semiconductor material and, as such, is not sensitive to the quantum confinement effects in SNs. In this work we demonstrate that the quantum confinement, via the so called band mixing, can result in a significant suppression of the strength of electron interaction with electromagnetic field. Within the envelope function formalism we show how this suppression can be described by introducing an effective energy-dependent Kane momentum. Then, the effect of band mixing on the efficiencies of various photoinduced processes can be fully captured by the conventional formulae (e.g., spontaneous emission rate), once the conventional Kane momentum is substituted with the renormalized energy-dependent Kane momentum introduced in here. Lastly, as an example, we evaluate the energy-dependent Kane momentum for spherical PbSe and PbS SNs (i.e., quantum dots) and show that neglecting band mixing in these systems can result in the overestimation of absorption cross sections and emission rates by a factor of ~2.

  20. Growth evolution and phase transition from chalcocite to digenite in nanocrystalline copper sulfide: Morphological, optical and electrical properties

    PubMed Central

    Quintana-Ramirez, Priscilla Vasthi; Santos-Cruz, José; Vega-González, Marina; Martínez-Alvarez, Omar; Castaño-Meneses, Víctor Manuel; Acosta-Torres, Laura Susana; de la Fuente-Hernández, Javier

    2014-01-01

    Summary Copper sulfide is a promising p-type inorganic semiconductor for optoelectronic devices such as solar cells, due its small band gap energy and its electrical properties. In this work nanocrystalline copper sulfide (CuxS), with two stoichiometric ratios (x = 2, 1.8) was obtained by one-pot synthesis at 220, 230, 240 and 260 °C in an organic solvent and amorphous CuxS was obtained in aqueous solution. Nanoparticle-like nucleation centers are formed at lower temperatures (220 °C), mixtures of morphologies (nanorods, nanodisks and nanoprisms) are seen at 230 and 240 °C, in which the nanodisks are predominant, while big hexagonal/prismatic crystals are obtained at 260 °C according to TEM results. A mixture of chalcocite and digenite phases was found at 230 and 240 °C, while a clear transition to a pure digenite phase was seen at 260 °C. The evolution of morphology and transition of phases is consistent to the electrical, optical, and morphological properties of the copper sulfide. In fact, digenite Cu1.8S is less resistive (346 Ω/sq) and has a lower energy band gap (1.6 eV) than chalcocite Cu2S (5.72 × 105 Ω/sq, 1.87 eV). Low resistivity was also obtained in CuxS synthesized in aqueous solution, despite its amorphous structure. All CuxS products could be promising for optoelectronic applications. PMID:25247136

  1. Growth evolution and phase transition from chalcocite to digenite in nanocrystalline copper sulfide: Morphological, optical and electrical properties.

    PubMed

    Quintana-Ramirez, Priscilla Vasthi; Arenas-Arrocena, Ma Concepción; Santos-Cruz, José; Vega-González, Marina; Martínez-Alvarez, Omar; Castaño-Meneses, Víctor Manuel; Acosta-Torres, Laura Susana; de la Fuente-Hernández, Javier

    2014-01-01

    Copper sulfide is a promising p-type inorganic semiconductor for optoelectronic devices such as solar cells, due its small band gap energy and its electrical properties. In this work nanocrystalline copper sulfide (Cu x S), with two stoichiometric ratios (x = 2, 1.8) was obtained by one-pot synthesis at 220, 230, 240 and 260 °C in an organic solvent and amorphous Cu x S was obtained in aqueous solution. Nanoparticle-like nucleation centers are formed at lower temperatures (220 °C), mixtures of morphologies (nanorods, nanodisks and nanoprisms) are seen at 230 and 240 °C, in which the nanodisks are predominant, while big hexagonal/prismatic crystals are obtained at 260 °C according to TEM results. A mixture of chalcocite and digenite phases was found at 230 and 240 °C, while a clear transition to a pure digenite phase was seen at 260 °C. The evolution of morphology and transition of phases is consistent to the electrical, optical, and morphological properties of the copper sulfide. In fact, digenite Cu1.8S is less resistive (346 Ω/sq) and has a lower energy band gap (1.6 eV) than chalcocite Cu2S (5.72 × 10(5) Ω/sq, 1.87 eV). Low resistivity was also obtained in Cu x S synthesized in aqueous solution, despite its amorphous structure. All Cu x S products could be promising for optoelectronic applications.

  2. Ultracold fermions in a one-dimensional bipartite optical lattice: Metal-insulator transitions driven by shaking

    NASA Astrophysics Data System (ADS)

    Di Liberto, M.; Malpetti, D.; Japaridze, G. I.; Morais Smith, C.

    2014-08-01

    We theoretically investigate the behavior of a system of fermionic atoms loaded in a bipartite one-dimensional optical lattice that is under the action of an external time-periodic driving force. By using Floquet theory, an effective model is derived. The bare hopping coefficients are renormalized by zeroth-order Bessel functions of the first kind with different arguments for the nearest-neighbor and next-nearest-neighbor hopping. The insulating behavior characterizing the system at half filling in the absence of driving is dynamically suppressed, and for particular values of the driving parameter the system becomes either a standard metal or an unconventional metal with four Fermi points. The existence of the four-Fermi-point metal relies on the fact that, as a consequence of the shaking procedure, the next-nearest-neighbor hopping coefficients become significant compared to the nearest-neighbor ones. We use the bosonization technique to investigate the effect of on-site Hubbard interactions on the four-Fermi-point metal-insulator phase transition. Attractive interactions are expected to enlarge the regime of parameters where the unconventional metallic phase arises, whereas repulsive interactions reduce it. This metallic phase is known to be a Luther-Emery liquid (spin-gapped metal) for both repulsive and attractive interactions, contrary to the usual Hubbard model, which exhibits a Mott-insulator phase for repulsive interactions. Ultracold fermions in driven one-dimensional bipartite optical lattices provide an interesting platform for the realization of this long-studied four-Fermi-point unconventional metal.

  3. Band edge modulation and interband optical transition in AlN:Mg_{{\\rm{Al}}}-O_{{\\rm{N}}} nanotubes

    NASA Astrophysics Data System (ADS)

    Huang, Pu; Shi, Jun-jie; Zhang, Min; Jiang, Xin-he; Zhong, Hong-xia; Ding, Yi-min; Lu, Jing; Wang, Xihua

    2014-04-01

    AlN nanotubes (NTs) have many novel characteristics and great potential applications in electronic and optoelectronic nanodevices. However, little is known about the influence of Mg_{{\\rm{Al}}}-O_{{\\rm{N}}} co-doping effects on their optical properties. Here, we focus on investigating the electronic structures, clarify the interband optical transition mechanism and give a clear atomic picture for the important electron/hole localization centre in AlN:Mg_{{\\rm{Al}}}-O_{{\\rm{N}}} NTs using the GGA-1/2 method. We find that the Mg_{{\\rm{Al}}} doping efficiency can be improved effectively due to O_{{\\rm{N}}} doping in AlN NTs. The Mg_{{\\rm{Al}}} and O_{{\\rm{N}}} form Mg_{{\\rm{Al}}}-O_{{\\rm{N}}} defect complex easily along the AlN NT axis (C-axis). The Mg_{{\\rm{Al}}}-O_{{\\rm{N}}} defect complex can result in a remarkable charge transfer around it and modify the valence band maximum and conduction band minimum significantly. Meanwhile, the Mg_{{\\rm{Al}}}-O_{{\\rm{N}}} defect complex also forms the important exciton localization centre and effectively enhances the interband radiative recombination rate. Moreover, the light emission/absorption sensitively depends on its polarization. The parallel polarized light ({\\mathbf{E}}\\shortparallel {\\rm{C}}) is much stronger than the perpendicular one ({\\mathbf{E}}\\bot {\\rm{C}}). The Mg_{{\\rm{Al}}}-O_{{\\rm{N}}} co-doping thus paves a new way for improving the performance of electronic and optoelectronic nanodevices based on AlN NTs.

  4. Antiferromagnetic Ordering Effect on the Optical Transitions in Manganese-Difluoride

    NASA Astrophysics Data System (ADS)

    Abumansoor, Sabri Asaad

    Temperature dependence of all the optical absorption bands of MnF(,2) in the range 2000-6000 (ANGSTROM) has been studied using Cary 14 spectrophotometer in conjunction with Air Products Displex, a closed cycle helium refrigerator. Peak position, width and oscillator strength of the bands, namely A through I, were measured as a function of temperature in the region between 10 K-300 K, with a particular attention to the region near the Neel temperature (T(,N) = 67.3 K). On lowering the temperature through T(,N), all bands undergo blue-shifts, the intensity and line-width of main bands decreased except band G and I whose intensity increased, the splitting of the bands became clearly defined and fine structures appeared. The temperature dependence of the oscillator strength of the bands can be classified into two groups; Group I whose intensity decreases on cooling through T(,N) and Group II whose intensity increases below T(,N). The temperature dependence of the oscillator strength of group I agreed semiquantitatively with the theory of Shinagawa and Tanabe. Based on this, these bands have been identified as exciton-magnon or exciton-magnon-phonon bands. The temperature dependence of group II show a semiquantitative agreement with the theory of Fujiwara et al. and these bands have been identified as double exciton bands. The blue-shift of peak position of band C and F below T(,N) (whose line-positions are nearly temperature independent above T(,N)) has been explained in terms of molecular field theory of Yen, Imbush and Huber. Both bands are blue-shifted by (DELTA)E ((TURNEQ)60 cm('-1) for C and 80 cm('-1) for F between T(,N) and 10 K). It is found that (DELTA)E varies as the sublattice magnetization below T(,N) and nearly as the magnetic energy above T(,N). Some of the bands in the fine structure can be associated with magnons or phonons. However complete identification of all the fine structure bands still needs to be carried out.

  5. Contribution of the transition moments, form of the absorption band, exciton, and the correlation effects in the linear and nonlinear optical properties of conjugated polymers

    NASA Astrophysics Data System (ADS)

    Díaz-Ponce, Javier Alejandro

    2017-04-01

    This work compares the linear and nonlinear optical properties of polyenes and polyenynes. The simulation was made for finite and infinite conjugation of conjugated polymers, such as polyacetylene, β-carotene, bis (p-toluene sulfonate) (PTS) polyenyne, and a short conjugated polyenyne poly-2,6-decadyin-1,6-ylene azelate (PHDAz). The resonance energy and degree of conjugation are determined by fitting the linear absorption spectra. These parameters are then used for calculating the two photon and third-order nonlinear optical properties. The contribution of the transition moment, the form of the absorption band, the exciton, and phonons in the optical properties are determined. The difference of the experimental values is assigned to correlation effects. We found that the exciton, the correlation effects, and the conduction band are more important in the optical properties of polyenynes than of polyenes. In this way, the dependence of the optical properties of polyenynes on the conduction band makes it possible to increase their nonlinear optical properties by interaction with photons (θ ≈ 0). The dependence of the optical properties on the conduction band also produces that the finiteness of the conjugation strongly decreases the optical properties of polyenynes in relation to polyenes with similar conjugation. On the other hand, the phonons are more important in the optical properties of polyenes than of polyenynes. Consequently, the band is indirect for the studied polyenes and direct for the polyenynes. Therefore, the nonlinear optical properties in the resonance frequency of polyenyne PTS are higher than those for polyacetylene. We also found that asymmetric oscillations of χ(3)/SUP> in the Brillouin zone increases the χ(3)/SUP> final value in polyenynes. In addition, we found a change of sign of the wave function coefficients by the Peierls distortion of polyenes to become polyenynes, but this change of sign does not affect the optical properties. As a

  6. Optical trapping of ultracold dysprosium atoms: transition probabilities, dynamic dipole polarizabilities and van der Waals C 6 coefficients

    NASA Astrophysics Data System (ADS)

    Li, H.; Wyart, J.-F.; Dulieu, O.; Nascimbène, S.; Lepers, M.

    2017-01-01

    The efficiency of the optical trapping of ultracold atoms depends on the atomic dynamic dipole polarizability governing the atom-field interaction. In this article, we have calculated the real and imaginary parts of the dynamic dipole polarizability of dysprosium in the ground and first excited levels. Due to the high electronic angular momentum of those two states, the polarizabilities possess scalar, vector and tensor contributions that we have computed, on a wide range of trapping wavelengths, using the sum-over-state formula. Using the same formalism, we have also calculated the C 6 coefficients characterizing the van der Waals interaction between two dysprosium atoms in the two lowest levels. We have computed the energies of excited states and the transition probabilities appearing in the sums, using a combination of ab initio and least-square-fitting techniques provided by the Cowan codes and extended in our group. Regarding the real part of the polarizability, for field frequencies far from atomic resonances, the vector and tensor contributions are two-orders-of-magnitude smaller than the scalar contribution, whereas for the imaginary part, the vector and tensor contributions represent a noticeable fraction of the scalar contribution. Finally, our anisotropic C 6 coefficients are much smaller than those published in the literature.

  7. Development of an optical transition radiation detector for profile monitoring of antiproton and proton beams at FNAL

    SciTech Connect

    Scarpine, V.E.; Lindenmeyer, C.W.; Tassotto, G.R.; Lumpkin, A.H.; /Argonne

    2005-05-01

    Optical transition radiation (OTR) detectors are being developed at Fermi National Accelerator Laboratory (FNAL) as part of the collider Run II upgrade program and as part of the NuMI primary beam line. These detectors are designed to measure 150 GeV antiprotons as well as 120 GeV proton beams over a large range of intensities. Design and development of an OTR detector capable of measuring beam in both directions down to beam intensities of {approx}5e9 particles for nominal beam sizes are presented. Applications of these OTR detectors as an on-line emittance monitor for both antiproton transfers and reverse-injected protons, as a Tevatron injection profile monitor, and as a high-intensity beam profile monitor for NuMI are discussed. In addition, different types of OTR foils are being evaluated for operation over the intensity range of {approx}5e9 to 5e13 particles per pulse, and these are described.

  8. Coherent optical transition radiation and self-amplified spontaneous emission generated by chicane-compressed electron beams

    SciTech Connect

    Lumpkin, A.H.; Dejus, R.J.; Sereno, N.S.; /Argonne

    2009-02-01

    Observations of strongly enhanced optical transition radiation (OTR) following significant bunch compression of photoinjector beams by a chicane have been reported during the commissioning of the Linac Coherent Light Source (LCLS) accelerator and recently at the Advanced Photon Source (APS) linac. These localized transverse spatial features involve signal enhancements of nearly a factor of 10 and 100 in the APS case at the 150-MeV and 375-MeV OTR stations, respectively. They are consistent with a coherent process seeded by noise and may be evidence of a longitudinal space charge (LSC) microbunching instability which leads to coherent OTR (COTR) emissions. Additionally, we suggest that localized transverse structure in the previous self-amplified spontaneous emission (SASE) free-electron laser (FEL) data at APS in the visible-UV regime as reported at FEL02 may be attributed to such beam structure entering the FEL undulators and inducing the SASE startup at those structures. Separate beam structures 120 microns apart in x and 2.9 nm apart in wavelength were reported. The details of these observations and operational parameters will be presented.

  9. Coherent optical transition radiation and self-amplified spontaneous emission generated by chicane-compressed electron beams

    NASA Astrophysics Data System (ADS)

    Lumpkin, A. H.; Dejus, R. J.; Sereno, N. S.

    2009-04-01

    Observations of strongly enhanced optical transition radiation (OTR) following significant bunch compression of photoinjector beams by a chicane have been reported during the commissioning of the Linac Coherent Light Source accelerator and recently at the Advanced Photon Source (APS) linac. These localized transverse spatial features involve signal enhancements of nearly a factor of 10 and 100 in the APS case at the 150-MeV and 375-MeV OTR stations, respectively. They are consistent with a coherent process seeded by noise and may be evidence of a longitudinal space charge microbunching instability which leads to coherent OTR emissions. Additionally, we suggest that localized transverse structure in the previous self-amplified spontaneous emission (SASE) free-electron laser (FEL) data at APS in the visible regime as reported at FEL02 may be attributed to such beam structure entering the FEL undulators and inducing the SASE startup at those “prebunched” structures. Separate beam structures 120 microns apart in x and 2.9 nm apart in wavelength were reported. The details of these observations and operational parameters will be presented.

  10. Optical transition radiation used in the diagnostic of low energy and low current electron beams in particle accelerators

    NASA Astrophysics Data System (ADS)

    Silva, T. F.; Bonini, A. L.; Lima, R. R.; Maidana, N. L.; Malafronte, A. A.; Pascholati, P. R.; Vanin, V. R.; Martins, M. N.

    2012-09-01

    Optical transition radiation (OTR) plays an important role in beam diagnostics for high energy particle accelerators. Its linear intensity with beam current is a great advantage as compared to fluorescent screens, which are subject to saturation. Moreover, the measurement of the angular distribution of the emitted radiation enables the determination of many beam parameters in a single observation point. However, few works deals with the application of OTR to monitor low energy beams. In this work we describe the design of an OTR based beam monitor used to measure the transverse beam charge distribution of the 1.9-MeV electron beam of the linac injector of the IFUSP microtron using a standard vision machine camera. The average beam current in pulsed operation mode is of the order of tens of nano-Amps. Low energy and low beam current make OTR observation difficult. To improve sensitivity, the beam incidence angle on the target was chosen to maximize the photon flux in the camera field-of-view. Measurements that assess OTR observation (linearity with beam current, polarization, and spectrum shape) are presented, as well as a typical 1.9-MeV electron beam charge distribution obtained from OTR. Some aspects of emittance measurement using this device are also discussed.

  11. Optical transition radiation used in the diagnostic of low energy and low current electron beams in particle accelerators.

    PubMed

    Silva, T F; Bonini, A L; Lima, R R; Maidana, N L; Malafronte, A A; Pascholati, P R; Vanin, V R; Martins, M N

    2012-09-01

    Optical transition radiation (OTR) plays an important role in beam diagnostics for high energy particle accelerators. Its linear intensity with beam current is a great advantage as compared to fluorescent screens, which are subject to saturation. Moreover, the measurement of the angular distribution of the emitted radiation enables the determination of many beam parameters in a single observation point. However, few works deals with the application of OTR to monitor low energy beams. In this work we describe the design of an OTR based beam monitor used to measure the transverse beam charge distribution of the 1.9-MeV electron beam of the linac injector of the IFUSP microtron using a standard vision machine camera. The average beam current in pulsed operation mode is of the order of tens of nano-Amps. Low energy and low beam current make OTR observation difficult. To improve sensitivity, the beam incidence angle on the target was chosen to maximize the photon flux in the camera field-of-view. Measurements that assess OTR observation (linearity with beam current, polarization, and spectrum shape) are presented, as well as a typical 1.9-MeV electron beam charge distribution obtained from OTR. Some aspects of emittance measurement using this device are also discussed.

  12. Energy Spread Monitoring for the JLAB Experimental Program: Synchrotron Light Interferometers, Optical Transition Radiation Monitors and Wire Scanners

    SciTech Connect

    Arne Freyberger; Yu-Chiu Chao; Pavel Chevtsov; Anthony Day; William Hicks; Michele Joyce; Jean-Claude Denard

    2004-05-01

    The hypernuclear physics program at JLAB requires an electron beam with small transverse size (sigma {approx} 100 {micro}m) and an upper limit on the RMS energy spread of delta E / E < 3 x 10{sup -}5. To measure and monitor these parameters, a beam size and energy spread measurement system has been created. The system consists of a set of wire scanners, Optical Transition Radiation (OTR) detectors, and Synchrotron Light Interferometers (SLI). The energy spread is measured via a set of wire scans performed at specific locations in the transport line, which is an invasive process. During physics operation the energy spread is monitored continuously with the OTR and/or the SLI. These devices are noninvasive [or nearly non-invasive in the case of OTR] and operate over a very wide range of beam energies (1.6 GeV) and currents ({approx}100 {micro}A down to few {micro}A). All components of this system are automated in an EPICS accelerator control environment. The paper presents our operational experience with the beam size and energy spread measurement system and its maintenance.

  13. Pressure dependence of optical transitions in In{sub 0.15}Ga{sub 0.85}N/GaN multiple quantum wells

    SciTech Connect

    Shan, W.; Ager, J.W. III, and; Walukiewicz, W.; Haller, E.E. |; McCluskey, M.D.; Johnson, N.M.; Bour, D.P.

    1998-10-01

    The effects of hydrostatic pressure on optical transitions in In{sub 0.15}Ga{sub 0.85}N/GaN multiple quantum wells (MQW{close_quote}s) have been studied. The optical transition associated with confined electron and hole states in the MQW{close_quote}s was found to shift linearly to higher energy with pressure but exhibit a significantly weaker pressure dependence compared to bulklike thick epitaxial-layer samples. Similar pressure coefficients obtained by both photomodulation and photoluminescence measurements rule out the possibility of the transition involving localized states deep in the band gap. We found that the difference in the compressibility of In{sub x}Ga{sub 1{minus}x}N and GaN induces a tensile strain in the compressively strained In{sub x}Ga{sub 1{minus}x}N well layers, partially compensating the externally applied hydrostatic pressure. This mechanical effect is primarily responsible for the smaller pressure dependence of the optical transitions in the In{sub x}Ga{sub 1{minus}x}N/GaN MQW{close_quote}s. In addition, the pressure-dependent measurements allow us to identify a spectral feature observed at an energy below the GaN band gap. We conclude that this feature is due to transitions from ionized Mg acceptor states to the conduction band in the {ital p}-type GaN cladding layer rather than a confined transition in the MQW{close_quote}s. {copyright} {ital 1998} {ital The American Physical Society}

  14. Laser-induced phase transitions of Ge2Sb2Te5 thin films used in optical and electronic data storage and in thermal lithography.

    PubMed

    Chu, Cheng Hung; Shiue, Chiun Da; Cheng, Hsuen Wei; Tseng, Ming Lun; Chiang, Hai-Pang; Mansuripur, Masud; Tsai, Din Ping

    2010-08-16

    Amorphous thin films of Ge(2)Sb(2)Te(5), sputter-deposited on a ZnS-SiO(2) dielectric layer, are investigated for the purpose of understanding the structural phase-transitions that occur under the influence of tightly-focused laser beams. Selective chemical etching of recorded marks in conjunction with optical, atomic force, and electron microscopy as well as local electron diffraction analysis are used to discern the complex structural features created under a broad range of laser powers and pulse durations. Clarifying the nature of phase transitions associated with laser-recorded marks in chalcogenide Ge(2)Sb(2)Te(5) thin films provides useful information for reversible optical and electronic data storage, as well as for phase-change (thermal) lithography.

  15. Intra- and inter-atomic optical transitions of Fe, Co, and Ni ferrocyanides studied using first-principles many-electron calculations

    SciTech Connect

    Watanabe, Shinta E-mail: j-onoe@nucl.nagoya-u.ac.jp; Sawada, Yuki; Nakaya, Masato; Yoshino, Masahito; Nagasaki, Takanori; Onoe, Jun E-mail: j-onoe@nucl.nagoya-u.ac.jp; Kameyama, Tatsuya; Torimoto, Tsukasa; Inaba, Yusuke; Takahashi, Hideharu; Takeshita, Kenji

    2016-06-21

    We have investigated the electronic structures and optical properties of Fe, Co, and Ni ferrocyanide nanoparticles using first-principles relativistic many-electron calculations. The overall features of the theoretical absorption spectra for Fe, Ni, and Co ferrocyanides calculated using a first-principles many-electron method well reproduced the experimental one. The origins of the experimental absorption spectra were clarified by performing a configuration analysis based on the many-electron wave functions. For Fe ferrocyanide, the experimental absorption peaks originated from not only the charge-transfer transitions from Fe{sup 2+} to Fe{sup 3+} but also the 3d-3d intra-transitions of Fe{sup 3+} ions. In addition, the spin crossover transition of Fe{sup 3+} predicted by the many-electron calculations was about 0.24 eV. For Co ferrocyanide, the experimental absorption peaks were mainly attributed to the 3d-3d intra-transitions of Fe{sup 2+} ions. In contrast to the Fe and Co ferrocyanides, Ni ferrocyanide showed that the absorption peaks originated from the 3d-3d intra-transitions of Ni{sup 3+} ions in a low-energy region, while from both the 3d-3d intra-transitions of Fe{sup 2+} ions and the charge-transfer transitions from Fe{sup 2+} to Ni{sup 3+} in a high-energy region. These results were quite different from those of density-functional theory (DFT) calculations. The discrepancy between the results of DFT calculations and those of many-electron calculations suggested that the intra- and inter-atomic transitions of transition metal ions are significantly affected by the many-body effects of strongly correlated 3d electrons.

  16. Mg doping of thermochromic VO{sub 2} films enhances the optical transmittance and decreases the metal-insulator transition temperature

    SciTech Connect

    Mlyuka, N. R.; Niklasson, G. A.; Granqvist, C. G.

    2009-10-26

    Thermochromic films of Mg{sub x}V{sub 1-x}O{sub 2} were made by reactive dc magnetron sputtering onto heated glass. The metal-insulator transition temperature decreased by {approx}3 K/at. %Mg, while the optical transmittance increased concomitantly. Specifically, the transmittance of visible light and of solar radiation was enhanced by {approx}10% when the Mg content was {approx}7 at. %. Our results point at the usefulness of these films for energy efficient fenestration.

  17. An optical transmission spectrum of the transiting hot Jupiter in the metal-poor WASP-98 planetary system

    NASA Astrophysics Data System (ADS)

    Mancini, L.; Giordano, M.; Mollière, P.; Southworth, J.; Brahm, R.; Ciceri, S.; Henning, Th.

    2016-09-01

    The WASP-98 planetary system represents a rare case of a hot Jupiter hosted by a metal-poor main-sequence star. We present a follow-up study of this system based on multiband photometry and high-resolution spectroscopy. Two new transit events of WASP-98 b were simultaneously observed in four passbands (g', r', i', z'), using the telescope-defocusing technique, yielding eight high-precision light curves with point-to-point scatters of less than 1 mmag. We also collected three spectra of the parent star with a high-resolution spectrograph, which we used to remeasure its spectral characteristics, in particular its metallicity. We found this to be very low, [Fe/H] = -0.49 ± 0.10, but larger than was previously reported, [Fe/H] = -0.60 ± 0.19. We used these new photometric and spectroscopic data to refine the orbital and physical properties of this planetary system, finding that the stellar and planetary mass measurements are significantly larger than those in the discovery paper. In addition, the multiband light curves were used to construct an optical transmission spectrum of WASP-98 b and probe the characteristics of its atmosphere at the terminator. We measured a lower radius at z' compared with the other three passbands. The maximum variation is between the r' and z' bands, has a confidence level of roughly 6σ and equates to 5.5 pressure scale heights. We compared this spectrum to theoretical models, investigating several possible types of atmospheres, including hazy, cloudy, cloud-free, and clear atmospheres with titanium and vanadium oxide opacities. We could not find a good fit to the observations, except in the extreme case of a clear atmosphere with TiO and VO opacities, in which the condensation of Ti and V was suppressed. As this case is unrealistic, our results suggest the presence of an additional optical-absorbing species in the atmosphere of WASP-98 b, of unknown chemical nature.

  18. Optical Imaging of Mesenchymal Epithelial Transition Factor (MET) for Enhanced Detection and Characterization of Primary and Metastatic Hepatic Tumors

    PubMed Central

    Esfahani, Shadi A.; Heidari, Pedram; Kim, Sun A.; Ogino, Shuji; Mahmood, Umar

    2016-01-01

    Purpose: To assess optical imaging of Mesenchymal-Epithelial Transition factor (MET) for delineation and characterization of intrahepatic models of human hepatocellular carcinoma (HCC) and metastatic colorectal cancer (CRC), and thereby demonstrate its potential use in precision oncology. Materials and Methods: MET expression in human CRC and HCC was assessed in tissue microarrays. We used GE-137, a modified cyanine 5-tagged peptide for MET targeting. HepG2 and Huh-7 (HCC) and HT-29 (CRC) cells with MET overexpression, and LNCaP cells (negative control) with minimal MET expression were incubated with the probe. Correlation between the relative fluorescence signal intensity and cellular MET expression level was assessed. Flow cytometry was used to assess probe specific binding and dissociation constant (Kd). Orthotopic xenograft models of human HCC and metastatic CRC were generated in nu/nu mice by subcapsular implantation of cells. Epifluorescence imaging was performed to capture the changes in deferential probe accumulation at different time points after injection. Target-to-liver background ratio (TBR) was calculated and the probe biodistribution within different organs was assessed. Histopathologic analysis of extracted xenografts was performed to correlate the tumors MET expression with probe uptake by cancer cells. Results: Approximately 91.5% of HCC and 81% of CRC microarray cores showed MET expression. HCC and CRC cells incubated with the probe showed substantial fluorescence compared to control LNCaP, with strong correlation between fluorescence signal and MET expression (R2 = 0.99, p < 0.001). Probe binding affinity to MET (Kd) was measured to be 2.9 ± 0.36 nM. Epifluorescence imaging showed intense uptake in subcapsular tumors with peak TBR of 5.46 ± 0.46 in Huh-7, 3.55 ± 0.38 in HepG2, and 15.93 ± 0.61 in HT-29 orthotopic xenografts at 4 hours post-injection (mean ± standard deviation). We demonstrated that in vivo probe uptake in xenografts is

  19. Composition-dependent behavior of Co(d7) optical transitions in Cd1-x Cox Ga2S4 mixed crystals

    NASA Astrophysics Data System (ADS)

    Kim, Young-San; Park, Hyun; Hyun, Seung-Cheol; Jin, Moon-Seog; Park, Gye-Choon; Kim, Chang-Dae; Jang, Kiwan; Choi, In-Hwan; Kim, Wha-Tek

    2006-09-01

    The optical transitions due to the cobalt transition metal impurity centers with composition x in Cd1-k Cox Ga2S4 mixed crystals were investigated by optical absorption spectroscopy. The optical absorption spectra showed three crystal-field transitions between the ground state 4A2(4F) and the excited states 4T2(4F), 4T1(4F), and 4T1(4P) of substitutional Co2+ ions that were similar for all the investigated compositions. The crystal-field parameter (Dq ) and the Racah parameter (B ) obtained from the observed absorption bands showed a composition dependence such that the Dq parameter increases; on the other hand, the B parameter decreases with increasing composition x, which implies that the Racah parameter (B ) depends strongly on the host crystal. Also, the total splitting between the highest and the lowest states of the 4T1(4P) state split due to spin-orbit coupling showed a composition dependence varying from 1576 cm-1 to 1232 cm-1 with increasing x . The spin-orbit coupling parameter γ varied from 394 cm-1 to 308 cm-1 with composition x .

  20. Influence of structure-selective fluorene-based polymer wrapping on optical transitions of single-wall carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Tange, Masayoshi; Okazaki, Toshiya; Iijima, Sumio

    2013-12-01

    To understand how fluorene-based polymers selectively extract specific semiconducting single-wall carbon nanotubes (SWCNTs), we compared the optical transitions of SWCNTs wrapped with poly(9,9-dioctylfluorene-alt-pyridine) (PFOPy), i.e., structure-selective polymers, with those wrapped with poly(9,9-di-n-dodecylfluorene) (PFD), i.e., non-selective polymers, in organic solvents by using photoluminescence (PL) excitation spectroscopy. Two (n,m) species of PFOPy-wrapped SWCNTs with intermediate chiral angles exhibited blue-shifted emissions compared with the PFD-wrapped SWCNTs. The shifts in the peaks of PL signals cannot be explained in terms of the dielectric screening effect, but can plausibly be explained in terms of the strains of specific SWCNTs due to the PFOPy wrapping. Moreover, the emissions of specific SWCNTs wrapped with PFOPy were not blue-shifted as much when the solvent was changed from toluene to p-xylene, and this result could be accounted for by a change in the rigidity of the fluorene backbone. Moreover, using p-xylene instead of toluene lowered the selectivity of the SWCNT extraction, thereby suggesting the importance of having a rigid fluorene backbone for selective extraction of SWCNTs.To understand how fluorene-based polymers selectively extract specific semiconducting single-wall carbon nanotubes (SWCNTs), we compared the optical transitions of SWCNTs wrapped with poly(9,9-dioctylfluorene-alt-pyridine) (PFOPy), i.e., structure-selective polymers, with those wrapped with poly(9,9-di-n-dodecylfluorene) (PFD), i.e., non-selective polymers, in organic solvents by using photoluminescence (PL) excitation spectroscopy. Two (n,m) species of PFOPy-wrapped SWCNTs with intermediate chiral angles exhibited blue-shifted emissions compared with the PFD-wrapped SWCNTs. The shifts in the peaks of PL signals cannot be explained in terms of the dielectric screening effect, but can plausibly be explained in terms of the strains of specific SWCNTs due to the PFOPy

  1. Transition of radiative recombination channels from delocalized states to localized states in a GaInP alloy with partial atomic ordering: a direct optical signature of Mott transition?

    NASA Astrophysics Data System (ADS)

    Su, Z. C.; Ning, J. Q.; Deng, Z.; Wang, X. H.; Xu, S. J.; Wang, R. X.; Lu, S. L.; Dong, J. R.; Yang, H.

    2016-03-01

    Anderson localization is a predominant phenomenon in condensed matter and materials physics. In fact, localized and delocalized states often co-exist in one material. They are separated by a boundary called the mobility edge. Mott transition may take place between these two regimes. However, it is widely recognized that an apparent demonstration of Anderson localization or Mott transition is a challenging task. In this article, we present a direct optical observation of a transition of radiative recombination dominant channels from delocalized (i.e., local extended) states to Anderson localized states in the GaInP base layer of a GaInP/GaAs single junction solar cell by the means of the variable-temperature electroluminescence (EL) technique. It is found that by increasing temperature, we can boost a remarkable transition of radiative recombination dominant channels from the delocalized states to the localized states. The delocalized states are induced by the local atomic ordering domains (InP/GaP monolayer superlattices) while the localized states are caused by random distribution of indium (gallium) content. The efficient transfer and thermal redistribution of carriers between the two kinds of electronic states was revealed to result in both a distinct EL mechanism transition and an electrical resistance evolution with temperature. Our study gives rise to a self-consistent precise picture for carrier localization and transfer in a GaInP alloy, which is an extremely technologically important energy material for fabricating high-efficiency photovoltaic devices.

  2. Thermal properties and optical transition probabilities of Tm3 + doped TeO2-WO3 glass.

    PubMed

    Cenk, S; Demirata, B; Oveçoglu, M L; Ozen, G

    2001-10-01

    Glasses with the composition of (1 - x)TeO2 + (x)WO3, where x = 0.15, 0.25 and 0.3 were prepared and, their thermal and absorption measurements were carried out. Differential thermal analysis (DTA) curves taken in the 23-600 degrees C temperature range with a heating rate of 10 degrees C/min reveal a change in the value of the glass transition temperature, Tg, while crystallization was not observed for the glasses containing a WO3 content of more than 15 mol%. All the glasses were found to be moisture-resistant. The absorption bands corresponding to the absorption of the 1G4, 3F2, 3F3 and 3F4, 3H5 and 3H4 levels from the 3H6 ground level of the Tm3+ ion were observed in the optical absorption spectra. Integrated absorption cross-sections of each band except that of 3H5 level was found to vary with the glass composition. Judd-Ofelt analysis was carried out for the samples doped with 1.0 mol% Tm2O3. The omega2 parameter shows the strongest dependence on the host composition and it increases with the increasing WO3 amount. The value of omega4 increases rather slowly while the value of omega6 is practically independent of the composition. The strong dependence of the parameter omega2 indicates that this parameter is related to the structural change and the symmetry of the local environment of the Tm3+ ions in this glass.

  3. All-optical ultrafast logic gates based on saturable to reverse saturable absorption transition in CuPc-doped PMMA thin films

    NASA Astrophysics Data System (ADS)

    Roy, Sukhdev; Yadav, Chandresh

    2011-09-01

    A detailed theoretical analysis of femtosecond transition from saturable (SA) to reverse saturable absorption (RSA) has been carried out in Copper-Phthalocyanine (CuPc)-doped polymethylmethacrylate (PMMA) thin films. The transition due to fifth-order effect of excited-state absorption induced two-photon process has been optimized with respect to intensity, concentration and nonlinear coefficients to design various all-optical logic gates, namely, OR and AND at lower intensities (SA region), XOR at the transition intensity, and the universal NAND and NOR at higher intensities (RSA region). The advantages of ultrafast operation, simplicity, tunability, high contrast, stability of CuPc-doped PMMA thin film, and the possibility to control and realize various logic operations in the same film at the same wavelength by only controlling the pulse intensity, instead of a pump-probe configuration, make them attractive for practical implementation.

  4. The Effect of Annealing Above Glass Transition Temperature on the Optical Properties of Se85Te10Bi5 Thin Films

    NASA Astrophysics Data System (ADS)

    Atyia, H. E.; Farid, A. S.

    2016-01-01

    Se85Te10Bi5 films have been deposited using the thermal evaporation technique. Films with different thicknesses in the thickness range 590.2-273.9 nm were annealed at different annealing temperatures above the glass transition temperature for 120 min. The structure of the annealed films was checked by x-ray diffraction analysis, which indicated a polycrystalline nature for all annealed films, and that the degree of crystallinity increased with increasing annealing temperature. From the reflectance ( R) and transmittance ( T) measurements, the values of the optical absorption coefficient ( α) for the annealed films were estimated to be in the wavelength range of 500-2500 nm. Analysis of the absorption coefficient data reveals allowed indirect transitions and the values of optical band gap ( E g). The values of ( E g) were found to be obeying the Tauc's relation and decreasing with increasing annealing temperature. This behavior is discussed as due to thermal disordering with the structural changes upon annealing. Optical parameters such as lattice and the infinite frequency dielectric constant as ( ɛ L and ɛ ∞), plasma frequency ( ω p), carrier concentration to the effective mass ratio ( N/m*), single- oscillator and dispersion energies ( E o and E d) were found. The dependence of the optical parameters on the annealing temperature was studied and discussed.

  5. Observation and Absolute Frequency Measurements of the {sup 1}S{sub 0}-{sup 3}P{sub 0} Optical Clock Transition in Neutral Ytterbium

    SciTech Connect

    Hoyt, C.W.; Barber, Z.W.; Oates, C.W.; Fortier, T.M.; Diddams, S.A.; Hollberg, L.

    2005-08-19

    We report the direct excitation of the highly forbidden (6s{sup 2}){sup 1}S{sub 0}{r_reversible}(6s6p){sup 3}P{sub 0} optical transition in two odd isotopes of neutral ytterbium. As the excitation laser frequency is scanned, absorption is detected by monitoring the depletion from an atomic cloud at {approx}70 {mu}K in a magneto-optical trap. The measured frequency in {sup 171}Yb (F=1/2) is 518 295 836 591.6{+-}4.4 kHz. The measured frequency in {sup 173}Yb (F=5/2) is 518 294 576 847.6{+-}4.4 kHz. Measurements are made with a femtosecond-laser frequency comb calibrated by the National Institute of Standards and Technology cesium fountain clock and represent nearly a 10{sup 6}-fold reduction in uncertainty. The natural linewidth of these J=0 to J=0 transitions is calculated to be {approx}10 mHz, making them well suited to support a new generation of optical atomic clocks based on confinement in an optical lattice.

  6. Numerical simulation of the evolution of an intense 0{pi} pulse and formation of an optical breather at the inhomogeneously broadened resonance quantum transition

    SciTech Connect

    Parshkov, O M

    2007-09-30

    The interaction of a sufficiently intense 0{pi} pulse with the inhomogeneously broadened resonance quantum transition is studied numerically in the slowly varying envelope approximation. The formation of a single optical breather and evolution of the population of energy levels related to it are described. It is found that in the quasi-resonance case, two 2{pi} pulses of the same duration with different frequencies appear instead of the breather at a large distance. The frequency modulation also prevents the formation of the breather, giving rise to one 2{pi} pulse or two 2{pi} pulses of different frequencies and different durations. The results of numerical analysis of the known experiment on the observation of the 0{pi} pulse in a ruby crystal are presented. It is shown that due to the presence of irreversible relaxation in this experiment, an optical breather was detected at the stage of its transformation to a weak 0{pi} pulse. (nonlinear optical phenomena)

  7. Energy transfer and non-linear optical properties at near ultraviolet wavelengths: Rare earth 4f yields 5d transitions in crystals and glasses

    NASA Astrophysics Data System (ADS)

    Hamilton, D. S.

    1988-01-01

    Aspects of the optical properties of lanthanide (rare-earth) doped crystals and glasses at near ultraviolet wavelengths are considered. Measurements of the optical gain and loss at 325 nm in Ce3+:LiYF4 are presented. In addition to creating a cerium ion population inversion, the ultraviolet pumping forms transient and stable color centers via the excited cerium states. Crystals of Cr3+ GSGG show several sharp absorption lines in the 310 nm to 340 nm region which we have identified as transitions of the Gd3+ ion. Excitation spectra taken by monitoring the Cr3+ luminescence shows that a Gd3+ yields Cr3+ energy transfer process is active in this material. Measurements of the time dependance of the Cr3+ fluorescence following pulsed laser excitation of the Gd3+ ions indicates the characteristic time over which this energy transfer occurs. The 5d yields 4f transitions of cerium doped crystals are generally thought to have unity quantum efficiency of luminescence at room temperature. Measurements of the fluorescence lifetimes of the 5d yields 4f fluorescence transitions in Ce3+:CaF2, Ce3+:LiYF4, Ce3+:YAG, Ce3+:fluoroberyllate glass, and Ce3+:ZBLA glass at 300 K and 77K are presented. Progress in the construction of a high temperature oven with full optical access is also discussed. Cerium doped solids have the potential for laser action on the 5d yields 4f transitions. Such laser would be broadly tunable toward the near ultraviolet.

  8. Differential electron scattering cross sections for the first optically forbidden and resonance transitions in Mg II, Zn II and Cd II

    NASA Technical Reports Server (NTRS)

    Williams, I. D.; Chutjian, A.; Mawhorter, R. J.

    1986-01-01

    Differential electron scattering cross sections have been measured for dipole-forbidden and resonance transitions in Mg II, Zn II and Cd II in the angular range theta = 4-17 deg at 50 eV. These provide the first recorded angular distributions for an optically forbidden transition. It is found that while the cross section for excitation of the 4s (2)S-3d(9)4s(2) (2)D transition in Zn II is small, those for the 3s (2)S-3d (2)D, 4s (2)S (unresolved lines) in Mg II, and the 5s (2)S-4d(9)5s(2) D in Cd II are comparable in magnitude with the cross sections for resonance excitation. In addition, for Cd II it is found that the allowed and forbidden transitions have very similar angular distributions, and it is proposed that excitation to the 2D state may be dominated by a virtual 'double-dipole' transition via the 2P state. Also, the total excitation cross section of the resonance 2P state in Cd II is a factor of four higher than that predicted by the Gaunt factor approximation, suggesting that the accepted value for the oscillator strength may be too low.

  9. Infrared spectrum involving forbidden transitions & coriolis interaction and identification of optically pumped far infrared laser lines in asymmetrically mono-deuterated methanol (Methanol-D1)

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, Indra

    2016-05-01

    In this paper new type of ΔK = 2 and 0 transitions have been identified in the Fourier Transform spectrum of Methanol-D1 (CH2DOH). These transitions are normally forbidden but a "Coriolis" type interaction with nearby states is believed to be contributing sufficient transition strength through intensity borrowing effect. This is the first time such forbidden transitions are reported to be identified in the excited states, in this molecule. The present conjecture is supported by observation of a many strong allowed transitions to upper terminating levels which are seen to be highly perturbed. This conclusion has been reached by comparing calculated energy levels using known molecular parameters (Pearson et al., 2012; Coudert et al., 2014; El Hilali et al., 2011; Quade et al., 1998; Richard Quade, 1998, 1999; Mukhopadhyay, 1997) and the actually observed FIR lines. The upper levels are seen to be upshifted from expected position. A closer look at the calculated energy values seems to indicate a possible interaction between the above states and other proximate torsional-rotational states could occur. The possible candidates for the interacting level manifolds are narrowed down through the presence of the forbidden transition. We also take the opportunity to propose alternate rotational quantum numbers for some of the assignments recently reported in the literature (El Hilali et al., 2011). Some ambiguities are pointed out on the data and the reported analysis. There remain too many such irregularities and we propose to gather a large body assigned transitions in a future catalog. Assignments and relevant comments on optically pumped FIR laser radiation are also made.

  10. Optical Transitions in Hybrid Perovskite Solar Cells: Ellipsometry, Density Functional Theory, and Quantum Efficiency Analyses for CH3NH3PbI3

    NASA Astrophysics Data System (ADS)

    Shirayama, Masaki; Kadowaki, Hideyuki; Miyadera, Tetsuhiko; Sugita, Takeshi; Tamakoshi, Masato; Kato, Masato; Fujiseki, Takemasa; Murata, Daisuke; Hara, Shota; Murakami, Takurou N.; Fujimoto, Shohei; Chikamatsu, Masayuki; Fujiwara, Hiroyuki

    2016-01-01

    Light-induced photocarrier generation is an essential process in all solar cells, including organic-inorganic hybrid (CH3NH3PbI3 ) solar cells, which exhibit a high short-circuit current density (Jsc ) of approximately 20 mA /cm2 . Although the high Jsc observed in the hybrid solar cells relies on strong electron-photon interaction, the optical transitions in the perovskite material remain unclear. Here, we report artifact-free CH3NH3PbI3 optical constants extracted from ultrasmooth perovskite layers without air exposure and assign all of the optical transitions in the visible and ultraviolet region unambiguously, based on density-functional theory (DFT) analysis that assumes a simple pseudocubic crystal structure. From the self-consistent spectroscopic ellipsometry analysis of the ultrasmooth CH3NH3PbI3 layers, we find that the absorption coefficients of CH3NH3PbI3 (α =3.8 ×104 cm-1 at 2.0 eV) are comparable to those of CuInGaSe2 and CdTe, and high α values reported in earlier studies are overestimated seriously by the extensive surface roughness of CH3NH3PbI3 layers. The polarization-dependent DFT calculations show that CH3NH3 + interacts strongly with the PbI3 - cage, modifying the CH3NH3PbI3 dielectric function in the visible region rather significantly. In particular, the transition matrix element of CH3NH3PbI3 varies, depending on the position of CH3NH3 + within the Pb—I network. When the effect of CH3NH3 + on the optical transition is eliminated in the DFT calculation, the CH3NH3PbI3 dielectric function deduced from DFT shows an excellent agreement with the experimental result. As a result, distinct optical transitions observed at E0(Eg)=1.61 eV , E1=2.53 eV , and E2=3.24 eV in CH3NH3PbI3 are attributed to the direct semiconductor-type transitions at the R , M , and X points in the pseudocubic Brillouin zone, respectively. We further perform the quantum efficiency (QE) analysis for a standard hybrid-perovskite solar cell incorporating a mesoporous TiO2

  11. Investigation of fundamental and high order optical transitions in α-Fe2O3 thin films using surface barrier electroreflectance

    NASA Astrophysics Data System (ADS)

    Qayyum, H. A.; Al-Kuhaili, M. F.; Durrani, S. M. A.

    2017-10-01

    In this paper, we use surface barrier electroreflectance technique to probe the optical transitions in hematite (α-Fe2O3) thin film. An electric field was induced normal to the surface of α-Fe2O3 thin film in an Ag/α-Fe2O3/Ag based capacitor type structure and the corresponding electroreflectance analysis was performed. Based on the electroreflectance analysis, we observed the fundamental as well as two high order critical points associated with α-Fe2O3. Standard critical point model was used to find the exact energy locations and the broadening parameters associated with these critical points. The existence of the fundamental critical point was further confirmed by the spectrophotometric analysis. The quantitative analysis based on the electro-optic energy confirmed that the obtained electroreflectance spectrum was within the low field regime, and the obtained critical points above the fundamental transition were attributed to the high order transitions of electrons from the valence band to the deep in the conduction band.

  12. Transition metal and rare earth-doped ZnO: a comparison of optical, magnetic, and structural behavior of bulk and thin films

    NASA Astrophysics Data System (ADS)

    Fenwick, W. E.; Kane, M. H.; Varatharajan, R.; Zaidi, T.; Fang, Z.; Nemeth, B.; Keeble, D. J.; El-Mkami, H.; Smith, G. M.; Nause, J.; Summers, C. J.; Ferguson, I. T.

    2007-02-01

    Recent theoretical predictions of ferromagnetic behavior in transition metal (TM)-doped ZnO have focused significant attention on these materials for use as spintronic materials. Moreover, rare earth (RE) elements in wide bandgap semiconductors would be useful not only in spintronics but also in optoelectronic applications. This work presents results obtained from an investigation into the optical, magnetic, and structural properties of transition-metal (TM)- doped ZnO and rare earth (RE) doped ZnO (TM = Mn, Co, Ni, and Fe; RE = Gd, Eu, and Tb) bulk crystals and thin films. Properties of TM- and RE-doped ZnO bulk crystals and thin films were studied and compared in order to better understand the nature of these dopant centers and their effects on the properties of the host crystal. Optical properties confirm the incorporation of substitutional transition metal ions on cation sites. While most thin film samples show ferromagnetic behavior, the magnetic response of the bulk crystals varies. This suggests that the magnetic behavior of TM-doped ZnO is highly dependent on growth conditions, and growth conditions which favor the formation of grain boundaries and interfaces may be more likely to result in ferromagnetic behavior. Origins of this ferromagnetic behavior are still under investigation. Defect luminescence observed in the RE-doped samples suggests that these materials may prove useful in optoelectonic applications as well.

  13. Parity- and spin-forbidden optical transitions of Cr{sup +3} in GdAlO{sub 3}

    SciTech Connect

    Basso, H.C.

    1997-10-01

    In this paper, the electric-dipole transition induced by exchange is used to explain the strong dependence of spin- and parity-forbidden transitions of Cr{sup +3} on the sublattice magnetization of an antiferromagnet host. {copyright} {ital 1997} {ital The American Physical Society}

  14. Direct optical transitions at K- and H-point of Brillouin zone in bulk MoS{sub 2}, MoSe{sub 2}, WS{sub 2}, and WSe{sub 2}

    SciTech Connect

    Kopaczek, J.; Polak, M. P.; Scharoch, P.; Kudrawiec, R.; Wu, K.; Chen, B.; Tongay, S.

    2016-06-21

    Modulated reflectance (contactless electroreflectance (CER), photoreflectance (PR), and piezoreflectance (PzR)) has been applied to study direct optical transitions in bulk MoS{sub 2}, MoSe{sub 2}, WS{sub 2}, and WSe{sub 2}. In order to interpret optical transitions observed in CER, PR, and PzR spectra, the electronic band structure for the four crystals has been calculated from the first principles within the density functional theory for various points of Brillouin zone including K and H points. It is clearly shown that the electronic band structure at H point of Brillouin zone is very symmetric and similar to the electronic band structure at K point, and therefore, direct optical transitions at H point should be expected in modulated reflectance spectra besides the direct optical transitions at the K point of Brillouin zone. This prediction is confirmed by experimental studies of the electronic band structure of MoS{sub 2}, MoSe{sub 2}, WS{sub 2}, and WSe{sub 2} crystals by CER, PR, and PzR spectroscopy, i.e., techniques which are very sensitive to critical points of Brillouin zone. For the four crystals besides the A transition at K point, an A{sub H} transition at H point has been observed in CER, PR, and PzR spectra a few tens of meV above the A transition. The spectral difference between A and A{sub H} transition has been found to be in a very good agreement with theoretical predictions. The second transition at the H point of Brillouin zone (B{sub H} transition) overlaps spectrally with the B transition at K point because of small energy differences in the valence (conduction) band positions at H and K points. Therefore, an extra resonance which could be related to the B{sub H} transition is not resolved in modulated reflectance spectra at room temperature for the four crystals.

  15. Proposal for using optical transition radiation for electron beam alignment and emittance measurement for the free emittance measurement for the free electron laser experiments at ATF

    SciTech Connect

    Qiu, Xu Z.; Wang, Xijie; Ben-Zvi, I.

    1994-10-01

    Optical transiton radiation (OTR) produced from thin intercepting foils have been employed to image the spatial profile of the electron beam in several free electron laser experiments. It was found that the images from OTR were significantly sharper than the images produced from phosphor screens. Furthermore, OTR`s sensitivity of its angular distribution and polarization to energy and divergence of the electron beam was exploited to diagnose energy and emittance of the electron beam. OTR has been proven to be vital in electron beam alignment in FEL experiments. This report gives a summary of the basic theory of transition radiation and techniques using transition radiation for electron beam imaging and emittance measurement. The possibility was explored for employing these techniques in the HGHG FEL and the visible FEL experiments in ATF (Accelerator Test Facility).

  16. In-situ investigation of the order-disorder transition in Cu2ZnSnSe4 by optical transmission spectroscopy

    NASA Astrophysics Data System (ADS)

    Stroth, Christiane; Sayed, Mohamed H.; Neerken, Janet; Mikolajczak, Ulf; Rey, Germain; Parisi, Jürgen; Gütay, Levent

    2017-02-01

    The existence of disorder is one possible reason for the limited performance of kesterite solar cells. Therefore further knowledge of the order-disorder phase transition, of factors which influence the degree of order and of methods to determine this material property is still required. In this study we investigated the order-disorder transition in the kesterite material Cu2ZnSnSe4 by in-situ optical transmission spectroscopy during heat treatments. We show in-situ results for the temperature dependence of the band gap and its tailing properties. The influence of cooling rates on the phase transition was analyzed as well as the ordering kinetics during annealing at a constant temperature. The critical temperature of the phase transition was determined and the existence of a control temperature range is shown, which allows for controlling the degree of order by the cooling rate within this range. Additionally we performed Raman analysis to link Raman spectra to the degree of order in Cu2ZnSnSe4. A correlation between the intensity ratio of A-modes as well as B-/ E- Raman modes and the degree of order was found.

  17. Laser Induced Optical Pumping Measurements of Cross Sections for Fine and Hyperfine Structure Transitions in Sodium Induced by Collisions with Helium Argon Atoms

    NASA Technical Reports Server (NTRS)

    Dobson, Chris C.; Sung, C. C.

    1998-01-01

    Optical pumping of the ground states of sodium can radically alter the shape of the laser induced fluorescence excitation spectrum, complicating measurements of temperature, pressure, etc., which are based on these spectra. Modeling of the fluorescence using rate equations for the eight hyperfine states of the sodium D manifolds can be used to quantify the contribution to the ground state pumping of transitions among the hyperfine excited states induced by collisions with buffer gas atoms. This model is used here to determine, from the shape of experimental spectra, cross sections for (Delta)F transitions of the P(sub 3/2) state induced by collisions with helium and argon atoms, for a range of values assumed for the P(sub 1/2), (Delta)F cross sections. The hyperfine cross sections measured using this method, which is thought to be novel, are compared with cross sections for transitions involving polarized magnetic substates, m(sub F), measured previously using polarization sensitive absorption. Also, fine structure transition ((Delta)J) cross sections were measured in the pumped vapor, giving agreement with previous measurements made in the absence of pumping.

  18. Laser-Induced Optical Pumping Measurements of Cross Section for Fine- and Hyperfine-Structure Transitions in Sodium Induced by Collisions with Helium and Argon Atoms

    NASA Technical Reports Server (NTRS)

    Dobson, Chris C.; Sung, C. C.

    1999-01-01

    Optical pumping of the ground states of sodium can radically alter the shape of the laser-induced fluorescence excitation spectrum, complicating measurements of temperature, pressure, etc., which are based on these spectra. Modeling of the fluorescence using rate equations for the eight hyperfine states of the sodium D manifolds can be used to quantify the contribution to the ground state pumping of transitions among the hyperfine excited states induced by collisions with buffer gas atoms. This model is used here to determine, from the shape of experimental spectra, cross sections lor DELTA.F transitions of the P(sub 3/2) state induced by collisions with helium and argon atoms, for a range of values assumed for the P(sub 1/2), DELTA.F cross sections. The hyperfine cross sections measured using this method, which to our knowledge is novel, are compared with cross sections for transitions involving polarized magnetic substates m(sub F) measured previously using polarization sensitive absorption. Also, fine-structure transition cross sections were measured in the pumped vapor, giving agreement with previous measurements made in the absence of pumping.

  19. Laser-Induced Optical Pumping Measurements of Cross Section for Fine- and Hyperfine-Structure Transitions in Sodium Induced by Collisions with Helium and Argon Atoms

    NASA Technical Reports Server (NTRS)

    Dobson, Chris C.; Sung, C. C.

    1999-01-01

    Optical pumping of the ground states of sodium can radically alter the shape of the laser-induced fluorescence excitation spectrum, complicating measurements of temperature, pressure, etc., which are based on these spectra. Modeling of the fluorescence using rate equations for the eight hyperfine states of the sodium D manifolds can be used to quantify the contribution to the ground state pumping of transitions among the hyperfine excited states induced by collisions with buffer gas atoms. This model is used here to determine, from the shape of experimental spectra, cross sections lor DELTA.F transitions of the P(sub 3/2) state induced by collisions with helium and argon atoms, for a range of values assumed for the P(sub 1/2), DELTA.F cross sections. The hyperfine cross sections measured using this method, which to our knowledge is novel, are compared with cross sections for transitions involving polarized magnetic substates m(sub F) measured previously using polarization sensitive absorption. Also, fine-structure transition cross sections were measured in the pumped vapor, giving agreement with previous measurements made in the absence of pumping.

  20. Band-edge optical transitions in a nonpolar-plane GaN substrate: exciton-phonon coupling and temperature effects

    NASA Astrophysics Data System (ADS)

    Wang, M. Z.; Xu, S. J.

    2016-09-01

    We present a detailed investigation of the band-edge optical transitions involving the interacting exciton-phonon system, especially first-order longitudinal optical (LO) phonon-assisted luminescence of bound and free excitons in m- and c-plane GaN substrates in a low temperature range from 4 K to 40 K. The main luminescence features of all of the three kinds of excitons can be well described by the theoretical models that take exciton-LO-phonon coupling into account. The effective Bohr radii of the excitons play a key role in determining the Huang-Rhys factor characterizing the exciton-LO-phonon coupling strength in GaN. An interesting oscillatory structure is found to appear in the low-temperature luminescence spectra of the nonpolar-plane GaN substrate, which needs to be clarified by further investigations.

  1. Effect of magnetic ordering of Dy2BaNiO5 on the crystal-field levels of dysprosium: optical spectroscopy of f-f transitions

    NASA Astrophysics Data System (ADS)

    Galkin, A. S.; Klimin, S. A.

    2016-12-01

    Optical transmission spectroscopy study of the Haldane magnet Dy2BaNiO5 was performed in the region of f-f transitions of the Dy3+ ion in a wide range of temperatures (5-300 K). At temperatures lower than TN (59 K), Kramers doublets of the rare-earth ion split. Spectroscopic data obtained were used to calculate the Schottky-type anomaly in the temperature dependence of the magnetic susceptibility of Dy2BaNiO5 and to model the experimental data available in literature. Anomalous behavior of crystal-field energies of the Dy3+ ion was attributed to the magnetoelectric interactions.

  2. Growth and optical properties of Bi{sub 12}SiO{sub 20} single crystals doped with first row transition metal and aluminum

    SciTech Connect

    Petrova, D.; Gospodinov, M.; Sveshtarov, P.

    1995-10-01

    Bi{sub 12}SiO{sub 20} single crystals co-doped with first row transition metals and aluminum were grown from the melt by the Czochralski technique. Optimal growth conditions for optically homogeneous crystals have been established. Dopant molar concentrations in the crystal were determined and segregation coefficients calculated. Transmission spectra were measured in the 0.38--0.85 {micro}m range. It was established that adding Al to the melt bleached the crystals and blue-shifted the entire transmission spectrum. Doping with Cu produced a strong photochromic effect after daylight exposure, changing the crystal color from yellow to red.

  3. Spectroscopy of ^1S0 -- ^3P1^88Sr Atomic Transition in a 1.06 μm Optical Dipole Trap

    NASA Astrophysics Data System (ADS)

    Martinez de Escobar, Y. N.; Mickelson, P. G.; Traverso, A. J.; Killian, T. C.

    2008-05-01

    We studied the effects of laser light near-resonant with the ^1S0-- ^3P1^88Sr transition in an optical dipole trap (ODT). We observe laser cooling of our ODT atomic sample as the atoms collide in the presence of red-detuned 689 nm light. Heating of the atoms was also observed at a different range of frequency detunings while performing spectroscopy. Both processes were accompanied with atom loss, but the increase of phase space density observed during 689 nm laser cooling could aid pursuits of quantum degeneracy with Sr.

  4. Optical transitions of Tm3+ in oxyfluoride glasses and compositional and thermal effect on upconversion luminescence of Tm3+/Yb3+-codoped oxyfluoride glasses.

    PubMed

    Feng, Li; Wu, Yinsu; Liu, Zhuo; Guo, Tao

    2014-01-24

    Optical properties of Tm(3+)-doped SiO2-BaF2-ZnF2 glasses have been investigated on the basis of the Judd-Ofelt theory. Judd-Ofelt intensity parameters, radiative transition probabilities, fluorescence branching ratios and radiative lifetimes have been calculated for different glass compositions. Upconversion emissions were observed in Tm(3+)/Yb(3+)-codoped SiO2-BaF2-ZnF2 glasses under 980 nm excitation. The effects of composition, concentration of the doping ions, temperature, and excitation pump power on the upconversion emissions were also systematically studied. Copyright © 2013 Elsevier B.V. All rights reserved.

  5. Phase Transitions and Domain Structure in Mixed Tetragonal-Rhombohedral BiFeO3 thin films using Raman Spectroscopy and Nonlinear Optics

    NASA Astrophysics Data System (ADS)

    Vlahos, E.; Kumar, A.; Denev, S.; Melville, A.; Adamo, C.; Ihlefeld, J. F.; Sheng, G.; Zeches, R. J.; Zhang, J. X.; He, Q.; Yang, C. H.; Erni, R.; Rossell, M. D.; J, A.; Hatt; Chu, Y.-H.; Wang, C. H.; Ederer, C.; Gopalan, V.; Chen, L. Q.; Schlom, D. G.; Spaldin, N. A.; Martin, L. W.; Ramesh, R.; Tenne, Dmitri

    2010-03-01

    We have shown that biaxially strained BiFeO3 thin films can undergo an isosymmetric phase transition from a rhombohedral-like to a tetragonal-like phase. This talk discusses the evolution of the tetragonal and the mixed phases in BiFeO3/YAlO3 thin films with varying film thickness using optical second harmonic generation (SHG) and Raman spectroscopy. 25nm, 75nm, and 225 nm thick films were studied; thinner films are dominated by the tetragonal phase, whereas thicker films exhibit both tetragonal and rhombohedral phases. The evolution of these phases as function of film thickness and temperature was experimentally determined.

  6. Observation and Analysis of Optical Transitions Radiation at the NPS linac and its Use for Diagnostics of Electron Beams

    DTIC Science & Technology

    1990-06-01

    is the radiation caused by a charged particle moving in a medium at a speed faster than the speed of light in that same medium, had been known since... particle which experiences a change in the dielectric properties of the medium through which it travels produces electromagnetic radiation. This...energy of the charged particle causing the radiation. The radiation of photons which have frequencies in the optical region is known as optical

  7. The Optical Gravitational Lensing Experiment. Planetary and Low-Luminosity Object Transits in the Carina Fields of the Galactic Disk

    NASA Astrophysics Data System (ADS)

    Udalski, A.; Szewczyk, O.; Zebrun, K.; Pietrzynski, G.; Szymanski, M.; Kubiak, M.; Soszynski, I.; Wyrzykowski, L.

    2002-12-01

    We present results of the second "planetary and low-luminosity object transit" campaign conducted by the OGLE-III survey. Three fields (35' X 35' each) located in the Carina regions of the Galactic disk (l ≈ 290°) were monitored continuously in February-May 2002. About 1150 epochs were collected for each field. The search for low depth transits was conducted on about 103 000 stars with photometry better than 15 mmag. In total, we discovered 62 objects with shallow depth (≤ 0.08 mag) flat-bottomed transits. For each of these objects several individual transits were detected and photometric elements were determined. Also lower limits on radii of the primary and companion were calculated. The 2002 OGLE sample of stars with transiting companions contains considerably more objects that may be Jupiter-sized (R < 1.6 R_Jup) compared to our 2001 sample. There is a group of planetary candidates with the orbital periods close to or shorter than one day. If confirmed as planets, they would be the shortest period extrasolar planetary systems. In general, the transiting objects may be extrasolar planets, brown dwarfs, or M-type dwarfs. One should be, however, aware that in some cases unresolved blends of regular eclipsing stars can mimic transits. Future spectral analysis and eventual determination of the amplitude of radial velocity should allow final classification. High resolution spectroscopic follow-up observations are, therefore, strongly encouraged. All photometric data are available to the astronomical community from the OGLE INTERNET archive.

  8. Influence of thin AlAs layer insertion on intersubband optical transitions in GaAs/AlGaAs quantum- well structures

    NASA Astrophysics Data System (ADS)

    Liu, Dongfeng; Wang, Everett X.; Guo, Kangxian

    2017-02-01

    In this work, we demonstrate the thin AlAs layer insertion into GaAs/AlGaAs quantum well (QW) structures and its influence in energy transition in the frequency range of mid-infrared. To realize the more accurate calculation, the graded interface model of QW structures is integrated into our self-consistent solving of Schrodinger and Poisson equations to obtain the energy level and envelope wave functions of QW. We find the thin AlAs layer inserted at various positions in the well can obviously tune intersubband optical transitions. The corresponding tuning range can be 50 meV. We find that the thicker AlAs layer (2 monolayers) can provide wider tuning range and larger oscillator strength between subbands 1 and 3, compared with the thinner one (1 monolayer). Our results suggest that thin semiconductor layer may be an idea optimization design for the quantum well terahertz lasers which are based on optical pumping with mid-infrared lasers.

  9. Optical Imaging of Phase Transition and Li-Ion Diffusion Kinetics of Single LiCoO(2) Nanoparticles During Electrochemical Cycling.

    PubMed

    Jiang, Dan; Jiang, Yingyan; Li, Zhimin; Liu, Tao; Wo, Xiang; Fang, Yimin; Tao, Nongjian; Wang, Wei; Chen, Hong-Yuan

    2017-01-11

    Understanding the phase transition and Li-ion diffusion kinetics of Li-ion storage nanomaterials holds promising keys to further improve the cycle life and charge rate of the Li-ion battery. Traditional electrochemical studies were often based on a bulk electrode consisting of billions of electroactive nanoparticles, which washed out the intrinsic heterogeneity among individuals. Here, we employ optical microscopy, termed surface plasmon resonance microscopy (SPRM), to image electrochemical current of single LiCoO2 nanoparticles down to 50 fA during electrochemical cycling, from which the phase transition and Li-ion diffusion kinetics can be quantitatively resolved in a single nanoparticle, in operando and high throughput manner. SPRM maps the refractive index (RI) of single LiCoO2 nanoparticles, which significantly decreases with the gradual extraction of Li-ions, enabling the optical read-out of single nanoparticle electrochemistry. Further scanning electron microscopy characterization of the same batch of nanoparticles led to a bottom-up strategy for studying the structure-activity relationship. As RI is an intrinsic property of any material, the present approach is anticipated to be applicable for versatile kinds of anode and cathode materials, and to facilitate the rational design and optimization toward durable and fast-charging electrode materials.

  10. Observations of CEF-split intermultiplet transitions in optically opaque EuBa{sub 2}Cu{sub 3}O{sub 7} using inelastic neutron scattering

    SciTech Connect

    Staub, U.; Soderholm, L.; Osborn, R.; Balcar, E.; Trunov, V.

    1995-02-01

    Inelastic neutron scattering (INS) results on the intermultiplet transitions J=0 {yields} 1 and J=l {yields} 2 in optically opaque EuBa{sub 2}Cu{sub 3}O{sub 7} are reported. Whereas these multiplets are split by the crystalline electric field (CEF), their low J values are influenced to first order only by the 2 second-order (J=l) and additional fourth-order (J=2) CEF parameters. B{sub 0}{sup 2}, B{sub 2}{sup 2} and the spin-orbit coupling parameter were obtained by fitting the splitting of the J=1 multiplet and the energy separation between the J=0 and 1 multiplets. The J=0 to 1 splitting observed here is smaller than previously seen by optical spectroscopic studies on a variety of transparent, ionic compounds, necessitating fitting of the free-ion parameter. Additional spectroscopic information on the J=2 multiplet indicates that additional fitting of free ion parameters must be included to adequately model the observed low energy separation between the two lowest J-multiplets. Preliminary calculation on the Q-dependence of the CEF split J=0 to 1 transitions and the comparison with observations are presented.

  11. Understanding ferromagnetism and optical absorption in 3d transition metal-doped cubic ZrO{sub 2} with the modified Becke-Johnson exchange-correlation functional

    SciTech Connect

    Boujnah, M.; Zaari, H.; El Kenz, A.; Labrim, H.; Benyoussef, A.; Mounkachi, O.

    2014-03-28

    The electronic structure, magnetic, and optical properties in cubic crystalline phase of Zr{sub 1−x}TM{sub x}O{sub 2} (TM = V, Mn, Fe, and Co) at x = 6.25% are studied using density functional theory with the Generalized Gradient Approximation and the modified Becke-Johnson of the exchange-correlation energy and potential. In our calculations, the zirconia is a p-type semiconductor and has a large band gap. We evaluated the possibility of long-range magnetic order for transition metal ions substituting Zr. Our results show that ferromagnetism is the ground state in V, Mn, and Fe-doped ZrO{sub 2} and have a high value of energy in Mn-doped ZrO{sub 2}. However, in Co-doped ZrO{sub 2}, antiferromagnetic ordering is more stable than the ferromagnetic one. The exchange interaction mechanism has been discussed to explain the responsible of this stability. Moreover, it has been found that the V, Mn, and Fe transition metals provide half-metallic properties considered to be the leading cause, responsible for ferromagnetism. Furthermore, the optical absorption spectra in the TM -doped cubic ZrO{sub 2} are investigated.

  12. Optical Constants and Band Gap Evolution with Phase Transition in Sub-20-nm-Thick TiO2 Films Prepared by ALD.

    PubMed

    Shi, Yue-Jie; Zhang, Rong-Jun; Zheng, Hua; Li, Da-Hai; Wei, Wei; Chen, Xin; Sun, Yan; Wei, Yan-Feng; Lu, Hong-Liang; Dai, Ning; Chen, Liang-Yao

    2017-12-01

    Titanium dioxide (TiO2) ultrathin films with different thicknesses below 20 nm were grown by atomic layer deposition (ALD) on silicon substrates at 300 °C. Spectroscopic ellipsometry (SE) measurements were operated to investigate the effect of thickness on the optical properties of ultrathin films in the spectra range from 200 to 1000 nm with Forouhi-Bloomer (F-B) dispersion relation. It has been found that the refractive index and extinction coefficient of the investigated TiO2 ultrathin film increase while the band gap of TiO2 ultrathin film decreases monotonically with an increase in film thickness. Furthermore, with the purpose of studying the temperature dependence of optical properties of TiO2 ultrathin film, the samples were annealed at temperature from 400 to 900 °C in N2 atmosphere. The crystalline structure of deposited and annealed films was deduced by SE and supported by X-ray diffraction (XRD). It was revealed that the anatase TiO2 film started to transform into rutile phase when the annealing temperature was up to 800 °C. In this paper, a constructive and effective method of monitoring the phase transition in ultrathin films by SE has been proposed when the phase transition is not so obvious analyzed by XRD.

  13. Optical properties of light-sensitive liquid-crystal elastomers in the vicinity of the nematic-paranematic phase transition

    NASA Astrophysics Data System (ADS)

    Gregorc, Marko; Li, Hui; Domenici, Valentina; Ambrožič, Gabriela; Čopič, Martin; Drevenšek-Olenik, Irena

    2013-02-01

    We investigate light-induced patterning of a monodomain side-chain liquid crystal elastomer (SC-LCE) doped with light-sensitive azobenzene moiety in the temperature region close to the nematic-paranematic phase transition. We show that a strongly nonlinear relationship between the concentration of the cis isomers of the azomesogens and the refractive index modification of the material, which is characteristic for the phase transition region, results in nonmonotonous time dependence of the diffraction efficiency of a probe beam. From this effect we determine the sensitivity of the nematic transition temperature on the molar fraction of the cis isomers. The relation between the cis isomer molar fraction and nematic order also provides a possibility for recording hidden holograms, which can be made visible by cooling the sample from the paranematic to the nematic phase.

  14. Absolute measurement of the 1S0 − 3P0 clock transition in neutral 88Sr over the 330 km-long stabilized fibre optic link

    PubMed Central

    Morzyński, Piotr; Bober, Marcin; Bartoszek-Bober, Dobrosława; Nawrocki, Jerzy; Krehlik, Przemysław; Śliwczyński, Łukasz; Lipiński, Marcin; Masłowski, Piotr; Cygan, Agata; Dunst, Piotr; Garus, Michał; Lisak, Daniel; Zachorowski, Jerzy; Gawlik, Wojciech; Radzewicz, Czesław; Ciuryło, Roman; Zawada, Michał

    2015-01-01

    We report a stability below 7 × 10−17 of two independent optical lattice clocks operating with bosonic 88Sr isotope. The value (429 228 066 418 008.3(1.9)syst (0.9)stat Hz) of the absolute frequency of the 1S0 – 3P0 transition was measured with an optical frequency comb referenced to the local representation of the UTC by the 330 km-long stabilized fibre optical link. The result was verified by series of measurements on two independent optical lattice clocks and agrees with recommendation of Bureau International des Poids et Mesures. PMID:26639347

  15. Absolute measurement of the 1S0 - 3P0 clock transition in neutral 88Sr over the 330 km-long stabilized fibre optic link.

    PubMed

    Morzyński, Piotr; Bober, Marcin; Bartoszek-Bober, Dobrosława; Nawrocki, Jerzy; Krehlik, Przemysław; Śliwczyński, Łukasz; Lipiński, Marcin; Masłowski, Piotr; Cygan, Agata; Dunst, Piotr; Garus, Michał; Lisak, Daniel; Zachorowski, Jerzy; Gawlik, Wojciech; Radzewicz, Czesław; Ciuryło, Roman; Zawada, Michał

    2015-12-07

    We report a stability below 7 × 10(-17) of two independent optical lattice clocks operating with bosonic (88)Sr isotope. The value (429 228 066 418 008.3(1.9)(syst) (0.9)(stat) Hz) of the absolute frequency of the (1)S(0) - (3)P(0) transition was measured with an optical frequency comb referenced to the local representation of the UTC by the 330 km-long stabilized fibre optical link. The result was verified by series of measurements on two independent optical lattice clocks and agrees with recommendation of Bureau International des Poids et Mesures.

  16. Electronic and optical properties of BaTiO3 across tetragonal to cubic phase transition: An experimental and theoretical investigation

    NASA Astrophysics Data System (ADS)

    Mishra, Vikash; Sagdeo, Archna; Kumar, Vipin; Warshi, M. Kamal; Rai, Hari Mohan; Saxena, S. K.; Roy, Debesh R.; Mishra, Vinayak; Kumar, Rajesh; Sagdeo, P. R.

    2017-08-01

    Temperature dependent diffuse reflectance spectroscopy measurements were carried out on polycrystalline samples of BaTiO3 across the tetragonal to cubic structural phase transition temperature (TP). The values of various optical parameters such as band gap (Eg), Urbach energy (Eu), and Urbach focus (E0) were estimated in the temperature range of 300 K to 480 K. It was observed that with increasing temperature, Eg decreases and shows a sharp anomaly at TP. First principle studies were employed in order to understand the observed change in Eg due to the structural phase transition. Near TP, there exist two values of E0, suggesting the presence of electronic heterogeneity. Further, near TP, Eu shows metastability, i.e., the value of Eu at temperature T is not constant but is a function of time (t). Interestingly, it is observed that the ratio of Eu (t=0)/Eu (t = tm), almost remains constant at 300 K (pure tetragonal phase) and at 450 K (pure cubic phase), whereas this ratio decreases close to the transition temperature, which confirms the presence of electronic metastability in the pure BaTiO3. The time dependence of Eu, which also shows an influence of the observed metastability can be fitted with the stretched exponential function, suggesting the presence of a dynamic heterogeneous electronic disorder in the sample across TP. First principle studies suggest that the observed phase coexistence may be due to a very small difference between the total cohesive energy of the tetragonal and the cubic structure of BaTiO3. The present work implies that the optical studies may be a sensitive probe of disorder/heterogeneity in the sample.

  17. Effects of deposition methods and processing techniques on band gap, interband electronic transitions, and optical absorption in perovskite CH3NH3PbI3 films

    NASA Astrophysics Data System (ADS)

    Li, Wenwu; Sha, Tingting; Wang, Yan; Yu, Wenlei; Jiang, Kai; Zhou, Hang; Liu, Chuan; Hu, Zhigao; Chu, Junhao

    2017-07-01

    Despite intensive studies on the improvements of conversion efficiencies in solar cells, many questions regarding the effects of deposition techniques on optical properties and electronic band structures of CH3NH3PbI3 (MAPbI3) remain unresolved. Here, perovskite MAPbI3 films were prepared using different deposition methods and processing techniques. The effects of deposition and processing parameters on dielectric functions and optical absorption were investigated by fitting the reflectance spectra in the photon energy range of 0.5-5.16 eV. It is found that the bandgap (Eg) of the films deposited by two-step spinning (1.591 eV) is larger than that prepared by evaporations (1.514 eV), due to different Pb-I orbital hybridization and spin-orbit coupling. Moreover, the Eg value of the films increases from 1.543 eV to 1.591 eV after toluene solution dripping. Five interband electronic transitions ( Ep 1, Ep 2, Ep 3, Ep 4 , and Ep 5 ) are observed, and the origins of Ep 2, Ep 3 , and Ep 4 are assigned to the direct transitions between the highest valence band and the lowest lying conduction band at the R, M, and X symmetry points. Further, the transition energies of the films deposited by evaporation are less than those prepared by two-step spinning. The present results shed light on preparing more reliable and reproducible high performance MAPbI3-based solar cells.

  18. Metal mono-chalcogenides ZnX and CdX (X = S, Se and Te) monolayers: Chemical bond and optical interband transitions by first principles calculations

    NASA Astrophysics Data System (ADS)

    Safari, Mandana; Izadi, Zohreh; Jalilian, Jaafar; Ahmad, Iftikhar; Jalali-Asadabadi, Saeid

    2017-02-01

    In this paper, we explore the structural, electronic and optical properties of ZnX and CdX (X = S, Se and Te) compounds in the two-dimensional (2D) graphene-like structure using the full potential augmented plane waves plus local orbitals (FP-APW + lo) method. Unlike their bulk phase, they are optically inactive because of their indirect band gap nature except CdS and ZnS. These two compounds maintain their direct band gap nature and hence are optically active. The static dielectric constants for these monolayers illustrate increasing trend with decrease in the band gap values. Furthermore, an acceptable description of electron transitions in these monolayers is accomplished according to the imaginary parts of the dielectric functions and absorption spectra in ZnS and CdS as examples of each group of CdX and ZnX. The results presented in this article revealed that ZnS and CdS in the 2D structure can be effectively used in optoelectronic devices such as solar cell materials and so forth.

  19. Microstructural and Optical properties of transition metal (Cu) doped ZnO diluted magnetic semiconductor nano thin films fabricated by sol gel method

    NASA Astrophysics Data System (ADS)

    Ozturk, Ozgur; Asikuzun, Elif; Tasci, A. Tolga; Arda, Lutfi; Demirozu Senol, Sevim; Celik, Sukru; Terzioglu, Cabir

    Undoped and Cu (Copper) doped ZnO (Zn1-xCuxO) semiconductor thin films were produced by using sol-gel method. Cu was doped 1%, 2%, 3%, 4% and 5% ratio. Methanol and monoethanolamine (MEA) were used as solvent and stabilizer. In this study, the effect of Cu doping was investigated on microstructural and optical properties of ZnO DMS thin films. XRD, SEM, AFM and UV-VIS spectrometer measurements were performed for the microstructural and optical characterization. XRD, SEM and AFM results were showed that all of Cu doped ZnO based thin films have a hexagonal structure. The grain size of Cu doped ZnO thin films and morphology of surface were changed with increasing Cu doping. The optical transmittance of transition metal (Cu) doped ZnO thin films were decreased with doping. Keywords:Diluted Magnetic Semiconductor (DMS), Thin Film, Cu-doping, Bandgap Energy, ZnO. This research has been supported by the Kastamonu University Scientific Research Projects Coordination Department under the Grant No. KU-BAP-05/2015-12 and the Scientific and Technological Research Council of Turkey (TUBITAK) Project No. 114F259.

  20. Spatially direct and indirect optical transitions observed for AlInAs/AlGaAs quantum dots

    NASA Astrophysics Data System (ADS)

    Neffati, R.; Saïdi, I.; Ben Radhia, S.; Ben Daly, A.; Maaref, M. A.; Boujdaria, K.; Lemaître, A.; Bernardot, F.; Testelin, C.

    2016-09-01

    The effects of the Aluminium concentration on the emission of Al0.45In0.55As/AlyGa1-y As quantum dots (QDs) are investigated by photoluminescence (PL), with the excitation power density as a variable parameter. The influence of a varying barrier composition on the QD emission is investigated theoretically and discussed with respect to PL measurements. For the highest barrier composition value (y = 0.77), we interpret the QD emission as originating from indirect type-II transitions involving electrons in the barrier X valley and heavy holes (HH), with S and P symmetry, in Al0.45In0.55As QDs. The PL spectra of the y = 0.38 sample exhibits three lines: two of them are related to indirect type-II transitions, in which the electron ground state belongs to the indirect gap (L and X) minima in the barrier conduction band, whereas the third transition is attributed to a direct type-I transitions.

  1. Microstructure processes induced by phase transitions in a CuAu alloy as studied by acoustic emission and optical cinematography

    SciTech Connect

    Masek, P.; Chmelik, F.; Sima, V.; Brinck, A.; Neuhaeuser, H.

    1999-01-15

    Combined acoustic emission measurements and surface cinematography observations have been applied to determine the structure evolution during thermal loading of the CuAu alloy. Thermal history and the fashion of thermal loading have been shown to affect considerably the structure response of the CuAu alloy on temperature changes. On thermal loading, intense plastic deformation occurs in certain temperature intervals due to the relaxation of internal stresses induced by phase transitions and structure anisotropy. The main mechanism is twinning taking place most probably in (110) planes. Dislocation glide and grain-boundary sliding have also been observed as minor mechanisms. A shape-restoration effect associated with the order-disorder transition is revealed. Thermal cycling with upper temperatures over 500 C may also result in structural damage.

  2. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Study of Phase Transition Properties in Epitaxial Ferroelectric Film

    NASA Astrophysics Data System (ADS)

    Wang, Chun-Dong; Teng, Bao-Hua; Ju, Yong-Feng; Cheng, Deng-Mu; Zhang, Chun-Lai

    2010-10-01

    Based on the transverse Ising model and using decoupling approximation to the Fermi-type Green's function, we study the phase transition properties of the epitaxial ferroelectric film with one substrate. A general recursive equation of the ferroelectric thin film with two n-layer materials is obtained, which enables us to study the phase transition properties for any number layers for epitaxial ferroelectric thin film. With the help of this equation, we analyze the effect of the exchange interaction and the transverse field in the phase diagram, the influence to the polarizations and Curie temperature numerically. The results show that epitaxial ferroelectric film are able to induce a strong increase or decrease of Curie temperature to different exchange interactions and transverse fields within the epitaxial film layers. The theoretical results are in reasonable accordance with experimental data of different ferroelectric thin film.

  3. Free-Surface Optical Scattering as an Indicator of the Shock-Induced Solid-Liquid Phase Transition in Tin

    SciTech Connect

    Stevens, G. D.; Lutz, S. S.; Marshall, B. R.; Turley, W. D.; Veeser, L. R.; Furlanetto, M. R.; Hixson, R. S.; Holtkamp, D. B.; Jensen, B. J.; Rigg, P. A.; Wilke, M. D.

    2008-07-01

    When highly polished metal surfaces melt upon release after shock loading, they exhibit features that suggest significant surface changes accompany the phase transition. The reflection of light from such surfaces changes from specular (pre-shock) to diffuse upon melting. A familiar manifestation of this phenomenon is the loss of signal light in VISAR measurements, which occurs at pressures high enough to melt the free surface. Unlike many other potential material phase-sensitive diagnostics (e.g., reflectometry, conductivity) that show relatively small (1%–10%) changes, the specularity of reflection provides a more sensitive and definitive indication of the solid-liquid phase transition. Data will be presented that support the hypothesis that specularity changes indicate melt in a way that can be measured easily and unambiguously.

  4. Structure and optical properties of transition metal dichalcogenides (TMDs) - MX2 (M = Mo, W & X = S, Se) under high pressure and high temperature conditions

    NASA Astrophysics Data System (ADS)

    Bandaru, Nirup

    Layered structured materials such as transition metal dichalcogenides (TMDs) have gained immense interest in recent times due to their exceptional structural, electrical and optical properties. Recent studies show semiconducting TMDs such as MX2 (M= Mo, W & X = S, Se) could be used as potential shock absorbing material, which has resulted in extensive studies on structural stability of these materials under the influence of high pressure. Understanding the structural stability of transition metal dichalcogenides (TMDs) such as MoS2, MoSe2, WS2, and WSe2 under high pressure has been very challenging due to contradicting observations and interpretations reported in the past. Hence, the main objective of this work is to study the crystal structure and optical properties of bulk MX 2 at high hydrostatic pressures up to 51 GPa using a diamond anvil cell with synchrotron radiation in addition to high pressure Raman spectroscopic and high temperature X-ray diffraction (XRD) experiments. Crystal structures of MX2 materials are observed to be stable up to 500 °C with nonlinear thermal coefficients of expansion. Results of high pressure experiments show a pressure induced isostructural hexagonal distortion to a 2Ha-hexagonal P63/mmc phase, in MoS2 around 26 GPa as predicted by theoretical calculations reported earlier. No pressure induced phase transformation is observed in other MX2 (MoSe2, WS2, WSe 2). A semi empirical model based on the energy of interaction of bond electrons is proposed to explain the observed inconsistency between MoS 2 and other TMDs studied. Using this model, it is shown that except MoS2, no other MX2 within the scope of this study undergoes pressure induced phase transition in the pressure range 0 -- 50 GPa. High pressure Raman results show continuous red shifts in dominant vibrational modes with increase in pressure in MX2. Additionally, emergence of a new peak, namely 'd - band' associated with 2Ha structure in MoS2 supports the observation of a

  5. Assignment of the /Li-7/2 optically pumped laser transitions pumped by Ar/+/ and Kr/+/ laser lines

    NASA Technical Reports Server (NTRS)

    Verma, K. K.; Stwalley, W. C.; Zemke, W. T.

    1981-01-01

    Welling and Wellegehausen (1977) have reported a list of Na2 and Li2 lines (belonging to B-X and A-X systems) which lase when vapors of these dimers are pumped with an Ar(+) or Kr(+) laser. A description is presented of a fluorescence study of the A-X system of the (Li-7)2 molecule excited by a Kr(+) laser (6471 A). The optically pumped laser lines are identified as P and R doublets in two different fluorescence series. The conditions which favor lasing action of these lines are pointed out. All but one of the known optically pumped laser lines of (Li-7)2 along with their assignments are presented in a table. For each pumping line, several additional wavelengths are listed which satisfy the condition for laser oscillations and which might well lase well under slightly improved conditions.

  6. Measurement of Electron Beam Emittance Using Optical Transition Radiation and Development of a Diffuse Screen Electron Beam Monitor

    DTIC Science & Technology

    1990-12-01

    Zerodur ,irror, 2" relfects light. 1OZ20BD.1; 20th wave zerodur mirror , 1" reflects light. LS-35; 3’ x 5’ optical breadboard; for mounting components...profile measurements using the diffuse screen were compared with measurements using a front surface mirror and a fluorescent screen. The 20 DISTRIBUTION...Beam current and profile measurements using the diffuse screen were compared with measurements using a front surface mirror and a fluorescent screen

  7. Optical Properties of Li2B4O7 Glasses Doped with Rare-Earths and Transition Metal Ions

    DTIC Science & Technology

    2001-01-01

    K.P. O’Donnell, B. Henderson and D. Hollis, " Disorder and the optical spectroscopy of Cr 3+- doped glasses: II. Glasses with high and low ligand...ions in oxide compounds", Fiz. Tw. Tela, 31(1), pp. 243-249, 1989. 11. W. Chen, J.O. Maim, V. Zwiller, Y. Huang, S. Liu, R. Wallenberg , J.O. Bovin and L

  8. Warm ice giant GJ 3470b - II. Revised planetary and stellar parameters from optical to near-infrared transit photometry

    NASA Astrophysics Data System (ADS)

    Biddle, Lauren I.; Pearson, Kyle A.; Crossfield, Ian J. M.; Fulton, Benjamin J.; Ciceri, Simona; Eastman, Jason; Barman, Travis; Mann, Andrew W.; Henry, Gregory W.; Howard, Andrew W.; Williamson, Michael H.; Sinukoff, Evan; Dragomir, Diana; Vican, Laura; Mancini, Luigi; Southworth, John; Greenberg, Adam; Turner, Jake D.; Thompson, Robert; Taylor, Brian W.; Levine, Stephen E.; Webber, Matthew W.

    2014-09-01

    It is important to explore the diversity of characteristics of low-mass, low-density planets to understand the nature and evolution of this class of planets. We present a homogeneous analysis of 12 new and 9 previously published broad-band photometric observations of the Uranus-sized extrasolar planet GJ 3470b, which belongs to the growing sample of sub-Jovian bodies orbiting M dwarfs. The consistency of our analysis explains some of the discrepancies between previously published results and provides updated constraints on the planetary parameters. Our data are also consistent with previous transit observations of this system. The physical properties of the transiting system can only be constrained as well as the host star is characterized, so we provide new spectroscopic measurements of GJ 3470 from 0.33 to 2.42 μm to aid our analysis. We find R* = 0.48 ± 0.04 R⊙, M* = 0.51 ± 0.06 M⊙, and Teff = 3652 ± 50K for GJ 3470, along with a rotation period of 20.70 ± 0.15 d and an R-band amplitude of 0.01 mag, which is small enough that current transit measurements should not be strongly affected by stellar variability. However, to report definitively whether stellar activity has a significant effect on the light curves, this requires future multiwavelength, multi-epoch studies of GJ 3470. We also present the most precise orbital ephemeris for this system: To = 2455983.70472 ± 0.00021BJDTDB, P = 3.336 6487^{+0.000 0043}_{-0.000 0033} d, and we see no evidence for transit timing variations greater than 1 min. Our reported planet to star radius ratio is 0.076 42 ± 0.000 37. The physical parameters of this planet are Rp = 3.88 ± 0.32 R⊕ and Mp = 13.73 ± 1.61 M⊕. Because of our revised stellar parameters, the planetary radius we present is smaller than previously reported values. We also perform a second analysis of the transmission spectrum of the entire ensemble of transit observations to date, supporting the existence of an H2-dominated atmosphere

  9. Optical transition probabilities in Er3+- and Tm3+-doped LiLa9(SiO4)6O2 crystals.

    PubMed

    Cantelar, E; Quintanilla, M; Cussó, F; Cavalli, E; Bettinelli, M

    2010-06-02

    In this work, Er(3+) and Tm(3+)-doped LiLa(9)(SiO(4))(6)O(2) crystals have been grown from an Li(2)MoO(4) flux in the 1360-940 °C temperature range. Optical absorption spectra have been measured to obtain the experimental oscillator strengths of the transitions from the ground state to the excited levels. Judd-Ofelt calculations have been performed to estimate the Ω(2), Ω(4) and Ω(6) intensity parameters. The dynamics of selected Er(3+) and Tm(3+) manifolds have been investigated under selective pulsed excitation in order to determine the energy gap law by comparing the observed decay rates with the Judd-Ofelt predictions.

  10. Extra sub-Doppler lines in the vicinity of the third-resonance 6S-8P transition of atomic Cs attributed to optically induced Cs dimers

    NASA Astrophysics Data System (ADS)

    Passerat de Silans, Thierry; Maurin, Isabelle; Laliotis, Athanasios; Segundo, Pedro Chaves De Souza; Bloch, Daniel

    2011-04-01

    We report on the observation of additional sub-Doppler lines in a saturated absorption experiment when exploring the vicinity of the 6S1/2-8P3/2 transition of Cs (λ=388 nm). These additional lines are observed only under a relatively strong irradiation of both the pump and the probe beams. Extra narrow lines are also observed in copropagating nonlinear spectroscopy, and around the lines of the V-type three-level system 8P3/2-6S1/2-8P1/2 (λ1=388 nm, λ2=389 nm). We attribute theses additional lines to a probing of high-lying molecular cesium, produced as a result of the optical excitation of Cs atoms, as the low Cs atom density (≤1012cm-3) is unable to populate significantly the dimer states in the condition of thermal equilibrium.

  11. Bound internal conversion versus nuclear excitation by electron transition: Revision of the theory of optical pumping of the Thm229 isomer

    NASA Astrophysics Data System (ADS)

    Karpeshin, F. F.; Trzhaskovskaya, M. B.

    2017-03-01

    Two-photon optical pumping of the 7.6-eV nuclear isomer in the singly ionized atoms of 229Th is considered. Differences between two mechanisms of the pumping, nuclear excitation in the electronic transition (NEET) and bound internal conversion (BIC), are derived and analyzed numerically. The BIC mechanism turns out to be more effective, by orders of magnitude, in accordance with previous calculations. Moreover, a numerical smallness in the NEET scheme is explicitly pointed out concerning singly and doubly charged ions. That is related to the smallness of the final vertex, responsible for conservation of energy. In the case of BIC, the calculated pumping rate of the isomer for the most effective scheme may be as high as 0.03 s-1.

  12. Nonlinear atom-photon-interaction-induced population inversion and inverted quantum phase transition of Bose-Einstein condensate in an optical cavity

    NASA Astrophysics Data System (ADS)

    Zhao, Xiuqin; Liu, Ni; Liang, J.-Q.

    2014-08-01

    In this paper we explore the rich structure of macroscopic many-particle quantum states for a Bose-Einstein condensate in an optical cavity with a tunable nonlinear atom-photon interaction [K. Baumann et al., Nature (London) 464, 1301 (2010), 10.1038/nature09009]. Population inversion, bistable normal phases, and the coexistence of normal-superradiant phases are revealed by adjusting the experimentally realizable interaction strength and pump-laser frequency. For the negative (effective) cavity frequency we observe, remarkably, an inverted quantum phase transition (QPT) from the superradiant to the normal phases with an increase in atom-field coupling, which is just opposite the QPT in the normal Dicke model. Bistable macroscopic states are derived analytically in terms of the spin-coherent-state variational method by taking into account both normal and inverted pseudospin states.

  13. Effects of γ-irradiation on optical, electrical, and laser characteristics of pure and transition metal doped II-VI semiconductors

    NASA Astrophysics Data System (ADS)

    Konak, Tetyana; Tekavec, Michael; Fedorov, Vladimir V.; Mirov, Sergey B.

    2011-02-01

    We report a comprehensive study of gamma-irradiation on optical, electrical, and laser characteristics of pure and transition-metal doped single and polycrystalline ZnS and ZnSe. Polished pure, Cr-doped, and Ag, Au, Cu, Al, In, and Mn co-doped ZnS and ZnSe crystals after absorption and electro-conductivity characterization were gamma-irradiated at doses of 1.37x108, and 1.28x108 rad at +10 and -3°C, respectively. Dynamic RT absorption studies, electro-conductivity measurements and mid-IR lasing were performed for different exposition times of crystals at RT. Cr:ZnSe and Cr:ZnS lasers based on identical gamma-irradiated and non-irradiated crystals featured a very similar pump thresholds, slope efficiencies, and output powers.

  14. Influence of transition metal doping on the electronic and optical properties of ReS2 and ReSe2 monolayers.

    PubMed

    Obodo, Kingsley Onyebuchi; Ouma, Cecil Napthaly Moro; Obodo, Joshua Tobechukwu; Braun, Moritz

    2017-07-26

    We investigate the structural, electronic and optical properties of transition metal doped triclinic monolayered rhenium disulfide and diselenide (ReS2 and ReSe2) by means of quantum mechanical calculations. The calculated electronic band gaps for ReS2 and ReSe2 monolayers are 1.43 eV and 1.23 eV, respectively, with both having a non-magnetic ground state. The calculated dopant substitutional energies under both Re-rich and X(S or Se)-rich conditions show that it is possible to experimentally synthesize transition metal doped ReX2 (where X is S or Se) monolayer systems. We found that the presence of dopant ions (such as V, Cr, Mn, Fe Co, Nb, Mo, Ta and W) in the ReS2 and ReSe2 monolayers significantly modifies their electronic ground states with consequent introduction of defect levels and modification of the density of states profile. However, it was found that Mn doped structures show a very minute reduction of the electronic band gap. We found that a ferro- or a non-magnetic ground state configuration was obtained depending on the choice of dopant ions in ReS2 and ReSe2 monolayers. Cr, Fe and Co doping result in a ferro-magnetic ground state configuration of the ReX2 structures. The calculated absorption and reflectivity spectra show that this class of dopants causes a general increase in the absorption spectral peaks but only a minute influence on the reflectivity. Optical anisotropy was observed depending on whether the direction of polarization in the xy-plane is either parallel or perpendicular.

  15. Efficient Thermal-Light Interconversions Based on Optical Topological Transition in the Metal-Dielectric Multilayered Metamaterials.

    PubMed

    Zhou, Jing; Chen, Xi; Guo, L Jay

    2016-04-20

    Metal-dielectric multilayered metamaterials are proposed to work as wideband spectral-selective emitters/absorbers due to the topological change in isofrequency contour around the epsilon-near-zero point. By setting the transition at the border between the visible and IR ranges, the metal-dielectric multilayered metamaterials become good absorbers/emitters for visible light and good reflectors for IR light, which are desirable for efficient thermal-light interconversions. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. L-lysine-L-tartaric acid: New molecular complex with nonlinear optical properties. Structure, vibrational spectra and phase transitions

    SciTech Connect

    Debrus, S.; Marchewka, M.K. . E-mail: mkm@int.pan.wroc.pl; Baran, J.; Drozd, M.; Czopnik, R.; Pietraszko, A.; Ratajczak, H.

    2005-09-15

    The first X-ray diffraction and vibrational spectroscopic analysis of a novel complex between L-lysine and L-tartaric acid is reported. The structure was solved in two temperatures (320 and 260 K) showing incommensurate phase between them. Room-temperature powder infrared and Raman measurements for the L-lysine-L-tartaric acid molecular complex (1:1) were carried out. DSC measurements on powder samples indicate two phase transitions points at about 295, 300 and 293, 300 K, for heating and cooling, respectively, with noticeable temperature interval between them. Second harmonic generation efficiency d {sub eff}=0.35 d {sub eff} (KDP)

  17. Pressure dependence of the metal-insulator transition in κ-(BEDT-TTF)2Hg(SCN)2Cl: optical and transport studies

    NASA Astrophysics Data System (ADS)

    Löhle, A.; Rose, E.; Singh, S.; Beyer, R.; Tafra, E.; Ivek, T.; Zhilyaeva, E. I.; Lyubovskaya, R. N.; Dressel, M.

    2017-02-01

    The two-dimensional organic conductor κ-(BEDT-TTF)2-Hg(SCN)2Cl exhibits a pronounced metal-insulator transition at {{T}\\text{CO}}=30 K. From the splitting of the molecular vibrations, the phase transition can be unambiguously assigned to charge-ordering with 2{δρ}=0.2e . We have investigated the pressure evolution of this behavior by temperature-dependent electrical transport measurements and optical investigations applying hydrostatic pressure up to 12 kbar. The data reveal a mean-field like down-shift of {{T}\\text{CO}}≤ft( p\\right) with a critical pressure of {{p}c}=0.7+/- 0.1 kbar and a metallic state above the suppression of the charge-ordered state; no traces of superconductivity could be identified down to T  =  1.5 K. As the charge order {δρ} sets in abruptly with decreasing temperature, its size remains unaffected by pressure. However, the fraction of charge imbalanced molecules decreases until it is completely absent above 1.6 kbar.

  18. Two-dimensional Raman and Raman optical activity correlation analysis of the alpha-helix-to-disordered transition in poly(L-glutamic acid).

    PubMed

    Ashton, Lorna; Barron, Laurence D; Hecht, Lutz; Hyde, Jason; Blanch, Ewan W

    2007-05-01

    Rich and complex Raman scattering and Raman optical activity (ROA) spectra have been measured monitoring the pH induced alpha-helix-to-disordered conformational transition in poly(L-glutamic acid). Two-dimensional (2D) correlation techniques have been applied to facilitate a comprehensive analysis of these two complementary spectral sets. Synchronous contour plots have identified band assignments of alpha-helical and disordered conformations, and have revealed bands characteristic of changes in the protonation state of the polypeptide. Asynchronous plots, on the other hand, have probed the relative sequential orders of intensity changes indicating a decrease in intensity of alpha-helical bands in the backbone skeletal stretch region, followed by a subsequent decrease in intensity in the extended amide III and amide I regions, underlying the appearance of disordered structure, including poly(L-proline) II (PPII) helix. The application of a 2D correlation 'moving' window has also disclosed two distinct phases during helix unfolding in the alpha-helix-to-disordered transition, occurring at approximately pH 4.9 and approximately pH 5.2, possibly a result of the difference in helical stability between the end and central regions of the alpha-helix. This paper demonstrates the potential value of combining 2D Raman, 2D ROA and moving window correlation techniques for the detailed investigation of complex and subtle changes of secondary structure during the unfolding mechanisms of polypeptides and proteins.

  19. Pressure dependence of the metal-insulator transition in κ-(BEDT-TTF)2Hg(SCN)2Cl: optical and transport studies.

    PubMed

    Löhle, A; Rose, E; Singh, S; Beyer, R; Tafra, E; Ivek, T; Zhilyaeva, E I; Lyubovskaya, R N; Dressel, M

    2017-02-08

    The two-dimensional organic conductor κ-(BEDT-TTF)2-Hg(SCN)2Cl exhibits a pronounced metal-insulator transition at [Formula: see text] K. From the splitting of the molecular vibrations, the phase transition can be unambiguously assigned to charge-ordering with [Formula: see text]. We have investigated the pressure evolution of this behavior by temperature-dependent electrical transport measurements and optical investigations applying hydrostatic pressure up to 12 kbar. The data reveal a mean-field like down-shift of [Formula: see text] with a critical pressure of [Formula: see text] kbar and a metallic state above the suppression of the charge-ordered state; no traces of superconductivity could be identified down to T  =  1.5 K. As the charge order [Formula: see text] sets in abruptly with decreasing temperature, its size remains unaffected by pressure. However, the fraction of charge imbalanced molecules decreases until it is completely absent above 1.6 kbar.

  20. Compositional dependence of optical interband transition energies in GeSn and GeSiSn alloys

    NASA Astrophysics Data System (ADS)

    Xu, Chi; Senaratne, Charutha L.; Kouvetakis, John; Menéndez, José

    2015-08-01

    The dielectric functions of GeSn and GeSiSn alloys were measured in the 1-6 eV energy range using spectroscopic ellipsometry. The contributions from the E1, E1 + Δ1, E0‧, E2, and E1‧ critical points in the joint density of electronic states were enhanced by computing numerical second derivatives of the measured dielectric function, and the resulting lineshapes were fitted with model expressions from which the critical point energies, amplitudes, broadenings, and phases were determined. A detailed analysis of the compositional dependence of the different transition energies is presented. By describing this dependence in terms of quadratic polynomials, the bowing parameter (quadratic coefficient) for each transition is determined. It is shown that the bowing parameters in the ternary alloy follow a distinct chemical trend, in which the ternary is well described in terms of bowing parameters for the underlying binary alloys, and these bowing parameters increase as a function of the size and electronegativity mismatch of the alloy constituents.