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Sample records for aberration corrected photoemission

  1. An aberration corrected photoemission electron microscope at the advanced light source

    SciTech Connect

    Feng, J.; MacDowell, A.A.; Duarte, R.; Doran, A.; Forest, E.; Kelez, N.; Marcus, M.; Munson, D.; Padmore, H.; Petermann, K.; Raoux, S.; Robin, D.; Scholl, A.; Schlueter, R.; Schmid, P.; Stohr, J.; Wan, W.; Wei, D.H.; Wu, Y.

    2003-11-01

    Design of a new aberration corrected Photoemission electron microscope PEEM3 at the Advanced Light Source is outlined. PEEM3 will be installed on an elliptically polarized undulator beamline and will be used for the study of complex materials at high spatial and spectral resolution. The critical components of PEEM3 are the electron mirror aberration corrector and aberration-free magnetic beam separator. The models to calculate the optical properties of the electron mirror are discussed. The goal of the PEEM3 project is to achieve the highest possible transmission of the system at resolutions comparable to our present PEEM2 system (50 nm) and to enable significantly higher resolution, albeit at the sacrifice of intensity. We have left open the possibility to add an energy filter at a later date, if it becomes necessary driven by scientific need to improve the resolution further.

  2. Time-resolved magnetic imaging in an aberration-corrected, energy-filtered photoemission electron microscope.

    PubMed

    Nickel, F; Gottlob, D M; Krug, I P; Doganay, H; Cramm, S; Kaiser, A M; Lin, G; Makarov, D; Schmidt, O G; Schneider, C M

    2013-07-01

    We report on the implementation and usage of a synchrotron-based time-resolving operation mode in an aberration-corrected, energy-filtered photoemission electron microscope. The setup consists of a new type of sample holder, which enables fast magnetization reversal of the sample by sub-ns pulses of up to 10 mT. Within the sample holder current pulses are generated by a fast avalanche photo diode and transformed into magnetic fields by means of a microstrip line. For more efficient use of the synchrotron time structure, we developed an electrostatic deflection gating mechanism capable of beam blanking within a few nanoseconds. This allows us to operate the setup in the hybrid bunch mode of the storage ring facility, selecting one or several bright singular light pulses which are temporally well-separated from the normal high-intensity multibunch pulse pattern.

  3. Progress on PEEM3 - An Aberration Corrected X-Ray PhotoemissionElectron Microscope at the ALS

    SciTech Connect

    MacDowell, Alastair A.; Feng, J.; DeMello, A.; Doran, A.; Duarte,R.; Forest, E.; Kelez, N.; Marcus, M.A.; Miller, T.; Padmore, H.A.; Raoux, S.; Robin, D.; Scholl, A.; Schlueter, R.; Schmid, P.; Stohr, J.; Wan, W.; Wei, D.H.; Wu, Y.

    2006-05-20

    A new ultrahigh-resolution photoemission electron microscope called PEEM3 is being developed and built at the Advanced Light Source (ALS). An electron mirror combined with a much-simplified magnetic dipole separator is to be used to provide simultaneous correction of spherical and chromatic aberrations. It is installed on an elliptically polarized undulator (EPU) beamline, and will be operated with very high spatial resolution and high flux to study the composition, structure, electric and magnetic properties of complex materials. The instrument has been designed and is described. The instrumental hardware is being deployed in 2 phases. The first phase is the deployment of a standard PEEM type microscope consisting of the standard linear array of electrostatic electron lenses. The second phase will be the installation of the aberration corrected upgrade to improve resolution and throughput. This paper describes progress as the instrument enters the commissioning part of the first phase.

  4. Theoretical estimates of spherical and chromatic aberration in photoemission electron microscopy.

    PubMed

    Fitzgerald, J P S; Word, R C; Könenkamp, R

    2016-01-01

    We present theoretical estimates of the mean coefficients of spherical and chromatic aberration for low energy photoemission electron microscopy (PEEM). Using simple analytic models, we find that the aberration coefficients depend primarily on the difference between the photon energy and the photoemission threshold, as expected. However, the shape of the photoelectron spectral distribution impacts the coefficients by up to 30%. These estimates should allow more precise correction of aberration in PEEM in experimental situations where the aberration coefficients and precise electron energy distribution cannot be readily measured.

  5. Chicago aberration correction work.

    PubMed

    Beck, V D

    2012-12-01

    The author describes from his personal involvement the many improvements to electron microscopy Albert Crewe and his group brought by minimizing the effects of aberrations. The Butler gun was developed to minimize aperture aberrations in a field emission electron gun. In the 1960s, Crewe anticipated using a spherical aberration corrector based on Scherzer's design. Since the tolerances could not be met mechanically, a method of moving the center of the octopoles electrically was developed by adding lower order multipole fields. Because the corrector was located about 15 cm ahead of the objective lens, combination aberrations would arise with the objective lens. This fifth order aberration would then limit the aperture of the microscope. The transformation of the off axis aberration coefficients of a round lens was developed and a means to cancel anisotropic coma was developed. A new method of generating negative spherical aberration was invented using the combination aberrations of hexapoles. Extensions of this technique to higher order aberrations were developed. An electrostatic electron mirror was invented, which allows the cancellation of primary spherical aberration and first order chromatic aberration. A reduction of chromatic aberration by two orders of magnitude was demonstrated using such a system.

  6. Aberration correction of unstable resonators

    NASA Technical Reports Server (NTRS)

    Lang, Robert J. (Inventor)

    1994-01-01

    Construction of aspheric reflectors for unstable resonator lasers to provide an arbitrary laser mode inside the resonator to correct aberrations of an output beam by the construction of the shape of an end reflector opposite the output reflector of the resonator cavity, such as aberrations resulting from refraction of a beam exiting the solid of the resonator having an index of refraction greater than 1 or to produce an aberration in the output beam that will precisely compensate for the aberration of an optical train into which the resonator beam is coupled.

  7. Correction of Distributed Optical Aberrations

    SciTech Connect

    Baker, K; Olivier, S; Carrano, C; Phillion, D

    2006-02-12

    The objective of this project was to demonstrate the use of multiple distributed deformable mirrors (DMs) to improve the performance of optical systems with distributed aberrations. This concept is expected to provide dramatic improvement in the optical performance of systems in applications where the aberrations are distributed along the optical path or within the instrument itself. Our approach used multiple actuated DMs distributed to match the aberration distribution. The project developed the algorithms necessary to determine the required corrections and simulate the performance of these multiple DM systems.

  8. Phase and birefringence aberration correction

    DOEpatents

    Bowers, Mark; Hankla, Allen

    1996-01-01

    A Brillouin enhanced four wave mixing phase conjugate mirror corrects phase aberrations of a coherent electromagnetic beam and birefringence induced upon that beam. The stimulated Brillouin scattering (SBS) phase conjugation technique is augmented to include Brillouin enhanced four wave mixing (BEFWM). A seed beam is generated by a main oscillator which arrives at the phase conjugate cell before the signal beams in order to initiate the Brillouin effect. The signal beam which is being amplified through the amplifier chain is split into two perpendicularly polarized beams. One of the two beams is chosen to be the same polarization as some component of the seed beam, the other orthogonal to the first. The polarization of the orthogonal beam is then rotated 90.degree. such that it is parallel to the other signal beam. The three beams are then focused into cell containing a medium capable of Brillouin excitation. The two signal beams are focused such that they cross the seed beam path before their respective beam waists in order to achieve BEFWM or the two signal beams are focused to a point or points contained within the focused cone angle of the seed beam to achieve seeded SBS, and thus negate the effects of all birefringent and material aberrations in the system.

  9. Phase and birefringence aberration correction

    DOEpatents

    Bowers, M.; Hankla, A.

    1996-07-09

    A Brillouin enhanced four wave mixing phase conjugate mirror corrects phase aberrations of a coherent electromagnetic beam and birefringence induced upon that beam. The stimulated Brillouin scattering (SBS) phase conjugation technique is augmented to include Brillouin enhanced four wave mixing (BEFWM). A seed beam is generated by a main oscillator which arrives at the phase conjugate cell before the signal beams in order to initiate the Brillouin effect. The signal beam which is being amplified through the amplifier chain is split into two perpendicularly polarized beams. One of the two beams is chosen to be the same polarization as some component of the seed beam, the other orthogonal to the first. The polarization of the orthogonal beam is then rotated 90{degree} such that it is parallel to the other signal beam. The three beams are then focused into cell containing a medium capable of Brillouin excitation. The two signal beams are focused such that they cross the seed beam path before their respective beam waists in order to achieve BEFWM or the two signal beams are focused to a point or points contained within the focused cone angle of the seed beam to achieve seeded SBS, and thus negate the effects of all birefringent and material aberrations in the system. 5 figs.

  10. Pulse compressor with aberration correction

    SciTech Connect

    Mankos, Marian

    2015-11-30

    In this SBIR project, Electron Optica, Inc. (EOI) is developing an electron mirror-based pulse compressor attachment to new and retrofitted dynamic transmission electron microscopes (DTEMs) and ultrafast electron diffraction (UED) cameras for improving the temporal resolution of these instruments from the characteristic range of a few picoseconds to a few nanoseconds and beyond, into the sub-100 femtosecond range. The improvement will enable electron microscopes and diffraction cameras to better resolve the dynamics of reactions in the areas of solid state physics, chemistry, and biology. EOI’s pulse compressor technology utilizes the combination of electron mirror optics and a magnetic beam separator to compress the electron pulse. The design exploits the symmetry inherent in reversing the electron trajectory in the mirror in order to compress the temporally broadened beam. This system also simultaneously corrects the chromatic and spherical aberration of the objective lens for improved spatial resolution. This correction will be found valuable as the source size is reduced with laser-triggered point source emitters. With such emitters, it might be possible to significantly reduce the illuminated area and carry out ultrafast diffraction experiments from small regions of the sample, e.g. from individual grains or nanoparticles. During phase I, EOI drafted a set of candidate pulse compressor architectures and evaluated the trade-offs between temporal resolution and electron bunch size to achieve the optimum design for two particular applications with market potential: increasing the temporal and spatial resolution of UEDs, and increasing the temporal and spatial resolution of DTEMs. Specialized software packages that have been developed by MEBS, Ltd. were used to calculate the electron optical properties of the key pulse compressor components: namely, the magnetic prism, the electron mirror, and the electron lenses. In the final step, these results were folded

  11. Iteration of ultrasound aberration correction methods

    NASA Astrophysics Data System (ADS)

    Maasoey, Svein-Erik; Angelsen, Bjoern; Varslot, Trond

    2004-05-01

    Aberration in ultrasound medical imaging is usually modeled by time-delay and amplitude variations concentrated on the transmitting/receiving array. This filter process is here denoted a TDA filter. The TDA filter is an approximation to the physical aberration process, which occurs over an extended part of the human body wall. Estimation of the TDA filter, and performing correction on transmit and receive, has proven difficult. It has yet to be shown that this method works adequately for severe aberration. Estimation of the TDA filter can be iterated by retransmitting a corrected signal and re-estimate until a convergence criterion is fulfilled (adaptive imaging). Two methods for estimating time-delay and amplitude variations in receive signals from random scatterers have been developed. One method correlates each element signal with a reference signal. The other method use eigenvalue decomposition of the receive cross-spectrum matrix, based upon a receive energy-maximizing criterion. Simulations of iterating aberration correction with a TDA filter have been investigated to study its convergence properties. A weak and strong human-body wall model generated aberration. Both emulated the human abdominal wall. Results after iteration improve aberration correction substantially, and both estimation methods converge, even for the case of strong aberration.

  12. Correction and alignment strategies for the beam separator of the photoemission electron microscope 3 (PEEM3)

    NASA Astrophysics Data System (ADS)

    Schmid, Peter; Feng, Jun; Padmore, Howard; Robin, David; Rose, Harald; Schlueter, Ross; Wan, Weishi; Forest, Étienne; Wu, Ying

    2005-02-01

    A high-resolution aberration-corrected photoemission electron microscope (PEEM3) will be installed on an undulator beamline at the Advanced Light Source at the Lawrence Berkeley National Laboratory. The aim of this instrument is to provide a substantial flux and resolution improvement by employing an electron mirror for correcting both the third-order spherical aberration and the primary chromatic aberration. In order to utilize this concept of correction, a beam separator is a prerequisite. Crucial to achieving a resolution of 5nm for the high-resolution mode, and a 16-fold increase in throughput at the same resolution as its predecessor, PEEM2, specified as 20nm at 2% transmission, for the high flux mode is the double-symmetric design of the beam separator, which eliminates all the second-order geometric aberrations. Nonetheless, substantial tuning capabilities must be incorporated into the PEEM3 design to compensate for both systematic and random errors. In this article, we investigate how to correct for nonsystematic imperfections and for systematic uncertainties in the accuracy of the magnetic fields and focus on how degradation of the resolution and the field of view can be minimized. Finally, we outline a tentative correction strategy for PEEM3.

  13. Optical advantages of astigmatic aberration corrected heliostats

    NASA Astrophysics Data System (ADS)

    van Rooyen, De Wet; Schöttl, Peter; Bern, Gregor; Heimsath, Anna; Nitz, Peter

    2016-05-01

    Astigmatic aberration corrected heliostats adapt their shape in dependence of the incidence angle of the sun on the heliostat. Simulations show that this optical correction leads to a higher concentration ratio at the target and thus in a decrease in required receiver aperture in particular for smaller heliostat fields.

  14. Aberration corrected Lorentz scanning transmission electron microscopy.

    PubMed

    McVitie, S; McGrouther, D; McFadzean, S; MacLaren, D A; O'Shea, K J; Benitez, M J

    2015-05-01

    We present results from an aberration corrected scanning transmission electron microscope which has been customised for high resolution quantitative Lorentz microscopy with the sample located in a magnetic field free or low field environment. We discuss the innovations in microscope instrumentation and additional hardware that underpin the imaging improvements in resolution and detection with a focus on developments in differential phase contrast microscopy. Examples from materials possessing nanometre scale variations in magnetisation illustrate the potential for aberration corrected Lorentz imaging as a tool to further our understanding of magnetism on this lengthscale.

  15. Peripheral Aberrations and Image Quality for Contact Lens Correction

    PubMed Central

    Shen, Jie; Thibos, Larry N.

    2011-01-01

    Purpose Contact lenses reduced the degree of hyperopic field curvature present in myopic eyes and rigid contact lenses reduced sphero-cylindrical image blur on the peripheral retina, but their effect on higher order aberrations and overall optical quality of the eye in the peripheral visual field is still unknown. The purpose of our study was to evaluate peripheral wavefront aberrations and image quality across the visual field before and after contact lens correction. Methods A commercial Hartmann-Shack aberrometer was used to measure ocular wavefront errors in 5° steps out to 30° of eccentricity along the horizontal meridian in uncorrected eyes and when the same eyes are corrected with soft or rigid contact lenses. Wavefront aberrations and image quality were determined for the full elliptical pupil encountered in off-axis measurements. Results Ocular higher-order aberrations increase away from fovea in the uncorrected eye. Third-order aberrations are larger and increase faster with eccentricity compared to the other higher-order aberrations. Contact lenses increase all higher-order aberrations except 3rd-order Zernike terms. Nevertheless, a net increase in image quality across the horizontal visual field for objects located at the foveal far point is achieved with rigid lenses, whereas soft contact lenses reduce image quality. Conclusions Second order aberrations limit image quality more than higher-order aberrations in the periphery. Although second-order aberrations are reduced by contact lenses, the resulting gain in image quality is partially offset by increased amounts of higher-order aberrations. To fully realize the benefits of correcting higher-order aberrations in the peripheral field requires improved correction of second-order aberrations as well. PMID:21873925

  16. Adaptive phase aberration correction based on imperialist competitive algorithm.

    PubMed

    Yazdani, R; Hajimahmoodzadeh, M; Fallah, H R

    2014-01-01

    We investigate numerically the feasibility of phase aberration correction in a wavefront sensorless adaptive optical system, based on the imperialist competitive algorithm (ICA). Considering a 61-element deformable mirror (DM) and the Strehl ratio as the cost function of ICA, this algorithm is employed to search the optimum surface profile of DM for correcting the phase aberrations in a solid-state laser system. The correction results show that ICA is a powerful correction algorithm for static or slowly changing phase aberrations in optical systems, such as solid-state lasers. The correction capability and the convergence speed of this algorithm are compared with those of the genetic algorithm (GA) and stochastic parallel gradient descent (SPGD) algorithm. The results indicate that these algorithms have almost the same correction capability. Also, ICA and GA are almost the same in convergence speed and SPGD is the fastest of these algorithms.

  17. Adaptive aberration correction using a triode hyperbolic electron mirror.

    PubMed

    Fitzgerald, J P S; Word, R C; Könenkamp, R

    2011-01-01

    A converging electron mirror can be used to compensate spherical and chromatic aberrations in an electron microscope. This paper presents an analytical solution to a novel triode (three electrode) hyperbolic mirror as an improvement to the well-known diode (two electrode) hyperbolic mirror for aberration correction. A weakness of the diode mirror is a lack of flexibility in changing the chromatic and spherical aberration coefficients independently without changes in the mirror geometry. In order to remove this limitation, a third electrode can be added. We calculate the optical properties of the resulting triode mirror analytically on the basis of a simple model field distribution. We present the optical properties-the object/image distance, z(0), and the coefficients of spherical and chromatic aberration, C(s) and C(c), of both mirror types from an analysis of electron trajectories in the mirror field. From this analysis, we demonstrate that while the properties of both designs are similar, the additional parameters in the triode mirror improve the range of aberration that can be corrected. The triode mirror is also able to provide a dynamic adjustment range of chromatic aberration for fixed spherical aberration and focal length, or any permutation of these three parameters. While the dynamic range depends on the values of aberration correction needed, a nominal 10% tuning range is possible for most configurations accompanied by less than 1% change in the other two properties.

  18. SMART:. An Aberration-Corrected XPEEM/LEEM with Energy Filter

    NASA Astrophysics Data System (ADS)

    Wichtendahl, R.; Fink, R.; Kuhlenbeck, H.; Preikszas, D.; Rose, H.; Spehr, R.; Hartel, P.; Engel, W.; Schlögl, R.; Freund, H.-J.; Bradshaw, A. M.; Lilienkamp, G.; Schmidt, Th.; Bauer, E.; Benner, G.; Umbach, E.

    A new UHV spectroscopic X-ray photoelectron emission and low energy electron microscope is presently under construction for the installation at the PM-6 soft X-ray undulator beamline at BESSY II. Using a combination of a sophisticated magnetic beam splitter and an electrostatic tetrode mirror, the spherical and chromatic aberrations of the objective lens are corrected and thus the lateral resolution and sensitivity of the instrument improved. In addition a corrected imaging energy filter (a so-called omega filter) allows high spectral resolution (ΔE=0.1 eV) in the photoemission modes and back-ground suppression in LEEM and small-spot LEED modes. The theoretical prediction for the lateral resolution is 5 Å a realistic goal is about 2 nm. Thus, a variety of electron spectroscopies (XAS, XPS, UPS, XAES) and electron diffraction (LEED, LEEM) or reflection techniques (MEM) will be available with spatial resolution unreached so far.

  19. Lesion generation through ribs using histotripsy therapy without aberration correction.

    PubMed

    Kim, Yohan; Wang, Tzu-Yin; Xu, Zhen; Cain, Charles A

    2011-11-01

    This study investigates the feasibility of using high-intensity pulsed therapeutic ultrasound, or histotripsy, to non-invasively generate lesions through the ribs. Histotripsy therapy mechanically ablates tissue through the generation of a cavitation bubble cloud, which occurs when the focal pressure exceeds a certain threshold. We hypothesize that histotripsy can generate precise lesions through the ribs without aberration correction if the main lobe retains its shape and exceeds the cavitation initiation threshold and the secondary lobes remain below the threshold. To test this hypothesis, a 750-kHz focused transducer was used to generate lesions in tissue-mimicking phantoms with and without the presence of rib aberrators. In all cases, 8000 pulses with 16 to 18 MPa peak rarefactional pressure at a repetition frequency of 100 Hz were applied without aberration correction. Despite the high secondary lobes introduced by the aberrators, high-speed imaging showed that bubble clouds were generated exclusively at the focus, resulting in well-confined lesions with comparable dimensions. Collateral damage from secondary lobes was negligible, caused by single bubbles that failed to form a cloud. These results support our hypothesis, suggesting that histotripsy has a high tolerance for aberrated fields and can generate confined focal lesions through rib obstacles without aberration correction.

  20. Generalized Alvarez lens for correction of laser aberrations

    SciTech Connect

    LaFortune, K N

    2004-12-02

    The Alvarez lens (US Patent No. 3,305,294 [1]) is a compact aberration corrector. The original design emphasized in the patent consists of a pair of adjacent optical elements that provide a variable focus. A lens system with a variable effective focal length is nothing new. Such systems are widely used in cameras, for example. It is the compactness and simplicity of operation that is the key advantage of the Alvarez lens. All of the complexity is folded into the design and fabrication of the optical elements. As mentioned in the Alvarez patent [1] and elaborated upon in Palusinski et al. [2], if one is willing to fold even more complexity into the optical elements, it is possible to correct higher-order aberrations as well. There is no theoretical limit to the number or degree of wavefront distortions that can be corrected. The only limitation is that there must be a fixed relative magnitude of the aberrations. Independent correction of each component of the higher-order aberrations can not be performed without additional elements and degrees of freedom [3]. Under some circumstances, coupling may be observed between different aberrations. This can be mitigated with the appropriate choice of design parameters. New methods are available today that increase the practicality of making higher-order aberration correctors [4,5,6].

  1. Lesion Generation Through Ribs Using Histotripsy Therapy Without Aberration Correction

    PubMed Central

    Kim, Yohan; Wang, Tzu-Yin; Xu, Zhen; Cain, Charles A.

    2012-01-01

    This study investigates the feasibility of using high-intensity pulsed therapeutic ultrasound, or histotripsy, to non-invasively generate lesions through the ribs. Histotripsy therapy mechanically ablates tissue through the generation of a cavitation bubble cloud, which occurs when the focal pressure exceeds a certain threshold. We hypothesize that histotripsy can generate precise lesions through the ribs without aberration correction if the main lobe retains its shape and exceeds the cavitation initiation threshold and the secondary lobes remain below the threshold. To test this hypothesis, a 750-kHz focused transducer was used to generate lesions in tissue-mimicking phantoms with and without the presence of rib aberrators. In all cases, 8000 pulses with 16 to 18 MPa peak rarefactional pressure at a repetition frequency of 100 Hz were applied without aberration correction. Despite the high secondary lobes introduced by the aberrators, high-speed imaging showed that bubble clouds were generated exclusively at the focus, resulting in well-confined lesions with comparable dimensions. Collateral damage from secondary lobes was negligible, caused by single bubbles that failed to form a cloud. These results support our hypothesis, suggesting that histotripsy has a high tolerance for aberrated fields and can generate confined focal lesions through rib obstacles without aberration correction. PMID:22083767

  2. Aberration correction of zoom lenses using evolutionary programming.

    PubMed

    Pal, Sourav

    2013-08-10

    A systematic approach for the aberration correction of zoom systems is presented. It is assumed that the powers and movements of the components of the zoom systems are known. Each component is considered as a system of thin lenses in contact. An evolutionary algorithm is developed to explore the multivariate hyperspace of design variables formed by spherical aberration, central coma, and longitudinal chromatic aberration of each component for infinite conjugate. The primary aberrations for each component at any zoom position are deduced from three central aberration coefficients of the component for infinite conjugate using conjugate shift formulas. Overall system aberrations of the zoom systems are determined by using stop shift formulas. In most of the zoom lens systems it is important to achieve stability in the primary aberrations of the system over the zoom range. This is facilitated by proper formulation of the merit function for the optimization process. Investigations have been carried out on four-component zoom lenses, and an ab initio structure of a four-component zoom lens is presented.

  3. Intrinsic instability of aberration-corrected electron microscopes.

    PubMed

    Schramm, S M; van der Molen, S J; Tromp, R M

    2012-10-19

    Aberration-corrected microscopes with subatomic resolution will impact broad areas of science and technology. However, the experimentally observed lifetime of the corrected state is just a few minutes. Here we show that the corrected state is intrinsically unstable; the higher its quality, the more unstable it is. Analyzing the contrast transfer function near optimum correction, we define an "instability budget" which allows a rational trade-off between resolution and stability. Unless control systems are developed to overcome these challenges, intrinsic instability poses a fundamental limit to the resolution practically achievable in the electron microscope.

  4. Intrinsic Instability of Aberration-Corrected Electron Microscopes

    NASA Astrophysics Data System (ADS)

    Schramm, S. M.; van der Molen, S. J.; Tromp, R. M.

    2012-10-01

    Aberration-corrected microscopes with subatomic resolution will impact broad areas of science and technology. However, the experimentally observed lifetime of the corrected state is just a few minutes. Here we show that the corrected state is intrinsically unstable; the higher its quality, the more unstable it is. Analyzing the contrast transfer function near optimum correction, we define an “instability budget” which allows a rational trade-off between resolution and stability. Unless control systems are developed to overcome these challenges, intrinsic instability poses a fundamental limit to the resolution practically achievable in the electron microscope.

  5. Nanowire growth kinetics in aberration corrected environmental transmission electron microscopy

    SciTech Connect

    Chou, Yi -Chia; Panciera, Federico; Reuter, Mark C.; Stach, Eric A.; Ross, Frances M.

    2016-03-15

    Here, we visualize atomic level dynamics during Si nanowire growth using aberration corrected environmental transmission electron microscopy, and compare with lower pressure results from ultra-high vacuum microscopy. We discuss the importance of higher pressure observations for understanding growth mechanisms and describe protocols to minimize effects of the higher pressure background gas.

  6. Sub-ångstrom resolution using aberration corrected electron optics

    NASA Astrophysics Data System (ADS)

    Batson, P. E.; Dellby, N.; Krivanek, O. L.

    2002-08-01

    Following the invention of electron optics during the 1930s, lens aberrations have limited the achievable spatial resolution to about 50 times the wavelength of the imaging electrons. This situation is similar to that faced by Leeuwenhoek in the seventeenth century, whose work to improve the quality of glass lenses led directly to his discovery of the ubiquitous ``animalcules'' in canal water, the first hints of the cellular basis of life. The electron optical aberration problem was well understood from the start, but more than 60 years elapsed before a practical correction scheme for electron microscopy was demonstrated, and even then the remaining chromatic aberrations still limited the resolution. We report here the implementation of a computer-controlled aberration correction system in a scanning transmission electron microscope, which is less sensitive to chromatic aberration. Using this approach, we achieve an electron probe smaller than 1Å. This performance, about 20 times the electron wavelength at 120keV energy, allows dynamic imaging of single atoms, clusters of a few atoms, and single atomic layer `rafts' of atoms coexisting with Au islands on a carbon substrate. This technique should also allow atomic column imaging of semiconductors, for detection of single dopant atoms, using an electron beam with energy below the damage threshold for silicon.

  7. Holographic optical system for aberration corrections in laser Doppler velocimetry

    NASA Technical Reports Server (NTRS)

    Kim, R. C.; Case, S. K.; Schock, H. J.

    1985-01-01

    An optical system containing multifaceted holographic optical elements (HOEs) has been developed to correct for aberrations introduced by nonflat windows in laser Doppler velocimetry. The multifacet aberration correction approach makes it possible to record on one plate many sets of adjacent HOEs that address different measurement volume locations. By using 5-mm-diameter facets, it is practical to place 10-20 sets of holograms on one 10 x 12.5-cm plate, so that the procedure of moving the entire optical system to examine different locations may not be necessary. The holograms are recorded in dichromated gelatin and therefore are nonabsorptive and suitable for use with high-power argon laser beams. Low f-number optics coupled with a 90-percent efficient distortion-correcting hologram in the collection side of the system yield high optical efficiency.

  8. Phase aberration correction by correlation in digital holographic adaptive optics

    PubMed Central

    Liu, Changgeng; Yu, Xiao; Kim, Myung K.

    2013-01-01

    We present a phase aberration correction method based on the correlation between the complex full-field and guide-star holograms in the context of digital holographic adaptive optics (DHAO). Removal of a global quadratic phase term before the correlation operation plays an important role in the correction. Correlation operation can remove the phase aberration at the entrance pupil plane and automatically refocus the corrected optical field. Except for the assumption that most aberrations lie at or close to the entrance pupil, the presented method does not impose any other constraints on the optical systems. Thus, it greatly enhances the flexibility of the optical design for DHAO systems in vision science and microscopy. Theoretical studies show that the previously proposed Fourier transform DHAO (FTDHAO) is just a special case of this general correction method, where the global quadratic phase term and a defocus term disappear. Hence, this correction method realizes the generalization of FTDHAO into arbitrary DHAO systems. The effectiveness and robustness of this method are demonstrated by simulations and experiments. PMID:23669707

  9. Differential aberration correction (DAC) microscopy: a new molecular ruler.

    PubMed

    Vallotton, P

    2008-11-01

    Considerable efforts have been deployed towards measuring molecular range distances in fluorescence microscopy. In the 1-10 nm range, Förster energy transfer microscopy is difficult to beat. Above 300 nm, conventional diffraction limited microscopy is suitable. We introduce a simple experimental technique that allows bridging the gap between those two resolution scales in both 2D and 3D with a resolution of about 20 nm. The method relies on a computational approach to accurately correct optical aberrations over the whole field of view. The method is differential because the probes of interest are affected in exactly the same manner by aberrations as are the reference probes used to construct the aberration deformation field. We expect that this technique will have significant implications for investigating structural and functional questions in bio-molecular sciences.

  10. Conformal dome aberration correction by designing the inner surface

    NASA Astrophysics Data System (ADS)

    Zhang, Wang; Chen, Shouqian; Fan, Zhigang

    2016-12-01

    The ray transmission models of optical domes were established, and the characteristics of the rays while passing through a hemispherical dome and a conformal dome were comparatively analysed. Acquiring the minimum deviated angles from the inner surface of the conformal dome was then determined to be the designing goal for reducing the dynamic aberrations. Based on this, the inner surface of the conformal dome was optimized and thus, the dynamic aberrations were reduced. Finally, a completely cooled conformal optical system was designed. The results show that the optical system have produced good imaging quality within all the fields of regard, which further illustrates that designing the inner surface of a conformal dome is an effective method for aberration correction.

  11. Aberration correction for time-domain ultrasound diffraction tomography.

    PubMed

    Mast, T Douglas

    2002-07-01

    Extensions of a time-domain diffraction tomography method, which reconstructs spatially dependent sound speed variations from far-field time-domain acoustic scattering measurements, are presented and analyzed. The resulting reconstructions are quantitative images with applications including ultrasonic mammography, and can also be considered candidate solutions to the time-domain inverse scattering problem. Here, the linearized time-domain inverse scattering problem is shown to have no general solution for finite signal bandwidth. However, an approximate solution to the linearized problem is constructed using a simple delay-and-sum method analogous to "gold standard" ultrasonic beamforming. The form of this solution suggests that the full nonlinear inverse scattering problem can be approximated by applying appropriate angle- and space-dependent time shifts to the time-domain scattering data; this analogy leads to a general approach to aberration correction. Two related methods for aberration correction are presented: one in which delays are computed from estimates of the medium using an efficient straight-ray approximation, and one in which delays are applied directly to a time-dependent linearized reconstruction. Numerical results indicate that these correction methods achieve substantial quality improvements for imaging of large scatterers. The parametric range of applicability for the time-domain diffraction tomography method is increased by about a factor of 2 by aberration correction.

  12. Effect of chromatic aberration on atomic-resolved spherical aberration corrected STEM images.

    PubMed

    Kuramochi, Koji; Yamazaki, Takashi; Kotaka, Yasutoshi; Ohtsuka, Masahiro; Hashimoto, Iwao; Watanabe, Kazuto

    2009-12-01

    The effect of the chromatic aberration (C(c)) coefficient in a spherical aberration (C(s))- corrected electromagnetic lens on high-resolution high-angle annular dark field (HAADF) scanning transmission electron microscope (STEM) images is explored in detail. A new method for precise determination of the C(c) coefficient is demonstrated, requiring measurement of an atomic-resolution one-frame through-focal HAADF STEM image. This method is robust with respect to instrumental drift, sample thickness, all lens parameters except C(c), and experimental noise. It is also demonstrated that semi-quantitative structural analysis on the nanometer scale can be achieved by comparing experimental C(s)- corrected HAADF STEM images with their corresponding simulated images when the effects of the C(c) coefficient and spatial incoherence are included.

  13. Correcting for Beam Aberrations in a Beam-Waveguide Antenna

    NASA Technical Reports Server (NTRS)

    Franco, Manuel; Slobin, Stephen; Veruttipong, Watt

    2003-01-01

    A method for correcting the aim of a beam-waveguide microwave antenna compensates for the beam aberration that occurs during radio tracking of a target that has a component of velocity transverse to the line of sight from the tracking station. The method was devised primarily for use in tracking of distant target spacecraft by large terrestrial beam-waveguide antennas of NASA's Deep Space Network (DSN). The method should also be adaptable to tracking, by other beam-waveguide antennas, of targets that move with large transverse velocities at large distances from the antennas.

  14. Adaptive dispersion formula for index interpolation and chromatic aberration correction.

    PubMed

    Li, Chia-Ling; Sasián, José

    2014-01-13

    This paper defines and discusses a glass dispersion formula that is adaptive. The formula exhibits superior convergence with a minimum number of coefficients. Using this formula we rationalize the correction of chromatic aberration per spectrum order. We compare the formula with the Sellmeier and Buchdahl formulas for glasses in the Schott catalogue. The six coefficient adaptive formula is found to be the most accurate with an average maximum index of refraction error of 2.91 × 10(-6) within the visible band.

  15. Transcranial phase aberration correction using beam simulations and MR-ARFI

    SciTech Connect

    Vyas, Urvi Kaye, Elena; Pauly, Kim Butts

    2014-03-15

    Purpose: Transcranial magnetic resonance-guided focused ultrasound surgery is a noninvasive technique for causing selective tissue necrosis. Variations in density, thickness, and shape of the skull cause aberrations in the location and shape of the focal zone. In this paper, the authors propose a hybrid simulation-MR-ARFI technique to achieve aberration correction for transcranial MR-guided focused ultrasound surgery. The technique uses ultrasound beam propagation simulations with MR Acoustic Radiation Force Imaging (MR-ARFI) to correct skull-caused phase aberrations. Methods: Skull-based numerical aberrations were obtained from a MR-guided focused ultrasound patient treatment and were added to all elements of the InSightec conformal bone focused ultrasound surgery transducer during transmission. In the first experiment, the 1024 aberrations derived from a human skull were condensed into 16 aberrations by averaging over the transducer area of 64 elements. In the second experiment, all 1024 aberrations were applied to the transducer. The aberrated MR-ARFI images were used in the hybrid simulation-MR-ARFI technique to find 16 estimated aberrations. These estimated aberrations were subtracted from the original aberrations to result in the corrected images. Each aberration experiment (16-aberration and 1024-aberration) was repeated three times. Results: The corrected MR-ARFI image was compared to the aberrated image and the ideal image (image with zero aberrations) for each experiment. The hybrid simulation-MR-ARFI technique resulted in an average increase in focal MR-ARFI phase of 44% for the 16-aberration case and 52% for the 1024-aberration case, and recovered 83% and 39% of the ideal MR-ARFI phase for the 16-aberrations and 1024-aberration case, respectively. Conclusions: Using one MR-ARFI image and noa priori information about the applied phase aberrations, the hybrid simulation-MR-ARFI technique improved the maximum MR-ARFI phase of the beam's focus.

  16. Active Correction of Aberrations of Low-Quality Telescope Optics

    NASA Technical Reports Server (NTRS)

    Hemmati, Hamid; Chen, Yijian

    2007-01-01

    A system of active optics that includes a wavefront sensor and a deformable mirror has been demonstrated to be an effective means of partly correcting wavefront aberrations introduced by fixed optics (lenses and mirrors) in telescopes. It is envisioned that after further development, active optics would be used to reduce wavefront aberrations of about one wave or less in telescopes having aperture diameters of the order of meters or tens of meters. Although this remaining amount of aberration would be considered excessive in scientific applications in which diffraction-limited performance is required, it would be acceptable for free-space optical- communication applications at wavelengths of the order of 1 m. To prevent misunderstanding, it is important to state the following: The technological discipline of active optics, in which the primary or secondary mirror of a telescope is directly and dynamically tilted, distorted, and/or otherwise varied to reduce wavefront aberrations, has existed for decades. The term active optics does not necessarily mean the same thing as does adaptive optics, even though active optics and adaptive optics are related. The term "adaptive optics" is often used to refer to wavefront correction at speeds characterized by frequencies ranging up to between hundreds of hertz and several kilohertz high enough to enable mitigation of adverse effects of fluctuations in atmospheric refraction upon propagation of light beams. The term active optics usually appears in reference to wavefront correction at significantly lower speeds, characterized by times ranging from about 1 second to as long as minutes. Hence, the novelty of the present development lies, not in the basic concept of active or adaptive optics, but in the envisioned application of active optics in conjunction with a deformable mirror to achieve acceptably small wavefront errors in free-space optical communication systems that include multi-meter-diameter telescope mirrors that are

  17. High order aberration and straylight evaluation after cataract surgery with implantation of an aspheric, aberration correcting monofocal intraocular lens

    PubMed Central

    Kretz, Florian T A; Tandogan, Tamer; Khoramnia, Ramin; Auffarth, Gerd U

    2015-01-01

    AIM To evaluate the quality of vision in respect to high order aberrations and straylight perception after implantation of an aspheric, aberration correcting, monofocal intraocular lens (IOL). METHODS Twenty-one patients (34 eyes) aged 50 to 83y underwent cataract surgery with implantation of an aspheric, aberration correcting IOL (Tecnis ZCB00, Abbott Medical Optics). Three months after surgery they were examined for uncorrected (UDVA) and corrected distance visual acuity (CDVA), contrast sensitivity (CS) under photopic and mesopic conditions with and without glare source, ocular high order aberrations (HOA, Zywave II) and retinal straylight (C-Quant). RESULTS Postoperatively, patients achieved a postoperative CDVA of 0.0 logMAR or better in 97.1% of eyes. Mean values of high order abberations were +0.02±0.27 (primary coma components) and -0.04±0.16 (spherical aberration term). Straylight values of the C-Quant were 1.35±0.44 log which is within normal range of age matched phakic patients. The CS measurements under mesopic and photopic conditions in combination with and without glare did not show any statistical significance in the patient group observed (P≥0.28). CONCLUSION The implantation of an aspherical aberration correcting monofocal IOL after cataract surgery resulted in very low residual higher order aberration (HOA) and normal straylight. PMID:26309872

  18. Image transfer with spatial coherence for aberration corrected transmission electron microscopes.

    PubMed

    Hosokawa, Fumio; Sawada, Hidetaka; Shinkawa, Takao; Sannomiya, Takumi

    2016-08-01

    The formula of spatial coherence involving an aberration up to six-fold astigmatism is derived for aberration-corrected transmission electron microscopy. Transfer functions for linear imaging are calculated using the newly derived formula with several residual aberrations. Depending on the symmetry and origin of an aberration, the calculated transfer function shows characteristic symmetries. The aberrations that originate from the field's components, having uniformity along the z direction, namely, the n-fold astigmatism, show rotational symmetric damping of the coherence. The aberrations that originate from the field's derivatives with respect to z, such as coma, star, and three lobe, show non-rotational symmetric damping. It is confirmed that the odd-symmetric wave aberrations have influences on the attenuation of an image via spatial coherence. Examples of image simulations of haemoglobin and Si [211] are shown by using the spatial coherence for an aberration-corrected electron microscope.

  19. A method of dynamic chromatic aberration correction in low-voltage scanning electron microscopes.

    PubMed

    Khursheed, Anjam

    2005-07-01

    A time-of-flight concept that dynamically corrects for chromatic aberration effects in scanning electron microscopes (SEMs) is presented. The method is predicted to reduce the microscope's chromatic aberration by an order of magnitude. The scheme should significantly improve the spatial resolution of low-voltage scanning electron microscopes (LVSEMs). The dynamic means of correcting for chromatic aberration also allows for the possibility of obtaining high image resolution from electron guns that have relatively large energy spreads.

  20. Sextupole system for the correction of spherical aberration

    DOEpatents

    Crewe, A.V.; Kopf, D.A.

    In an electron beam device in which an electron beam is developed and then focused by a lens to a particular spot, there is provided a means for eliminating spherical aberration. A sextupole electromagnetic lens is positioned between two focusing lenses. The interaction of the sextupole with the beam compensates for spherical aberration. (GHT)

  1. Aspherical surfaces design for extreme ultraviolet lithographic objective with correction of thermal aberration

    NASA Astrophysics Data System (ADS)

    Liu, Yan; Li, Yanqiu

    2016-09-01

    At present, few projection objectives for extreme ultraviolet (EUV) lithography pay attention to correct thermal aberration in optical design phase, which would lead to poor image quality in a practical working environment. We present an aspherical modification method for helping the EUV lithographic objective additionally correct the thermal aberration. Based on the thermal aberration and deformation predicted by integrated optomechanical analysis, the aspherical surfaces in an objective are modified by an iterative algorithm. The modified aspherical surfaces could correct the thermal aberration and maintain the initial high image quality in a practical working environment. A six-mirror EUV lithographic objective with 0.33-numerical aperture is taken as an example to illustrate the presented method. The results show that the thermal aberration can be corrected effectively, and the image quality of the thermally deformed system is improved to the initial design level, which proves the availability of the method.

  2. Information transfer in a TEM corrected for spherical and chromatic aberration.

    PubMed

    Haider, M; Hartel, P; Müller, H; Uhlemann, S; Zach, J

    2010-08-01

    For the transmission electron aberration-corrected microscope (TEAM) initiative of five U.S. Department of Energy laboratories in the United States, a correction system for the simultaneous compensation of the primary axial aberrations, the spherical aberration Cs, and the chromatic aberration Cc has been developed and successfully installed. The performance of the resulting Cc /Cs-corrected TEAM instrument has been investigated thoroughly. A significant improvement of the linear contrast transfer can be demonstrated. The information about the instrument one obtains using Young's fringe method is compared for uncorrected, Cs-corrected, and Cc /Cs-corrected instruments. The experimental results agree well with simulations. The conclusions might be useful to others in understanding the process of image formation in a Cc /Cs-corrected transmission electron microscope.

  3. Study on the modification of measured wavefront aberration data for customized visual correction

    NASA Astrophysics Data System (ADS)

    Liu, Ming; Zhang, Yong; Zhang, Zhidong; Quan, Wei; An, Li

    2008-12-01

    Wavefront aberration of human eye is an important foundation for customized vision correction. In most current aberrometers, near infrared light is used to measure ocular wavefront aberration, whereas for customized visual correction, wavefront aberration data in visible range are required. With the measured wavefront aberration, corneal topography and eye's axial lengths data, individual eye models for twenty normal human eyes are constructed with the optical design software ZEMAX. Changing the incidence light wavelength and the refractive indexes of eye models, the values of defocus, astigmatism, higher-order aberrations in the measuring wavelength (833nm) and at the most sensitive wavelength of human eye (555nm) are obtained. Average focus shift between 833nm and 555nm is found to be about 0.94D, and different slightly for different individuals; the differences of astigmatism and higher-order aberrations between 833nm and 555nm are quite slight. For customized visual correction, the measured defocus value should be modified, whereas the measured astigmatism and higher-order aberrations could be used directly for the current correction precision. Individual eye model is a useful tool for accurate transformation of the measured wavefront aberration data into the data for visible spectrum.

  4. Adaptive Optics Analysis of Visual Benefit with Higher-order Aberrations Correction of Human Eye - Poster Paper

    NASA Astrophysics Data System (ADS)

    Xue, Lixia; Dai, Yun; Rao, Xuejun; Wang, Cheng; Hu, Yiyun; Liu, Qian; Jiang, Wenhan

    2008-01-01

    Higher-order aberrations correction can improve visual performance of human eye to some extent. To evaluate how much visual benefit can be obtained with higher-order aberrations correction we developed an adaptive optics vision simulator (AOVS). Dynamic real time optimized modal compensation was used to implement various customized higher-order ocular aberrations correction strategies. The experimental results indicate that higher-order aberrations correction can improve visual performance of human eye comparing with only lower-order aberration correction but the improvement degree and higher-order aberration correction strategy are different from each individual. Some subjects can acquire great visual benefit when higher-order aberrations were corrected but some subjects acquire little visual benefit even though all higher-order aberrations were corrected. Therefore, relative to general lower-order aberrations correction strategy, customized higher-order aberrations correction strategy is needed to obtain optimal visual improvement for each individual. AOVS provides an effective tool for higher-order ocular aberrations optometry for customized ocular aberrations correction.

  5. Correction of chromatic aberrations at television registration of image through protective viewing systems

    NASA Astrophysics Data System (ADS)

    Kulyas, Oleg L.; Nikitin, Konstantin A.

    2016-03-01

    Ways of chromatic aberration in images are examined and analyzed which are generated at television supervision through protective glasses of a considerable thickness. The results of experimental check up of the given method of correction is introduced and described.

  6. Accommodation with higher-order monochromatic aberrations corrected with adaptive optics

    NASA Astrophysics Data System (ADS)

    Chen, Li; Kruger, Philip B.; Hofer, Heidi; Singer, Ben; Williams, David R.

    2006-01-01

    Higher-order monochromatic aberrations in the human eye cause a difference in the appearance of stimuli at distances nearer and farther from best focus that could serve as a signed error signal for accommodation. We explored whether higher-order monochromatic aberrations affect the accommodative response to 0.5 D step changes in vergence in experiments in which these aberrations were either present as they normally are or removed with adaptive optics. Of six subjects, one could not accommodate at all for steps in either condition. One subject clearly required higher-order aberrations to accommodate at all. The remaining four subjects could accommodate in the correct direction even when higher-order aberrations were removed. No subjects improved their accommodation when higher-order aberrations were corrected, indicating that the corresponding decrease in the depth of field of the eye did not improve the accommodative response. These results are consistent with previous findings of large individual differences in the ability to accommodate in impoverished conditions. These results suggest that at least some subjects can use monochromatic higher-order aberrations to guide accommodation. They also show that some subjects can accommodate correctly when higher-order monochromatic aberrations as well as established cues to accommodation are greatly reduced.

  7. Recovering correct phase information in multiwavelength digital holographic microscopy by compensation for chromatic aberrations.

    PubMed

    De Nicola, S; Finizio, A; Pierattini, G; Alfieri, D; Grilli, S; Sansone, L; Ferraro, P

    2005-10-15

    We demonstrate experimentally that correct phase imaging without 2pi ambiguity is obtainable in digital holography by using a multiwavelength approach in the microscope configuration. We describe a general approach for removing chromatic aberrations and for controlling the pixel size of the reconstructed phase image in multiwavelength digital holography when the Fourier transform method is adopted for the numerical reconstruction of digital holograms. The retrieved phase is affected by the unavoidable, unwanted chromatic aberration. The correct phase can be obtained by evaluating the phase from the reference holograms reconstructed at different wavelengths to compensate for the chromatic aberration.

  8. Characterization of misfit dislocations in Si quantum well structures enabled by STEM based aberration correction.

    PubMed

    Batson, Philip E; Lagos, Maureen J

    2017-03-02

    The success of aberration correction techniques at the end of the 20th century came at a time of increasing need for atomic resolution imaging to better understand known structural defects that influence semiconductor device operation, and to advance the search for new structures and behavior that will form the basis for devices in the future. With this in mind, it is a pleasure to recognize the contributions of Ondrej Krivanek to the success of aberration correction techniques, and his extension of aberration techniques to EELS equipment that further promises to unite structural studies with characterization of behavior from meV to keV energies in the STEM.

  9. Design of macro-filter-lens with simultaneous chromatic and geometric aberration correction.

    PubMed

    Prasad, Dilip K; Brown, Michael S

    2014-01-01

    A macro-filter-lens design that can correct for chromatic and geometric aberrations simultaneously while providing for a long focal length is presented. The filter is easy to fabricate since it involves two spherical surfaces and a planar surface. Chromatic aberration correction is achieved by making all the rays travel the same optical distance inside the filter element (negative meniscus). Geometric aberration is corrected for by the lens element (plano-convex), which makes the output rays parallel to the optic axis. This macro-filter-lens design does not need additional macro lenses and it provides an inexpensive and optically good (aberration compensated) solution for macro imaging of objects not placed close to the camera.

  10. Surgical correction of an aberrant right subclavian artery in a dog

    PubMed Central

    Yoon, Hun-Young; Jeong, Soon-wuk

    2011-01-01

    A diagnosis of an aberrant right subclavian artery was made in a 3-month-old Boston terrier. Surgical correction was performed after confirming adequate collateral circulation. Reports of surgical correction and evaluation of the perioperative thoracic limb blood pressure are rare in dogs. PMID:22467968

  11. Manumycin A corrects aberrant splicing of Clcn1 in myotonic dystrophy type 1 (DM1) mice.

    PubMed

    Oana, Kosuke; Oma, Yoko; Suo, Satoshi; Takahashi, Masanori P; Nishino, Ichizo; Takeda, Shin'ichi; Ishiura, Shoichi

    2013-01-01

    Myotonic dystrophy type 1 (DM1) is the most common muscular dystrophy in adults and as yet no cure for DM1. Here, we report the potential of manumycin A for a novel DM1 therapeutic reagent. DM1 is caused by expansion of CTG repeat. Mutant transcripts containing expanded CUG repeats lead to aberrant regulation of alternative splicing. Myotonia (delayed muscle relaxation) is the most commonly observed symptom in DM1 patients and is caused by aberrant splicing of the skeletal muscle chloride channel (CLCN1) gene. Identification of small-molecule compounds that correct aberrant splicing in DM1 is attracting much attention as a way of improving understanding of the mechanism of DM1 pathology and improving treatment of DM1 patients. In this study, we generated a reporter screening system and searched for small-molecule compounds. We found that manumycin A corrects aberrant splicing of Clcn1 in cell and mouse models of DM1.

  12. Effect of correction of aberration dynamics on chaos in human ocular accommodation.

    PubMed

    Hampson, Karen M; Cufflin, Matthew P; Mallen, Edward A H

    2013-11-15

    We used adaptive optics to determine the effect of monochromatic aberration dynamics on the level of chaos in the accommodation control system. Four participants viewed a stationary target while the dynamics of their aberrations were either left uncorrected, defocus was corrected, or all aberrations except defocus were corrected. Chaos theory analysis was used to discern changes in the accommodative microfluctuations. We found a statistically significant reduction in the chaotic nature of the accommodation microfluctuations during correction of defocus, but not when all aberrations except defocus were corrected. The Lyapunov exponent decreased from 0.71 ± 0.07 D/s (baseline) to 0.55 ± 0.03 D/s (correction of defocus fluctuations). As the reduction of chaos in physiological signals is indicative of stress to the system, the results indicate that for the participants included in this study, fluctuations in defocus have a more profound effect than those of the other aberrations. There were no changes in the power spectrum between experimental conditions. Hence chaos theory analysis is a more subtle marker of changes in the accommodation control system and will be of value in the study of myopia onset and progression.

  13. Improving the quality perception of digital images using modified method of the eye aberration correction

    NASA Astrophysics Data System (ADS)

    Kvyetnyy, Roman; Sofina, Olga; Orlyk, Pavel; Utreras, Andres J.; Smolarz, Andrzej; Wójcik, Waldemar; Orazalieva, Sandugash

    2016-09-01

    A new approach to solve the problem of image correction to improve the quality perception of graphic information by people with aberrations of the eye optical system is considered in given article. The model of higher order aberrations which may appear in the human eye optical system is described. The developed approach is based on the pre-processing of digital images and applying of the filtration methods to the adjusted images.

  14. Modeling of Optical Aberration Correction using a Liquid Crystal Device

    NASA Technical Reports Server (NTRS)

    Xinghua, Wang; Bin, Wang; McManamon, Paul F.; Pouch, John J.; Miranda, Felix A.

    2006-01-01

    Gruneisen (sup 1-3), has shown that small, light weight, liquid crystal based devices can correct for the optical distortion caused by an imperfect primary mirror in a telescope and has discussed the efficiency of this correction. In this paper we expand on that work and propose a semi-analytical approach for quantifying the efficiency of a liquid crystal based wavefront corrector for this application.

  15. Aberration-corrected STEM/TEM imaging at 15kV.

    PubMed

    Sasaki, Takeo; Sawada, Hidetaka; Hosokawa, Fumio; Sato, Yuta; Suenaga, Kazu

    2014-10-01

    The performance of aberration-corrected (scanning) transmission electron microscopy (S/TEM) at an accelerating voltage of 15kV was evaluated in a low-voltage microscope equipped with a cold-field emission gun and a higher-order aberration corrector. Aberrations up to the fifth order were corrected by the aberration measurement and auto-correction system using the diffractogram tableau method in TEM and Ronchigram analysis in STEM. TEM observation of nanometer-sized particles demonstrated that aberrations up to an angle of 50mrad were compensated. A TEM image of Si[110] exhibited lattice fringes with a spacing of 0.192nm, and the power spectrum of the image showed spots corresponding to distances of 0.111nm. An annular dark-field STEM image of Si[110] showed lattice fringes of (111) and (22¯0) planes corresponding to lattice distances of 0.314nm and 0.192nm, respectively. At an accelerating voltage of 15kV, the developed low-voltage microscope achieved atomic-resolution imaging with a small chromatic aberration and a large uniform phase.

  16. High-resolution adaptive optics scanning laser ophthalmoscope with dual deformable mirrors for large aberration correction

    SciTech Connect

    Chen, D; Jones, S M; Silva, D A; Olivier, S S

    2007-01-25

    Scanning laser ophthalmoscopes with adaptive optics (AOSLO) have been shown previously to provide a noninvasive, cellular-scale view of the living human retina. However, the clinical utility of these systems has been limited by the available deformable mirror technology. In this paper, we demonstrate that the use of dual deformable mirrors can effectively compensate large aberrations in the human retina, making the AOSLO system a viable, non-invasive, high-resolution imaging tool for clinical diagnostics. We used a bimorph deformable mirror to correct low-order aberrations with relatively large amplitudes. The bimorph mirror is manufactured by Aoptix, Inc. with 37 elements and 18 {micro}m stroke in a 10 mm aperture. We used a MEMS deformable mirror to correct high-order aberrations with lower amplitudes. The MEMS mirror is manufactured by Boston Micromachine, Inc with 144 elements and 1.5 {micro}m stroke in a 3 mm aperture. We have achieved near diffraction-limited retina images using the dual deformable mirrors to correct large aberrations up to {+-} 3D of defocus and {+-} 3D of cylindrical aberrations with test subjects. This increases the range of spectacle corrections by the AO systems by a factor of 10, which is crucial for use in the clinical environment. This ability for large phase compensation can eliminate accurate refractive error fitting for the patients, which greatly improves the system ease of use and efficiency in the clinical environment.

  17. Transmissive liquid-crystal device correcting primary coma aberration and astigmatism in laser scanning microscopy

    NASA Astrophysics Data System (ADS)

    Tanabe, Ayano; Hibi, Terumasa; Ipponjima, Sari; Matsumoto, Kenji; Yokoyama, Masafumi; Kurihara, Makoto; Hashimoto, Nobuyuki; Nemoto, Tomomi

    2016-03-01

    Laser scanning microscopy allows 3D cross-sectional imaging inside biospecimens. However, certain aberrations produced can degrade the quality of the resulting images. We previously reported a transmissive liquid-crystal device that could compensate for the predominant spherical aberrations during the observations, particularly in deep regions of the samples. The device, inserted between the objective lens and the microscope revolver, improved the image quality of fixed-mouse-brain slices that were observed using two-photon excitation laser scanning microscopy, which was originally degraded by spherical aberration. In this study, we developed a transmissive device that corrects primary coma aberration and astigmatism, motivated by the fact that these asymmetric aberrations can also often considerably deteriorate image quality, even near the sample surface. The device's performance was evaluated by observing fluorescent beads using single-photon excitation laser scanning microscopy. The fluorescence intensity in the image of the bead under a cover slip tilted in the y-direction was increased by 1.5 times after correction by the device. Furthermore, the y- and z-widths of the imaged bead were reduced to 66% and 65%, respectively. On the other hand, for the imaged bead sucked into a glass capillary in the longitudinal x-direction, correction with the device increased the fluorescence intensity by 2.2 times compared to that of the aberrated image. In addition, the x-, y-, and z-widths of the bead image were reduced to 75%, 53%, and 40%, respectively. Our device successfully corrected several asymmetric aberrations to improve the fluorescent signal and spatial resolution, and might be useful for observing various biospecimens.

  18. Aberration and boresight error correction for conformal aircraft windows using the inner window surface and tilted fixed correctors.

    PubMed

    Zhao, Chunzhu; Cui, Qingfeng; Mao, Shan

    2016-04-01

    A static solution to aberrations and boresight error for tilted conformal aircraft windows at different look angles is reported. The solution uses the inner window surface to correct the window aberrations at a 0° look angle and uses fixed correctors behind the window to correct the residual window aberrations at other look angles. Then, the boresight error for the window at different look angles is corrected by tilting the fixed correctors. The principle of the solution is discussed, and a design example shows that the solution is effective in correcting the aberrations and boresight error for a tilted conformal aircraft window at different look angles.

  19. Digital aberration correction of fluorescent images with coherent holographic image reconstruction by phase transfer (CHIRPT)

    NASA Astrophysics Data System (ADS)

    Field, Jeffrey J.; Bartels, Randy A.

    2016-03-01

    Coherent holographic image reconstruction by phase transfer (CHIRPT) is an imaging method that permits digital holographic propagation of fluorescent light. The image formation process in CHIRPT is based on illuminating the specimen with a precisely controlled spatio-temporally varying intensity pattern. This pattern is formed by focusing a spatially coherent illumination beam to a line focus on a spinning modulation mask, and image relaying the mask plane to the focal plane of an objective lens. Deviations from the designed spatio-temporal illumination pattern due to imperfect mounting of the circular modulation mask onto the rotation motor induce aberrations in the recovered image. Here we show that these aberrations can be measured and removed non-iteratively by measuring the disk aberration phase externally. We also demonstrate measurement and correction of systematic optical aberrations in the CHIRPT microscope.

  20. CLASSICAL AREAS OF PHENOMENOLOGY: Conformal optical design with combination of static and dynamic aberration corrections

    NASA Astrophysics Data System (ADS)

    Li, Yan; Li, Lin; Huang, Yi-Fan; Liu, Jia-Guo

    2009-02-01

    Conformal domes that are shaped to meet aerodynamic requirements can increase range and speed for the host platform. Because these domes typically deviate greatly from spherical surface descriptions, a variety of aberrations are induced which vary with the field-of-regard (FOR) angle. A system for correcting optical aberrations created by a conformal dome has an outer surface and an inner surface. Optimizing the inner surface is regard as static aberration correction. A deformable mirror is placed at the position of the secondary mirror in the two-mirror all reflective imaging system, which is the dynamic aberration correction. An ellipsoidal MgF2 conformal dome with a fineness ratio of 1.0 is designed as an example. The FOR angle is 0°- 30°, and the design wavelength is 4 μm. After the optimization at 7 zoom positions by using the design tools Code V, the root-mean-square (RMS) spot size is reduced to approximately 0.99 to 1.48 times the diffraction limit. The design results show that the performances of the conformal optical systems can be greatly improved by the combination of the static correction and the dynamic correction.

  1. Energy-based adaptive focusing of waves: application to noninvasive aberration correction of ultrasonic wavefields.

    PubMed

    Herbert, Eric; Pernot, Mathieu; Montaldo, Gabriel; Fink, Mathias; Tanter, Mickael

    2009-11-01

    An aberration correction method based on the maximization of the wave intensity at the focus of an emitting array is presented. The potential of this new adaptive focusing technique is investigated for ultrasonic focusing in biological tissues. The acoustic intensity is maximized noninvasively through direct measurement or indirect estimation of the beam energy at the focus for a series of spatially coded emissions. For ultrasonic waves, the acoustic energy at the desired focus can be indirectly estimated from the local displacements induced in tissues by the ultrasonic radiation force of the beam. Based on the measurement of these displacements, this method allows determination of the precise estimation of the phase and amplitude aberrations, and consequently the correction of aberrations along the beam travel path. The proof of concept is first performed experimentally using a large therapeutic array with strong electronic phase aberrations (up to 2pi). Displacements induced by the ultrasonic radiation force at the desired focus are indirectly estimated using the time shift of backscattered echoes recorded on the array. The phase estimation is deduced accurately using a direct inversion algorithm which reduces the standard deviation of the phase distribution from sigma = 1.89 radian before correction to sigma = 0.53 radian following correction. The corrected beam focusing quality is verified using a needle hydrophone. The peak intensity obtained through the aberrator is found to be -7.69 dB below the reference intensity obtained without any aberration. Using the phase correction, a sharp focus is restored through the aberrator with a relative peak intensity of -0.89 dB. The technique is tested experimentally using a linear transmit/receive array through a real aberrating layer. The array is used to automatically correct its beam quality, as it both generates the radiation force with coded excitations and indirectly estimates the acoustic intensity at the focus

  2. Chromatic aberration correction of the human eye for retinal imaging in the near infrared

    NASA Astrophysics Data System (ADS)

    Fernández, Enrique J.; Unterhuber, Angelika; Považay, Boris; Hermann, Boris; Artal, Pablo; Drexler, Woflgang

    2006-06-01

    An achromatizing lens has been designed for the human eye in the near infrared range, from 700 to 900 nm, for retinal imaging purposes. Analysis of the performance of the lens, including tolerance to misalignments, has been mathematically accomplished by using an existing eye model. The calculations have shown a virtually perfect correction of the ocular longitudinal chromatic aberration, while still keeping a high optical quality. Ocular aberrations in five subjects have been measured with and without the achromatizing lens by using a Hartmann-Shack wavefront sensor and a broad bandwidth femtosecond Ti:sapphire laser in the spectral range of interest with a set of interference filters, studying the benefits and limits in the use of the achromatizing lens. Ocular longitudinal chromatic aberration has been experimentally demonstrated to be fully corrected by the proposed lens, with no induction of any other parasitic aberration. The practical implementation of the achromatizing lens for Ophthalmoscopy, specifically for optical coherence tomography where the use of polychromatic light sources in the near infrared portion of the spectrum is mandatory, has been considered. The potential benefits of using this lens in combination with adaptive optics to achieve a full aberration correction of the human eye for retinal imaging have also been discussed.

  3. Chromatic aberration correction of the human eye for retinal imaging in the near infrared.

    PubMed

    Fernández, Enrique J; Unterhuber, Angelika; Povazay, Boris; Hermann, Boris; Artal, Pablo; Drexler, Woflgang

    2006-06-26

    An achromatizing lens has been designed for the human eye in the near infrared range, from 700 to 900 nm, for retinal imaging purposes. Analysis of the performance of the lens, including tolerance to misalignments, has been mathematically accomplished by using an existing eye model. The calculations have shown a virtually perfect correction of the ocular longitudinal chromatic aberration, while still keeping a high optical quality. Ocular aberrations in five subjects have been measured with and without the achromatizing lens by using a Hartmann-Shack wavefront sensor and a broad bandwidth femtosecond Ti:sapphire laser in the spectral range of interest with a set of interference filters, studying the benefits and limits in the use of the achromatizing lens. Ocular longitudinal chromatic aberration has been experimentally demonstrated to be fully corrected by the proposed lens, with no induction of any other parasitic aberration. The practical implementation of the achromatizing lens for Ophthalmoscopy, specifically for optical coherence tomography where the use of polychromatic light sources in the near infrared portion of the spectrum is mandatory, has been considered. The potential benefits of using this lens in combination with adaptive optics to achieve a full aberration correction of the human eye for retinal imaging have also been discussed.

  4. Dynamic aberration correction for conformal optics using model-based wavefront sensorless adaptive optics

    NASA Astrophysics Data System (ADS)

    Han, Xinli; Dong, Bing; Li, Yan; Wang, Rui; Hu, Bin

    2016-10-01

    For missiles and airplanes with high Mach number, traditional spherical or flat window can cause a lot of air drag. Conformal window that follow the general contour of surrounding surface can substantially decrease air drag and extend operational range. However, the local shape of conformal window changes across the Field Of Regard (FOR), leading to time-varying FOR-dependent wavefront aberration and degraded image. So the correction of dynamic aberration is necessary. In this paper, model-based Wavefront Sensorless Adaptive Optics (WSAO) algorithm is investigated both by simulation and experiment for central-obscured pupil. The algorithm is proved to be effective and the correction accuracy of using DM modes is higher than Lukosz modes. For dynamic aberration in our system, the SR can be better than 0.8 when the change of looking angle is less than 2° after t seconds which is the time delay of the control system.

  5. High performance Czerny-Turner imaging spectrometer with aberrations corrected by tilted lenses

    NASA Astrophysics Data System (ADS)

    Zhong, Xing; Zhang, Yuan; Jin, Guang

    2015-03-01

    The design of the high performance imaging spectrometer using low-cost plane grating is researched in this paper. In order to correct the aberrations well, under the guidance of the vector aberration theory, the modification of Czerny-Turner system with inserted tilt lenses is proposed. The novel design of a short-wave infrared imaging spectrometer working at between wavelengths of 1-2.5 μm is shown as an example, whose numerical aperture achieves 0.15 in image space. The aberrations are corrected well and the Modulation Transfer Function (MTF) performance is the same as the convex gratings systems. The smiles and keystones of the spectral image are acceptable. Advantages of the proposed design with a plane grating are obviously that the diffraction efficiency is high while the cost is very low.

  6. Characterization of deformable mirrors for spherical aberration correction in optical sectioning microscopy.

    PubMed

    Shaw, Michael; Hall, Simon; Knox, Steven; Stevens, Richard; Paterson, Carl

    2010-03-29

    In this paper we describe the wavefront aberrations that arise when imaging biological specimens using an optical sectioning microscope and generate simulated wavefronts for a planar refractive index mismatch. We then investigate the capability of two deformable mirrors for correcting spherical aberration at different focusing depths for three different microscope objective lenses. Along with measurement and analysis of the mirror influence functions we determine the optimum mirror pupil size and number of spatial modes included in the wavefront expansion and we present measurements of actuator linearity and hysteresis. We find that both mirrors are capable of correcting the wavefront aberration to improve imaging and greatly extend the depth at which diffraction limited imaging is possible.

  7. The correction of aberrations computed in the aperture plane of multifrequency microwave radiometer antennas

    NASA Technical Reports Server (NTRS)

    Schmidt, R. F.

    1984-01-01

    An analytical/numerical approach to identifying and correcting the aberrations introduced by a general displacement of the feed from the focal point of a single offset paraboloid antenna used in deployable radiometer systems is developed. A 15 meter reflector with 18 meter focal length is assumed for the analysis, which considers far field radiation pattern quality, focal region fields, and aberrations appearing in the aperture plane. The latter are obtained by ray tracing in the transmit mode and are expressed in terms of optical notation. Attention is given to the physical restraints imposed on corrective elements by real microwave systems and to the intermediate near field aspects of the problem in three dimensions. The subject of wave fronts and caustics in the receive mode is introduced for comparative purposes. Several specific examples are given for aberration reduction at eight beamwidths of scan at a frequency of 1.414 GHz.

  8. Non-common path aberration correction in an adaptive optics scanning ophthalmoscope.

    PubMed

    Sulai, Yusufu N; Dubra, Alfredo

    2014-09-01

    The correction of non-common path aberrations (NCPAs) between the imaging and wavefront sensing channel in a confocal scanning adaptive optics ophthalmoscope is demonstrated. NCPA correction is achieved by maximizing an image sharpness metric while the confocal detection aperture is temporarily removed, effectively minimizing the monochromatic aberrations in the illumination path of the imaging channel. Comparison of NCPA estimated using zonal and modal orthogonal wavefront corrector bases provided wavefronts that differ by ~λ/20 in root-mean-squared (~λ/30 standard deviation). Sequential insertion of a cylindrical lens in the illumination and light collection paths of the imaging channel was used to compare image resolution after changing the wavefront correction to maximize image sharpness and intensity metrics. Finally, the NCPA correction was incorporated into the closed-loop adaptive optics control by biasing the wavefront sensor signals without reducing its bandwidth.

  9. Device and method for creating Gaussian aberration-corrected electron beams

    SciTech Connect

    McMorran, Benjamin; Linck, Martin

    2016-01-19

    Electron beam phase gratings have phase profiles that produce a diffracted beam having a Gaussian or other selected intensity profile. Phase profiles can also be selected to correct or compensate electron lens aberrations. Typically, a low diffraction order produces a suitable phase profile, and other orders are discarded.

  10. Wavefront-guided correction of ocular aberrations: Are phase plate and refractive surgery solutions equal?

    NASA Astrophysics Data System (ADS)

    Marchese, Linda E.; Munger, Rejean; Priest, David

    2005-08-01

    Wavefront-guided laser eye surgery has been recently introduced and holds the promise of correcting not only defocus and astigmatism in patients but also higher-order aberrations. Research is just beginning on the implementation of wavefront-guided methods in optical solutions, such as phase-plate-based spectacles, as alternatives to surgery. We investigate the theoretical differences between the implementation of wavefront-guided surgical and phase plate corrections. The residual aberrations of 43 model eyes are calculated after simulated refractive surgery and also after a phase plate is placed in front of the untreated eye. In each case, the current wavefront-guided paradigm that applies a direct map of the ocular aberrations to the correction zone is used. The simulation results demonstrate that an ablation map that is a Zernike fit of a direct transform of the ocular wavefront phase error is not as efficient in correcting refractive errors of sphere, cylinder, spherical aberration, and coma as when the same Zernike coefficients are applied to a phase plate, with statistically significant improvements from 2% to 6%.

  11. Gold clusters showing pentagonal atomic arrays revealed by aberration-corrected scanning transmission electron microscopy.

    PubMed

    Mayoral, Alvaro; Blom, Douglas A; Mariscal, Marcelo M; Guiterrez-Wing, Claudia; Aspiazu, Juan; Jose-Yacaman, Miguel

    2010-12-14

    In this work we present the analysis by aberration corrected electron microscopy of the formation of gold clusters based on the proton irradiation of larger nanoparticles (NP). Pentagonal arrays have been observed and energetic calculations have been performed in order to prove the stability of these materials.

  12. Eigenfunction analysis of stochastic backscatter for aberration correction in medical ultrasound imaging

    NASA Astrophysics Data System (ADS)

    Varslot, Trond; Mo, Eirik; Krogstad, Harald; Angelsen, Bjørn

    2004-05-01

    A filter for aberration correction in medical ultrasound imaging is presented. The filter is optimal in the sense of maximizing the expected energy in a modified beamformer output of the received acoustic backscatter. The situation considered is frequently found in applications when imaging organs through a body wall: aberration is introduced in a layer close to the transducer, and acoustic backscatter from a scattering region behind the body wall is measured at the transducer surface. The scattering region consists of scatterers randomly distributed with very short correlation length compared to the acoustic wave length of the transmit pulse. The scatterer distribution is therefore assumed to be δ-correlated. Theoretical considerations imply that maximizing the expected energy in a modified beamformer output signal naturally leads to eigenfunctions of a Fredholm integral operator, where the associated kernel function is a spatial correlation function of the received stochastic signal. Aberration characterization and aberration correction have been studied for simulated data constructed to mimic aberration introduced by the abdominal wall. The results compare well with what is obtained using a diffraction limited time-reversal filter based on simulated point source data.

  13. Chromatic Aberration Correction for Atomic Resolution TEM Imaging from 20 to 80 kV

    NASA Astrophysics Data System (ADS)

    Linck, Martin; Hartel, Peter; Uhlemann, Stephan; Kahl, Frank; Müller, Heiko; Zach, Joachim; Haider, Max.; Niestadt, Marcel; Bischoff, Maarten; Biskupek, Johannes; Lee, Zhongbo; Lehnert, Tibor; Börrnert, Felix; Rose, Harald; Kaiser, Ute

    2016-08-01

    Atomic resolution in transmission electron microscopy of thin and light-atom materials requires a rigorous reduction of the beam energy to reduce knockon damage. However, at the same time, the chromatic aberration deteriorates the resolution of the TEM image dramatically. Within the framework of the SALVE project, we introduce a newly developed Cc/Cs corrector that is capable of correcting both the chromatic and the spherical aberration in the range of accelerating voltages from 20 to 80 kV. The corrector allows correcting axial aberrations up to fifth order as well as the dominating off-axial aberrations. Over the entire voltage range, optimum phase-contrast imaging conditions for weak signals from light atoms can be adjusted for an optical aperture of at least 55 mrad. The information transfer within this aperture is no longer limited by chromatic aberrations. We demonstrate the performance of the microscope using the examples of 30 kV phase-contrast TEM images of graphene and molybdenum disulfide, showing unprecedented contrast and resolution that matches image calculations.

  14. Chromatic Aberration Correction for Atomic Resolution TEM Imaging from 20 to 80 kV.

    PubMed

    Linck, Martin; Hartel, Peter; Uhlemann, Stephan; Kahl, Frank; Müller, Heiko; Zach, Joachim; Haider, Max; Niestadt, Marcel; Bischoff, Maarten; Biskupek, Johannes; Lee, Zhongbo; Lehnert, Tibor; Börrnert, Felix; Rose, Harald; Kaiser, Ute

    2016-08-12

    Atomic resolution in transmission electron microscopy of thin and light-atom materials requires a rigorous reduction of the beam energy to reduce knockon damage. However, at the same time, the chromatic aberration deteriorates the resolution of the TEM image dramatically. Within the framework of the SALVE project, we introduce a newly developed C_{c}/C_{s} corrector that is capable of correcting both the chromatic and the spherical aberration in the range of accelerating voltages from 20 to 80 kV. The corrector allows correcting axial aberrations up to fifth order as well as the dominating off-axial aberrations. Over the entire voltage range, optimum phase-contrast imaging conditions for weak signals from light atoms can be adjusted for an optical aperture of at least 55 mrad. The information transfer within this aperture is no longer limited by chromatic aberrations. We demonstrate the performance of the microscope using the examples of 30 kV phase-contrast TEM images of graphene and molybdenum disulfide, showing unprecedented contrast and resolution that matches image calculations.

  15. Characterization and correction of spherical aberration due to glass substrate in the design and fabrication of Fresnel zone lenses.

    PubMed

    Vijayakumar, A; Bhattacharya, S

    2013-08-20

    As with a conventional lens, a Fresnel zone lens (FZL) can be used to image objects at infinity or nearby. In the latter case, the FZL converts a diverging spherical wavefront into a converging spherical wavefront. The glass substrate on which the FZL is fabricated introduces spherical aberration resulting in a shift of the image plane and blurring of the image. Two novel schemes for correction of this spherical aberration are proposed and studied in this paper. To demonstrate them, FZLs are designed with and without aberration correction. They are fabricated using electron beam direct writing. The devices are evaluated and the accuracy of the proposed aberration correction schemes is validated.

  16. Training to improve contrast sensitivity in amblyopia: correction of high-order aberrations

    PubMed Central

    Liao, Meng; Zhao, Haoxing; Liu, Longqian; Li, Qian; Dai, Yun; Zhang, Yudong; Zhou, Yifeng

    2016-01-01

    Perceptual learning is considered a potential treatment for amblyopia even in adult patients who have progressed beyond the critical period of visual development because adult amblyopes retain sufficient visual plasticity. When perceptual learning is performed with the correction of high-order aberrations (HOAs), a greater degree of neural plasticity is present in normal adults and those with highly aberrated keratoconic eyes. Because amblyopic eyes show more severe HOAs than normal eyes, it is interesting to study the effects of HOA-corrected visual perceptual learning in amblyopia. In the present study, we trained twenty-six older child and adult anisometropic amblyopes while their HOAs were corrected using a real-time closed-loop adaptive optics perceptual learning system (AOPL). We found that adaptive optics (AO) correction improved the modulation transfer functions (MTFs) and contrast sensitivity functions (CSFs) of older children and adults with anisometropic amblyopia. When perceptual learning was performed with AO correction of the ocular HOAs, the improvements in visual function were not only demonstrated in the condition with AO correction but were also maintained in the condition without AO correction. Additionally, the learning effect with AO correction was transferred to the untrained visual acuity and fellow eyes in the condition without AO correction. PMID:27752122

  17. Automatic low-order aberration correction based on geometry optics: simulations

    NASA Astrophysics Data System (ADS)

    Yu, Xin; Dong, Lizhi; Liu, Yong; Yang, Ping; Tang, Guomao; Xu, Bing

    2016-10-01

    The slab laser is a promising architecture to achieve high beam quality and high power. By propagating the laser beams in zigzag geometries, the temperature gradient in the gain medium can be well averaged, and the beam quality in this direction can be excellent. However, the temperature gradient in the non-zigzag direction is not compensated, resulting in aberrations in this direction which lead to poorer beam quality. Among the overall aberrations, the main contributors are two low-order aberrations: astigmatism and defocus. These aberrations will magnify beam divergence angle and degrade beam quality. If the beam divergence angles in both directions are almost zero, the astigmatism and defocus are well corrected. Besides, the output beams of slab lasers are generally in a rectangular aperture with high aspect ratio (normally 1:10), which need to be reshaped into square in many applications. In this paper, a new method is proposed to correct low-order aberrations and reshape the beams of slab lasers. Three lenses are adapted, one is a spherical lens and the others are cylindrical lenses. These lenses work as a beam shaping system, which converts the beam from rectangular into square and the low-order aberrations are compensated simultaneously. Two wavefront sensors are used to detect input and output beam parameters. The initial size of the beam is 4mm×20mm, and peak to valley (PV) value of the wavefront is several tens of microns. Simulation results show that after correction, the dimension becomes 40mm×40mm, and peak to valley (PV) value of the wavefront is less than 1microns.

  18. Combined phase screen aberration correction and minimum variance beamforming in medical ultrasound.

    PubMed

    Ziksari, Mahsa Sotoodeh; Asl, Babak Mohammadzadeh

    2017-03-01

    In recent years, applying adaptive beamforming to ultrasound imaging improves image quality in terms of resolution and contrast. One of the best adaptive beamformers in this field is the minimum variance (MV) beamformer which presents better resolution and edge definition compared to the traditional delay-and-sum (DAS) beamformer. However, in real situations, sound-velocity inhomogeneities cause phase aberration which leads to ambiguity in targets' location and degradation in resolution. This effect is a fundamental obstacle to utilize advantages of MV beamformer, although, in aberrating medium MV beamformer results in better performance compared to DAS. In this paper, two different levels of phase screens have been applied to simulate aberrator layers located close to the transducer. Also, prior to beamforming process, a conventional correction technique based on phase screen model is used. Simulations are performed in majority resolution of MV which has the lowest robustness. The results demonstrate that applying this correction method can retrieve the efficiency of the MV beamformer. Moreover, the method improves the performance of the MV in both terms of resolution and contrast. As corrected MV achieved at least 22% improvement in sidelobe reduction and 24% increase in contrast to noise ratio (CNR) with respect to the DAS corrected data. Also, according to experimental dataset 17% enhancement in CNR is yielded by MV.

  19. The three-dimensional point spread function of aberration-corrected scanning transmission electron microscopy.

    PubMed

    Lupini, Andrew R; de Jonge, Niels

    2011-10-01

    Aberration correction reduces the depth of field in scanning transmission electron microscopy (STEM) and thus allows three-dimensional (3D) imaging by depth sectioning. This imaging mode offers the potential for sub-Ångstrom lateral resolution and nanometer-scale depth sensitivity. For biological samples, which may be many microns across and where high lateral resolution may not always be needed, optimizing the depth resolution even at the expense of lateral resolution may be desired, aiming to image through thick specimens. Although there has been extensive work examining and optimizing the probe formation in two dimensions, there is less known about the probe shape along the optical axis. Here the probe shape is examined in three dimensions in an attempt to better understand the depth resolution in this mode. Examples are presented of how aberrations change the probe shape in three dimensions, and it is found that off-axial aberrations may need to be considered for focal series of large areas. It is shown that oversized or annular apertures theoretically improve the vertical resolution for 3D imaging of nanoparticles. When imaging nanoparticles of several nanometer size, regular STEM can thereby be optimized such that the vertical full-width at half-maximum approaches that of the aberration-corrected STEM with a standard aperture.

  20. Simultaneous and independent adaptive correction of spherical and chromatic aberration using an electron mirror and lens combination.

    PubMed

    Fitzgerald, J P S; Word, R C; Könenkamp, R

    2012-04-01

    We present a theoretical analysis of an electrostatic triode mirror combined with an einzel lens for the correction of spherical and chromatic aberration. We show that this device adaptively corrects spherical and chromatic aberration simultaneously and independently. Chromatic aberration can be compensated over a relative range of -38% to +100%, and spherical aberration over ±100% range. We compare the analytic calculation with a numerical simulation and show that the two descriptions agree to within 5% in the relevant operating regime of the device.

  1. Apparatus for and method of correcting for aberrations in a light beam

    DOEpatents

    Sawicki, Richard H.

    1996-01-01

    A technique for adjustably correcting for aberrations in a light beam is disclosed herein. This technique utilizes first means which defines a flat, circular light reflecting surface having opposite reinforced circumferential edges and a central post and which is resiliently distortable, to a limited extent, into different concave and/or convex curvatures, which may be Gaussian-like, about the central axis, and second means acting on the first means for adjustably distorting the light reflecting surface into a particular selected one of the different curvatures depending upon the aberrations to be corrected for and for fixedly maintaining the curvature selected. In the embodiment disclosed, the light reflecting surface is adjustably distorted into the selected curvature by application of particular axial moments to the central post on the opposite side from the light reflecting surface and lateral moments to the circumference of the reflecting surface.

  2. Apparatus for and method of correcting for aberrations in a light beam

    DOEpatents

    Sawicki, R.H.

    1996-09-17

    A technique for adjustably correcting for aberrations in a light beam is disclosed herein. This technique utilizes first means which defines a flat, circular light reflecting surface having opposite reinforced circumferential edges and a central post and which is resiliently distortable, to a limited extent, into different concave and/or convex curvatures, which may be Gaussian-like, about the central axis, and second means acting on the first means for adjustably distorting the light reflecting surface into a particular selected one of the different curvatures depending upon the aberrations to be corrected for and for fixedly maintaining the curvature selected. In the embodiment disclosed, the light reflecting surface is adjustably distorted into the selected curvature by application of particular axial moments to the central post on the opposite side from the light reflecting surface and lateral moments to the circumference of the reflecting surface. 8 figs.

  3. Performance and Image Analysis of the Aberration Corrected Hitachi HD-2700C Stem

    SciTech Connect

    Inada, H.; Zhu, Y.; Wu, L.; Wall, J.; Su, D.

    2009-03-01

    We report the performance of the first aberration-corrected scanning transmission electron microscope (STEM) manufactured by Hitachi. We describe its unique features and versatile capabilities in atomic-scale characterization and its applications in materials research. We also discuss contrast variation of the STEM images obtained from different annular dark-field (ADF) detectors of the instrument, and the increased complexity in contrast interpretation and quantification due to the increased convergent angles of the electron probe associated with the aberration corrector. We demonstrate that the intensity of atomic columns in an ADF image depends strongly on a variety of imaging parameters, sample thickness, as well as the nuclear charge and the deviation from their periodic position of the atoms we are probing. Image simulations are often required to correctly interpret the atomic structure of an ADF-STEM image.

  4. Depth Sectioning with the Aberration-Corrected Scanning Transmission Electron Microscope

    SciTech Connect

    Borisevich, Albina Y; Lupini, Andrew R; Pennycook, Stephen J

    2006-01-01

    The ability to correct the aberrations of the probe-forming lens in the scanning transmission electron microscope provides not only a significant improvement in transverse resolution but in addition brings depth resolution at the nanometer scale. Aberration correction therefore opens up the possibility of 3D imaging by optical sectioning. Here we develop a definition for the depth resolution for scanning transmission electron microscope depth sectioning and present initial results from this method. Objects such as catalytic metal clusters and single atoms on various support materials are imaged in three dimensions with a resolution of several nanometers. Effective focal depth is determined by statistical analysis and the contributing factors are discussed. Finally, current challenges and future capabilities available through new instruments are discussed.

  5. In situ correction of the spherical aberration in a double-toroidal electron analyzer

    NASA Astrophysics Data System (ADS)

    Liu, Xiao-Jing; Nicolas, Christophe; Miron, Catalin

    2017-02-01

    In an energy-dispersive electron spectrometer, the electrons with the same kinetic energy but different polar angles fly along different paths and impinge upon the detector at different locations. This behavior materializes the spherical aberration of the electron optics, which deteriorates the focussing quality on the detector, and thus the energy resolution of the instrument. Here, we demonstrate that, in general, the electron time of flight changes monotonically as a function of the polar angle. Combining the impact position on the detector and the time of flight of electrons, the spherical aberration can be corrected and the energy resolution can be significantly improved, 1.5× in the case of our double toroidal analyser. This correction method has a general applicability and can be of interest to experimentalists willing to push further the performances of their electron spectrometers when the time of flight is available.

  6. Aberration and boresight error correction for conformal windows using tilted and decentered fixed correctors

    NASA Astrophysics Data System (ADS)

    Zhao, Chunzhu; Mao, Shan

    2016-10-01

    A static solution to aberrations and boresight error for tilted conformal aircraft windows at different look angles is reported, which is the use of tilted and decentered fixed correctors. The principle of the static solution is discussed, and three tilted and decentered fixed correctors are designed to correct the aberrations and boresight error for a conformal window. The correctors are fixed in position between the conformal window and the gimbaled imaging system, thus requiring no moving parts. The design result shows that the predominant astigmatism introduced by the conformal window is corrected by the tilted and decentered fixed correctors at different look angles. Moreover, the boresight error for the conformal window, as a function of look angle, is also corrected by the correctors. The root mean square wavefront aberration for the final conformal window imaging system is less than 0.2 wave across the full field of regard on the visible spectrum, and the boresight error is less than 0.5' across the full field of regard.

  7. Correction of NIRI/ Altair non-common path aberrations using focal plane sharpening

    NASA Astrophysics Data System (ADS)

    Ball, Jesse G.; Lai, Olivier; Trujillo, Chadwick; White, John

    2016-07-01

    Non-common path aberrations (NCPA), in an adaptive optics system, are static aberrations induced by the science and wavefront sensor's (WFS) separate light paths, for which the latter is corrected (although not present in the former), and the former is not. It was suspected1 that this type of aberration may significantly affect the image quality performance of Altair + NIRI, the Gemini North Observatory's adaptive optics facility instrument and the near-infrared imaging camera. A simple and effective focal plane sharpening technique was developed to optimize these static aberrations for Altair & NIRI at f/32, and 2.12μm. By varying the shape of the deformable mirror (DM) to introduce Zernike aberration coefficients through a reasonable range of values, the images produced were read out on the NIRI detector and analyzed for Strehl ratio. Fitting a second-order polynomial to this data set gave an optimized value for each coefficient out to Z49. The Strehl ratio was improved by 6% +/- 2% and the Z5 (45° astigmatism) term showed the only appreciable error contribution to the current NCPA offset of 0.15μm in k-prime (2.12μm). Aside from resulting in a slight improvement in image quality, the technique developed is non-invasive and will be implemented in other instruments and cameras that typically couple with Altair and have outdated or erroneous NCPA files currently. Furthermore, some high spatial-frequency structure in the PSF was found that limited the effect of these corrections, and may be a key component in further investigations towards image quality degradation in Altair + NIRI.

  8. A correction method for the axial maladjustment of transmission-type optical system based on aberration theory

    NASA Astrophysics Data System (ADS)

    Xu, Chunmei; Huang, Fu-yu; Yin, Jian-ling; Chen, Yu-dan; Mao, Shao-juan

    2016-10-01

    The influence of aberration on misalignment of optical system is considered fully, the deficiencies of Gauss optical correction method is pointed, and a correction method for transmission-type misalignment optical system is proposed based on aberration theory. The variation regularity of single lens aberration caused by axial displacement is analyzed, and the aberration effect is defined. On this basis, through calculating the size of lens adjustment induced by the image position error and the magnifying rate error, the misalignment correction formula based on the constraints of the aberration is deduced mathematically. Taking the three lens collimation system for an example, the test is carried out to validate this method, and its superiority is proved.

  9. Active site of bimetallic heterogeneous catalyst by atomic resolution aberration-corrected STEM

    NASA Astrophysics Data System (ADS)

    Hsiao, Chien-Nan; Lin, Chun-Ting

    2015-11-01

    The localized defect of Au-Pd bimetallic heterogeneous nanoparticles catalyst was investigated using HRTEM and aberration-corrected HRSTEM. The phase plates were calculated from the aberration coefficients of the measured probe tableau for various outer tilt angle of the optical axis and the accuracy required for the compensation of the various residual aberration coefficients in order to achieve sub-angstrom resolution with the electron optics system was evaluated up to the fifth order aberrations. It is found that the interplanar spacing of the Au-Pd nanoparticle (1 1 1) planes observed along the [1 1 0] zone axis was approximately 0.24 nm measured by HRTEM. In addition, the HRSTEM HAADF image demonstrated that the twin boundaries on the surfaces of heterogeneous nanoparticles catalysts at atomic scale. These defects might be introduced during the growth to alleviate the internal stress caused by the 4.6% lattice mismatch of Au-Pd bimetallic system. Current research could be applied to the study of active sites in nanocatalysts.

  10. Design and progress toward a multi-conjugate adaptive optics system for distributed aberration correction

    SciTech Connect

    Baker, K; Olivier, S; Tucker, J; Silva, D; Gavel, D; Lim, R; Gratrix, E

    2004-08-17

    This article investigates the use of a multi-conjugate adaptive optics system to improve the field-of-view for the system. The emphasis of this research is to develop techniques to improve the performance of optical systems with applications to horizontal imaging. The design and wave optics simulations of the proposed system are given. Preliminary results from the multi-conjugate adaptive optics system are also presented. The experimental system utilizes a liquid-crystal spatial light modulator and an interferometric wave-front sensor for correction and sensing of the phase aberrations, respectively.

  11. Some recent advances in gold-based catalysis facilitated by aberration corrected analytical electron microscopy

    NASA Astrophysics Data System (ADS)

    Tiruvalam, R.; He, Q.; Herzing, A. A.; Pritchard, J.; Dimitratos, N.; Lopez-Sanchez, J. A.; Edwards, J. K.; Carley, A. F.; Hutchings, G. J.; Kiely, C. J.

    2012-07-01

    The recent availability of aberration corrected analytical electron microscopes (ACAEM) is revolutionizing our ability to characterize nanostructured catalyst materials. Some recent case studies are presented whereby the application of the high angle annular dark field (HAADF) imaging technique, coupled with STEM-XEDS analysis, has given us a more detailed and realistic view of the catalyst morphology. The examples chosen include supported Au catalysts for low temperature CO oxidation and supported AuPd bimetallic alloy catalysts for the direct production of H2O2.

  12. New views of materials through aberration-corrected scanning transmission electron microscopy.

    PubMed

    Pennycook, S J; Varela, M

    2011-01-01

    The successful correction of third-order and, more recently, fifth-order aberrations has enormously enhanced the capabilities of the scanning transmission electron microscope (STEM), by not only achieving record resolution, but also allowing near 100% efficiency for electron energy loss spectroscopy, and higher currents for two-dimensional spectrum imaging. These advances have meant that the intrinsic advantages of the STEM, incoherent imaging and simultaneous collection of multiple complementary images can now give new insights into many areas of materials physics. Here, we review a number of examples, mostly from the field of complex oxides, and look towards new directions for the future.

  13. Derivative Form of Off-axis Aberration Correction Surface and Its Application in Solar Energy Concentration

    NASA Astrophysics Data System (ADS)

    Li, Li; Chen, Ying-Tian; Hu, Sen

    2009-02-01

    By using the derivative method, we obtained the same result with that of the previous work of Chen et al. in 2006. Different from the integral form, the derivative form of the surface expression published in this paper is derived from differential equation and based on the theory of non-imaging focusing heliostat proposed by Chen et al. in 2001. The comparison of the derivative form of fixed aberration correction surface has been made with that of integral form surface as well as that of spherical surface in concentrating the solar ray.

  14. Dynamic Aberration Correction for Conformal Window of High-Speed Aircraft Using Optimized Model-Based Wavefront Sensorless Adaptive Optics.

    PubMed

    Dong, Bing; Li, Yan; Han, Xin-Li; Hu, Bin

    2016-09-02

    For high-speed aircraft, a conformal window is used to optimize the aerodynamic performance. However, the local shape of the conformal window leads to large amounts of dynamic aberrations varying with look angle. In this paper, deformable mirror (DM) and model-based wavefront sensorless adaptive optics (WSLAO) are used for dynamic aberration correction of an infrared remote sensor equipped with a conformal window and scanning mirror. In model-based WSLAO, aberration is captured using Lukosz mode, and we use the low spatial frequency content of the image spectral density as the metric function. Simulations show that aberrations induced by the conformal window are dominated by some low-order Lukosz modes. To optimize the dynamic correction, we can only correct dominant Lukosz modes and the image size can be minimized to reduce the time required to compute the metric function. In our experiment, a 37-channel DM is used to mimic the dynamic aberration of conformal window with scanning rate of 10 degrees per second. A 52-channel DM is used for correction. For a 128 × 128 image, the mean value of image sharpness during dynamic correction is 1.436 × 10(-5) in optimized correction and is 1.427 × 10(-5) in un-optimized correction. We also demonstrated that model-based WSLAO can achieve convergence two times faster than traditional stochastic parallel gradient descent (SPGD) method.

  15. Dynamic Aberration Correction for Conformal Window of High-Speed Aircraft Using Optimized Model-Based Wavefront Sensorless Adaptive Optics

    PubMed Central

    Dong, Bing; Li, Yan; Han, Xin-li; Hu, Bin

    2016-01-01

    For high-speed aircraft, a conformal window is used to optimize the aerodynamic performance. However, the local shape of the conformal window leads to large amounts of dynamic aberrations varying with look angle. In this paper, deformable mirror (DM) and model-based wavefront sensorless adaptive optics (WSLAO) are used for dynamic aberration correction of an infrared remote sensor equipped with a conformal window and scanning mirror. In model-based WSLAO, aberration is captured using Lukosz mode, and we use the low spatial frequency content of the image spectral density as the metric function. Simulations show that aberrations induced by the conformal window are dominated by some low-order Lukosz modes. To optimize the dynamic correction, we can only correct dominant Lukosz modes and the image size can be minimized to reduce the time required to compute the metric function. In our experiment, a 37-channel DM is used to mimic the dynamic aberration of conformal window with scanning rate of 10 degrees per second. A 52-channel DM is used for correction. For a 128 × 128 image, the mean value of image sharpness during dynamic correction is 1.436 × 10−5 in optimized correction and is 1.427 × 10−5 in un-optimized correction. We also demonstrated that model-based WSLAO can achieve convergence two times faster than traditional stochastic parallel gradient descent (SPGD) method. PMID:27598161

  16. Performance analysis of adaptive fiber laser array propagating in atmosphere with correction of high order aberrations in sub-aperture

    NASA Astrophysics Data System (ADS)

    Li, Feng; Geng, Chao; Li, Xinyang; Qiu, Qi

    2016-10-01

    Recently developed adaptive fiber laser array technique provides a promising way incorporating aberrations correction with laser beams transmission. Existing researches are focused on sub-aperture low order aberrations (pistons and tips/tilts) compensation and got excellent correction results for weak and moderate turbulence in short range. While such results are not adequate for future laser applications which face longer range and stronger turbulence. So sub-aperture high aberrations compensation is necessary. Relationship between corrigible orders of sub-aperture aberrations and far-field metrics as power-in-the-bucket (PIB) and Strehl ratio is investigated with numeric simulation in this paper. Numerical investigation results shows that increment in array number won't result in effective improvement of the far-field metric if sub-aperture size is fixed. Low order aberrations compensation in sub-apertures gets its best performances only when turbulence strength is weak. Pistons compensation becomes invalid and higher order aberrations compensation is necessary when turbulence gets strong enough. Cost functions of the adaptive fiber laser array with high order aberrations correction in sub-apertures are defined and the optimum corrigible orders are discussed. Results shows that high order (less than first ten Zernike orders) compensation is acceptable where balance between increment of the far-field metric and the cost and complexity of the system could be reached.

  17. Miniature optical planar camera based on a wide-angle metasurface doublet corrected for monochromatic aberrations

    NASA Astrophysics Data System (ADS)

    Arbabi, Amir; Arbabi, Ehsan; Kamali, Seyedeh Mahsa; Horie, Yu; Han, Seunghoon; Faraon, Andrei

    2016-11-01

    Optical metasurfaces are two-dimensional arrays of nano-scatterers that modify optical wavefronts at subwavelength spatial resolution. They are poised to revolutionize optics by enabling complex low-cost systems where multiple metasurfaces are lithographically stacked and integrated with electronics. For imaging applications, metasurface stacks can perform sophisticated image corrections and can be directly integrated with image sensors. Here we demonstrate this concept with a miniature flat camera integrating a monolithic metasurface lens doublet corrected for monochromatic aberrations, and an image sensor. The doublet lens, which acts as a fisheye photographic objective, has a small f-number of 0.9, an angle-of-view larger than 60° × 60°, and operates at 850 nm wavelength with 70% focusing efficiency. The camera exhibits nearly diffraction-limited image quality, which indicates the potential of this technology in the development of optical systems for microscopy, photography, and computer vision.

  18. Miniature optical planar camera based on a wide-angle metasurface doublet corrected for monochromatic aberrations

    PubMed Central

    Arbabi, Amir; Arbabi, Ehsan; Kamali, Seyedeh Mahsa; Horie, Yu; Han, Seunghoon; Faraon, Andrei

    2016-01-01

    Optical metasurfaces are two-dimensional arrays of nano-scatterers that modify optical wavefronts at subwavelength spatial resolution. They are poised to revolutionize optics by enabling complex low-cost systems where multiple metasurfaces are lithographically stacked and integrated with electronics. For imaging applications, metasurface stacks can perform sophisticated image corrections and can be directly integrated with image sensors. Here we demonstrate this concept with a miniature flat camera integrating a monolithic metasurface lens doublet corrected for monochromatic aberrations, and an image sensor. The doublet lens, which acts as a fisheye photographic objective, has a small f-number of 0.9, an angle-of-view larger than 60° × 60°, and operates at 850 nm wavelength with 70% focusing efficiency. The camera exhibits nearly diffraction-limited image quality, which indicates the potential of this technology in the development of optical systems for microscopy, photography, and computer vision. PMID:27892454

  19. Aberration correction in an adaptive free-space optical interconnect with an error diffusion algorithm

    NASA Astrophysics Data System (ADS)

    Gil-Leyva, Diego; Robertson, Brian; Wilkinson, Timothy D.; Henderson, Charley J.

    2006-06-01

    Aberration correction within a free-space optical interconnect based on a spatial light modulator for beam steering and holographic wavefront correction is presented. The wavefront sensing technique is based on an extension of a modal wavefront sensor described by Neil et al. [J. Opt. Soc. Am. A 17, 1098 (2000)], which uses a diffractive element. In this analysis such a wavefront sensor is adapted with an error diffusion algorithm that yields a low reconstruction error and fast reconfigurability. Improvement of the beam propagation quality (Strehl ratio) for different channels across the input plane is achieved. However, due to the space invariancy of the system, a trade-off among the beam propagation quality for channels is obtained. Experimental results are presented and discussed.

  20. Sensor-less aberration correction in optical imaging systems using blind optimization

    NASA Astrophysics Data System (ADS)

    Avanaki, Mohammad R. N.; Mazraeh Khoshki, R.; Hojjatoleslami, S. A.; Podoleanu, A. Gh.

    2012-02-01

    The imperfection of optical devices in an optical imaging system deteriorates wavefront which results in aberration. This reduces the optical signal to noise ratio of the imaging system and the quality of the produced images. Adaptive optics composed of wavefront sensor (WFS) and deformable mirror (DM) is a straightforward solution for this problem. The need for a WFS in an AO system, raises the cost of the overall system, and there are also instances when they cannot be used, such as in microscopy. Moreover stray reflections from lens surfaces affect the performance of the WFS. In this paper, we describe a blind optimization technique with an in-expensive electronics without using the WFS to correct the aberration in order to achieve better quality images. The correction system includes an electromagnetic DM from Imagine, Mirao52d, with 52 actuators which are controlled by particle swarm optimization (PSO) algorithm. The results of the application of simulated annealing (SA), and genetic algorithm (GA) techniques that we have implemented in the sensor-less AO are used for comparison.

  1. Real-Time 3D Contrast-Enhanced Transcranial Ultrasound and Aberration Correction

    PubMed Central

    Ivancevich, Nikolas M.; Pinton, Gianmarco F.; Nicoletto, Heather A.; Bennett, Ellen; Laskowitz, Daniel T.; Smith, Stephen W.

    2008-01-01

    Contrast-enhanced (CE) transcranial ultrasound (US) and reconstructed 3D transcranial ultrasound have shown advantages over traditional methods in a variety of cerebrovascular diseases. We present the results from a novel ultrasound technique, namely real-time 3D contrast-enhanced transcranial ultrasound. Using real-time 3D (RT3D) ultrasound and micro-bubble contrast agent, we scanned 17 healthy volunteers via a single temporal window and 9 via the sub-occipital window and report our detection rates for the major cerebral vessels. In 71% of subjects, both of our observers identified the ipsilateral circle of Willis from the temporal window, and in 59% we imaged the entire circle of Willis. From the sub-occipital window, both observers detected the entire vertebrobasilar circulation in 22% of subjects, and in 44% the basilar artery. After performing phase aberration correction on one subject, we were able to increase the diagnostic value of the scan, detecting a vessel not present in the uncorrected scan. These preliminary results suggest that RT3D CE transcranial US and RT3D CE transcranial US with phase aberration correction have the potential to greatly impact the field of neurosonology. PMID:18395321

  2. Pitch-catch phase aberration correction of multiple isoplanatic patches for 3-D transcranial ultrasound imaging.

    PubMed

    Lindsey, Brooks D; Smith, Stephen W

    2013-03-01

    Having previously presented the ultrasound brain helmet, a system for simultaneous 3-D ultrasound imaging via both temporal bone acoustic windows, the scanning geometry of this system is utilized to allow each matrix array to serve as a correction source for the opposing array. Aberration is estimated using cross-correlation of RF channel signals, followed by least mean squares solution of the resulting overdetermined system. Delay maps are updated and real-time 3-D scanning resumes. A first attempt is made at using multiple arrival time maps to correct multiple unique aberrators within a single transcranial imaging volume, i.e., several isoplanatic patches. This adaptive imaging technique, which uses steered unfocused waves transmitted by the opposing, or beacon, array, updates the transmit and receive delays of 5 isoplanatic patches within a 64° x 64° volume. In phantom experiments, color flow voxels above a common threshold have also increased by an average of 92%, whereas color flow variance decreased by an average of 10%. This approach has been applied to both temporal acoustic windows of two human subjects, yielding increases in echo brightness in 5 isoplanatic patches with a mean value of 24.3 ± 9.1%, suggesting that such a technique may be beneficial in the future for performing noninvasive 3-D color flow imaging of cerebrovascular disease, including stroke.

  3. Phase aberration correction by multi-stencils fast marching method using sound speed image in ultrasound computed tomography

    NASA Astrophysics Data System (ADS)

    Qu, Xiaolei; Azuma, Takashi; Lin, Hongxiang; Imoto, Haruka; Tamano, Satoshi; Takagi, Shu; Umemura, Shin-Ichiro; Sakuma, Ichiro; Matsumoto, Yoichiro

    2016-04-01

    Reflection image from ultrasound computed tomography (USCT) system can be obtained by synthetic aperture technique, however its quality is decreased by phase aberration caused by inhomogeneous media. Therefore, phase aberration correction is important to improve image quality. In this study, multi-stencils fast marching method (MSFMM) is employed for phase correction. The MSFMM is an accurate and fast solution of Eikonal equation which considers the refraction. The proposed method includes two steps. First, the MSFMM is used to compute sound propagation time from each element to each image gird point using sound speed image of USCT. Second, synthetic aperture technique is employed to obtain reflection image using the computed propagation time. To evaluate the proposed method, both numerical simulation and phantom experiment were conducted. With regard to numerical simulation, both quantitative and qualitative comparisons between reflection images with and without phase aberration correction were given. In the quantitative comparison, the diameters of point spread function (PSF) in reflection images of a two layer structure were presented. In the qualitative comparison, reflection images of simple circle and complex breast modes with phase aberration correction show higher quality than that without the correction. In respect to phantom experiment, a piece of breast phantom with artificial glandular structure inside was scanned by a USCT prototype, and the artificial glandular structure is able to be visible more clearly in the reflection image with phase aberration correction than in that without the correction. In this study, a phase aberration correction method by the MSFMM are proposed for reflection image of the USCT.

  4. Chromatic aberration correction and deconvolution for UV sensitive imaging of fluorescent sterols in cytoplasmic lipid droplets.

    PubMed

    Wüstner, Daniel; Faergeman, Nils J

    2008-08-01

    Intrinsically fluorescent sterols, like dehydroergosterol (DHE), mimic cholesterol closely and are therefore suitable to determine cholesterol transport by fluorescence microscopy. Disadvantages of DHE are its low quantum yield, rapid bleaching, and the fact that its excitation and emission is in the UV region of the spectrum. Thus, one has to deal with chromatic aberration and low signal-to-noise ratio. We developed a method to correct for chromatic aberration between the UV channel and the red/green channel in multicolor imaging of DHE compared with the lipid droplet marker Nile Red in living macrophage foam cells and in adipocytes. We used deconvolution microscopy and developed image segmentation techniques to assess the DHE content of lipid droplets in both cell types in an automated manner. Pulse-chase studies and colocalization analysis were performed to monitor the redistribution of DHE upon adipocyte differentiation. DHE is targeted to transferrin-positive recycling endosomes in preadipocytes but associates with droplets in mature adipocytes. Only in adipocytes but not in foam cells fluorescent sterol was confined to the droplet-limiting membrane. We developed an approach to visualize and quantify sterol content of lipid droplets in living cells with potential for automated high content screening of cellular sterol transport.

  5. Ultrahigh-resolution optical coherence tomography with monochromatic and chromatic aberration correction.

    PubMed

    Zawadzki, Robert J; Cense, Barry; Zhang, Yan; Choi, Stacey S; Miller, Donald T; Werner, John S

    2008-05-26

    We have developed an improved adaptive optics - optical coherence tomography (AO-OCT) system and evaluated its performance for in vivo imaging of normal and pathologic retina. The instrument provides unprecedented image quality at the retina with isotropic 3D resolution of 3.5 x 3.5 x 3.5 microm(3). Critical to the instrument's resolution is a customized achromatizing lens that corrects for the eye's longitudinal chromatic aberration and an ultra broadband light source (Delta lambda=112 nm lambda(0)= approximately 836 nm). The eye's transverse chromatic aberrations is modeled and predicted to be sufficiently small for the imaging conditions considered. The achromatizing lens was strategically placed at the light input of the AO-OCT sample arm. This location simplifies use of the achromatizing lens and allows straightforward implementation into existing OCT systems. Lateral resolution was achieved with an AO system that cascades two wavefront correctors, a large stroke bimorph deformable mirror (DM) and a micro-electromechanical system (MEMS) DM with a high number of actuators. This combination yielded diffraction-limited imaging in the eyes examined. An added benefit of the broadband light source is the reduction of speckle size in the axial dimension. Additionally, speckle contrast was reduced by averaging multiple B-scans of the same proximal patch of retina. The combination of improved micron-scale 3D resolution, and reduced speckle size and contrast were found to significantly improve visibility of microscopic structures in the retina.

  6. Perfect X-ray focusing via fitting corrective glasses to aberrated optics.

    PubMed

    Seiboth, Frank; Schropp, Andreas; Scholz, Maria; Wittwer, Felix; Rödel, Christian; Wünsche, Martin; Ullsperger, Tobias; Nolte, Stefan; Rahomäki, Jussi; Parfeniukas, Karolis; Giakoumidis, Stylianos; Vogt, Ulrich; Wagner, Ulrich; Rau, Christoph; Boesenberg, Ulrike; Garrevoet, Jan; Falkenberg, Gerald; Galtier, Eric C; Ja Lee, Hae; Nagler, Bob; Schroer, Christian G

    2017-03-01

    Due to their short wavelength, X-rays can in principle be focused down to a few nanometres and below. At the same time, it is this short wavelength that puts stringent requirements on X-ray optics and their metrology. Both are limited by today's technology. In this work, we present accurate at wavelength measurements of residual aberrations of a refractive X-ray lens using ptychography to manufacture a corrective phase plate. Together with the fitted phase plate the optics shows diffraction-limited performance, generating a nearly Gaussian beam profile with a Strehl ratio above 0.8. This scheme can be applied to any other focusing optics, thus solving the X-ray optical problem at synchrotron radiation sources and X-ray free-electron lasers.

  7. Element discrimination in a hexagonal boron nitride nanosheet by aberration corrected transmission electron microscopy.

    PubMed

    Mitome, Masanori; Sawada, Hidetaka; Kondo, Yukihito; Tanishiro, Yasumasa; Takayanagi, Kunio

    2012-11-01

    Boron nitride nanosheets prepared by an exfoliation technique were observed by aberration corrected transmission electron microscopy at 300 kV acceleration voltage. Single boron and nitrogen atoms in a monolayer region were imaged with different image contrast; a boron atom gave 16% less intensity reduction than a nitrogen atom. The number of atoms at each hexagonal ring site was determined by the image intensity that changed discretely with a 0.25-0.30 intensity difference. A double BN sheet was found to have a boron vacancy layer, and a triple BN layer has also a boron deficient layer on the incident surface resulting from the electron beam thinning process. The high sensitivity for atomic species was achieved by the high resolution and a small information limit due to the use of a cold field emission electron source.

  8. Observations of carbon nanotube oxidation in an aberration-corrected environmental transmission electron microscope.

    PubMed

    Koh, Ai Leen; Gidcumb, Emily; Zhou, Otto; Sinclair, Robert

    2013-03-26

    We report the first direct study on the oxidation of carbon nanotubes at the resolution of an aberration-corrected environmental transmission electron microscope (ETEM), as we locate and identify changes in the same nanotubes as they undergo oxidation at increasing temperatures in situ in the ETEM. Contrary to earlier reports that CNT oxidation initiates at the end of the tube and proceeds along its length, our findings show that only the outside graphene layer is being removed and, on occasion, the interior inner wall is oxidized, presumably due to oxygen infiltrating into the hollow nanotube through an open end or breaks in the tube. We believe that this work provides the foundation for a greater scientific understanding of the mechanism underlying the nanotube oxidation process, as well as guidelines to manipulate the nanotubes' structure or prevent their oxidation.

  9. Observations of Carbon Nanotube Oxidation in an Aberration-Corrected, Environmental Transmission Electron Microscope

    PubMed Central

    Koh, Ai Leen; Gidcumb, Emily; Zhou, Otto; Sinclair, Robert

    2013-01-01

    We report the first direct study on the oxidation of carbon nanotubes at the resolution of an aberration-corrected environmental transmission electron microscope (ETEM), as we locate and identify changes in the same nanotubes as they undergo oxidation at increasing temperatures in-situ in the ETEM. Contrary to earlier reports that CNT oxidation initiates at the end of the tube and proceeds along its length, our findings show that only the outside graphene layer is being removed and on occasion, the interior inner wall is oxidized, presumably due to oxygen infiltrating into the hollow nanotube through an open end or breaks in the tube. We believe that this work provides the foundation for much scientific understanding of the mechanism underlying the nanotube oxidation process, as well as guidelines to manipulate their structure or prevent their oxidation. PMID:23360330

  10. Optical aberration correction by real-time holography in liquid crystals.

    PubMed

    Karaguleff, C; Clark, G L

    1990-07-15

    We present results of experiments that use nematic-phase liquid crystal as a real-time holographic recording medium. Plane-wave gratings were written with as little as 10 mJ/cm(2) of incident write-beam energy from a pulsed Nd:YAG laser, and diffraction efficiencies greater than 25% were measured at 633 nm. Grating decay times were observed to fall within two distinct time regimes: a rapid-decay time of 60 to 100 microsec and a slower-decay time of 6 to 30 msec. The rapid-decay regime was used to demonstrate real-time correction of severely aberrated images by degenerate four-wave mixing.

  11. Bright-field scanning confocal electron microscopy using a double aberration-corrected transmission electron microscope.

    PubMed

    Wang, Peng; Behan, Gavin; Kirkland, Angus I; Nellist, Peter D; Cosgriff, Eireann C; D'Alfonso, Adrian J; Morgan, Andrew J; Allen, Leslie J; Hashimoto, Ayako; Takeguchi, Masaki; Mitsuishi, Kazutaka; Shimojo, Masayuki

    2011-06-01

    Scanning confocal electron microscopy (SCEM) offers a mechanism for three-dimensional imaging of materials, which makes use of the reduced depth of field in an aberration-corrected transmission electron microscope. The simplest configuration of SCEM is the bright-field mode. In this paper we present experimental data and simulations showing the form of bright-field SCEM images. We show that the depth dependence of the three-dimensional image can be explained in terms of two-dimensional images formed in the detector plane. For a crystalline sample, this so-called probe image is shown to be similar to a conventional diffraction pattern. Experimental results and simulations show how the diffracted probes in this image are elongated in thicker crystals and the use of this elongation to estimate sample thickness is explored.

  12. Perfect X-ray focusing via fitting corrective glasses to aberrated optics

    NASA Astrophysics Data System (ADS)

    Seiboth, Frank; Schropp, Andreas; Scholz, Maria; Wittwer, Felix; Rödel, Christian; Wünsche, Martin; Ullsperger, Tobias; Nolte, Stefan; Rahomäki, Jussi; Parfeniukas, Karolis; Giakoumidis, Stylianos; Vogt, Ulrich; Wagner, Ulrich; Rau, Christoph; Boesenberg, Ulrike; Garrevoet, Jan; Falkenberg, Gerald; Galtier, Eric C.; Ja Lee, Hae; Nagler, Bob; Schroer, Christian G.

    2017-03-01

    Due to their short wavelength, X-rays can in principle be focused down to a few nanometres and below. At the same time, it is this short wavelength that puts stringent requirements on X-ray optics and their metrology. Both are limited by today's technology. In this work, we present accurate at wavelength measurements of residual aberrations of a refractive X-ray lens using ptychography to manufacture a corrective phase plate. Together with the fitted phase plate the optics shows diffraction-limited performance, generating a nearly Gaussian beam profile with a Strehl ratio above 0.8. This scheme can be applied to any other focusing optics, thus solving the X-ray optical problem at synchrotron radiation sources and X-ray free-electron lasers.

  13. Perfect X-ray focusing via fitting corrective glasses to aberrated optics

    PubMed Central

    Seiboth, Frank; Schropp, Andreas; Scholz, Maria; Wittwer, Felix; Rödel, Christian; Wünsche, Martin; Ullsperger, Tobias; Nolte, Stefan; Rahomäki, Jussi; Parfeniukas, Karolis; Giakoumidis, Stylianos; Vogt, Ulrich; Wagner, Ulrich; Rau, Christoph; Boesenberg, Ulrike; Garrevoet, Jan; Falkenberg, Gerald; Galtier, Eric C.; Ja Lee, Hae; Nagler, Bob; Schroer, Christian G.

    2017-01-01

    Due to their short wavelength, X-rays can in principle be focused down to a few nanometres and below. At the same time, it is this short wavelength that puts stringent requirements on X-ray optics and their metrology. Both are limited by today's technology. In this work, we present accurate at wavelength measurements of residual aberrations of a refractive X-ray lens using ptychography to manufacture a corrective phase plate. Together with the fitted phase plate the optics shows diffraction-limited performance, generating a nearly Gaussian beam profile with a Strehl ratio above 0.8. This scheme can be applied to any other focusing optics, thus solving the X-ray optical problem at synchrotron radiation sources and X-ray free-electron lasers. PMID:28248317

  14. Identification of light elements in silicon nitride by aberration-corrected scanning transmission electron microscopy.

    PubMed

    Idrobo, Juan C; Walkosz, Weronika; Klie, Robert F; Oğüt, Serdar

    2012-12-01

    In silicon nitride structural ceramics, the overall mechanical and thermal properties are controlled by the atomic and electronic structures at the interface between the ceramic grains and the amorphous intergranular films (IGFs) formed by various sintering additives. In the last ten years the atomic arrangements of heavy elements (rare-earths) at the Si(3)N(4)/IGF interfaces have been resolved. However, the atomic position of light elements, without which it is not possible to obtain a complete description of the interfaces, has been lacking. This review article details the authors' efforts to identify the atomic arrangement of light elements such as nitrogen and oxygen at the Si(3)N(4)/SiO(2) interface and in bulk Si(3)N(4) using aberration-corrected scanning transmission electron microscopy.

  15. Morphology of the ferritin iron core by aberration corrected scanning transmission electron microscopy.

    PubMed

    Jian, Nan; Dowle, Miriam; Horniblow, Richard D; Tselepis, Chris; Palmer, Richard E

    2016-11-18

    As the major iron storage protein, ferritin stores and releases iron for maintaining the balance of iron in fauna, flora, and bacteria. We present an investigation of the morphology and iron loading of ferritin (from equine spleen) using aberration-corrected high angle annular dark field scanning transmission electron microscopy. Atom counting method, with size selected Au clusters as mass standards, was employed to determine the number of iron atoms in the nanoparticle core of each ferritin protein. Quantitative analysis shows that the nuclearity of iron atoms in the mineral core varies from a few hundred iron atoms to around 5000 atoms. Moreover, a relationship between the iron loading and iron core morphology is established, in which mineral core nucleates from a single nanoparticle, then grows along the protein shell before finally forming either a solid or hollow core structure.

  16. Morphology of the ferritin iron core by aberration corrected scanning transmission electron microscopy

    NASA Astrophysics Data System (ADS)

    Jian, Nan; Dowle, Miriam; Horniblow, Richard D.; Tselepis, Chris; Palmer, Richard E.

    2016-11-01

    As the major iron storage protein, ferritin stores and releases iron for maintaining the balance of iron in fauna, flora, and bacteria. We present an investigation of the morphology and iron loading of ferritin (from equine spleen) using aberration-corrected high angle annular dark field scanning transmission electron microscopy. Atom counting method, with size selected Au clusters as mass standards, was employed to determine the number of iron atoms in the nanoparticle core of each ferritin protein. Quantitative analysis shows that the nuclearity of iron atoms in the mineral core varies from a few hundred iron atoms to around 5000 atoms. Moreover, a relationship between the iron loading and iron core morphology is established, in which mineral core nucleates from a single nanoparticle, then grows along the protein shell before finally forming either a solid or hollow core structure.

  17. Influence of adaptive-optics ocular aberration correction on visual acuity at different luminances and contrast polarities.

    PubMed

    Marcos, Susana; Sawides, Lucie; Gambra, Enrique; Dorronsoro, Carlos

    2008-10-06

    We evaluated the visual benefit of correcting astigmatism and high-order aberrations with adaptive optics (AO) on visual acuity (VA) measured at 7 different luminances (ranging from 0.8 to 50 cd/m(2)) and two contrast polarities (black letters on white background, BoW, and white letters on black background, WoB) on 7 subjects. For the BoW condition, VA increased with background luminance in both natural and AO-corrected conditions, and there was a benefit of AO correction at all luminances (by a factor of 1.29 on average across luminances). For WoB VA increased with foreground luminance but decreased for the highest luminances. In this reversed polarity condition AO correction increased VA by a factor of 1.13 on average and did not produce a visual benefit at high luminances. The improvement of VA (averaged across conditions) was significantly correlated (p = 0.04) with the amount of corrected aberrations (in terms of Strehl ratio). The improved performance with WoB targets with respect to BoW targets is decreased when correcting aberrations, suggesting a role of ocular aberrations in the differences in visual performance between contrast polarities.

  18. Surgical Correction of Aberrant Right Coronary Anomalies Stranding an Aortic Commissure with and Without Unroofing.

    PubMed

    Abdelhady, Khaled; Durgam, Samarth; Elzein, Chawki; Ilbawi, Michel N; Rhoiney, David; Massad, Malek G

    2017-02-18

    The technique for successful surgical correction of an anomalous origin of the right coronary artery from the opposite aortic cusp with an aberrant course between the aorta and pulmonary artery is illustrated in a symptomatic 62-year-old woman. The intramural course of the right coronary artery traversed the tip of the commissure between the anterior and posterior leaflets, and its repair entailed unroofing of the intramural segment from inside the aortic intima. This technique required resuspension of the overlying commissure to maintain optimal aortic valve leaflet coaptation and prevent aortic insufficiency. Modifications of this technique have been utilized by us whenever the intramural segment traversed behind the commissure. In these cases, partial or subtotal unroofing of the intramural segment was performed to preserve the integrity of the intima behind the overlying commissure. More recently, we have performed the surgical correction by probing the intramural segment within the aortic wall to its most anterior location and then performing a wide anterior unroofing in the aortic intima, and marsupializing the aortic and coronary intima to avoid dissection or intimal flap development. We favor utilizing these techniques of anatomic correction of the anomalous coronary to other techniques involving coronary artery bypass grafting of the anomalous coronary, especially in adult patients, as unroofing provides more lasting results.

  19. Conduction band offset at GeO{sub 2}/Ge interface determined by internal photoemission and charge-corrected x-ray photoelectron spectroscopies

    SciTech Connect

    Zhang, W. F.; Nishimula, T.; Nagashio, K.; Kita, K.; Toriumi, A.

    2013-03-11

    We report a consistent conduction band offset (CBO) at a GeO{sub 2}/Ge interface determined by internal photoemission spectroscopy (IPE) and charge-corrected X-ray photoelectron spectroscopy (XPS). IPE results showed that the CBO value was larger than 1.5 eV irrespective of metal electrode and substrate type variance, while an accurate determination of valence band offset (VBO) by XPS requires a careful correction of differential charging phenomena. The VBO value was determined to be 3.60 {+-} 0.2 eV by XPS after charge correction, thus yielding a CBO (1.60 {+-} 0.2 eV) in excellent agreement with the IPE results. Such a large CBO (>1.5 eV) confirmed here is promising in terms of using GeO{sub 2} as a potential passivation layer for future Ge-based scaled CMOS devices.

  20. Correction of axial and lateral chromatic aberration with false color filtering.

    PubMed

    Chang, Joonyoung; Kang, Hee; Kang, Moon Gi

    2013-03-01

    In this paper, we propose a chromatic aberration (CA) correction algorithm based on a false color filtering technique. In general, CA produces color distortions called color fringes near the contrasting edges of captured images, and these distortions cause false color artifacts. In the proposed method, a false color filtering technique is used to filter out the false color components from the chroma-signals of the input image. The filtering process is performed with the adaptive weights obtained from both the gradient and color differences, and the weights are designed to reduce the various types of color fringes regardless of the colors of the artifacts. Moreover, as preprocessors of the filtering process, a transient improvement (TI) technique is applied to enhance the slow transitions of the red and blue channels that are blurred by the CA. The TI process improves the filtering performance by narrowing the false color regions before the filtering process when severe color fringes (typically purple fringes) occur widely. Last, the CA-corrected chroma-signal is combined with the TI chroma-signal to avoid incorrect color adjustment. The experimental results show that the proposed method substantially reduces the CA artifacts and provides natural-looking replacement colors, while it avoids incorrect color adjustment.

  1. Nanostructural and Chemical Characterization of Supported Metal Oxide Catalysts by Aberration Corrected Analytical Electron Microscopy

    NASA Astrophysics Data System (ADS)

    Zhou, Wu

    In this thesis, aberration corrected STEM imaging and chemical analysis techniques have been extensively applied in the structural and chemical characterization of supported tungsten oxide catalysts in an attempt to reveal the structure-activity relationships at play in these catalyst systems. The supported WO3/ZrO2 solid acid catalyst system is a major focal point of this thesis, and detailed aberration-corrected STEM-HAADF imaging studies were performed on a systematic set of catalysts showing different level of catalytic performance. The nature of the catalytically most active WOx species was identified by correlating structural information, obtained from STEM-HAADF and in-situ optical spectroscopy studies, with catalytic testing results. Specifically, ˜1nm distorted Zr-WOx mixed oxide clusters were identified to be the most active species for both the methanol dehydration and n-pentane isomerization reactions in the WO3/ZrO2 catalyst system. The use of amorphous zirconia as a precursor support material makes it much easier to extract and incorporate Zr cations into the surface WOx clusters during calcination. The calcination temperature was also identified to also play an important role in the formation of these most active Zr-WOx clusters. When the calcination temperature is comparable to or higher than the 896K Huttig temperature of ZrO2 (at which surface ZrO x species have sufficient mobility to agglomerate and sinter), the chance for successful surface WOx and ZrOx intermixing is significantly increased. Based on this perceived structure-activity relationship, several new catalyst synthesis strategies were developed in an attempt to optimize the catalytic performance of WOx-based catalysts. We have demonstrated in Chapter 3 that co-impregnation of WOx and ZrOx precursors onto an inactive model WO3/ZrO2 catalyst, followed by a calcination treatment above the 896K Huttig temperature of ZrO 2, promotes the surface diffusion of ZrO2 and intermixing of Zr

  2. Application of polymer graded-index materials for aberration correction of progressive addition lenses

    NASA Astrophysics Data System (ADS)

    Shitanoki, Yuki; Tagaya, Akihiro; Koike, Yasuhiro

    2009-02-01

    Graded-index (GRIN) progressive addition lens (PAL) was successfully fabricated, and GRIN's potential for aberration correction of PAL was confirmed. GRIN material was prepared by partial diffusion of methyl methacrylate (MMA (nd at polymer = 1.492)) monomer into cross-linked benzyl methacrylate (BzMA (nd at polymer=1.568)) flat gel, and GRINPAL was prepared by polymerization of the GRIN material attached to a mold of commercially available PAL. GRIN polymer materials have been used for various applications such as rod lenses and optical fibers. GRIN represents gradual change of refractive index in a material, which adds or reduces light focusing power of the material. PAL is a multifocal spectacle lens for presbyopia. However, some localized aberrations (especially astigmatism) in PAL have not yet been reduced satisfactorily for decades by optimizing surface geometry of a lens. In this research, we propose to employ GRIN materials for astigmatism reduction of PALs. BzMA flat gel was prepared by UV polymerization of BzMA, crosslinking agent ethylene glycol dimethacrylate (EDMA) and photopolymerization initiator DAROCURE 1173. MMA monomer was diffused into BzMA flat gel from a portion of periphery for several hours. The obtained GRIN material was attached to a mold of commercially available PAL and polymerized by UV. As a result, reduction of astigmatism was confirmed locally in the fabricated PAL and GRIN-PAL using lens meter. In conclusion, GRIN-PAL was successfully fabricated. The validity of GRIN employment for the astigmatism reduction in PAL was demonstrated experimentally.

  3. Polyvinylidene fluoride molecules in nanofibers, imaged at atomic scale by aberration corrected electron microscopy

    NASA Astrophysics Data System (ADS)

    Lolla, Dinesh; Gorse, Joseph; Kisielowski, Christian; Miao, Jiayuan; Taylor, Philip L.; Chase, George G.; Reneker, Darrell H.

    2015-12-01

    Atomic scale features of polyvinylidene fluoride molecules (PVDF) were observed with aberration corrected transmission electron microscopy. Thin, self-supporting PVDF nanofibers were used to create images that show conformations and relative locations of atoms in segments of polymer molecules, particularly segments near the surface of the nanofiber. Rows of CF2 atomic groups, at 0.25 nm intervals, which marked the paths of segments of the PVDF molecules, were seen. The fact that an electron microscope image of a segment of a PVDF molecule depended upon the particular azimuthal direction, along which the segment was viewed, enabled observation of twist around the molecular axis. The 0.2 nm side-by-side distance between the two fluorine atoms attached to the same carbon atom was clearly resolved. Morphological and chemical changes produced by energetic electrons, ranging from no change to fiber scission, over many orders of magnitude of electrons per unit area, promise quantitative new insights into radiation chemistry. Relative movements of segments of molecules were observed. Promising synergism between high resolution electron microscopy and molecular dynamic modeling was demonstrated. This paper is at the threshold of growing usefulness of electron microscopy to the science and engineering of polymer and other molecules.Atomic scale features of polyvinylidene fluoride molecules (PVDF) were observed with aberration corrected transmission electron microscopy. Thin, self-supporting PVDF nanofibers were used to create images that show conformations and relative locations of atoms in segments of polymer molecules, particularly segments near the surface of the nanofiber. Rows of CF2 atomic groups, at 0.25 nm intervals, which marked the paths of segments of the PVDF molecules, were seen. The fact that an electron microscope image of a segment of a PVDF molecule depended upon the particular azimuthal direction, along which the segment was viewed, enabled observation of

  4. Quantitative Phase Microscopy of microstructures with extended measurement range and correction of chromatic aberrations by multiwavelength digital holography.

    PubMed

    Ferraro, P; Miccio, L; Grilli, S; Paturzo, M; De Nicola, S; Finizio, A; Osellame, R; Laporta, P

    2007-10-29

    Quantitative Phase Microscopy (QPM) by interferometric techniques can require a multiwavelength configuration to remove 2pi ambiguity and improve accuracy. However, severe chromatic aberration can affect the resulting phase-contrast map. By means of classical interference microscope configuration it is quite unpractical to correct such aberration. We propose and demonstrate that by Digital Holography (DH) in a microscope configuration it is possible to clear out the QPM map from the chromatic aberration in a simpler and more effective way with respect to other approaches. The proposed method takes benefit of the unique feature of DH to record in a plane out-of-focus and subsequently reconstruct numerically at the right focal image plane. In fact, the main effect of the chromatic aberration is to shift differently the correct focal image plane at each wavelength and this can be readily compensated by adjusting the corresponding reconstruction distance for each wavelength. A procedure is described in order to determine easily the relative focal shift among different imaging wavelengths by performing a scanning of the numerical reconstruction along the optical axis, to find out the focus and to remove at the same time the chromatic aberration.

  5. High Resolution Imaging with an Aberration Corrected JEOL 2200FS-AC STEM/TEM

    SciTech Connect

    Blom, Douglas Allen; Allard Jr, Lawrence Frederick; O'Keefe, Michael A.; Mishina, Satoshi

    2005-01-01

    A new JEOL 2200FS 200kV field emission STEM/TEM with a hexapole Cs-corrector (CEOS GmbH) for the probe-forming lens and an in-column Omega-type energy filter has recently been installed at the Advanced Microscopy Laboratory (AML) at Oak Ridge National Laboratory (ORNL). The microscope is intended primarily for high-resolution imaging of catalyst systems that are of interest to the U.S. Department of Energy for increased energy efficiency and energy security. In this paper we report on the high-resolution imaging characteristics of our microscope for both conventional high-resolution TEM and STEM imaging. The TEM Scherzer point resolution for our objective lens polepiece (C{sub s} = 0.5 mm) is 0.19 nm, but more significantly the information limit has been demonstrated to be better than 0.09 nm, as shown in Fig. 1. This figure shows a Young's fringe experiment carried out on an amorphous Ge specimen which was estimated to be 10 nm thick. The thickness of the sample damps out the Thon rings to some extent, but the information transfer to sub 0.1 nm resolution is clearly evident. The electron wave at the specimen exit surface with resolution out to the information limit of a microscope may be reconstructed via computational processing of a focal or tilt series of images. The extension of the TEM information limit to the sub-0.1 nm range in our microscope can be attributed primarily to the improved objective lens and high tension power supply stabilities provided by JEOL Co. to satisfy our instrument specifications. A contrast transfer function (CTF) calculated using the parameters for our microscope is shown in Fig. 2, computed at the alpha-null defocus condition used for FSR processing. The CTF closely matches the demonstrated Young's fringe pattern, indicating the ability of the microscope to achieve ultimate performance in TEM mode. Characterization of catalyst systems will be a primary focus of the aberration-corrected JEOL 2200FS and therefore high-resolution STEM

  6. Polyvinylidene fluoride molecules in nanofibers, imaged at atomic scale by aberration corrected electron microscopy.

    PubMed

    Lolla, Dinesh; Gorse, Joseph; Kisielowski, Christian; Miao, Jiayuan; Taylor, Philip L; Chase, George G; Reneker, Darrell H

    2016-01-07

    Atomic scale features of polyvinylidene fluoride molecules (PVDF) were observed with aberration corrected transmission electron microscopy. Thin, self-supporting PVDF nanofibers were used to create images that show conformations and relative locations of atoms in segments of polymer molecules, particularly segments near the surface of the nanofiber. Rows of CF2 atomic groups, at 0.25 nm intervals, which marked the paths of segments of the PVDF molecules, were seen. The fact that an electron microscope image of a segment of a PVDF molecule depended upon the particular azimuthal direction, along which the segment was viewed, enabled observation of twist around the molecular axis. The 0.2 nm side-by-side distance between the two fluorine atoms attached to the same carbon atom was clearly resolved. Morphological and chemical changes produced by energetic electrons, ranging from no change to fiber scission, over many orders of magnitude of electrons per unit area, promise quantitative new insights into radiation chemistry. Relative movements of segments of molecules were observed. Promising synergism between high resolution electron microscopy and molecular dynamic modeling was demonstrated. This paper is at the threshold of growing usefulness of electron microscopy to the science and engineering of polymer and other molecules.

  7. Recursive wavefront aberration correction method for LCoS spatial light modulators

    NASA Astrophysics Data System (ADS)

    García-Márquez, J.; Landgrave, J. E. A.; Alcalá-Ochoa, N.; Pérez-Santos, C.

    2011-06-01

    We present two accurate and relatively simple interferometric methods for the correction of wavefront aberrations of about 3 wavelengths (3 λ) in spatial light modulators (SLMs) of the liquid crystal on silicon (LCoS) type. The first is based on a recursive use of a wavefront fitting algorithm in a Wyko™ interferometer, in which Zernike polynomials are employed as the basis functions. We show here that the successive use of only three measurements is required to obtain a peak-to-valley (PV) error as low as λ/10, with an uncertainty of λ/30, in the compensated wavefront. The second method makes use of the actual optical path difference (OPD) computed by the interferometer at each pixel of the image of the interferogram of the LCoS modulator (LCoS-M). From numerical interpolation of these OPD values we were able to assign the required OPD compensation at each pixel of the LCoS-M. With this method, PV errors of the compensated wavefront as low as λ/16, with an uncertainty of λ/30, were obtained for the entire LCoS-M, or of λ/33 for the disk that we used as the domain of the Zernike polynomials in the first method.

  8. Double aberration-corrected TEM/STEM of tungstated zirconia nanocatalysts for the synthesis of paracetamol

    NASA Astrophysics Data System (ADS)

    Yoshida, K.; Shiju, N. R.; Brown, D. R.; Boyes, E. D.; Gai, P. L.

    2010-07-01

    We report highly active tungstated zirconia nanocatalysts for the synthesis of paracetamol by Beckmann rearrangement of 4-hydroxyacetophenone oxime. Double aberration-corrected (2AC)-TEM/STEM studies were performed in a JEOL 2200FS FEG TEM/STEM at the 1 Angstrom (1 Å = 0.1 nanometer) level. Observations at close to zero defocus were carried out using the AC-TEM as well as AC-STEM including high angle annular dark field (HAADF) imaging, from the same areas of the catalyst crystallites. The studies from the same areas have revealed the location and the nanostructure of the polytungstate species (clusters) and the nanograins of zirconia. The AC (S)TEM was crucial to observe the nanostructure and location of polytungstate clusters on the zirconia grains. Polytungstate clusters as small as 0.5 nm have been identified using the HAADF-STEM. The nanostructures of the catalyst and the W surface density have been correlated with paracetamol reaction studies. The results demonstrate the nature of active sites and high activity of the tungstated zirconia nanocatalyst, which is an environmentally clean alternative to the current homogeneous process.

  9. Aberration Corrected Scanning Transmission Electron Microscopy of (Ca , Sr)Fe2O5 Brownmillerite superlattices

    NASA Astrophysics Data System (ADS)

    Mukherjee, Debangshu; Stone, Greg; Moon, Eun Ju; Young, Joshua; Gopalan, Venkatraman; Rondinelli, James; May, Steven; Alem, Nasim

    The brownmillerite phase A2B2O5 consists of ordered oxygen vacancies in alternate perovskite layers forming chiral tetrahedral chains. The handedness of these tetrahedral chains control the polarization of the structure. The current study focuses on 1-1 brownmillerite superlattices grown on a SrTiO3 substrates using molecular beam epitaxy. The B-site in this structure is iron throughout the superlattice film, while the A-site alternates between calcium and strontium in the superlattice layers. In this study, we use atomic resolution aberration corrected scanning transmission electron microscopy (STEM) to investigate the structure and chemistry of the film-substrate interface as well as the chemical structure of the superlattice. Atom positions are determined to measure displacement vectors of A-site cations in the superlattice structure. D.M., G.A.S., V.G. and N.A. were supported by the National Science Foundation under Grant No. DMR-1420620. E.J.M. and S.J.M. were supported by the National Science Foundation under Grant No. DMR-1151649.

  10. Chromatic-aberration-corrected diffractive lenses for ultra-broadband focusing

    PubMed Central

    Wang, Peng; Mohammad, Nabil; Menon, Rajesh

    2016-01-01

    We exploit the inherent dispersion in diffractive optics to demonstrate planar chromatic-aberration-corrected lenses. Specifically, we designed, fabricated and characterized cylindrical diffractive lenses that efficiently focus the entire visible band (450 nm to 700 nm) onto a single line. These devices are essentially pixelated, multi-level microstructures. Experiments confirm an average optical efficiency of 25% for a three-wavelength apochromatic lens whose chromatic focus shift is only 1.3 μm and 25 μm in the lateral and axial directions, respectively. Super-achromatic performance over the continuous visible band is also demonstrated with averaged lateral and axial focus shifts of only 1.65 μm and 73.6 μm, respectively. These lenses are easy to fabricate using single-step grayscale lithography and can be inexpensively replicated. Furthermore, these devices are thin (<3 μm), error tolerant, has low aspect ratio (<1:1) and offer polarization-insensitive focusing, all significant advantages compared to alternatives that rely on metasurfaces. Our design methodology offers high design flexibility in numerical aperture and focal length, and is readily extended to 2D. PMID:26868264

  11. Chromatic-aberration-corrected diffractive lenses for ultra-broadband focusing

    DOE PAGES

    Wang, Peng; Mohammad, Nabil; Menon, Rajesh

    2016-02-12

    We exploit the inherent dispersion in diffractive optics to demonstrate planar chromatic-aberration-corrected lenses. Specifically, we designed, fabricated and characterized cylindrical diffractive lenses that efficiently focus the entire visible band (450 nm to 700 nm) onto a single line. These devices are essentially pixelated, multi-level microstructures. Experiments confirm an average optical efficiency of 25% for a three-wavelength apochromatic lens whose chromatic focus shift is only 1.3 μm and 25 μm in the lateral and axial directions, respectively. Super-achromatic performance over the continuous visible band is also demonstrated with averaged lateral and axial focus shifts of only 1.65 μm and 73.6 μm,more » respectively. These lenses are easy to fabricate using single-step grayscale lithography and can be inexpensively replicated. Furthermore, these devices are thin (<3 μm), error tolerant, has low aspect ratio (<1:1) and offer polarization-insensitive focusing, all significant advantages compared to alternatives that rely on metasurfaces. Lastly, our design methodology offers high design flexibility in numerical aperture and focal length, and is readily extended to 2D.« less

  12. Phase-contrast imaging in aberration-corrected scanning transmission electron microscopy.

    PubMed

    Krumeich, F; Müller, E; Wepf, R A

    2013-06-01

    Although the presence of phase-contrast information in bright field images recorded with a scanning transmission electron microscope (STEM) has been known for a long time, its systematic exploitation for the structural characterization of materials began only with the availability of aberration-corrected microscopes that allow sufficiently large illumination angles. Today, phase-contrast STEM (PC-STEM) imaging represents an increasingly important alternative to the well-established HRTEM method. In both methods, the image contrast is coherently generated and thus depends not only on illumination and collection angles but on defocus and specimen thickness as well. By PC-STEM, a projection of the crystal potential is obtained in thin areas, with the scattering sites being represented either with dark or bright contrast at two different defocus values which are both close to Gaussian defocus. This imaging behavior can be further investigated by image simulations performed with standard HRTEM simulation software based on the principle of reciprocity. As examples for the application of this method, PC-STEM results obtained on metal nanoparticles and dodecagonal quasicrystals dd-(Ta,V)₁.₆Te are discussed.

  13. Chromatic-aberration-corrected diffractive lenses for ultra-broadband focusing

    SciTech Connect

    Wang, Peng; Mohammad, Nabil; Menon, Rajesh

    2016-02-12

    We exploit the inherent dispersion in diffractive optics to demonstrate planar chromatic-aberration-corrected lenses. Specifically, we designed, fabricated and characterized cylindrical diffractive lenses that efficiently focus the entire visible band (450 nm to 700 nm) onto a single line. These devices are essentially pixelated, multi-level microstructures. Experiments confirm an average optical efficiency of 25% for a three-wavelength apochromatic lens whose chromatic focus shift is only 1.3 μm and 25 μm in the lateral and axial directions, respectively. Super-achromatic performance over the continuous visible band is also demonstrated with averaged lateral and axial focus shifts of only 1.65 μm and 73.6 μm, respectively. These lenses are easy to fabricate using single-step grayscale lithography and can be inexpensively replicated. Furthermore, these devices are thin (<3 μm), error tolerant, has low aspect ratio (<1:1) and offer polarization-insensitive focusing, all significant advantages compared to alternatives that rely on metasurfaces. Lastly, our design methodology offers high design flexibility in numerical aperture and focal length, and is readily extended to 2D.

  14. New insights on ion track morphology in pyrochlores by aberration corrected scanning transmission electron microscopy

    SciTech Connect

    Sachan, Ritesh; Zhang, Yanwen; Ou, Xin; Trautmann, Christina; Chisholm, Matthew F.; Weber, William J.

    2016-12-13

    Here we demonstrate the enhanced imaging capabilities of an aberration corrected scanning transmission electron microscope to advance the understanding of ion track structure in pyrochlore structured materials (i.e., Gd2Ti2O7 and Gd2TiZrO7). Track formation occurs due to the inelastic transfer of energy from incident ions to electrons, and atomic-level details of track morphology as a function of energy-loss are revealed in the present work. A comparison of imaging details obtained by varying collection angles of detectors is discussed in the present work. A quantitative analysis of phase identification using high-angle annular dark field imaging is performed on the ion tracks. Finally, a novel 3-dimensional track reconstruction method is provided that is based on depth dependent imaging of the ion tracks. The technique is used in extracting the atomic-level details of nanoscale features, such as the disordered ion tracks, which are embedded in relatively thicker matrix. Another relevance of the method is shown by measuring the tilt of the ion tracks relative to the electron beam incidence that helps in knowing the structure and geometry of ion tracks quantitatively.

  15. New insights on ion track morphology in pyrochlores by aberration corrected scanning transmission electron microscopy

    DOE PAGES

    Sachan, Ritesh; Zhang, Yanwen; Ou, Xin; ...

    2016-12-13

    Here we demonstrate the enhanced imaging capabilities of an aberration corrected scanning transmission electron microscope to advance the understanding of ion track structure in pyrochlore structured materials (i.e., Gd2Ti2O7 and Gd2TiZrO7). Track formation occurs due to the inelastic transfer of energy from incident ions to electrons, and atomic-level details of track morphology as a function of energy-loss are revealed in the present work. A comparison of imaging details obtained by varying collection angles of detectors is discussed in the present work. A quantitative analysis of phase identification using high-angle annular dark field imaging is performed on the ion tracks. Finally,more » a novel 3-dimensional track reconstruction method is provided that is based on depth dependent imaging of the ion tracks. The technique is used in extracting the atomic-level details of nanoscale features, such as the disordered ion tracks, which are embedded in relatively thicker matrix. Another relevance of the method is shown by measuring the tilt of the ion tracks relative to the electron beam incidence that helps in knowing the structure and geometry of ion tracks quantitatively.« less

  16. Chromatic-aberration-corrected diffractive lenses for ultra-broadband focusing

    NASA Astrophysics Data System (ADS)

    Wang, Peng; Mohammad, Nabil; Menon, Rajesh

    2016-02-01

    We exploit the inherent dispersion in diffractive optics to demonstrate planar chromatic-aberration-corrected lenses. Specifically, we designed, fabricated and characterized cylindrical diffractive lenses that efficiently focus the entire visible band (450 nm to 700 nm) onto a single line. These devices are essentially pixelated, multi-level microstructures. Experiments confirm an average optical efficiency of 25% for a three-wavelength apochromatic lens whose chromatic focus shift is only 1.3 μm and 25 μm in the lateral and axial directions, respectively. Super-achromatic performance over the continuous visible band is also demonstrated with averaged lateral and axial focus shifts of only 1.65 μm and 73.6 μm, respectively. These lenses are easy to fabricate using single-step grayscale lithography and can be inexpensively replicated. Furthermore, these devices are thin (<3 μm), error tolerant, has low aspect ratio (<1:1) and offer polarization-insensitive focusing, all significant advantages compared to alternatives that rely on metasurfaces. Our design methodology offers high design flexibility in numerical aperture and focal length, and is readily extended to 2D.

  17. Chromatic-aberration-corrected diffractive lenses for ultra-broadband focusing.

    PubMed

    Wang, Peng; Mohammad, Nabil; Menon, Rajesh

    2016-02-12

    We exploit the inherent dispersion in diffractive optics to demonstrate planar chromatic-aberration-corrected lenses. Specifically, we designed, fabricated and characterized cylindrical diffractive lenses that efficiently focus the entire visible band (450 nm to 700 nm) onto a single line. These devices are essentially pixelated, multi-level microstructures. Experiments confirm an average optical efficiency of 25% for a three-wavelength apochromatic lens whose chromatic focus shift is only 1.3 μm and 25 μm in the lateral and axial directions, respectively. Super-achromatic performance over the continuous visible band is also demonstrated with averaged lateral and axial focus shifts of only 1.65 μm and 73.6 μm, respectively. These lenses are easy to fabricate using single-step grayscale lithography and can be inexpensively replicated. Furthermore, these devices are thin (<3 μm), error tolerant, has low aspect ratio (<1:1) and offer polarization-insensitive focusing, all significant advantages compared to alternatives that rely on metasurfaces. Our design methodology offers high design flexibility in numerical aperture and focal length, and is readily extended to 2D.

  18. Practical spatial resolution of electron energy loss spectroscopy in aberration corrected scanning transmission electron microscopy.

    PubMed

    Shah, A B; Ramasse, Q M; Wen, J G; Bhattacharya, A; Zuo, J M

    2011-08-01

    The resolution of electron energy loss spectroscopy (EELS) is limited by delocalization of inelastic electron scattering rather than probe size in an aberration corrected scanning transmission electron microscope (STEM). In this study, we present an experimental quantification of EELS spatial resolution using chemically modulated 2×(LaMnO(3))/2×(SrTiO(3)) and 2×(SrVO(3))/2×(SrTiO(3)) superlattices by measuring the full width at half maxima (FWHM) of integrated Ti M(2,3), Ti L(2,3), V L(2,3), Mn L(2,3), La N(4,5), La N(2,3) La M(4,5) and Sr L(3) edges over the superlattices. The EELS signals recorded using large collection angles are peaked at atomic columns. The FWHM of the EELS profile, obtained by curve-fitting, reveals a systematic trend with the energy loss for the Ti, V, and Mn edges. However, the experimental FWHM of the Sr and La edges deviates significantly from the observed experimental tendency.

  19. Fabrication of polarization-independent waveguides deeply buried in lithium niobate crystal using aberration-corrected femtosecond laser direct writing

    NASA Astrophysics Data System (ADS)

    Wang, Peng; Qi, Jia; Liu, Zhengming; Liao, Yang; Chu, Wei; Cheng, Ya

    2017-01-01

    Writing optical waveguides with femtosecond laser pulses provides the capability of forming three-dimensional photonic circuits for manipulating light fields in both linear and nonlinear manners. To fully explore this potential, large depths of the buried waveguides in transparent substrates are often desirable to facilitate achieving vertical integration of waveguides in a multi-layer configuration, which, however, is hampered by rapidly degraded axial resolution caused by optical aberration. Here, we show that with the correction of the spherical aberration, polarization-independent waveguides can be inscribed in a nonlinear optical crystal lithium niobate (LN) at depths up to 1400 μm, which is more than one order of magnitude deeper than the waveguides written with aberration uncorrected femtosecond laser pulses. Our technique is beneficial for applications ranging from miniaturized nonlinear light sources to quantum information processing.

  20. Fabrication of polarization-independent waveguides deeply buried in lithium niobate crystal using aberration-corrected femtosecond laser direct writing

    PubMed Central

    Wang, Peng; Qi, Jia; Liu, Zhengming; Liao, Yang; Chu, Wei; Cheng, Ya

    2017-01-01

    Writing optical waveguides with femtosecond laser pulses provides the capability of forming three-dimensional photonic circuits for manipulating light fields in both linear and nonlinear manners. To fully explore this potential, large depths of the buried waveguides in transparent substrates are often desirable to facilitate achieving vertical integration of waveguides in a multi-layer configuration, which, however, is hampered by rapidly degraded axial resolution caused by optical aberration. Here, we show that with the correction of the spherical aberration, polarization-independent waveguides can be inscribed in a nonlinear optical crystal lithium niobate (LN) at depths up to 1400 μm, which is more than one order of magnitude deeper than the waveguides written with aberration uncorrected femtosecond laser pulses. Our technique is beneficial for applications ranging from miniaturized nonlinear light sources to quantum information processing. PMID:28112246

  1. Fabrication of polarization-independent waveguides deeply buried in lithium niobate crystal using aberration-corrected femtosecond laser direct writing.

    PubMed

    Wang, Peng; Qi, Jia; Liu, Zhengming; Liao, Yang; Chu, Wei; Cheng, Ya

    2017-01-23

    Writing optical waveguides with femtosecond laser pulses provides the capability of forming three-dimensional photonic circuits for manipulating light fields in both linear and nonlinear manners. To fully explore this potential, large depths of the buried waveguides in transparent substrates are often desirable to facilitate achieving vertical integration of waveguides in a multi-layer configuration, which, however, is hampered by rapidly degraded axial resolution caused by optical aberration. Here, we show that with the correction of the spherical aberration, polarization-independent waveguides can be inscribed in a nonlinear optical crystal lithium niobate (LN) at depths up to 1400 μm, which is more than one order of magnitude deeper than the waveguides written with aberration uncorrected femtosecond laser pulses. Our technique is beneficial for applications ranging from miniaturized nonlinear light sources to quantum information processing.

  2. Chromosome therapy. Correction of large chromosomal aberrations by inducing ring chromosomes in induced pluripotent stem cells (iPSCs).

    PubMed

    Kim, Taehyun; Bershteyn, Marina; Wynshaw-Boris, Anthony

    2014-01-01

    The fusion of the short (p) and long (q) arms of a chromosome is referred to as a "ring chromosome." Ring chromosome disorders occur in approximately 1 in 50,000-100,000 patients. Ring chromosomes can result in birth defects, mental disabilities, and growth retardation if additional genes are deleted during the formation of the ring. Due to the severity of these large-scale aberrations affecting multiple contiguous genes, no possible therapeutic strategies for ring chromosome disorders have so far been proposed. Our recent study (Bershteyn et al.) using patient-derived fibroblast lines containing ring chromosomes, found that cellular reprogramming of these fibroblasts into induced pluripotent stem cells (iPSCs) resulted in the cell-autonomous correction of the ring chromosomal aberration via compensatory uniparental disomy (UPD). These observations have important implications for studying the mechanism of chromosomal number control and may lead to the development of effective therapies for other, more common, chromosomal aberrations.

  3. Early results from an aberration-corrected JEOL 2200FS STEM/TEM at Oak Ridge National Laboratory.

    PubMed

    Blom, Douglas A; Allard, Lawrence E; Mishina, Satoshi; O'Keefe, Michael A

    2006-12-01

    The resolution-limiting aberrations of round electromagnetic lenses can now be successfully overcome via the use of multipole element "aberration correctors." The installation and performance of a hexapole-based corrector (CEOS GmbH) integrated on the probe-forming side of a JEOL 2200FS FEG STEM/TEM is described. For the resolution of the microscope not to be severely compromised by its environment, a new, specially designed building at Oak Ridge National Laboratory has been built. The Advanced Microscopy Laboratory was designed with the goal of providing a suitable location for aberration-corrected electron microscopes. Construction methods and performance of the building are discussed in the context of the performance of the microscope. Initial performance of the microscope on relevant specimens and modifications made to eliminate resolution-limiting conditions are also discussed.

  4. Aberration correction of double-sided telecentric zoom lenses using lens modules.

    PubMed

    Zhang, Jinkai; Chen, Xiaobo; Xi, Juntong; Wu, Zhuoqi

    2014-09-20

    A systematic approach for the aberration design of a four-component double-sided telecentric zoom lens system is presented. The Gaussian structure of the zoom system is specified previously which means the powers and movements of components are known. Each component is treated as a lens module during the design stage with specified first-order properties and third-order aberration targets. The third-order aberration targets of the first component are determined by minimizing the whole aberrations of the zoom lens system using a genetic algorithm (GA). And the aberration targets of components behind are determined by reoptimization with already fixed structures of previous components. Mean pupil spherical aberration of every component in every zoom position is adopted in the objective function to control high-order aberrations. The thin lens structure of each component can be determined from their first-order properties and aberration targets. After lens thickening and reoptimization, the zoom lens system can finally be determined.

  5. A Novel Concept for a Deformable Membrane Mirror for Correction of Large Amplitude Aberrations

    NASA Technical Reports Server (NTRS)

    Moore, Jim; Patrick, Brian

    2006-01-01

    Very large, light weight mirrors are being developed for applications in space. Due to launch mass and volume restrictions these mirrors will need to be much more flexible than traditional optics. The use of primary mirrors with these characteristics will lead to requirements for adaptive optics capable of correcting wave front errors with large amplitude relatively low spatial frequency aberrations. The use of low modulus membrane mirrors actuated with electrostatic attraction forces is a potential solution for this application. Several different electrostatic membrane mirrors are now available commercially. However, as the dynamic range requirement of the adaptive mirror is increased the separation distance between the membrane and the electrodes must increase to accommodate the required face sheet deformations. The actuation force applied to the mirror decreases inversely proportional to the square of the separation distance; thus for large dynamic ranges the voltage requirement can rapidly increase into the high voltage regime. Experimentation with mirrors operating in the KV range has shown that at the higher voltages a serious problem with electrostatic field cross coupling between actuators can occur. Voltage changes on individual actuators affect the voltage of other actuators making the system very difficult to control. A novel solution has been proposed that combines high voltage electrodes with mechanical actuation to overcome this problem. In this design an array of electrodes are mounted to a backing structure via light weight large dynamic range flextensional actuators. With this design the control input becomes the separation distance between the electrode and the mirror. The voltage on each of the actuators is set to a uniform relatively high voltage, thus the problem of cross talk between actuators is avoided and the favorable distributed load characteristic of electrostatic actuation is retained. Initial testing and modeling of this concept

  6. Aberration correction for transcranial photoacoustic tomography of primates employing adjunct image data

    PubMed Central

    Huang, Chao; Schoonover, Robert W.; Guo, Zijian; Schirra, Carsten O.; Anastasio, Mark A.; Wang, Lihong V.

    2012-01-01

    Abstract. A challenge in photoacoustic tomography (PAT) brain imaging is to compensate for aberrations in the measured photoacoustic data due to their propagation through the skull. By use of information regarding the skull morphology and composition obtained from adjunct x-ray computed tomography image data, we developed a subject-specific imaging model that accounts for such aberrations. A time-reversal-based reconstruction algorithm was employed with this model for image reconstruction. The image reconstruction methodology was evaluated in experimental studies involving phantoms and monkey heads. The results establish that our reconstruction methodology can effectively compensate for skull-induced acoustic aberrations and improve image fidelity in transcranial PAT. PMID:22734772

  7. Parallel direct laser writing in three dimensions with spatially dependent aberration correction.

    PubMed

    Jesacher, Alexander; Booth, Martin J

    2010-09-27

    We propose a hologram design process which aims at reducing aberrations in parallel three-dimensional direct laser writing applications. One principle of the approach is to minimise the diffractive power of holograms while retaining the degree of parallelisation. This reduces focal distortion caused by chromatic aberration. We address associated problems such as the zero diffraction order and aberrations induced by a potential refractive index mismatch between the immersion medium of the microscope objective and the fabrication substrate. Results from fabrication in diamond, fused silica and lithium niobate are presented.

  8. Aberration correction for transcranial photoacoustic tomography of primates employing adjunct image data

    NASA Astrophysics Data System (ADS)

    Huang, Chao; Nie, Liming; Schoonover, Robert W.; Guo, Zijian; Schirra, Carsten O.; Anastasio, Mark A.; Wang, Lihong V.

    2012-06-01

    A challenge in photoacoustic tomography (PAT) brain imaging is to compensate for aberrations in the measured photoacoustic data due to their propagation through the skull. By use of information regarding the skull morphology and composition obtained from adjunct x-ray computed tomography image data, we developed a subject-specific imaging model that accounts for such aberrations. A time-reversal-based reconstruction algorithm was employed with this model for image reconstruction. The image reconstruction methodology was evaluated in experimental studies involving phantoms and monkey heads. The results establish that our reconstruction methodology can effectively compensate for skull-induced acoustic aberrations and improve image fidelity in transcranial PAT.

  9. Design and commissioning of an aberration-corrected ultrafast spin-polarized low energy electron microscope with multiple electron sources.

    PubMed

    Wan, Weishi; Yu, Lei; Zhu, Lin; Yang, Xiaodong; Wei, Zheng; Liu, Jefferson Zhe; Feng, Jun; Kunze, Kai; Schaff, Oliver; Tromp, Ruud; Tang, Wen-Xin

    2016-12-27

    We describe the design and commissioning of a novel aberration-corrected low energy electron microscope (AC-LEEM). A third magnetic prism array (MPA) is added to the standard AC-LEEM with two prism arrays, allowing the incorporation of an ultrafast spin-polarized electron source alongside the standard cold field emission electron source, without degrading spatial resolution. The high degree of symmetries of the AC-LEEM are utilized while we design the electron optics of the ultrafast spin-polarized electron source, so as to minimize the deleterious effect of time broadening, while maintaining full control of electron spin. A spatial resolution of 2nm and temporal resolution of 10ps (ps) are expected in the future time resolved aberration-corrected spin-polarized LEEM (TR-AC-SPLEEM). The commissioning of the three-prism AC-LEEM has been successfully finished with the cold field emission source, with a spatial resolution below 2nm.

  10. Aberration corrected 1.2-MV cold field-emission transmission electron microscope with a sub-50-pm resolution

    SciTech Connect

    Akashi, Tetsuya; Takahashi, Yoshio; Tanigaki, Toshiaki Shimakura, Tomokazu; Kawasaki, Takeshi; Furutsu, Tadao; Shinada, Hiroyuki; Osakabe, Nobuyuki; Müller, Heiko; Haider, Maximilian; Tonomura, Akira

    2015-02-16

    Atomic-resolution electromagnetic field observation is critical to the development of advanced materials and to the unveiling of their fundamental physics. For this purpose, a spherical-aberration corrected 1.2-MV cold field-emission transmission electron microscope has been developed. The microscope has the following superior properties: stabilized accelerating voltage, minimized electrical and mechanical fluctuation, and coherent electron emission. These properties have enabled to obtain 43-pm information transfer. On the bases of these performances, a 43-pm resolution has been obtained by correcting lens aberrations up to the third order. Observations of GaN [411] thin crystal showed a projected atomic locations with a separation of 44 pm.

  11. Custom photorefractive keratectomy ablations for the correction of spherical and cylindrical refractive error and higher-order aberration.

    PubMed

    Schwiegerling, J; Snyder, R W

    1998-09-01

    Photorefractive keratectomy is an evolving refractive procedure for correcting myopia, hyperopia, and astigmatism. Earlier descriptions of the patterns required for this surgery are based on paraxial optics. In this investigation the required pattern is generalized to account for spherical refractive error (defocus), axial astigmatism of arbitrary orientation, and fourth-order aberrations of the eye. The patterns described in this study can be used to customize photorefractive keratectomy and to provide corrections that account for aberration content as well as paraxial values. Furthermore, a description of the pattern along the boundary of the optical zone is given, which may prove useful in designing blending zones. An example of the use of these techniques is given for a schematic eye model.

  12. Multiple sextupole system for the correction of third and higher order aberration

    DOEpatents

    Crewe, Albert V.

    1983-01-01

    A means is provided for compensating for third and higher order aberration in charged particle beam devices. The means includes two sextupoles with an intermediate focusing lens, all positioned between two focusing lenses.

  13. Higher-order aberrations and best-corrected visual acuity in Native American children with a high prevalence of astigmatism

    PubMed Central

    Miller, Joseph M.; Harvey, Erin M.; Schwiegerling, Jim

    2016-01-01

    Purpose To determine whether higher-order aberrations (HOAs) in children from a highly astigmatic population differ from population norms and whether HOAs are associated with astigmatism and reduced best-corrected visual acuity. Methods Subjects were 218 Tohono O’odham Native American children 5–9 years of age. Noncycloplegic HOA measurements were obtained with a handheld Shack-Hartmann sensor (SHS). Signed (z06s to z14s) and unsigned (z06u to z14u) wavefront aberration Zernike coefficients Z(3,−3) to Z(4,4) were rescaled for a 4 mm diameter pupil and compared to adult population norms. Cycloplegic refraction and best-corrected logMAR letter visual acuity (BCVA) were also measured. Regression analyses assessed the contribution of astigmatism (J0) and HOAs to BCVA. Results The mean root-mean-square (RMS) HOA of 0.191 ± 0.072 μm was significantly greater than population norms (0.100 ± 0.044 μm. All unsigned HOA coefficients (z06u to z14u) and all signed coefficients except z09s, z10s, and z11s were significantly larger than population norms. Decreased BCVA was associated with astigmatism (J0) and spherical aberration (z12u) but not RMS coma, with the effect of J0 about 4 times as great as z12u. Conclusions Tohono O’odham children show elevated HOAs compared to population norms. Astigmatism and unsigned spherical aberration are associated with decreased acuity, but the effects of spherical aberration are minimal and not clinically significant. PMID:26239206

  14. Implementation of the near-field signal redundancy phase-aberration correction algorithm on two-dimensional arrays.

    PubMed

    Li, Yue; Robinson, Brent

    2007-01-01

    Near-field signal-redundancy (NFSR) algorithms for phase-aberration correction have been proposed and experimentally tested for linear and phased one-dimensional arrays. In this paper the performance of an all-row-plus-two-column, two-dimensional algorithm has been analyzed and tested with simulated data sets. This algorithm applies the NFSR algorithm for one-dimensional arrays to all the rows as well as the first and last columns of the array. The results from the two column measurements are used to derive a linear term for each row measurement result. These linear terms then are incorporated into the row results to obtain a two-dimensional phase aberration profile. The ambiguity phase aberration profile, which is the difference between the true and the derived phase aberration profiles, of this algorithm is not linear. Two methods, a trial-and-error method and a diagonal-measurement method, are proposed to linearize the ambiguity profile. The performance of these algorithms is analyzed and tested with simulated data sets.

  15. Dynamic optical aberration correction with adaptive coded apertures techniques in conformal imaging

    NASA Astrophysics Data System (ADS)

    Li, Yan; Hu, Bin; Zhang, Pengbin; Zhang, Binglong

    2015-02-01

    Conformal imaging systems are confronted with dynamic aberration in optical design processing. In classical optical designs, for combination high requirements of field of view, optical speed, environmental adaption and imaging quality, further enhancements can be achieved only by the introduction of increased complexity of aberration corrector. In recent years of computational imaging, the adaptive coded apertures techniques which has several potential advantages over more traditional optical systems is particularly suitable for military infrared imaging systems. The merits of this new concept include low mass, volume and moments of inertia, potentially lower costs, graceful failure modes, steerable fields of regard with no macroscopic moving parts. Example application for conformal imaging system design where the elements of a set of binary coded aperture masks are applied are optimization designed is presented in this paper, simulation results show that the optical performance is closely related to the mask design and the reconstruction algorithm optimization. As a dynamic aberration corrector, a binary-amplitude mask located at the aperture stop is optimized to mitigate dynamic optical aberrations when the field of regard changes and allow sufficient information to be recorded by the detector for the recovery of a sharp image using digital image restoration in conformal optical system.

  16. Comparison of analytical and numerical approaches for CT-based aberration correction in transcranial passive acoustic imaging

    NASA Astrophysics Data System (ADS)

    Jones, Ryan M.; Hynynen, Kullervo

    2016-01-01

    Computed tomography (CT)-based aberration corrections are employed in transcranial ultrasound both for therapy and imaging. In this study, analytical and numerical approaches for calculating aberration corrections based on CT data were compared, with a particular focus on their application to transcranial passive imaging. Two models were investigated: a three-dimensional full-wave numerical model (Connor and Hynynen 2004 IEEE Trans. Biomed. Eng. 51 1693-706) based on the Westervelt equation, and an analytical method (Clement and Hynynen 2002 Ultrasound Med. Biol. 28 617-24) similar to that currently employed by commercial brain therapy systems. Trans-skull time delay corrections calculated from each model were applied to data acquired by a sparse hemispherical (30 cm diameter) receiver array (128 piezoceramic discs: 2.5 mm diameter, 612 kHz center frequency) passively listening through ex vivo human skullcaps (n  =  4) to emissions from a narrow-band, fixed source emitter (1 mm diameter, 516 kHz center frequency). Measurements were taken at various locations within the cranial cavity by moving the source around the field using a three-axis positioning system. Images generated through passive beamforming using CT-based skull corrections were compared with those obtained through an invasive source-based approach, as well as images formed without skull corrections, using the main lobe volume, positional shift, peak sidelobe ratio, and image signal-to-noise ratio as metrics for image quality. For each CT-based model, corrections achieved by allowing for heterogeneous skull acoustical parameters in simulation outperformed the corresponding case where homogeneous parameters were assumed. Of the CT-based methods investigated, the full-wave model provided the best imaging results at the cost of computational complexity. These results highlight the importance of accurately modeling trans-skull propagation when calculating CT-based aberration corrections

  17. Magnitude of speed of sound aberration corrections for ultrasound image guided radiotherapy for prostate and other anatomical sites

    SciTech Connect

    Fontanarosa, Davide; Meer, Skadi van der; Bloemen-van Gurp, Esther; Stroian, Gabriela; Verhaegen, Frank

    2012-08-15

    Purpose: The purpose of this work is to assess the magnitude of speed of sound (SOS) aberrations in three-dimensional ultrasound (US) imaging systems in image guided radiotherapy. The discrepancy between the fixed SOS value of 1540 m/s assumed by US systems in human soft tissues and its actual nonhomogeneous distribution in patients produces small but systematic errors of up to a few millimeters in the positions of scanned structures. Methods: A correction, provided by a previously published density-based algorithm, was applied to a set of five prostate, five liver, and five breast cancer patients. The shifts of the centroids of target structures and the change in shape were evaluated. Results: After the correction the prostate cases showed shifts up to 3.6 mm toward the US probe, which may explain largely the reported positioning discrepancies in the literature on US systems versus other imaging modalities. Liver cases showed the largest changes in volume of the organ, up to almost 9%, and shifts of the centroids up to more than 6 mm either away or toward the US probe. Breast images showed systematic small shifts of the centroids toward the US probe with a maximum magnitude of 1.3 mm. Conclusions: The applied correction in prostate and liver cancer patients shows positioning errors of several mm due to SOS aberration; the errors are smaller in breast cancer cases, but possibly becoming more important when breast tissue thickness increases.

  18. First experimental proof for aberration correction in XPEEM: resolution, transmission enhancement, and limitation by space charge effects.

    PubMed

    Schmidt, Th; Sala, A; Marchetto, H; Umbach, E; Freund, H-J

    2013-03-01

    The positive effect of double aberration correction in x-ray induced Photoelectron Emission Microscopy (XPEEM) has been successfully demonstrated for both, the lateral resolution and the transmission, using the Au 4f XPS peak for element specific imaging at a kinetic energy of 113 eV. The lateral resolution is improved by a factor of four, compared to a non-corrected system, whereas the transmission is enhanced by a factor of 5 at a moderate resolution of 80 nm. With an optimized system setting, a lateral resolution of 18 nm could be achieved, which is up to now the best value reported for energy filtered XPEEM imaging. However, the absolute resolution does not yet reach the theoretical limit of 2 nm, which is due to space charge limitation. This occurs along the entire optical axis up to the contrast aperture. In XPEEM the pulsed time structure of the exciting soft x-ray light source causes a short and highly intense electron pulse, which results in an image blurring. In contrast, the imaging with elastically reflected electrons in the low energy electron microscopy (LEEM) mode yields a resolution clearly below 5 nm. Technical solutions to reduce the space charge effect in an aberration-corrected spectro-microscope are discussed.

  19. Characterization of durable nanostructured thin film catalysts tested under transient conditions using analytical aberration-corrected electron microscopy

    SciTech Connect

    Cullen, David A; More, Karren Leslie; Reeves, Kimberly Shawn; Vernstrom, George; Atanasoska, Liliana; Haugen, Gregory; Atanasoski, Radoslav

    2011-01-01

    The stability of Ru0.1Ir0.9 oxidation evolution reaction (OER) catalysts deposited on Pt-coated nanostructured thin films (NSTFs) has been investigated by aberration-corrected electron microscopy. Accelerated stress tests showed that the OER catalysts significantly improved the durability of the Pt under cell reversal conditions. High-resolution images of the end-of-life NSTFs showed significant Ir loss from the whisker surfaces, while no Pt loss was observed, indicating that the OER catalysts had protected the catalyst coated whisker surfaces from degradation.

  20. Multiphoton Fluorescence Microscopy with GRIN Objective Aberration Correction by Low Order Adaptive Optics

    PubMed Central

    Bortoletto, Favio; Bonoli, Carlotta; Panizzolo, Paolo; Ciubotaru, Catalin D.; Mammano, Fabio

    2011-01-01

    Graded Index (GRIN) rod microlenses are increasingly employed in the assembly of optical probes for microendoscopy applications. Confocal, two–photon and optical coherence tomography (OCT) based on GRIN optical probes permit in–vivo imaging with penetration depths into tissue up to the centimeter range. However, insertion of the probe can be complicated by the need of several alignment and focusing mechanisms along the optical path. Furthermore, resolution values are generally not limited by diffraction, but rather by optical aberrations within the endoscope probe and feeding optics. Here we describe a multiphoton confocal fluorescence imaging system equipped with a compact objective that incorporates a GRIN probe and requires no adjustment mechanisms. We minimized the effects of aberrations with optical compensation provided by a low–order electrostatic membrane mirror (EMM) inserted in the optical path of the confocal architecture, resulting in greatly enhanced image quality. PMID:21814575

  1. Resolution Improvement in Aberration-Corrected Low- Voltage TEM with Monochromator at 60 kV

    NASA Astrophysics Data System (ADS)

    Morishita, S.; Mukai, M.; Sasaki, T.; Suenaga, K.; Sawada, H.

    2015-10-01

    We have developed a low-voltage electron microscope equipped with a monochromator and Delta-type Cs correctors, which shows atomic resolution at accelerating voltages of 60, 30 and 15 kV. In theory, resolution of TEM images at 60 kV is severely affected by chromatic aberration, which is proven by our calculations of contrast transfer functions and multi-slice image simulation taking chromatic aberration into account with experimental conditions. Experimentally, TEM images of gold nano-particles were observed with non-monochromated and monochromated electron sources at 60 kV. Detectable spatial frequency in the image with the monochromated source was higher than that with non- monochromated source. We have demonstrated that the TEM image resolution at the low- voltage is improved by using a monochromated electron source, which reduce the energy spread of the electron source.

  2. Evaluating optical aberrations using fluorescent microspheres: methods, analysis, and corrective actions.

    PubMed

    Goodwin, Paul C

    2013-01-01

    Obtaining optimal performance from a microscopy system requires careful evaluation of the entire optics train of the imaging system. This evaluation starts with a fundamental evaluation of the optical components in the microscope. Concise and visual methods are provided for understanding the optical performance of the microscope as a system using subdiffraction fluorescent microspheres to evaluate both monochromatic and polychromatic aberrations. Further practical guides are given to troubleshooting optical problems and final comments are made on optimizing sample preparation.

  3. Spindle checkpoint protein Bub1 corrects mitotic aberrancy induced by human T-cell leukemia virus type I Tax.

    PubMed

    Sasaki, M; Sugimoto, K; Tamayose, K; Ando, M; Tanaka, Y; Oshimi, K

    2006-06-22

    Bub1 is a component of the mitotic spindle checkpoint apparatus. Abnormality of this apparatus is known to cause multinuclei formation, a hallmark of chromosomal instability (CIN). A549, aneuploid cell line, aberrantly passed through the mitotic phase and became multinuclei morphology in the presence of nocodazole. Time-lapse videomicroscopy showed unreported bizarre morphology, which we named 'mitotic lobulation' in A549 cells just before the exit from mitosis and multinuclei formation. External expression of wild-type Bub1-EGFP clearly suppressed the multinuclei formation by retaining A549 cells at the mitotic phase during 48 h of time-lapse observation. This suppressive effect on mitotic aberrancy should not be mere restoration of normal Bub1 function, because A549 cells express proper amount of Bub1, which distributed cytoplasm during interphase and concentrated at kinetochore in metaphase. Furthermore, external expression of wild-type Bub1-EGFP suppressed multinuclei formation induced by Tax both in A549 and HeLa cells. Tax is known to induce mitotic abnormality by binding and inactivating Mad1. These observations, therefore, suggest functional redundancy between Bub1 and other mitotic checkpoint protein(s) and a possibility of correction of mitotic aberrancy by external Bub1 expression.

  4. Pupil-phase optimization for extended-focus, aberration-corrected imaging systems

    NASA Astrophysics Data System (ADS)

    Prasad, Sudhakar; Pauca, V. Paul; Plemmons, Robert J.; Torgersen, Todd C.; van der Gracht, Joseph

    2004-10-01

    The insertion of a suitably designed phase plate in the pupil of an imaging system makes it possible to encode the depth dimension of an extended three-dimensional scene by means of an approximately shift-invariant PSF. The so-encoded image can then be deblurred digitally by standard image recovery algorithms to recoup the depth dependent detail of the original scene. A similar strategy can be adopted to compensate for certain monochromatic aberrations of the system. Here we consider two approaches to optimizing the design of the phase plate that are somewhat complementary - one based on Fisher information that attempts to reduce the sensitivity of the phase encoded image to misfocus and the other based on a minimax formulation of the sum of singular values of the system blurring matrix that attempts to maximize the resolution in the final image. Comparisons of these two optimization approaches are discussed. Our preliminary demonstration of the use of such pupil-phase engineering to successfully control system aberrations, particularly spherical aberration, is also presented.

  5. Full correction for spatially distributed speed-of-sound in echo ultrasound based on measuring aberration delays via transmit beam steering

    NASA Astrophysics Data System (ADS)

    Jaeger, Michael; Robinson, Elise; Günhan Akarçay, H.; Frenz, Martin

    2015-06-01

    Aberrations of the acoustic wave front, caused by spatial variations of the speed-of-sound, are a main limiting factor to the diagnostic power of medical ultrasound imaging. If not accounted for, aberrations result in low resolution and increased side lobe level, over all reducing contrast in deep tissue imaging. Various techniques have been proposed for quantifying aberrations by analysing the arrival time of coherent echoes from so-called guide stars or beacons. In situations where a guide star is missing, aperture-based techniques may give ambiguous results. Moreover, they are conceptually focused on aberrators that can be approximated as a phase screen in front of the probe. We propose a novel technique, where the effect of aberration is detected in the reconstructed image as opposed to the aperture data. The varying local echo phase when changing the transmit beam steering angle directly reflects the varying arrival time of the transmit wave front. This allows sensing the angle-dependent aberration delay in a spatially resolved way, and thus aberration correction for a spatially distributed volume aberrator. In phantoms containing a cylindrical aberrator, we achieved location-independent diffraction-limited resolution as well as accurate display of echo location based on reconstructing the speed-of-sound spatially resolved. First successful volunteer results confirm the clinical potential of the proposed technique.

  6. MAGNETIC LIQUID DEFORMABLE MIRRORS FOR ASTRONOMICAL APPLICATIONS: ACTIVE CORRECTION OF OPTICAL ABERRATIONS FROM LOWER-GRADE OPTICS AND SUPPORT SYSTEM

    SciTech Connect

    Borra, E. F.

    2012-08-01

    Deformable mirrors are increasingly used in astronomy. However, they still are limited in stroke for active correction of high-amplitude optical aberrations. Magnetic liquid deformable mirrors (MLDMs) are a new technology that has the advantages of high-amplitude deformations and low costs. In this paper, we demonstrate extremely high strokes and interactuator strokes achievable by MLDMs which can be used in astronomical instrumentation. In particular, we consider the use of such a mirror to suggest an interesting application for the next generation of large telescopes. We present a prototype 91 actuator deformable mirror made of a magnetic liquid (ferrofluid). This mirror uses a technique that linearizes the response of such mirrors by superimposing a large and uniform magnetic field on the magnetic field produced by an array of small coils. We discuss experimental results that illustrate the performance of MLDMs. A most interesting application of MLDMs comes from the fact they could be used to correct the aberrations of large and lower optical quality primary mirrors held by simple support systems. We estimate basic parameters of the needed MLDMs, obtaining reasonable values.

  7. Transcranial passive acoustic mapping with hemispherical sparse arrays using CT-based skull-specific aberration corrections: a simulation study.

    PubMed

    Jones, Ryan M; O'Reilly, Meaghan A; Hynynen, Kullervo

    2013-07-21

    The feasibility of transcranial passive acoustic mapping with hemispherical sparse arrays (30 cm diameter, 16 to 1372 elements, 2.48 mm receiver diameter) using CT-based aberration corrections was investigated via numerical simulations. A multi-layered ray acoustic transcranial ultrasound propagation model based on CT-derived skull morphology was developed. By incorporating skull-specific aberration corrections into a conventional passive beamforming algorithm (Norton and Won 2000 IEEE Trans. Geosci. Remote Sens. 38 1337-43), simulated acoustic source fields representing the emissions from acoustically-stimulated microbubbles were spatially mapped through three digitized human skulls, with the transskull reconstructions closely matching the water-path control images. Image quality was quantified based on main lobe beamwidths, peak sidelobe ratio, and image signal-to-noise ratio. The effects on the resulting image quality of the source's emission frequency and location within the skull cavity, the array sparsity and element configuration, the receiver element sensitivity, and the specific skull morphology were all investigated. The system's resolution capabilities were also estimated for various degrees of array sparsity. Passive imaging of acoustic sources through an intact skull was shown possible with sparse hemispherical imaging arrays. This technique may be useful for the monitoring and control of transcranial focused ultrasound (FUS) treatments, particularly non-thermal, cavitation-mediated applications such as FUS-induced blood-brain barrier disruption or sonothrombolysis, for which no real-time monitoring techniques currently exist.

  8. Evolution of gold structure during thermal treatment of Au/FeOx catalysts revealed by aberration-corrected electron microscopy.

    PubMed

    Allard, Lawrence F; Borisevich, Albina; Deng, Weiling; Si, Rui; Flytzani-Stephanopoulos, Maria; Overbury, Steven H

    2009-06-01

    High-resolution aberration-corrected electron microscopy was performed on a series of catalysts derived from a parent material, 2 at.% Au/Fe(2)O(3) (WGC ref. no. 60C), prepared by co-precipitation and calcined in air at 400 degrees C, and a catalyst prepared by leaching surface gold from the parent catalyst and exposed to various treatments, including use in the water-gas shift reaction at 250 degrees C. Aberration-corrected JEOL 2200FS (JEOL USA, Peabody, MA) and Vacuum Generators HB-603U STEM instruments were used to image fresh, reduced, leached, used and re-oxidized catalyst samples. A new in situ heating technology (Protochips Inc., Raleigh, NC, USA), which permits full sub-Angström imaging resolution in the JEOL 2200FS was used to study the effects of temperature on the behavior of gold species. A remarkable stability of gold to redox treatments up to 400 degrees C, with atomic gold decorating step surfaces of iron oxide was identified. On heating the samples in vacuum to 700 degrees C, it was found that monodispersed gold began to sinter to form nanoparticles above 500 degrees C. Gold species internal to the iron oxide support material was shown to diffuse to the surface at elevated temperature, coalescing into discrete nanocrystals. The results demonstrate the value of in situ heating for understanding morphological changes in the catalyst with elevated temperature treatments.

  9. Transcranial passive acoustic mapping with hemispherical sparse arrays using CT-based skull-specific aberration corrections: a simulation study

    PubMed Central

    Jones, Ryan M.; O’Reilly, Meaghan A.; Hynynen, Kullervo

    2013-01-01

    The feasibility of transcranial passive acoustic mapping with hemispherical sparse arrays (30 cm diameter, 16 to 1372 elements, 2.48 mm receiver diameter) using CT-based aberration corrections was investigated via numerical simulations. A multi-layered ray acoustic transcranial ultrasound propagation model based on CT-derived skull morphology was developed. By incorporating skull-specific aberration corrections into a conventional passive beamforming algorithm (Norton and Won 2000 IEEE Trans. Geosci. Remote Sens. 38 1337–43), simulated acoustic source fields representing the emissions from acoustically-stimulated microbubbles were spatially mapped through three digitized human skulls, with the transskull reconstructions closely matching the water-path control images. Image quality was quantified based on main lobe beamwidths, peak sidelobe ratio, and image signal-to-noise ratio. The effects on the resulting image quality of the source’s emission frequency and location within the skull cavity, the array sparsity and element configuration, the receiver element sensitivity, and the specific skull morphology were all investigated. The system’s resolution capabilities were also estimated for various degrees of array sparsity. Passive imaging of acoustic sources through an intact skull was shown possible with sparse hemispherical imaging arrays. This technique may be useful for the monitoring and control of transcranial focused ultrasound (FUS) treatments, particularly non-thermal, cavitation-mediated applications such as FUS-induced blood-brain barrier disruption or sonothrombolysis, for which no real-time monitoring technique currently exists. PMID:23807573

  10. Transcranial passive acoustic mapping with hemispherical sparse arrays using CT-based skull-specific aberration corrections: a simulation study

    NASA Astrophysics Data System (ADS)

    Jones, Ryan M.; O'Reilly, Meaghan A.; Hynynen, Kullervo

    2013-07-01

    The feasibility of transcranial passive acoustic mapping with hemispherical sparse arrays (30 cm diameter, 16 to 1372 elements, 2.48 mm receiver diameter) using CT-based aberration corrections was investigated via numerical simulations. A multi-layered ray acoustic transcranial ultrasound propagation model based on CT-derived skull morphology was developed. By incorporating skull-specific aberration corrections into a conventional passive beamforming algorithm (Norton and Won 2000 IEEE Trans. Geosci. Remote Sens. 38 1337-43), simulated acoustic source fields representing the emissions from acoustically-stimulated microbubbles were spatially mapped through three digitized human skulls, with the transskull reconstructions closely matching the water-path control images. Image quality was quantified based on main lobe beamwidths, peak sidelobe ratio, and image signal-to-noise ratio. The effects on the resulting image quality of the source’s emission frequency and location within the skull cavity, the array sparsity and element configuration, the receiver element sensitivity, and the specific skull morphology were all investigated. The system’s resolution capabilities were also estimated for various degrees of array sparsity. Passive imaging of acoustic sources through an intact skull was shown possible with sparse hemispherical imaging arrays. This technique may be useful for the monitoring and control of transcranial focused ultrasound (FUS) treatments, particularly non-thermal, cavitation-mediated applications such as FUS-induced blood-brain barrier disruption or sonothrombolysis, for which no real-time monitoring techniques currently exist.

  11. Correcting lateral chromatic aberrations in non-monochromatic X-ray microscopy

    NASA Astrophysics Data System (ADS)

    Falch, Ken Vidar; Detlefs, Carsten; Di Michiel, Marco; Snigireva, Irina; Snigirev, Anatoly; Mathiesen, Ragnvald H.

    2016-08-01

    Lateral chromatic aberration in microscopy based on refractive optics may be reduced significantly by adjustments to the illumination scheme. By taking advantage of a broadened bandwidth illumination, the proposed scheme could open for x-ray microscopy with spatial resolution in the range 150-200 nm at millisecond frame rates. The scheme is readily implemented and is achievable using only standard refractive x-ray lenses, which has the advantage of high efficiency. It also maximizes the transmission and removes the spatial filtering effects associated with absorption in x-ray lenses.

  12. Practical correction of a phase-aberrated laser beam using a triphenyldiamine-based photorefractive composite

    NASA Astrophysics Data System (ADS)

    Liang, Yichen; Winiarz, Jeffrey G.

    2017-03-01

    A photorefractive composite based on a triphenyldiamine (TPD) derivative was used to restore a severely phase-aberrated laser beam to a nearly aberration-free state. Here, a forward degenerate four-wave mixing geometry was employed for the elimination of phase distortions and its practical applicability in the transmission of optically encoded data is demonstrated. In addition, it is demonstrated that the experimental geometry is able to effectively restore dynamically updating images. Conventional two-beam coupling and degenerate four-wave mixing experiments were used to characterize the composite subject to the current experimental setup. The two-beam coupling net gain coefficient was 100 cm-1 with an applied external electric field of 70 V/µm. Internal and external diffraction efficiencies of 10 and 6%, respectively, were observed with a similar external electric field. Due to its superior charge-carrier mobility, the TPD-based composite exhibited a response time of 0.28 s, approximately five times faster than traditional PVK-based composites.

  13. Correcting spherical aberrations in a biospecimen using a transmissive liquid crystal device in two-photon excitation laser scanning microscopy

    NASA Astrophysics Data System (ADS)

    Tanabe, Ayano; Hibi, Terumasa; Ipponjima, Sari; Matsumoto, Kenji; Yokoyama, Masafumi; Kurihara, Makoto; Hashimoto, Nobuyuki; Nemoto, Tomomi

    2015-10-01

    Two-photon excitation laser scanning microscopy has enabled the visualization of deep regions in a biospecimen. However, refractive-index mismatches in the optical path cause spherical aberrations that degrade spatial resolution and the fluorescence signal, especially during observation at deeper regions. Recently, we developed transmissive liquid-crystal devices for correcting spherical aberration without changing the basic design of the optical path in a conventional laser scanning microscope. In this study, the device was inserted in front of the objective lens and supplied with the appropriate voltage according to the observation depth. First, we evaluated the device by observing fluorescent beads in single- and two-photon excitation laser scanning microscopes. Using a 25× water-immersion objective lens with a numerical aperture of 1.1 and a sample with a refractive index of 1.38, the device recovered the spatial resolution and the fluorescence signal degraded within a depth of ±0.6 mm. Finally, we implemented the device for observation of a mouse brain slice in a two-photon excitation laser scanning microscope. An optical clearing reagent with a refractive index of 1.42 rendered the fixed mouse brain transparent. The device improved the spatial resolution and the yellow fluorescent protein signal within a depth of 0-0.54 mm.

  14. Chromatic aberration-corrected tilt series transmission electron microscopy of nanoparticles in a whole mount macrophage cell.

    PubMed

    Baudoin, Jean-Pierre; Jinschek, Joerg R; Boothroyd, Chris B; Dunin-Borkowski, Rafal E; de Jonge, Niels

    2013-08-01

    Transmission electron microscopy (TEM) in combination with electron tomography is widely used to obtain nanometer scale three-dimensional (3D) structural information about biological samples. However, studies of whole eukaryotic cells are limited in resolution and/or contrast on account of the effect of chromatic aberration of the TEM objective lens on electrons that have been scattered inelastically in the specimen. As a result, 3D information is usually obtained from sections and not from whole cells. Here, we use chromatic aberration-corrected TEM to record bright-field TEM images of nanoparticles in a whole mount macrophage cell. Tilt series of images are used to generate electron tomograms, which are analyzed to assess the spatial resolution that can be achieved for different vertical positions in the specimen. The uptake of gold nanoparticles coated with low-density lipoprotein (LDL) is studied. The LDL is found to assemble in clusters. The clusters contain nanoparticles taken up on different days, which are joined without mixing their nanoparticle cargo.

  15. The Stanford Nanocharacterization Laboratory (SNL) and Recent Applications of an Aberration-Corrected Environmental Transmission Electron Microscope.

    PubMed

    Sinclair, Robert; Kempen, Paul Joseph; Chin, Richard; Koh, Ai Leen

    2014-05-01

    This article describes the establishment, over a period of ten years or so, of a multi-user, institution-wide facility for the characterization of materials and devices at the nano-scale. Emphasis is placed on the type of equipment that we have found to be most useful for our users, and the business strategy that maintains its operations. A central component of our facility is an aberration-corrected environmental transmission electron microscope and its application is summarized in the studies of plasmon energies of silver nanoparticles, the band gap of PbS quantum dots, atomic site occupancy near grain boundaries in yttria stabilized zirconia, the lithiation of silicon nanoparticles, in situ observations on carbon nanotube oxidation and the electron tomography of varicella zoster virus nucleocapsids.

  16. The Stanford Nanocharacterization Laboratory (SNL) and Recent Applications of an Aberration-Corrected Environmental Transmission Electron Microscope**

    PubMed Central

    Sinclair, Robert; Kempen, Paul Joseph; Chin, Richard; Koh, Ai Leen

    2014-01-01

    This article describes the establishment, over a period of ten years or so, of a multi-user, institution-wide facility for the characterization of materials and devices at the nano-scale. Emphasis is placed on the type of equipment that we have found to be most useful for our users, and the business strategy that maintains its operations. A central component of our facility is an aberration-corrected environmental transmission electron microscope and its application is summarized in the studies of plasmon energies of silver nanoparticles, the band gap of PbS quantum dots, atomic site occupancy near grain boundaries in yttria stabilized zirconia, the lithiation of silicon nanoparticles, in situ observations on carbon nanotube oxidation and the electron tomography of varicella zoster virus nucleocapsids. PMID:25364299

  17. Direct measurement of precipitate induced strain in an Al-Zn-Mg-Cu alloy with aberration corrected transmission electron microscopy.

    PubMed

    Ying, X R; Du, Y X; Song, M; Lu, N; Ye, H Q

    2016-11-01

    Precipitates and their associated strain fields significantly influence mechanical properties and, consequently, the industrial performance of aluminum alloys. In this work, we present a direct measurement of strains induced by η' and η precipitates in an Al-Zn-Mg-Cu alloy using aberration-corrected high-resolution transmission electron microscopy and quantitative strain analysis. The results demonstrate that the strain induced by precipitates in the Al-Zn-Mg-Cu alloy shows significant tensile strains perpendicular to the longitudinal direction of the precipitate discs on the side of the discs and along the longitudinal direction at both ends of the η' and η precipitates. This strain field can be described by an equivalent dislocation model, in which the lattice mismatch between the precipitate and the matrix is equivalent to a series of dislocation pairs along the precipitate/matrix interfaces.

  18. Controlled polarity of sputter-deposited aluminum nitride on metals observed by aberration corrected scanning transmission electron microscopy

    SciTech Connect

    Harumoto, T.; Sannomiya, T.; Matsukawa, Y.; Muraishi, S.; Shi, J.; Nakamura, Y.; Sawada, H.; Tanaka, T.; Tanishiro, Y.; Takayanagi, K.

    2013-02-28

    The polarity determination process of sputter-deposited aluminum nitride (AlN) on metals has been analyzed using aberration corrected atomic resolution scanning transmission electron microscope. Direct growth of c-axis orientated AlN on face centered cubic metals (fcc) (111) with the local epitaxy has been observed, and the polarity was determined at the AlN/metal interface. We found that the AlN polarity can be controlled by the base metal layer: N-polarity AlN grows on Pt(111) while Al-polarity AlN forms on Al(111). Based on these results, the growth mechanism of AlN on metals is discussed.

  19. The influence of the sample thickness on the lateral and axial resolution of aberration-corrected scanning transmission electron microscopy.

    PubMed

    Ramachandra, Ranjan; Demers, Hendrix; de Jonge, Niels

    2013-02-01

    The lateral and axial resolution of three-dimensional (3D) focal series aberration-corrected scanning transmission electron microscopy was studied for samples of different thicknesses. The samples consisted of gold nanoparticles placed on the top and at the bottom of silicon nitride membranes of thickness between 50 and 500 nm. Atomic resolution was obtained for nanoparticles on top of 50-, 100-, and 200-nm-thick membranes with respect to the electron beam traveling downward. Atomic resolution was also achieved for nanoparticles placed below 50-, 100-, and 200-nm-thick membranes but with a lower contrast at the larger thicknesses. Beam broadening led to a reduced resolution for a 500-nm-thick membrane. The influence of the beam broadening on the axial resolution was also studied using Monte Carlo simulations with a 3D sample geometry.

  20. Compositional analysis with atomic column spatial resolution by 5th-order aberration-corrected scanning transmission electron microscopy.

    PubMed

    Hernández-Maldonado, David; Herrera, Miriam; Alonso-González, Pablo; González, Yolanda; González, Luisa; Gazquez, Jaume; Varela, María; Pennycook, Stephen J; Guerrero-Lebrero, María de la Paz; Pizarro, Joaquín; Galindo, Pedro L; Molina, Sergio I

    2011-08-01

    We show in this article that it is possible to obtain elemental compositional maps and profiles with atomic-column resolution across an InxGa1-xAs multilayer structure from 5th-order aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images. The compositional profiles obtained from the analysis of HAADF-STEM images describe accurately the distribution of In in the studied multilayer in good agreement with Muraki's segregation model [Muraki, K., Fukatsu, S., Shiraki, Y. & Ito, R. (1992). Surface segregation of In atoms during molecular beam epitaxy and its influence on the energy levels in InGaAs/GaAs quantums wells. Appl Phys Lett 61, 557-559].

  1. Atomic resolution imaging of YAlO3: Ce in the chromatic and spherical aberration corrected PICO electron microscope.

    PubMed

    Jin, Lei; Barthel, Juri; Jia, Chun-Lin; Urban, Knut W

    2017-01-31

    The application of combined chromatic and spherical aberration correction in high-resolution transmission electron microscopy enables a significant improvement of the spatial resolution down to 50 pm. We demonstrate that such a resolution can be achieved in practice at 200kV. Diffractograms of images of gold nanoparticles on amorphous carbon demonstrate corresponding information transfer. The Y atom pairs in [010] oriented yttrium orthoaluminate are successfully imaged together with the Al and the O atoms. Although the 57 pm pair separation is well demonstrated separations between 55 pm and 80 pm are measured. This observation is tentatively attributed to structural relaxations and surface reconstruction in the very thin samples used. Quantification of the resolution limiting effective image spread is achieved based on an absolute match between experimental and simulated image intensity distributions.

  2. Letter: A method for the chromatic aberration correction of a laser time of-flight mass analyzer.

    PubMed

    Sysoeva, Elizaveta A; Sysoev, Alexander A

    2016-01-01

    The new ion-optical system of the laser time-of-flight (TOF) mass spectrometer on the basis of two tandem wedge-shape reflectors has been offered and implemented. A new method of correcting chromatic aberration by the ion energy was proposed that used a wire electrode unit with adjustable potentials. This unit allows one to adjust the local TOF of the ions in a narrow energy range ± (1-2)% within the total ion packet with an energy spread of ± 20%. The method reduces the duration of the ion packets by up to 1.5ns, which enables us to obtain the restriction of resolution at a level not worse than R ~ 10500 for a TOF ~35 µs. The aim of the project is to increase the separation of isobaric ions to improve the limit of detection of the laser TOF-MS for the analysis of high-purity samples.

  3. High-energy-resolution monochromator for aberration-corrected scanning transmission electron microscopy/electron energy-loss spectroscopy.

    PubMed

    Krivanek, Ondrej L; Ursin, Jonathan P; Bacon, Neil J; Corbin, George J; Dellby, Niklas; Hrncirik, Petr; Murfitt, Matthew F; Own, Christopher S; Szilagyi, Zoltan S

    2009-09-28

    An all-magnetic monochromator/spectrometer system for sub-30 meV energy-resolution electron energy-loss spectroscopy in the scanning transmission electron microscope is described. It will link the energy being selected by the monochromator to the energy being analysed by the spectrometer, without resorting to decelerating the electron beam. This will allow it to attain spectral energy stability comparable to systems using monochromators and spectrometers that are raised to near the high voltage of the instrument. It will also be able to correct the chromatic aberration of the probe-forming column. It should be able to provide variable energy resolution down to approximately 10 meV and spatial resolution less than 1 A.

  4. Correcting field-dependent aberrations with nanoscale accuracy in three-dimensional single-molecule localization microscopy

    PubMed Central

    von Diezmann, Alex; Lee, Maurice Y.; Lew, Matthew D.; Moerner, W. E.

    2016-01-01

    The localization of single fluorescent molecules enables the imaging of molecular structure and dynamics with subdiffraction precision and can be extended to three dimensions using point spread function (PSF) engineering. However, the nanoscale accuracy of localization throughout a 3D single-molecule microscope’s field of view has not yet been rigorously examined. By using regularly spaced subdiffraction apertures filled with fluorescent dyes, we reveal field-dependent aberrations as large as 50–100 nm and show that they can be corrected to less than 25 nm over an extended 3D focal volume. We demonstrate the applicability of this technique for two engineered PSFs, the double-helix PSF and the astigmatic PSF. We expect these results to be broadly applicable to 3D single-molecule tracking and superresolution methods demanding high accuracy. PMID:26973863

  5. Anisotropic aberration correction using region of interest based digital adaptive optics in Fourier domain OCT.

    PubMed

    Kumar, Abhishek; Kamali, Tschackad; Platzer, René; Unterhuber, Angelika; Drexler, Wolfgang; Leitgeb, Rainer A

    2015-04-01

    In this paper a numerical technique is presented to compensate for anisotropic optical aberrations, which are usually present across the lateral field of view in the out of focus regions, in high resolution optical coherence tomography and microscopy (OCT/OCM) setups. The recorded enface image field at different depths in the tomogram is digitally divided into smaller sub-regions or the regions of interest (ROIs), processed individually using subaperture based digital adaptive optics (DAO), and finally stitched together to yield a final image with a uniform diffraction limited resolution across the entire field of view (FOV). Using this method, a sub-micron lateral resolution is achieved over a depth range of 218 [Formula: see text]for a nano-particle phantom sample imaged using a fiber based point scanning spectral domain (SD) OCM system with a limited depth of focus (DOF) of ~7 [Formula: see text]at a numerical aperture (NA) of 0.6. Thus, an increase in DOF by ~30x is demonstrated in this case. The application of this method is also shown in ex vivo mouse adipose tissue.

  6. Anisotropic aberration correction using region of interest based digital adaptive optics in Fourier domain OCT

    PubMed Central

    Kumar, Abhishek; Kamali, Tschackad; Platzer, René; Unterhuber, Angelika; Drexler, Wolfgang; Leitgeb, Rainer A.

    2015-01-01

    In this paper a numerical technique is presented to compensate for anisotropic optical aberrations, which are usually present across the lateral field of view in the out of focus regions, in high resolution optical coherence tomography and microscopy (OCT/OCM) setups. The recorded enface image field at different depths in the tomogram is digitally divided into smaller sub-regions or the regions of interest (ROIs), processed individually using subaperture based digital adaptive optics (DAO), and finally stitched together to yield a final image with a uniform diffraction limited resolution across the entire field of view (FOV). Using this method, a sub-micron lateral resolution is achieved over a depth range of 218 μmfor a nano-particle phantom sample imaged using a fiber based point scanning spectral domain (SD) OCM system with a limited depth of focus (DOF) of ~7 μmat a numerical aperture (NA) of 0.6. Thus, an increase in DOF by ~30x is demonstrated in this case. The application of this method is also shown in ex vivo mouse adipose tissue. PMID:25908999

  7. Aberration-corrected scanning transmission electron microscopy for complex transition metal oxides

    NASA Astrophysics Data System (ADS)

    Qing-Hua, Zhang; Dong-Dong, Xiao; Lin, Gu

    2016-06-01

    Lattice, charge, orbital, and spin are the four fundamental degrees of freedom in condensed matter, of which the interactive coupling derives tremendous novel physical phenomena, such as high-temperature superconductivity (high-T c SC) and colossal magnetoresistance (CMR) in strongly correlated electronic system. Direct experimental observation of these freedoms is essential to understanding the structure-property relationship and the physics behind it, and also indispensable for designing new materials and devices. Scanning transmission electron microscopy (STEM) integrating multiple techniques of structure imaging and spectrum analysis, is a comprehensive platform for providing structural, chemical and electronic information of materials with a high spatial resolution. Benefiting from the development of aberration correctors, STEM has taken a big breakthrough towards sub-angstrom resolution in last decade and always steps forward to improve the capability of material characterization; many improvements have been achieved in recent years, thereby giving an in-depth insight into material research. Here, we present a brief review of the recent advances of STEM by some representative examples of perovskite transition metal oxides; atomic-scale mapping of ferroelectric polarization, octahedral distortions and rotations, valence state, coordination and spin ordering are presented. We expect that this brief introduction about the current capability of STEM could facilitate the understanding of the relationship between functional properties and these fundamental degrees of freedom in complex oxides. Project supported by the National Key Basic Research Project, China (Grant No. 2014CB921002), the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB07030200), and the National Natural Science Foundation of China (Grant Nos. 51522212 and 51421002).

  8. Three-dimensional transcranial ultrasound imaging with bilateral phase aberration correction of multiple isoplanatic patches: A pilot human study with microbubble contrast enhancement

    PubMed Central

    Lindsey, Brooks D.; Nicoletto, Heather A.; Bennett, Ellen R.; Laskowitz, Daniel T.; Smith, Stephen W.

    2013-01-01

    With stroke currently the second-leading cause of death globally, and 87% of all strokes classified as ischemic, the development of a fast, accessible, cost-effective approach for imaging occlusive stroke could have a significant impact on healthcare outcomes and costs. While clinical examination and standard CT alone do not provide adequate information for understanding the complex temporal events that occur during an ischemic stroke, ultrasound imaging is well-suited to the task of examining blood flow dynamics in real-time and may allow for localization of a clot. A prototype bilateral 3D ultrasound imaging system utilizing two matrix array probes on either side of the head allows for correction of skull-induced aberration throughout two entire phased array imaging volumes. We investigated the feasibility of applying this custom correction technique in 5 healthy volunteers with Definity® microbubble contrast enhancement. Subjects were scanned simultaneously via both temporal acoustic windows in 3D color flow mode. The number of color flow voxels above a common threshold increased due to aberration correction in 5/5 subjects, with a mean increase of 33.9%. The percentage of large arteries visualized in 3D color Doppler imaging increased from 46% without aberration correction to 60% with aberration correction. PMID:24239360

  9. 3-D transcranial ultrasound imaging with bilateral phase aberration correction of multiple isoplanatic patches: a pilot human study with microbubble contrast enhancement.

    PubMed

    Lindsey, Brooks D; Nicoletto, Heather A; Bennett, Ellen R; Laskowitz, Daniel T; Smith, Stephen W

    2014-01-01

    With stroke currently the second-leading cause of death globally, and 87% of all strokes classified as ischemic, the development of a fast, accessible, cost-effective approach for imaging occlusive stroke could have a significant impact on health care outcomes and costs. Although clinical examination and standard computed tomography alone do not provide adequate information for understanding the complex temporal events that occur during an ischemic stroke, ultrasound imaging is well suited to the task of examining blood flow dynamics in real time and may allow for localization of a clot. A prototype bilateral 3-D ultrasound imaging system using two matrix array probes on either side of the head allows for correction of skull-induced aberration throughout two entire phased array imaging volumes. We investigated the feasibility of applying this custom correction technique in five healthy volunteers with Definity microbubble contrast enhancement. Subjects were scanned simultaneously via both temporal acoustic windows in 3-D color flow mode. The number of color flow voxels above a common threshold increased as a result of aberration correction in five of five subjects, with a mean increase of 33.9%. The percentage of large arteries visualized by 3-D color Doppler imaging increased from 46% without aberration correction to 60% with aberration correction.

  10. A speed of sound aberration correction algorithm for curvilinear ultrasound transducers in ultrasound-based image-guided radiotherapy.

    PubMed

    Fontanarosa, Davide; Pesente, Silvia; Pascoli, Francesco; Ermacora, Denis; Rumeileh, Imad Abu; Verhaegen, Frank

    2013-03-07

    Conventional ultrasound (US) devices use the time of flight (TOF) of reflected US pulses to calculate distances inside the scanned tissues and thus create images. The speed of sound (SOS) is assumed to be constant in all human soft tissues at a generally accepted average value of 1540 m s(-1). This assumption is a source of systematic errors up to several millimeters and of image distortion in quantitative US imaging. In this work, an extension of a method recently published by Fontanarosa et al (2011 Med. Phys. 38 2665-73) is presented: the aim is to correct SOS aberrations in three-dimensional (3D) US images in those cases where a spatially co-registered computerized tomography (CT) scan is also available; the algorithm is then applicable to a more general case where the lines of view (LOV) of the US device are not necessarily parallel and coplanar, thus allowing correction also for US transducers other than linear. The algorithm was applied on a multi-modality pelvic US phantom, scanned through three different liquid layers on top of the phantom with different SOS values; the results show that the correction restores a better match between the CT and the US images, reducing the differences to sub-millimeter agreement. Fifteen clinical cases of prostate cancer patients were also investigated: the SOS corrections of prostate centroids were on average +3.1 mm (max + 4.9 mm-min + 1.3 mm). This is in excellent agreement with reports in the literature on differences between measured prostate positions by US and other techniques, where often the discrepancy was attributed to other causes.

  11. A speed of sound aberration correction algorithm for curvilinear ultrasound transducers in ultrasound-based image-guided radiotherapy

    NASA Astrophysics Data System (ADS)

    Fontanarosa, Davide; Pesente, Silvia; Pascoli, Francesco; Ermacora, Denis; Abu Rumeileh, Imad; Verhaegen, Frank

    2013-03-01

    Conventional ultrasound (US) devices use the time of flight (TOF) of reflected US pulses to calculate distances inside the scanned tissues and thus create images. The speed of sound (SOS) is assumed to be constant in all human soft tissues at a generally accepted average value of 1540 m s-1. This assumption is a source of systematic errors up to several millimeters and of image distortion in quantitative US imaging. In this work, an extension of a method recently published by Fontanarosa et al (2011 Med. Phys. 38 2665-73) is presented: the aim is to correct SOS aberrations in three-dimensional (3D) US images in those cases where a spatially co-registered computerized tomography (CT) scan is also available; the algorithm is then applicable to a more general case where the lines of view (LOV) of the US device are not necessarily parallel and coplanar, thus allowing correction also for US transducers other than linear. The algorithm was applied on a multi-modality pelvic US phantom, scanned through three different liquid layers on top of the phantom with different SOS values; the results show that the correction restores a better match between the CT and the US images, reducing the differences to sub-millimeter agreement. Fifteen clinical cases of prostate cancer patients were also investigated: the SOS corrections of prostate centroids were on average +3.1 mm (max + 4.9 mm-min + 1.3 mm). This is in excellent agreement with reports in the literature on differences between measured prostate positions by US and other techniques, where often the discrepancy was attributed to other causes.

  12. Transmissive liquid-crystal device for correcting primary coma aberration and astigmatism in biospecimen in two-photon excitation laser scanning microscopy

    NASA Astrophysics Data System (ADS)

    Tanabe, Ayano; Hibi, Terumasa; Ipponjima, Sari; Matsumoto, Kenji; Yokoyama, Masafumi; Kurihara, Makoto; Hashimoto, Nobuyuki; Nemoto, Tomomi

    2016-12-01

    All aberrations produced inside a biospecimen can degrade the quality of a three-dimensional image in two-photon excitation laser scanning microscopy. Previously, we developed a transmissive liquid-crystal device to correct spherical aberrations that improved the image quality of a fixed-mouse-brain slice treated with an optical clearing reagent. In this study, we developed a transmissive device that corrects primary coma aberration and astigmatism. The motivation for this study is that asymmetric aberration can be induced by the shape of a biospecimen and/or by a complicated refractive-index distribution in a sample; this can considerably degrade optical performance even near the sample surface. The device's performance was evaluated by observing fluorescence beads. The device was inserted between the objective lens and microscope revolver and succeeded in improving the spatial resolution and fluorescence signal of a bead image that was originally degraded by asymmetric aberration. Finally, we implemented the device for observing a fixed whole mouse brain with a sloping surface shape and complicated internal refractive-index distribution. The correction with the device improved the spatial resolution and increased the fluorescence signal by ˜2.4×. The device can provide a simple approach to acquiring higher-quality images of biospecimens.

  13. Detection of Single Atoms and Buried Defects in Three Dimensions by Aberration-corrected Electron Microscope with 0.5 ? Information Limit

    SciTech Connect

    Kisielowski, Christian; Bischoff, Maarten; van Lin, Hans; Lazar, Sorin; Freitag, Bernhard; Knippels, Georg; Tiemeijer, Peter; van der Stam, Maarten; von Harrach, Sebastian; Stekelenburg, Michael; Haider, Maximilian; M�ller, Hans; Hartel, Peter; Kabius, Bernd; Miller, Dean; Petrov, Ivan; Olson, Eric; Donchev, Tomas; Kenik, Edward A; Lupini, Andrew R; Bentley, James; Pennycook, Stephen J; Minor, Andrew; Schmid, Andreas; Duden, Thomas; Radmilovic, Velimir; Ramasse, Quentin; Watanabe, Masashi; Stach, Eric; Denes, Peter; Dahmen, Ulrich

    2008-01-01

    The ability of electron microscopes to analyze all the atoms in individual nanostructures is limited by lens aberrations. However, recent advances in aberration-correcting electron optics have led to greatly enhanced instrument performance and new techniques of electron microscopy. The development of an ultrastable electron microscope with aberration-correcting optics and a monochromated high-brightness source has significantly improved instrument resolution and contrast. In the present work, we report information transfer beyond 50 pm and show images of single gold atoms with a signal-to-noise ratio as large as 10. The instrument's new capabilities were exploited to detect a buried Σ3 {112} grain boundary and observe the dynamic arrangements of single atoms and atom pairs with sub- ngstrom resolution. These results mark an important step toward meeting the challenge of determining the 3D atomic-scale structure of nanomaterials.

  14. Experimental demonstration of passive acoustic imaging in the human skull cavity using CT-based aberration corrections

    SciTech Connect

    Jones, Ryan M.; O’Reilly, Meaghan A.; Hynynen, Kullervo

    2015-07-15

    Purpose: Experimentally verify a previously described technique for performing passive acoustic imaging through an intact human skull using noninvasive, computed tomography (CT)-based aberration corrections Jones et al. [Phys. Med. Biol. 58, 4981–5005 (2013)]. Methods: A sparse hemispherical receiver array (30 cm diameter) consisting of 128 piezoceramic discs (2.5 mm diameter, 612 kHz center frequency) was used to passively listen through ex vivo human skullcaps (n = 4) to acoustic emissions from a narrow-band fixed source (1 mm diameter, 516 kHz center frequency) and from ultrasound-stimulated (5 cycle bursts, 1 Hz pulse repetition frequency, estimated in situ peak negative pressure 0.11–0.33 MPa, 306 kHz driving frequency) Definity™ microbubbles flowing through a thin-walled tube phantom. Initial in vivo feasibility testing of the method was performed. The performance of the method was assessed through comparisons to images generated without skull corrections, with invasive source-based corrections, and with water-path control images. Results: For source locations at least 25 mm from the inner skull surface, the modified reconstruction algorithm successfully restored a single focus within the skull cavity at a location within 1.25 mm from the true position of the narrow-band source. The results obtained from imaging single bubbles are in good agreement with numerical simulations of point source emitters and the authors’ previous experimental measurements using source-based skull corrections O’Reilly et al. [IEEE Trans. Biomed. Eng. 61, 1285–1294 (2014)]. In a rat model, microbubble activity was mapped through an intact human skull at pressure levels below and above the threshold for focused ultrasound-induced blood–brain barrier opening. During bursts that led to coherent bubble activity, the location of maximum intensity in images generated with CT-based skull corrections was found to deviate by less than 1 mm, on average, from the position

  15. Experimental demonstration of passive acoustic imaging in the human skull cavity using CT-based aberration corrections

    PubMed Central

    Jones, Ryan M.; O’Reilly, Meaghan A.; Hynynen, Kullervo

    2015-01-01

    Purpose: Experimentally verify a previously described technique for performing passive acoustic imaging through an intact human skull using noninvasive, computed tomography (CT)-based aberration corrections Jones et al. [Phys. Med. Biol. 58, 4981–5005 (2013)]. Methods: A sparse hemispherical receiver array (30 cm diameter) consisting of 128 piezoceramic discs (2.5 mm diameter, 612 kHz center frequency) was used to passively listen through ex vivo human skullcaps (n = 4) to acoustic emissions from a narrow-band fixed source (1 mm diameter, 516 kHz center frequency) and from ultrasound-stimulated (5 cycle bursts, 1 Hz pulse repetition frequency, estimated in situ peak negative pressure 0.11–0.33 MPa, 306 kHz driving frequency) Definity™ microbubbles flowing through a thin-walled tube phantom. Initial in vivo feasibility testing of the method was performed. The performance of the method was assessed through comparisons to images generated without skull corrections, with invasive source-based corrections, and with water-path control images. Results: For source locations at least 25 mm from the inner skull surface, the modified reconstruction algorithm successfully restored a single focus within the skull cavity at a location within 1.25 mm from the true position of the narrow-band source. The results obtained from imaging single bubbles are in good agreement with numerical simulations of point source emitters and the authors’ previous experimental measurements using source-based skull corrections O’Reilly et al. [IEEE Trans. Biomed. Eng. 61, 1285–1294 (2014)]. In a rat model, microbubble activity was mapped through an intact human skull at pressure levels below and above the threshold for focused ultrasound-induced blood–brain barrier opening. During bursts that led to coherent bubble activity, the location of maximum intensity in images generated with CT-based skull corrections was found to deviate by less than 1 mm, on average, from the position

  16. Lowered threshold energy for femtosecond laser induced optical breakdown in a water based eye model by aberration correction with adaptive optics.

    PubMed

    Hansen, Anja; Géneaux, Romain; Günther, Axel; Krüger, Alexander; Ripken, Tammo

    2013-06-01

    In femtosecond laser ophthalmic surgery tissue dissection is achieved by photodisruption based on laser induced optical breakdown. In order to minimize collateral damage to the eye laser surgery systems should be optimized towards the lowest possible energy threshold for photodisruption. However, optical aberrations of the eye and the laser system distort the irradiance distribution from an ideal profile which causes a rise in breakdown threshold energy even if great care is taken to minimize the aberrations of the system during design and alignment. In this study we used a water chamber with an achromatic focusing lens and a scattering sample as eye model and determined breakdown threshold in single pulse plasma transmission loss measurements. Due to aberrations, the precise lower limit for breakdown threshold irradiance in water is still unknown. Here we show that the threshold energy can be substantially reduced when using adaptive optics to improve the irradiance distribution by spatial beam shaping. We found that for initial aberrations with a root-mean-square wave front error of only one third of the wavelength the threshold energy can still be reduced by a factor of three if the aberrations are corrected to the diffraction limit by adaptive optics. The transmitted pulse energy is reduced by 17% at twice the threshold. Furthermore, the gas bubble motions after breakdown for pulse trains at 5 kilohertz repetition rate show a more transverse direction in the corrected case compared to the more spherical distribution without correction. Our results demonstrate how both applied and transmitted pulse energy could be reduced during ophthalmic surgery when correcting for aberrations. As a consequence, the risk of retinal damage by transmitted energy and the extent of collateral damage to the focal volume could be minimized accordingly when using adaptive optics in fs-laser surgery.

  17. Simultaneous fluorescence and high-resolution bright-field imaging with aberration correction over a wide field-of-view with Fourier ptychographic microscopy (FPM) (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Chung, Jaebum; Kim, Jinho; Ou, Xiaoze; Horstmeyer, Roarke; Yang, Changhuei

    2016-03-01

    We present a method to acquire both fluorescence and high-resolution bright-field images with correction for the spatially varying aberrations over a microscope's wide field-of-view (FOV). First, the procedure applies Fourier ptychographic microscopy (FPM) to retrieve the amplitude and phase of a sample, at a resolution that significantly exceeds the cutoff frequency of the microscope objective lens. At the same time, FPM algorithm is able to leverage on the redundancy within the set of acquired FPM bright-field images to estimate the microscope aberrations, which usually deteriorate in regions further away from the FOV's center. Second, the procedure acquires a raw wide-FOV fluorescence image within the same setup. Lack of moving parts allows us to use the FPM-estimated aberration map to computationally correct for the aberrations in the fluorescence image through deconvolution. Overlaying the aberration-corrected fluorescence image on top of the high-resolution bright-field image can be done with accurate spatial correspondence. This can provide means to identifying fluorescent regions of interest within the context of the sample's bright-field information. An experimental demonstration successfully improves the bright-field resolution of fixed, stained and fluorescently tagged HeLa cells by a factor of 4.9, and reduces the error caused by aberrations in a fluorescence image by 31%, over a field of view of 6.2 mm by 9.3 mm. For optimal deconvolution, we show the fluorescence image needs to have a signal-to-noise ratio of ~18.

  18. Wavefront correction for static and dynamic aberrations to within 1 second of the system shot in the NIF Beamlet demonstration facility

    SciTech Connect

    Hartley, R.; Kartz, M.; Behrendt, W.

    1996-10-01

    The laser wavefront of the NIF Beamlet demonstration system is corrected for static aberrations with a wavefront control system. The system operates closed loop with a probe beam prior to a shot and has a loop bandwidth of about 3 Hz. However, until recently the wavefront control system was disabled several minutes prior to the shot to allow time to manually reconfigure its attenuators and probe beam insertion mechanism to shot mode. Thermally-induced dynamic variations in gas density in the Beamlet main beam line produce significant wavefront error. After about 5-8 seconds, the wavefront error has increased to a new, higher level due to turbulence- induced aberrations no longer being corrected- This implies that there is a turbulence-induced aberration noise bandwidth of less than one Hertz, and that the wavefront controller could correct for the majority of turbulence-induced aberration (about one- third wave) by automating its reconfiguration to occur within one second of the shot, This modification was recently implemented on Beamlet; we call this modification the t{sub 0}-1 system.

  19. Deconvolution and chromatic aberration corrections in quantifying colocalization of a transcription factor in three-dimensional cellular space.

    PubMed

    Abraham, Thomas; Allan, Sarah E; Levings, Megan K

    2010-08-01

    with DNA molecules. In conclusion, our studies clearly demonstrate the importance of PSF measurements, chromatic aberration corrections followed by deconvolution in the accurate determination of transcription factors in the 3D cellular space. The reported imaging and processing methods can be a practical guide for quantitative fluorescence imaging of similar cellular systems and can provide a basis for further development.

  20. Double-aberration corrected TEM/STEM of solid acid nanocatalysts in the development of pharmaceutical NSAIDS

    NASA Astrophysics Data System (ADS)

    Yoshida, K.; Shiju, N.; Brown, R.; Wright, I.; Boyes, E. D.; Gai, P. L.

    2012-07-01

    We report nanostructural and physico-chemical studies in the development of an efficient low temperature heterogeneous catalytic process for nonsteroidal anti-inflammatory drugs (NSAIDS) such as N-acetyl-p-aminophenol (paracetamol or acetaminophen) on tungstated zirconia nanocatalysts. Using a double-aberration corrected TEM/STEM, modified in-house for in-situ studies at the sub-Angstrom level, we directly observed in real-time, the dynamic precursor transformation to the active catalyst. We quantified the observations with catalytic activity studies for the NSAIDS. The studies have provided the direct evidence for single tungsten promoter atoms and surface WOx species of <= 0.35 nm, with nanoclusters of WOx (0.6 to 1nm), located at grain boundaries on the surface of the zirconia nanoparticles. The correlation between the nanostructure and catalytic activity indicates that the species create Brønsted acid sites highly active for the low temperature process. The results open up opportunities for developing green heterogeneous methods for pharmaceuticals.

  1. Optimized deconvolution for maximum axial resolution in three-dimensional aberration-corrected scanning transmission electron microscopy.

    PubMed

    Ramachandra, Ranjan; de Jonge, Niels

    2012-02-01

    Three-dimensional (3D) datasets were recorded of gold nanoparticles placed on both sides of silicon nitride membranes using focal series aberration-corrected scanning transmission electron microscopy (STEM). Deconvolution of the 3D datasets was applied to obtain the highest possible axial resolution. The deconvolution involved two different point spread functions, each calculated iteratively via blind deconvolution. Supporting membranes of different thicknesses were tested to study the effect of beam broadening on the deconvolution. It was found that several iterations of deconvolution was efficient in reducing the imaging noise. With an increasing number of iterations, the axial resolution was increased, and most of the structural information was preserved. Additional iterations improved the axial resolution by maximal a factor of 4 to 6, depending on the particular dataset, and up to 8 nm maximal, but also led to a reduction of the lateral size of the nanoparticles in the image. Thus, the deconvolution procedure optimized for the highest axial resolution is best suited for applications where one is interested in the 3D locations of nanoparticles only.

  2. New Insights into the structure of Pd-Au nanoparticles as revealed by aberration-corrected STEM

    PubMed Central

    Deepak, Francis Leonard; Casillas-Garcia, Gilberto; Esparza, Rodrigo; Barron, H.; Jose-Yacaman, Miguel

    2011-01-01

    Bimetallic nanoparticles of Au-Pd find important applications in catalysis. Their catalytic performance is directly related to the structure, alloy formation and variation of composition in the structure. A standard idea is that bimetallic nanoparticles can be either an alloy or a core shell structure. Our group has investigated the structure and composition of Pd-Au nanoparticles by using aberration corrected high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). We reported previously that the nanoparticles are composed of an evenly alloyed inner core, an Au-rich intermediate layer, and a Pd-rich outer shell. The structure is more complicated than what simple models can predict. In this paper we report additional studies of this system wherein by carrying out spectral and chemical analysis (STEM*-EDAX, STEM-EELS) the interface structure can now be better identified and understood. Apart from the three-layered core-shell structures we have also been able to observe in some cases a four-layered core-shell structure as well. The entire core-shell structure is not rigid and there is indeed intercalation of Au-Pd into the other layers as well. In addition we have been able to locate stacking faults present in the nanoparticles. We also address the problem of the interface structure between the layers. By using nanodiffraction we have found that the whole structure of the nanoparticles becomes hcp in contrast to the bulk structure of Au or Pd. PMID:21804646

  3. Separating strain from composition in unit cell parameter maps obtained from aberration corrected high resolution transmission electron microscopy imaging

    SciTech Connect

    Schulz, T.; Remmele, T.; Korytov, M.; Markurt, T.; Albrecht, M.; Duff, A.; Lymperakis, L.; Neugebauer, J.; Chèze, C.

    2014-01-21

    Based on the evaluation of lattice parameter maps in aberration corrected high resolution transmission electron microscopy images, we propose a simple method that allows quantifying the composition and disorder of a semiconductor alloy at the unit cell scale with high accuracy. This is realized by considering, next to the out-of-plane, also the in-plane lattice parameter component allowing to separate the chemical composition from the strain field. Considering only the out-of-plane lattice parameter component not only yields large deviations from the true local alloy content but also carries the risk of identifying false ordering phenomena like formations of chains or platelets. Our method is demonstrated on image simulations of relaxed supercells, as well as on experimental images of an In{sub 0.20}Ga{sub 0.80}N quantum well. Principally, our approach is applicable to all epitaxially strained compounds in the form of quantum wells, free standing islands, quantum dots, or wires.

  4. Exploring the atomic structure of 1.8nm monolayer-protected gold clusters with aberration-corrected STEM.

    PubMed

    Liu, Jian; Jian, Nan; Ornelas, Isabel; Pattison, Alexander J; Lahtinen, Tanja; Salorinne, Kirsi; Häkkinen, Hannu; Palmer, Richard E

    2016-11-22

    Monolayer-protected (MP) Au clusters present attractive quantum systems with a range of potential applications e.g. in catalysis. Knowledge of the atomic structure is needed to obtain a full understanding of their intriguing physical and chemical properties. Here we employed aberration-corrected scanning transmission electron microscopy (ac-STEM), combined with multislice simulations, to make a round-robin investigation of the atomic structure of chemically synthesised clusters with nominal composition Au144(SCH2CH2Ph)60 provided by two different research groups. The MP Au clusters were "weighed" by the atom counting method, based on their integrated intensities in the high angle annular dark field (HAADF) regime and calibrated exponent of the Z dependence. For atomic structure analysis, we compared experimental images of hundreds of clusters, with atomic resolution, against a variety of structural models. Across the size range 123-151 atoms, only 3% of clusters matched the theoretically predicted Au144(SR)60 structure, while a large proportion of the clusters were amorphous (i.e. did not match any model structure). However, a distinct ring-dot feature, characteristic of local icosahedral symmetry, was observed in about 20% of the clusters.

  5. Long-range chemical orders in Au-Pd nanoparticles revealed by aberration-corrected electron microscopy.

    PubMed

    Nelayah, Jaysen; Nguyen, Nhat Tai; Alloyeau, Damien; Wang, Guillaume Yangshu; Ricolleau, Christian

    2014-09-07

    Despite the importance of gold-palladium nanoalloys in heterogeneous catalysis, the phase stability of Au-Pd alloys still remains unclear. We report here on the alloying and chemical ordering in epitaxially-grown and post-annealed gold-palladium nanoparticles (NPs) using aberration-corrected transmission electron microscopy. Au-Pd NPs with a controlled size, composition and structure were grown by pulsed laser deposition on freshly-cleaved NaCl(001) single crystals heated at 300 °C. After transfer to an amorphous carbon support, the NPs were annealed in vacuum at elevated temperatures above 400 °C for a few hours (6-10 hours) to promote chemical ordering. The as-grown NPs were mostly monocrystalline with a chemically-disordered face-centered cubic structure. Upon high-temperature annealing, a high degree of chemical ordering was observed in nanometer-sized NPs. Electron microscopy measurements showed that both L10 and L12 orders are stabilized in the Au-rich region of the Au-Pd phase diagram. These ordered phases exist at temperatures as high as 600 °C. Moreover, compositional analysis of single annealed particles revealed that the observed chemical ordering occurs in parallel to a two-tiered Ostwald ripening process. Due to this ripening process, a clear dependence between chemical composition and particle size is established during annealing with an enrichment in Pd as the NPs grow in size. Our results, besides clarifying some controversial aspects about long-range order in Au-Pd alloys, shed light on the structural stability of Au-Pd nanoalloys at elevated temperatures.

  6. In-situ Study of Dynamic Phenomena at Metal Nanosolder Interfaces Using Aberration Corrected Scanning Transmission Electron Microcopy.

    SciTech Connect

    Lu, Ping

    2014-10-01

    Controlling metallic nanoparticle (NP) interactions plays a vital role in the development of new joining techniques (nanosolder) that bond at lower processing temperatures but remain viable at higher temperatures. The pr imary objective of this project is t o develop a fundamental understanding of the actual reaction processes, associated atomic mechanisms, and the resulting microstructure that occur during thermally - driven bond formation concerning metal - metal nano - scale (%3C50nm) interfaces. In this LDRD pr oject, we have studied metallic NPs interaction at the elevated temperatures by combining in - situ transmission electron microscopy (TEM ) using an aberration - corrected scanning transmission electron microscope (AC - STEM) and atomic - scale modeling such as m olecular dynamic (MD) simulations. Various metallic NPs such as Ag, Cu and Au are synthesized by chemical routines. Numerous in - situ e xperiments were carried out with focus of the research on study of Ag - Cu system. For the first time, using in - situ STEM he ating experiments , we directly observed t he formation of a 3 - dimensional (3 - D) epitaxial Cu - Ag core - shell nanoparticle during the thermal interaction of Cu and Ag NPs at elevated temperatures (150 - 300 o C). The reaction takes place at temperatures as low as 150 o C and was only observed when care was taken to circumvent the effects of electron beam irradiation during STEM imaging. Atomic - scale modeling verified that the Cu - Ag core - shell structure is energetically favored, and indicated that this phenomenon is a nano - scale effect related to the large surface - to - volume ratio of the NPs. The observation potentially can be used for developing new nanosolder technology that uses Ag shell as the "glue" that stic ks the particles of Cu together. The LDRD has led to several journal publications and numerous conference presentations, and a TA. In addition, we have developed new TEM characterization techniques and phase

  7. Correction of Depth-Dependent Aberrations in 3D Single Molecule Localization and Super-resolution Microscopy

    PubMed Central

    McGorty, Ryan; Schnitzbauer, Joerg; Zhang, Wei; Huang, Bo

    2014-01-01

    Single molecule switching based super-resolution microscopy techniques have been extended into three dimensions through various 3D single molecule localization methods. However, the localization accuracy in z can be severely degraded by the presence of aberrations, particularly the spherical aberration introduced by the refractive-index-mismatch when imaging into an aqueous sample with an oil immersion objective. This aberration confines the imaging depth in most experiments to regions close to the coverslip. Here, we show a method to obtain accurate, depth dependent z calibrations by measuring the point spread function (PSF) at the coverslip surface, calculating the microscope pupil function through phase retrieval, and then computing the depth dependent PSF with the addition of spherical aberrations. We demonstrate experimentally that this method can maintain z localization accuracy over a large range of imaging depths. Our super-resolution images of a mammalian cell nucleus acquired between 0 and 2.5 μm past the coverslip show that this method produces accurate z localizations even in the deepest focal plane. PMID:24562125

  8. Design and Performance Characteristics of the ORNL Advanced Microscopy Laboratory and JEOL 2200FS-AC Aberration-Corrected STEM/TEM

    SciTech Connect

    Allard Jr, Lawrence Frederick; Blom, Douglas Allen; O'Keefe, Michael A.; Mishina, Satoshi

    2005-01-01

    To achieve the highest performance with today's generation of aberration-corrected electron microscopes, it is increasingly evident that the environment of the facility in which the microscope is installed must be considered an integral component of the microscopy program. Such instruments are the world's best detectors of the influence of parameters such as alternating magnetic fields, floor vibrations, acoustic vibrations, airflow, and temperature and pressure fluctuations. At ORNL, the new Advanced Microscopy Laboratory (AML) has recently been completed, with two aberration-corrected instruments installed, and two more planned in the near future to fill the 4-laboratory building. Design criteria for the facility include the following: magnetic fields below 0.1mG rms in all directions, floor vibrations below 1{mu}m/sec, air flow less than 5cm/sec horizontally, temperature stability {+-}0.2 C/hr, and provision for instrument operation from an adjacent control room to minimize the influence of the operator on instrument performance. The JEOL 2200FS-AC, being installed as of this writing, has demonstrated a TEM information limit of 0.9 {angstrom}. This is the limit expected given the measured instrument parameters (HT and OL power supply stabilities, beam energy spread, etc.), and illustrates that the environmental influences are not adversely affecting the instrument performance. However, in STEM high-angle annular dark-field (HA-ADF) mode, images of a thin Si crystal in <1 1 0> zone axis orientation, after primary aberrations in the illuminating beam were optimally corrected, showed a significant vibration effect.

  9. Aberrant splicing in the ocular albinism type 1 gene (OA1/GPR143) is corrected in vitro by morpholino antisense oligonucleotides.

    PubMed

    Vetrini, Francesco; Tammaro, Roberta; Bondanza, Sergio; Surace, Enrico M; Auricchio, Alberto; De Luca, Michele; Ballabio, Andrea; Marigo, Valeria

    2006-05-01

    An intronic point mutation was identified in the ocular albinism type 1 (OA1) gene (HUGO symbol, GPR143) in a family with the X-linked form of ocular albinism. Interestingly, the mutation creates a new acceptor splice site in intron 7 of the OA1 gene. In addition to low levels of normally spliced mRNA product of the OA1 gene, the patient samples contained also an aberrantly spliced mRNA with a 165 bp fragment of intron 7 (from position +750 to +914) inserted between exons 7 and 8. The abnormal transcript contained a premature stop codon and was unstable, as revealed by Northern blot analysis. We defined that mutation NC_000023.8:g.25288G>A generated a consensus binding motif for the splicing factor enhancer ASF/SF2, which most likely favored transcription of the aberrant mRNA. Furthermore, it activated a cryptic donor-splice site causing the inclusion between exons 7 and 8 of the 165 bp intronic fragment. Thus, the aberrant splicing is most likely explained by the generation of a de novo splicing enhancer motif. Finally, to rescue OA1 expression in the patient's melanocytes, we designed an antisense morpholino modified oligonucleotide complementary to the mutant sequence. The morpholino oligonucleotide (MO) was able to rescue OA1 expression and restore the OA1 protein level in the patient's melanocytes through skipping of the aberrant inclusion. The use of MO demonstrated that the lack of OA1 was caused by the generation of a new splice site. Furthermore, this technique will lead to new approaches to correct splice site mutations that cause human diseases.

  10. Three-dimensional locations of gold-labeled proteins in a whole mount eukaryotic cell obtained with 3nm precision using aberration-corrected scanning transmission electron microscopy.

    PubMed

    Dukes, Madeline J; Ramachandra, Ranjan; Baudoin, Jean-Pierre; Gray Jerome, W; de Jonge, Niels

    2011-06-01

    Three-dimensional (3D) maps of proteins within the context of whole cells are important for investigating cellular function. However, 3D reconstructions of whole cells are challenging to obtain using conventional transmission electron microscopy (TEM). We describe a methodology to determine the 3D locations of proteins labeled with gold nanoparticles on whole eukaryotic cells. The epidermal growth factor receptors on COS7 cells were labeled with gold nanoparticles, and critical-point dried whole-mount cell samples were prepared. 3D focal series were obtained with aberration-corrected scanning transmission electron microscopy (STEM), without tilting the specimen. The axial resolution was improved with deconvolution. The vertical locations of the nanoparticles in a whole-mount cell were determined with a precision of 3nm. From the analysis of the variation of the axial positions of the labels we concluded that the cellular surface was ruffled. To achieve sufficient stability of the sample under electron beam irradiation during the recording of the focal series, the sample was carbon coated. A quantitative method was developed to analyze the stability of the ultrastructure after electron beam irradiation using TEM. The results of this study demonstrate the feasibility of using aberration-corrected STEM to study the 3D nanoparticle distribution in whole cells.

  11. Thickness variations and absence of lateral compositional fluctuations in aberration-corrected STEM images of InGaN LED active regions at low dose.

    PubMed

    Yankovich, Andrew B; Kvit, Alexander V; Li, Xing; Zhang, Fan; Avrutin, Vitaliy; Liu, Huiyong; Izyumskaya, Natalia; Özgür, Ümit; Van Leer, Brandon; Morkoç, Hadis; Voyles, Paul M

    2014-06-01

    Aberration-corrected scanning transmission electron microscopy images of the In(0.15)Ga(0.85)N active region of a blue light-emitting diode, acquired at ~0.1% of the electron dose known to cause electron beam damage, show no lateral compositional fluctuations, but do exhibit one to four atomic plane steps in the active layer's upper boundary. The area imaged was measured to be 2.9 nm thick using position averaged convergent beam electron diffraction, ensuring the sample was thin enough to capture compositional variation if it was present. A focused ion beam prepared sample with a very large thin area provides the possibility to directly observe large fluctuations in the active layer thickness that constrict the active layer at an average lateral length scale of 430 nm.

  12. Design and Performance Characteristics of the ORNL AdvancedMicroscopy Laboratory and JEOL 2200FS-AC Aberration-CorrectedSTEM/TEM

    SciTech Connect

    Allard, Lawrence F.; Blom, Douglas A.; O'Keefe, Michael A.; Mishina, S.

    2005-02-15

    At ORNL, the new Advanced Microscopy Laboratory (AML) has recently been completed, with two aberration-corrected instruments installed, and two more planned in the near future to fill the 4-laboratory building. The installed JEOL 2200FS-AC has demonstrated aTEM information limit of 0.9A. This limit is expected given the measured instrument parameters (HT and OL power supply stabilities, beam energy spread, etc.), and illustrates that the environmental influences are not adversely affecting the instrument performance. In STEM high-angle annular dark-field (HA-ADF) mode, images of a thin Si crystal in<110>zone axis orientation, after primary aberrations in the illuminating beam were optimally corrected, showed a significant vibration effect. The microscope is fitted with three magnetically levitated turbo pumps (one on the column at about the specimen position,and two near floor level) that pump the Omega energy filter and detector chamber. These pumps run at 48,000 rpm, precisely equivalent to 800Hz. It was determined that the upper turbo pump was contributing essentially all of the 800Hz signal to the image, and in fact that the pump was defective. After replacing the pump with one significantly quieter than the original, the Si atomic column image and associated diffractogram(Fig. 4b) show a much-reduced effect of the 800Hz signal, but still some residual effect from the turbo pump. The upper pump will be removed from the main column to an adjacent frame on the floor, and will have a large-diameter, well-damped, pump line to the original connection to the column to effectively isolate the pump from the column. If the 800Hz signal results from mechanical vibrations, they will be damped, and if the signal results from acoustic coupling to the column, it can be damped by appropriate acoustic materials.

  13. Algorithms and applications of aberration correction and American standard-based digital evaluation in surface defects evaluating system

    NASA Astrophysics Data System (ADS)

    Wu, Fan; Cao, Pin; Yang, Yongying; Li, Chen; Chai, Huiting; Zhang, Yihui; Xiong, Haoliang; Xu, Wenlin; Yan, Kai; Zhou, Lin; Liu, Dong; Bai, Jian; Shen, Yibing

    2016-11-01

    The inspection of surface defects is one of significant sections of optical surface quality evaluation. Based on microscopic scattering dark-field imaging, sub-aperture scanning and stitching, the Surface Defects Evaluating System (SDES) can acquire full-aperture image of defects on optical elements surface and then extract geometric size and position information of defects with image processing such as feature recognization. However, optical distortion existing in the SDES badly affects the inspection precision of surface defects. In this paper, a distortion correction algorithm based on standard lattice pattern is proposed. Feature extraction, polynomial fitting and bilinear interpolation techniques in combination with adjacent sub-aperture stitching are employed to correct the optical distortion of the SDES automatically in high accuracy. Subsequently, in order to digitally evaluate surface defects with American standard by using American military standards MIL-PRF-13830B to judge the surface defects information obtained from the SDES, an American standard-based digital evaluation algorithm is proposed, which mainly includes a judgment method of surface defects concentration. The judgment method establishes weight region for each defect and adopts the method of overlap of weight region to calculate defects concentration. This algorithm takes full advantage of convenience of matrix operations and has merits of low complexity and fast in running, which makes itself suitable very well for highefficiency inspection of surface defects. Finally, various experiments are conducted and the correctness of these algorithms are verified. At present, these algorithms have been used in SDES.

  14. Migration of Single Iridium Atoms and Tri-iridium Clusters on MgO Surfaces. Aberration-Corrected STEM Imaging and ab-initio Calculations

    SciTech Connect

    Han, Chang W.; Iddir, Hakim; Uzun, Alper; Curtiss, Larry A.; Browning, Nigel D.; Gates, Bruce C.; Ortalan, Volkan

    2015-11-06

    To address the challenge of fast, direct atomic-scale visualization of the diffusion of atoms and clusters on surfaces, we used aberration-corrected scanning transmission electron microscopy (STEM) with high scan speeds (as little as ~0.1 s per frame) to visualize the diffusion of (1) a heavy atom (Ir) on the surface of a support consisting of light atoms, MgO(100), and (2) an Ir3 cluster on MgO(110). Sequential Z-contrast images elucidate the diffusion mechanisms, including the hopping of Ir1 and the rotational migration of Ir3 as two Ir atoms remain anchored to the surface. Density functional theory (DFT) calculations provided estimates of the diffusion energy barriers and binding energies of the iridium species to the surfaces. The results show how the combination of fast-scan STEM and DFT calculations allow real-time visualization and fundamental understanding of surface diffusion phenomena pertaining to supported catalysts and other materials.

  15. On the benefit of aberration-corrected HAADF-STEM for strain determination and its application to tailoring ferroelectric domain patterns.

    PubMed

    Tang, Y L; Zhu, Y L; Ma, X L

    2016-01-01

    Revealing strains on the unit-cell level is essential for understanding the particular performance of materials. Large-scale strain variations with a unit-cell resolution are important for studying ferroelectric materials since the spontaneous polarizations of such materials are strongly coupled with strains. Aberration-corrected high-angle-annular-dark-field scanning transmission electron microscopy (AC-HAADF-STEM) is not so sensitive to the sample thickness and therefore thickness gradients. Consequently it is extremely useful for large-scale strain determination, which can be readily extracted by geometrical phase analysis (GPA). Such a combination has various advantages: it is straightforward, accurate on the unit-cell scale, relatively insensitive to crystal orientation and therefore helpful for large-scale. We take a tetragonal ferroelectric PbTiO3 film as an example in which large-scale strains are determined. Furthermore, based on the specific relationship between lattice rotation and spontaneous polarization (Ps) at 180° domain-walls, the Ps directions are identified, which makes the investigation of ferroelectric domain structures accurate and straightforward. This method is proposed to be suitable for investigating strain-related phenomena in other ferroelectric materials.

  16. High resolution structural and compositional mapping of the SrTiO3/LaFeO3 interface using chromatic aberration corrected energy filtered imaging

    NASA Astrophysics Data System (ADS)

    Kabius, Bernd; Houben, Lothar; Dwyer, Christian; Colby, Robert; Chambers, Scott A.; Dunin-Borkowski, Rafal

    2014-03-01

    Interfaces between insulating polar perovskites have demonstrated a wealth of electronic and magnetic properties. Understanding and predicting the properties of a specific interface requires atomic level knowledge of interface structure and chemistry. Electron microscopy is capable of this task, and has been frequently applied to oxide interfaces using a combination of high-angle angular dark field scanning transmission electron microscopy (HAADF-STEM) and electron energy-loss spectroscopy (EELS). Energy-filtered TEM (EFTEM) captures a full image for a given energy losses, allowing a larger field of view than typical for STEM-EELS in far less time. However, EFTEM has not, to date, demonstrated the spatial resolution of STEM-EELS due to the limits set by chromatic aberration Cc. This study of LaFeO3/SrTiO3 demonstrates that Cc correction enhances the resolution of EFTEM for elemental mapping, allowing a unit cell-by-unit cell analysis of the concentration gradients across the SrTiO3/LaFeO3 interface. The charge distribution at the interface will be discussed. The research was performed using EMSL, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory

  17. Fine structural features of nanoscale zero-valent iron characterized by spherical aberration corrected scanning transmission electron microscopy (Cs-STEM).

    PubMed

    Liu, Airong; Zhang, Wei-xian

    2014-09-21

    An angstrom-resolution physical model of nanoscale zero-valent iron (nZVI) is generated with a combination of spherical aberration corrected scanning transmission electron microscopy (Cs-STEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDS) and electron energy-loss spectroscopy (EELS) on the Fe L-edge. Bright-field (BF), high-angle annular dark-field (HAADF) and secondary electron (SE) imaging of nZVI acquired by a Hitachi HD-2700 STEM show near atomic resolution images and detailed morphological and structural information of nZVI. The STEM-EDS technique confirms that the fresh nZVI comprises of a metallic iron core encapsulated with a thin layer of iron oxides or oxyhydroxides. SAED patterns of the Fe core suggest the polycrystalline structure in the metallic core and amorphous nature of the oxide layer. Furthermore, Fe L-edge of EELS shows varied structural features from the innermost Fe core to the outer oxide shell. A qualitative analysis of the Fe L(2,3) edge fine structures reveals that the shell of nZVI consists of a mixed Fe(II)/Fe(III) phase close to the Fe (0) interface and a predominantly Fe(III) at the outer surface of nZVI.

  18. Direct atomic-scale imaging of hydrogen and oxygen interstitials in pure niobium using atom-probe tomography and aberration-corrected scanning transmission electron microscopy.

    PubMed

    Kim, Yoon-Jun; Tao, Runzhe; Klie, Robert F; Seidman, David N

    2013-01-22

    Imaging the three-dimensional atomic-scale structure of complex interfaces has been the goal of many recent studies, due to its importance to technologically relevant areas. Combining atom-probe tomography and aberration-corrected scanning transmission electron microscopy (STEM), we present an atomic-scale study of ultrathin (~5 nm) native oxide layers on niobium (Nb) and the formation of ordered niobium hydride phases near the oxide/Nb interface. Nb, an elemental type-II superconductor with the highest critical temperature (T(c) = 9.2 K), is the preferred material for superconducting radio frequency (SRF) cavities in next-generation particle accelerators. Nb exhibits high solubilities for oxygen and hydrogen, especially within the RF-field penetration depth, which is believed to result in SRF quality factor losses. STEM imaging and electron energy-loss spectroscopy followed by ultraviolet laser-assisted local-electrode atom-probe tomography on the same needle-like sample reveals the NbO(2), Nb(2)O(5), NbO, Nb stacking sequence; annular bright-field imaging is used to visualize directly hydrogen atoms in bulk β-NbH.

  19. Aberration-corrected X-ray spectrum imaging and Fresnel contrast to differentiate nanoclusters and cavities in helium-irradiated alloy 14YWT

    SciTech Connect

    Miller, Michael K; Parish, Chad M

    2014-01-01

    Helium accumulation negatively impacts structural materials used in neutron-irradiated environments, such as fission and fusion reactors. Next-generation fission and fusion reactors will require structural materials, such as steels, resistant to large neutron doses yet see service temperatures in the range most affected by helium embrittlement. Previous work has indicated the difficulty of experimentally differentiating nanometer-sized helium bubbles from the Ti-Y-O rich nanoclustsers (NCs) in radiation-tolerant nanostructured ferritic alloys (NFAs). Because the NCs are expected to sequester helium away from grain boundaries and reduce embrittlement, experimental methods to study simultaneously the NC and bubble populations are needed. In this study, aberration-corrected scanning transmission electron microscopy (STEM) results combining high-collection-efficiency X-ray spectrum images (SIs), multivariate statistical analysis (MVSA), and Fresnel-contrast bright-field STEM imaging have been used for such a purpose. Results indicate that Fresnel-contrast imaging, with careful attention to TEM-STEM reciprocity, differentiates bubbles from NCs, and MVSA of X-ray SIs unambiguously identifies NCs. Therefore, combined Fresnel-contrast STEM and X-ray SI is an effective STEM-based method to characterize helium-bearing NFAs.

  20. Camera processing with chromatic aberration.

    PubMed

    Korneliussen, Jan Tore; Hirakawa, Keigo

    2014-10-01

    Since the refractive index of materials commonly used for lens depends on the wavelengths of light, practical camera optics fail to converge light to a single point on an image plane. Known as chromatic aberration, this phenomenon distorts image details by introducing magnification error, defocus blur, and color fringes. Though achromatic and apochromatic lens designs reduce chromatic aberration to a degree, they are complex and expensive and they do not offer a perfect correction. In this paper, we propose a new postcapture processing scheme designed to overcome these problems computationally. Specifically, the proposed solution is comprised of chromatic aberration-tolerant demosaicking algorithm and post-demosaicking chromatic aberration correction. Experiments with simulated and real sensor data verify that the chromatic aberration is effectively corrected.

  1. Holographically Correcting Synthetic Aperture Aberrations.

    DTIC Science & Technology

    1987-12-01

    Malacara (20:105-148). The synthetic aperture was aligned in accordance with the synthetic-aperture alignment technique of Gill (8:61-64). The...1987. 20. Malacara , Daniel, ed. Optical Shop Testing. New York: John Wiley & Sons, 1978. 21. Marciniak, Capt Michael. Tutorial Presentation of mV

  2. Cosmic Aberration, and Its Correction

    ERIC Educational Resources Information Center

    Dixon, Robert

    2011-01-01

    Because the speed of light is finite, the further we look into space, the earlier we see. A galaxy seen 50 million light years away is 50 million years ago. How far out in space and how far back in time can we expect to see, and what should it look like? To a first approximation and ignoring local galactic interactions, the Hubble model of the…

  3. Plasmon Enhanced Photoemission

    NASA Astrophysics Data System (ADS)

    Polyakov, Aleksandr N.

    Next generation ultrabright light sources will operate at megahertz repetition rates with temporal resolution in the attosecond regime. For an X-Ray Free Electron Laser (FEL) to operate at such repetition rate requires a high quantum efficiency (QE) cathode to produce electron bunches of 300 pC per 1.5mu J incident laser pulse. Semiconductor photocathodes have sufficient QE in the ultraviolet (UV) and the visible spectrum, however, they produce picosecond electron pulses due to the electron-phonon scattering. On the other hand, metals have two orders of magnitude less QE, but can produce femtosecond pulses, that are required to form the optimum electron distribution for high efficiency FEL operation. In this work, a novel metallic photocathode design is presented, where a set of nano-cavities is introduced on the metal surface to increase its QE to meet the FEL requirements, while maintaining the fast time response. Photoemission can be broken up into three steps: (1) photon absorption, (2) electron transport to the surface, and (3) crossing the metal-vacuum barrier. The first two steps can be improved by making the metal completely absorbing and by localizing the fields closer to the metal surface, thereby reducing the electron travel distance. Both of these effects can be achieved by coupling the incident light to an electron density wave on the metal surface, represented by a quasi-particle, the Surface Plasmon Polariton (SPP). The photoemission then becomes a process where the photon energy is transferred to an SPP and then to an electron. The dispersion relation for the SPP defines the region of energies where such process can occur. For example, for gold, the maximum SPP energy is 2.4 eV, however, the work function is 5.6 eV, therefore, only a fourth order photoemission process is possible. In such process, four photons excite four plasmons that together excite only one electron. The yield of such non-linear process depends strongly on the light intensity. In

  4. Plasmon Enhanced Photoemission

    SciTech Connect

    Polyakov, Aleksandr

    2012-05-08

    Next generation ultrabright light sources will operate at megahertz repetition rates with temporal resolution in the attosecond regime. For an X-Ray Free Electron Laser (FEL) to operate at such repetition rate requires a high quantum efficiency (QE) cathode to produce electron bunches of 300 pC per 1.5 μJ incident laser pulse. Semiconductor photocathodes have sufficient QE in the ultraviolet (UV) and the visible spectrum, however, they produce picosecond electron pulses due to the electron-phonon scattering. On the other hand, metals have two orders of magnitude less QE, but can produce femtosecond pulses, that are required to form the optimum electron distribution for high efficiency FEL operation. In this work, a novel metallic photocathode design is presented, where a set of nano-cavities is introduced on the metal surface to increase its QE to meet the FEL requirements, while maintaining the fast time response. Photoemission can be broken up into three steps: (1) photon absorption, (2) electron transport to the surface, and (3) crossing the metal-vacuum barrier. The first two steps can be improved by making the metal completely absorbing and by localizing the fields closer to the metal surface, thereby reducing the electron travel distance. Both of these effects can be achieved by coupling the incident light to an electron density wave on the metal surface, represented by a quasi-particle, the Surface Plasmon Polariton (SPP). The photoemission then becomes a process where the photon energy is transferred to an SPP and then to an electron. The dispersion relation for the SPP defines the region of energies where such process can occur. For example, for gold, the maximum SPP energy is 2.4 eV, however, the work function is 5.6 eV, therefore, only a fourth order photoemission process is possible. In such process, four photons excite four plasmons that together excite only one electron. The yield of such non-linear process depends strongly on the light intensity. In

  5. A Site-isolated Mononuclear Iridium Complex Catalyst Supported on MgO: Characterization by Spectroscopy and Aberration-corrected Scanning Transmission Electron Microscopy

    SciTech Connect

    Uzun, A.; Ortalan, V; Browning, N; Gates , B

    2010-01-01

    Supported mononuclear iridium complexes with ethene ligands were prepared by the reaction of Ir(C{sub 2}H{sub 4}){sub 2}(acac) (acac is CH{sub 3}COCHCOCH{sub 3}) with highly dehydroxylated MgO. Characterization of the supported species by extended X-ray absorption fine structure (EXAFS) and infrared (IR) spectroscopies showed that the resultant supported organometallic species were Ir(C{sub 2}H{sub 4}){sub 2}, formed by the dissociation of the acac ligand from Ir(C{sub 2}H{sub 4}){sub 2}(acac) and bonding of the Ir(C{sub 2}H{sub 4}){sub 2} species to the MgO surface. Direct evidence of the site-isolation of these mononuclear complexes was obtained by aberration-corrected scanning transmission electron microscopy (STEM); the images demonstrate the presence of the iridium complexes in the absence of any clusters. When the iridium complexes were probed with CO, the resulting IR spectra demonstrated the formation of Ir(CO){sub 2} complexes on the MgO surface. The breadth of the {nu}{sub CO} bands demonstrates a substantial variation in the metal-support bonding, consistent with the heterogeneity of the MgO surface; the STEM images are not sufficient to characterize this heterogeneity. The supported iridium complexes catalyzed ethene hydrogenation at room temperature and atmospheric pressure in a flow reactor, and EXAFS spectra indicated that the mononuclear iridium species remained intact. STEM images of the used catalyst confirmed that almost all of the iridium complexes remained intact, but this method was sensitive enough to detect a small degree of aggregation of the iridium on the support.

  6. Polarization Aberrations

    NASA Technical Reports Server (NTRS)

    Mcguire, James P., Jr.; Chipman, Russell A.

    1990-01-01

    The analysis of the polarization characteristics displayed by optical systems can be divided into two categories: geometrical and physical. Geometrical analysis calculates the change in polarization of a wavefront between pupils in an optical instrument. Physical analysis propagates the polarized fields wherever the geometrical analysis is not valid, i.e., near the edges of stops, near images, in anisotropic media, etc. Polarization aberration theory provides a starting point for geometrical design and facilitates subsequent optimization. The polarization aberrations described arise from differences in the transmitted (or reflected) amplitudes and phases at interfaces. The polarization aberration matrix (PAM) is calculated for isotropic rotationally symmetric systems through fourth order and includes the interface phase, amplitude, linear diattenuation, and linear retardance aberrations. The exponential form of Jones matrices used are discussed. The PAM in Jones matrix is introduced. The exact calculation of polarization aberrations through polarization ray tracing is described. The report is divided into three sections: I. Rotationally Symmetric Optical Systems; II. Tilted and Decentered Optical Systems; and Polarization Analysis of LIDARs.

  7. Determination of aberration center of Ronchigram for automated aberration correctors in scanning transmission electron microscopy.

    PubMed

    Sannomiya, Takumi; Sawada, Hidetaka; Nakamichi, Tomohiro; Hosokawa, Fumio; Nakamura, Yoshio; Tanishiro, Yasumasa; Takayanagi, Kunio

    2013-12-01

    A generic method to determine the aberration center is established, which can be utilized for aberration calculation and axis alignment for aberration corrected electron microscopes. In this method, decentering induced secondary aberrations from inherent primary aberrations are minimized to find the appropriate axis center. The fitness function to find the optimal decentering vector for the axis was defined as a sum of decentering induced secondary aberrations with properly distributed weight values according to the aberration order. Since the appropriate decentering vector is determined from the aberration values calculated at an arbitrary center axis, only one aberration measurement is in principle required to find the center, resulting in /very fast center search. This approach was tested for the Ronchigram based aberration calculation method for aberration corrected scanning transmission electron microscopy. Both in simulation and in experiments, the center search was confirmed to work well although the convergence to find the best axis becomes slower with larger primary aberrations. Such aberration center determination is expected to fully automatize the aberration correction procedures, which used to require pre-alignment of experienced users. This approach is also applicable to automated aperture positioning.

  8. Bilateral Symmetry before and Six Months after Aberration-Free™ Correction with the SCHWIND AMARIS TotalTech Laser: Clinical Outcomes

    PubMed Central

    Arbelaez, Maria Clara; Vidal, Camila; Arba-Mosquera, Samuel

    2010-01-01

    Purpose To compare the preoperative and postoperative bilateral symmetry between OD and OS eyes that have undergone femto-LASIK using the Ziemer LDV femtosecond laser system, the SCHWIND AMARIS Excimer Laser and the Aberrationfree™ profiles implemented in the SCHWIND Custom Ablation Manager software. Methods A total of 25 LASIK patients were bilaterally evaluated at the six-month follow-up visit. In all cases standard examinations, pre- and postoperative analysis with corneal wavefront topography (OPTIKON Scout) were performed. Aberration-free™ aspheric treatments were devised using the Custom Ablation Manager software and ablations were performed by means of the SCHWIND AMARIS flying-spot excimer laser system (both SCHWIND eyetech- solutions). In all cases LASIK flaps were created using an LDV femtosecond laser (Ziemer Group). The OD/OS bilateral symmetry was evaluated in terms of corneal wavefront aberration. Results Preoperatively, 11 Zernike terms showed significant bilateral (OS-vs.-OD) symmetry, and only 6 Zernike terms were significantly different. Overall, 23 out of the 25 patients showed significant bilateral symmetry, and only 2 out of 25 patients showed significant differences. None of the aberration metrics changed from pre- to postoperative values by a clinically relevant amount. At the 6-month postoperative visit, 12 Zernike terms showed significant symmetry, and 8 terms were significantly different. Overall, 22 out of 25 patients showed significant bilateral symmetry (OS vs. OD), and only 3 out of 25 patients showed significant differences. Also, this postoperative examination revealed that 6 Zernike terms lost significant OS-vs.-OD symmetry, but 4 Zernike terms gained significant symmetry. Finally, 4 patients lost significant bilaterality, and 2 patients gained significant bilaterality: bilateral symmetry between eyes was better maintained in those patients with a clear preoperative bilateral symmetry. Conclusions Aberration-Free Treatments with

  9. Neural compensation for the eye's optical aberrations.

    PubMed

    Artal, Pablo; Chen, Li; Fernández, Enrique J; Singer, Ben; Manzanera, Silvestre; Williams, David R

    2004-04-16

    A fundamental problem facing sensory systems is to recover useful information about the external world from signals that are corrupted by the sensory process itself. Retinal images in the human eye are affected by optical aberrations that cannot be corrected with ordinary spectacles or contact lenses, and the specific pattern of these aberrations is different in every eye. Though these aberrations always blur the retinal image, our subjective impression is that the visual world is sharp and clear, suggesting that the brain might compensate for their subjective influence. The recent introduction of adaptive optics to control the eye's aberrations now makes it possible to directly test this idea. If the brain compensates for the eye's aberrations, vision should be clearest with the eye's own aberrations rather than with unfamiliar ones. We asked subjects to view a stimulus through an adaptive optics system that either recreated their own aberrations or a rotated version of them. For all five subjects tested, the stimulus seen with the subject's own aberrations was always sharper than when seen through the rotated version. This supports the hypothesis that the neural visual system is adapted to the eye's aberrations, thereby removing somehow the effects of blur generated by the sensory apparatus from visual experience. This result could have important implications for methods to correct higher order aberrations with customized refractive surgery because some benefits of optimizing the correction optically might be undone by the nervous system's compensation for the old aberrations.

  10. Corrections.

    PubMed

    2015-07-01

    Lai Y-S, Biedermann P, Ekpo UF, et al. Spatial distribution of schistosomiasis and treatment needs in sub-Saharan Africa: a systematic review and geostatistical analysis. Lancet Infect Dis 2015; published online May 22. http://dx.doi.org/10.1016/S1473-3099(15)00066-3—Figure 1 of this Article should have contained a box stating ‘100 references added’ with an arrow pointing inwards, rather than a box stating ‘199 records excluded’, and an asterisk should have been added after ‘1473 records extracted into GNTD’. Additionally, the positioning of the ‘§ and ‘†’ footnotes has been corrected in table 1. These corrections have been made to the online version as of June 4, 2015.

  11. Correction.

    PubMed

    2016-02-01

    In the article by Guessous et al (Guessous I, Pruijm M, Ponte B, Ackermann D, Ehret G, Ansermot N, Vuistiner P, Staessen J, Gu Y, Paccaud F, Mohaupt M, Vogt B, Pechère-Bertschi A, Martin PY, Burnier M, Eap CB, Bochud M. Associations of ambulatory blood pressure with urinary caffeine and caffeine metabolite excretions. Hypertension. 2015;65:691–696. doi: 10.1161/HYPERTENSIONAHA.114.04512), which published online ahead of print December 8, 2014, and appeared in the March 2015 issue of the journal, a correction was needed.One of the author surnames was misspelled. Antoinette Pechère-Berstchi has been corrected to read Antoinette Pechère-Bertschi.The authors apologize for this error.

  12. Time-resolved photoemission using attosecond streaking

    NASA Astrophysics Data System (ADS)

    Nagele, S.; Pazourek, R.; Wais, M.; Wachter, G.; Burgdörfer, J.

    2014-04-01

    We theoretically study time-resolved photoemission in atoms as probed by attosecond streaking. We review recent advances in the study of the photoelectric efect in the time domain and show that the experimentally accessible time shifts can be decomposed into distinct contributions that stem from the feld-free photoionization process itself and from probe-field induced corrections. We perform accurate quantum-mechanical as well as classical simulations of attosecond streaking for efective one-electron systems and determine all relevant contributions to the time delay with attosecond precision. In particular, we investigate the properties and limitations of attosecond streaking for the transition from short-ranged potentials (photodetachment) to long-ranged Coulomb potentials (photoionization). As an example for a more complex system, we study time-resolved photoionization for endohedral fullerenes A@C60 and discuss how streaking time shifts are modifed due to the interaction of the C60 cage with the probing infrared streaking field.

  13. Correction

    NASA Astrophysics Data System (ADS)

    1998-12-01

    Alleged mosasaur bite marks on Late Cretaceous ammonites are limpet (patellogastropod) home scars Geology, v. 26, p. 947 950 (October 1998) This article had the following printing errors: p. 947, Abstract, line 11, “sepia” should be “septa” p. 947, 1st paragraph under Introduction, line 2, “creep” should be “deep” p. 948, column 1, 2nd paragraph, line 7, “creep” should be “deep” p. 949, column 1, 1st paragraph, line 1, “creep” should be “deep” p. 949, column 1, 1st paragraph, line 5, “19774” should be “1977)” p. 949, column 1, 4th paragraph, line 7, “in particular” should be “In particular” CORRECTION Mammalian community response to the latest Paleocene thermal maximum: An isotaphonomic study in the northern Bighorn Basin, Wyoming Geology, v. 26, p. 1011 1014 (November 1998) An error appeared in the References Cited. The correct reference appears below: Fricke, H. C., Clyde, W. C., O'Neil, J. R., and Gingerich, P. D., 1998, Evidence for rapid climate change in North America during the latest Paleocene thermal maximum: Oxygen isotope compositions of biogenic phosphate from the Bighorn Basin (Wyoming): Earth and Planetary Science Letters, v. 160, p. 193 208.

  14. Momentum resolution in inverse photoemission

    SciTech Connect

    Zumbülte, A.; Schmidt, A. B.; Donath, M.

    2015-01-15

    We present a method to determine the electron beam divergence, and thus the momentum resolution, of an inverse-photoemission setup directly from a series of spectra measured on Cu(111). Simulating these spectra with different beam divergences shows a distinct influence of the divergence on the appearance of the Shockley surface state. Upon crossing the Fermi level, its rise in intensity can be directly linked with the beam divergence. A comparison of measurement and simulation enables us to quantify the momentum resolution independent of surface quality, energy resolution, and experimental geometry. With spin resolution, a single spectrum taken around the Fermi momentum of a spin-split surface state, e.g., on Au(111), is sufficient to derive the momentum resolution of an inverse-photoemission setup.

  15. Photoemission-based microelectronic devices

    PubMed Central

    Forati, Ebrahim; Dill, Tyler J.; Tao, Andrea R.; Sievenpiper, Dan

    2016-01-01

    The vast majority of modern microelectronic devices rely on carriers within semiconductors due to their integrability. Therefore, the performance of these devices is limited due to natural semiconductor properties such as band gap and electron velocity. Replacing the semiconductor channel in conventional microelectronic devices with a gas or vacuum channel may scale their speed, wavelength and power beyond what is available today. However, liberating electrons into gas/vacuum in a practical microelectronic device is quite challenging. It often requires heating, applying high voltages, or using lasers with short wavelengths or high powers. Here, we show that the interaction between an engineered resonant surface and a low-power infrared laser can cause enough photoemission via electron tunnelling to implement feasible microelectronic devices such as transistors, switches and modulators. The proposed photoemission-based devices benefit from the advantages of gas-plasma/vacuum electronic devices while preserving the integrability of semiconductor-based devices. PMID:27811946

  16. Photoemission-based microelectronic devices

    NASA Astrophysics Data System (ADS)

    Forati, Ebrahim; Dill, Tyler J.; Tao, Andrea R.; Sievenpiper, Dan

    2016-11-01

    The vast majority of modern microelectronic devices rely on carriers within semiconductors due to their integrability. Therefore, the performance of these devices is limited due to natural semiconductor properties such as band gap and electron velocity. Replacing the semiconductor channel in conventional microelectronic devices with a gas or vacuum channel may scale their speed, wavelength and power beyond what is available today. However, liberating electrons into gas/vacuum in a practical microelectronic device is quite challenging. It often requires heating, applying high voltages, or using lasers with short wavelengths or high powers. Here, we show that the interaction between an engineered resonant surface and a low-power infrared laser can cause enough photoemission via electron tunnelling to implement feasible microelectronic devices such as transistors, switches and modulators. The proposed photoemission-based devices benefit from the advantages of gas-plasma/vacuum electronic devices while preserving the integrability of semiconductor-based devices.

  17. Study of Photoemissive Dusty Plasma

    SciTech Connect

    Gavrikov, A. V.; Fortov, V. E.; Petrov, O. F.; Babichev, V. N.; Filippov, A. V.; Pal', A. F.; Starostin, A. N.

    2008-09-07

    The present work deals with the experimental and theoretical investigation of photoemissive charging of polydisperse dust particles. The characteristic size of dust particles under consideration was 0.1-25 mkm. The experimental part of this work was devoted to the study of positive charging of macroparticles under UV-radiation that acted on dusty formations. Investigations were carried out in argon at normal pressure with particles of different materials. Dust structure was subjected to radiation. The power and frequency spectrum of this radiation was close to corresponding parameters of sun radiation near the top layers of Earth atmosphere. Owing to electron photoemission the macroparticles became positively charged. On the basis of experimental data the estimation of this charge was performed. It was about 500 elementary charges for micron particles. The theoretical part of present work included the numerical simulation of photoemissive dusty plasma decay in a drift-diffusion approximation. The model included equilibrium equation for positively charged macroparticles (in experiment, the percent of these particles was about 90), negatively charged dust particles (about 10%), positive ions (those were born by electron strike of buffered gas atoms) and electrons. Also the model included the Poisson equation for determination of potential distribution in the discharge region. The results of numerical calculations were in a satisfactory correspondence with experimental data both for time dependences of positively and negatively charged macroparticles concentrations and for their velocities.

  18. Study of Photoemissive Dusty Plasma

    NASA Astrophysics Data System (ADS)

    Gavrikov, A. V.; Fortov, V. E.; Petrov, O. F.; Babichev, V. N.; Filippov, A. V.; Pal', A. F.; Starostin, A. N.

    2008-09-01

    The present work deals with the experimental and theoretical investigation of photoemissive charging of polydisperse dust particles. The characteristic size of dust particles under consideration was 0.1-25 mkm. The experimental part of this work was devoted to the study of positive charging of macroparticles under UV-radiation that acted on dusty formations. Investigations were carried out in argon at normal pressure with particles of different materials. Dust structure was subjected to radiation. The power and frequency spectrum of this radiation was close to corresponding parameters of sun radiation near the top layers of Earth atmosphere. Owing to electron photoemission the macroparticles became positively charged. On the basis of experimental data the estimation of this charge was performed. It was about 500 elementary charges for micron particles. The theoretical part of present work included the numerical simulation of photoemissive dusty plasma decay in a drift-diffusion approximation. The model included equilibrium equation for positively charged macroparticles (in experiment, the percent of these particles was about 90), negatively charged dust particles (about 10%), positive ions (those were born by electron strike of buffered gas atoms) and electrons. Also the model included the Poisson equation for determination of potential distribution in the discharge region. The results of numerical calculations were in a satisfactory correspondence with experimental data both for time dependences of positively and negatively charged macroparticles concentrations and for their velocities.

  19. Photocathode device that replenishes photoemissive coating

    SciTech Connect

    Moody, Nathan A.; Lizon, David C.

    2016-06-14

    A photocathode device may replenish its photoemissive coating to replace coating material that desorbs/evaporates during photoemission. A linear actuator system may regulate the release of a replenishment material vapor, such as an alkali metal, from a chamber inside the photocathode device to a porous cathode substrate. The replenishment material deposits on the inner surface of a porous membrane and effuses through the membrane to the outer surface, where it replenishes the photoemissive coating. The rate of replenishment of the photoemissive coating may be adjusted using the linear actuator system to regulate performance of the photocathode device during photoemission. Alternatively, the linear actuator system may adjust a plasma discharge gap between a cartridge containing replenishment material and a metal grid. A potential is applied between the cartridge and the grid, resulting in ejection of metal ions from the cartridge that similarly replenish the photoemissive coating.

  20. A novel microRNA-132-sirtuin-1 axis underlies aberrant B-cell cytokine regulation in patients with relapsing-remitting multiple sclerosis [corrected].

    PubMed

    Miyazaki, Yusei; Li, Rui; Rezk, Ayman; Misirliyan, Hétoum; Moore, Craig; Farooqi, Nasr; Solis, Mayra; Goiry, Lorna Galleguillos; de Faria Junior, Omar; Dang, Van Duc; Colman, David; Dhaunchak, Ajit Singh; Antel, Jack; Gommerman, Jennifer; Prat, Alexandre; Fillatreau, Simon; Bar-Or, Amit

    2014-01-01

    Clinical trial results demonstrating that B-cell depletion substantially reduces new relapses in patients with multiple sclerosis (MS) have established that B cells play a role in the pathophysiology of MS relapses. The same treatment appears not to impact antibodies directed against the central nervous system, which underscores the contribution of antibody-independent functions of B cells to disease activity. One mechanism by which B cells are now thought to contribute to MS activity is by over-activating T cells, including through aberrant expression of B cell pro-inflammatory cytokines. However, the mechanisms underlying the observed B cell cytokine dysregulation in MS remain unknown. We hypothesized that aberrant expression of particular microRNAs might be involved in the dysregulated pro-inflammatory cytokine responses of B cells of patients with MS. Through screening candidate microRNAs in activated B cells of MS patients and matched healthy subjects, we discovered that abnormally increased secretion of lymphotoxin and tumor necrosis factor α by MS B cells is associated with abnormally increased expression of miR-132. Over-expression of miR-132 in normal B cells significantly enhanced their production of lymphotoxin and tumor necrosis factor α. The over-expression of miR-132 also suppressed the miR-132 target, sirtuin-1. We confirmed that pharmacological inhibition of sirtuin-1 in normal B cells induces exaggerated lymphotoxin and tumor necrosis factor α production, while the abnormal production of these cytokines by MS B cells can be normalized by resveratrol, a sirtuin-1 activator. These results define a novel miR-132-sirtuin-1 axis that controls pro-inflammatory cytokine secretion by human B cells, and demonstrate that a dysregulation of this axis underlies abnormal pro-inflammatory B cell cytokine responses in patients with MS.

  1. Skew aberration: a form of polarization aberration.

    PubMed

    Yun, Garam; Crabtree, Karlton; Chipman, Russell A

    2011-10-15

    We define a new class of aberration, skew aberration, which is a component of polarization aberration. Skew aberration is an intrinsic rotation of polarization states due to the geometric transformation of local coordinates, independent of coatings and interface polarization. Skew aberration in a radially symmetric system has the form of a circular retardance tilt plus coma aberration. Skew aberration causes undesired polarization distribution in the exit pupil. We demonstrate statistics on skew aberration of 2383 optical systems described in Code V's U.S. patent library [Code V Version 10.3 (Synopsys, 2011), pp. 22-24]; the mean skew aberration is 0.89° and the standard deviation is 1.37°. The maximum skew aberration found is 17.45° and the minimum is -11.33°. U.S. patent 2,896,506, which has ±7.01° of skew aberration, is analyzed in detail. Skew aberration should be of concern in microlithography optics and other high NA and large field of view optical systems.

  2. Accommodative lag and fluctuations when optical aberrations are manipulated.

    PubMed

    Gambra, Enrique; Sawides, Lucie; Dorronsoro, Carlos; Marcos, Susana

    2009-06-09

    We evaluated the accommodative response to a stimulus moving from 0 to 6 D following a staircase function under natural, corrected, and induced optical aberrations, using an adaptive-optics (AO) electromagnetic deformable mirror. The accommodative response of the eye (through the mirror) and the change of aberrations were measured on 5 subjects using a Hartmann-Shack wavefront sensor operating at 12.8 Hz. Five conditions were tested: (1) natural aberrations, (2) AO correction of the unaccommodated state and induction (over 6-mm pupils) of (3) +1 microm and (4) -1 microm of spherical aberration and (5) -2 microm of vertical coma. Four subjects showed a better accommodative response with AO correction than with their natural aberrations. The induction of negative spherical aberration also produced a better accommodative response in the same subjects. Accommodative lag increased in all subjects when positive spherical aberration and coma were induced. Fluctuations of the accommodative response (computed during each 1-D period of steady accommodation) increased with accommodative response when high-order aberrations were induced. The largest fluctuations occurred for induced negative spherical aberration and the smallest for natural and corrected aberrations. The study demonstrates that aberrations influence accommodative lag and fluctuations of accommodation and that correcting aberrations improves rather than compromises the accommodative response.

  3. A Dust Grain Photoemission Experiment

    NASA Technical Reports Server (NTRS)

    Venturini, C. C.; Spann, J. F., Jr.; Abbas, M. M.; Comfort, R. H.

    2000-01-01

    A laboratory experiment has been developed at Marshall Space Flight Center to study the interaction of micron-sized particles with plasmas and FUV radiation. The intent is to investigate the conditions under which particles of various compositions and sizes become charged, or discharged, while exposed to an electron beam and/or UV radiation. This experiment uses a unique laboratory where a single charged micron size particle is suspended in a quadrupole trap and then subjected to a controlled environment. Tests are performed using different materials and sizes, ranging from 10 microns to 1 micron, to determine the particle's charge while being subjected to an electron beam and /or UV radiation. The focus of this presentation will be on preliminary results from UV photoemission tests, but past results from electron beam, secondary electron emission tests will also be highlighted. A monochromator is used to spectrally resolve UV in the 120 nm to 300 nm range. This enables photoemission measurements as a function of wavelength. Electron beam tests are conducted using I to 3 micron sized aluminum oxide particles subjected to energies between 100 eV to 3 KeV. It was found that for both positive and negative particles the potential tended toward neutrality over time with possible equilibrium potentials between -0.8 Volts and 0.8 Volts.

  4. HEAVY ION FUSION SCIENCE VIRTUAL NATIONAL LABORATORY 1ST QUARTER 2010 MILESTONE REPORT: Simulations of fast correction of chromatic aberrations to establish physics specifications for implementation on NDCX-1 and NDCX-2

    SciTech Connect

    LIDIA, S.M.; LUND, S.M.; SEIDL, P.A.

    2010-01-04

    This milestone has been accomplished. The Heavy Ion Fusion Science Virtual National Laboratory has completed simulations of a fast correction scheme to compensate for chromatic and time-dependent defocusing effects in the transport of ion beams to the target plane in the NDCX-1 facility. Physics specifications for implementation in NDCX-1 and NDCX-2 have been established. This milestone has been accomplished. The Heavy Ion Fusion Science Virtual National Laboratory has completed simulations of a fast correction scheme to compensate for chromatic and time-dependent defocusing effects in the transport of ion beams to the target plane in the NDCX-1 facility. Physics specifications for implementation in NDCX-1 and NDCX-2 have been established. Focal spot differences at the target plane between the compressed and uncompressed regions of the beam pulse have been modeled and measured on NDCX-1. Time-dependent focusing and energy sweep from the induction bunching module are seen to increase the compressed pulse spot size at the target plane by factors of two or more, with corresponding scaled reduction in the peak intensity and fluence on target. A time-varying beam envelope correction lens has been suggested to remove the time-varying aberration. An Einzel (axisymmetric electric) lens system has been analyzed and optimized for general transport lines, and as a candidate correction element for NDCX-1. Attainable high-voltage holdoff and temporal variations of the lens driving waveform are seen to effect significant changes on the beam envelope angle over the duration of interest, thus confirming the utility of such an element on NDCX-1. Modeling of the beam dynamics in NDCX-1 was performed using a time-dependent (slice) envelope code and with the 3-D, self-consistent, particle-in-cell code WARP. Proof of concept was established with the slice envelope model such that the spread in beam waist positions relative to the target plane can be minimized with a carefully designed

  5. Correction of Aberrant NADPH Oxidase Activity in Blood-Derived Mononuclear Cells from Type II Diabetes Mellitus Patients by a Naturally Fermented Papaya Preparation

    PubMed Central

    Dickerson, Ryan; Deshpande, Bhakthi; Gnyawali, Urmila; Lynch, Debbie; Gordillo, Gayle M.; Schuster, Dara; Osei, Kwame

    2012-01-01

    Abstract Supplementation of standardized fermented papaya preparation (FPP) to adult diabetic mice improves dermal wound healing outcomes. Peripheral blood mononuclear cells (PBMC) from type II diabetes mellitus (T2DM) patients elicit a compromised respiratory burst activity resulting in increased risk of infections for the diabetic patients. Aims: The objectives of the current study were to determine the effect of FPP supplementation on human diabetic PBMC respiratory burst activity and to understand underlying mechanisms of such action of FPP. Results: When stimulated with phorbol 12-myristate 13-acetate, the production of reactive oxygen species by T2DM PBMC was markedly compromised compared to that of the PBMC from non-DM donors. FPP treated ex vivo improved respiratory burst outcomes in T2DM PBMC. FPP treatment significantly increased phosphorylation of the p47phox subunit of NADPH oxidase. In addition, the protein and mRNA expression of Rac2 was potently upregulated after FPP supplemention. The proximal human Rac2 gene promoter is G–C rich and contains consensus binding sites for Sp1 and AP-1. While FPP had no significant effect on the AP-1 DNA binding activity, the Sp1 DNA binding activity was significantly upregulated in PBMC after treatment of the cells with FPP. Innovation: This work provided first evidence that compromised respiratory burst performance of T2DM PBMC may be corrected by a nutritional supplement. Conclusion: FPP can correct respiratory burst performance of T2DM PBMC via an Sp-1-dependant pathway. Studies testing the outcome of FPP supplementation in diabetic patients are warranted. Antioxid. Redox Signal. 17, 485–491. PMID:22369197

  6. Coherent and incoherent processes in resonant photoemission

    SciTech Connect

    Magnuson, M.; Karis, O.; Weinelt, M.

    1997-04-01

    In this contribution the authors present the distinction between coherent and incoherent processes in resonant photoemission. As a first step they determine whether an autoionization process is photoemission-like or Auger-like. The discussion is based on measurements for a weakly bonded adsorption system, Ar/Pt(111). This type of system is well adapted to investigate these effects since it yields distinctly shifted spectral features depending on the nature of the process. After this, the question of resonance photoemission in metallic systems is addressed. This is done in connection with measurements at the 2p edges for Ni metal. Ni has been one of the prototype systems for resonant photoemission. The resonances have been discussed in connection with the strong correlation and d-band localization effects in this system. Based on the results some general comments about the appearance of resonant effects in metallic systems are made.

  7. Laser-assisted photoemission from surfaces

    SciTech Connect

    Saathoff, G.; Miaja-Avila, L.; Murnane, M. M.; Kapteyn, H. C.; Aeschlimann, M.

    2008-02-15

    We investigate the laser-assisted photoelectric effect from a solid surface. By illuminating a Pt(111) sample simultaneously with ultrashort 1.6 and 42 eV pulses, we observe sidebands in the extreme ultraviolet photoemission spectrum, and accurately extract their amplitudes over a wide range of laser intensities. Our results agree with a simple model, in which soft x-ray photoemission is accompanied by the interaction of the photoemitted electron with the laser field. This strong effect can definitively be distinguished from other laser surface interaction phenomena, such as hot electron excitation, above-threshold photoemission, and space-charge acceleration. Thus, laser-assisted photoemission from surfaces promises to extend pulse duration measurements to higher photon energies, as well as opening up measurements of femtosecond-to-attosecond electron dynamics in solid and surface-adsorbate systems.

  8. Calculations of Photoemission from Rutile

    NASA Astrophysics Data System (ADS)

    Hjalmarson, Harold; Schultz, Peter; Moore, Chris

    2015-03-01

    Photoemission is a well-known mechanism for release of electrons from a surface during electrical breakdown of a gas such as air. During air breakdown, UV photons, which are emitted from the highly excited gas molecules, are absorbed in the surfaces such as the cathode and the anode. These absorbed photons create energetic electrons, and a small portion of these electrons reach the surface. Those that overcome the potential energy barrier at the surface tend to be emitted. In this talk, the Boltzmann equation that describes these phenomena is formulated. A Monte Carlo probabilistic method is used to obtain the rate of electron emission as a function of photon energy. The role of bandstructure effects will be discussed. This bandstructure information is obtained by using a density-functional theory (DFT) method. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  9. Photoemission studies of semiconductor nanocrystals

    SciTech Connect

    Hamad, K. S.; Roth, R.; Alivisatos, A. P.

    1997-04-01

    Semiconductor nanocrystals have been the focus of much attention in the last ten years due predominantly to their size dependent optical properties. Namely, the band gap of nanocrystals exhibits a shift to higher energy with decreasing size due to quantum confinement effects. Research in this field has employed primarily optical techniques to study nanocrystals, and in this respect this system has been investigated extensively. In addition, one is able to synthesize monodisperse, crystalline particles of CdS, CdSe, Si, InP, InAs, as well as CdS/HgS/CdS and CdSe/CdS composites. However, optical spectroscopies have proven ambiguous in determining the degree to which electronic excitations are interior or surface admixtures or giving a complete picture of the density of states. Photoemission is a useful technique for understanding the electronic structure of nanocrystals and the effects of quantum confinement, chemical environments of the nanocrystals, and surface coverages. Of particular interest to the authors is the surface composition and structure of these particles, for they have found that much of the behavior of nanocrystals is governed by their surface. Previously, the authors had performed x-ray photoelectron spectroscopy (XPS) on CdSe nanocrystals. XPS has proven to be a powerful tool in that it allows one to determine the composition of the nanocrystal surface.

  10. Structural Channels and Atomic-Cluster Insertion in CsxBi4Te6 (1 ≤ x ≤ 1.25) As Observed by Aberration-Corrected Scanning Transmission Electron Microscopy.

    PubMed

    Zhang, Ruixin; Yang, Huaixin; Guo, Cong; Tian, Huanfang; Shi, Honglong; Chen, Genfu; Li, Jianqi

    2016-12-19

    Microstructural analyses based on aberration-corrected scanning transmission electron microscopy (STEM) observations demonstrate that low-dimensional CsxBi4Te6 materials, known to be a novel thermoelectric and superconducting system, contain notable structural channels that go directly along the b axis, which can be partially filled by atom clusters depending on the thermal treatment process. We successfully prepared two series of CsxBi4Te6 single-crystalline samples using two different sintering processes. The CsxBi4Te6 samples prepared using an air-quenching method show superconductivity at approximately 4 K, while the CsxBi4Te6 with the same nominal compositions prepared by slowly cooling are nonsuperconductors. Moreover, atomic structural investigations of typical samples reveal that the structural channels are often empty in superconducting materials; thus, we can represent the superconducting phase as Cs1-yBi4Te6 with considering the point defects in the Cs layers. In addition, the channels in the nonsuperconducting crystals are commonly partially occupied by triplet Bi clusters. Moreover, the average structures for these two phases are also different in their monoclinic angles (β), which are estimated to be 102.3° for superconductors and 100.5° for nonsuperconductors.

  11. Correcting Aberrated Wavefronts from Synthetic Apertures Holographically.

    DTIC Science & Technology

    1986-12-01

    subject and reference legs was proven to be planar through both shear-plate interferometric analysis ( Malacara , pp 105-48) and by observing the...London: Cam- bridge University Press, 1969 Malacara . Daniel, ed. Optical Shop Testing. New York: John Wiley and Sons, 1978. Marathay, Arvind S

  12. Bulk photoemission from metal films and nanoparticles

    SciTech Connect

    Ikhsanov, R Sh; Babicheva, V E; Protsenko, I E; Uskov, A V; Guzhva, M E

    2015-01-31

    Internal emission of photoelectrons from metal films and nanoparticles (nanowires and nanospheres) into a semiconductor matrix is studied theoretically by taking into account the jump of the effective electron mass at the metal – semiconductor interface and the cooling effect of hot electrons due to electron – electron collisions in the metal. The internal quantum efficiency of photoemission for the film and nanoparticles of two types (nanospheres and nanowires) is calculated. It is shown that the reduction of the effective mass of the electron during its transition from metal to semiconductor may lead to a significant (orders of magnitude and higher) decrease in the internal quantum efficiency of bulk photoemission. (nanostructures)

  13. Interpreting Chromosome Aberration Spectra

    NASA Technical Reports Server (NTRS)

    Levy, Dan; Reeder, Christopher; Loucas, Bradford; Hlatky, Lynn; Chen, Allen; Cornforth, Michael; Sachs, Rainer

    2007-01-01

    Ionizing radiation can damage cells by breaking both strands of DNA in multiple locations, essentially cutting chromosomes into pieces. The cell has enzymatic mechanisms to repair such breaks; however, these mechanisms are imperfect and, in an exchange process, may produce a large-scale rearrangement of the genome, called a chromosome aberration. Chromosome aberrations are important in killing cells, during carcinogenesis, in characterizing repair/misrepair pathways, in retrospective radiation biodosimetry, and in a number of other ways. DNA staining techniques such as mFISH ( multicolor fluorescent in situ hybridization) provide a means for analyzing aberration spectra by examining observed final patterns. Unfortunately, an mFISH observed final pattern often does not uniquely determine the underlying exchange process. Further, resolution limitations in the painting protocol sometimes lead to apparently incomplete final patterns. We here describe an algorithm for systematically finding exchange processes consistent with any observed final pattern. This algorithm uses aberration multigraphs, a mathematical formalism that links the various aspects of aberration formation. By applying a measure to the space of consistent multigraphs, we will show how to generate model-specific distributions of aberration processes from mFISH experimental data. The approach is implemented by software freely available over the internet. As a sample application, we apply these algorithms to an aberration data set, obtaining a distribution of exchange cycle sizes, which serves to measure aberration complexity. Estimating complexity, in turn, helps indicate how damaging the aberrations are and may facilitate identification of radiation type in retrospective biodosimetry.

  14. Correcting Hubble Vision.

    ERIC Educational Resources Information Center

    Shaw, John M.; Sheahen, Thomas P.

    1994-01-01

    Describes the theory behind the workings of the Hubble Space Telescope, the spherical aberration in the primary mirror that caused a reduction in image quality, and the corrective device that compensated for the error. (JRH)

  15. Sensing Phase Aberrations behind Lyot Coronagraphs

    NASA Astrophysics Data System (ADS)

    Sivaramakrishnan, Anand; Soummer, Rémi; Pueyo, Laurent; Wallace, J. Kent; Shao, Michael

    2008-11-01

    Direct detection of young extrasolar planets orbiting nearby stars can be accomplished from the ground with extreme adaptive optics and coronagraphy in the near-infrared, as long as this combination can provide an image with a dynamic range of 107 after the data are processed. Slowly varying speckles due to residual phase aberrations that are not measured by the primary wave-front sensor are the primary obstacle to achieving such a dynamic range. In particular, non-common optical path aberrations occurring between the wave-front sensor and the coronagraphic occulting spot degrade performance the most. We analyze the passage of both low and high spatial frequency phase ripples, as well as low-order Zernike aberrations, through an apodized pupil Lyot coronagraph in order to demonstrate the way coronagraphic filtering affects various aberrations. We derive the coronagraphically induced cutoff frequency of the filtering and estimate coronagraphic contrast losses due to low-order Zernike aberrations: tilt, astigmatism, defocus, coma, and spherical aberration. Such slowly varying path errors can be measured behind a coronagraph and corrected by a slowly updated optical path delay precompensation or offset asserted on the wave front by the adaptive optics (AO) system. We suggest ways of measuring and correcting all but the lowest spatial frequency aberrations using Lyot plane wave-front data, in spite of the complex interaction between the coronagraph and those mid-spatial frequency aberrations that cause image plane speckles near the coronagraphic focal plane mask occulter's edge. This investigation provides guidance for next-generation coronagraphic instruments currently under construction.

  16. A New Spin on Photoemission Spectroscopy

    SciTech Connect

    Jozwiak, Chris

    2008-12-01

    The electronic spin degree of freedom is of general fundamental importance to all matter. Understanding its complex roles and behavior in the solid state, particularly in highly correlated and magnetic materials, has grown increasingly desirable as technology demands advanced devices and materials based on ever stricter comprehension and control of the electron spin. However, direct and efficient spin dependent probes of electronic structure are currently lacking. Angle Resolved Photoemission Spectroscopy (ARPES) has become one of the most successful experimental tools for elucidating solid state electronic structures, bolstered by-continual breakthroughs in efficient instrumentation. In contrast, spin-resolved photoemission spectroscopy has lagged behind due to a lack of similar instrumental advances. The power of photoemission spectroscopy and the pertinence of electronic spin in the current research climate combine to make breakthroughs in Spin and Angle Resolved Photoemission Spectroscopy (SARPES) a high priority . This thesis details the development of a unique instrument for efficient SARPES and represents a radical departure from conventional methods. A custom designed spin polarimeter based on low energy exchange scattering is developed, with projected efficiency gains of two orders of magnitude over current state-of-the-art polarimeters. For energy analysis, the popular hemispherical analyzer is eschewed for a custom Time-of-Flight (TOF) analyzer offering an additional order of magnitude gain in efficiency. The combined instrument signifies the breakthrough needed to perform the high resolution SARPES experiments necessary for untangling the complex spin-dependent electronic structures central to today's condensed matter physics.

  17. Tuning fifth-order aberrations in a Quadrupole-Octupole Corrector

    SciTech Connect

    Lupini, Andrew R; Pennycook, Stephen J

    2012-01-01

    The resolution of conventional electron microscopes is usually limited by spherical aberration. Microscopes equipped with aberration-correctors are then primarily limited by higher-order, chromatic, and misalignment aberrations. In particular the Nion third-order aberration correctors installed on machines with a low energy spread and possessing sophisticated alignment software were limited by the uncorrected fifth-order aberrations. Here we show how the Nion fifth-order aberration corrector can be used to adjust and reduce some of the fourth and fifth-order aberrations in a probe-corrected scanning transmission electron microscope.

  18. Reactivation of latently infected HIV-1 viral reservoirs and correction of aberrant alternative splicing in the LMNA gene via AMPK activation: Common mechanism of action linking HIV-1 latency and Hutchinson-Gilford progeria syndrome.

    PubMed

    Finley, Jahahreeh

    2015-09-01

    AMPK, a master regulator of cellular metabolism which has been shown to activate PKC-theta (θ) and is essential for T cell activation, may modulate the splicing activities of SRp55 as well as enhance a p32-mediated inhibition of ASF/SF2-induced alternative splicing, potentially correcting aberrant alternative splicing in the LMNA gene and reactivating latent viral HIV-1 reservoirs. Moreover, similar epigenetic modifications and cell cycle regulators also characterize the analogous stages of premature senescence in progeroid cells and latency in HIV-1 infected T cells. AMPK-activating compounds including metformin and resveratrol may thus embody a novel treatment paradigm linking the pathophysiology of HGPS with that of HIV-1 latency.

  19. PHOTOEMISSION AS A PROBE OF THE COLLECTIVE EXCITATIONS IN CONDENSED MATTER SYSTEMS.

    SciTech Connect

    JOHNSON, P.D.; VALLA, T.

    2006-08-01

    New developments in instrumentation have recently allowed photoemission measurements to be performed with very high energy and momentum resolution.[1] This has allowed detailed studies of the self-energy corrections to the lifetime and mass renormalization of excitations in the vicinity of the Fermi level. These developments come at an opportune time. Indeed the discovery of high temperature superconductivity in the cuprates and related systems is presenting a range of challenges for condensed matter physics.[2] Does the mechanism of high T{sub c} superconductivity represent new physics? Do we need to go beyond Landau's concept of the Fermi liquid?[3] What, if any, is the evidence for the presence or absence of quasiparticles in the excitation spectra of these complex oxides? The energy resolution of the new instruments is comparable to or better than the energy or temperature scale of superconductivity and the energy of many collective excitations. As such, photoemission has again become recognized as an important probe of condensed matter. Studies of the high T{sub c} superconductors and related materials are aided by the observation that they are two dimensional. To understand this, we note that the photoemission process results in both an excited photoelectron and a photohole in the final state. Thus the experimentally measured photoemission peak is broadened to a width reflecting contributions from both the finite lifetime of the photohole and the momentum broadening of the outgoing photoelectron.

  20. Angle-resolved photoemission extended fine structure

    SciTech Connect

    Barton, J.J.

    1985-03-01

    Measurements of the Angle-Resolved Photoemission Extended Fine Structure (ARPEFS) from the S(1s) core level of a c(2 x 2)S/Ni(001) are analyzed to determine the spacing between the S overlayer and the first and second Ni layers. ARPEFS is a type of photoelectron diffraction measurement in which the photoelectron kinetic energy is swept typically from 100 to 600 eV. By using this wide range of intermediate energies we add high precision and theoretical simplification to the advantages of the photoelectron diffraction technique for determining surface structures. We report developments in the theory of photoelectron scattering in the intermediate energy range, measurement of the experimental photoemission spectra, their reduction to ARPEFS, and the surface structure determination from the ARPEFS by combined Fourier and multiple-scattering analyses. 202 refs., 67 figs., 2 tabs.

  1. Two photon photoemission of deposited silver clusters

    NASA Astrophysics Data System (ADS)

    Busolt, U.; Cottancin, E.; Röhr, H.; Socaciu, L.; Leisner, T.; Wöste, L.

    We use time resolved two photon photoemission to study the stability of size selected silver clusters deposited onto highly oriented pyrolytic graphite (HOPG) substrates. Size-selected Agn+ clusters (n=2-9) are deposited at low coverage onto HOPG surfaces at liquid nitrogen temperatures. After deposition, the samples are irradiated by a series of ultrashort laser pulse pairs. Photoelectrons created by two photon photoemission are collected in a magnetic bottle type time-of-flight photoelectron spectrometer. Their kinetic energy distribution is recorded as a function of the delay time between subsequent light pulses. With the exception of Ag3 the size dependence of the photoelectron spectra reveals a pronounced odd/even effect, which is well known for gas phase silver clusters. This indicates that the deposited clusters retain their size and identity on the sample. The lifetime of the photoexcitation rises with cluster size. This is attributed to an increasing electronic density of states for larger clusters.

  2. Wide-angle chromatic aberration corrector for the human eye.

    PubMed

    Benny, Yael; Manzanera, Silvestre; Prieto, Pedro M; Ribak, Erez N; Artal, Pablo

    2007-06-01

    The human eye is affected by large chromatic aberration. This may limit vision and makes it difficult to see fine retinal details in ophthalmoscopy. We designed and built a two-triplet system for correcting the average longitudinal chromatic aberration of the eye while keeping a reasonably wide field of view. Measurements in real eyes were conducted to examine the level and optical quality of the correction. We also performed some tests to evaluate the effect of the corrector on visual performance.

  3. 5f Resonant photoemission from plutonium

    NASA Astrophysics Data System (ADS)

    Terry, J.; Schulze, R. K.; Farr, J. D.; Zocco, T.; Heinzelman, K.; Rotenberg, E.; Shuh, D. K.; Van der Laan, G.; Arena, D. A.; Tobin, J. G.

    2002-02-01

    Experimental resonant photoemission (ResPes) results for α-Pu and δ-Pu bulk samples are presented and compared to the results of an atomic model calculation. Both Pu samples exhibit limited agreement with the atomic model calculations. As expected, α-Pu appears to have more 5f valence band delocalization than δ-Pu. Evidence of an enhanced sensitivity to surface corruption, by using synchrotron radiation as the excitation, is presented.

  4. Angle resolved photoemission spectroscopy and surface states

    NASA Astrophysics Data System (ADS)

    Kar, Nikhiles

    2016-10-01

    Angle Resolved Photo Emission Spectroscopy (ARPES) has been a very effective tool to study the electronic states of solids, from simple metals to complex systems like cuprate superconductors. For photon energy in the range of 10 - 100 eV, it is a surface sensitive process as the free path of the photo emitted electrons is of the order of a few lattice parameters. However to interpret the experimental data one needs to have a theoretical foundation for the photoemission process. From the theory of photoemission it may be seen that one can get information about the state from which the electron has been excited. As the translational periodicity is broken normal to the surface, a new type of electron state in the forbidden energy gap can exist localized in the surface region. ARPES can reveal the existence and the property of such surface states. We shall also discuss briefly how the electromagnetic field of the photons are influenced by the presence of the surface and how one can try to take that into account in photoemission theory.

  5. Laser correcting mirror

    DOEpatents

    Sawicki, Richard H.

    1994-01-01

    An improved laser correction mirror (10) for correcting aberrations in a laser beam wavefront having a rectangular mirror body (12) with a plurality of legs (14, 16, 18, 20, 22, 24, 26, 28) arranged into opposing pairs (34, 36, 38, 40) along the long sides (30, 32) of the mirror body (12). Vector force pairs (49, 50, 52, 54) are applied by adjustment mechanisms (42, 44, 46, 48) between members of the opposing pairs (34, 36, 38, 40) for bending a reflective surface 13 of the mirror body 12 into a shape defining a function which can be used to correct for comatic aberrations.

  6. Measurement of large low-order aberrations by using a series of through-focus Ronchigrams.

    PubMed

    Akima, Hisanao; Yoshida, Takaho

    2014-08-01

    A method for measuring large aberrations up to second order (defocus, 2-fold astigmatism and axial coma), which uses a through-focus series of Ronchigrams, is proposed. The method is based on the principle that line-focus conditions in Ronchigrams can be locally detected and low-order aberrations can thereby be measured. The proposed method provides auto-tuning of large low-order aberration; in particular, iterative aberration measurement and correction reduce low-order aberrations from several thousand nanometers to less than a few hundred nanometers, which can be handled by conventional fine-aberration tuning methods.

  7. Near-field focused photoemission from polystyrene microspheres studied with photoemission electron microscopy

    SciTech Connect

    Peppernick, Samuel J.; Joly, Alan G.; Beck, Kenneth M.; Hess, Wayne P.

    2012-07-07

    We use photoemission electron microscopy(PEEM) to image 3 μm diameter polystyrene spheres supported on a metalthin film illuminated by 400 nm (~3.1 eV) and 800 nm (~1.5 eV) femtosecond (fs) laser pulses. Intense photoemission is generated by microspheres even though polystyrene is an insulator and its ionization threshold is well above the photon energies employed. We observe intense photoemission from the far side (the side opposite the incident light) of the illuminated microsphere that is attributed to light focusing within the microsphere. For the case of p-polarized, 800 nm fs laser pulses, we observe photoemission exclusively from the far side of the microsphere and additionally resolve sub-50 nm hot spots in the supporting Pt/Pd thin film that are located only within the focal region of the microsphere. We compare the PEEM images with finite difference time domain(FDTD) electrodynamic simulations to model our experimental results. Finally, the FDTD simulations predict light focusing in the microsphere and subsequent interaction with the supporting metal surface that is consistent with the experimental observations.

  8. Monochromatic electron photoemission from diamondoid monolayers

    SciTech Connect

    Yang, Wanli; Yang, Wanli L.; Fabbri, J.D.; Willey, T.M.; Lee, J.R.I.; Dahl, J.E.; Carlson, R.M.K.; Schreiner, P.R.; Fokin, A.A.; Tkachenko, B.A.; Fokina, N.A.; Meevasana, W.; Mannella, N.; Tanaka, K.; Zhou, X.J.; van Buuren, T.; Kelly, M.A.; Hussain, Z.; Melosh, N.A.; Shen, Z.-X.

    2007-02-27

    We found monochromatic electron photoemission from large-area self-assembled monolayers of a functionalized diamondoid, [121]tetramantane-6-thiol. Photoelectron spectra of the diamondoid monolayers exhibited a peak at the low-kinetic energy threshold; up to 68percent of all emitted electrons were emitted within this single energy peak. The intensity of the emission peak is indicative of diamondoids being negative electron affinity materials. With an energy distribution width of less than 0.5 electron volts, this source of monochromatic electrons may find application in technologies such as electron microscopy, electron beam lithography, and field-emission flatpanel displays.

  9. Monochromatic Electron Photoemission from DiamondoidMonolayers

    SciTech Connect

    Yang, W.L.

    2010-04-15

    We found monochromatic electron photoemission from large-area self-assembled monolayers of a functionalized diamondoid, [121]tetramantane-6-thiol. Photoelectron spectra of the diamondoid monolayers exhibited a peak at the low-kinetic energy threshold; up to 68% of all emitted electrons were emitted within this single energy peak. The intensity of the emission peak is indicative of diamondoids being negative electron affinity materials. With an energy distribution width of less than 0.5 electron volts, this source of monochromatic electrons may find application in technologies such as electron microscopy, electron beam lithography, and field-emission flat-panel displays.

  10. Resonant photoemission in f-electron systems: Pu and Gd

    NASA Astrophysics Data System (ADS)

    Tobin, J. G.; Chung, B. W.; Schulze, R. K.; Terry, J.; Farr, J. D.; Shuh, D. K.; Heinzelman, K.; Rotenberg, E.; Waddill, G. D.; van der Laan, G.

    2003-10-01

    Resonant photoemission in the Pu 5f and Pu 6p states is compared to that in the Gd 4f and Gd 5p states. Spectral simulations, based upon an atomic model with angular momentum coupling, are compared to the Gd and Pu results. Additional spectroscopic measurements of Pu, including core level photoemission and x-ray absorption, are also presented.

  11. Resonant Photoemission in f Electron Systems: Pu& Gd

    SciTech Connect

    Tobin, J G; Chung, B W; Schulze, R K; Terry, J; Farr, J D; Shuh, D K; Heinzelman, K; Rotenberg, E; Waddill, G D; van der Laan, G

    2003-03-07

    Resonant photoemission in the Pu5f and Pu6p states is compared to that in the Gd4f and Gd5p states. Spectral simulations, based upon and atomic model with angular momentum coupling, are compared to the Gd and Pu results. Additional spectroscopic measurements of Pu, including core level photoemission and x-ray absorption are also presented.

  12. Resonant photoemission in f electron systems: Pu and Gd

    SciTech Connect

    Tobin, J.G.; Chung, B.W.; Waddill, G.D.; Schulze, R.K.; Terry,J.; Farr, J.D.; Zocco, T.; Shuh, D.K.; Heinzelman, K.; Rotenberg, E.; Vander Laan, G.

    2003-10-14

    Resonant photoemission in the Pu 5f and Pu 6p states is compared to that in the Gd 4f and Gd 5p states. Spectral simulations, based upon an atomic model with angular momentum coupling, are compared to the Gd and Pu results. Additional spectroscopic measurements of Pu, including core level photoemission and x-ray absorption, are also presented.

  13. Ambient pressure photoemission spectroscopy of metal surfaces

    NASA Astrophysics Data System (ADS)

    Baikie, Iain D.; Grain, Angela C.; Sutherland, James; Law, Jamie

    2014-12-01

    We describe a novel photoemission technique utilizing a traditional Kelvin probe as a detector of electrons/atmospheric ions ejected from metallic surfaces (Au, Ag, Cu, Fe, Ni, Ti, Zn, Al) illuminated by a deep ultra-violet (DUV) source under ambient pressure. To surmount the limitation of electron scattering in air the incident photon energy is rastered rather than applying a variable retarding electric field as is used with UPS. This arrangement can be applied in several operational modes: using the DUV source to determine the photoemission threshold (Φ) with 30-50 meV resolution and also the Kelvin probe, under dark conditions, to measure contact potential difference (CPD) between the Kelvin probe tip and the metallic sample with an accuracy of 1-3 meV. We have studied the relationship between the photoelectric threshold and CPD of metal surfaces cleaned in ambient conditions. Inclusion of a second spectroscopic visible source was used to confirm a semiconducting oxide, possibly Cu2O, via surface photovoltage measurements with the KP. This dual detection system can be easily extended to controlled gas conditions, relative humidity control and sample heating/cooling.

  14. Effects of aberrations in spatiotemporal focusing of ultrashort laser pulses.

    PubMed

    Sun, Bangshan; Salter, Patrick S; Booth, Martin J

    2014-04-01

    Spatiotemporal focusing, or simultaneous spatial and temporal focusing (SSTF), has already been adopted for various applications in microscopy, photoactivation for biological studies, and laser fabrication. We investigate the effects of aberrations on focus formation in SSTF, in particular, the effects of phase aberrations related to low-order Zernike modes and a refractive index mismatch between the immersion medium and sample. By considering a line focus, we are able to draw direct comparison between the performance of SSTF and conventional spatial focusing (SF). Wide-field SSTF is also investigated and is found to be much more robust to aberrations than either line SSTF or SF. These results show the sensitivity of certain focusing methods to specific aberrations, and can inform on the necessity and benefit of aberration correction.

  15. Ultrahigh-spatial-resolution chemical and magnetic imaging by laser-based photoemission electron microscopy

    SciTech Connect

    Taniuchi, Toshiyuki Kotani, Yoshinori; Shin, Shik

    2015-02-15

    We report the first experiments carried out on a new chemical and magnetic imaging system, which combines the high spatial resolution of a photoemission electron microscope (PEEM) with a continuous-wave deep-ultraviolet laser. Threshold photoemission is sensitive to the chemical and magnetic structures of the surface of materials. The spatial resolution of PEEM is limited by space charging when using pulsed photon sources as well as aberrations in the electron optics. We show that the use of a continuous-wave laser enabled us to overcome such a limit by suppressing the space-charge effect, allowing us to obtain a resolution of approximately 2.6 nm. With this system, we demonstrated the imaging of surface reconstruction domains on Si(001) by linear dichroism with normal incidence of the laser beam. We also succeeded in magnetic imaging of thin films with the use of magnetic circular dichroism near the Fermi level. The unique features of the ultraviolet laser will give us fast switching of the incident angles and polarizations of the photon source, which will be useful for the characterization of antiferromagnetic materials as well as ferromagnetic materials.

  16. Multiplexed aberration measurement for deep tissue imaging in vivo

    PubMed Central

    Wang, Chen; Liu, Rui; Milkie, Daniel E.; Sun, Wenzhi; Tan, Zhongchao; Kerlin, Aaron; Chen, Tsai-Wen; Kim, Douglas S.; Ji, Na

    2014-01-01

    We describe a multiplexed aberration measurement method that modulates the intensity or phase of light rays at multiple pupil segments in parallel to determine their phase gradients. Applicable to fluorescent-protein-labeled structures of arbitrary complexity, it allows us to obtain diffraction-limited resolution in various samples in vivo. For the strongly scattering mouse brain, a single aberration correction improves structural and functional imaging of fine neuronal processes over a large imaging volume. PMID:25128976

  17. Optical aberration compensation in a multiplexed optical trapping system

    NASA Astrophysics Data System (ADS)

    Čižmár, T.; Dalgarno, H. I. C.; Ashok, P. C.; Gunn-Moore, F. J.; Dholakia, K.

    2011-04-01

    In this paper we discuss optical aberrations within a multiplexed optical trapping system. We analyze two of the most powerful methods for optical trap multiplexing: time-shared beam steering and holographic beam shaping in a tandem system with an acousto-optic deflector and spatial light modulator. We show how to isolate and correct for the aberrations introduced by these individual optical components using the spatial light modulator and demonstrate the enhancement this provides to optical trapping.

  18. Three-dimensional polarization aberration functions in optical system based on three-dimensional polarization ray-tracing calculus

    NASA Astrophysics Data System (ADS)

    He, Wenjun; Fu, Yuegang; Liu, Zhiying; Zhang, Lei; Wang, Jiake; Zheng, Yang; Li, Yahong

    2017-03-01

    The polarization aberrations of a complex optical system with multi-element lens have been investigated using a 3D polarization aberration function. The 3D polarization ray-tracing matrix has been combined with the optical path difference to obtain a 3D polarization aberration function, which avoids the need for a complicated phase unwrapping process. The polarization aberrations of a microscope objective have been analyzed to include, the distributions of 3D polarization aberration functions, diattenuation aberration, retardance aberration, and polarization-dependent intensity on the exit pupil. Further, the aberrations created by the field of view and the coating on the distribution rules of 3D polarization aberration functions are discussed in detail. Finally a novel appropriate field of view and wavelength correction is proposed for a polarization aberration function which optimizes the image quality of a multi-element optical system.

  19. Cosmological parameter estimation: impact of CMB aberration

    SciTech Connect

    Catena, Riccardo; Notari, Alessio E-mail: notari@ffn.ub.es

    2013-04-01

    The peculiar motion of an observer with respect to the CMB rest frame induces an apparent deflection of the observed CMB photons, i.e. aberration, and a shift in their frequency, i.e. Doppler effect. Both effects distort the temperature multipoles a{sub lm}'s via a mixing matrix at any l. The common lore when performing a CMB based cosmological parameter estimation is to consider that Doppler affects only the l = 1 multipole, and neglect any other corrections. In this paper we reconsider the validity of this assumption, showing that it is actually not robust when sky cuts are included to model CMB foreground contaminations. Assuming a simple fiducial cosmological model with five parameters, we simulated CMB temperature maps of the sky in a WMAP-like and in a Planck-like experiment and added aberration and Doppler effects to the maps. We then analyzed with a MCMC in a Bayesian framework the maps with and without aberration and Doppler effects in order to assess the ability of reconstructing the parameters of the fiducial model. We find that, depending on the specific realization of the simulated data, the parameters can be biased up to one standard deviation for WMAP and almost two standard deviations for Planck. Therefore we conclude that in general it is not a solid assumption to neglect aberration in a CMB based cosmological parameter estimation.

  20. Photoemission study of cerium silicate model systems

    NASA Astrophysics Data System (ADS)

    Skála, Tomáš; Matolín, Vladimír

    2013-01-01

    Interaction of silicon with cerium oxide was studied by photoelectron spectroscopy using two model systems CeOx/Si(1 1 1) and Si/CeO2(1 1 1)/Cu(1 1 1) which can be used for fundamental studies in the field of microelectronics and heterogeneous catalysis. The interaction was found to be strong and lead to a formation of cerium silicate films of the proposed stoichiometry Ce4.67Si3O13. Their maximum thickness was limited by diffusion of silicon. Beside silicate other compounds were growing on the surface - SiO2, Si2O, Si, and CeO2. The assignment of the formed species is based on the interpretation of photoemission spectra involving the measurements of various reference O/Si and Sisbnd O/Cu systems.

  1. Timing analysis of two-electron photoemission

    NASA Astrophysics Data System (ADS)

    Kheifets, A. S.; Ivanov, I. A.; Bray, Igor

    2011-05-01

    We predict a significant delay of two-electron photoemission from the helium atom after absorption of an attosecond XUV pulse. We establish this delay by solving the time-dependent Schrödinger equation and by subsequently tracing the field-free evolution of the two-electron wave packet. This delay can also be related to the energy derivative of the phase of the complex double-photoionization (DPI) amplitude which we evaluate by using the convergent close-coupling method. Our observations indicate that future attosecond time delay measurements on DPI of He can provide information on the absolute quantum phase and elucidate various mechanisms of this strongly correlated ionization process.

  2. A Correction to the Photoelectric Current in the Planck's Constant Experiment.

    ERIC Educational Resources Information Center

    Snyder, Evan S.

    1985-01-01

    Provides a method for correcting the photoemission from a collector when using the photoelectric effect experiment to determine Planck's constant. The problem results from a negative current through the cell and makes the measurement of the cutoff potential difficult. (DH)

  3. Tetragonal and collapsed-tetragonal phases of CaFe2As2 : A view from angle-resolved photoemission and dynamical mean-field theory

    NASA Astrophysics Data System (ADS)

    van Roekeghem, Ambroise; Richard, Pierre; Shi, Xun; Wu, Shangfei; Zeng, Lingkun; Saparov, Bayrammurad; Ohtsubo, Yoshiyuki; Qian, Tian; Sefat, Athena S.; Biermann, Silke; Ding, Hong

    2016-06-01

    We present a study of the tetragonal to collapsed-tetragonal transition of CaFe2As2 using angle-resolved photoemission spectroscopy and dynamical mean field theory-based electronic structure calculations. We observe that the collapsed-tetragonal phase exhibits reduced correlations and a higher coherence temperature due to the stronger Fe-As hybridization. Furthermore, a comparison of measured photoemission spectra and theoretical spectral functions shows that momentum-dependent corrections to the density functional band structure are essential for the description of low-energy quasiparticle dispersions. We introduce those using the recently proposed combined "screened exchange + dynamical mean field theory" scheme.

  4. Photolithography for the static compensation of human eye aberrations

    NASA Astrophysics Data System (ADS)

    Bara, Salvador; Jaroszewicz, Zbigniew

    2004-08-01

    Recent developments in human eye aberration measurements allow to design and fabricate compensating elements aiming to achieve aberration-limited imaging. This is important not merely from a subject's viewpoint (improving the sharpness of the outer world images formed at the retina) but mainly for clinical instrumentation purposes, especially those dealing with high-resolution retinal imaging (eye fundus cameras, scanning laser ophtlalmosopes, etc.). Here we report recent developments in the correction of the static component of the eye aberrations. Aberration data of several subjects were used for manufacturing personally customized phase plates designed to compensate for the wave aberration in the human eye. These plates were made by gray-level single-mask photosculpture in photoresist and then placed in front of the eye. The effects of misalignments as well as the strategy to design wide-field correcting elements are briefly revised. Applications include improving images in scanning laser ophtalmoscopes. The future plans of research including application of axicons for compensation of the lack of accommodation and kinoforms cancelling high amounts of eye's aberrations in monochromatic illumination are also sketched.

  5. Theory of hot electron photoemission from graphene

    NASA Astrophysics Data System (ADS)

    Ang, Lay Kee; Liang, Shijun

    Motivated by the development of Schottky-type photodetectors, some theories have been proposed to describe how the hot carriers generated by the incident photon are transported over the Schottky barrier through the internal photoelectric effect. One of them is Fowler's law proposed as early as 1931, which studied the temperature dependence of photoelectric curves of clean metals. This law is very successful in accounting for mechanism of detecting photons of energy lower than the band gap of semiconductor based on conventional metal/semiconductor Schottky diode. With the goal of achieving better performance, graphene/silicon contact-based- graphene/WSe2 heterostructure-based photodetectors have been fabricated to demonstrate superior photodetection efficiency. However, the theory of how hot electrons is photo-excited from graphene into semiconductor remains unknown. In the current work, we first examine the photoemission process from suspended graphene and it is found that traditional Einstein photoelectric effect may break down for suspended graphene due to the unique linear band structure. Furthermore, we find that the same conclusion applies for 3D graphene analog (e.g. 3D topological Dirac semi-metal). These findings are very useful to further improve the performance of graphene-based photodetector, hot-carrier solar cell and other kinds of sensor.

  6. Spin-orbit delays in photoemission

    NASA Astrophysics Data System (ADS)

    Jordan, I.; Huppert, M.; Pabst, S.; Kheifets, A. S.; Baykusheva, D.; Wörner, H. J.

    2017-01-01

    Attosecond delays between photoelectron wave packets emitted from different electronic shells are now well established. Is there any delay between electrons originating from the same electronic shell but leaving the cation in different fine-structure states? This question is relevant for all attosecond photoemission studies involving heavy elements, be it atoms, molecules or solids. We answer this fundamental question by measuring energy-dependent delays between photoelectron wave packets associated with the 3/2 2P and 1/2 2P components of the electronic ground states of Xe+ and Kr+. We observe delays reaching up to 33 ±6 as in the case of Xe. Our results are compared with two state-of-the-art theories. Whereas both theories quantitatively agree with the results obtained for Kr, neither of them fully reproduces the experimental results in Xe. Performing delay measurements very close to the ionization thresholds, we compare the agreement of several analytical formulas for the continuum-continuum delays with experimental data. Our results show an important influence of spin-orbit coupling on attosecond photoionization delays, highlight the requirement for additional theory development, and offer a precision benchmark for such work.

  7. Ultrahigh-resolution Photoemission of Correlated Systems

    NASA Astrophysics Data System (ADS)

    Grioni, Marco

    2001-03-01

    Photoelectron spectroscopy (ARPES) offers a unique k-selective view of the electronic excitations in solids. This capability can be fully exploited by a new generation of very high energy and momentum resolution experiments which directly probe the properties of the elementary quasiparticle excitations. I will discuss recent ARPES results addressing fundamental aspects of the electronic properties of strongly correlated materials. In model normal metal systems like TiTe2 ARPES can test the range of validity of standard Fermi liquid predictions. From a temperature-dependent lineshape analysis it is possible to identify and separately evaluate the strength of the various quasiparticle scattering processes. Photoemission can also clarify the mechanisms leading to electronic phase transitions, e.g. the role of the Fermi surface topology in charge-density-wave (CDW) instabilities in one- and two-dimensions. In these Peierls systems ARPES can probe the momentum and temperature dependence of the energy gap, but also the unconventional nature of the quasiparticles, and their response to the conflicting lattice and CDW periodicities [1]. [1] J. Voit, L. Perfetti, F. Zwick, H. Berger, G. Margaritondo, G. Gruner, H. Hoechst, and M. Grioni, Science 290, 501 (2000).

  8. Measuring chromatic aberrations in imaging systems using plasmonic nanoparticles

    NASA Astrophysics Data System (ADS)

    Gennaro, Sylvain D.; Roschuk, Tyler R.; Maier, Stefan A.; Oulton, Rupert F.

    2016-04-01

    Chromatic aberration in optical systems arises from the wavelength dependence of a glass's refractive index. Polychromatic rays incident upon an optical surface are refracted at slightly different angles and in traversing an optical system follow distinct paths creating images displaced according to color. Although arising from dispersion, it manifests as a spatial distortion correctable only with compound lenses with multiple glasses and accumulates in complicated imaging systems. While chromatic aberration is measured with interferometry, simple methods are attractive for their ease of use and low cost. In this letter we retrieve the longitudinal chromatic focal shift of high numerical aperture (NA) microscope objectives from the extinction spectra of metallic nanoparticles within the focal plane. The method is accurate for high NA objectives with apochromatic correction, and enables rapid assessment of the chromatic aberration of any complete microscopy systems, since it is straightforward to implement

  9. Diffractively corrected counter-rotating Risley prisms.

    PubMed

    Nie, Xin; Yang, Hongfang; Xue, Changxi

    2015-12-10

    Using the vector refraction equation and the vector diffraction equation, we obtain the expressions of the direction cosines of the refractive rays for the two wedge prisms, and the direction cosines of the diffractive rays for two wedge grisms, in which diffractive gratings were etched into the prism faces to correct the chromatic aberrations. A mathematical model between the two vector equations is proposed to compare the difference angle chromatic aberrations when the Risley prisms/grisms are rotating at different angles. We conclude that the use of diffractively corrected prisms offers a new method to correct chromatic aberrations in Risley prisms.

  10. Using Aberrant Behaviors as Reinforcers for Autistic Children.

    ERIC Educational Resources Information Center

    Charlop, Marjorie H.; And Others

    1990-01-01

    Three experiments assessed the efficacy of various reinforcers to increase correct task responding in a total of 10 autistic children, aged 6-9. Of the reinforcers used (stereotypy, delayed echolalia, perseverative behavior, and food), task performance was highest with opportunities to engage in aberrant behaviors, and lowest with edible…

  11. Spectroscopic imaging, diffraction, and holography with x-ray photoemission

    SciTech Connect

    Not Available

    1992-02-01

    X-ray probes are capable of determining the spatial structure of an atom in a specific chemical state, over length scales from about a micron all the way down to atomic resolution. Examples of these probes include photoemission microscopy, energy-dependent photoemission diffraction, photoelectron holography, and X-ray absorption microspectroscopy. Although the method of image formation, chemical-state sensitivity, and length scales can be very different, these X-ray techniques share a common goal of combining a capability for structure determination with chemical-state specificity. This workshop will address recent advances in holographic, diffraction, and direct imaging techniques using X-ray photoemission on both theoretical and experimental fronts. A particular emphasis will be on novel structure determinations with atomic resolution using photoelectrons.

  12. Chromosome Aberrations in Astronauts

    NASA Technical Reports Server (NTRS)

    George, Kerry A.; Durante, M.; Cucinotta, Francis A.

    2007-01-01

    A review of currently available data on in vivo induced chromosome damage in the blood lymphocytes of astronauts proves that, after protracted exposure of a few months or more to space radiation, cytogenetic biodosimetry analyses of blood collected within a week or two of return from space provides a reliable estimate of equivalent radiation dose and risk. Recent studies indicate that biodosimetry estimates from single spaceflights lie within the range expected from physical dosimetry and biophysical models, but very large uncertainties are associated with single individual measurements and the total sample population remains low. Retrospective doses may be more difficult to estimate because of the fairly rapid time-dependent loss of "stable" aberrations in blood lymphocytes. Also, biodosimetry estimates from individuals who participate in multiple missions, or very long (interplanetary) missions, may be complicated by an adaptive response to space radiation and/or changes in lymphocyte survival and repopulation. A discussion of published data is presented and specific issues related to space radiation biodosimetry protocols are discussed.

  13. Image Ellipticity from Atmospheric Aberrations

    SciTech Connect

    de Vries, W H; Olivier, S S; Asztalos, S J; Rosenberg, L J; Baker, K L

    2007-03-06

    We investigate the ellipticity of the point-spread function (PSF) produced by imaging an unresolved source with a telescope, subject to the effects of atmospheric turbulence. It is important to quantify these effects in order to understand the errors in shape measurements of astronomical objects, such as those used to study weak gravitational lensing of field galaxies. The PSF modeling involves either a Fourier transform of the phase information in the pupil plane or a ray-tracing approach, which has the advantage of requiring fewer computations than the Fourier transform. Using a standard method, involving the Gaussian weighted second moments of intensity, we then calculate the ellipticity of the PSF patterns. We find significant ellipticity for the instantaneous patterns (up to more than 10%). Longer exposures, which we approximate by combining multiple (N) images from uncorrelated atmospheric realizations, yield progressively lower ellipticity (as 1/{radical}N). We also verify that the measured ellipticity does not depend on the sampling interval in the pupil plane using the Fourier method. However, we find that the results using the ray-tracing technique do depend on the pupil sampling interval, representing a gradual breakdown of the geometric approximation at high spatial frequencies. Therefore, ray tracing is generally not an accurate method of modeling PSF ellipticity induced by atmospheric turbulence unless some additional procedure is implemented to correctly account for the effects of high spatial frequency aberrations. The Fourier method, however, can be used directly to accurately model PSF ellipticity, which can give insights into errors in the statistics of field galaxy shapes used in studies of weak gravitational lensing.

  14. Photoemission Electron Microscopy of a Plasmonic Silver Nanoparticle Trimer

    SciTech Connect

    Peppernick, Samuel J.; Joly, Alan G.; Beck, Kenneth M.; Hess, Wayne P.; Wang, Jinyong; Wang, Yi-Chung; Wei, Wei

    2013-07-01

    We present a combined experimental and theoretical study to investigate the spatial distribution of photoelectrons emitted from core-shell silver (Ag) nanoparticles. We use two-photon photoemission microscopy (2P-PEEM) to spatially resolve electron emission from a trimeric core-shell aggregate of triangular symmetry. Finite difference time domain (FDTD) simulations are performed to model the intensity distributions of the electromagnetic near-fields resulting from femtosecond (fs) laser excitation of localized surface plasmon oscillations in the triangular core-shell structure. We demonstrate that the predicted FDTD near-field intensity distribution reproduces the 2P-PEEM photoemission pattern.

  15. Real-time observation of collective excitations in photoemission

    NASA Astrophysics Data System (ADS)

    Lemell, C.; Neppl, S.; Wachter, G.; Tőkési, K.; Ernstorfer, R.; Feulner, P.; Kienberger, R.; Burgdörfer, J.

    2015-06-01

    Ejection of an electron by absorption of an extreme ultraviolet (xuv) photon probes the many-electron response of a solid well beyond the single-particle picture. Photoemission spectra feature complex correlation satellite structures signifying the simultaneous excitation of single or multiple plasmons. The time delay of the plasmon satellites relative to the main line can be resolved in attosecond streaking experiments. Time-resolved photoemission thus provides the key to discriminate between intrinsic and extrinsic plasmon excitation. We demonstrate the determination of the branching ratio between intrinsic and extrinsic plasmon generation for simple metals.

  16. Measurement of chromatic aberration in STEM and SCEM by coherent convergent beam electron diffraction.

    PubMed

    Zheng, C L; Etheridge, J

    2013-02-01

    A simple method is described for the accurate and precise measurement of chromatic aberration under electron-optical conditions pertinent to scanning transmission electron microscopy (STEM) and scanning confocal electron microscopy (SCEM). The method requires only the measurement of distances in a coherent CBED pattern and knowledge of the electron wavelength and the lattice spacing of a calibration specimen. The chromatic aberration of a spherical-aberration corrected 300 kV thermal field emission TEM is measured in STEM and SCEM operating modes and under different condenser lens settings. The effect of the measured chromatic aberrations on the 3 dimensional intensity distribution of the electron probe is also considered.

  17. Einstein's Photoemission from Quantum Confined Superlattices.

    PubMed

    Debbarma, S; Ghatak, K P

    2016-01-01

    This paper is dedicated to the 83th Birthday of Late Professor B. R. Nag, D.Sc., formerly Head of the Departments of Radio Physics and Electronics and Electronic Science of the University of Calcutta, a firm believer of the concept of theoretical minimum of Landau and an internationally well known semiconductor physicist, to whom the second author remains ever grateful as a student and research worker from 1974-2004. In this paper, an attempt is made to study, the Einstein's photoemission (EP) from III-V, II-VI, IV-VI, HgTe/CdTe and strained layer quantum well heavily doped superlattices (QWHDSLs) with graded interfaces in the presence of quantizing magnetic field on the basis of newly formulated electron dispersion relations within the frame work of k · p formalism. The EP from III-V, II-VI, IV-VI, HgTe/CdTe and strained layer quantum wells of heavily doped effective mass superlattices respectively has been presented under magnetic quantization. Besides the said emissions, from the quantum dots of the aforementioned heavily doped SLs have further investigated for the purpose of comparison and complete investigation in the context of EP from quantum confined superlattices. Using appropriate SLs, it appears that the EP increases with increasing surface electron concentration and decreasing film thickness in spiky manners, which are the characteristic features of such quantized hetero structures. Under magnetic quantization, the EP oscillates with inverse quantizing magnetic field due to Shuvnikov-de Haas effect. The EP increases with increasing photo energy in a step-like manner and the numerical values of EP with all the physical variables are totally band structure dependent for all the cases. The most striking features are that the presence of poles in the dispersion relation of the materials in the absence of band tails create the complex energy spectra in the corresponding HD constituent materials of such quantum confined superlattices and effective electron

  18. DNA Repair Defects and Chromosomal Aberrations

    NASA Technical Reports Server (NTRS)

    Hada, Megumi; George, K. A.; Huff, J. L.; Pluth, J. M.; Cucinotta, F. A.

    2009-01-01

    Yields of chromosome aberrations were assessed in cells deficient in DNA doublestrand break (DSB) repair, after exposure to acute or to low-dose-rate (0.018 Gy/hr) gamma rays or acute high LET iron nuclei. We studied several cell lines including fibroblasts deficient in ATM (ataxia telangiectasia mutated; product of the gene that is mutated in ataxia telangiectasia patients) or NBS (nibrin; product of the gene mutated in the Nijmegen breakage syndrome), and gliomablastoma cells that are proficient or lacking in DNA-dependent protein kinase (DNA-PK) activity. Chromosomes were analyzed using the fluorescence in situ hybridization (FISH) chromosome painting method in cells at the first division post irradiation, and chromosome aberrations were identified as either simple exchanges (translocations and dicentrics) or complex exchanges (involving >2 breaks in 2 or more chromosomes). Gamma irradiation induced greater yields of both simple and complex exchanges in the DSB repair-defective cells than in the normal cells. The quadratic dose-response terms for both simple and complex chromosome exchanges were significantly higher for the ATM- and NBS-deficient lines than for normal fibroblasts. However, in the NBS cells the linear dose-response term was significantly higher only for simple exchanges. The large increases in the quadratic dose-response terms in these repair-defective cell lines points the importance of the functions of ATM and NBS in chromatin modifications to facilitate correct DSB repair and minimize the formation of aberrations. The differences found between ATM- and NBS-deficient cells at low doses suggest that important questions should with regard to applying observations of radiation sensitivity at high dose to low-dose exposures. For aberrations induced by iron nuclei, regression models preferred purely linear dose responses for simple exchanges and quadratic dose responses for complex exchanges. Relative biological effectiveness (RBE) factors of all of

  19. One-step theory of two-photon photoemission

    NASA Astrophysics Data System (ADS)

    Braun, J.; Rausch, R.; Potthoff, M.; Ebert, H.

    2016-09-01

    A theoretical frame for two-photon photoemission is derived from the general theory of pump-probe photoemission, assuming that not only the probe but also the pump pulse is sufficiently weak. This allows us to use a perturbative approach to compute the lesser Green function within the Keldysh formalism. Two-photon photoemission spectroscopy is a widely used analytical tool to study nonequilibrium phenomena in solid materials. Our theoretical approach aims at a material-specific, realistic, and quantitative description of the time-dependent spectrum based on a picture of effectively independent electrons as described by the local-density approximation in band-structure theory. To this end we follow Pendry's one-step theory of the photoemission process as close as possible and heavily make use of concepts of relativistic multiple-scattering theory, such as the representation of the final state by a time-reversed low-energy electron diffraction state. The formalism allows for a quantitative calculation of the time-dependent photocurrent for moderately correlated systems like simple metals or more complex compounds like topological insulators. An application to the Ag(100) surface is discussed in detail.

  20. Photoemission of Single Dust Grains for Heliospheric Conditions

    NASA Technical Reports Server (NTRS)

    Spann, James F., Jr.; Venturini, Catherine C.; Abbas, Mian M.; Comfort, Richard H.

    2000-01-01

    Initial results of an experiment to measure the photoemission of single dust grains as a function of far ultraviolet wavelengths are presented. Coulombic forces dominate the interaction of the dust grains in the heliosphere. Knowledge of the charge state of dust grains, whether in a dusty plasma (Debye length < intergrain distance) or in the diffuse interplanetary region, is key to understanding their interaction with the solar wind and other solar system constituents. The charge state of heliospheric grains is primarily determined by primary electron and ion collisions, secondary electron emission and photoemission due to ultraviolet sunlight. We have established a unique experimental technique to measure the photoemission of individual micron-sized dust grains in vacuum. This technique resolves difficulties associated with statistical measurements of dust grain ensembles and non-static dust beams. The photoemission yield of Aluminum Oxide 3-micron grains For wavelengths from 120-300 nm with a spectral resolution of 1 nm FWHM is reported. Results are compared to interplanetary conditions.

  1. Photoemission of Mn6Cr single-molecule magnets

    NASA Astrophysics Data System (ADS)

    Heinzmann, U.; Merschjohann, F.; Helmstedt, A.; Gryzia, A.; Winter, A.; Steppeler, S.; Müller, N.; Brechling, A.; Sacher, M.; Richthofen, C.-G. Freiherr v.; Glaser, T.; Voss, S.; Fonin, M.; Rüdiger, U.

    2009-11-01

    We present the status of new experimental studies of X-ray absorption spectroscopy, magnetic circular dichroism in photoemission and spin-resolved photoelectron spectroscopy of Mn6Cr single-molecule magnet systems by use of circularly-polarized synchrotron radiation of the electron storage rings in Maxlab Lund, Sweden und BESSY, Berlin, Germany.

  2. A Monte Carlo photocurrent/photoemission computer program

    NASA Technical Reports Server (NTRS)

    Chadsey, W. L.; Ragona, C.

    1972-01-01

    A Monte Carlo computer program was developed for the computation of photocurrents and photoemission in gamma (X-ray)-irradiated materials. The program was used for computation of radiation-induced surface currents on space vehicles and the computation of radiation-induced space charge environments within space vehicles.

  3. Relativistic calculations of angle-dependent photoemission time delay

    NASA Astrophysics Data System (ADS)

    Kheifets, Anatoli; Mandal, Ankur; Deshmukh, Pranawa C.; Dolmatov, Valeriy K.; Keating, David A.; Manson, Steven T.

    2016-07-01

    Angular dependence of photoemission time delay for the valence n p3 /2 and n p1 /2 subshells of Ar, Kr, and Xe is studied in the dipole relativistic random phase approximation. Strong angular anisotropy of the time delay is reproduced near respective Cooper minima while the spin-orbit splitting affects the time delay near threshold.

  4. Electronic Properties of Pseudomorphic Metallic Films: Photoemission and Inverse Photoemission Measurements

    NASA Astrophysics Data System (ADS)

    Mankey, Gary Jay

    Recent developments in experimental physics have made possible the production and characterization of ultrathin metallic films of atomic dimension. The methods used to grow pseudomorphic fcc films of Ni, Co, and Fe on Cu(001) are described. High-quality epitaxial films are produced by vapor deposition in an ultra-high vacuum environment on suitably prepared substrates. The morphology of these films is characterized using a variety of experimental techniques: Auger electron spectroscopy, low-energy electron diffraction, reflection high-energy electron diffraction, and thermal desorption spectroscopy of adsorbed hydrogen. The magnetic properties of the films are measured with a surface magneto-optic Kerr effect magnetometer. The occupied and unoccupied electronic band dispersions and critical point energies are determined with photoemission and inverse photoemission measurements. These measurements are used as eigenvalues for an empirical combined interpolation scheme bandstructure calculation of the energy bands along the fcc(001) surface normal. Results are presented for Cu(001), Ni(001), Co(001), and paramagnetic Fe(001). Changes in the unoccupied electronic states in the ultrathin film limit are determined for Co and Fe films on Cu(111). The Co films exhibit a bulk-like electronic structure similar to hcp Co(0001) down to films one atomic layer thick. The low-spin ferromagnetic phase of fcc Fe is produced on Cu(111) for films below 5 atomic layers thick. Above this thickness, the Fe films revert to a bulk-like bcc(110) phase. The development of the electronic structure is measured for ultrathin Cu films grown on a specially prepared fcc Co(001) substrate. The Cu 3d band is significantly narrowed for films 1 atomic layer thick and bulk-like for films 3 atomic layers thick (one fcc unit cell). The s, p band exhibits quantum-well states due to the discretization of reciprocal space in the direction perpendicular to the film surface. These quantum-well states are

  5. Angle resolved photo-emission spectroscopy signature of the resonant excitonic state

    NASA Astrophysics Data System (ADS)

    Montiel, X.; Kloss, T.; Pépin, C.

    2016-09-01

    We calculate the angle resolved photo-emission spectroscopy (ARPES) signature of the resonant excitonic state (RES) that was proposed as the pseudo-gap state of cuprate superconductors (Kloss T. et al., arXiv:1510.03038 (2015)). This new state can be described as a set of excitonic (particle-hole) patches with an internal checkerboard modulation. Here, we modelize the RES as a charge order with 2\\textbf{p}F wave vectors, where 2\\textbf{p}F is the ordering vector connecting two opposite sides of the Fermi surface. We calculate the spectral weight and the density of states in the RES and we find that our model correctly reproduces the opening of the PG in Bi-2201.

  6. Intracavity adaptive correction of a 10 kW, solid-state, heat-capacity laser.

    SciTech Connect

    LaFortune, K N; Hurd, R L; Johansson, E M; Dane, C B; Fochs, S N; Brase, J M

    2004-01-12

    The Solid-State, Heat-Capacity Laser (SSHCL), under development at Lawrence Livermore National Laboratory is a large aperture (100 cm{sup 2}), confocal, unstable resonator requiring near-diffraction-limited beam quality. There are two primary sources of the aberrations in the system: residual, static aberrations from the fabrication of the optical components and predictable, time-dependent, thermally-induced index gradients within the gain medium. A deformable mirror placed within the cavity is used to correct the aberrations that are sensed externally with a Shack-Hartmann wavefront sensor. Although it is more challenging than external correction, intracavity correction enables control of the mode growth within the resonator, resulting in the ability to correct a more aberrated system longer. The overall system design, measurement techniques and correction algorithms are discussed. Experimental results from initial correction of the static aberrations and dynamic correction of the time-dependent aberrations are presented.

  7. Intracavity adaptive correction of a 10 kW, solid-state, heat-capacity laser

    SciTech Connect

    LaFortune, K N; Hurd, R L; Brase, J M; Yamamoto, R M

    2004-05-13

    The Solid-State, Heat-Capacity Laser (SSHCL), under development at Lawrence Livermore National Laboratory (LLNL) is a large aperture (100 cm{sup 2}), confocal, unstable resonator requiring near-diffraction-limited beam quality. There are two primary sources of the aberrations in the system: residual, static aberrations from the fabrication of the optical components and predictable, time-dependent, thermally-induced index gradients within the gain medium. A deformable mirror placed within the cavity is used to correct the aberrations that are sensed externally with a Shack-Hartmann wavefront sensor. Although the complexity of intracavity adaptive correction is greater than that of external correction, it enables control of the mode growth within the resonator, resulting in the ability to correct a more aberrated system longer. The overall system design, measurement techniques and correction algorithms are discussed. Experimental results from initial correction of the static aberrations and dynamic correction of the time-dependent aberrations are presented.

  8. How To Measure Gravitational Aberration?

    NASA Astrophysics Data System (ADS)

    Krizek, M.; Solcova, A.

    2007-08-01

    In 1905, Henri Poincaré predicted the existence of gravitational waves and assumed that their speed c[g] would be that of the speed of light c. If the gravitational aberration would also have the same magnitude as the aberration of light, we would observe several paradoxical phenomena. For instance, the orbit of two bodies of equal mass would be unstable, since two attractive forces arise that are not in line and hence form a couple. This tends to increase the angular momentum, period, and total energy of the system. This can be modelled by a system of ordinary differential equations with delay. A big advantage of computer simulation is that we can easily perform many test for various possible values of the speed of gravity [1]. In [2], Carlip showed that gravitational aberration in general relativity is almost cancelled out by velocity-dependent interactions. This means that rays of sunlight are not parallel to the attractive gravitational force of the Sun, i.e., we do not see the Sun in the direction of its attractive force, but slightly shifted about an angle less than 20``. We show how the actual value of the gravitational aberration can be obtained by measurement of a single angle at a suitable time instant T corresponding to the perihelion of an elliptic orbit. We also derive an a priori error estimate that expresses how acurately T has to be determined to attain the gravitational aberration to a prescribed tolerance. [1] M. Křížek: Numerical experience with the finite speed of gravitational interaction, Math. Comput. Simulation 50 (1999), 237-245. [2] S. Carlip: Aberration and the speed of gravity, Phys. Lett. A 267 (2000), 81-87.

  9. Mapping magnetism with atomic resolution using aberrated electron probes

    NASA Astrophysics Data System (ADS)

    Idrobo, Juan; Rusz, Ján; McGuire, Michael A.; Symons, Christopher T.; Vatsavai, Ranga Raju; Lupini, Andrew R.

    2015-03-01

    In this talk, we report a direct experimental real-space mapping of magnetic circular dichroism with atomic resolution in aberration-corrected scanning transmission electron microscopy (STEM). Using an aberrated electron probe with customized phase distribution, we reveal with electron energy-loss (EEL) spectroscopy the checkerboard antiferromagnetic ordering of Mn moments in LaMnAsO by observing a dichroic signal in the Mn L-edge. The aberrated probes allow the collection of EEL spectra using the transmitted beam, which results in a magnetic circular dichroic signal with intrinsically larger signal-to-noise ratios than those obtained via nanodiffraction techniques (where most of the transmitted electrons are discarded). The novel experimental setup presented here, which can easily be implemented in aberration-corrected STEM, opens new paths for probing dichroic signals in materials with unprecedented spatial resolution. This research was supported by DOE SUFD MSED, by UT-Battelle, LLC, under Contract No. DE-AC05-00OR22725 with the US DOE, and by the Swedish Research Council and Swedish National Infrastructure for Computing (NSC center)

  10. Eigenfunction analysis of stochastic backscatter for characterization of acoustic aberration in medical ultrasound imaging

    NASA Astrophysics Data System (ADS)

    Varslot, Trond; Krogstad, Harald; Mo, Eirik; Angelsen, Bjørn A.

    2004-06-01

    Presented here is a characterization of aberration in medical ultrasound imaging. The characterization is optimal in the sense of maximizing the expected energy in a modified beamformer output of the received acoustic backscatter. Aberration correction based on this characterization takes the form of an aberration correction filter. The situation considered is frequently found in applications when imaging organs through a body wall: aberration is introduced in a layer close to the transducer, and acoustic backscatter from a scattering region behind the body wall is measured at the transducer surface. The scattering region consists of scatterers randomly distributed with very short correlation length compared to the acoustic wavelength of the transmit pulse. The scatterer distribution is therefore assumed to be δ correlated. This paper shows how maximizing the expected energy in a modified beamformer output signal naturally leads to eigenfunctions of a Fredholm integral operator, where the associated kernel function is a spatial correlation function of the received stochastic signal. Aberration characterization and aberration correction are presented for simulated data constructed to mimic aberration introduced by the abdominal wall. The results compare well with what is obtainable using data from a simulated point source.

  11. Aberration corrected STEM to study an ancient hair dyeing formula

    NASA Astrophysics Data System (ADS)

    Patriarche, G.; Van Elslande, E.; Castaing, J.; Walter, P.

    2014-05-01

    Lead-based chemistry was initiated in ancient Egypt for cosmetic preparation more than 4000 years ago. Here, we study a hair-dyeing recipe using lead salts described in text since Greco-Roman times. We report direct evidence about the shape and distribution of PbS nanocrystals that form within the hair during blackening.

  12. Non-iterative Aberration Correction of a Multiple Transmitter System

    DTIC Science & Technology

    2011-09-01

    pupil. The shift due to transmitter locations is given by xT and yT. Note that for a given aperture the phase error value is static and doesn’t shift ...wpafb.af.mil Abstract: Multi-transmitter aperture synthesis provides aperture gain and improves effective aperture fill factor by shifting the received...techniques; (090.1995) Digital holography . References and links 1. J. C. Marron and R. L. Kendrick, “Distributed aperture active imaging,” Proc. SPIE

  13. Attosecond Time-Resolved Photoelectron Dispersion and Photoemission Time Delays

    NASA Astrophysics Data System (ADS)

    Liao, Q.; Thumm, U.

    2014-01-01

    We compute spectrograms and relative time delays for laser-assisted photoemission by single attosecond extreme ultraviolet pulses from valence band (VB) and 2p core levels (CLs) of a Mg(0001) surface within a quantum-mechanical model. Comparing the time-dependent dispersion of photoelectron (PE) wave packets for VB and CL emission, we find striking differences in their dependence on the (i) electron mean free path (MFP) in the solid, (ii) screening of the streaking laser field, and (iii) chirp of the attosecond pulse. The relative photoemission delay between VB and 2p PEs is shown to be sensitive to the electron MFP and screening of the streaking laser field inside the solid. Our model is able to reproduce a recent attosecond-streaking experiment [S. Neppl et al., Phys. Rev. Lett. 109, 087401 (2012)], which reveals no relative streaking time delay between VB and 2p PEs.

  14. Soft X-ray photoemission studies of Hf oxidation

    SciTech Connect

    Suzer, S.; Sayan, S.; Banaszak Holl, M.M.; Garfunkel, E.; Hussain, Z.; Hamdan, N.M.

    2002-02-01

    Soft X-Ray Photoemission Spectroscopy using surface sensitive Synchrotron Radiation has been applied to accurately determine the binding energy shifts and the valence band offset of the HfO2 grown on Hf metal. Charging of oxide films under x-rays (or other irradiation) is circumvented by controlled and sequential in-situ oxidation. Photoemission results show the presence of metallic Hf (from the substrate) with the 4f7/2 binding energy of 14.22 eV, fully oxidized Hf (from HfO2) with the 4f7/2 binding energy of 18.16 eV, and at least one clear suboxide peak. The position of the valence band of HfO2 with respect to the Hf(m) Fermi level is determined as 4.05 eV.

  15. Angle- and spin-resolved photoemission from ferromagnets

    NASA Astrophysics Data System (ADS)

    Cherepkov, N. A.; Kuznetsov, V. V.

    1996-07-01

    Equations for angle- and spin-resolved photoemission from core levels of ferromagnets are derived using the atomic model. They are applied to the n p subshells and to the particular geometries of experiment with the photoemission normal to the surface, which have been used already in several experiments. It is shown that for these geometries the spin-resolved spectra obtained with linearly polarized light are especially simple and contain the contribution of only one or two magnetic sublevels of the 0953-8984/8/27/008/img5 state, and of only one sublevel of the 0953-8984/8/27/008/img6 state, which allow one to resolve the magnetic splitting of core levels. The use of circularly polarized or unpolarized light gives a less transparent picture.

  16. The origin of Monochromatic Photoemission Peak in Diamondod Monolayer

    SciTech Connect

    Clay, W. A.

    2010-02-24

    Recent photoemission experiments have discovered a highly monochromatized secondary electron peak emitted from diamondoid self-assembled monolayers on metal substrates. New experimental data and simulation results are presented to show that a combination of negative electron affinity and strong electron-phonon scattering is responsible for this behavior. The simulation results are generated using a simple Monte Carlo transport algorithm. The simulated spectra recreate the main spectral features of the measured ones.

  17. Bulk sensitive hard x-ray photoemission electron microscopy

    SciTech Connect

    Patt, M. Wiemann, C.; Weber, N.; Escher, M.; Merkel, M.; Gloskovskii, A.; Drube, W.; Schneider, C. M.

    2014-11-15

    Hard x-ray photoelectron spectroscopy (HAXPES) has now matured into a well-established technique as a bulk sensitive probe of the electronic structure due to the larger escape depth of the highly energetic electrons. In order to enable HAXPES studies with high lateral resolution, we have set up a dedicated energy-filtered hard x-ray photoemission electron microscope (HAXPEEM) working with electron kinetic energies up to 10 keV. It is based on the NanoESCA design and also preserves the performance of the instrument in the low and medium energy range. In this way, spectromicroscopy can be performed from threshold to hard x-ray photoemission. The high potential of the HAXPEEM approach for the investigation of buried layers and structures has been shown already on a layered and structured SrTiO{sub 3} sample. Here, we present results of experiments with test structures to elaborate the imaging and spectroscopic performance of the instrument and show the capabilities of the method to image bulk properties. Additionally, we introduce a method to determine the effective attenuation length of photoelectrons in a direct photoemission experiment.

  18. Photoemission Experiments for Charge Characteristics of Individual Dust Grains

    NASA Technical Reports Server (NTRS)

    Abbas, M. M.; Craven, P. D.; Spann, J. F.; West, E.; Pratico, J.; Tankosic, D.; Venturini, C. C.; Six, N. Frank (Technical Monitor)

    2001-01-01

    Photoemission experiments with UV radiation have been performed to investigate the microphysics and charge characteristics of individual isolated dust grains of various compositions and sizes by using the electrodynamic balance facility at NASA Marshall Space Flight Center. Dust particles of 2-10 gm diameter are levitated in a vacuum chamber at pressures approximately 10(exp-5) torr and exposed to a collimated beam of UV radiation in the 120-200 nm spectral range from a deuterium lamp source with a MgF2 window. A monochromator is used to select the UV wavelength with a spectral resolution of 8 nm. The electrodynamic facility permits measurements of the charge and diameters of particles of known composition, and monitoring of photoemission rates with the incident UV radiation. Experiments have been conducted on test particles of silica and polystyrene to determine the photoelectric yields and surface equilibrium potentials when exposed to UV radiation. A brief description of an experimental procedure for photoemission studies is given and some preliminary laboratory measurements of the photoelectric yields of individual dust particles are presented.

  19. Photoemission Experiments for Charge Characteristics of Individual Dust Grains

    NASA Technical Reports Server (NTRS)

    Abbas, M. M.; Spann, James F., Jr.; Craven, Paul D.; West, E.; Pratico, Jared; Scheianu, D.; Tankosic, D.; Venturini, C. C.; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    Photoemission experiments with UV radiation have been performed to investigate the microphysics and charge characteristics of individual isolated dust grains of various compositions and sizes by using the electrodynamic balance facility at NASA Marshall Space Flight Center. Dust particles of 1 - 100 micrometer diameter are levitated in a vacuum chamber at pressures approx. 10(exp -5) torr and exposed to a collimated beam of UV radiation in the 120-300 nanometers spectral range from a deuterium lamp source with a MgF2 window. A monochromator is used to select the UV radiation wavelength with a spectral resolution of 8 nanometers. The electrodynamic facility permits measurements of the charge and diameters of particles of known composition, and monitoring of photoemission rates with the incident UV radiation. Experiments have been conducted on Al2O3 and silicate particles, and in particular on JSC-1 Mars regolith simulants, to determine the photoelectron yields and surface equilibrium potentials of dust particles when exposed to UV radiation in the 120-250 micrometers spectral range. A brief discussion of the experimental procedure, the results of photoemission experiments, and comparisons with theoretical models will be presented.

  20. Phase aberration simulation study of MRgFUS breast treatments

    PubMed Central

    Farrer, Alexis I.; Almquist, Scott; Dillon, Christopher R.; Neumayer, Leigh A.; Parker, Dennis L.; Christensen, Douglas A.; Payne, Allison

    2016-01-01

    Purpose: This simulation study evaluates the effects of phase aberration in breast MR-guided focused ultrasound (MRgFUS) ablation treatments performed with a phased-array transducer positioned laterally to the breast. A quantification of these effects in terms of thermal dose delivery and the potential benefits of phase correction is demonstrated in four heterogeneous breast numerical models. Methods: To evaluate the effects of varying breast tissue properties on the quality of the focus, four female volunteers with confirmed benign fibroadenomas were imaged using 3T MRI. These images were segmented into numerical models with six tissue types, with each tissue type assigned standard acoustic properties from the literature. Simulations for a single-plane 16-point raster-scan treatment trajectory centered in a fibroadenoma in each modeled breast were performed for a breast-specific MRgFUS system. At each of the 16 points, pressure patterns both with and without applying a phase correction technique were determined with the hybrid-angular spectrum method. Corrected phase patterns were obtained using a simulation-based phase aberration correction technique to adjust each element’s transmit phase to obtain maximized constructive interference at the desired focus. Thermal simulations were performed for both the corrected and uncorrected pressure patterns using a finite-difference implementation of the Pennes bioheat equation. The effect of phase correction was evaluated through comparison of thermal dose accumulation both within and outside a defined treatment volume. Treatment results using corrected and uncorrected phase aberration simulations were compared by evaluating the power required to achieve a 20 °C temperature rise at the first treatment location. The extent of the volumes that received a minimum thermal dose of 240 CEM at 43 °C inside the intended treatment volume as well as the volume in the remaining breast tissues was also evaluated in the form of

  1. Evidence of the nature of core-level photoemission satellites using angle-resolved photoemission extended fine structure

    SciTech Connect

    Moler, E.J.; Kellar, S.A.; Huff, W.R.A.

    1997-04-01

    The authors present a unique method of experimentally determining the angular momentum and intrinsic/extrinsic origin of core-level photoemission satellites by examining the satellite diffraction pattern in the Angle Resolved Photoemission Extended Fine Structure (ARPEFS) mode. They show for the first time that satellite peaks not associated with chemically differentiated atomic species display an ARPEFS intensity oscillation. They present ARPEFS data for the carbon 1s from ({radical}3x{radical}3)R30 CO/Cu(111) and p2mg(2xl)CO/Ni(110), nitrogen 1s from c(2x2) N{sub 2}/Ni(100), cobalt 1s from p(1x1)Co/Cu(100), and nickel 3p from clean nickel (111). The satellite peaks and tails of the Doniach-Sunjic line shapes in all cases exhibit ARPEFS curves which indicate an angular momentum identical to the main peak and are of an intrinsic nature.

  2. Time- and angle-resolved photoemission spectroscopy of hydrated electrons near a liquid water surface.

    PubMed

    Yamamoto, Yo-ichi; Suzuki, Yoshi-Ichi; Tomasello, Gaia; Horio, Takuya; Karashima, Shutaro; Mitríc, Roland; Suzuki, Toshinori

    2014-05-09

    We present time- and angle-resolved photoemission spectroscopy of trapped electrons near liquid surfaces. Photoemission from the ground state of a hydrated electron at 260 nm is found to be isotropic, while anisotropic photoemission is observed for the excited states of 1,4-diazabicyclo[2,2,2]octane and I- in aqueous solutions. Our results indicate that surface and subsurface species create hydrated electrons in the bulk side. No signature of a surface-bound electron has been observed.

  3. Te concentration dependent photoemission and inverse-photoemission study of FeSe1−xTex

    PubMed Central

    Yokoya, Takayoshi; Yoshida, Rikiya; Utsumi, Yuki; Tsubota, Koji; Okazaki, Hiroyuki; Wakita, Takanori; Mizuguchi, Yoshikazu; Takano, Yoshihiko; Muro, Takayuki; Kato, Yukako; Kumigashira, Hiroshi; Oshima, Masaharu; Harima, Hisatomo; Aiura, Yoshihiro; Sato, Hitoshi; Ino, Akihiro; Namatame, Hirofumi; Taniguchi, Masaki; Hirai, Masaaki; Muraoka, Yuji

    2012-01-01

    We have characterized the electronic structure of FeSe1−xTex for various x values using soft x-ray photoemission spectroscopy (SXPES), high-resolution photoemission spectroscopy (HRPES) and inverse photoemission spectroscopy (IPES). The SXPES valence band spectral shape shows that the 2 eV feature in FeSe, which was ascribed to the lower Hubbard band in previous theoretical studies, becomes less prominent with increasing x. HRPES exhibits systematic x dependence of the structure near the Fermi level (EF): its splitting near EF and filling of the pseudogap in FeSe. IPES shows two features, near EF and approximately 6 eV above EF; the former may be related to the Fe 3d states hybridized with chalcogenide p states, while the latter may consist of plane-wave-like and Se d components. In the incident electron energy dependence of IPES, the density of states near EF for FeSe and FeTe has the Fano lineshape characteristic of resonant behavior. These compounds exhibit different resonance profiles, which may reflect the differences in their electronic structures. By combining the PES and IPES data the on-site Coulomb energy was estimated at 3.5 eV for FeSe. PMID:27877521

  4. Wave aberration function and its definition

    NASA Astrophysics Data System (ADS)

    Zverev, V. A.; Rytova, E. S.; Timoshchuk, I. N.

    2011-06-01

    A definition of a wave aberration as a phase shift upon composition of light waves in the image of a point is given using the concept of point eikonal. An expression that determines the total differential of a wave aberration function is obtained and the condition of its integrability is determined. The sequence of the wave aberration function definition at the known functions of the meridional and sagittal components of lateral aberration is presented.

  5. Using geometric algebra to study optical aberrations

    SciTech Connect

    Hanlon, J.; Ziock, H.

    1997-05-01

    This paper uses Geometric Algebra (GA) to study vector aberrations in optical systems with square and round pupils. GA is a new way to produce the classical optical aberration spot diagrams on the Gaussian image plane and surfaces near the Gaussian image plane. Spot diagrams of the third, fifth and seventh order aberrations for square and round pupils are developed to illustrate the theory.

  6. Analysis of nodal aberration properties in off-axis freeform system design.

    PubMed

    Shi, Haodong; Jiang, Huilin; Zhang, Xin; Wang, Chao; Liu, Tao

    2016-08-20

    Freeform surfaces have the advantage of balancing off-axis aberration. In this paper, based on the framework of nodal aberration theory (NAT) applied to the coaxial system, the third-order astigmatism and coma wave aberration expressions of an off-axis system with Zernike polynomial surfaces are derived. The relationship between the off-axis and surface shape acting on the nodal distributions is revealed. The nodal aberration properties of the off-axis freeform system are analyzed and validated by using full-field displays (FFDs). It has been demonstrated that adding Zernike terms, up to nine, to the off-axis system modifies the nodal locations, but the field dependence of the third-order aberration does not change. On this basis, an off-axis two-mirror freeform system with 500 mm effective focal length (EFL) and 300 mm entrance pupil diameter (EPD) working in long-wave infrared is designed. The field constant aberrations induced by surface tilting are corrected by selecting specific Zernike terms. The design results show that the nodes of third-order astigmatism and coma move back into the field of view (FOV). The modulation transfer function (MTF) curves are above 0.4 at 20 line pairs per millimeter (lp/mm) which meets the infrared reconnaissance requirement. This work provides essential insight and guidance for aberration correction in off-axis freeform system design.

  7. CLASSICAL AREAS OF PHENOMENOLOGY: Study on the design and Zernike aberrations of a segmented mirror telescope

    NASA Astrophysics Data System (ADS)

    Jiang, Zhen-Yu; Li, Lin; Huang, Yi-Fan

    2009-07-01

    The segmented mirror telescope is widely used. The aberrations of segmented mirror systems are different from single mirror systems. This paper uses the Fourier optics theory to analyse the Zernike aberrations of segmented mirror systems. It concludes that the Zernike aberrations of segmented mirror systems obey the linearity theorem. The design of a segmented space telescope and segmented schemes are discussed, and its optical model is constructed. The computer simulation experiment is performed with this optical model to verify the suppositions. The experimental results confirm the correctness of the model.

  8. Phase Aberrations in Diffraction Microscopy

    SciTech Connect

    Marchesini, S; Chapman, H N; Barty, A; Howells, M R; Spence, J H; Cui, C; Weierstall, U; Minor, A M

    2005-09-29

    In coherent X-ray diffraction microscopy the diffraction pattern generated by a sample illuminated with coherent x-rays is recorded, and a computer algorithm recovers the unmeasured phases to synthesize an image. By avoiding the use of a lens the resolution is limited, in principle, only by the largest scattering angles recorded. However, the imaging task is shifted from the experiment to the computer, and the algorithm's ability to recover meaningful images in the presence of noise and limited prior knowledge may produce aberrations in the reconstructed image. We analyze the low order aberrations produced by our phase retrieval algorithms. We present two methods to improve the accuracy and stability of reconstructions.

  9. Pathophysiology of MDS: genomic aberrations.

    PubMed

    Ichikawa, Motoshi

    Myelodysplastic syndromes (MDS) are characterized by clonal proliferation of hematopoietic stem/progenitor cells and their apoptosis, and show a propensity to progress to acute myelogenous leukemia (AML). Although MDS are recognized as neoplastic diseases caused by genomic aberrations of hematopoietic cells, the details of the genetic abnormalities underlying disease development have not as yet been fully elucidated due to difficulties in analyzing chromosomal abnormalities. Recent advances in comprehensive analyses of disease genomes including whole-genome sequencing technologies have revealed the genomic abnormalities in MDS. Surprisingly, gene mutations were found in approximately 80-90% of cases with MDS, and the novel mutations discovered with these technologies included previously unknown, MDS-specific, mutations such as those of the genes in the RNA-splicing machinery. It is anticipated that these recent studies will shed new light on the pathophysiology of MDS due to genomic aberrations.

  10. Features in the electronic structure and photoemission spectra of organic molecular semiconductors: The molecules of metal-phthalocyanines and PTCDA

    NASA Astrophysics Data System (ADS)

    Tikhonov, E. V.; Uspenskii, Yu. A.; Khokhlov, D. R.

    2013-09-01

    The role of many-electron effects in the formation of electronic quasiparticle spectra in organic molecular semiconductors (OMS) is analyzed. Many-body perturbation theory, ab initio calculations of metal phthalocyanines and PTCDA molecules, and experimental photoemission spectra are applied to this analysis. It is shown that density functional theory (DFT) poorly reproduces the electronic spectra of OMS. The use of a hybrid functional method (HFM) provides precise reproduction of both valence and conducting bands, while the HOMO-LUMO gap remains underestimated. The correct gap width is obtained in both DFT and HFM, when it is calculated through ionization and affinity energies. It is shown that such an approach gives a formula for gap correction due to electron correlations, which is close to an expression derived from the GW approximation.

  11. Eliminating chromatic aberration in Gauss-type lens design using a novel genetic algorithm.

    PubMed

    Fang, Yi-Chin; Tsai, Chen-Mu; Macdonald, John; Pai, Yang-Chieh

    2007-05-01

    Two different types of Gauss lens design, which effectively eliminate primary chromatic aberration, are presented using an efficient genetic algorithm (GA). The current GA has to deal with too many targets in optical global optimization so that the performance is not much improved. Generally speaking, achromatic aberrations have a great relationship with variable glass sets for all elements. For optics whose design is roughly convergent, glass sets for optics will play a significant role in axial and lateral color aberration. Therefore better results might be derived from the optimal process of eliminating achromatic aberration, which could be carried out by finding feasible glass sets in advance. As an alternative, we propose a new optimization process by using a GA and involving theories of geometrical optics in order to select the best optical glass combination. Two Gauss-type lens designs are employed in this research. First, a telephoto lens design is sensitive to axial aberration because of its long focal length, and second, a wide-angle Gauss design is complicated by lateral color aberration at the extreme corners because Gauss design is well known not to deal well with wide-angle problems. Without numbers of higher chief rays passing the element, it is difficult to correct lateral color aberration altogether for the Gauss design. The results and conclusions show that the attempts to eliminate primary chromatic aberrations were successful.

  12. Wide-field aberration corrector for spherical gossamer primary mirrors

    NASA Astrophysics Data System (ADS)

    Beach, David A.

    2000-10-01

    If gossamer primary mirrors were to be constructed in a spherical form, it would be possible to arrange a simple null- test in situ. However, spherical mirrors would require correction of the large amount of spherical aberration created in pupils that generally will be greater than 2 m diameter. The design requirement is for diffraction-limited performance over a useful angular field. The otherwise excellent wide- field design solutions of the classical Schmidt and Maksutov are inapplicable in gossamer structures because of the mass and size penalty of large refractive components. However, it is possible for this mode of correction to be achieved near the prime focus by means of pupil transfer optics that minify the large entrance pupil down to more acceptable dimensions. A problem with these solutions is constraint of field coverage due to pupil aberrations created by the large spherical aberration of the primary mirror. This leads the designer towards slower primaries and the penalty of larger, heavier structures. A solution is presented here for spherical primaries with speeds up to f/4. This is based on the 'KiwiStar' principle presented here in 1997, in which a large spherical catoptric is combined by pupil-transfer with a smaller spherical catadioptric to give well corrected wide field images of high speed. This system is well suited to correction at the prime focus of large spherical mirrors, and has only one relatively small weak aspheric surface to provide zonal correction, all other surfaces being spherical. An example is presented of a 4 m diameter, f/2.5 system that is diffraction-limited over the whole of a 0.25 degree field (43 mm diameter), for a bandpass of 486 - 850 nm.

  13. Seidel aberrations of the Gabor superlens.

    PubMed

    Hamilton Shepard, R

    2014-02-10

    Equations are presented for the third-order Seidel aberrations of the Gabor superlens (GSL) as a function of microtelescope channel position within the aperture array. To reveal the origin and form of increasing aberration with channel height, Seidel coefficients are derived as a function of the accumulating pitch difference between the lens arrays and the aberrations present in the centered channel. Two- and three-element Gabor lenses are investigated and their aberrations are expressed as a function of first-order design parameters. The derived theory is then compared to a real ray trace simulation to demonstrate the accuracy of third-order aberration theory to predict GSL image quality.

  14. Aberration

    NASA Astrophysics Data System (ADS)

    Murdin, P.

    2000-11-01

    (1) The apparent displacement of a star from its mean position on the celestial sphere due to the velocity of the Earth in its orbit around the Sun. The phenomenon was discovered in 1729 by James Bradley (1693-1762) who was, in fact, trying to measure stellar parallax. The displacement is caused by the combination of the velocity of the Earth and the velocity of light approaching from the source. ...

  15. Correlations between corneal and total wavefront aberrations

    NASA Astrophysics Data System (ADS)

    Mrochen, Michael; Jankov, Mirko; Bueeler, Michael; Seiler, Theo

    2002-06-01

    Purpose: Corneal topography data expressed as corneal aberrations are frequently used to report corneal laser surgery results. However, the optical image quality at the retina depends on all optical elements of the eye such as the human lens. Thus, the aim of this study was to investigate the correlations between the corneal and total wavefront aberrations and to discuss the importance of corneal aberrations for representing corneal laser surgery results. Methods: Thirty three eyes of 22 myopic subjects were measured with a corneal topography system and a Tschernig-type wavefront analyzer after the pupils were dilated to at least 6 mm in diameter. All measurements were centered with respect to the line of sight. Corneal and total wavefront aberrations were calculated up to the 6th Zernike order in the same reference plane. Results: Statistically significant correlations (p < 0.05) between the corneal and total wavefront aberrations were found for the astigmatism (C3,C5) and all 3rd Zernike order coefficients such as coma (C7,C8). No statistically significant correlations were found for all 4th to 6th order Zernike coefficients except for the 5th order horizontal coma C18 (p equals 0.003). On average, all Zernike coefficients for the corneal aberrations were found to be larger compared to Zernike coefficients for the total wavefront aberrations. Conclusions: Corneal aberrations are only of limited use for representing the optical quality of the human eye after corneal laser surgery. This is due to the lack of correlation between corneal and total wavefront aberrations in most of the higher order aberrations. Besides this, the data present in this study yield towards an aberration balancing between corneal aberrations and the optical elements within the eye that reduces the aberration from the cornea by a certain degree. Consequently, ideal customized ablations have to take both, corneal and total wavefront aberrations, into consideration.

  16. Plasmon-enhanced internal photoemission for photovoltaics: Theoretical efficiency limits

    NASA Astrophysics Data System (ADS)

    White, Thomas P.; Catchpole, Kylie R.

    2012-08-01

    Plasmon-enhanced internal photoemission in metal-semiconductor Schottky junctions has recently been proposed as an alternative photocurrent mechanism for solar cells. Here, we identify and discuss the requirements for efficient operation of such cells and analyze their performance limits under standard solar illumination. We show that the maximum efficiency limit is <8% even if perfect optical absorption can be achieved using plasmonic nanostructures. This limit results from the fundamental electronic properties of metallic absorbers. Modifying the electron density of states of the absorber could increase the efficiency to >20%.

  17. Photon Detector For Inverse Photoemission Spectroscopy With Improved Energy Resolution

    SciTech Connect

    Maniraj, M.; D'Souza, S. W.; Barman, S. R.

    2011-07-15

    We present the results from newly designed and fabricated double window photon detector to improve the overall energy resolution for inverse photoemission spectroscopy (IPES). This simple design allows us to introduce an absorption gas (Krypton) to decrease the band-width of the energy selective photon detector and thus improve the resolution. Resonance absorption line of Kr of wavelength of 123.6 nm was used. By fitting the Fermi edge of the IPES spectrum of silver, we find an overall energy resolution improved by 73 meV. The design is modular and ensures ease and safety of handling.

  18. Temperature dependent core photoemission in Ce 24Co 11

    NASA Astrophysics Data System (ADS)

    Abbati, I.; Braicovich, L.; Michelis, B.; Fasana, A.; Olcese, G. L.; Canepa, F.; Costa, G. A.

    1985-09-01

    We present Ce 3 d photoemission results (XPS with Al Kα) in the temperature range 100-660°K. The mixed valence behaviour of Ce is very clear with an increase of the valence at lower temperature. A model analysis (of the Gunnarsson and Schönhammer type) gives the weight of the ⨍ 0 configuration equal to 0.19 at 300°K and equal to 0.23 at 100°K. This soft temperature dependence is discussed in connection with the temperature dependence of magnetic properties and with the chemistry of Ce intermetallics.

  19. Spin polarized photoemission studies of interfacial and thin film magnetism

    SciTech Connect

    Johnson, P.D.; Brookes, N.B.; Chang, Y.; Garrison, K.

    1993-01-01

    Spin polarized photoemission is used to study the electronic structure of noble metals deposited on ferromagnetic substrates. Studies of Ag deposited on an Fe(001) substrate reveal a series of minority spin interface or quantum well states with binding energies dependent on the thickness of the silver. Similar behavior is observed for Cu films deposited on a fct Co(001) substrate. Tight-binding modeling reproduces many of the observations and shows that hybridization of the sp-bands with the noble metal d-bands cannot be ignored.

  20. Spin polarized photoemission studies of interfacial and thin film magnetism

    SciTech Connect

    Johnson, P.D.; Brookes, N.B.; Chang, Y.; Garrison, K.

    1993-06-01

    Spin polarized photoemission is used to study the electronic structure of noble metals deposited on ferromagnetic substrates. Studies of Ag deposited on an Fe(001) substrate reveal a series of minority spin interface or quantum well states with binding energies dependent on the thickness of the silver. Similar behavior is observed for Cu films deposited on a fct Co(001) substrate. Tight-binding modeling reproduces many of the observations and shows that hybridization of the sp-bands with the noble metal d-bands cannot be ignored.

  1. Surface plasmon enhanced photodetectors based on internal photoemission

    NASA Astrophysics Data System (ADS)

    Alavirad, Mohammad; Roy, Langis; Berini, Pierre

    2016-10-01

    Surface plasmon photodetectors are of broad interest. They are promising for several applications including telecommunications, photovoltaic solar cells, photocatalysis, color-sensitive detection, and sensing, as they can provide highly enhanced fields and strong confinement (to subwavelength scales). Such photodetectors typically combine a nanometallic structure that supports surface plasmons with a photodetection structure based on internal photoemission or electron-hole pair creation. Photodetector architectures are highly varied, including waveguides, gratings, nanoparticles, nanoislands, or nanoantennas. We review the operating principles behind surface plasmon photodetectors based on the internal photoelectric effect, and we survey and compare the most recent and leading edge concepts reported in the literature.

  2. Aberration estimation from single point image in a simulated adaptive optics system.

    PubMed

    Grisan, Enrico; Frassetto, Fabio; Da Deppo, Vania; Naletto, Giampiero; Ruggeri, Alfredo

    2005-01-01

    Adaptive optics has been recently applied for the development of ophthalmic devices, with the main objective of obtaining higher resolution images for diagnostic purposes or ideally correcting high-order eye aberrations. The core of every adaptive optics systems is an optical device that is able to modify the wavefront shape of the light entering a system: once the shape of the incoming wavefront has been estimated, by means of this device it is possible to correct the aberrations introduced along the optical path. The aim of this paper is to demonstrate the feasibility, although in a simulated system, of estimating and correcting the wavefront shape simply by means of an iterative software analysis of a single point source image, thus avoiding expensive wavefront sensors or the burdensome computation of the PSF of the optical system. To test the proposed algorithm, a simple optical system has been simulated with a ray-tracing software and a program to estimate the Zernike coefficients of the simulated aberration from the analysis of the source image has been developed. Numerical indexes were used to evaluate the capability of the software of correctly estimating the Zernike coefficients. Even if only defocus, astigmatism and coma were considered, the very satisfactory results obtained confirm the soundness of this new approach and encourage further work in this direction, in order to develop a system able to estimate also spherical aberration, tilt and field curvature. An implementation of this aberration estimation in a real AO system is also currently in progress.

  3. Extreme regimes of femtosecond photoemission from a copper cathode in a dc electron gun

    NASA Astrophysics Data System (ADS)

    Pasmans, P. L. E. M.; van Vugt, D. C.; van Lieshout, J. P.; Brussaard, G. J. H.; Luiten, O. J.

    2016-10-01

    The femtosecond photoemission yield from a copper cathode and the emittance of the created electron beams has been studied in a 12 MeV /m , 100 keV dc electron gun over a wide range of laser fluence, from the linear photoemission regime until the onset of image charge limitations and cathode damaging. The measured photoemission curves can be described well with available theory which includes the Schottky effect, second-order photoemission, and image charge limitation. The second-order photoemission can be explained by thermally assisted one-photon photoemission (1PPE) and by above-threshold two-photon photoemission (2PPE). Measurements with a fresh cathode suggest that the 2PPE process is dominant. The beam emittance has been measured for the entire range of initial surface charge densities as well. The emittance measurements of space-charge dominated beams can be described well by an envelope equation with generalized perveance. The dc gun produces 0.1 pC bunches with 25 nm rms normalized emittance, corresponding to a normalized brightness usually associated with rf photoguns. In this experimental study the limits of femtosecond photoemission from a copper cathode have been explored and analyzed in great detail, resulting in improved understanding of the underlying mechanisms.

  4. Aberrations for Grazing Incidence Optics

    NASA Technical Reports Server (NTRS)

    Saha, Timo T.

    2008-01-01

    Large number of grazing incidence telescope configurations have been designed and studied. Wolte1 telescopes are commonly used in astronomical applications. Wolter telescopes consist of a paraboloidal primary mirror and a hyperboloidal or an ellipsoidal secondary mirror. There are 8 possible combinations of Wolter telescopes. Out of these possible designs only type 1 and type 2 telescopes are widely used. Type 1 telescope is typically used for x-ray applications and type 2 telescopes are used for EUV applications. Wolter-Schwarzshild (WS) telescopes offer improved image quality over a small field of view. The WS designs are stigmatic and free of third order coma and, therefore, the PSF is significantly better over a small field of view. Typically the image is more symmetric about its centroid. As for the Wolter telescopes there are 8 possible combinations of WS telescopes. These designs have not been widely used because the surface equations are complex parametric equations complicating the analysis and typically the resolution requirements are too low to take full advantage of the WS designs. There are several other design options. Most notable are wide field x-ray telescope designs. Polynomial designs were originally suggested by Burrows4 and hyperboloid-hyperboloid designs for solar physics applications were designed by Harvey5. No general aberration theory exists for grazing incidence telescopes that would cover all the design options. Several authors have studied the aberrations of grazing incidence telescopes. A comprehensive theory of Wolter type 1 and 2 telescopes has been developed. Later this theory was expanded to include all possible combinations of grazing incidence and also normal incidence paraboloid-hyperboloid and paraboloid-ellipsoid telescopes. In this article the aberration theory of Wolter type telescopes is briefly reviewed.

  5. The Sensitivity of Shaped Pupil Coronagraphs to Optical Aberrations

    NASA Technical Reports Server (NTRS)

    Green, Joseph J.; Shaklan, Stuart B.; Vanderbei, Robert J.; Kasdin, N. Jeremy

    2004-01-01

    Unlike focal-plane coronagraphs that use occulting spots and Lyot stops to eliminate diffraction, pupil-plane coronagraphs operate by shaping the pupil to redirect the diffracted stellar light into a tight core. As in focal-plane coronagraphs, the optical aberrations in the telescope must be sufficiently corrected to enable high contrast imaging. However, in shaped-pupil coronagraphs, the low-order aberrations resulting from misalignment and optical figure drift have a much smaller influence upon the contrast at at the inner working angle. These weaker sensitivities greatly relax the strict low-order wavefront stability required for high-contrast imaging the cost of some throughput. In this paper, we present the simulated performance of the concentric ring shaped pupil concepts comparing them to focal-plane coronagraphs that are optimized for the same inner working angles.

  6. Filtering chromatic aberration for wide acceptance angle electrostatic lenses.

    PubMed

    Fazekas, Ádám; Tóth, László

    2014-07-01

    Chromatic aberration is a major issue for imaging mainly with large acceptance angle electrostatic lenses. Its correction is necessary to take advantage of the outstanding spatial and angular resolution that these lenses provide. We propose a method to eliminate the effect of chromatic aberration on the measured images by determining the impact resulting from higher and lower kinetic energies. Based on a spectral image sequence and a matrix, which describes the transmission function of the lens, a system of linear equations is solved to approximate the 2D spectral intensity distribution of the sample surface. We present the description of our method and preliminary test results, which show significant contrast and image quality improvement. The presented algorithm can also be applied as a software-based energy analyzer.

  7. Inverse-Photoemission Spectroscopy of Iron Oxides, Silver

    NASA Astrophysics Data System (ADS)

    Kim, Bongsoo

    1990-01-01

    I measured the inverse-photoemission spectra (IPES) of iron oxides grown on an Fe substrate, and calculated the band structure of paramagnetic FeO to analyze the IPES. The band calculation showed some overlap between Fe _3_{rm d} states and O_2_{rm p} states in the region of occupied states, and s,p-like states of Fe in the unoccupied region. Isochromatic IPES showed structures at ~2.5 eV and ~7.5 eV above the Fermi energy. I estimate the full band gap of FeO as 2.5 eV from the IPES data. Angle-resolved inverse-photoemission spectra (ARIPES) have been measured on single-crystal Ag. The results are compared with the predictions of bulk band-structure theory and a free-electron model. The latter gives good agreement for the structure with a final state near the Fermi energy. Band theory is needed for the structure 17 eV above the Fermi energy. This structure is very nondispersive, indicating the existence of a very flat band throughout the IXUL plane.

  8. Image aberrations in optical three-dimensional measurement systems with fringe projection.

    PubMed

    Brakhage, Peter; Notni, Gunther; Kowarschik, Richard

    2004-06-01

    In optical shape measurement systems, systematic errors appear as a result of imaging aberrations of the lens assemblies in the cameras and projectors. A mathematical description of this effect is intended to correct the whole measurement area with a few independent coefficients. We apply the ideas of photogrammetry to one- and two-dimensional fringe projection techniques. We also introduce some new terms for close-range applications and telecentric objectives. Further, an algorithm for distance-dependent corrections is introduced. Also, we describe a new method with which to determine coefficients of aberration with an optimization-based method.

  9. The misalignment induced aberrations of TMA telescopes.

    PubMed

    Thompson, Kevin P; Schmid, Tobias; Rolland, Jannick P

    2008-12-08

    The next major space-borne observatory, the James Webb Space Telescope, will be a 6.6M field-biased, obscured, three-mirror anastigmat (TMA). Over the used field of view, the performance of TMA telescopes is dominated by 3(rd) order misalignment aberrations. Here it is shown that two dominant 3(rd) order misalignment aberrations arise for any TMA telescope. One aberration, field constant 3(rd) order coma is a well known misalignment aberration commonly seen in two-mirror Ritchey Chretien telescopes. The second aberration, field-asymmetric, field-linear, 3(rd) order astigmatism is a new and unique image orientation dependence with field derived here for the first time using nodal aberration theory.

  10. Aberrations of ellipsoidal reflectors for unit magnification.

    PubMed

    Mielenz, K D

    1974-12-01

    Ellipsoidal reflectors are useful for the 1:1 imaging of small objects without spherical and chromatic aberration. The magnitude of the off-axis aberrations of such reflectors is computed by application of Fermat's principle to the Hamiltonian point characteristic. The limiting form of the mirror aperture for which these aberrations do not exceed a set tolerance is an ellipse whose semiaxes depend on object size and angle of incidence.

  11. Adaptive electron beam shaping using a photoemission gun and spatial light modulator

    NASA Astrophysics Data System (ADS)

    Maxson, Jared; Lee, Hyeri; Bartnik, Adam C.; Kiefer, Jacob; Bazarov, Ivan

    2015-02-01

    The need for precisely defined beam shapes in photoelectron sources has been well established. In this paper, we use a spatial light modulator and simple shaping algorithm to create arbitrary, detailed transverse laser shapes with high fidelity. We transmit this shaped laser to the photocathode of a high voltage dc gun. Using beam currents where space charge is negligible, and using an imaging solenoid and fluorescent viewscreen, we show that the resultant beam shape preserves these detailed features with similar fidelity. Next, instead of transmitting a shaped laser profile, we use an active feedback on the unshaped electron beam image to create equally accurate and detailed shapes. We demonstrate that this electron beam feedback has the added advantage of correcting for electron optical aberrations, yielding shapes without skew. The method may serve to provide precisely defined electron beams for low current target experiments, space-charge dominated beam commissioning, as well as for online adaptive correction of photocathode quantum efficiency degradation.

  12. Breaking the spherical and chromatic aberration barrier in transmission electron microscopy.

    PubMed

    Freitag, B; Kujawa, S; Mul, P M; Ringnalda, J; Tiemeijer, P C

    2005-02-01

    Since the invention of transmission electron microscopy (TEM) in 1932 (Z. Physik 78 (1932) 318) engineering improvements have advanced system resolutions to levels that are now limited only by the two fundamental aberrations of electron lenses; spherical and chromatic aberration (Z. Phys. 101 (1936) 593). Since both aberrations scale with the dimensions of the lens, research resolution requirements are pushing the designs to lenses with only a few mm space in the pole-piece gap for the specimen. This is in conflict with the demand for more and more space at the specimen, necessary in order to enable novel techniques in TEM, such as He-cooled cryo electron microscopy, 3D-reconstruction through tomography (Science 302 (2003) 1396) TEM in gaseous environments, or in situ experiments (Nature 427 (2004) 426). All these techniques will only be able to achieve Angstrom resolution when the aberration barriers have been overcome. The spherical aberration barrier has recently been broken by introducing spherical aberration correctors (Nature 392 (1998) 392, 418 (2002) 617), but the correction of the remaining chromatic aberrations have proved to be too difficult for the present state of technology (Optik 57 (1980) 73). Here we present an alternative and successful method to eliminate the chromatic blur, which consists of monochromating the TEM beam (Inst. Phys. Conf. Ser. 161 (1999) 191). We show directly interpretable resolutions well below 1A for the first time, which is significantly better than any TEM operating at 200 KV has reached before.

  13. Revisiting Photoemission and Inverse Photoemission Spectra of Nickel Oxide from First Principles: Implications for Solar Energy Conversion

    SciTech Connect

    Alidoust, Nima; Toroker, Maytal; Carter, Emily A.

    2014-07-17

    We use two different ab initio quantum mechanics methods, complete active space self-consistent field theory applied to electrostatically embedded clusters and periodic many-body G₀W₀ calculations, to reanalyze the states formed in nickel(II) oxide upon electron addition and ionization. In agreement with interpretations of earlier measurements, we find that the valence and conduction band edges consist of oxygen and nickel states, respectively. However, contrary to conventional wisdom, we find that the oxygen states of the valence band edge are localized whereas the nickel states at the conduction band edge are delocalized. We argue that these characteristics may lead to low electron-hole recombination and relatively efficient electron transport, which, coupled with band gap engineering, could produce higher solar energy conversion efficiency compared to that of other transition-metal oxides. Both methods find a photoemission/inverse-photoemission gap of 3.6-3.9 eV, in good agreement with the experimental range, lending credence to our analysis of the electronic structure of NiO.

  14. Electronic Structure of the Kitaev Material α-RuCl3 Probed by Photoemission and Inverse Photoemission Spectroscopies.

    PubMed

    Sinn, Soobin; Kim, Choong Hyun; Kim, Beom Hyun; Lee, Kyung Dong; Won, Choong Jae; Oh, Ji Seop; Han, Moonsup; Chang, Young Jun; Hur, Namjung; Sato, Hitoshi; Park, Byeong-Gyu; Kim, Changyoung; Kim, Hyeong-Do; Noh, Tae Won

    2016-12-21

    Recently, α-RuCl3 has attracted much attention as a possible material to realize the honeycomb Kitaev model of a quantum-spin-liquid state. Although the magnetic properties of α-RuCl3 have been extensively studied, its electronic structure, which is strongly related to its Kitaev physics, is poorly understood. Here, the electronic structure of α-RuCl3 was investigated by photoemission (PE) and inverse-photoemission (IPE) spectroscopies. The band gap was directly measured from the PE and IPE spectra and was found to be 1.9 eV, much larger than previously estimated values. Local density approximation (LDA) calculations showed that the on-site Coulomb interaction U could open the band gap without spin-orbit coupling (SOC). However, the SOC should also be incorporated to reproduce the proper gap size, indicating that the interplay between U and SOC plays an essential role. Several features of the PE and IPE spectra could not be explained by the results of LDA calculations. To explain such discrepancies, we performed configuration-interaction calculations for a RuCl6(3-) cluster. The experimental data and calculations demonstrated that the 4d compound α-RuCl3 is a Jeff = 1/2 Mott insulator rather than a quasimolecular-orbital insulator. Our study also provides important physical parameters required for verifying the proposed Kitaev physics in α-RuCl3.

  15. Electronic Structure of the Kitaev Material α-RuCl3 Probed by Photoemission and Inverse Photoemission Spectroscopies

    NASA Astrophysics Data System (ADS)

    Sinn, Soobin; Kim, Choong Hyun; Kim, Beom Hyun; Lee, Kyung Dong; Won, Choong Jae; Oh, Ji Seop; Han, Moonsup; Chang, Young Jun; Hur, Namjung; Sato, Hitoshi; Park, Byeong-Gyu; Kim, Changyoung; Kim, Hyeong-Do; Noh, Tae Won

    2016-12-01

    Recently, α-RuCl3 has attracted much attention as a possible material to realize the honeycomb Kitaev model of a quantum-spin-liquid state. Although the magnetic properties of α-RuCl3 have been extensively studied, its electronic structure, which is strongly related to its Kitaev physics, is poorly understood. Here, the electronic structure of α-RuCl3 was investigated by photoemission (PE) and inverse-photoemission (IPE) spectroscopies. The band gap was directly measured from the PE and IPE spectra and was found to be 1.9 eV, much larger than previously estimated values. Local density approximation (LDA) calculations showed that the on-site Coulomb interaction U could open the band gap without spin-orbit coupling (SOC). However, the SOC should also be incorporated to reproduce the proper gap size, indicating that the interplay between U and SOC plays an essential role. Several features of the PE and IPE spectra could not be explained by the results of LDA calculations. To explain such discrepancies, we performed configuration-interaction calculations for a RuCl63‑ cluster. The experimental data and calculations demonstrated that the 4d compound α-RuCl3 is a Jeff = 1/2 Mott insulator rather than a quasimolecular-orbital insulator. Our study also provides important physical parameters required for verifying the proposed Kitaev physics in α-RuCl3.

  16. Electronic Structure of the Kitaev Material α-RuCl3 Probed by Photoemission and Inverse Photoemission Spectroscopies

    PubMed Central

    Sinn, Soobin; Kim, Choong Hyun; Kim, Beom Hyun; Lee, Kyung Dong; Won, Choong Jae; Oh, Ji Seop; Han, Moonsup; Chang, Young Jun; Hur, Namjung; Sato, Hitoshi; Park, Byeong-Gyu; Kim, Changyoung; Kim, Hyeong-Do; Noh, Tae Won

    2016-01-01

    Recently, α-RuCl3 has attracted much attention as a possible material to realize the honeycomb Kitaev model of a quantum-spin-liquid state. Although the magnetic properties of α-RuCl3 have been extensively studied, its electronic structure, which is strongly related to its Kitaev physics, is poorly understood. Here, the electronic structure of α-RuCl3 was investigated by photoemission (PE) and inverse-photoemission (IPE) spectroscopies. The band gap was directly measured from the PE and IPE spectra and was found to be 1.9 eV, much larger than previously estimated values. Local density approximation (LDA) calculations showed that the on-site Coulomb interaction U could open the band gap without spin-orbit coupling (SOC). However, the SOC should also be incorporated to reproduce the proper gap size, indicating that the interplay between U and SOC plays an essential role. Several features of the PE and IPE spectra could not be explained by the results of LDA calculations. To explain such discrepancies, we performed configuration-interaction calculations for a RuCl63− cluster. The experimental data and calculations demonstrated that the 4d compound α-RuCl3 is a Jeff = 1/2 Mott insulator rather than a quasimolecular-orbital insulator. Our study also provides important physical parameters required for verifying the proposed Kitaev physics in α-RuCl3. PMID:28000731

  17. Revisiting photoemission and inverse photoemission spectra of nickel oxide from first principles: implications for solar energy conversion.

    PubMed

    Alidoust, Nima; Toroker, Maytal Caspary; Carter, Emily A

    2014-07-17

    We use two different ab initio quantum mechanics methods, complete active space self-consistent field theory applied to electrostatically embedded clusters and periodic many-body G0W0 calculations, to reanalyze the states formed in nickel(II) oxide upon electron addition and ionization. In agreement with interpretations of earlier measurements, we find that the valence and conduction band edges consist of oxygen and nickel states, respectively. However, contrary to conventional wisdom, we find that the oxygen states of the valence band edge are localized whereas the nickel states at the conduction band edge are delocalized. We argue that these characteristics may lead to low electron-hole recombination and relatively efficient electron transport, which, coupled with band gap engineering, could produce higher solar energy conversion efficiency compared to that of other transition-metal oxides. Both methods find a photoemission/inverse-photoemission gap of 3.6-3.9 eV, in good agreement with the experimental range, lending credence to our analysis of the electronic structure of NiO.

  18. Chromatic aberration measurement for transmission interferometric testing.

    PubMed

    Seong, Kibyung; Greivenkamp, John E

    2008-12-10

    A method of chromatic aberration measurement is described based on the transmitted wavefront of an optical element obtained from a Mach-Zehnder interferometer. The chromatic aberration is derived from transmitted wavefronts measured at five different wavelengths. Reverse ray tracing is used to remove induced aberrations associated with the interferometer from the measurement. In the interferometer, the wavefront transmitted through the sample is tested against a plano reference, allowing for the absolute determination of the wavefront radius of curvature. The chromatic aberrations of a singlet and a doublet have been measured.

  19. Monochromatic ocular wave aberrations in young monkeys

    PubMed Central

    Ramamirtham, Ramkumar; Kee, Chea-su; Hung, Li-Fang; Qiao-Grider, Ying; Roorda, Austin; Smith, Earl L.

    2006-01-01

    High-order monochromatic aberrations could potentially influence vision-dependent refractive development in a variety of ways. As a first step in understanding the effects of wave aberration on refractive development, we characterized the maturational changes that take place in the high-order aberrations of infant rhesus monkey eyes. Specifically, we compared the monochromatic wave aberrations of infant and adolescent animals and measured the longitudinal changes in the high-order aberrations of infant monkeys during the early period when emmetropization takes place. Our main findings were that (1) adolescent monkey eyes have excellent optical quality, exhibiting total RMS errors that were slightly better than those for adult human eyes that have the same numerical aperture and (2) shortly after birth, infant rhesus monkeys exhibited relatively larger magnitudes of high-order aberrations predominately spherical aberration, coma, and trefoil, which decreased rapidly to assume adolescent values by about 200 days of age. The results demonstrate that rhesus monkey eyes are a good model for studying the contribution of individual ocular components to the eye’s overall aberration structure, the mechanisms responsible for the improvements in optical quality that occur during early ocular development, and the effects of high-order aberrations on ocular growth and emmetropization. PMID:16750549

  20. Aberrations of varied line-space grazing incidence gratings in converging light beams

    NASA Technical Reports Server (NTRS)

    Hettrick, M. C.

    1984-01-01

    Analyses of the imaging properties of several designs for varied-line space gratings in converging beams of light in grazing-incidence spectrometers are presented. An explicit model is defined for the case of a plane-reflection grating intercepting light that converges and is reflected to a stigmatic point associated with the zero-order image of the grating. Smooth spatial variation of the grating constant then permits aberration correction. The aberrations are expressed as polynomials in the grating lens coordinates using power series expansions. Application of the model is illustrated in terms of aberrations experienced with the short wavelength spectrometer on the EUVE satellite. Attention is given to straight and parallel in-plane grooves, curved groove in-plane designs and off-plane grooves. Aberrations due to dispersions and misalignment are also considered.

  1. Binocular adaptive optics visual simulator: understanding the impact of aberrations on actual vision

    NASA Astrophysics Data System (ADS)

    Fernández, Enrique J.; Prieto, Pedro M.; Artal, Pablo

    2010-02-01

    A novel adaptive optics system is presented for the study of vision. The apparatus is capable for binocular operation. The binocular adaptive optics visual simulator permits measuring and manipulating ocular aberrations of the two eyes simultaneously. Aberrations can be corrected, or modified, while the subject performs visual testing under binocular vision. One of the most remarkable features of the apparatus consists on the use of a single correcting device, and a single wavefront sensor (Hartmann-Shack). Both the operation and the total cost of the instrument largely benefit from this attribute. The correcting device is a liquid-crystal-on-silicon (LCOS) spatial light modulator. The basic performance of the visual simulator consists in the simultaneous projection of the two eyes' pupils onto both the corrector and sensor. Examples of the potential of the apparatus for the study of the impact of the aberrations under binocular vision are presented. Measurements of contrast sensitivity with modified combinations of spherical aberration through focus are shown. Special attention was paid on the simulation of monovision, where one eye is corrected for far vision while the other is focused at near distance. The results suggest complex binocular interactions. The apparatus can be dedicated to the better understanding of the vision mechanism, which might have an important impact in developing new protocols and treatments for presbyopia. The technique and the instrument might contribute to search optimized ophthalmic corrections.

  2. Photoemission studies of novel charge density wave systems

    NASA Astrophysics Data System (ADS)

    Kidd, Timothy Edward

    Photoelectron spectroscopy is a powerful tool for probing the properties of surfaces and interfaces. Linked with a tunable light source such as the Synchrotron Radiation Center in Stoughton, WI, one is able to obtain information concerning the sample's crystal structure, the interfacial properties of thin films, valence band structure, and chemical environment. This thesis is mainly focused on the use of angle-resolved photoemission to study the electronic structure of charge density wave (CDW) systems. CDW systems undergo a temperature dependent structural phase transition accompanied by a modulation of the conduction electron density. These materials share many properties with complex systems. These systems display many novel properties including high-Tc superconductivity and the colossal magnetoresistance effect. One of the shared properties of these systems is a high sensitivity to doping and defects. This sensitivity will be explored in the context of two CDW systems in this thesis. The first system to be studied was the 1/3 ML Sn/Ge(111) surface. It is a simple 2D binary semiconductor system which appears to undergo a CDW phase transition at low temperatures. Photoemission spectroscopy was used to determine the mechanism for the phase transition, and the influence of defects upon the system. It appears the defects play a strong role in defining both the normal and ground state for the system, and are perhaps essential for the phase transition. The second system studied is the layered compound TiSe2. Unlike other group IV transition metal dichalcogenides, TiSe2 undergoes a CDW phase transition at low temperatures. Although the system has been studied for decades, there is still no consensus on the mechanism driving the phase transition. There is also some doubt as to whether the normal state is semi-metallic or semiconducting. Again, defects have a strong effect upon the system. Photoemission studies were used to measure the system's electronic structure near

  3. Angle-resolved photoemission extended fine structure: Multiple layers of emitters and multiple initial states

    SciTech Connect

    Huff, W.R.A.; Kellar, S.A.; Moler, E.J. |; Chen, Y.; Wu, H.; Shirley, D.A.; Hussain, Z.

    1995-08-01

    Recently, angle-resolved photoemission extended fine structure (ARPEFS) has been applied to experimental systems involving multiple layers of emitters and non-s core-level photoemission in an effort to broaden the utility of the technique. Most of the previous systems have been comprised of atomic or molecular overlayers adsorbed onto a single-crystal, metal surface and the photoemission data were taken from an s atomic core-level in the overlayer. For such a system, the acquired ARPEFS data is dominated by the p{sub o} final state wave backscattering from the substrate atoms and is well understood. In this study, we investigate ARPEFS as a surface-region structure determination technique when applied to experimental systems comprised of multiple layers of photoemitters and arbitrary initial state core-level photoemission. Understanding the data acquired from multiple layers of photoemitters is useful for studying multilayer interfaces, ''buried'' surfaces, and clean crystals in ultra- high vacuum. The ability to apply ARPEFS to arbitrary initial state core-level photoemission obviously opens up many systems to analysis. Efforts have been ongoing to understand such data in depth. We present clean Cu(111) 3s, 3p, and 3d core-level, normal photoemission data taken on a high resolution soft x-ray beamline 9.3.2 at the Advanced Light Source in Berkeley, California and clean Ni(111) 3p normal photoemission data taken at the National Synchrotron Light Source in Upton, New York, USA.

  4. Simultaneous measurements of photoemission and morphology of various Al alloys during mechanical deformation

    SciTech Connect

    Cai, M.; Li, W.; Dickinson, J. T.

    2006-11-15

    We report simultaneous measurements of strain and photoelectron emission from high purity Al (1350), Al-Mg (5052), Al-Mn (3003), Al-Cu (2024), and Al-Mg-Si (6061) alloys under uniaxial tension due to pulsed excimer laser radiation (248 nm). The emission of low-energy photoelectrons is sensitive to deformation-induced changes in surface morphology, including the formation of slip lines and slip bands. Alloy composition and surface treatment significantly influence the photoemission during deformation. Surface oxide enhances the signal-to-noise level during photoemission measurement. In the early stage of deformation (strain {<=}0.04), photoemission intensity increases gradually in a nonlinear fashion. While subsequent photoemission increases almost linearly with strain until failure in samples with thin oxide layer ({approx}31 A ring ), there are two linear segments of photoemission for the samples with oxide of 45 A ring . The onset of strain localization corresponds to the intersection point of two linear segments, usually at a strain of 0.08-0.20. A constitutive model incorporating microstructure evolution and work hardening during tensile deformation is proposed to qualitatively interpret the growth of the photoemission as a function of strain. Photoemissions from various alloys are interpreted in the light of surface treatment, work function, composition, and microstructural development during deformation.

  5. Extremely high-power CO2 laser beam correction.

    PubMed

    Kudryashov, Alexis; Alexandrov, Alexander; Rukosuev, Alexey; Samarkin, Vadim; Galarneau, Pierre; Turbide, Simon; Châteauneuf, François

    2015-05-10

    This paper presents the results of high-power CO2 laser-aberration correction and jitter stabilization. A bimorph deformable mirror and two tip-tilt piezo correctors were used as executive elements. Two types of wavefront sensors, one Hartmann to measure higher-order aberrations (defocus, astigmatism etc.) based on an uncooled microbolometer long-wave infrared camera and the other a tip-tilt one based on the technology of obliquely sputtered, thin chromium films on Si substrates, were applied to measure wavefront aberrations. We discuss both positive and negative attributes of suggested wavefront sensors. The adaptive system is allowed to reduce aberrations of incoming laser radiation by seven times peak-to-valley and to stabilize the jitter of incoming beams up to 25 μrad at a speed of 100 Hz. The adaptive system frequency range for high-order aberration correction was 50 Hz.

  6. Removing lateral chromatic aberration in bright field optical microscopy.

    PubMed

    Guzmán-Altamirano, Miguel; Gutiérrez-Medina, Braulio

    2015-06-01

    We present an efficient alternative to remove lateral chromatic aberration (LCA) in bright field light microscopy images. Our procedure is based on error calibration using time-sequential acquisition at different wavelengths, and error correction through digital image warping. Measurement of the displacements of fiducial marks in the red and green images relative to blue provide calibration factors that are subsequently used in test images to realign color channels digitally. We demonstrate quantitative improvement in the position and boundaries of objects in target slides and in the color content and morphology of specimens in stained biological samples. Our results show a reduction of LCA content below the 0.1% level.

  7. Importance of semicore states in GW calculations for simulating accurately the photoemission spectra of metal phthalocyanine molecules

    NASA Astrophysics Data System (ADS)

    Umari, P.; Fabris, S.

    2012-05-01

    The quasi-particle energy levels of the Zn-Phthalocyanine (ZnPc) molecule calculated with the GW approximation are shown to depend sensitively on the explicit description of the metal-center semicore states. We find that the calculated GW energy levels are in good agreement with the measured experimental photoemission spectra only when explicitly including the Zn 3s and 3p semicore states in the valence. The main origin of this effect is traced back to the exchange term in the self-energy GW approximation. Based on this finding, we propose a simplified approach for correcting GW calculations of metal phthalocyanine molecules that avoids the time-consuming explicit treatment of the metal semicore states. Our method allows for speeding up the calculations without compromising the accuracy of the computed spectra.

  8. Electric field stimulation setup for photoemission electron microscopes.

    PubMed

    Buzzi, M; Vaz, C A F; Raabe, J; Nolting, F

    2015-08-01

    Manipulating magnetisation by the application of an electric field in magnetoelectric multiferroics represents a timely issue due to the potential applications in low power electronics and the novel physics involved. Thanks to its element sensitivity and high spatial resolution, X-ray photoemission electron microscopy is a uniquely suited technique for the investigation of magnetoelectric coupling in multiferroic materials. In this work, we present a setup that allows for the application of in situ electric and magnetic fields while the sample is analysed in the microscope. As an example of the performances of the setup, we present measurements on Ni/Pb(Mg(0.66)Nb(0.33))O3-PbTiO3 and La(0.7)Sr(0.3)MnO3/PMN-PT artificial multiferroic nanostructures.

  9. Electric field stimulation setup for photoemission electron microscopes

    SciTech Connect

    Buzzi, M.; Vaz, C. A. F.; Raabe, J.; Nolting, F.

    2015-08-15

    Manipulating magnetisation by the application of an electric field in magnetoelectric multiferroics represents a timely issue due to the potential applications in low power electronics and the novel physics involved. Thanks to its element sensitivity and high spatial resolution, X-ray photoemission electron microscopy is a uniquely suited technique for the investigation of magnetoelectric coupling in multiferroic materials. In this work, we present a setup that allows for the application of in situ electric and magnetic fields while the sample is analysed in the microscope. As an example of the performances of the setup, we present measurements on Ni/Pb(Mg{sub 0.66}Nb{sub 0.33})O{sub 3}-PbTiO{sub 3} and La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/PMN-PT artificial multiferroic nanostructures.

  10. heterojunction interface investigated by X-ray photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Lin, Lingyan; Yu, Jinling; Cheng, Shuying; Lu, Peimin; Lai, Yunfeng; Lin, Sile; Zhao, Pengyi

    2014-09-01

    The band alignment at the In2S3/Cu2ZnSnS4 heterojunction interface is investigated by X-ray photoemission spectroscopy. In2S3 is thermally evaporated onto the contamination-free polycrystalline Cu2ZnSnS4 surface prepared by magnetron sputtering. The valence band offset is measured to be 0.46 ± 0.1 eV, which matches well with the valance band offset value 0.49 eV calculated using "transitivity" method. The conduction band offset is determined to be 0.82 ± 0.1 eV, indicating a `type I' band alignment at the heterojunction interface.

  11. Electric field stimulation setup for photoemission electron microscopes

    NASA Astrophysics Data System (ADS)

    Buzzi, M.; Vaz, C. A. F.; Raabe, J.; Nolting, F.

    2015-08-01

    Manipulating magnetisation by the application of an electric field in magnetoelectric multiferroics represents a timely issue due to the potential applications in low power electronics and the novel physics involved. Thanks to its element sensitivity and high spatial resolution, X-ray photoemission electron microscopy is a uniquely suited technique for the investigation of magnetoelectric coupling in multiferroic materials. In this work, we present a setup that allows for the application of in situ electric and magnetic fields while the sample is analysed in the microscope. As an example of the performances of the setup, we present measurements on Ni/Pb(Mg0.66Nb0.33)O3-PbTiO3 and La0.7Sr0.3MnO3/PMN-PT artificial multiferroic nanostructures.

  12. Photoemission microscopy from magnetically coupled thin-film systems

    NASA Astrophysics Data System (ADS)

    Schneider, C. M.; de Haas, O.; Muschiol, U.; Cramer, N.; Oelsner, A.; Klais, M.; Schmidt, O.; Fecher, G. H.; Jark, W.; Schönhense, G.

    2001-07-01

    The magnetic microstructure and magnetic coupling phenomena in thin-film systems, relevant for applications in magneto-electronics, are investigated by means of photoemission electron microscopy. Element-selective magnetic information is obtained by exploiting magnetic circular dichroism in the soft X-ray regime. The domain shape and sizes found at the surface of antiferromagnetically coupled metallic multilayers indicate the presence of a ferromagnetic coupling contribution, presumably caused by a build-up of roughness during the growth process. The magnetic domain patterns in FeNi microstructures on sputtered NiO films reflect the presence of a local exchange anisotropy, causing the phenomenon of exchange biasing or pinning of the ferromagnetic layer.

  13. Calculation of 3s photoemission spectra of vanadium on graphite

    SciTech Connect

    Krueger, P.; Taguchi, M.; Parlebas, J.C.; Kotani, A.

    1997-06-01

    A few years ago, a satellite structure in the vanadium 3s x-ray photoemission spectroscopy (XPS) spectrum of V clusters upon graphite was observed and attributed to the presence of magnetic moments on the V surface. Here, we present calculations of these spectra using a cluster model that takes into account intra-atomic d-d and d{endash}core electron correlation and hybridization between V d and graphite {pi} states. When the V-graphite distance is increased from 1.5 to 2.0 {Angstrom} the system undergoes a low-to-high spin transition, which is clearly evidenced in the evolution of the XPS line shape. Although direct comparison with experiment is difficult, our study suggests that the observed satellite is due to core hole screening rather than a magnetic moment on the V atom. {copyright} {ital 1997} {ital The American Physical Society}

  14. Photoemission Electron Microscopy as a Tool for Studying Steel Grains

    NASA Astrophysics Data System (ADS)

    Roese, Peter; Keutner, Christoph; Berges, Ulf; Espeter, Philipp; Westphal, Carsten

    2017-01-01

    Key properties of steel like stability, weldability, or ability for absorbing deformation energy are defined by their grain structure. The knowledge about their micrometer and submicrometer structure is of particular interest for tailor-cut macroscopic steel properties. We report on photoemission electron microscopy studies which in principle yield a higher magnification than comparable optical techniques. A flat surface without any topographic features was obtained by applying a non-etching preparation procedure. PEEM images showed very tiny phase islands embedded within a steel phase matrix. Furthermore, we developed an analysis procedure for PEEM images for dual-phase steels. As a result, it is possible to identify the individual work functions of different steel phases at the surface.

  15. Photoemission characteristics of thin GaAs-based heterojunction photocathodes

    SciTech Connect

    Feng, Cheng; Zhang, Yijun Qian, Yunsheng; Shi, Feng; Zou, Jijun; Zeng, Yugang

    2015-01-14

    To better understand the different photoemission mechanism of thin heterojunction photocathodes, the quantum efficiency models of reflection-mode and transmission-mode GaAs-based heterojunction photocathodes are revised based on one-dimensional continuity equations, wherein photoelectrons generated from both the emission layer and buffer layer are taken into account. By comparison of simulated results between the revised and conventional models, it is found that the electron contribution from the buffer layer to shortwave quantum efficiency is closely related to some factors, such as the thicknesses of emission layer and buffer layer and the interface recombination velocity. Besides, the experimental quantum efficiency data of reflection-mode and transmission-mode AlGaAs/GaAs photocathodes are well fitted to the revised models, which confirm the applicability of the revised quantum efficiency models.

  16. Photoemission Electron Microscopy as a Tool for Studying Steel Grains

    NASA Astrophysics Data System (ADS)

    Roese, Peter; Keutner, Christoph; Berges, Ulf; Espeter, Philipp; Westphal, Carsten

    2017-03-01

    Key properties of steel like stability, weldability, or ability for absorbing deformation energy are defined by their grain structure. The knowledge about their micrometer and submicrometer structure is of particular interest for tailor-cut macroscopic steel properties. We report on photoemission electron microscopy studies which in principle yield a higher magnification than comparable optical techniques. A flat surface without any topographic features was obtained by applying a non-etching preparation procedure. PEEM images showed very tiny phase islands embedded within a steel phase matrix. Furthermore, we developed an analysis procedure for PEEM images for dual-phase steels. As a result, it is possible to identify the individual work functions of different steel phases at the surface.

  17. Widespread spin polarization effects in photoemission from topological insulators

    SciTech Connect

    Jozwiak, C.; Chen, Y. L.; Fedorov, A. V.; Analytis, J. G.; Rotundu, C. R.; Schmid, A. K.; Denlinger, J. D.; Chuang, Y.-D.; Lee, D.-H.; Fisher, I. R.; Birgeneau, R. J.; Shen, Z.-X.; Hussain, Z.; Lanzara, A.

    2011-06-22

    High-resolution spin- and angle-resolved photoemission spectroscopy (spin-ARPES) was performed on the three-dimensional topological insulator Bi{sub 2}Se{sub 3} using a recently developed high-efficiency spectrometer. The topological surface state's helical spin structure is observed, in agreement with theoretical prediction. Spin textures of both chiralities, at energies above and below the Dirac point, are observed, and the spin structure is found to persist at room temperature. The measurements reveal additional unexpected spin polarization effects, which also originate from the spin-orbit interaction, but are well differentiated from topological physics by contrasting momentum and photon energy and polarization dependencies. These observations demonstrate significant deviations of photoelectron and quasiparticle spin polarizations. Our findings illustrate the inherent complexity of spin-resolved ARPES and demonstrate key considerations for interpreting experimental results.

  18. Two-photon photoemission from metals induced by picosecond laser pulses

    NASA Technical Reports Server (NTRS)

    Bechtel, J. H.; Smith, W. L.; Bloembergen, N.

    1977-01-01

    We have measured the two-photon photoemission current density from tungsten, tantalum, and molybdenum when irradiated by 532-nm wavelength radiation. This wavelength was produced by the second-harmonic radiation of single picosecond laser pulses from a mode-locked neodymium-doped yttrium-aluminum-garnet laser. The results are interpreted in terms of both a simple temperature-independent two-photon photoemission effect and a generalization of the Fowler-DuBridge theory of photoemission. The laser polarization dependence of the emitted current is also reported.

  19. Inverse photoemission of adsorbed xenon multilayers on Ru(001): Refutation of final-state screening effects

    NASA Astrophysics Data System (ADS)

    Wandelt, K.; Jacob, W.; Memmel, N.; Dose, V.

    1986-09-01

    In this Letter we describe photoemission and inverse photoemission spectra of adsorbed xenon multilayers on Ru(001). Electron energy-loss spectra of xenon adsorbed on gold by Demuth, Avouris, and Schmeisser are included in the discussion. The observed layer-dependent shifts of the inverse photoemission spectra closer to the Fermi level clearly invalidate image screening effects as being the dominant cause of these shifts but support a ``floating'' of the adsorbed Xe potential well as a whole with the surface potential in the initial state.

  20. Learning Disorders and Sex Chromosome Aberrations.

    ERIC Educational Resources Information Center

    Hier, D. B.; And Others

    1980-01-01

    In a prospective study of 20 adult dyslexic men, no sex chromosome aberrations were detected. A retrospective study of 89 Ss with known sex chromosome aberrations revealed 20 of them to be mentally retarded. Among the 69 Ss of normal intelligence, learning, speech, and attention disorders were frequent. (Author/DLS)

  1. The research of calibration method on lens-tilt displacement transmission-type system based on the aberration bounded model

    NASA Astrophysics Data System (ADS)

    Xu, Chun-mei; Liu, Bing-qi; Li, Li; Huang, Fu-yu; Zhang, Chu

    2015-10-01

    As the developing appliance range of high-resolution optical design, the requirement on the aberration of system design is becoming higher and higher, but the installation and adjustment error of optical components is an important element which influences the aberration. The decentration and tilt of optical components result not only the image lateral displacement but also the aberration enlargement of the optical system, the research on image quality of plane symmetric optical system is becoming more and more popular. The Gaussian correction methods on lens decentration already exist, but it is short of theoretical research to guide the correction on the lens tilt, which leads to the effect of image lateral displacement. This thesis analyzes theoretically a mathematical model between the lens tilt degree and wave aberration, and deduces mathematically the correction equation of zero aberration increment under the aberration constraint condition. Taking an example of some type optical sight, the ZEMAX simulation is carried out to validate this method, and the results show that: This method can effectively guide the correction of lens tilt, and reduce the influence of lens position change on the optical imaging quality. It has important practical significance to guide high-resolution optical design.

  2. The BHVI-EyeMapper: Peripheral Refraction and Aberration Profiles

    PubMed Central

    Fedtke, Cathleen; Ehrmann, Klaus; Falk, Darrin; Bakaraju, Ravi C.; Holden, Brien A.

    2014-01-01

    ABSTRACT Purpose The aim of this article was to present the optical design of a new instrument (BHVI-EyeMapper, EM), which is dedicated to rapid peripheral wavefront measurements across the visual field for distance and near, and to compare the peripheral refraction and higher-order aberration profiles obtained in myopic eyes with and without accommodation. Methods Central and peripheral refractive errors (M, J180, and J45) and higher-order aberrations (C[3, 1], C[3, 3], and C[4, 0]) were measured in 26 myopic participants (mean [±SD] age, 20.9 [±2.0] years; mean [±SD] spherical equivalent, −3.00 [±0.90] diopters [D]) corrected for distance. Measurements were performed along the horizontal visual field with (−2.00 to −5.00 D) and without (+1.00 D fogging) accommodation. Changes as a function of accommodation were compared using tilt and curvature coefficients of peripheral refraction and aberration profiles. Results As accommodation increased, the relative peripheral refraction profiles of M and J180 became significantly (p < 0.05) more negative and the profile of M became significantly (p < 0.05) more asymmetric. No significant differences were found for the J45 profiles (p > 0.05). The peripheral aberration profiles of C[3, 1], C[3, 3], and C[4, 0] became significantly (p < 0.05) less asymmetric as accommodation increased, but no differences were found in the curvature. Conclusions The current study showed that significant changes in peripheral refraction and higher-order aberration profiles occurred during accommodation in myopic eyes. With its extended measurement capabilities, that is, permitting rapid peripheral refraction and higher-order aberration measurements up to visual field angles of ±50 degrees for distance and near (up to −5.00 D), the EM is a new advanced instrument that may provide additional insights in the ongoing quest to understand and monitor myopia development. PMID:25105690

  3. Aberration-Coreected Electron Microscopy at Brookhaven National Laboratory

    SciTech Connect

    Zhu,Y.; Wall, J.

    2008-04-01

    The last decade witnessed the rapid development and implementation of aberration correction in electron optics, realizing a more-than-70-year-old dream of aberration-free electron microscopy with a spatial resolution below one angstrom [1-9]. With sophisticated aberration correctors, modern electron microscopes now can reveal local structural information unavailable with neutrons and x-rays, such as the local arrangement of atoms, order/disorder, electronic inhomogeneity, bonding states, spin configuration, quantum confinement, and symmetry breaking [10-17]. Aberration correction through multipole-based correctors, as well as the associated improved stability in accelerating voltage, lens supplies, and goniometers in electron microscopes now enables medium-voltage (200-300kV) microscopes to achieve image resolution at or below 0.1nm. Aberration correction not only improves the instrument's spatial resolution but, equally importantly, allows larger objective lens pole-piece gaps to be employed thus realizing the potential of the instrument as a nanoscale property-measurement tool. That is, while retaining high spatial resolution, we can use various sample stages to observe the materials response under various temperature, electric- and magnetic- fields, and atmospheric environments. Such capabilities afford tremendous opportunities to tackle challenging science and technology issues in physics, chemistry, materials science, and biology. The research goal of the electron microscopy group at the Dept. of Condensed Matter Physics and Materials Science and the Center for Functional Nanomaterials, as well as the Institute for Advanced Electron Microscopy, Brookhaven National Laboratory (BNL), is to elucidate the microscopic origin of the physical- and chemical-behavior of materials, and the role of individual, or groups of atoms, especially in their native functional environments. We plan to accomplish this by developing and implementing various quantitative electron

  4. Surface studies of solids using integral X-ray-induced photoemission yield

    PubMed Central

    Stoupin, Stanislav; Zhernenkov, Mikhail; Shi, Bing

    2016-01-01

    X-ray induced photoemission yield contains structural information complementary to that provided by X-ray Fresnel reflectivity, which presents an advantage to a wide variety of surface studies if this information is made easily accessible. Photoemission in materials research is commonly acknowledged as a method with a probing depth limited by the escape depth of the photoelectrons. Here we show that the integral hard-X-ray-induced photoemission yield is modulated by the Fresnel reflectivity of a multilayer structure and carries structural information that extends well beyond the photoelectron escape depth. A simple electric self-detection of the integral photoemission yield and Fourier data analysis permit extraction of thicknesses of individual layers. The approach does not require detection of the reflected radiation and can be considered as a framework for non-invasive evaluation of buried layers with hard X-rays under grazing incidence. PMID:27874041

  5. Quantitative Analysis of Valence Photoemission Spectra and Quasiparticle Excitations at Chromophore-Semiconductor Interfaces

    NASA Astrophysics Data System (ADS)

    Patrick, Christopher E.; Giustino, Feliciano

    2012-09-01

    Investigating quasiparticle excitations of molecules on surfaces through photoemission spectroscopy forms a major part of nanotechnology research. Resolving spectral features at these interfaces requires a comprehensive theory of electron removal and addition processes in molecules and solids which captures the complex interplay of image charges, thermal effects, and configurational disorder. Here, we develop such a theory and calculate the quasiparticle energy-level alignment and the valence photoemission spectrum for the prototype biomimetic solar cell interface between anatase TiO2 and the N3 chromophore. By directly matching our calculated photoemission spectrum to experimental data, we clarify the atomistic origin of the chromophore peak at low binding energy. This case study sets a new standard in the interpretation of photoemission spectroscopy at complex chromophore-semiconductor interfaces.

  6. Surface studies of solids using integral x-ray-induced photoemission yield

    DOE PAGES

    Stoupin, Stanislav; Zhernenkov, Mikhail; Shi, Bing

    2016-11-22

    X-ray induced photoemission yield contains structural information complementary to that provided by X-ray Fresnel reflectivity, which presents an advantage to a wide variety of surface studies if this information is made easily accessible. Photoemission in materials research is commonly acknowledged as a method with a probing depth limited by the escape depth of the photoelectrons. Here we show that the integral hard-X-ray-induced photoemission yield is modulated by the Fresnel reflectivity of a multilayer structure and carries structural information that extends well beyond the photoelectron escape depth. A simple electric self-detection of the integral photoemission yield and Fourier data analysis permitmore » extraction of thicknesses of individual layers. The approach does not require detection of the reflected radiation and can be considered as a framework for non-invasive evaluation of buried layers with hard X-rays under grazing incidence.« less

  7. Surface studies of solids using integral x-ray-induced photoemission yield

    SciTech Connect

    Stoupin, Stanislav; Zhernenkov, Mikhail; Shi, Bing

    2016-11-22

    X-ray induced photoemission yield contains structural information complementary to that provided by X-ray Fresnel reflectivity, which presents an advantage to a wide variety of surface studies if this information is made easily accessible. Photoemission in materials research is commonly acknowledged as a method with a probing depth limited by the escape depth of the photoelectrons. Here we show that the integral hard-X-ray-induced photoemission yield is modulated by the Fresnel reflectivity of a multilayer structure and carries structural information that extends well beyond the photoelectron escape depth. A simple electric self-detection of the integral photoemission yield and Fourier data analysis permit extraction of thicknesses of individual layers. The approach does not require detection of the reflected radiation and can be considered as a framework for non-invasive evaluation of buried layers with hard X-rays under grazing incidence.

  8. Spin polarization and magnetic dichroism in core-level photoemission from ferromagnets

    SciTech Connect

    Menchero, Jose Gabriel

    1997-05-01

    In this thesis we present a theoretical investigation of angle- and spin-resolved core-level photoemission from ferromagnetic Fe and Ni. We also consider magneto-dichroic effects due to reversal of the photon helicity or reversal of the sample magnetization direction. In chapter 1, we provide a brief outline of the history of photoemission, and show how it has played an important role in the development of modern physics. We then review the basic elements of the theory of core-level photoemission, and discuss the validity of the some of the commonly-used approximations. In chapter 2, we present a one-electron theory to calculate spin- and angle-resolved photoemission spectra for an arbitrary photon polarization. The Hamiltonian includes both spin-orbit and exchange interactions. As test cases for the theory, we calculate the spin polarization and magnetic dichroism for the Fe 2p core level, and find that agreement with experiment is very good.

  9. Effects, determination, and correction of count rate nonlinearity in multi-channel analog electron detectors

    SciTech Connect

    Reber, T. J.; Plumb, N. C.; Waugh, J. A.; Dessau, D. S.

    2014-04-15

    Detector counting rate nonlinearity, though a known problem, is commonly ignored in the analysis of angle resolved photoemission spectroscopy where modern multichannel electron detection schemes using analog intensity scales are used. We focus on a nearly ubiquitous “inverse saturation” nonlinearity that makes the spectra falsely sharp and beautiful. These artificially enhanced spectra limit accurate quantitative analysis of the data, leading to mistaken spectral weights, Fermi energies, and peak widths. We present a method to rapidly detect and correct for this nonlinearity. This algorithm could be applicable for a wide range of nonlinear systems, beyond photoemission spectroscopy.

  10. High-harmonic XUV source for time- and angle-resolved photoemission spectroscopy

    SciTech Connect

    Dakovski, Georgi L; Li, Yinwan; Durakiewicz, Tomasz; Rodriguez, George

    2009-01-01

    We present a laser-based apparatus for visible pump/XUV probe time- and angle-resolved photoemission spectroscopy (TRARPES) utilizing high-harmonic generation from a noble gas. Femtosecond temporal resolution for each selected harmonic is achieved by using a time-delay-compensated monochromator (TCM). The source has been used to obtain photoemission spectra from insulators (UO{sub 2}) and ultrafast pump/probe processes in semiconductors (GaAs).

  11. Active optics concept for hypertelescope aberration control and pupil densification

    NASA Astrophysics Data System (ADS)

    Dohlen, Kjetil; Dargent, Pascal; Ferrari, Marc; Lemaitre, Gerard R.

    2003-02-01

    One of the instrumental concepts under study for large baseline interferometers for high resolution astronomical imaging, in particular applied to exoplanet search and characterisation, is the hypertelescope (HT). Mainly considered for space deployment, this sparse array of mirror segments supported either by a struss structure or by free-flying micro satellites form a giant, diluted primary mirror. The focal plane instrumentation, including pupil densification optics, is located in the primary focus instrument space craft (ISC). Baselines considered for first-generation HTs are of the order of 100 m, but one can envisage kilometric arrays capable of unprecedented angular resolution. Pointing with such a telescope poses orbital navigation problems. Letting the entire array perform a slow sky-scanning motion and navigating the ISC within the primary focal plane in order to follow the image of the object may solve these problems. The ISC must therefore be equipped with aberration correction optics capable of covering a sufficiently large primary field of view, of the order of a few degrees. In this paper we present optical and mechanical concepts for combined aberration correction and pupil densification using multimode deformable mirror (MDM) and mechanically amplified piezo actuator technologies. Among the advantages of such a system over large monolithic corrector optics is the relaxation of piston alignment requirements for primary segments.

  12. Polarization aberrations of crossed folding mirrors

    NASA Astrophysics Data System (ADS)

    Crandall, David G.; Chipman, Russell A.

    1995-08-01

    Polarization aberrations due to varying polarization state across the field of view (FOV) are investigated for crossed folding mirrors. We define crossed mirrors as oriented in space such that s-polarized light incident on the first mirror is p-polarized at the second mirror. This completely compensates for polarization state changes at one point in the field of view. The resulting polarization aberrations are explored across the FOV using the example of aluminum mirrors overcoated with a 12 layer, highly reflective, dielectric stack. The polarization aberration is very low along a band across the field of view. For arbitrary points in the FOV, the retardance and diattenuation are slightly elliptical.

  13. Pharmacological correction of misfolding of ABC proteins☆

    PubMed Central

    Rudashevskaya, Elena L.; Stockner, Thomas; Trauner, Michael; Freissmuth, Michael; Chiba, Peter

    2014-01-01

    The endoplasmic reticulum (ER) quality control system distinguishes between correctly and incorrectly folded proteins to prevent processing of aberrantly folded conformations along the secretory pathway. Non-synonymous mutations can lead to misfolding of ABC proteins and associated disease phenotypes. Specific phenotypes may at least partially be corrected by small molecules, so-called pharmacological chaperones. Screening for folding correctors is expected to open an avenue for treatment of diseases such as cystic fibrosis and intrahepatic cholestasis. PMID:25027379

  14. Core-Exciton Decay in Photoemission and the Nonmetal - Transition.

    NASA Astrophysics Data System (ADS)

    Zhang, Jiandi

    Ultra thin films or overlayers of materials, normally metallic in the bulk case, can exhibit nonmetallic characters. Typically, these systems undergo a nonmetal-to-metal transition with changing film density, crystalline structure, or thickness. The purpose of this thesis is to identify this electronic phase transition and to investigate the corresponding fundamental mechanisms by studying the detailed electronic structure. In particular, I attempted to look at the evolution of electronic structure in films undergoing this transition. The core -exciton decay in the resonant photoemission was probed, from both theoretical and experimental points of view, to correlate with the change of film metallicity. Resonant photoemission, combining with normal photoemission, was found to be a sensitive and successful method to identify the overlayer nonmetal-metal transition, both from static and dynamic pictures. In most of this work, we concentrate on the studies of the evolution of electronic structure of ultra thin films of divalent metals, on different crystalline surfaces. The formation of new Hg electronic states arising from the electron orbital hybridization between adjacent adatoms, the formation of quantum well states in the overlayers, and the evolution of mercury shape resonance due to 5d to epsilonf excitation, all provide indications of when mercury overlayers undergo a nonmetal to metal transition. This transition has been found to be associated the changes in adatom coordination number. On both Cu(100) and W(110), the interactions between the Hg adatoms and the substrates are very weak and the surface bonding is more like covalent bonding at low coverages. The Hg overlayers on these two surfaces resembles free-standing layers, and the metallicity of the overlayers is largely determined by the nearest neighbor interactions of Hg adatoms. Comparing Hg overlayers on Ni(111) where there exists a nonmetal to metal transition caused by the structure phase transition

  15. High-energy photoemission studies of oxide interfaces

    NASA Astrophysics Data System (ADS)

    Claessen, Ralph

    2015-03-01

    The interfaces of complex oxide heterostructures can host novel quantum phases not existing in the bulk of the constituents, with the high-mobility 2D electron system (2DES) in LaAlO3/SrTiO3 (LAO/STO) representing a prominent example. Despite extensive research the origin of the 2DES and its unusual properties - including the supposed coexistence of superconductivity and ferromagnetism - are still a matter of intense debate. Photoelectron spectroscopy, recently extended into the soft (SX-ARPES) and hard (HAXPES) X-ray regime, is a powerful method to provide detailed insight into the electronic structure of these heterostructures and, in particular, of the buried interface. This includes the identification of the orbital character of the 2DES as well as the determination of vital band structure information, such as band alignment, band bending, and even k-resolved band dispersions and Fermi surface topology. Moreover, resonant photoemission at the Ti L-edge reveals the existence of two different species of Ti 3d states, localized and itinerant, which can be distinguished and identified by their different resonance behavior. The role of oxygen vacancies is studied by controlled in-situ oxidation, which allows us to vary the composition from fully stoichiometric to strongly O-deficient. By comparison to free STO surfaces we can thus demonstrate that the metallicity of the heteointerfaces is intrinsic, i . e . it persists even in the absence of O defects. I will discuss our photoemission results on LAO/STO heterostructures in both (100) and (111) orientation as well as on the related system γ-Al2O3/STO(100), which also hosts a 2DES with an even higher mobility. Work in collaboration with J. Mannhart (MPI-FKF, Stuttgart), N. Pryds (TU Denmark), G. Rijnders (U Twente), S. Suga (U Osaka), M. Giorgoi (BESSY, HZB), W. Drube (DESY Photon Science), V.N. Strocov (Swiss Light Source), J. Denlinger (Advanced Light Source, LBNL), and T.-L. Lee (Diamond Light Source). Support by

  16. Implementation and Optimization of an Inverse Photoemission Spectroscopy Setup

    NASA Astrophysics Data System (ADS)

    Gina, Ervin

    Inverse photoemission spectroscopy (IPES) is utilized for determining the unoccupied electron states of materials. It is a complementary technique to the widely used photoemission spectroscopy (PES) as it analyzes what PES cannot, the states above the Fermi energy. This method is essential to investigating the structure of a solid and its states. IPES has a broad range of uses and is only recently being utilized. This thesis describes the setup, calibration and operation of an IPES experiment. The IPES setup consists of an electron gun which emits electrons towards a sample, where photons are released, which are measured in isochromat mode via a photon detector of a set energy bandwidth. By varying the electron energy at the source, a spectrum of the unoccupied density of states can be obtained. Since IPES is not commonly commercially available the design consists of many custom made components. The photon detector operates as a bandpass filter with a mixture of acetone/argon and a CaF2 window setting the cutoff energies. The counter electronics consist of a pre-amplifier, amplifier and analyzer to detect the count rate at each energy level above the Fermi energy. Along with designing the hardware components, a Labview program was written to capture and log the data for further analysis. The software features several operating modes including automated scanning which allows the user to enter the desired scan parameters and the program will scan the sample accordingly. Also implemented in the program is the control of various external components such as the electron gun and high voltage power supply. The new setup was tested for different gas mixtures and an optimum ratio was determined. Subsequently, IPES scans of several sample materials were performed for testing and optimization. A scan of Au was utilized for the determination of the Fermi edge energy and for comparison to literature spectra. The Fermi edge energy was then used in a measurement of indium tin

  17. Visual and optical performance of eyes with different corneal spherical aberration implanted with aspheric intraocular lens

    PubMed Central

    Gong, Xian-Hui; Zheng, Qin-Xiang; Wang, Na; Chen, Ding; Zhao, Juan; Li, Jin; Zhao, Yun-E

    2012-01-01

    AIM To compare the visual and optical performance of eyes with different corneal spherical aberration (SA) implanted with spherical aberration-free intraocular lens (IOLs). METHODS Thirty-six patients with different corneal SA had phacoemulsification with implantation of spherical aberration-free IOLs. Patients were divided into 3 groups according to the value of preoperative corneal SA. Eyes with corneal SA <0.10µm were assigned to group A, those with 0.10 ≤corneal SA <0.20µm to Group B, and those with 0.20≤ corneal SA <0.35µm to Group C. Best-corrected visual acuity (BCVA), contrast sensitivity, corneal SA, total ocular aberrations, and depth of focus were recorded 3 months postoperatively. Distance-corrected near and intermediate visual acuity was studied to measure depth of focus. RESULTS BCVA and contrast sensitivity were similar between groups. There were no significant differences in distance-corrected near or intermediate visual acuity. Corneal SA was similar before and 3 months after surgery in the 3 groups. With a 5.0mm pupil diameter, root mean square values for total ocular higher-order aberrations (HOAs) were lower in groups A and B than in group C. Total ocular SA was lower in group A than in groups B and C. SA was also lower in group B than in group C. Coma and trefoil were similar between the groups. CONCLUSION Implantation of spherical aberration-free IOLs in eyes with different corneal SA results in similar visual performance at BCVA, contrast sensitivity and depth of focus. PMID:22773981

  18. Prediction of Visual Acuity from Wavefront Aberrations

    NASA Technical Reports Server (NTRS)

    Watson, Andrew B. (Inventor); Ahumada, Albert J. (Inventor)

    2013-01-01

    A method for generating a visual acuity metric, based on wavefront aberrations (WFAs), associated with a test subject and representing classes of imperfections, such as defocus, astigmatism, coma and spherical aberrations, of the subject's visual system. The metric allows choices of different image template, can predict acuity for different target probabilities, can incorporate different and possibly subject-specific neural transfer functions, can predict acuity for different subject templates, and incorporates a model of the optotype identification task.

  19. Chromosome aberrations in decondensed sperm DNA

    SciTech Connect

    Preston, R.J.

    1982-01-01

    Factors that could influence the chromosomal aberration frequency observed at first cleavage following in vivo exposure of germ cells to chemical mutagens are discussed. The techniques of chromosome aberration analysis following sperm DNA condensation by in vitro fertilization or fusion seem to be viable research areas for providing information of human germ cell exposures. However, the potential sensitivity of the assay needs to be better understood, and factors that can influence this sensitivity require a great deal of further study using animal models.

  20. Internal photoemission in molecular junctions: parameters for interfacial barrier determinations.

    PubMed

    Fereiro, Jerry A; Kondratenko, Mykola; Bergren, Adam Johan; McCreery, Richard L

    2015-01-28

    The photocurrent spectra for large-area molecular junctions are reported, where partially transparent copper top contacts permit illumination by UV-vis light. The effect of variation of the molecular structure and thickness are discussed. Internal photoemission (IPE), a process involving optical excitation of hot carriers in the contacts followed by transport across internal system barriers, is dominant when the molecular component does not absorb light. The IPE spectrum contains information regarding energy level alignment within a complete, working molecular junction, with the photocurrent sign indicating transport through either the occupied or unoccupied molecular orbitals. At photon energies where the molecular layer absorbs, a secondary phenomenon is operative in addition to IPE. In order to distinguish IPE from this secondary mechanism, we show the effect of the source intensity as well as the thickness of the molecular layer on the observed photocurrent. Our results clearly show that the IPE mechanism can be differentiated from the secondary mechanism by the effects of variation of experimental parameters. We conclude that IPE can provide valuable information regarding interfacial energetics in intact, working molecular junctions, including clear discrimination of charge transport mediated by electrons through unoccupied system orbitals from that mediated by hole transport through occupied system orbitals.

  1. Photoemission study of Au on a-Si:H

    NASA Astrophysics Data System (ADS)

    Pi, Tun-Wen; Yang, A.-B.; Olson, C. G.; Lynch, D. W.

    1990-11-01

    We report a high-resolution photoemission study of Au evaporated on rf-sputtered a-Si:H at room temperature. Three regions of coverage can be classified according to the behavior of the valence-band and core-level spectra: an unreacted region with an equivalent thickness of 2 Å, followed by an intermixed Au/a-Si overlayer (~9 Å), and a dual-phase region at higher coverage. Au adatoms are dispersed in the unreacted region. They subsequently cluster in the intermixed region, where they attach to Si atoms that are not hydrogen bonded, suggesting that the intermixed Si is mainly from those that have dangling bonds. In the dual-phase region, two sets of Au 4f core levels evolve with higher binding energy, one from Au intermixed with Si, and the lower one exhibiting pure gold character. The interface eventually ends up with the sequence: a-Si:H(sub.)+(pure Au mixed with intermixed Au/Si)+(vac). This is unlike the case of Au on c-Si, which has a pure gold layer sandwiched by intermixed Au/Si complexes along the surface normal. Traces of silicon atoms on top of composite surfaces appear even at the highest coverage, 205 Å, of the gold deposit. The applicability of the four models previously used for the Au/c-Si interface is also briefly discussed.

  2. Photoemission studies using femtosecond pulses for high brightness electron beams

    NASA Astrophysics Data System (ADS)

    Srinivasan-Rao, T.; Tsang, T.; Fischer, J.

    1990-06-01

    We present the results of a series of experiments where various metal photocathodes are irradiated with ultrashort laser pulses, whose characteristics are: (lambda) = 625 nm, (tau) = 100 fs, PRR = 89.5 MHz, H(nu) = 2 eV and average power 25 mW in each of the two beams. The quantum efficiency of the metals range from approximately 10(exp -12) to 10(exp -8) at a power density of 100 MW/sq cm at normal incidence. Since all the electrons are emitted due to multiphoton processes, these efficiencies are expected to increase substantially at large intensities. The efficiency at 100 MW/sq cm was increased by using p-polarized light at oblique incidence by approximately 20 x and by mediating the electron emission through surface plasmon excitation by approximately 10(exp 3) x. For the low intensities used in these experiments, the electron pulse duration is almost the same as the laser pulse duration for both the bulk and the surface plasmon mediated photoemission.

  3. Direct surface magnetometry with photoemission magnetic x-ray dichroism

    SciTech Connect

    Tobin, J.G.; Goodman, K.W.; Schumann, F.O.

    1997-04-01

    Element specific surface magnetometry remains a central goal of synchrotron radiation based studies of nanomagnetic structures. One appealing possibility is the combination of x-ray absorption dichroism measurements and the theoretical framework provided by the {open_quotes}sum rules.{close_quotes} Unfortunately, sum rule analysis are hampered by several limitations including delocalization of the final state, multi-electronic phenomena and the presence of surface dipoles. An alternative experiment, Magnetic X-Ray Dichroism in Photoelectron Spectroscopy, holds out promise based upon its elemental specificity, surface sensitivity and high resolution. Computational simulations by Tamura et al. demonstrated the relationship between exchange and spin orbit splittings and experimental data of linear and circular dichroisms. Now the authors have developed an analytical framework which allows for the direct extraction of core level exchange splittings from circular and linear dichroic photoemission data. By extending a model initially proposed by Venus, it is possible to show a linear relation between normalized dichroism peaks in the experimental data and the underlying exchange splitting. Since it is reasonable to expect that exchange splittings and magnetic moments track together, this measurement thus becomes a powerful new tool for direct surface magnetometry, without recourse to time consuming and difficult spectral simulations. The theoretical derivation will be supported by high resolution linear and circular dichroism data collected at the Spectromicroscopy Facility of the Advanced Light Source.

  4. Photoemission experiments of a large area scandate dispenser cathode

    NASA Astrophysics Data System (ADS)

    Zhang, Huang; Liu, Xing-guang; Chen, Yi; Chen, De-biao; Jiang, Xiao-guo; Yang, An-min; Xia, Lian-sheng; Zhang, Kai-zhi; Shi, Jin-shui; Zhang, Lin-wen

    2010-09-01

    A 100-mm-diameter scandate dispenser cathode was tested as a photocathode with a 10 ns Nd:YAG laser (266 nm) on an injector test stand for linear induction accelerators. This thermionic dispenser cathode worked at temperatures ranging from room temperature to 930 °C (below or near the thermionic emission threshold) while the vacuum was better than 4×10 -7 Torr. The laser pulse was synchronized with a 120 ns diode voltage pulse stably and they were in single pulse mode. Emission currents were measured by a Faraday cup. The maximum peak current collected at the anode was about 100 A. The maximum quantum efficiency measured at low laser power was 2.4×10 -4. Poisoning effect due to residual gas was obvious and uninterrupted heating was needed to keep cathode's emission capability. The cathode was exposed to air one time between experiments and recovered after being reconditioned. Photoemission uniformity of the cathode was also explored by changing the laser spot's position.

  5. Individual eye model based on wavefront aberration

    NASA Astrophysics Data System (ADS)

    Guo, Huanqing; Wang, Zhaoqi; Zhao, Qiuling; Quan, Wei; Wang, Yan

    2005-03-01

    Based on the widely used Gullstrand-Le Grand eye model, the individual human eye model has been established here, which has individual corneal data, anterior chamber depth and the eyeball depth. Furthermore, the foremost thing is that the wavefront aberration calculated from the individual eye model is equal to the eye's wavefront aberration measured with the Hartmann-shack wavefront sensor. There are four main steps to build the model. Firstly, the corneal topography instrument was used to measure the corneal surfaces and depth. And in order to input cornea into the optical model, high-order aspheric surface-Zernike Fringe Sag surface was chosen to fit the corneal surfaces. Secondly, the Hartmann-shack wavefront sensor, which can offer the Zernike polynomials to describe the wavefront aberration, was built to measure the wavefront aberration of the eye. Thirdly, the eye's axial lengths among every part were measured with A-ultrasonic technology. Then the data were input into the optical design software-ZEMAX and the crystalline lens's shapes were optimized with the aberration as the merit function. The individual eye model, which has the same wavefront aberrations with the real eye, is established.

  6. Measuring aberrations in the rat brain by coherence-gated wavefront sensing using a Linnik interferometer

    PubMed Central

    Wang, Jinyu; Léger, Jean-François; Binding, Jonas; Boccara, A. Claude; Gigan, Sylvain; Bourdieu, Laurent

    2012-01-01

    Aberrations limit the resolution, signal intensity and achievable imaging depth in microscopy. Coherence-gated wavefront sensing (CGWS) allows the fast measurement of aberrations in scattering samples and therefore the implementation of adaptive corrections. However, CGWS has been demonstrated so far only in weakly scattering samples. We designed a new CGWS scheme based on a Linnik interferometer and a SLED light source, which is able to compensate dispersion automatically and can be implemented on any microscope. In the highly scattering rat brain tissue, where multiply scattered photons falling within the temporal gate of the CGWS can no longer be neglected, we have measured known defocus and spherical aberrations up to a depth of 400 µm. PMID:23082292

  7. Measuring aberrations in the rat brain by coherence-gated wavefront sensing using a Linnik interferometer.

    PubMed

    Wang, Jinyu; Léger, Jean-François; Binding, Jonas; Boccara, A Claude; Gigan, Sylvain; Bourdieu, Laurent

    2012-10-01

    Aberrations limit the resolution, signal intensity and achievable imaging depth in microscopy. Coherence-gated wavefront sensing (CGWS) allows the fast measurement of aberrations in scattering samples and therefore the implementation of adaptive corrections. However, CGWS has been demonstrated so far only in weakly scattering samples. We designed a new CGWS scheme based on a Linnik interferometer and a SLED light source, which is able to compensate dispersion automatically and can be implemented on any microscope. In the highly scattering rat brain tissue, where multiply scattered photons falling within the temporal gate of the CGWS can no longer be neglected, we have measured known defocus and spherical aberrations up to a depth of 400 µm.

  8. Photoemission and magnetic circular dichroism studies of magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Fujimori, Atsushi

    2005-03-01

    Recently, a series of novel ferromagnetic semiconductors have been synthesized using MBE and related techniques and have attracted much attention because of unknown mechanisms of carrier-induced ferromagnetism and potential applications as "spin electronics" devices. Some new materials show ferromagnetism even well above room temperature. Photoemission spectroscopy has been used to study the d orbitals of the dilute transition-metal atoms, mostly Mn, and their hybridization with the host band states [1]. Soft x-ray absorption spectroscopy (XAS) and magnetic circular dichroism (MCD) at the transition-metal 2p-3d absorption edges are useful techniques to study the valence and spin states of the transition-metal atoms. Furthermore, since MCD has different sensitivities to the ferromagnetic and paramagnetic components at different temperatures and magnetic fileds, if the sample is a mixture of ferromagnetic and non-ferromagnetic transition- metal atoms, it can be used to separate the two components and to study their electronic structures. In this talk, results are presented for the prototypical diluted ferromagnetic semiconductor Ga1-xMnxAs [2] and the room-temperature ferromagnets Zn1-xCoxO and Ti1-xCoxO2.I acknowledge collaboration with Y. Ishida, J.-I. Hwang, M. Kobayashi, Y. Takeda, Y. Saitoh, J. Okamoto, T. Okane, Y. Muramatsu, K. Mamiya, T. Koide, A. Tanaka, M. Tanaka, Hayashi, S. Ohya, T. Kondo, H. Munekata, H. Saeki, H. Tabata, T. Kawai, Y. Matsumoto, H. Koinuma, T. Fukumura and M. Kawasaki. This work was supported by a Grant-in-Aid for Scientific Research in Priority Area "Semiconductor nano-spintronics" (14076209) from MEXT, Japan.1. J. Okabayashi et al., Phys. Rev. B 64, 125304 (2001).2. A. Fujimori et al., J. Electron Spectrosc. Relat. Phenom., in press.

  9. Xe and Ar nanobubbles in Al studied by photoemission spectroscopy

    SciTech Connect

    Dhaka, R. S.; Biswas, C.; Shukla, A. K.; Barman, S. R.; Chakrabarti, Aparna

    2008-03-01

    We have studied xenon and argon bubbles formed in the subsurface region of Al(111) by x-ray photoelectron spectroscopy. As a consequence of the nanometer size of the bubbles, the photohole formed by Xe 3d or Ar 2p photoemission is screened by the Al conduction electrons, which substantially lowers the binding energy (BE) as compared to the gas phase. As the bubble size increases, the Al conduction electron screening decreases and the BE increases. On the basis of density functional theory, we show that the change in the bubble pressure with size is not responsible for the BE shift of inner shell core levels, such as Xe 3d or Ar 2p. On the other hand, an increase in BE with bubble size for outer shell core levels, such as Ar 3p, could be due to a decrease in both pressure and Al conduction electron screening. The core level line shape also changes with bubble size. For example, the spectra are broadened due to the distribution of the bubble radius around its mean value, and an asymmetry for small bubbles is observed that decreases for larger bubbles. An annealing of Xe and Ar bubbles after an implantation up to 640 K shows that the BE increases with annealing temperature. Since it is well known that bubble size increases with annealing temperature, this further supports our contention of BE shift with bubble size. A defect induced partial disorder of the Al(111) surface by Xe and Ar bombardment is observed by low energy electron diffraction, but this does not affect the Al 2p BE and line shape.

  10. Striatal Activity is Associated with Deficits of Cognitive Control and Aberrant Salience for Patients with Schizophrenia

    PubMed Central

    Ceaser, Alan E.; Barch, Deanna M.

    2016-01-01

    A recent meta-analysis has shown that a large dopamine abnormality exists in the striatum when comparing patients with schizophrenia and controls, and this abnormality is thought to contribute to aberrant salience assignment (or a misattribution of relevance to irrelevant stimuli). This abnormality may also disrupt striatal contributions to cognitive control processing. We examined the relationship between striatal involvement in cognition and aberrant salience symptoms using a task of cognitive control that involves updating, interference control, and simple maintenance. The current study included a sample of 22 patients with schizophrenia and 20 healthy controls and used a slow event-related fMRI design. We predicted that (1) aberrant salience symptoms would be greater for patient's, (2) patients would demonstrate increased errors during interference control trials, given that patients may be inappropriately assigning salience to distracters, and (3) striatal activity during those errors would be correlated with aberrant salience symptoms. We found a trend toward a significant difference between patients and controls on aberrant salience symptoms, and a significant difference between groups on select task conditions. During interference control trials, patients were more likely to inappropriately encode distracters. For patients, both prefrontal and striatal activity was significantly greater when patients inappropriately identified the distracter as correct compared to activity during distracter rejection. During updating, patient prefrontal and striatal activity was significantly lower for incorrect than correct updating trials. Finally, as predicted, for patients the increase of activity during incorrect distracter trials was positively correlated with aberrant salience symptoms, but only for the striatal region. These relationships may have implications for treatments that improve cognitive function and reduce symptom expression. PMID:26869912

  11. Impact of Treatment Decentration on Higher-Order Aberrations after SMILE

    PubMed Central

    Zhang, Wenwen; Cheng, Xinliang; Cai, Jianru

    2017-01-01

    Purpose. To evaluate decentration following femtosecond laser small incision lenticule extraction (SMILE) and sub-Bowman keratomileusis (SBK) and its impact on higher-order aberrations (HOAs). Methods. Prospective, nonrandom, and comparison study. There were 96 eyes of 52 patients who received SMILE and 96 eyes of 49 patients who received SBK in this study. Decentration was calculated 6 months after surgery with Pentacam. HOAs and visual acuity after the surgery were examined for patients in both groups before and 6 months after surgery. Results. The mean decentration displacement in SMILE group was significantly less than SBK group (P = 0.020). 89 eyes were decentered within 0.50 mm after SMILE and SBK. The association between vertical decentration and the induced spherical aberration was insignificant in SMILE group (P = 0.035). There was an association between decentration and safety index, efficacy index, vertical coma, spherical aberration, and HOAs in root mean square (RMS, μm) after SBK (all P < 0.05). No difference was found in uncorrected and corrected distance visual acuity, safety index, efficacy index, and wavefront aberrations between the two subgroups at any delimited value after SMILE (all P > 0.05). Decentration exceeding 0.37 mm affected vertical coma and RMSh of SBK eyes (P = 0.002, 0.005). Conclusion. SMILE surgery achieved more accurate centration than SBK surgery. Vertical decentration is associated with the induced spherical aberration in SMILE.

  12. Exaggerated translation causes synaptic and behavioural aberrations associated with autism.

    PubMed

    Santini, Emanuela; Huynh, Thu N; MacAskill, Andrew F; Carter, Adam G; Pierre, Philippe; Ruggero, Davide; Kaphzan, Hanoch; Klann, Eric

    2013-01-17

    Autism spectrum disorders (ASDs) are an early onset, heterogeneous group of heritable neuropsychiatric disorders with symptoms that include deficits in social interaction skills, impaired communication abilities, and ritualistic-like repetitive behaviours. One of the hypotheses for a common molecular mechanism underlying ASDs is altered translational control resulting in exaggerated protein synthesis. Genetic variants in chromosome 4q, which contains the EIF4E locus, have been described in patients with autism. Importantly, a rare single nucleotide polymorphism has been identified in autism that is associated with increased promoter activity in the EIF4E gene. Here we show that genetically increasing the levels of eukaryotic translation initiation factor 4E (eIF4E) in mice results in exaggerated cap-dependent translation and aberrant behaviours reminiscent of autism, including repetitive and perseverative behaviours and social interaction deficits. Moreover, these autistic-like behaviours are accompanied by synaptic pathophysiology in the medial prefrontal cortex, striatum and hippocampus. The autistic-like behaviours displayed by the eIF4E-transgenic mice are corrected by intracerebroventricular infusions of the cap-dependent translation inhibitor 4EGI-1. Our findings demonstrate a causal relationship between exaggerated cap-dependent translation, synaptic dysfunction and aberrant behaviours associated with autism.

  13. Computation of astigmatic and trefoil figure errors and misalignments for two-mirror telescopes using nodal-aberration theory.

    PubMed

    Ju, Guohao; Yan, Changxiang; Gu, Zhiyuan; Ma, Hongcai

    2016-05-01

    In active optics systems, one concern is how to quantitatively separate the effects of astigmatic and trefoil figure errors and misalignments that couple together in determining the total aberration fields when wavefront measurements are available at only a few field points. In this paper, we first quantitatively describe the impact of mount-induced trefoil deformation on the net aberration fields by proposing a modified theoretical formulation for the field-dependent aberration behavior of freeform surfaces based on the framework of nodal aberration theory. This formulation explicitly expresses the quantitative relationships between the magnitude of freeform surfaces and the induced aberration components where the freeform surfaces can be located away from the aperture stop and decentered from the optical axis. On this basis, and in combination with the mathematical presentation of nodal aberration theory for the effects of misalignments, we present the analytic expressions for the aberration fields of two-mirror telescopes in the presence of astigmatic primary mirror figure errors, mount-induced trefoil deformations on both mirrors, and misalignments. We quantitatively separate these effects using the analytical expressions with wavefront measurements at a few field points and pointing errors. Valuable insights are provided on how to separate these coupled effects in the computation process. Monte Carlo simulations are conducted to demonstrate the correctness and accuracy of the analytic method presented in this paper.

  14. Corrective work.

    ERIC Educational Resources Information Center

    Hill, Leslie A.

    1978-01-01

    Discusses some general principles for planning corrective instruction and exercises in English as a second language, and follows with examples from the areas of phonemics, phonology, lexicon, idioms, morphology, and syntax. (IFS/WGA)

  15. Transition from the adiabatic to the sudden limit in core-electron photoemission

    NASA Astrophysics Data System (ADS)

    Hedin, Lars; Michiels, John; Inglesfield, John

    1998-12-01

    Experimental results for core-electron photoemission Jk(ω) are often compared with the one-electron spectral function Ac(ɛk-ω), where ω is the photon energy, ɛk is the photoelectron energy, and the optical transition matrix elements are taken as constant. Since Jk(ω) is nonzero only for ɛk>0, we must actually compare it with Ac(ɛk-ω)θ(ɛk). For metals Ac(ω) is known to have a quasiparticle (QP) peak with an asymmetric power-law [theories of Mahan, Nozières, de Dominicis, Langreth, and others (MND)] singularity due to low-energy particle-hole excitations. The QP peak starts at the core-electron energy ɛc, and is followed by an extended satellite (shakeup) structure at smaller ω. For photon energies ω just above threshold, ωth=-ɛc, Ac(ɛk-ω)θ(ɛk) as a function of ɛk (ω constant) is cut just behind the quasiparticle peak, and neither the tail of the MND line nor the plasmon satellites are present. The sudden (high-energy) limit is given by a convolution of Ac(ω) and a loss function, i.e., by the Berglund-Spicer two-step expression. Thus Ac(ω) alone does not give the correct photoelectron spectrum, neither at low nor at high energies. We present an extension of the quantum-mechanical (QM) models developed earlier by Inglesfield, and by Bardyszewski and Hedin to calculate Jk(ω). It includes recoil and damping, as well as shakeup effects and extrinsic losses, is exact in the high-energy limit, and allows calculations of Jk(ω) including the MND line and multiple plasmon losses. The model, which involves electrons coupled to quasibosons, is motivated by detailed arguments. As an illustration we have made quantitative calculations for a semi-infinite jellium with the density of aluminum metal and an embedded atom. The coupling functions (fluctuation potentials) between the electron and the quasibosons are related to the random-phase-approximation dielectric function, and different levels of approximations are evaluated numerically. The differences

  16. A photoemission study of the diamond and the single crystal C60

    SciTech Connect

    Wu, Jin

    1994-03-01

    This report studied the elctronic structure of diamond (100) and diamond/metal interface and C60, using angle-resolved and core level photoemission. The C(100)-(2X1) surface electronic structure was studied using both core level and angle resolved valence band photoemission spectroscopy. The surface component of the C 1s core level spectrum agrees with theoretical existence of only symmetrical dimers. In the case of metal/diamond interfaces, core level and valence photoelectron spectroscopy and LEED studies WERE MADE OF B and Sb on diamond (100) and (111) surfaces. In the case of single-crystal C60, photoemission spectra show sharp molecular features, indicating that the molecular orbitals are relatively undisturbed in solid C60.

  17. Aberration Compensation Using Nematic Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Somalingam, S.; Hain, M.; Tschudi, T.; Knittel, J.; Richter, H.

    We have developed a novel transmissive nematic liquid crystal device which is capable of compensating spherical wavefront aberration that occurs during the operation of optical pickup systems. In order to increase the storage capacity, next generation optical data storage systems beyond CD and DVD will use according to the Blu-Ray specification (BD) blue laser light and an objective lens with high numerical aperture (N.A.) of 0.85. However, such high N.A. systems have an inherent higher sensitivity on aberrations. For example spherical aberration is inversely proportional to the wavelength and grows with the fourth power of N.A. of the objective lens. In an optical pickup system there are two sources for spherical aberration: The first one is the variation of the substrate thickness due to manufacturing tolerances under mass production conditions. The second one concerns disks with multiple data-layers, which cause spherical aberration when layers are switched, as the objective lens can only be optimized for a single layer thickness. We report a method for effective compensation of spherical aberration by utilizing a novel liquid crystal device, which generates a parabolic wavefront profile. This particular shape makes the device highly tolerant against lateral movement. A sophisticated electrode design allows us to reduce the number of driving electrodes down to two by using the method of conductive ladder mashing. Further evaluation in a blue-DVD test drive has been carried out with good results. By placing the device into an optical pick-up we were able to readout a dual-layer ROM disk with a total capacity of 50 gigabytes (GB). A data-to-clock jitter of 6.9% for the 80 μm and of 8.0% for the 100 μm cover layer could be realized.

  18. Effect of incision types for Artisan phakic intraocular lens implantation on ocular higher order aberrations

    PubMed Central

    Park, Young Min; Choi, Bong Joon; Lee, Jong Soo

    2016-01-01

    AIM To evaluate the effect of incision types for Artisan phakic intraocular lens (PIOL) implantation on ocular higher-order aberrations (HOAs). METHODS A retrospective review was conducted of the patients who had undergone Artisan PIOL implantation for the correction of myopia and followed up for at least 6mo. Patients are classified into 2 groups considering the incision type: cornea group with patients undergone clear corneal incision; sclera group with patients undergone sclera tunnel incision. All patients with postoperative astigmatism of under 1 diopter (D) were included to minimize the effect of residual astigmatism on postoperative HOAs. Visual acuity, special equivalents, astigmatism, predictability (±1 D from target refraction), HOAs (coma, trefoil, spherical aberration), and corneal endothelial counts were analyzed preoperatively and 6mo postoperatively. RESULTS At the postoperative 6mo, all patients of both groups achieved uncorrected visual acuity of 16/20 or better, and significantly decreased the spherical equivalents compared with preoperative values. The predictability of refractive correction was 96% in the former, and 94% in the latter. Unlike the sclera group, preoperative astigmatism decreased significantly in cornea group at postoperative 6mo. The HOAs increased significantly at postoperative 6mo compared to the preoperative values in both groups, and the root mean square (RMS) total and trefoil wavefront aberration of cornea group were significantly higher than those of sclera group. CONCLUSION Although corneal incision significantly reduces preexisting astigmatism, the postoperative 6mo of total RMS and trefoil aberration change may deteriorate the visual quality after Artisan PIOL implantation. PMID:28003980

  19. Chromosome aberration test for hydroxyapatite in sheep.

    PubMed

    Kannan, T P; Nik Ahmad Shah, N L; Azlina, A; Samsudin, A R; Narazah, M Y; Salleh, Ma'arof

    2004-05-01

    The present study is aimed at finding the mutagenicity and cytotoxicity of dense form of synthetic hydroxyapatite (Source: School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia) in the blood of sheep. The biomaterial was implanted in the tibia of Malin, an indigenous sheep breed of Malaysia. Blood was collected from the sheep before implantation of the biomaterial, cultured and a karyological study was made. Six weeks after implantation, blood was collected from the same animal, cultured and screened for chromosome aberrations. The mitotic indices and karyological analysis indicated that the implantation of synthetic hydroxyapatite (dense form) did not produce any cytotoxicity or chromosome aberrations in the blood of sheep.

  20. Geometrical Aberration Suppression for Large Aperture Sub-THz Lenses

    NASA Astrophysics Data System (ADS)

    Rachon, M.; Liebert, K.; Siemion, A.; Bomba, J.; Sobczyk, A.; Knap, W.; Coquillat, D.; Suszek, J.; Sypek, M.

    2017-03-01

    Advanced THz setups require high performance optical elements with large numerical apertures and small focal lengths. This is due to the high absorption of humid air and relatively low efficiency of commercially available detectors. Here, we propose a new type of double-sided sub-THz diffractive optical element with suppressed geometrical aberration for narrowband applications (0.3 THz). One side of the element is designed as thin structure in non-paraxial approach which is the exact method, but only for ideally flat elements. The second side will compensate phase distribution differences between ideal thin structure and real volume one. The computer-aided optimization algorithm is performed to design an additional phase distribution of correcting layer assuming volume designing of the first side of the element. The experimental evaluation of the proposed diffractive component created by 3D printing technique shows almost two times larger performance in comparison with uncorrected basic diffractive lens.

  1. Geometrical Aberration Suppression for Large Aperture Sub-THz Lenses

    NASA Astrophysics Data System (ADS)

    Rachon, M.; Liebert, K.; Siemion, A.; Bomba, J.; Sobczyk, A.; Knap, W.; Coquillat, D.; Suszek, J.; Sypek, M.

    2016-11-01

    Advanced THz setups require high performance optical elements with large numerical apertures and small focal lengths. This is due to the high absorption of humid air and relatively low efficiency of commercially available detectors. Here, we propose a new type of double-sided sub-THz diffractive optical element with suppressed geometrical aberration for narrowband applications (0.3 THz). One side of the element is designed as thin structure in non-paraxial approach which is the exact method, but only for ideally flat elements. The second side will compensate phase distribution differences between ideal thin structure and real volume one. The computer-aided optimization algorithm is performed to design an additional phase distribution of correcting layer assuming volume designing of the first side of the element. The experimental evaluation of the proposed diffractive component created by 3D printing technique shows almost two times larger performance in comparison with uncorrected basic diffractive lens.

  2. Misalignment induced aberration off-axis optical system

    NASA Astrophysics Data System (ADS)

    Pang, Zhihai; Fan, Xuewu; Ma, Zhen; Zou, Gangyi

    2016-10-01

    Through introducing transformed pupil vector and shifted center of aberration fields vector into the nodal aberration expansions of an axially symmetric optical system, the aberration expression in third order of an off-axis optical system and misaligned off-axis optical system are detailed. Nodal aberration characteristics of misaligned off-axis optical system are revealed only by analyzing the pupil decentration vector, aberration fields shifted vector and the aberration coefficients of the axially symmetric optical system. Actually, it is well demonstrated that the 3rd spherical aberration, 3rd coma, 3rd astigmatism in a misalignment off-axis system are comparable to the aberrations in a misalignment axially symmetric system. Otherwise it will not only induced constant 3rd spherical aberration but also constant 3rd coma and 3rd astigmatism over the field of view, when aligned an off-axis optical system elements with error axial spacing.

  3. Generating few-cycle pulses for nanoscale photoemission easily with an erbium-doped fiber laser.

    PubMed

    Thomas, Sebastian; Holzwarth, Ronald; Hommelhoff, Peter

    2012-06-18

    We demonstrate a simple setup capable of generating four-cycle pulses at a center wavelength of 1700 nm for nanoscale photoemission. Pulses from an amplified erbium-doped fiber laser are spectrally broadened by propagation through a highly non-linear fiber. Subsequently, we exploit dispersion in two different types of glass to compress the pulses. The pulse length is estimated by measuring an interferometric autocorrelation trace and comparing it to a numerical simulation. We demonstrate highly non-linear photoemission of electrons from a nanometric tungsten tip in a hitherto unexplored pulse parameter range.

  4. Resonant-photoemission identification of the valence states of NiPS 3

    NASA Astrophysics Data System (ADS)

    Kelly, M. K.; Daniels, R. R.; Margaritondo, G.; Lévy, F.

    1984-04-01

    We monitored the resonant behavior of the Ni d satellite peaks in the valence band photoemission spectra of NiPS 3 at photon energies immediately below and immediately above the Ni3p threshold. The observed resonance gives an unequivocal identification of the satellite peaks and of the corresponding main Ni d features. The study of the electronic structure of this material and of the related compounds FePS 3 and HgPS 3 was extended to unoccupied states by means of partial-yield synchrotron-radiation photoemission spectroscopy.

  5. Polarity effects in the x-ray photoemission of ZnO and other wurtzite semiconductors

    NASA Astrophysics Data System (ADS)

    Allen, M. W.; Zemlyanov, D. Y.; Waterhouse, G. I. N.; Metson, J. B.; Veal, T. D.; McConville, C. F.; Durbin, S. M.

    2011-03-01

    Significant polarity-related effects were observed in the near-surface atomic composition and valence band electronic structure of ZnO single crystals, investigated by x-ray photoemission spectroscopy using both Al Kα (1486.6 eV) and synchrotron radiation (150 to 1486 eV). In particular, photoemission from the lowest binding energy valence band states was found to be significantly more intense on the Zn-polar face compared to the O-polar face. This is a consistent effect that can be used as a simple, nondestructive indicator of crystallographic polarity in ZnO and other wurtzite semiconductors.

  6. Two-Color Coherent Control of Femtosecond Above-Threshold Photoemission from a Tungsten Nanotip

    NASA Astrophysics Data System (ADS)

    Förster, Michael; Paschen, Timo; Krüger, Michael; Lemell, Christoph; Wachter, Georg; Libisch, Florian; Madlener, Thomas; Burgdörfer, Joachim; Hommelhoff, Peter

    2016-11-01

    We demonstrate coherent control of multiphoton and above-threshold photoemission from a single solid-state nanoemitter driven by a fundamental and a weak second harmonic laser pulse. Depending on the relative phase of the two pulses, electron emission is modulated with a contrast of the oscillating current signal of up to 94%. Electron spectra reveal that all observed photon orders are affected simultaneously and similarly. We confirm that photoemission takes place within 10 fs. Accompanying simulations indicate that the current modulation with its large contrast results from two interfering quantum pathways leading to electron emission.

  7. Two-Color Coherent Control of Femtosecond Above-Threshold Photoemission from a Tungsten Nanotip.

    PubMed

    Förster, Michael; Paschen, Timo; Krüger, Michael; Lemell, Christoph; Wachter, Georg; Libisch, Florian; Madlener, Thomas; Burgdörfer, Joachim; Hommelhoff, Peter

    2016-11-18

    We demonstrate coherent control of multiphoton and above-threshold photoemission from a single solid-state nanoemitter driven by a fundamental and a weak second harmonic laser pulse. Depending on the relative phase of the two pulses, electron emission is modulated with a contrast of the oscillating current signal of up to 94%. Electron spectra reveal that all observed photon orders are affected simultaneously and similarly. We confirm that photoemission takes place within 10 fs. Accompanying simulations indicate that the current modulation with its large contrast results from two interfering quantum pathways leading to electron emission.

  8. Quantum-electrodynamic treatment of photoemission by a single-electron wave packet

    SciTech Connect

    Corson, John P.; Peatross, Justin

    2011-11-15

    A quantum-field-theory description of photoemission by a laser-driven single-electron wave packet is presented. We show that, when the incident light is represented with multimode coherent states then, to all orders of perturbation theory, the relative phases of the electron's constituent momenta have no influence on the amount of scattered light. These results are extended using the Furry picture, where the (unidirectional) arbitrary incident light pulse is treated nonperturbatively with Volkov functions. This analysis increases the scope of our prior results in [Phys. Rev. A 84, 053831 (2011)], which demonstrate that the spatial size of the electron wave packet does not influence photoemission.

  9. The Organic LED Surface:. a Synchrotron Radiation Photoemission Study

    NASA Astrophysics Data System (ADS)

    Pi, Tun-Wen; Yu, T. C.

    Tris(8-hydroxyquinolato) aluminum (Alq3), a prototypical molecule for organic light-emitting devices, has been studied via synchrotron radiation photoemission to investigate (1) the surface electronic structure of the molecules at room temperature and at elevated temperatures, (2) adsorption onto the inorganic Si(001)-2×1 surface, and (3) doping with the alkaline metal Mg. For case (1), three chemical environments of carbon are resolved. Moreover, the shake-up satellite structures are detected in all the N 1s, C 1s, O 1s, and Al 2p core-level spectra, but with different magnitudes. Annealing allows for a charge redistribution within Alq3 itself. As to case (2), the organic molecules not only passivate the dangling bonds, but also rupture the dimer bonds. The wave function of the surface dangling bonds and of the pyridyl side of an 8-quinolinol ligand overlaps greatly so that charge is polarized towards, the organic adlayer. However, the polarization diminishes at greater coverage. With regard to case (3), the N 1s core-level spectra appear as an Mg-induced charge-transfer component with a binding energy lower than the original component. This new component grows gradually in intensity with increasing concentration of the dopant. Moreover, Mg also affects the O 1s core, as manifested by a component lying at a +1.09 eV higher binding energy than the original component. The Mg 2p core-level spectra, although rather broad, exhibit a shift toward a lower binding energy with increasing Mg vapor. Upon examining all these experimental results, we propose that Mg in the surface Alq3 molecules forms clusters. Each cluster attaches to a pyridyl ring, affecting not only the nitrogen atom at that ring, but also the oxygen atom in the adjacent phenoxide ring. The depleted charge in the affected oxygen then flows about its adherent ligand and resides on the pyridyl ring at that ligand, resulting in a high Alq3 anion state.

  10. High resolution photoemission experiments on copper oxide superconductors

    NASA Astrophysics Data System (ADS)

    Rameau, Jonathan David

    The mechanism for achieving high transition temperatures (T c) in copper oxide superconductors and the nature of the mysterious "pseudogap" phase from which this phenomenon arises are two of the most pressing issues in solid state physics. High resolution angle resolved photoemission spectroscopy (ARPES), which can directly probe the momentum and energy dependence of the electronic structure of a crystal, is considered one of the foremost tools for unraveling these mysteries. In this thesis we present work on both the further development of the ARPES technique itself and the results of two experiments on the high temperature superconductor Bi2Sr2CaCu2O8+delta (BSCCO)---the drosophila of copper oxide superconductors---based upon these analytical and experimental advances. On the analytical side we have shown that the precision of any ARPES experiment can be radically enhanced by using the Lucy-Richardson method (LRM) of iterative deconvolution to remove the worst effects of experimental resolution broadening present in all ARPES spectra. On the experimental side we have constructed a deep ultraviolet laser system capable of increasing our data acquisition rate by more than an order of magnitude compared to what is possible using traditional synchrotron radiation sources at the same momentum and energy resolutions. Using the LRM, in conjunction with synchrotron radiation, spectroscopic evidence was found for the existence of incoherent Cooper pairs in underdoped BSCCO in the normal pseudogap state (above Tc). At the same time an asymmetry between the particle and hole states of BSCCO was found, implying that doped Mott insulators, of which BSCCO is a primordial example, are characterized by the presence of a Fermi-Luttinger surface, rather than a Fermi surface, as would be the case for a simple metal. This study provided the first spectroscopic evidence for either phenomenon. In our second experiment we were able to use the LRM on data acquired with the laser ARPES

  11. Angle-resolved photoemission spectroscopy (ARPES) studies of cuprate superconductors

    SciTech Connect

    Palczewski, Ari Deibert

    2010-01-01

    This dissertation is comprised of three different angle-resolved photoemission spectroscopy (ARPES) studies on cuprate superconductors. The first study compares the band structure from two different single layer cuprates Tl2Ba2CuO6+δ (Tl2201) Tc, max ≈ 95 K and (Bi 1.35Pb0.85)(Sr1.47La0.38)CuO6+δ (Bi2201) Tc, max ≈ 35 K. The aim of the study was to provide some insight into the reasons why single layer cuprate's maximum transition temperatures are so different. The study found two major differences in the band structure. First, the Fermi surface segments close to (π,0) are more parallel in Tl2201 than in Bi2201. Second, the shadow band usually related to crystal structure is only present in Bi2201, but absent in higher Tc Tl2201. The second study looks at the different ways of doping Bi2Sr2CaCu2O8+δ (Bi2212) in-situ by only changing the post bake-out vacuum conditions and temperature. The aim of the study is to systematically look into the generally overlooked experimental conditions that change the doping of a cleaved sample in ultra high vacuum (UHV) experiments. The study found two major experimental facts. First, in inadequate UHV conditions the carrier concentration of Bi2212 increases with time, due to the absorption of oxygen from CO2/CO molecules, prime contaminants present in UHV systems. Second, in a very clean UHV system at elevated temperatures (above about 200 K), the carrier concentration decreases due to the loss of oxygen atoms from the Bi-O layer. The final study probed the particle-hole symmetry of the pseudogap phase in high temperature superconducting cuprates by looking at the thermally excited bands above the Fermi level. The data showed a particle-hole symmetric pseudogap which symmetrically closes away from the nested FS before the node. The data is consistent

  12. Recent Photoemission Results for the Electron-Doped Superconductors

    NASA Astrophysics Data System (ADS)

    Matsui, Hiroaki

    2006-03-01

    Recent improvement in the energy and angular resolution of angle-resolved photoemission spectroscopy (ARPES) enabled us to investigate the detailed electronic structure in electron-doped high-temperature superconductors (HTSC), which have a relatively smaller energy-scale of superconductivity compared to hole-doped systems. In this talk, we report our recent ARPES results1,2 focusing on the many-body interaction and the superconducting-gap symmetry in electron-doped HTSC. We have performed high-resolution ARPES measurements on Nd2-xCexCuO4 and observed that the quasiparticle (QP) effective mass around oπ sg&_slash;p is strongly enhanced due to opening of an antiferromagnetic (AF) pseudogap. Both the QP effective mass and the AF pseudogap are strongly anisotropic with the largest magnitude near the hot spot, which is defined as an intersection point of the Fermi surface and the AF zone boundary. Temperature-dependent measurements have revealed that the AF pseudogap survives at temperatures much higher than TN (N'{e}el temperature), possibly due to the short-range AF correlation remaining even above TN. The AF pseudogap gradually decreases with doping and is abruptly filled up near the boundary between the AF and superconducting phases. To study the anisotropy of superconducting gap in electron-doped HTSC, we have performed high-resolution ARPES on Pr0.89LaCe0.11CuO4. We observed that the momentum dependence of superconducting gap is basically consistent with the dx2-y2-wave symmetry, but it obviously deviates from the simple dx2-y2 gap function. The maximum superconducting gap is not observed at the zone boundary as expected from the simple dx2-y2 gap symmetry, but it is located around the hot spot where electrons are thought to be strongly coupled to the AF spin fluctuation. All these ARPES results suggest that the electronic stricture and the superconducting behavior are strongly dominated by the AF interaction in electron-doped HTSC. 1) H. Matsui, K. Terashima

  13. Aberrations of diffracted wave fields. II. Diffraction gratings.

    PubMed

    Mahajan, V N

    2000-12-01

    The Rayleigh-Sommerfeld theory is applied to diffraction of a spherical wave by a grating. The grating equation is obtained from the aberration-free diffraction pattern, and its aberrations are shown to be the same as the conventional aberrations obtained by using Fermat's principle. These aberrations are shown to be not associated with the diffraction process. Moreover, it is shown that the irradiance distribution of a certain diffraction order is the Fraunhofer diffraction pattern of the grating aperture as a whole aberrated by the aberration of that order.

  14. Anti-forensics of chromatic aberration

    NASA Astrophysics Data System (ADS)

    Mayer, Owen; Stamm, Matthew C.

    2015-03-01

    Over the past decade, a number of information forensic techniques have been developed to identify digital image manipulation and falsification. Recent research has shown, however, that an intelligent forger can use anti-forensic countermeasures to disguise their forgeries. In this paper, an anti-forensic technique is proposed to falsify the lateral chromatic aberration present in a digital image. Lateral chromatic aberration corresponds to the relative contraction or expansion between an image's color channels that occurs due to a lens's inability to focus all wavelengths of light on the same point. Previous work has used localized inconsistencies in an image's chromatic aberration to expose cut-and-paste image forgeries. The anti-forensic technique presented in this paper operates by estimating the expected lateral chromatic aberration at an image location, then removing deviations from this estimate caused by tampering or falsification. Experimental results are presented that demonstrate that our anti-forensic technique can be used to effectively disguise evidence of an image forgery.

  15. Aberration features in directional dark matter detection

    SciTech Connect

    Bozorgnia, Nassim; Gelmini, Graciela B.; Gondolo, Paolo E-mail: gelmini@physics.ucla.edu

    2012-08-01

    The motion of the Earth around the Sun causes an annual change in the magnitude and direction of the arrival velocity of dark matter particles on Earth, in a way analogous to aberration of stellar light. In directional detectors, aberration of weakly interacting massive particles (WIMPs) modulates the pattern of nuclear recoil directions in a way that depends on the orbital velocity of the Earth and the local galactic distribution of WIMP velocities. Knowing the former, WIMP aberration can give information on the latter, besides being a curious way of confirming the revolution of the Earth and the extraterrestrial provenance of WIMPs. While observing the full aberration pattern requires extremely large exposures, we claim that the annual variation of the mean recoil direction or of the event counts over specific solid angles may be detectable with moderately large exposures. For example, integrated counts over Galactic hemispheres separated by planes perpendicular to Earth's orbit would modulate annually, resulting in Galactic Hemisphere Annual Modulations (GHAM) with amplitudes larger than the usual non-directional annual modulation.

  16. Functional Analysis and Treatment of Aberrant Behavior.

    ERIC Educational Resources Information Center

    Mace, F. Charles; And Others

    1991-01-01

    This article reviews general classes of variables which help to maintain aberrant behavior including attention seeking, sensory and perceptual consequences, and access to materials or activities. Suggestions for a methodology providing a comprehensive functional analysis are offered which include descriptive analysis, hypothesis forming,…

  17. The Extent of Mismeasurement for Aberrant Examinees

    ERIC Educational Resources Information Center

    Petridou, Alexandra; Williams, Julian

    2010-01-01

    The person-fit literature assumes that aberrant response patterns could be a sign of person mismeasurement, but this assumption has rarely, if ever, been empirically investigated before. We explore the validity of test responses and measures of 10-year-old examinees whose response patterns on a commercial standardized paper-and-pencil mathematics…

  18. Assessing the construct validity of aberrant salience.

    PubMed

    Schmidt, Kristin; Roiser, Jonathan P

    2009-01-01

    We sought to validate the psychometric properties of a recently developed paradigm that aims to measure salience attribution processes proposed to contribute to positive psychotic symptoms, the Salience Attribution Test (SAT). The "aberrant salience" measure from the SAT showed good face validity in previous results, with elevated scores both in high-schizotypy individuals, and in patients with schizophrenia suffering from delusions. Exploring the construct validity of salience attribution variables derived from the SAT is important, since other factors, including latent inhibition/learned irrelevance (LIrr), attention, probabilistic reward learning, sensitivity to probability, general cognitive ability and working memory could influence these measures. Fifty healthy participants completed schizotypy scales, the SAT, a LIrr task, and a number of other cognitive tasks tapping into potentially confounding processes. Behavioural measures of interest from each task were entered into a principal components analysis, which yielded a five-factor structure accounting for approximately 75% of the variance in behaviour. Implicit aberrant salience was found to load onto its own factor, which was associated with elevated "Introvertive Anhedonia" schizotypy, replicating our previous finding. LIrr loaded onto a separate factor, which also included implicit adaptive salience, but was not associated with schizotypy. Explicit adaptive and aberrant salience, along with a measure of probabilistic learning, loaded onto a further factor, though this also did not correlate with schizotypy. These results suggest that the measures of LIrr and implicit adaptive salience might be based on similar underlying processes, which are dissociable both from implicit aberrant salience and explicit measures of salience.

  19. Jitter Correction

    NASA Technical Reports Server (NTRS)

    Waegell, Mordecai J.; Palacios, David M.

    2011-01-01

    Jitter_Correct.m is a MATLAB function that automatically measures and corrects inter-frame jitter in an image sequence to a user-specified precision. In addition, the algorithm dynamically adjusts the image sample size to increase the accuracy of the measurement. The Jitter_Correct.m function takes an image sequence with unknown frame-to-frame jitter and computes the translations of each frame (column and row, in pixels) relative to a chosen reference frame with sub-pixel accuracy. The translations are measured using a Cross Correlation Fourier transformation method in which the relative phase of the two transformed images is fit to a plane. The measured translations are then used to correct the inter-frame jitter of the image sequence. The function also dynamically expands the image sample size over which the cross-correlation is measured to increase the accuracy of the measurement. This increases the robustness of the measurement to variable magnitudes of inter-frame jitter

  20. Differentiated Effects of Sensory Activities as Abolishing Operations via Non-Contingent Reinforcement on Academic and Aberrant Behavior

    ERIC Educational Resources Information Center

    Mancil, G. Richmond; Haydon, Todd; Boman, Marty

    2016-01-01

    The purpose of the study was to evaluate the effectiveness of sensory activities used as antecedent interventions on the percentage correct on academic tasks and rate of aberrant behavior in three elementary aged children with Autism Spectrum Disorders (ASD). Study activities were conducted in an after school program for children with ASD where…

  1. Wavefront correction performed by a deformable mirror of arbitrary actuator pattern within a multireflection waveguide.

    PubMed

    Ma, Xingkun; Huang, Lei; Bian, Qi; Gong, Mali

    2014-09-10

    The wavefront correction ability of a deformable mirror with a multireflection waveguide was investigated and compared via simulations. By dividing a conventional actuator array into a multireflection waveguide that consisted of single-actuator units, an arbitrary actuator pattern could be achieved. A stochastic parallel perturbation algorithm was proposed to find the optimal actuator pattern for a particular aberration. Compared with conventional an actuator array, the multireflection waveguide showed significant advantages in correction of higher order aberrations.

  2. Long-Wavelength Stacked Si(sub 1-x)/Si Heterojunction Internal Photoemission Infrared Detectors

    NASA Technical Reports Server (NTRS)

    Park, J. S.; Lin, T. L.; Jones, E. W.; Castillo, H. M. Del; George, T.; Gunapala, S. D.

    1993-01-01

    Utilizing the low temperature silicon molecular beam epitaxy (MBE) growth of degenerately doped SiGe layers on Si, long wavelength stacked SiGe/Si heterojunction internal photoemission (HIP) infrared detectors with multiple SiGe/Se layers have been fabricated and demonstrated.

  3. A medium-energy photoemission and ab-initio investigation of cubic yttria-stabilised zirconia

    SciTech Connect

    Cousland, G. P.; Cui, X. Y.; Smith, A. E.; Stampfl, C. M.; Wong, L.; Tayebjee, M.; Yu, D.; Triani, G.; Evans, P. J.; Ruppender, H.-J.; Jang, L.-Y.; Stampfl, A. P. J.

    2014-04-14

    Experimental and theoretical investigations into the electronic properties and structure of cubic yttria-stabilized zirconia are presented. Medium-energy x-ray photoemission spectroscopy measurements have been carried out for material with a concentration of 8-9 mol. % yttria. Resonant photoemission spectra are obtained for a range of photon energies that traverse the L2 absorption edge for both zirconium and yttrium. Through correlation with results from density-functional theory (DFT) calculations, based on structural models proposed in the literature, we assign photoemission peaks appearing in the spectra to core lines and Auger transitions. An analysis of the core level features enables the identification of shifts in the core level energies due to different local chemical environments of the constituent atoms. In general, each core line feature can be decomposed into three contributions, with associated energy shifts. Their identification with results of DFT calculations carried out for proposed atomic structures, lends support to these structural models. The experimental results indicate a multi-atom resonant photoemission effect between nearest-neighbour oxygen and yttrium atoms. Near-edge x-ray absorption fine structure spectra for zirconium and yttrium are also presented, which correlate well with calculated Zr- and Y-4d electron partial density-of-states and with Auger electron peak area versus photon energy curve.

  4. Comparative time-resolved photoemission from the Cu(100) and Cu(111) surfaces

    NASA Astrophysics Data System (ADS)

    Ambrosio, Marcelo J.; Thumm, Uwe

    2016-12-01

    Motivated by the striking dependence of the valence electronic structure of transition metal surfaces on their crystallographic orientation, and by emerging experiments on laser-assisted extended ultraviolet (XUV) photoemission from solid surfaces, we calculate photoemission spectra from Cu(100) and Cu(111) surfaces as a function of the photoelectron final kinetic energy and the delay between the ionizing attosecond XUV pulse train and assisting infrared (IR) laser pulse. Our numerical simulations predict distinct differences in delay-dependent photoelectron energy distributions and photoemission time delays for Cu(100) and Cu(111) surfaces. These differences can be scrutinized experimentally with existing technology in a suggested in situ comparative RABBITT (reconstruction of attosecond beating by interference of two-photon transitions) configuration by placing the two surfaces on a sliding platform while keeping all optical components and pathlengths fixed. Our calculations also show that the inclusion of the Fresnel-reflected incident IR pulse at the metal-vacuum interface modifies photoelectron spectra and photoemission time delays in a characteristic way that reveals the degree of spatial location of the initial electronic states.

  5. Alkaline Earth Core Level Photoemission Spectroscopy of High-Temperature Superconductors

    NASA Technical Reports Server (NTRS)

    Vasquez, R.

    1993-01-01

    This paper examines photoemission measurements of the alkaline Earth core levels of high-temperature superconductors and related materials, models that seek to explain the large negative shifts observed relative to the corresponding alkaline Earth metals, and the effect of lattice site disorder on the core level spectra and the presence or absence of intrinsic surface peaks.

  6. Spin Polarization and Attosecond Time Delay in Photoemission from Spin Degenerate States of Solids.

    PubMed

    Fanciulli, Mauro; Volfová, Henrieta; Muff, Stefan; Braun, Jürgen; Ebert, Hubert; Minár, Jan; Heinzmann, Ulrich; Dil, J Hugo

    2017-02-10

    After photon absorption, electrons from a dispersive band of a solid require a finite time in the photoemission process before being photoemitted as free particles, in line with recent attosecond-resolved photoemission experiments. According to the Eisenbud-Wigner-Smith model, the time delay is due to a phase shift of different transitions that occur in the process. Such a phase shift is also at the origin of the angular dependent spin polarization of the photoelectron beam, observable in spin degenerate systems without angular momentum transfer by the incident photon. We propose a semiquantitative model which permits us to relate spin and time scales in photoemission from condensed matter targets and to better understand spin- and angle-resolved photoemission spectroscopy (SARPES) experiments on spin degenerate systems. We also present the first experimental determination by SARPES of this time delay in a dispersive band, which is found to be greater than 26 as for electrons emitted from the sp-bulk band of the model system Cu(111).

  7. Streaking and Wigner time delays in photoemission from atoms and surfaces

    SciTech Connect

    Zhang, C.-H.; Thumm, U.

    2011-09-15

    Streaked photoemission metrology allows the observation of an apparent relative time delay between the detection of photoelectrons from different initial electronic states. This relative delay is obtained by recording the photoelectron yield as a function of the delay between an ionizing ultrashort extended ultraviolet pulse and a streaking infrared (IR) pulse. Theoretically, photoemission delays can be defined based on (i) the phase shift the photoelectron wave function accumulates during the release and propagation of the photoelectron (''Wigner delay'') and, alternatively, (ii) the streaking trace in the calculated photoemission spectrum (''streaking delay''). We investigate the relation between Wigner and streaking delays in the photoemission from atomic and solid-surface targets. For solid targets and assuming a vanishing IR skin depth, both Wigner and streaking delays can be interpreted as an average propagation time needed by photoelectrons to reach the surface, while the two delays differ for nonvanishing skin depths. For atomic targets, the difference between Wigner and streaking delays depends on the range of the ionic potential.

  8. Spin Polarization and Attosecond Time Delay in Photoemission from Spin Degenerate States of Solids

    NASA Astrophysics Data System (ADS)

    Fanciulli, Mauro; Volfová, Henrieta; Muff, Stefan; Braun, Jürgen; Ebert, Hubert; Minár, Jan; Heinzmann, Ulrich; Dil, J. Hugo

    2017-02-01

    After photon absorption, electrons from a dispersive band of a solid require a finite time in the photoemission process before being photoemitted as free particles, in line with recent attosecond-resolved photoemission experiments. According to the Eisenbud-Wigner-Smith model, the time delay is due to a phase shift of different transitions that occur in the process. Such a phase shift is also at the origin of the angular dependent spin polarization of the photoelectron beam, observable in spin degenerate systems without angular momentum transfer by the incident photon. We propose a semiquantitative model which permits us to relate spin and time scales in photoemission from condensed matter targets and to better understand spin- and angle-resolved photoemission spectroscopy (SARPES) experiments on spin degenerate systems. We also present the first experimental determination by SARPES of this time delay in a dispersive band, which is found to be greater than 26 as for electrons emitted from the sp-bulk band of the model system Cu(111).

  9. High resolution-angle resolved photoemission studies of high temperature superconductors

    SciTech Connect

    Olson, C.G.; Liu, R.; Lynch, D.W.; Veal, B.W.; Chang, Y.C.; Jiang, P.Z.; Liu, J.Z.; Paulikas, A.P.; Arko, A.J.; List, R.S.; Argonne National Lab., IL; Los Alamos National Lab., NM )

    1989-08-01

    Recent photoemission studies of Y 123 and Bi 2212 performed with high energy and angular resolution have provided detailed information on the nature of the states near the Fermi level. Measurements of the superconducting gap, band dispersion, and the density of states near the Fermi level in the normal state all support a Fermi liquid description of these materials. 5 refs., 4 figs.

  10. Attosecond-controlled photoemission from metal nanowire tips in the few-electron regime

    NASA Astrophysics Data System (ADS)

    Ahn, B.; Schötz, J.; Kang, M.; Okell, W. A.; Mitra, S.; Förg, B.; Zherebtsov, S.; Süßmann, F.; Burger, C.; Kübel, M.; Liu, C.; Wirth, A.; Di Fabrizio, E.; Yanagisawa, H.; Kim, D.; Kim, B.; Kling, M. F.

    2017-03-01

    Metal nanotip photoemitters have proven to be versatile in fundamental nanoplasmonics research and applications, including, e.g., the generation of ultrafast electron pulses, the adiabatic focusing of plasmons, and as light-triggered electron sources for microscopy. Here, we report the generation of high energy photoelectrons (up to 160 eV) in photoemission from single-crystalline nanowire tips in few-cycle, 750-nm laser fields at peak intensities of (2-7.3) × 1012 W/cm2. Recording the carrier-envelope phase (CEP)-dependent photoemission from the nanowire tips allows us to identify rescattering contributions and also permits us to determine the high-energy cutoff of the electron spectra as a function of laser intensity. So far these types of experiments from metal nanotips have been limited to an emission regime with less than one electron per pulse. We detect up to 13 e/shot and given the limited detection efficiency, we expect up to a few ten times more electrons being emitted from the nanowire. Within the investigated intensity range, we find linear scaling of cutoff energies. The nonlinear scaling of electron count rates is consistent with tunneling photoemission occurring in the absence of significant charge interaction. The high electron energy gain is attributed to field-induced rescattering in the enhanced nanolocalized fields at the wires apex, where a strong CEP-modulation is indicative of the attosecond control of photoemission.

  11. Effects of interactions among wave aberrations on optical image quality.

    PubMed

    McLellan, J S; Prieto, P M; Marcos, S; Burns, S A

    2006-09-01

    Wave aberrations degrade the optical quality of the eye relative to the diffraction limit, but there are situations in which having slightly aberrated optics can provide some relative visual benefits. This fact led us to consider whether interactions among aberrations in the eye's wavefront produce an advantage for image quality relative to wavefronts with randomized combinations of aberrations with the same total RMS error. Total ocular wave aberrations from two experimental groups and corneal wave aberrations from one group were measured and expressed as Zernike polynomial expansions through the seventh-order. In a series of Monte Carlo simulations, modulation transfer functions (MTFs) for the measured wave aberrations were compared to distributions of artificial MTFs for wavefronts created by randomizing the sign or orientation of the aberrations, while maintaining the RMS error within each Zernike order. In a control condition, "synthetic" model eyes were produced by choosing each individual aberration term at random from individuals in the experimental group, and again MTFs were compared for original and randomized signs. Results were summarized by the MTF ratio: real MTF/mean simulated MTF, as a function of spatial frequency. For a 6mm pupil, the mean MTF ratio for total ocular aberrations was greater than 1.0 up to 60 cycles per degree, suggesting that the eye's aberrations are not independent and that there may be a positive functional consequences to their interrelations. This positive relation did not hold for corneal aberrations alone, or for the synthetic eyes.

  12. Aberrations of diffracted wave fields: distortion.

    PubMed

    Harvey, James E; Bogunovic, Dijana; Krywonos, Andrey

    2003-03-01

    Near-field diffraction patterns are merely aberrated Fraunhofer diffraction patterns. These aberrations, inherent to the diffraction process, provide insight and understanding into wide-angle diffraction phenomena. Nonparaxial patterns of diffracted orders produced by a laser beam passing through a grating and projected upon a plane screen exhibit severe distortion (W311). This distortion is an artifact of the configuration chosen to observe diffraction patterns. Grating behavior expressed in terms of the direction cosines of the propagation vectors of the incident and diffracted orders exhibits no distortion. Use of a simple direction cosine diagram provides an elegant way to deal with nonparaxial diffraction patterns, particularly when large obliquely incident beams produce conical diffraction.

  13. [A rare observation of intralaryngeal aberrant goiter].

    PubMed

    Gadzhimirzaev, G A; Shakhnazarov, A M; Gadzhimirzaeva, R G

    This paper was designed to report a rare observation of intralaryngeal aberrant goiter associated with goiter of the main thyroid tissue and chronic suppurative otitis media complicated by the polyp that causes occlusion of the auditory passage. The histomorphological investigation of the material harvested intraoperatively following rehabilitation of the purulent focus in the middle ear and the removal of the tumour from the inside of the right vestibular fold confirmed the diagnosis of colloid goiter.

  14. The aberrant retroesophageal right subclavian artery.

    PubMed

    Seres-Sturm, M; Maros, T N; Seres-Sturm, L

    1985-01-01

    Two cases with arteria lusoria were found at 278 routine dissections. These arteria arise as the last branches of the aortic arch and have a retroesophageal position. At the crossing point, the esophagus narrows due to the groove caused by the artery. The appearance of this malposition is the consequence of the perturbation in the organo-genesis of the right dorsal aorta and fourth branchial artery. The aberration can lead to disphagia lusoria.

  15. Misalignment-induced nodal aberration fields in two-mirror astronomical telescopes.

    PubMed

    Schmid, Tobias; Thompson, Kevin P; Rolland, Jannick P

    2010-06-01

    We present the effects of misalignments on the field dependence of the third-order aberration fields of traditional, two-mirror astronomical telescopes in the context of nodal aberration theory, which we believe is the most general and extensible framework for describing and improving on-station performance. While many of the advantages of nodal aberration theory, compared to other, often power series expansion-based descriptions of misalignment effects on aberrations, become particularly important when analyzing telescopes with more than two mirrors, or in the presence of figure errors; this paper aims to provide and demonstrate the fundamental concepts needed to fully describe the state of correction of misaligned two-mirror telescopes. Importantly, it is shown that the assumption that perfect performance on axis ensures a fully aligned telescope is false, and we demonstrate that if Ritchey-Chrétien telescopes are aligned for zero coma on axis as the sole criterion, formidable misalignments will likely remain, leading to image quality degradation, particularly beyond midfield caused by astigmatism with binodal field dependence (i.e., astigmatism goes to zero at two points in the field).

  16. Ocular aberrations as a function of wavelength in the near infrared measured with a femtosecond laser

    NASA Astrophysics Data System (ADS)

    Fernández, Enrique J.; Unterhuber, Angelika; Prieto, Pedro M.; Hermann, Boris; Drexler, Wolfgang; Artal, Pablo

    2005-01-01

    A compact mode-locked Ti:sapphire laser, emitting a broad spectrum of 277 nm bandwidth, centered at 790 nm, was used to measure the dependence of the aberrations of the human eye with wavelength in the near infrared region. The aberrations were systematically measured with a Hartmann-Shack wave-front sensor at the following wavelengths: 700, 730, 750, 780, 800, 850, 870 and 900 nm, in four normal subjects. During the measurements, the wavelengths were selected by using 10 nm band-pass filters. We found that monochromatic high order aberrations, beyond defocus, were nearly constant across 700 to 900 nm wavelength in the four subjects. The average chromatic difference in defocus was 0.4 diopters in the considered wavelength band. The predictions of a simple water-eye model were compared with the experimental results in the near infrared. These results have potential applications in those situations where defocus or higher order aberration correction in the near infrared is required. This is the case of many imaging techniques: scanning laser ophthalmoscope, flood illumination fundus camera, or optical coherence tomography.

  17. Variable aberration generator using a high-order even aspheric singlet for testing optical surfaces

    NASA Astrophysics Data System (ADS)

    Lu, Jinfeng; Chen, Shanyong; Xue, Shuai

    2016-10-01

    Traditional null optics is generally designed for a particular optical surface. It must be redesigned when the test surface is changed no matter the null optic is reflective, transmitted or a CGH. Development of advanced optical machining and testing based on deterministic figuring and null test makes it possible to apply high-order aspheres. This paper presents a plano-concave singlet to realize variable aberration correction for testing different surfaces. The concave surface is an even asphere with high-order terms. By changing the axial distances among the transmission sphere, the null singlet and the test surface, variable aberrations are generated to meet the aberration balance requirement for various surfaces. The residual aberrations are confirmed within the vertical dynamic range of measurement of the interferometer. It enables flexible testing of optical surfaces without dedicated null optics. The optical design verifies that the aspheric singlet can be used to test conic surfaces with different conic constant and radius of curvature ranging from ellipsoid, paraboloid to hyperboloid and an even asphere.

  18. [Familial, structural aberration of the Y chromosome with fertility disorders].

    PubMed

    Gall, H; Schmid, M; Schmidtke, J; Schempp, W; Weber, L

    1985-11-01

    Cytogenetic studies on a patient with Klinefelter's syndrome revealed an inherited, structural aberration of the Y-chromosome which has not been described before. The aberrant Y-chromosome was characterized by eight different banding methods. The value of individual staining techniques in studies on Y-heterochromatin aberrations is emphasized. Analysis of the cytogenetic studies (banding methods, restriction endonuclease of DNA, and measurement of the length of the Y-chromosome) permits an interpretation to be made on how the aberrant Y-chromosome originated. The functions of the Y-chromosome are discussed. The decrease in fertility (cryptozoospermia) in the two brothers with the same aberrant Y-chromosome was striking.

  19. Influence of ocular chromatic aberration and pupil size on transverse resolution in ophthalmic adaptive optics optical coherence tomography.

    PubMed

    Fernández, Enrique; Drexler, Wolfgang

    2005-10-03

    Optical coherence tomography (OCT) enables visualization of the living human retina with unprecedented high axial resolution. The transverse resolution of existing OCT approaches is relatively modest as compared to other retinal imaging techniques. In this context, the use of adaptive optics (AO) to correct for ocular aberrations in combination with OCT has recently been demonstrated to notably increase the transverse resolution of the retinal OCT tomograms. AO is required when imaging is performed through moderate and large pupil sizes. A fundamental difference of OCT as compared to other imaging techniques is the demand of polychromatic light to accomplish high axial resolution. In ophthalmic OCT applications, the performance is therefore also limited by ocular chromatic aberrations. In the current work, the effects of chromatic and monochromatic ocular aberrations on the quality of retinal OCT tomograms, especially concerning transverse resolution, sensitivity and contrast, are theoretically studied and characterized. The repercussion of the chosen spectral bandwidth and pupil size on the final transverse resolution of OCT tomograms is quantitatively examined. It is found that losses in the intensity of OCT images obtained with monochromatic aberration correction can be up to 80 %, using a pupil size of 8 mm diameter in combination with a spectral bandwidth of 120 nm full width at half maximum for AO ultrahigh resolution OCT. The limits to the performance of AO for correction of monochromatic aberrations in OCT are established. The reduction of the detected signal and the resulting transverse resolution caused by chromatic aberration of the human eye is found to be strongly dependent on the employed bandwidth and pupil size. Comparison of theoretical results with experimental findings obtained in living human eyes is also provided.

  20. Chromatic variation of aberration: the role of induced aberrations and raytrace direction

    NASA Astrophysics Data System (ADS)

    Berner, A.; Nobis, T.; Shafer, D.; Gross, H.

    2015-09-01

    The design and optimization process of an optical system contains several first order steps. The definition of the appropriate lens type and the fixation of the raytrace direction are some of them. The latter can be understood as a hidden assumption rather than an aware design step. This is usually followed by the determination of the paraxial lens layout calculated for the primary wavelength. It is obvious, that for this primary wavelength the paraxial calculations are independent of raytrace direction. Today, most of the lens designs are specified not to work only for one wavelength, but in a certain wavelength range. Considering such rays of other wavelengths, one can observe that depending on the direction there will already occur differences in the first order chromatic aberrations and additionally in the chromatic variation of the third-order aberrations. The reason for this effect are induced aberrations emerging from one surface to the following surfaces by perturbed ray heights and ray angles. It can be shown, that the total amount of surface-resolved first order chromatic aberrations and the chromatic variation of the five primary aberrations can be split into an intrinsic part and an induced part. The intrinsic part is independent of the raytrace direction whereas the induced part is not.

  1. Nodal aberration theory for wild-filed asymmetric optical systems

    NASA Astrophysics Data System (ADS)

    Chen, Yang; Cheng, Xuemin; Hao, Qun

    2016-10-01

    Nodal Aberration Theory (NAT) was used to calculate the zero field position in Full Field Display (FFD) for the given aberration term. Aiming at wide-filed non-rotational symmetric decentered optical systems, we have presented the nodal geography behavior of the family of third-order and fifth-order aberrations. Meanwhile, we have calculated the wavefront aberration expressions when one optical element in the system is tilted, which was not at the entrance pupil. By using a three-piece-cellphone lens example in optical design software CodeV, the nodal geography is testified under several situations; and the wavefront aberrations are calculated when the optical element is tilted. The properties of the nodal aberrations are analyzed by using Fringe Zernike coefficients, which are directly related with the wavefront aberration terms and usually obtained by real ray trace and wavefront surface fitting.

  2. Closed-loop adaptive optics using a spatial light modulator for sensing and compensating of optical aberrations in ophthalmic applications

    NASA Astrophysics Data System (ADS)

    Akondi, Vyas; Jewel, Md. Atikur Rahman; Vohnsen, Brian

    2014-09-01

    Sensing and compensating of optical aberrations in closed-loop mode using a single spatial light modulator (SLM) for ophthalmic applications is demonstrated. Notwithstanding the disadvantages of the SLM, in certain cases, this multitasking capability of the device makes it advantageous over existing deformable mirrors (DMs), which are expensive and in general used for aberration compensation alone. A closed-loop adaptive optics (AO) system based on a single SLM was built. Beam resizing optics were used to utilize the large active area of the device and hence make it feasible to generate 137 active subapertures for wavefront sensing. While correcting Zernike aberrations up to fourth order introduced with the help of a DM (for testing purposes), diffraction-limited resolution was achieved. It is shown that matched filter and intensity-weighted centroiding techniques stand out among others. Closed-loop wavefront correction of aberrations in backscattered light from the eyes of three healthy human subjects was demonstrated after satisfactory results were obtained using an artificial eye, which was simulated with a short focal length lens and a sheet of white paper as diffuser. It is shown that the closed-loop AO system based on a single SLM is capable of diffraction-limited correction for ophthalmic applications.

  3. Observation of two-photon photoemission from cesium telluride photocathodes excited by a near-infrared laser

    NASA Astrophysics Data System (ADS)

    Panuganti, H.; Piot, P.

    2017-02-01

    We explore the nonlinear photoemission in cesium telluride (Cs2Te) photocathodes where an ultrashort (˜100 fs full width at half max) 800-nm infrared laser is used as the drive-laser in lieu of the typical ˜266-nm ultraviolet laser. An important figure of merit for photocathodes, the quantum efficiency, we define here for nonlinear photoemission processes in order to compare with linear photoemission. The charge against drive-laser (infrared) energy is studied for different laser energy and intensity values and cross-compared with previously performed similar studies on copper [P. Musumeci et al., Phys. Rev. Lett. 104, 084801 (2010)], a metallic photocathode. We particularly observe two-photon photoemission in Cs2Te using the infrared laser in contrast to the anticipated three-photon process as observed for metallic photocathodes.

  4. Spin-orbit-induced photoelectron spin polarization in angle-resolved photoemission from both atomic and condensed matter targets.

    PubMed

    Heinzmann, Ulrich; Dil, J Hugo

    2012-05-02

    The existence of highly spin polarized photoelectrons emitted from non-magnetic solids as well as from unpolarized atoms and molecules has been found to be very common in many studies over the past 40 years. This so-called Fano effect is based upon the influence of the spin-orbit interaction in the photoionization or the photoemission process. In a non-angle-resolved photoemission experiment, circularly polarized radiation has to be used to create spin polarized photoelectrons, while in angle-resolved photoemission even unpolarized or linearly polarized radiation is sufficient to get a high spin polarization. In past years the Rashba effect has become very important in the angle-resolved photoemission of solid surfaces, also with an observed high photoelectron spin polarization. It is the purpose of the present topical review to cross-compare the spin polarization experimentally found in angle-resolved photoelectron emission spectroscopy of condensed matter with that of free atoms, to compare it with the Rashba effect and topological insulators to describe the influence and the importance of the spin-orbit interaction and to show and disentangle the matrix element and phase shift effects therein.The relationship between the energy dispersion of these phase shifts and the emission delay of photoelectron emission in attosecond-resolved photoemission is also discussed. Furthermore the influence of chiral structures of the photo-effect target on the spin polarization, the interferences of different spin components in coherent superpositions in photoemission and a cross-comparison of spin polarization in photoemission from non-magnetic solids with XMCD on magnetic materials are presented; these are all based upon the influence of the spin-orbit interaction in angle-resolved photoemission.

  5. A CORRECTION.

    PubMed

    Johnson, D

    1940-03-22

    IN a recently published volume on "The Origin of Submarine Canyons" the writer inadvertently credited to A. C. Veatch an excerpt from a submarine chart actually contoured by P. A. Smith, of the U. S. Coast and Geodetic Survey. The chart in question is Chart IVB of Special Paper No. 7 of the Geological Society of America entitled "Atlantic Submarine Valleys of the United States and the Congo Submarine Valley, by A. C. Veatch and P. A. Smith," and the excerpt appears as Plate III of the volume fist cited above. In view of the heavy labor involved in contouring the charts accompanying the paper by Veatch and Smith and the beauty of the finished product, it would be unfair to Mr. Smith to permit the error to go uncorrected. Excerpts from two other charts are correctly ascribed to Dr. Veatch.

  6. Color-corrected Fresnel lens for solar concentration

    SciTech Connect

    Kritchman, E.M.

    1980-01-01

    A new linear convex Fresnel lens with its groove side down is described. The design philosophy is similar to that of the highly concentrating two-focal Fresnel lens but includes a correction for chromatic aberration. A solar-concentration ratio as high as 80 is achieved. For wide-acceptance angles, the concentration nears the theoretical maximum.

  7. 77 FR 72199 - Technical Corrections; Correction

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-12-05

    ... COMMISSION 10 CFR Part 171 RIN 3150-AJ16 Technical Corrections; Correction AGENCY: Nuclear Regulatory... corrections, including updating the street address for the Region I office, correcting authority citations and... rule. DATES: The correction is effective on December 5, 2012. FOR FURTHER INFORMATION CONTACT:...

  8. Orbital-differentiated coherence-incoherence crossover identified by photoemission spectroscopy in LiFeAs

    NASA Astrophysics Data System (ADS)

    Miao, H.; Yin, Z. P.; Wu, S. F.; Li, J. M.; Ma, J.; Lv, B.-Q.; Wang, X. P.; Qian, T.; Richard, P.; Xing, L.-Y.; Wang, X.-C.; Jin, C. Q.; Haule, K.; Kotliar, G.; Ding, H.

    2016-11-01

    In iron-based superconductors (FeSCs), orbital differentiation is an important phenomenon, whereby correlations stronger on the dx y orbital than on the dx z/dy z orbital yield quasiparticles with a dx y orbital character having larger mass renormalization and an abnormal temperature evolution. However, the physical origin of this orbital differentiation is debated between the Hund's coupling-induced unbinding of spin and orbital degrees of freedom and the Hubbard interaction instigated orbital-selective Mott transition. Here we use angle-resolved photoemission spectroscopy to identify an orbital-dependent correlation-induced quasiparticle (QP) anomaly in LiFeAs. The excellent agreement between our photoemission measurements and first-principles many-body theory calculations shows that the orbital-differentiated QP lifetime anomalies in LiFeAs are controlled by the Hund's coupling.

  9. Orbital-differentiated coherence-incoherence crossover identified by photoemission spectroscopy in LiFeAs

    DOE PAGES

    Miao, H.; Yin, Z. P.; Wu, S. F.; ...

    2016-11-14

    In the iron-based superconductors (FeSCs), orbital differentiation is an important phenomenon, whereby correlations stronger on the dxy orbital than on the dxz/dyz orbital yield quasi-particles with dxy orbital character having larger mass renormalization and abnormal temperature evolution. However, the physical origin of this orbital di erentiation is debated between the Hund's coupling induced unbinding of spin and orbital degrees of freedom and the Hubbard interaction instigated orbital selective Mott transition. Here we use angle-resolved photoemission spectroscopy to identify an orbital-dependent correlation-induced quasi-particle (QP) anomaly in LiFeAs. Lastly, the excellent agreement between our photoemission measurements and first-principles many-body theory calculations showsmore » that the orbital-differentiated QP lifetime anomalies in LiFeAs are controlled by the Hund's coupling.« less

  10. Orbital-differentiated coherence-incoherence crossover identified by photoemission spectroscopy in LiFeAs

    SciTech Connect

    Miao, H.; Yin, Z. P.; Wu, S. F.; Li, J. M.; Ma, J.; Lv, B. -Q.; Wang, X. P.; Qian, T.; Richard, P.; Xing, L. -Y.; Wang, X. -C.; Jin, C. Q.; Haule, K.; Kotliar, G.; Ding, H.

    2016-11-14

    In the iron-based superconductors (FeSCs), orbital differentiation is an important phenomenon, whereby correlations stronger on the dxy orbital than on the dxz/dyz orbital yield quasi-particles with dxy orbital character having larger mass renormalization and abnormal temperature evolution. However, the physical origin of this orbital di erentiation is debated between the Hund's coupling induced unbinding of spin and orbital degrees of freedom and the Hubbard interaction instigated orbital selective Mott transition. Here we use angle-resolved photoemission spectroscopy to identify an orbital-dependent correlation-induced quasi-particle (QP) anomaly in LiFeAs. Lastly, the excellent agreement between our photoemission measurements and first-principles many-body theory calculations shows that the orbital-differentiated QP lifetime anomalies in LiFeAs are controlled by the Hund's coupling.

  11. Core and valence level photoemission and photoabsorption study of icosahedral Al Pd Mn quasicrystals

    NASA Astrophysics Data System (ADS)

    Horn, K.; Theis, W.; Paggel, J. J.; Barman, S. R.; Rotenberg, E.; Ebert, Ph; Urban, K.

    2006-01-01

    The electronic structure of quasicrystalline Al-Pd-Mn is investigated by means of valence and core level photoelectron spectroscopy. Variations of the photoionization cross section in the constituents' valence electronic levels as a function of photon energy are used to identify contributions from the different atomic species, in particular near the Pd 4d Cooper minimum. Resonant photoemission at the Mn 2p absorption edge shows the contribution of the Mn 3d states to the density of states in a region near the Fermi level. The asymmetry of Pd 3d and Mn 2p core level photoemission lines, and its difference for emission from metallic and quasicrystalline phases, are utilized to infer the contributions of the different constituents to the density of states at the Fermi level.

  12. Plasmonic silicon Schottky photodetectors: The physics behind graphene enhanced internal photoemission

    NASA Astrophysics Data System (ADS)

    Levy, Uriel; Grajower, Meir; Gonçalves, P. A. D.; Mortensen, N. Asger; Khurgin, Jacob B.

    2017-02-01

    Recent experiments have shown that the plasmonic assisted internal photoemission from a metal to silicon can be significantly enhanced by introducing a monolayer of graphene between the two media. This is despite the limited absorption in a monolayer of undoped graphene ( ˜ π α = 2.3 % ). Here we propose a physical model where surface plasmon polaritons enhance the absorption in a single-layer graphene by enhancing the field along the interface. The relatively long relaxation time in graphene allows for multiple attempts for the carrier to overcome the Schottky barrier and penetrate into the semiconductor. Interface disorder is crucial to overcome the momentum mismatch in the internal photoemission process. Our results show that quantum efficiencies in the range of few tens of percent are obtainable under reasonable experimental assumptions. This insight may pave the way for the implementation of compact, high efficiency silicon based detectors for the telecom range and beyond.

  13. Interference of spin states in resonant photoemission induced by circularly polarized light from magnetized Gd

    SciTech Connect

    Mueller, N.; Khalil, T.; Pohl, M.; Uphues, T.; Heinzmann, U.; Polcik, M.; Rader, O.; Heigl, F.; Starke, K.; Fritzsche, S.; Kabachnik, N. M.

    2006-10-15

    We have observed the spin-state interference by measuring the photoelectron spin polarization in the resonant preedge 4d{yields}4f photoemission from magnetized Gd. The photoemission is induced by circularly polarized light which determines one preferential direction of electron spin orientation due to polarization transfer and spin-orbit interaction. Another direction perpendicular to the first one is determined by the target electron spin orientation connected with the target magnetization. We have measured the component of spin polarization perpendicular to those two directions which can only appear due to spin-state interference which implies coherence of the spin states produced by the two mechanisms of the photoelectron spin polarization.

  14. One-step model of photoemission from single-crystal surfaces

    NASA Astrophysics Data System (ADS)

    Karkare, Siddharth; Wan, Weishi; Feng, Jun; Chiang, Tai C.; Padmore, Howard A.

    2017-02-01

    In this paper, we present a three-dimensional one-step photoemission model that can be used to calculate the quantum efficiency and momentum distributions of electrons photoemitted from ordered single-crystal surfaces close to the photoemission threshold. Using Ag(111) as an example, we show that the model can not only calculate the quantum efficiency from the surface state accurately without using any ad hoc parameters, but also provides a theoretical quantitative explanation of the vectorial photoelectric effect. This model in conjunction with other band structure and wave function calculation techniques can be effectively used to screen single-crystal photoemitters for use as electron sources for particle accelerator and ultrafast electron diffraction applications.

  15. Electronic and spin structures of solids investigated by means of synchrotron radiation photoemission

    NASA Astrophysics Data System (ADS)

    Taniguchi, M.; Iwasawa, H.; Miyamoto, K.; Okuda, T.

    2013-12-01

    Recent progress in research on electronic and spin structures of solids and instrumentation on spin-resolved photoemission at Hiroshima Synchrotron Radiation Center are reported. The fine details of electron dynamics of a typical multiband superconductor Sr2RuO4 were uncovered by high-resolution angle-resolved photoemission spectroscopy (ARPES) with tunable polarizations, and the surface of W(1 1 0) was found to have a Dirac-corn-like state of d character with nearly massless energy dispersion by high-resolution ARPES and spin-resolved ARPES (SARPES). The SARPES system with very low energy electron diffraction spin detector and modified VG-SCIENTA R4000 electron analyzer brought a breakthrough in spin detection efficiency as well as energy and angular resolution, and enables precise SARPES measurements for materials that require high energy and angular resolution.

  16. Cluster-surface interaction studied by time-resolved two-photon photoemission

    NASA Astrophysics Data System (ADS)

    Busolt, U.; Cottancin, E.; Röhr, H.; Socaciu, L.; Leisner, T.; Wöste, L.

    We use time-resolved two-photon photoemission to study the stability of size selected Agn+ clusters (n=2-9)deposited onto highly oriented pyrolytic graphite (HOPG) substrates at liquid nitrogen temperatures. The deposition was carried out with variable kinetic energies of the clusters. Clusters deposited with high kinetic energy (up to 60 eV/cluster) become fragmented upon impact. For low deposition energies (1-4 eV/cluster) the size dependence of the photoelectron spectra reveals a pronounced odd/even effect, which is well known for gas phase silver clusters. This indicates that the soft deposited clusters retain their size and identity on the sample. The phase of the odd/even effect suggests that transient negatively charged cluster ions serve as an intermediate step in the two-photon photoemission process. The lifetime of the anions rises with cluster size. This is attributed to an increasing electronic density of states for larger clusters.

  17. Angle-resolved photoemission spectroscopy of liquid water at 29.5 eV

    PubMed Central

    Nishitani, Junichi; West, Christopher W.; Suzuki, Toshinori

    2017-01-01

    Angle-resolved photoemission spectroscopy of liquid water was performed using extreme ultraviolet radiation at 29.5 eV and a time-of-flight photoelectron spectrometer. SiC/Mg coated mirrors were employed to select the single-order 19th harmonic from laser high harmonics, which provided a constant photon flux for different laser polarizations. The instrument was tested by measuring photoemission anisotropy for rare gases and water molecules and applied to a microjet of an aqueous NaI solution. The solute concentration was adjusted to eliminate an electric field gradient around the microjet. The observed photoelectron spectra were analyzed considering contributions from liquid water, water vapor, and an isotropic background. The anisotropy parameters of the valence bands (1b1, 3a1, and 1b2) of liquid water are considerably smaller than those of gaseous water, which is primarily attributed to electron scattering in liquid water.

  18. Quantum-electrodynamic treatment of photoemission by a single-electron wave packet

    NASA Astrophysics Data System (ADS)

    Corson, John P.; Peatross, Justin

    2011-11-01

    A quantum-field-theory description of photoemission by a laser-driven single-electron wave packet is presented. We show that, when the incident light is represented with multimode coherent states then, to all orders of perturbation theory, the relative phases of the electron's constituent momenta have no influence on the amount of scattered light. These results are extended using the Furry picture, where the (unidirectional) arbitrary incident light pulse is treated nonperturbatively with Volkov functions. This analysis increases the scope of our prior results in [Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.84.053831 84, 053831 (2011)], which demonstrate that the spatial size of the electron wave packet does not influence photoemission.

  19. Wavefront aberrations of x-ray dynamical diffraction beams.

    PubMed

    Liao, Keliang; Hong, Youli; Sheng, Weifan

    2014-10-01

    The effects of dynamical diffraction in x-ray diffractive optics with large numerical aperture render the wavefront aberrations difficult to describe using the aberration polynomials, yet knowledge of them plays an important role in a vast variety of scientific problems ranging from optical testing to adaptive optics. Although the diffraction theory of optical aberrations was established decades ago, its application in the area of x-ray dynamical diffraction theory (DDT) is still lacking. Here, we conduct a theoretical study on the aberration properties of x-ray dynamical diffraction beams. By treating the modulus of the complex envelope as the amplitude weight function in the orthogonalization procedure, we generalize the nonrecursive matrix method for the determination of orthonormal aberration polynomials, wherein Zernike DDT and Legendre DDT polynomials are proposed. As an example, we investigate the aberration evolution inside a tilted multilayer Laue lens. The corresponding Legendre DDT polynomials are obtained numerically, which represent balanced aberrations yielding minimum variance of the classical aberrations of an anamorphic optical system. The balancing of classical aberrations and their standard deviations are discussed. We also present the Strehl ratio of the primary and secondary balanced aberrations.

  20. Chromosomal aberrations in ISS crew members

    NASA Astrophysics Data System (ADS)

    Johannes, Christian; Goedecke, Wolfgang; Antonopoulos, Alexandra

    2012-07-01

    High energy radiation is a major risk factor in manned space missions. Astronauts and cosmonauts are exposed to ionising radiations of cosmic and solar origin, while on the Earth's surface people are well protected by the atmosphere and a deflecting magnetic field. There are now data available describing the dose and the quality of ionising radiation on-board of the International Space Station (ISS). Nonetheless, the effect of increased radiation dose on mutation rates of ISS crew members are hard to predict. Therefore, direct measurements of mutation rates are required in order to better estimate the radiation risk for longer duration missions. The analysis of chromosomal aberrations in peripheral blood lymphocytes is a well established method to measure radiation-induced mutations. We present data of chromosome aberration analyses from lymphocyte metaphase spreads of ISS crew members participating in short term (10-14 days) or long term (around 6 months) missions. From each subject we received two blood samples. The first sample was drawn about 10 days before launch and a second one within 3 days after return from flight. From lymphocyte cultures metaphase plates were prepared on glass slides. Giemsa stained and in situ hybridised metaphases were scored for chromosome changes in pre-flight and post-flight blood samples and the mutation rates were compared. Results obtained in chromosomal studies on long-term flight crew members showed pronounced inter-individual differences in the response to elevated radiation levels. Overall slight but significant elevations of typical radiation induced aberrations, i.e., dicentric chromosomes and reciprocal translocations have been observed. Our data indicate no elevation of mutation rates due to short term stays on-board the ISS.

  1. Aberration-free volumetric high-speed imaging of in vivo retina

    PubMed Central

    Hillmann, Dierck; Spahr, Hendrik; Hain, Carola; Sudkamp, Helge; Franke, Gesa; Pfäffle, Clara; Winter, Christian; Hüttmann, Gereon

    2016-01-01

    Certain topics in research and advancements in medical diagnostics may benefit from improved temporal and spatial resolution during non-invasive optical imaging of living tissue. However, so far no imaging technique can generate entirely diffraction-limited tomographic volumes with a single data acquisition, if the target moves or changes rapidly, such as the human retina. Additionally, the presence of aberrations may represent further difficulties. We show that a simple interferometric setup–based on parallelized optical coherence tomography–acquires volumetric data with 10 billion voxels per second, exceeding previous imaging speeds by an order of magnitude. This allows us to computationally obtain and correct defocus and aberrations resulting in entirely diffraction-limited volumes. As demonstration, we imaged living human retina with clearly visible nerve fiber layer, small capillary networks, and photoreceptor cells. Furthermore, the technique can also obtain phase-sensitive volumes of other scattering structures at unprecedented acquisition speeds. PMID:27762314

  2. Aberration-free volumetric high-speed imaging of in vivo retina

    NASA Astrophysics Data System (ADS)

    Hillmann, Dierck; Spahr, Hendrik; Hain, Carola; Sudkamp, Helge; Franke, Gesa; Pfäffle, Clara; Winter, Christian; Hüttmann, Gereon

    2016-10-01

    Certain topics in research and advancements in medical diagnostics may benefit from improved temporal and spatial resolution during non-invasive optical imaging of living tissue. However, so far no imaging technique can generate entirely diffraction-limited tomographic volumes with a single data acquisition, if the target moves or changes rapidly, such as the human retina. Additionally, the presence of aberrations may represent further difficulties. We show that a simple interferometric setup–based on parallelized optical coherence tomography–acquires volumetric data with 10 billion voxels per second, exceeding previous imaging speeds by an order of magnitude. This allows us to computationally obtain and correct defocus and aberrations resulting in entirely diffraction-limited volumes. As demonstration, we imaged living human retina with clearly visible nerve fiber layer, small capillary networks, and photoreceptor cells. Furthermore, the technique can also obtain phase-sensitive volumes of other scattering structures at unprecedented acquisition speeds.

  3. 3D holographic head mounted display using holographic optical elements with astigmatism aberration compensation.

    PubMed

    Yeom, Han-Ju; Kim, Hee-Jae; Kim, Seong-Bok; Zhang, HuiJun; Li, BoNi; Ji, Yeong-Min; Kim, Sang-Hoo; Park, Jae-Hyeung

    2015-12-14

    We propose a bar-type three-dimensional holographic head mounted display using two holographic optical elements. Conventional stereoscopic head mounted displays may suffer from eye fatigue because the images presented to each eye are two-dimensional ones, which causes mismatch between the accommodation and vergence responses of the eye. The proposed holographic head mounted display delivers three-dimensional holographic images to each eye, removing the eye fatigue problem. In this paper, we discuss the configuration of the bar-type waveguide head mounted displays and analyze the aberration caused by the non-symmetric diffraction angle of the holographic optical elements which are used as input and output couplers. Pre-distortion of the hologram is also proposed in the paper to compensate the aberration. The experimental results show that proposed head mounted display can present three-dimensional see-through holographic images to each eye with correct focus cues.

  4. Aberrations in Fresnel Lenses and Mirrors

    NASA Technical Reports Server (NTRS)

    Gregory, Don

    1999-01-01

    The NASA/MSFC Shooting Star program revealed a number of technical problems that must be solved before solar thermal propulsion can become a reality. The fundamental problem of interest here is the collection of solar energy. This is the first step in the propulsion process and indeed the most important. Everything else depends on the efficiency and focusing ability of the collection lens or mirror. An initial model of Fresnel lens behavior using a wave optics approach has been completed and the results were encouraging enough to warrant an experimental investigation. This experimental investigation confirmed some of the effects predicted and produced invaluable photographic evidence of coherence based diffraction and aberration.

  5. Microcollimated laser diode with low wavefront aberration

    SciTech Connect

    Ogata, S.; Sekii, H.; Maeda, T.; Goto, H.; Yamashita, T.; Imanaka, K. )

    1989-11-01

    The authors developed microcollimated laser diode( MCLD) utilizing a 1 mm short focal length, phi, lc 0.5 mm small diameter micro Fresnel lens (MFL) for the first time as the collimating lens. The MCLD is assembled with a 780 nm quantum-well laser diode dice and an MFL in the smallest commercial available laser package. The radiated laser beam form the MCLD has higher than 2mW power at 50 mA driving current, narrow enough as a phi 2 mm beam diameter with nearly Gaussian intensity profile, and low wavefront aberration less than {lambda}14 (rms value) measured at 1 m distance.

  6. A sample holder with integrated laser optics for an ELMITEC photoemission electron microscope

    SciTech Connect

    Gierster, L.; Pape, L.; Ünal, A. A.; Kronast, F.

    2015-02-15

    We present a new sample holder compatible with ELMITEC Photoemission Electron Microscopes (PEEMs) containing an optical lens and a mirror. With the integrated optical elements, a laser beam is focused from the back side of the sample at normal incidence, yielding a minimum spot size of about 1 μm. This opens up new possibilities for local laser excitations in PEEM experiments such as imaging all-optical magnetization switching at a small length scale.

  7. Time-resolved photoemission electron microscopy imaging of mode coupling between three interacting magnetic vortices

    SciTech Connect

    Wang, Xiao; Cheng, X. M.; Keavney, D. J.; Asmat-Uceda, M.; Buchanan, K. S.; Melikyan, A.

    2014-09-08

    The interactions between three magnetic vortices in a planar equilateral triangular arrangement were studied by time-resolved photoemission electron microscopy. The gyrotropic resonance frequencies of the three individual vortices in the tri-disk system are different from one another and also shifted from that of an isolated vortex by as much as 12%. A comparison with analytical calculations and numerical simulations shows that the observed frequency shifts result from the dipolar interaction between the vortices.

  8. X-ray photo-emission and energy dispersive spectroscopy of HA coated titanium

    SciTech Connect

    Drummond, J.L.; Steinberg, A.D.; Krauss, A.R.

    1997-08-01

    The purpose of this study was to determine the chemical composition changes of hydroxyapatite (HA) coated titanium using surface analysis (x-ray photo-emission) and bulk analysis (energy dispersive spectroscopy). The specimens examined were controls, 30 minutes and 3 hours aged specimens in distilled water or 0.2M sodium phosphate buffer (pH 7.2) at room temperature. Each x-ray photo-emission cycle consisted of 3 scans followed by argon sputtering for 10 minutes for a total of usually 20 cycles, corresponding to a sampling depth of {approximately} 1500 {angstrom}. The energy dispersive spectroscopy analysis was on a 110 by 90 {mu}m area for 500 sec. Scanning electron microscopy examination showed crystal formation (3P{sub 2}O{sub 5}*2CAO*?H{sub 2}O by energy dispersive spectroscopy analysis) on the HA coating for the specimens aged in sodium phosphate buffer. The x-ray photo-emission results indicated the oxidation effect of water on the titanium (as TiO{sub 2}) and the effect of the buffer to increase the surface concentration of phosphorous. No differences in the chemical composition were observed by energy dispersive spectroscopy analysis. The crystal growth was only observed for the sodium phosphate buffer specimens and only on the HA surface.

  9. Photoemission electron microscopy of localized surface plasmons in silver nanostructures at telecommunication wavelengths

    SciTech Connect

    Mårsell, Erik; Larsen, Esben W.; Arnold, Cord L.; Xu, Hongxing; Mauritsson, Johan; Mikkelsen, Anders

    2015-02-28

    We image the field enhancement at Ag nanostructures using femtosecond laser pulses with a center wavelength of 1.55 μm. Imaging is based on non-linear photoemission observed in a photoemission electron microscope (PEEM). The images are directly compared to ultra violet PEEM and scanning electron microscopy (SEM) imaging of the same structures. Further, we have carried out atomic scale scanning tunneling microscopy on the same type of Ag nanostructures and on the Au substrate. Measuring the photoelectron spectrum from individual Ag particles shows a larger contribution from higher order photoemission processes above the work function threshold than would be predicted by a fully perturbative model, consistent with recent results using shorter wavelengths. Investigating a wide selection of both Ag nanoparticles and nanowires, field enhancement is observed from 30% of the Ag nanoparticles and from none of the nanowires. No laser-induced damage is observed of the nanostructures neither during the PEEM experiments nor in subsequent SEM analysis. By direct comparison of SEM and PEEM images of the same nanostructures, we can conclude that the field enhancement is independent of the average nanostructure size and shape. Instead, we propose that the variations in observed field enhancement could originate from the wedge interface between the substrate and particles electrically connected to the substrate.

  10. Plasmonic Field Enhancement of Individual Nanoparticles by Correlated Scanning and Photoemission Electron Microscopy

    SciTech Connect

    Peppernick, Samuel J.; Joly, Alan G.; Beck, Kenneth M.; Hess, Wayne P.

    2011-01-21

    We present results of a combined two-photon photoemission and scanning electron microscopy investigation to determine the electromagnetic enhancement factors of silver-coated spherical nanoparticles deposited on an atomically flat mica substrate. Femtosecond laser excitation, of the nanoparticles, produces intense photoemission, attributed to near-resonant excitation of localized surface plasmons. Enhancement factors are determined by comparing the respective two-photon photoemission yield measured for equal areas between single nanoparticles to that of the surrounding flat surface. For s-polarized, 400 nm (~ 3.1 eV) femtosecond radiation a distribution of enhancement factors are found with a large percentage (77%) of the nanoparticles falling within a median range. A correlated scanning electron microscopy analysis demonstrated that the nanoparticles typifying the median of the distribution were characterized by ideal spherical shapes and defect-free morphologies. The single largest enhancement factors were in contrast produced by a very small percentage (8%) of the total, for which evidence of silver defect anomalies were found that contributed to the overall structure of the nanoparticle. Comparisons are made between the experimentally measured enhancement factors and previously reported theoretical predictions of the localized surface plasmon near-field intensities for isolated nanometer-sized silver spheres.

  11. Bypassing the energy-time uncertainty in time-resolved photoemission

    NASA Astrophysics Data System (ADS)

    Randi, Francesco; Fausti, Daniele; Eckstein, Martin

    2017-03-01

    The energy-time uncertainty is an intrinsic limit for time-resolved experiments imposing a tradeoff between the duration of the light pulses used in experiments and their frequency content. In standard time-resolved photoemission, this limitation maps directly onto a tradeoff between the time resolution of the experiment and the energy resolution that can be achieved on the electronic spectral function. Here we propose a protocol to disentangle the energy and time resolutions in photoemission. We demonstrate that dynamical information on all time scales can be retrieved from time-resolved photoemission experiments using suitably shaped light pulses of quantum or classical nature. As a paradigmatic example, we study the dynamical buildup of the Kondo peak, a narrow feature in the electronic response function arising from the screening of a magnetic impurity by the conduction electrons. After a quench, the electronic screening builds up on timescales shorter than the inverse width of the Kondo peak and we demonstrate that the proposed experimental scheme could be used to measure the intrinsic time scales of such electronic screening. The proposed approach provides an experimental framework to access the nonequilibrium response of collective electronic properties beyond the spectral uncertainty limit and will enable the direct measurement of phenomena such as excited Higgs modes and, possibly, the retarded interactions in superconducting systems.

  12. Automatic low-order aberration compensator for solid-state slab lasers

    NASA Astrophysics Data System (ADS)

    Yu, Xin; Dong, Lizhi; Lai, Boheng; Yang, Ping; Kong, Qingfeng; Yang, Kangjian; Liu, Yong; Tang, Guomao; Xu, Bing

    2016-09-01

    Slab geometry is a promising architecture for power scaling of solid-state lasers. By propagating the laser beams along zigzag path in the gain medium, the thermal effects can be well compensated. However, in the non-zigzag direction, the thermal effects are not compensated. Among the overall aberrations in the slab lasers, the major contributors are two low-order aberrations: astigmatism and defocus, which can range up to over 100 microns (peak to valley), leading to detracted beam quality. Another problem with slab lasers is that the output beams are generally in a rectangular aperture with high aspect ratio (normally 1:10), where square beams are favorable for many applications. In order to solve these problems, we propose an automatic low-order aberration compensation system. This system is composed of three lenses fixed on a motorized rail, one is a spherical lens and the others are cylindrical lenses. Astigmatism and defocus can be compensated by merely adjusting the distances between the lenses. Two wave-front sensors are employed in this compensation system, one is used for detecting the initial parameters of the beams, and the other one is used for detecting the remaining aberrations after correction. The adjustments of the three lenses are directly calculated based on beam parameters using ray tracing method. The initial size of the beam is 3.2mm by 26mm, and peak to valley(PV) value of the wave-front is 33.07λ(λ=1064nm). After correction, the dimension becomes 40mm by 40mm, and peak to valley (PV) value of the wave-front is less than 2 microns.

  13. A Monte-Carlo Model for the Formation of Radiation-induced Chromosomal Aberrations

    NASA Technical Reports Server (NTRS)

    Ponomarev, Artem L.; Cornforth, Michael N.; Loucas, Brad D.; Cucinotta, Francis A.

    2009-01-01

    multi-centrics were also recorded. Conclusion: High-LET DNA damage affects the frequencies of chromosomal aberrations. The ratio of rings to dicentrics is correct for the genomic size cut-offs corresponding to available experimental data. The present work predicts a relative abundance of small rings following irradiation by heavy ions.

  14. Relationships between chromosome structure and chromosomal aberrations

    NASA Astrophysics Data System (ADS)

    Eidelman, Yuri; Andreev, Sergey

    An interphase nucleus of human lymphocyte was simulated by the novel Monte Carlo tech-nique. The main features of interphase chromosome structure and packaging were taken into account: different levels of chromatin organisation; nonrandom localisation of chromosomes within a nucleus; chromosome loci dynamics. All chromosomes in a nucleus were modelled as polymer globules. A dynamic pattern of intra/interchromosomal contacts was simulated. The detailed information about chromosomal contacts, such as distribution of intrachromoso-mal contacts over the length of each chromosome and dependence of contact probability on genomic separation between chromosome loci, were calculated and compared to the new exper-imental data obtained by the Hi-C technique. Types and frequencies of simple and complex radiation-induced chromosomal exchange aberrations (CA) induced by X-rays were predicted with taking formation and decay of chromosomal contacts into account. Distance dependence of exchange formation probability was calculated directly. mFISH data for human lymphocytes were analysed. The calculated frequencies of simple CA agreed with the experimental data. Complex CA were underestimated despite the dense packaging of chromosome territories within a nucleus. Possible influence of chromosome-nucleus structural organisation on the frequency and spectrum of radiation-induced chromosome aberrations is discussed.

  15. Aberrant DNA Methylation and Prostate Cancer

    PubMed Central

    Majumdar, Sunipa; Buckles, Eric; Estrada, John; Koochekpour, Shahriar

    2011-01-01

    Prostate cancer (PCa) is the most prevalent cancer, a significant contributor to morbidity and a leading cause of cancer-related death in men in Western industrialized countries. In contrast to genetic changes that vary among individual cases, somatic epigenetic alterations are early and highly consistent events. Epigenetics encompasses several different phenomena, such as DNA methylation, histone modifications, RNA interference, and genomic imprinting. Epigenetic processes regulate gene expression and can change malignancy-associated phenotypes such as growth, migration, invasion, or angiogenesis. Methylations of certain genes are associated with PCa progression. Compared to normal prostate tissues, several hypermethylated genes have also been identified in benign prostate hyperplasia, which suggests a role for aberrant methylation in this growth dysfunction. Global and gene-specific DNA methylation could be affected by environmental and dietary factors. Among other epigenetic changes, aberrant DNA methylation might have a great potential as diagnostic or prognostic marker for PCa and could be tested in tumor tissues and various body fluids (e.g., serum, urine). The DNA methylation markers are simple in nature, have high sensitivity, and could be detected either quantitatively or qualitatively. Availability of genome-wide screening methodologies also allows the identification of epigenetic signatures in high throughput population studies. Unlike irreversible genetic changes, epigenetic alterations are reversible and could be used for PCa targeted therapies. PMID:22547956

  16. Lymphocyte chromosomal aberration assay in radiation biodosimetry

    PubMed Central

    Agrawala, Paban K.; Adhikari, J. S.; Chaudhury, N. K.

    2010-01-01

    Exposure to ionizing radiations, whether medical, occupational or accidental, leads to deleterious biological consequences like mortality or carcinogenesis. It is considered that no dose of ionizing radiation exposure is safe. However, once the accurate absorbed dose is estimated, one can be given appropriate medical care and the severe consequences can be minimized. Though several accurate physical dose estimation modalities exist, it is essential to estimate the absorbed dose in biological system taking into account the individual variation in radiation response, so as to plan suitable medical care. Over the last several decades, lots of efforts have been taken to design a rapid and easy biological dosimeter requiring minimum invasive procedures. The metaphase chromosomal aberration assay in human lymphocytes, though is labor intensive and requires skilled individuals, still remains the gold standard for radiation biodosimetry. The current review aims at discussing the human lymphocyte metaphase chromosomal aberration assay and recent developments involving the application of molecular cytogenetic approaches and other technological advancements to make the assay more authentic and simple to use even in the events of mass radiation casualties. PMID:21829315

  17. Impact of Primary Spherical Aberration, Spatial Frequency and Stiles Crawford Apodization on Wavefront determined Refractive Error: A Computational Study

    PubMed Central

    Xu, Renfeng; Bradley, Arthur; Thibos, Larry N.

    2013-01-01

    Purpose We tested the hypothesis that pupil apodization is the basis for central pupil bias of spherical refractions in eyes with spherical aberration. Methods We employed Fourier computational optics in which we vary spherical aberration levels, pupil size, and pupil apodization (Stiles Crawford Effect) within the pupil function, from which point spread functions and optical transfer functions were computed. Through-focus analysis determined the refractive correction that optimized retinal image quality. Results For a large pupil (7 mm), as spherical aberration levels increase, refractions that optimize the visual Strehl ratio mirror refractions that maximize high spatial frequency modulation in the image and both focus a near paraxial region of the pupil. These refractions are not affected by Stiles Crawford Effect apodization. Refractions that optimize low spatial frequency modulation come close to minimizing wavefront RMS, and vary with level of spherical aberration and Stiles Crawford Effect. In the presence of significant levels of spherical aberration (e.g. C40 = 0.4 µm, 7mm pupil), low spatial frequency refractions can induce −0.7D myopic shift compared to high SF refraction, and refractions that maximize image contrast of a 3 cycle per degree square-wave grating can cause −0.75D myopic drift relative to refractions that maximize image sharpness. Discussion Because of small depth of focus associated with high spatial frequency stimuli, the large change in dioptric power across the pupil caused by spherical aberration limits the effective aperture contributing to the image of high spatial frequencies. Thus, when imaging high spatial frequencies, spherical aberration effectively induces an annular aperture defining that portion of the pupil contributing to a well-focused image. As spherical focus is manipulated during the refraction procedure, the dimensions of the annular aperture change. Image quality is maximized when the inner radius of the induced

  18. Imaging System Using Shared Optics and Aberration Exploitation

    DTIC Science & Technology

    2014-02-11

    the past it has generally been accepted that the resolution of lenses with geometric aberrations cannot be increased beyond a certain threshold. In...this work we aim to overcome this limitation and demonstrate very high resolution imagery for aberrated lenses through the use of hybrid optical and...of any camera is fundamentally limited by geometric aberrations. In the past it has generally been accepted that the resolution of lenses with

  19. Calculation of angle-resolved photoemission and tunneling for a CuO[sub 2] layer in the normal and superconducting states

    SciTech Connect

    Dickinson, P.H.; Doniach, S. )

    1993-05-01

    We represent the normal-state electronic structure of a CuO[sub 2] layer in terms of a three-band model having an infinite Cu intrasite Coulomb repulsion. We express the Lagrangian for this model using a slave-boson formalism and approximate it in a large-[ital N] expansion to order 1/[ital N] in the zero-temperature limit. The angle-resolved spectral weight determined from the resulting Green's functions suggests that within this picture higher-order corrections in 1/[ital N] are necessary for good agreement with the corresponding angle-resolved photoemission data. We phenomenologically add spin-dependent Heisenberg interactions between neighboring Cu sites and neighboring Cu and O sites. These interactions form the basis of a nonretarded calculation of the superconducting state. For the case of an interaction between neighboring Cu spins only, the lowest-energy solution possesses [ital d]([ital x][sup 2][minus][ital y][sup 2]) symmetry. The use of a three-band model leads to the possibility of the addition of the interaction between Cu and O spins. The resulting [ital d]+[ital idp] superconducting state involves pairing of carriers in Cu orbitals both with themselves and with holes on the O orbitals. This additional pairing will remove the node in the [ital d]-wave state at [ital T]=0 by an amount that depends on the Cu-O coupling parameter; however, the mixed-symmetry state occurs only for a narrow range of coupling parameters. The angle-resolved photoemission and tunneling results are calculated and compared to experimental findings.

  20. Unbiased Estimation of Refractive State of Aberrated Eyes

    PubMed Central

    Martin, Jesson; Vasudevan, Balamurali; Himebaugh, Nikole; Bradley, Arthur; Thibos, Larry

    2011-01-01

    To identify unbiased methods for estimating the target vergence required to maximize visual acuity based on wavefront aberration measurements. Experiments were designed to minimize the impact of confounding factors that have hampered previous research. Objective wavefront refractions and subjective acuity refractions were obtained for the same monochromatic wavelength. Accommodation and pupil fluctuations were eliminated by cycloplegia. Unbiased subjective refractions that maximize visual acuity for high contrast letters were performed with a computer controlled forced choice staircase procedure, using 0.125 diopter steps of defocus. All experiments were performed for two pupil diameters (3mm and 6mm). As reported in the literature, subjective refractive error does not change appreciably when the pupil dilates. For 3 mm pupils most metrics yielded objective refractions that were about 0.1D more hyperopic than subjective acuity refractions. When pupil diameter increased to 6 mm, this bias changed in the myopic direction and the variability between metrics also increased. These inaccuracies were small compared to the precision of the measurements, which implies that most metrics provided unbiased estimates of refractive state for medium and large pupils. A variety of image quality metrics may be used to determine ocular refractive state for monochromatic (635nm) light, thereby achieving accurate results without the need for empirical correction factors. PMID:21777601