88,876 research outputs found
Steering Proton Migration in Hydrocarbons Using Intense Few-Cycle Laser Fields
No full textCitation: Kübel, M., Siemering, R., Burger, C., Kling, N. G., Li, H., Alnaser, A. S., . . . Kling, M. F. (2016). Steering Proton Migration in Hydrocarbons Using Intense Few-Cycle Laser Fields. Physical Review Letters, 116(19). doi:10.1103/PhysRevLett.116.193001Proton migration is a ubiquitous process in chemical reactions related to biology, combustion, and catalysis. Thus, the ability to manipulate the movement of nuclei with tailored light within a hydrocarbon molecule holds promise for far-reaching applications. Here, we demonstrate the steering of hydrogen migration in simple hydrocarbons, namely, acetylene and allene, using waveform-controlled, few-cycle laser pulses. The rearrangement dynamics is monitored using coincident 3D momentum imaging spectroscopy and described with a widely applicable quantum-dynamical model. Our observations reveal that the underlying control mechanism is due to the manipulation of the phases in a vibrational wave packet by the intense off-resonant laser field. © 2016 American Physical Society
Complete characterization of single-cycle double ionization of argon from the nonsequential to the sequential ionization regime
No full textCitation: Kubel, M., Burger, C., Kling, N. G., Pischke, T., Beaufore, L., Ben-Itzhak, I., . . . Bergues, B. (2016). Complete characterization of single-cycle double ionization of argon from the nonsequential to the sequential ionization regime. Physical Review A, 93(5), 9. doi:10.1103/PhysRevA.93.053422Selected features of nonsequential double ionization have been qualitatively reproduced by a multitude of different (quantum and classical) approaches. In general, however, the typical uncertainty of laser pulse parameters and the restricted number of observables measured in individual experiments leave room for adjusting theoretical results to match the experimental data. While this has been hampering the assessment of different theoretical approaches leading to conflicting interpretations, comprehensive experimental data that would allow such an ultimate and quantitative assessment have been missing so far. To remedy this situation we have performed a kinematically complete measurement of single-cycle multiple ionization of argon over a one order of magnitude range of intensity. The momenta of electrons and ions resulting from the ionization of the target gas are measured in coincidence, while each ionization event is tagged with the carrier-envelope phase and intensity of the 4-fs laser pulse driving the process. The acquired highly differential experimental data provide a benchmark for a rigorous test of the many competing theoretical models used to describe nonsequential double ionization
Laser-based repair of carbon fiber reinforced plastics
No full textThe recent progress in laser system technology enables innovative techniques for machining of carbon fiber reinforced plastics (CFRPs). A representative application is the layer-by-layer removal of damaged composite material to provide a cavity for refilling with repair plies. Results show that it is possible to achieve a reliable and automatable removal rate to perform arbitrary repair cavity geometries, obtaining a relevant time-reduction with respect to the conventional manual grinding process. The combination of modern UV-laser sources with a scanning technology enabling deflection speeds up to 2 m/s, suppresses heat affected zones (HAZs) and detachment of fibers from the polymer matrix. A method for the selective removal of surface matrix without damaging the fibers beneath is also presented
A study on UV laser drilling of PEEK reinforced with carbon fibers
No full textThis paper deals with the application of Nd-YAG laser emitting at 355 nm to the drilling process of Carbon Fiber Reinforced Polyetheretherkethone (PEEK-CF) laminates. The combination of a modern UV-laser source with a scanning technology enabling speeds up to 4 m/s, suppresses heat affected zones (HAZ) and consequently detachment of fibers from the polymer matrix. A removal technique based on the ablation of superimposed layers of composite material is proposed and analyzed in detail as a function of energy density delivered to the surface, hatch strategy and thickness of the laminate to be drilled. The hatching technique discussed in the paper is compared with conventional laser trepanning and percussion drilling through holes for the realization of 2 mm and 0.1 mm diameter, respectively. In both the cases benefits were noticed in terms of extension of HAZ and quality of the cut edges
Kafkas Zeiten im 'Process'
No full textDer Beitrag untersucht die komplexen Figurationen der Zeit in Kafkas Romanfragment "Der Prozess
Plasmon-enhanced-attosecond-extreme ultraviolet source
No full textA compact high repetition rate attosecond light source based on a standard laser oscillator combined with plasmonic enhancement is analyzed. At repetition rates of tens of MHz, we predict focusable pulses with durations of ≲300 as and a spherical wave front at collimation angles ≲5° . Plasmonic mode and guiding of the attosecond radiation determine the beam parameters. The beam is robust with respect to variations of driver pulse focus and duration
Variations on the Author
No full text“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Laser as an innovative tool for laminates repair
No full textThe challenges during the mechanical machining of Fiber Reinforced Plastics like
delamination, fiber tearing and rapid tool wear are well known, nevertheless, the
relevance of CFRPs in the industrial community is still increasing. Due to this fact the
development of new methods for machining and treatment is needed to close this
technological gap. A promising cost-saving and time-saving technique is represented
by the laser ablation of bulk material. This paper presents the implementation of a
laser system for the treatment of laminates whose mechanical properties have been
compromised by external damage during the operation. The purpose of this
approach is to remove damaged material to provide a cavity for refilling with repair
plies. Our results show that it is possible to achieve a reliable and automatable
process with an even removal rate to perform arbitrary repair cavity geometries. The
laser machining set-up, equipped with a pulsed UV-laser and a galvo-scanning head,
avoids heat affected zones (HAZ) and detachment of fibers from the thermoplastic
matrix (here: PEEK). The laser-ablated and repaired laminates were then used to
prepare standard specimens to be tested according to DIN 65148. Detailed results of
the DIN 65148 of the repaired structure are presented in the final part of the paper
Laser-based repair for carbon fiber reinforced composites
No full textRecent progress in laser system technology enables innovative techniques for the machining of CFRPs. A representative application is the layer-by-layer removal of damaged composite material to provide a cavity for refilling with repair plies. Results show that it is possible to achieve a reliable and automatable removal rate to perform arbitrary repair cavity geometries, obtaining a relevant time reduction with respect to the conventional manual grinding process. The combination of modern UV-laser sources with a scanning technology enables scanning speeds of up to 4.0 m s-1, and suppresses heat affected zones and detachment of fibers from the polymer matrix. The interlaminar shear strength of repaired laminates and reference specimens have been measured and evaluated according to DIN 65148, and the results are reported here
Chapter 12: Laser-based repair for carbon fiber reinforced composites.
No full textThe recent progress in laser system technology enables innovative techniques for machining of CFRPs. A representative application is the layer by layer removal of damaged composite material to provide a cavity for refilling with repair plies. Results show that it is possible to achieve a reliable and automatable removal rate to perform arbitrary repair cavity geometries, obtaining a relevant time-reduction respect to the conventional manual grinding process. The combination of modern UV-laser sources with a scanning technology enabling deflection speeds up to 4,0m/s, suppresses heat affected zones (HAZ) and detachment of fibers from the polymer matrix. Finally, according to DIN 65148, the interlaminar shear strength of repaired laminates and reference specimens were measured and evaluated
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