| 1. |
- Maroju, P. K., et al.
(författare)
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Analysis of two-color photoelectron spectroscopy for attosecond metrology at seeded free-electron lasers
- 2021
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 23:4
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Tidskriftsartikel (refereegranskat)abstract
- The generation of attosecond pulse trains at free-electron lasers opens new opportunities in ultrafast science, as it gives access, for the first time, to reproducible, programmable, extreme ultraviolet (XUV) waveforms with high intensity. In this work, we present a detailed analysis of the theoretical model underlying the temporal characterization of the attosecond pulse trains recently generated at the free-electron laser FERMI. In particular, the validity of the approximations used for the correlated analysis of the photoelectron spectra generated in the two-color photoionization experiments are thoroughly discussed. The ranges of validity of the assumptions, in connection with the main experimental parameters, are derived.
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| 2. |
- Blackburn, Thomas, 1989, et al.
(författare)
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From local to nonlocal: higher fidelity simulations of photon emission in intense laser pulses
- 2021
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 23:8
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Tidskriftsartikel (refereegranskat)abstract
- State-of-the-art numerical simulations of quantum electrodynamical (QED) processes in strong laser fields rely on a semiclassical combination of classical equations of motion and QED rates, which are calculated in the locally constant field approximation. However, the latter approximation is unreliable if the amplitude of the fields, a (0), is comparable to unity. Furthermore, it cannot, by definition, capture interference effects that give rise to harmonic structure. Here we present an alternative numerical approach, which resolves these two issues by combining cycle-averaged equations of motion and QED rates calculated in the locally monochromatic approximation. We demonstrate that it significantly improves the accuracy of simulations of photon emission across the full range of photon energies and laser intensities, in plane-wave, chirped and focused background fields.
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| 3. |
- He, Y., et al.
(författare)
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A single-laser scheme for observation of linear Breit-Wheeler electron-positron pair creation
- 2021
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 23:11
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Tidskriftsartikel (refereegranskat)abstract
- We show that a single laser pulse, traveling through a dense plasma, produces a population of MeV photons of sufficient density to generate a large number of electron-positron pairs via the linear Breit-Wheeler process. While it may be expected that the photons are emitted predominantly in the forward direction, parallel to the laser propagation, we find that a longitudinal plasma electric field drives the emission of photons in the backwards direction. This enables the collision of oppositely directed, MeV-level photons necessary to overcome the mass threshold for the linear Breit-Wheeler process. Our calculations predict the production of 10(7) electron-positron pairs, per shot, by a laser with peak intensity of just 3 x 10(22) W cm(-2). By using only a single laser pulse, the scheme sidesteps the practical difficulties associated with the multiple-laser schemes previously investigated.
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| 4. |
- Axelsson, S., et al.
(författare)
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Theoretical and experimental investigations of three-terminal carbon nanotube nanorelays
- 2005
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Ingår i: New J. Phys. - : IOP Publishing. - 1367-2630. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- We present theoretical and experimental investigations of three-terminal nanoelectromechanical relays based on suspended carbon nanotubes. A charge is induced in the nanotube by applying a voltage to an underlying gate electrode thus inducing the nanotube to bend and make contact with a drain electrode. Such devices have potential applications as fast switches, logic devices, memory elements and pulse generators. We describe two modes of operation: a contact mode where the nanotube makes physical contact with the drain electrode and a non-contact mode where electrical contact between the nanotube and the drain electrode is made via a field emission current.
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| 5. |
- Gorelik, Leonid, 1952, et al.
(författare)
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Spin-controlled nanoelectromechanics in magnetic NEM-SET systems
- 2005
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- We present a theory of the nanoelectromechanical coupling in a magnetic nanoelectromechanical single-electron tunnelling (NEM-SET) device, where a nanometre-sized metallic cluster or 'dot' is suspended between two magnetic leads. In this device, the spin projections of the tunnelling electrons, which can be manipulated by an external magnetic field, control the strength of the tunnel current. The magnitude of the current, in turn, determines the power that can be supplied to the vibrational degree of freedom of the suspended cluster. The electromechanical instability that occurs in the system if the dissipation rate of the mechanical cluster vibration energy is slow enough, is shown to strongly depend on the external magnetic field. As a result different regimes of 'shuttle' vibrations appear and are analysed. The strength of the magnetic field required to control the nanomechanical vibrations decreases as the tunnel resistance of the device increases and can be as low as 10 gauss for gigaohm tunnel structures.
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| 6. |
- Bahrova, O. M., et al.
(författare)
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Nanomechanics driven by the superconducting proximity effect
- 2022
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 24:3
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Tidskriftsartikel (refereegranskat)abstract
- We consider a nanoelectromechanical weak link composed of a carbon nanotube suspended above a trench in a normal metal electrode and positioned in a gap between two superconducting leads. The nanotube is treated as a movable single-level quantum dot (QD) in which the position-dependent superconducting order parameter is induced as a result of Cooper pair tunneling. We show that in such a system, self-sustained bending vibrations can emerge if a bias voltage is applied between normal and superconducting electrodes. The occurrence of this effect crucially depends on the direction of the bias voltage and the relative position of the QD level. We also demonstrate that the nanotube vibrations strongly affect the dc current through the system, a characteristic that can be used for the direct experimental observation of the predicted phenomenon.
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| 7. |
- Baird, C. D., et al.
(författare)
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Realising single-shot measurements of quantum radiation reaction in high-intensity lasers
- 2019
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 21:5
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Tidskriftsartikel (refereegranskat)abstract
- Modern laser technology is now sufficiently advanced that collisions between high-intensity laser pulses and laser-wakefield-accelerated (LWFA) electron beams can reach the strong-field regime, so that it is possible to measure the transition between the classical and quantum regimes of light-matter interactions. However, the energy spectrum of LWFA electron beams can fluctuate significantly from shot to shot, making it difficult to clearly discern quantum effects in radiation reaction (RR), for example. Here we show how this can be accomplished in only a single laser shot. A millimetre-scale pre-collision drift allows the electron beam to expand to a size larger than the laser focal spot and develop a correlation between transverse position and angular divergence. In contrast to previous studies, this means that a measurement of the beam's energy-divergence spectrum automatically distinguishes components of the beam that hit or miss the laser focal spot and therefore do and do not experience RR.
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| 8. |
- Blackburn, Thomas, 1989, et al.
(författare)
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Reaching supercritical field strengths with intense lasers
- 2019
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 21:5
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Tidskriftsartikel (refereegranskat)abstract
- It is conjectured that all perturbative approaches to quantum electrodynamics (QED) break down in the collision of a high-energy electron beam with an intense laser, when the laser fields are boosted to supercritical strengths far greater than the critical field of QED. As field strengths increase toward this regime, cascades of photon emission and electron-positron pair creation are expected, as well as the onset of substantial radiative corrections. Here we identify the important role played by the collision angle in mitigating energy losses to photon emission that would otherwise prevent the electrons reaching the supercritical regime. Weshow that a collision between an electron beam with energy in the tens of GeV and a laser pulse of intensity 10 W cm 24 2 - at oblique, or even normal, incidence is a viable platform for studying the breakdown of perturbative strong-field QED. Our results have implications for the design of near-term experiments as they predict that certain quantum effects are enhanced at oblique incidence. © 2019 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft.
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| 9. |
- Bradley, L. E., et al.
(författare)
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Effect of laser temporal intensity skew on enhancing pair production in laser-electron-beam collisions
- 2021
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 23:9
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Tidskriftsartikel (refereegranskat)abstract
- Recent high-intensity laser experiments (Cole et al 2018 Phys. Rev. X 8 011020; Poder et al 2018 Phys. Rev. X 8 031004) have shown evidence of strong radiation reaction in the quantum regime. Experimental evidence of quantum effects on radiation reaction and electron-positron pair cascades has, however, proven challenging to obtain and crucially depends on maximising the quantum parameter of the electron (defined as the ratio of the electric field it feels in its rest frame to the Schwinger field). The quantum parameter can be suppressed as the electrons lose energy by radiation reaction as they traverse the initial rise in the laser intensity. As a result the shape of the intensity temporal envelope becomes important in enhancing quantum radiation reaction effects and pair cascades. Here we show that a realistic laser pulse with a faster rise time on the leading edge, achieved by skewing the temporal envelope, results in curtailing of pair yields as the peak power is reduced. We find a reduction in pair yields by orders of magnitude in contrast to only small reductions reported previously in large-scale particle-in-cell code simulations (Hojbota et al 2018 Plasma Phys. Control. Fusion 60 064004). Maximum pairs per electron are found in colliding 1.5 GeV electrons with a laser wakefield produced envelope 7.90 x 10(-2) followed by a short 50 fs Gaussian envelope, 1.90 x 10(-2), while it is reduced to 8.90 x 10(-5), a factor of 100, for an asymmetric envelope.
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| 10. |
- Dietrich, K., et al.
(författare)
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Two-dimensional nature of the active Brownian motion of catalytic microswimmers at solid and liquid interfaces
- 2017
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 19
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Tidskriftsartikel (refereegranskat)abstract
- Colloidal particles equipped with platinum patches can establish chemical gradients in H2O2-enriched solutions and undergo self-propulsion due to local diffusiophoretic migration. In bulk (3D), this class of active particles swim in the direction of the surface heterogeneities introduced by the patches and consequently reorient with the characteristic rotational diffusion time of the colloids. In this article, we present experimental and numerical evidence that planar 2D confinements defy this simple picture. Instead, the motion of active particles both on solid substrates and at flat liquid-liquid interfaces is captured by a 2D active Brownian motion model, in which rotational and translational motion are constrained in the xy-plane. This leads to an active motion that does not follow the direction of the surface heterogeneities and to timescales of reorientation that do not match the free rotational diffusion times. Furthermore, 2D-confinement at fluid-fluid interfaces gives rise to a unique distribution of swimming velocities: the patchy colloids uptake two main orientations leading to two particle populations with velocities that differ up to one order of magnitude. Our results shed new light on the behavior of active colloids in 2D, which is of interest for modeling and applications where confinements are present.
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