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- ItemUltrafast Structural Changes in Chiral Molecules Measured with Free-Electron Lasers(Bristol : IOP Publ., 2020) Schmidt, P.; Music, V.; Hartmann, G.; Boll, R.; Erk, B.; Bari, S.; Allum, F.; Baumann, T.M.; Brenner, G.; Brouard, M.; Burt, M.; Coffee, R.; Dörner, S.; Galler, A.; Grychtol, P.; Heathcote, D.; Inhester, L.; Kazemi, M.; Larsson, M.; Li, Z.; Lutmann, A.; Manschwetus, B.; Marder, L.; Mason, R.; Moeller, S.; Osipov, T.; Otto, H.; Passow, C.; Rolles, D.; Rupprecht, P.; Schubert, K.; Schwob, L.; Thomas, R.; Vallance, C.; Von Korff Schmising, C.; Wagner, R.; Walter, P.; Wolf, T.J.A.; Zhaunerchyk, V.; Meyer, M.; Ehresmann, A.; Knie, A.; Demekhin, P.V.; Ilchen, M.(X-ray) free-electron lasers are employed to site specifically interrogate atomic fragments during ultra-fast photolysis of chiral molecules via time-resolved photoelectron circular dichroism. © 2020 Institute of Physics Publishing. All rights reserved.
- ItemAtomic processes in bicircular fields(Bristol : IOP Publ., 2016) Odžak, S.; Hasović, E.; Becker, W.; Milošević, D.B.We investigate laser-assisted electron-ion recombination (LAR), high-order harmonic generation (HHG) and above-threshold ionization (ATI) of argon atoms by a bicircular laser field, which consists of two coplanar counter-rotating circularly polarized fields of frequencies rω and sω. The energy of soft x rays generated in the LAR process is analyzed as a function of the incident electron angle and numerical results of direct recombination of electrons with Ar+ ions are presented. We also present the results of HHG by a bicircular field and confirm the selection rules derived earlier for inert-gas atoms in a p ground state. We show that the photoelectron spectra in the ATI process, presented in the momentum plane, as well as the LAR spectra exhibit the same discrete rotational symmetry as the applied field.
- ItemAttosecond time delays in C60 valence photoemissions at the giant plasmon(Bristol : IOP Publ., 2015) Barillot, T.; Magrakvelidze, M.; Loriot, V.; Bordas, C.; Hervieux, P.-A.; Gisselbrecht, M.; Johnsson, P.; Laksman, J.; Mansson, E.P.; Sorensen, S.; Canton, S.E.; Dahlström, J.M.; Dixit, G.; Madjet, M.E.; Lépine, F.; Chakraborty, H.S.We perform time-dependent local density functional calculations of the time delay in C60 HOMO and HOMO-1 photoionization at giant plasmon energies. A semiclassical model is used to develop further insights.
- ItemThe influence of the driving-bicircular-field component intensities on the helicities of emitted high-order harmonics(Bristol : IOP Publ., 2019) Milošević, D.B.High-order harmonics generated by a linearly polarized laser field are also linearly polarized. Having in mind that for various application, such as the exploration of magnetic materials, chiral molecules etc., we need circularly polarized high harmonics which serve as coherent soft x-rays, we explore high-order harmonic generation by the so-called bicircular laser field. This field consists of two coplanar counter-rotating circularly polarized fields of different frequencies equal to integer multiples of a fundamental frequency ω. High harmonics generated by such field are circularly polarized with helicity alternating between +1 and −1. Combining a group of such harmonics, instead of obtaining a circularly polarized attosecond pulse train, one obtains a pulse with unusual polarization properties. But, if the harmonics of particular helicity are stronger, i.e., if we have helicity asymmetry in a high-harmonic energy interval, then it is possible to generate an elliptical or even circular pulse train. We theoretically investigated a wide range of bicircular field-component intensities (I1 and I2) and found regions where both the harmonic intensity is high and the helicity asymmetry is large. Particular attention is devoted to the ω−2ω and ω−3ω bicircular fields and atoms having the s and p ground states. In our calculations we use strong-field approximation and quantum-orbit theory. We show that, even in the extreme case of I2 = 8I1, for an ω−3ω bicircular field, high-order harmonic generation is more efficient than in the I2 = I1 case. The obtained results are explained analyzing the relevant electron trajectories and velocities, which follow from the quantum-orbit theory. For the atoms having p ground state the helicity asymmetry parameter is large for a wide range of high-harmonic photon energies, while for the atoms having s ground state the helicity asymmetry parameter can be large only for low harmonics. We confirm this by averaging the obtained results over the intensity distribution in the laser focus.
- ItemKinematic origin for near-zero energy structures in mid-IR strong field ionization(Bristol : IOP Publ., 2016) Pisanty, Emilio; Ivanov, MishaWe propose and discuss a kinematic mechanism underlying the recently discovered 'near-zero energy structure' in the photoionization of atoms in strong mid-infrared laser fields, based on trajectories which revisit the ion at low velocities exactly analogous to the series responsible for low-energy structures. The different scaling of the new series, as $E\sim {I}_{p}^{2}/{U}_{p}$, suggests that the near-zero energy structure can be lifted to higher energies, where it can be better resolved and studied, using harder targets with higher ionization potential.
- ItemMicro Fresnel mirror array with individual mirror control(Bristol : IOP Publ., 2020) Poyyathuruthy Bruno, Binal; Schütze, Robert; Grunwald, Ruediger; Wallrabe, UlrikeWe present the design and fabrication of a miniaturized array of piezoelectrically actuated high speed Fresnel mirrors with individual mirror control. These Fresnel mirrors can be used to generate propagation invariant and self-healing interference patterns. The mirrors are actuated using piezobimorph actuators, and the consequent change of the tilting angle of the mirrors changes the fringe spacing of the interference pattern generated. The array consists of four Fresnel mirrors each having an area of 2 × 2 mm2 arranged in a 2x2 configuration. The device, optimized using FEM simulations, is able to achieve maximum mirror deflections of 15 mrad, and has a resonance frequency of 28 kHz.
- ItemStability of quantum linear logic circuits against perturbations(Bristol : IOP Publ., 2020) Babushkin, Ihar; Morgner, Uwe; Demircan, AyhanHere we study transformation of waveshapes of photons under the action of the linear logic circuits and other related architectures involving only linear optical networks and measurements. We show that the gates are working well not only in the case when all photons are separable and located in the same mode, but in some more general cases. For instance, the photonic waveshapes are allowed to be slightly different in different channels; in this case, Zeno effect prevents the photons from decoherence after the measurement, and the gate thus remains neutral to the small waveshape perturbations. © 2020 The Author(s). Published by IOP Publishing Ltd Printed in the UK
- ItemChiral dichroism in bi-elliptical high-order harmonic generation(Bristol : IOP Publ., 2018-02-28) Ayuso, David; Decleva, Piero; Patchkovskii, Serguei; Smirnova, OlgaThe application of strong bi-elliptically polarized laser fields to the generation of high-order harmonics in organic molecules offers exceptional opportunities for chiral recognition and chiral discrimination. These fields are made by combining an elliptically polarized fundamental, typically in the infrared range, with its counter-rotating second harmonic. Here we present a theoretical study of the harmonic emission from the chiral molecule propylene oxide in bi-elliptical fields. Our calculations include, for the first time in such a complex system, accurate photorecomination matrix elements, evaluated using the static-exchange density functional theory method. We show that bi-elliptical light can induce strong chiral dichroism in the harmonic spectra of chiral molecules in a broad range of harmonic numbers and ellipticities.
- ItemPhase- and intensity-resolved measurements of above threshold ionization by few-cycle pulses(Bristol : IOP Publ., 2018-06-11) Kübel, M.; Arbeiter, M.; Burger, C.; Kling, Nora G.; Pischke, T.; Moshammer, R.; Fennel, T.; Kling, M.F.; Bergues, B.We investigate the carrier-envelope phase (CEP) and intensity dependence of the longitudinal momentum distribution of photoelectrons resulting from above threshold ionization of argon by few-cycle laser pulses. The intensity of the pulses with a center wavelength of 750 nm is varied in a range between 0.7 × 1014 and . Our measurements reveal a prominent maximum in the CEP-dependent asymmetry at photoelectron energies of 2 U P (U P being the ponderomotive potential), that is persistent over the entire intensity range. Further local maxima are observed around 0.3 and 0.8 U P. The experimental results are in good agreement with theoretical results obtained by solving the three-dimensional time-dependent Schrödinger equation. We show that for few-cycle pulses, the amplitude of the CEP-dependent asymmetry provides a reliable measure for the peak intensity on target. Moreover, the measured asymmetry amplitude exhibits an intensity-dependent interference structure at low photoelectron energy, which could be used to benchmark model potentials for complex atoms.
- ItemTime-resolved site-selective imaging of predissociation and charge transfer dynamics: The CH3I B-band(Bristol : IOP Publ., 2020) Forbes, Ruaridh; Allum, Felix; Bari, Sadia; Boll, Rebecca; Borne, Kurtis; Brouard, Mark; Bucksbaum, Philip H.; Ekanayake, Nagitha; Erk, Benjamin; Howard, Andrew J.; Johnsson, Per; Lee, Jason W.L.; Manschwetus, Bastian; Mason, Robert; Passow, Christopher; Peschel, Jasper; Rivas, Daniel E.; Rörig, Aljoscha; Rouzée, Arnaud; Vallance, Claire; Ziaee, Farzaneh; Rolles, Daniel; Burt, MichaelThe predissociation dynamics of the 6s (B2E) Rydberg state of gas-phase CH3I were investigated by time-resolved Coulomb-explosion imaging using extreme ultraviolet (XUV) free-electron laser pulses. Inner-shell ionization at the iodine 4d edge was utilized to provide a site-specific probe of the ensuing dynamics. The combination of a velocity-map imaging (VMI) spectrometer coupled with the pixel imaging mass spectrometry (PImMS) camera permitted three-dimensional ionic fragment momenta to be recorded simultaneously for a wide range of iodine charge states. In accord with previous studies, initial excitation at 201.2 nm results in internal conversion and subsequent dissociation on the lower-lying A-state surface on a picosecond time scale. Examination of the time-dependent yield of low kinetic energy iodine fragments yields mechanistic insights into the predissociation and subsequent charge transfer following multiple ionization of the iodine products. The effect of charge transfer was observed through differing delay-dependencies of the various iodine charge states, from which critical internuclear distances for charge transfer could be inferred and compared to a classical over-the-barrier model. Time-dependent photofragment angular anisotropy parameters were extracted from the central slice of the Newton sphere, without Abel inversion, and highlight the effect of rotation of the parent molecule before dissociation, as observed in previous © 2020 The Author(s). Published by IOP Publishing Ltd Printed in the UK