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- ItemTracing dynamics of laser-induced fields on ultra-thin foils using complementary imaging with streak deflectometry(College Park, MD : American Physical Society, 2016) Abicht, Florian; Braenzel, Julia; Priebe, Gerd; Koschitzki, Christian; Andreev, Alexander; Nickles, Peter; Sander, Wolfgang; Schnürer, MatthiasWe present a detailed study of the electric and magnetic fields, which are created on plasma vacuum interfaces as a result of highly intense laser-matter interactions. For the field generation ultrathin polymer foils (30–50 nm) were irradiated with high intensity femtosecond (1019–1020 W/cm2) and picosecond (∼1017 W/cm2) laser pulses with ultrahigh contrast (1010–1011). To determine the temporal evolution and the spatial distribution of these fields the proton streak deflectometry method has been developed further and applied in two different imaging configurations. It enabled us to gather complementary information about the investigated field structure, in particular about the influence of different field components (parallel and normal to the target surface) and the impact of a moving ion front. The applied ultrahigh laser contrast significantly increased the reproducibility of the experiment and improved the accuracy of the imaging method. In order to explain the experimental observations, which were obtained by applying ultrashort laser pulses, two different analytical models have been studied in detail. Their ability to reproduce the streak deflectometry measurements was tested on the basis of three-dimensional particle simulations. A modification and combination of the two models allowed for an extensive and accurate reproduction of the experimental results in both imaging configurations. The controlled change of the laser pulse duration from 50 femtoseconds to 2.7 picoseconds led to a transition of the dominating force acting on the probing proton beam at the rear side of the polymer foil. In the picosecond case the (⇀vx⇀B)-term of the Lorentz force dominated over the counteracting ⇀E-field and was responsible for the direction of the net force. The applied proton deflectometry method allowed for an unambiguous determination of the magnetic field polarity at the rear side of the ultrathin foil.
- ItemGigaGauss solenoidal magnetic field inside bubbles excited in under-dense plasma([London] : Macmillan Publishers Limited, part of Springer Nature, 2016) Lécz, Z.; Konoplev, I.V.; Seryi, A.; Andreev, A.This paper proposes a novel and effective method for generating GigaGauss level, solenoidal quasi-static magnetic fields in under-dense plasma using screw-shaped high intensity laser pulses. This method produces large solenoidal fields that move with the driving laser pulse and are collinear with the accelerated electrons. This is in contrast with already known techniques which rely on interactions with over-dense or solid targets and generates radial or toroidal magnetic field localized at the stationary target. The solenoidal field is quasi-stationary in the reference frame of the laser pulse and can be used for guiding electron beams. It can also provide synchrotron radiation beam emittance cooling for laser-plasma accelerated electron and positron beams, opening up novel opportunities for designs of the light sources, free electron lasers, and high energy colliders based on laser plasma acceleration.
- ItemPopulation difference gratings created on vibrational transitions by nonoverlapping subcycle THz pulses([London] : Macmillan Publishers Limited, part of Springer Nature, 2021) Arkhipov, Rostislav; Pakhomov, Anton; Arkhipov, Mikhail; Babushkin, Ihar; Demircan, Ayhan; Morgner, Uwe; Rosanov, NikolayWe study theoretically a possibility of creation and ultrafast control (erasing, spatial frequency multiplication) of population density gratings in a multi-level resonant medium having a resonance transition frequency in the THz range. These gratings are produced by subcycle THz pulses coherently interacting with a nonlinear medium, without any need for pulses to overlap, thereby utilizing an indirect pulse interaction via an induced coherent polarization grating. High values of dipole moments of the transitions in the THz range facilitate low field strength of the needed THz excitation. Our results clearly show this possibility in multi-level resonant media. Our theoretical approach is based on an approximate analytical solution of time-dependent Schrödinger equation (TDSE) using perturbation theory. Remarkably, as we show here, quasi-unipolar subcycle pulses allow more efficient excitation of higher quantum levels, leading to gratings with a stronger modulation depth. Numerical simulations, performed for THz resonances of the H20 molecule using Bloch equations for density matrix elements, are in agreement with analytical results in the perturbative regime. In the strong-field non-perturbative regime, the spatial shape of the gratings becomes non-harmonic. A possibility of THz radiation control using such gratings is discussed. The predicted phenomena open novel avenues in THz spectroscopy of molecules with unipolar and quasi-unipolar THz light bursts and allow for better control of ultra-short THz pulses.
- ItemElliptically polarized high-harmonic radiation for production of isolated attosecond pulses([London] : Macmillan Publishers Limited, part of Springer Nature, 2021) Bengs, Ulrich; Zhavoronkov, NickolaiCircularly polarized attosecond pulses are powerful tool to study chiral light-matter interaction via chiral electron dynamics. However, access to isolated circularly polarized attosecond pulses enabling straightforward interpretation of measurements, still remains a challenge. In this work, we experimentally demonstrate the generation of highly elliptically polarized high-harmonics in a two-color, bi-circular, collinear laser field. The intensity and shape of the combined few-cycle driving radiation is optimized to produce a broadband continuum with enhanced spectral chirality in the range of 15-55 eV supporting the generation of isolated attosecond pulses with duration down to 150 as. We apply spectrally resolved polarimetry to determine the full Stokes vector of different spectral components of the continuum, yielding a homogenous helicity distribution with ellipticity in the range of 0.8-0.95 and a negligible unpolarized content.
- ItemTailoring optical properties and stimulated emission in nanostructured polythiophene([London] : Macmillan Publishers Limited, part of Springer Nature, 2019) Portone, Alberto; Ganzer, Lucia; Branchi, Federico; Ramos, Rodrigo; Caldas, Marília J.; Pisignano, Dario; Molinari, Elisa; Cerullo, Giulio; Persano, Luana; Prezzi, Deborah; Virgili, TersillaPolythiophenes are the most widely utilized semiconducting polymers in organic electronics, but they are scarcely exploited in photonics due to their high photo-induced absorption caused by interchain polaron pairs, which prevents the establishment of a window of net optical gain. Here we study the photophysics of poly(3-hexylthiophene) configured with different degrees of supramolecular ordering, spin-coated thin films and templated nanowires, and find marked differences in their optical properties. Transient absorption measurements evidence a partially-polarized stimulated emission band in the nanowire samples, in contrast with the photo-induced absorption band observed in spin-coated thin films. In combination with theoretical modeling, our experimental results reveal the origin of the primary photoexcitations dominating the dynamics for different supramolecular ordering, with singlet excitons in the nanostructured samples superseding the presence of polaron pairs, which are present in the disordered films. Our approach demonstrates a viable strategy to direct optical properties through structural control, and the observation of optical gain opens the possibility to the use of polythiophene nanostructures as building blocks of organic optical amplifiers and active photonic devices. © 2019, The Author(s).