We review the main research directions ongoing in the development of high-harmonic generation-based extreme ultraviolet sources for the synthesization and application of trains and isolated ...attosecond pulses to time-resolved spectroscopy. A few experimental and theoretical works will be discussed in connection to well-established attosecond techniques. In this context, we present the unique possibilities offered for time-resolved investigations on the attosecond timescale by the new Extreme Light Infrastructure Attosecond Light Pulse Source, which is currently under construction.
Attosecond pulses are fundamental for the investigation of valence and core-electron dynamics on their natural timescale. At present the reproducible generation and characterisation of attosecond ...waveforms has been demonstrated only through the process of high-order harmonic generation. Several methods for the shaping of attosecond waveforms have been proposed, including metallic filters, multilayer mirrors and manipulation of the driving field. However, none of these approaches allow for the flexible manipulation of the temporal characteristics of the attosecond waveforms, and they suffer from the low conversion efficiency of the high-order harmonic generation process. Free Electron Lasers, on the contrary, deliver femtosecond, extreme ultraviolet and X-ray pulses with energies ranging from tens of \(\mathrm{\mu}\)J to a few mJ. Recent experiments have shown that they can generate sub-fs spikes, but with temporal characteristics that change shot-to-shot. Here we show the first demonstration of reproducible generation of high energy (\(\mathrm{\mu}\)J level) attosecond waveforms using a seeded Free Electron Laser. We demonstrate amplitude and phase manipulation of the harmonic components of an attosecond pulse train in combination with a novel approach for its temporal reconstruction. The results presented here open the way to perform attosecond time-resolved experiments with Free Electron Lasers.
Guglielmo Gonzaga's apartments in the complex of the Palazzo Ducale in Mantua were finished in the eighth decade of the Cinquecento. The decor is of particular interest not only because of its formal ...elements, but also because of the meaning it conveys. In 1573 Pirro Ligorio completed the three areas which make up the so-called apartments of Tasso. Although of exceptionally high quality, the decor is rather conventional: sequences of allegories celebrate the conquest of civilization and the virtues of the Prince. In the other rooms, which were intended for public functions, the decoration changes radically. In the Salone di Manto (1586-80), Lorenzo Costa the Younger illustrated the foundation of the city and other significant episodes during its construction. In the Sala dei Capitani, the Sala dei Marchesi and the Sala dei Duchi, large canvases by the younger Costa and Tintoretto (1579-80) commemorate key events in the history of Mantua in which the Gonzaga played a significant role from the time of their rise to power in 1328 (investiture, wars, visits from famous people...). The iconographical themes in these rooms represent a novelty within the context of the Gonzaga residence. The meaning conveyed in these paintings appears to be coherent with the innovative politics of Guglielmo, who had absolutist intentions of reforming government institutions. History bursts forth as the dominant element in this decor. When Federico II, Guglielmo's father, was in power, metaphor and allegory triumphed (the decorative cycles in the palazzo del Te, the frescoes in the Sala di Troia in the palazzo Ducale). With Guglielmo, metaphor and allegory fade, and the images become history. Power is revealed not by way of subtle allusions and cryptic tropes, but through explicit, visual documents, the meaning of which is immediately intelligible. In Guglielmo's apartments, frescoes and canvases set a coherent, representative itinerary. In a logical sequence with Mantua and the Gonzaga as protagonists, the city and leading family appears as essential parts of each other. The destiny of the Gonzaga and the role of the city are legitimated by history.
Quantum mechanically, photoionization can be fully described by the complex photoionization amplitudes that describe the transition between the ground state and the continuum state. Knowledge of the ...value of the phase of these amplitudes has been a central interest in photoionization studies and newly developing attosecond science, since the phase can reveal important information about phenomena such as electron correlation. We present a new attosecond-precision interferometric method of angle-resolved measurement for the phase of the photoionization amplitudes, using two phase-locked Extreme Ultraviolet pulses of frequency \(\omega\) and \(2\omega\), from a Free-Electron Laser. Phase differences \(\Delta \tilde \eta\) between one- and two-photon ionization channels, averaged over multiple wave packets, are extracted for neon \(2p\) electrons as a function of emission angle at photoelectron energies 7.9, 10.2, and 16.6 eV. \(\Delta \tilde \eta\) is nearly constant for emission parallel to the electric vector but increases at 10.2 eV for emission perpendicular to the electric vector. We model our observations with both perturbation and \textit{ab initio} theory, and find excellent agreement. In the existing method for attosecond measurement, Reconstruction of Attosecond Beating By Interference of Two-photon Transitions (RABBITT), a phase difference between two-photon pathways involving absorption and emission of an infrared photon is extracted. Our method can be used for extraction of a phase difference between single-photon and two-photon pathways and provides a new tool for attosecond science, which is complementary to RABBITT.
Ultrashort extreme ultraviolet (EUV) laser pulses with a controllable polarization state are highly desirable for time-resolved studies and applications involving chirality, circular dichroism, spin ...dynamics and magnetism in the gas phase or condensed matter. A convenient method to generate such radiation is higher-order harmonic generation (HHG) as applied in numerous laboratories worldwide. Unless special techniques are employed, however, this process will produce predominantly linearly polarized EUV radiation as imposed by the symmetry of the generating field-medium system. To overcome this fundamental limitation, intense research activity has focused on shaping the time-dependent field vector of the generating light pulse 1. In the current contribution we present an alternative method to generate EUV pulses with a widely controllable polarization state utilizing field-free aligned molecules as an anisotropically shaped medium for HHG.
An electrical pulse is completely defined by its time-dependent amplitude, phase and polarization state. For optical and near-infrared pulses the manipulation and characterization of the last one is ...fundamental due to its relevance in several scientific and technological fields. Although the complete characterization of optical waveform has been already demonstrated, a technique both capable to fully characterize also weak probe pulses, with energy in the 10-100nJ, and, at the same time, free of systematic distortions, would be highly desirable. In this work, we report on new theoretical and experimental results to demonstrate a novel approach for the complete characterization of the electric field of an optical pulse. Our method is based on the combination of two elements: the implementation of extreme ultraviolet (XUV) interferometry, with time resolution in the attosecond domain, and the demonstration that the motion of an attosecond electronic wave packet, created by an intense laser pulse, allows to sample an unknown electric field along a controllable, fixed direction. Combining these elements, we demonstrate the full reconstruction of electric fields with intensities as low as I~10 9 W/cm 2 and with a generic time-dependent polarization state, with an all-optical method.
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