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JPhys photonics 4, 034003 (2022). doi:10.1088/2515-7647/ac6ea5 special issue: "Focus on Nanophotonics and Biophotonics for Biomedical and Environmental Applications", The dynamics of biologically relevant molecules exposed to ionizing radiation contains many facets and spans several orders of magnitude in time and energy. In the extreme ultraviolet (XUV) spectral range, multi-electronic phenomena and bands of correlated states with inner-valence holes must be accounted for in addition to a plethora of vibrational modes and available dissociation channels. The ability to track changes in charge density and bond length during ultrafast reactions is an important endeavor toward more general abilities to simulate and control photochemical processes, possibly inspired by those that have evolved biologically. By using attosecond XUV pulses extending up to 35 eV and few-femtosecond near-infrared pulses, we have previously time-resolved correlated electronic dynamics and charge migration occurring in the biologically relevant molecule adenine after XUV-induced sudden ionization. Here, using additional experimental data, we comprehensively report on both electronic and vibrational dynamics of this nucleobase in an energy range little explored to date with high temporal resolution. The time-dependent yields of parent and fragment ions in the mass spectra are analyzed to extract exponential time constants and oscillation periods. Together with time-dependent density functional theory and ab-initio Green's function methods, we identify different vibrational and electronic processes. Beyond providing further insights into the XUV-induced dynamics of an important nucleobase, our work demonstrates that yields of specific dissociation outcomes can be influenced by sufficiently well-timed ultrashort pulses, therefore providing a new route for the control of the multi-electronic and dissociative dynamics of a DNA building block., Published by IOP Publishing, Bristol

We demonstrate sub-20 fs single-stage post-compression of an Ytterbium-doped fiber laser. Dispersion-engineered dielectric cavity mirrors are used to control spectral broadening in a gas-filled multi-pass cell supporting a throughput of 98%.

A novel light source delivering few-cycle UV pulses is used to reveal an ultrafast modulation of the chiroptical properties of photoexcited chiral molecules, probed by time-resolved photoelectron circular dichroism. We report a periodic inversion of photoelectron emission direction in methyl-lactate on a timescale as short as 6fs.

Chapter 5 describes the efforts being made to reach the few-optical-cycle regime for ultraviolet pulses. The main route to achieve this task is to exploit low dispersion gas media for frequency up-conversion of Ti:Sa and Ytterbium:YAG laser sources. UV generation methods to obtain few-fs (sub 3-fs) pulse duration are discussed, providing state-of-the-art UV sources as a key ingredient in the field of ultrafast UV spectroscopy. Applications to study in real time the ultrafast response of photoexcited states of matter are discussed by the authors.

Detailed knowledge about photo-induced electron dynamics in water is key to the understanding of several biological and chemical mechanisms, in particular for those resulting from ionizing radiation [1] . While several studies reporting on detailed low-energy electron scattering cross sections in amorphous ice, liquid water and large water clusters [2] and a time-resolved approach to investigate electron scattering in water has been reported [3] , such investigations in gas-phase water clusters have shown to be a promising bridge in between the gas and liquid phase, allowing for many technological limitations to be overcome and setting a clear route to perform attosecond-resolved spectroscopy of hydrated molecules. Indeed, extreme ultraviolet (XUV) attosecond pulses may be used to photo-ionize a water sample and to investigate the electron dynamics and transport properties with extremely high temporal resolution [4] .

As an important branch of molecular science, time-resolved ultraviolet (UV) spectroscopy promises to address ultrafast photochemical and photobiological processes that play key roles in nature, from ozone photolysis to UV-induced DNA damage [1] , [2] . At the few-femtosecond and attosecond timescales, the study of UV-induced molecular dynamics has been hampered due to the technical challenges for the generation and manipulation of ultrabroadband, few-cycle UV pulses [3] – [5] .

The field of ultrafast spectroscopy is based on lasers being able to produce pulses that are as short as a few femtoseconds. Due to their broad bandwidth, these ultrashort light transients are strongly affected by propagation through materials. Therefore, a careful characterization of their temporal profile is required before any application. We propose a scheme for their characterization in situ, ensuring that the pulse parameters are measured in the region where the interaction with the sample takes place. Our method is based on first-principles calculations for strong-field ionization of rare-gas atoms and autocorrelation. We introduce a machine-learning algorithm, called vector space Newton interpolation cage (VSNIC), that uses the results from the first-principles calculations as input and reconstructs from a strong-field autocorrelation pattern for an unknown pulse the pulse length and spectral width by narrow margins.

The journal of physical chemistry letters 11(3), 891 - 899 (2020). doi:10.1021/acs.jpclett.9b03517, Extreme-ultraviolet-induced charge migration in biorelevant molecules is a fundamental step in the complex path leading to photodamage. In this work we propose a simple interpretation of the charge migration recently observed in an attosecond pump–probe experiment on the amino acid tryptophan. We find that the decay of the prominent low-frequency spectral structure with increasing pump–probe delay is due to a quantum beating between two geometrically distinct, almost degenerate charge oscillations. Quantum beating is ubiquitous in these systems, and at least on the few-to-tens of femtosecond time scales, it may dominate over decoherence the line intensities of time-resolved spectra. We also address the experimentally observed phase shift in the charge oscillations of two different amino acids, tryptophan and phenylalanine. Our results indicate that a beyond mean-field treatment of the electron dynamics is necessary to reproduce the correct behavior., Published by ACS, Washington, DC

We demonstrate post-compression of 1.2 ps pulses to the few-cycle regime via multi-pass spectral broadening. We achieve compression factors of 40 via single and >90 via dual stage compression employing mJ pulses.

We report post-compression of 1.2 ps pulses into the few-cycle regime via multi-pass spectral broadening. We achieve compression factors of 40 in single and 93 in a dual stage scheme using a compact setup.

We performed angle-resolved photoelectron spectroscopy of water clusters ionized by an extreme-ultraviolet attosecond pulse train. A clean signature of the clusters was isolated from the water monomer contribution, to be used for time-resolved attosecond spectroscopy.

Nature photonics 13(2), 91 - 95 (2019). doi:10.1038/s41566-018-0308-z, A key challenge in attosecond science is the temporal characterization of attosecond pulses that are essential for understanding the evolution of electronic wavefunctions in atoms, molecules and solids. Current characterization methods, based on nonlinear light–matter interactions, are limited in terms of stability and waveform complexity. Here, we experimentally demonstrate a conceptually new linear and all-optical pulse characterization method, inspired by double-blind holography. Holography is realized by measuring the extreme ultraviolet (XUV) spectra of two unknown attosecond signals and their interference. Assuming a finite pulse duration constraint, we reconstruct the missing spectral phases and characterize the unknown signals in both isolated pulse and double pulse scenarios. This method can be implemented in a wide range of experimental realizations, enabling the study of complex electron dynamics via a single-shot and linear measurement., Published by Nature Publ. Group, London [u.a.]

In the above article [1] , the text in the box of Fig. 9(b) should report $\varepsilon$ @95% = 1.17 m rather than $\varepsilon$ @95% = 0.40 m.

In this work, we demonstrate postcompression of 1.2 ps laser pulses to 13 fs via gas-based multipass spectral broadening. Our results yield a single-stage compression factor of about 40 at 200 W in-burst average power and a total compression factor > 90 at reduced power. The employed scheme represents a route toward compact few-cycle sources driven by industrial-grade Yb:YAG lasers at high average power.

We present time-resolved ultraviolet-pump x-ray probe Auger spectra of 2-thiouracil. An ultraviolet induced shift towards higher kinetic energies is observed in the sulfur 2p Auger decay. The difference Auger spectra of pumped and unpumped molecules exhibit ultrafast dynamics in the shift amplitude, in which three phases can be recognized. In the first 100 fs, a shift towards higher kinetic energies is observed, followed by a 400 fs shift back to lower kinetic energies and a 1 ps shift again to higher kinetic energies. We use a simple Coulomb-model, aided by quantum chemical calculations of potential energy states, to deduce a C–S bond expansion within the first 100 fs. The bond elongation triggers internal conversion from the photoexcited S2 to the S1 state. Based on timescales, the subsequent dynamics can be interpreted in terms of S1 nuclear relaxation and S1-triplet internal conversion.

Hydrogen migration in the glycine cation has been investigated using a combination of a short train of attosecond extreme ultraviolet pulses with few-optical-cycle near-infrared pulses. The yield of the photofragments produced has been measured as a function of pump–probe delay. These time-dependent measurements reveal the presence of a hydrogen migration process occurring in 48 fs. Previous mass spectrometric experiments and theoretical calculations have allowed us to identify the conformations and cation states involved in the process induced by the broad band extreme ultraviolet radiation.

Optics express 26(6), 6771 - 6784 (2018). doi:10.1364/OE.26.006771, Sub-10-fs pulses tunable in the extreme-ultraviolet (XUV) spectral region are particularly important in many research fields: from atomic and molecular spectroscopy to the study of relaxation processes in solids and transition phase processes, from holography to free-electron laser injection. A crucial prerequisite for all applications is the accurate measurement of the temporal characteristics of these pulses. To fulfill this purpose, many phase retrieval algorithms have been successfully applied to reconstruct XUV attosecond pulses. Nevertheless, their extension to XUV femtosecond pulses is not trivial and has never been investigated/reported so far. We demonstrate that ultrashort XUV pulses, produced by high-order harmonic generation, spectrally filtered by a time-delay compensated monochromator, can be fully characterized, in terms of temporal intensity and phase, by employing the ptychographic reconstruction technique while other common reconstruction algorithms fail. This allows us to report on the generation and complete temporal characterization of XUV pulses with duration down to 5 fs, which constitute the shortest XUV pulse ever achieved via a time-delay compensated monochromator., Published by OSA, Washington, DC

Nature Communications 9(1), 302 (2018). doi:10.1038/s41467-017-02702-x, Coherent diffractive imaging of individual free nanoparticles has opened routes for the in situ analysis of their transient structural, optical, and electronic properties. So far, single-shot single-particle diffraction was assumed to be feasible only at extreme ultraviolet and X-ray free-electron lasers, restricting this research field to large-scale facilities. Here we demonstrate single-shot imaging of isolated helium nanodroplets using extreme ultraviolet pulses from a femtosecond-laser-driven high harmonic source. We obtain bright wide-angle scattering patterns, that allow us to uniquely identify hitherto unresolved prolate shapes of superfluid helium droplets. Our results mark the advent of single-shot gas-phase nanoscopy with lab-based short-wavelength pulses and pave the way to ultrafast coherent diffractive imaging with phase-controlled multicolor fields and attosecond pulses., Published by Nature Publishing Group UK, [London]

Attosecond pump-probe experiments performed in small molecules have allowed tracking charge dynamics in the natural time scale of electron motion. That this is also possible in biologically relevant molecules is still a matter of debate, because the large number of available nuclear degrees of freedom might destroy the coherent charge dynamics induced by the attosecond pulse. Here we investigate extreme ultraviolet-induced charge dynamics in the amino acid tryptophan. We find that, although nuclear motion and nonadiabatic effects introduce some decoherence in the moving electron wave packet, these do not significantly modify the coherence induced by the attosecond pulse during the early stages of the dynamics, at least for molecules in their equilibrium geometry. Our conclusions are based on elaborate theoretical calculations and the experimental observation of sub-4 fs dynamics, which can only be reasonably assigned to electronic motion. Hence, attosecond pump-probe spectroscopy appears as a promising approach to induce and image charge dynamics in complex molecules.

We report on single-shot coherent diffractive imaging of isolated helium nanodroplets obtained with intense multicolor XUV pulses from a high harmonic source. The wide-angle scattering patterns yield the droplets’ shapes and refractive indices.

The hitherto unexplored two-photon doubly excited states [Ne∗(2p-13s)]2 were experimentally identified using the seeded, fully coherent, intense extreme ultraviolet free-electron laser FERMI. These states undergo ultrafast interatomic Coulombic decay (ICD), which predominantly produces singly ionized dimers. In order to obtain the rate of ICD, the resulting yield of Ne2+ ions was recorded as a function of delay between the extreme ultraviolet pump and UV probe laser pulses. The extracted lifetimes of the long-lived doubly excited states, 390(-130/+450) fs, and of the short-lived ones, less than 150 fs, are in good agreement with ab initio quantum mechanical calculations.

Nature Communications, 8 (1), ISSN:2041-1723

We used isolated attosecond pulses to trigger pure electron dynamics in aromatic amino acids on a sub-4.5-fs temporal scale. Our work opens new perspectives for attosecond science, moving toward the investigation of bio-relevant systems.

We demonstrate a novel approach for the extension of self-referenced spectral interferometry to the temporal characterization of few-optical cycle pulses. The new experimental setup is characterized by low dispersion and a collinear geometry. 4-fs pulses have been characterized by performing single-shot measurements, with high dynamic range on a broad temporal region. An independent measurement of the pulse duration, obtained by using attosecond streaking, allowed us to cross-check the experimental technique.

Electron transfer is a fundamental process in biochemistry, which triggers a number of biochemical processes such as photosynthesis, cellular respiration and electron transport along DNA [1]. It has been recognized that the evolution of many biological processes is strictly related to the ultrafast time scale of the corresponding electron dynamics. With the advent of attosecond technology, it was proposed to track and control this electron dynamics in real time. Indeed, the electron dynamics occurring in a biomolecule after sudden ionization can be driven by purely electronic effects and charge migration (CM) from one end of the molecule to the other and back has been theoretically predicted to occur within a time scale ranging from few-femtoseconds down to hundreds-attoseconds [2].

Studying the interaction of molecular nitrogen with extreme ultraviolet (XUV) radiation is of prime importance to understand radiation-induced processes occurring in Earth’s upper atmosphere. In particular, photoinduced dissociation dynamics involving excited states of N2+ leads to N and N+ atomic species that are relevant in atmospheric photochemical processes. However, tracking the relaxation dynamics of highly excited states of N2+ is difficult to achieve, and its theoretical modeling is notoriously complex. Here, we report on an experimental and theoretical investigation of the dissociation dynamics of N2+ induced by isolated attosecond XUV pulses in combination with few-optical-cycle near-infrared/visible (NIR/VIS) pulses. The momentum distribution of the produced N+ fragments is measured as a function of pump-probe delay with subfemtosecond resolution using a velocity map imaging spectrometer. The time-dependent measurements reveal the presence of NIR/VIS-induced transitions between N2+ states together with an interference pattern that carries the signature of the potential energy curves activated by the XUV pulse. We show that the subfemtosecond characterization of the interference pattern is essential for a semiquantitative determination of the repulsive part of these curves, We acknowledge support from the European ResearchCouncil under ERC Grants No. 637756 STARLIGHT, No. 227355 ELYCHE, and No. 290853 XCHEM, from LASERLAB-EUROPE (Grant Agreement No. 284464,EC’s Seventh Framework Programme), from European COST Action CM1204 XLIC, the MICINN ProjectFIS2013-42002-R, the ERA-Chemistry Project PIM2010EEC-00751, the European Grant MC-ITNCORINF. Calculations were performed at the Centro deComputación of the Universidad Autónoma de Madrid(CC-UAM) and the Barcelona Supercomputing Center(BSC). G. S. acknowledges the Italian Ministry of Research Project FIRB No. RBID08CRXK. R. L. and M. H. acknowledge a Marie Curie International Research Staff Exchange Scheme Fellowship (Grant AgreementNo. PIRSES-GA-2012-31754, EC’s Seventh Framework Programme) and the COST Action CM1405 MOLIM.C. L. acknowledges National Natural Science Foundationof China (Grants No. 11127901, No. 61221064, andNo. 11404356), 973 Project (Grant No. 2011CB808103)..

We wish to understand the processes underlying the ionization dynamics of N2 as experimentally induced and studied by recording the kinetic energy release (KER) in a XUV-pump/IR-probe setup. To this end a theoretical model was developed describing the ionization process using Dyson Orbitals and, subsequently, the dissociation process using a large set of diabatic potential energy surfaces (PES) on which to propagate. From said set of PES, a small subset is extracted allowing for the identification of one and two photon processes chiefly responsible for the experimentally observed features We acknowledge support from the European Research Council under ERC Grants No. 637756 STARLIGHT, No. 227355 ELYCHE, and No. 290853 XCHEM, from LASERLAB-EUROPE (Grant Agreement No. 284464, EC’s Seventh Framework Programme), from European COST Action CM1204 XLIC, the MICINN Project FIS2013-42002-R, the ERA-Chemistry Project PIM2010EEC-00751, the European Grant MC-ITN CORINF. Calculations were performed at the Centro de Computación of the Universidad Autónoma de Madrid (CC-UAM) and the Barcelona Supercomputing Center (BSC). G. S. acknowledges the Italian Ministry of Research Project FIRB No. RBID08CRXK. R. L. and M. H. acknowledge a Marie Curie International Research Staff Exchange Scheme Fellowship (Grant Agreement No. PIRSES-GA-2012-31754, EC’s Seventh Framework Programme) and the COST Action CM1405 MOLIM. C. L. acknowledges National Natural Science Foundation of China (Grants No. 11127901, No. 61221064, and No. 11404356), 973 Project (Grant No. 2011CB808103). We are very grateful to Alicia Palacios for fruitful discussions on the ionization model

The possibility to obtain micrometric focal spot in the extreme-ultraviolet (XUV) region opens the way to XUV-XUV experiments in high-order harmonics beamlines. A beamline designed for this purpose is here presented. The peculiarity of the optical design relies on the use of only toroidal mirrors in place of the more expensive Cartesian optics. The coma aberration, usually dominating the quality of the focal spot when toroidal mirrors are used with high levels of demagnification, is compensated using mirrors in a subtractive (Z-shape) configuration. In addition, the compensating output mirror decouples the length of the exit arm from the de-magnification factor, in this way the length of the exit arm can be increased to install even a large experimental chamber. Three mirrors with optical power are required, in order to assure an optimal focalization. In order to guarantee a day-to-day reproducible working condition, the mirrors are mounted on remotely adjustable optical stages, that are controlled via a genetic algorithm with the feedback on the quality of the focal spot. This solution helps the users to reach the best focalization conditions in a reliable way. The results obtained during the beamline commissioning phase are presented. Emphasis is placed in the characterization of the spot size and in the performances of the genetic algorithm.

We report on a single-shot, in-situ interferometric method for measuring intensity-dependent phase changes in laser pulse propagation. With this method, the impact of hollow fiber compressors on phase stability was characterized.

We present a single-shot, in-situ interferometric method for measuring phase changes experienced by laser pulses upon nonlinear propagation. With this method we characterized the intensity-dependent phase fluctuations emerging in hollow fiber compressors.

The design of optical systems for micro-focusing of extreme-ultraviolet (XUV) and soft X-ray pulses through grazing-incidence toroidal mirrors is presented. Aim of the configuration here presented is to provide a micro-focused image through a high demagnification of the source with almost negligible aberrations and a long exit arm to accommodate at the output a large experimental chamber. We present the analytical and numerical study of two configurations to fulfill these requirements with two toroidal mirrors. The first mirror provides a demagnified image of the source in the intermediate plane that is free from defocusing but has a large coma aberration, the second mirror is mounted in Z-shaped geometry with respect to the previous one, in order to give a stigmatic image with a coma that is opposite to that provided by the first one. Some examples are provided to demonstrate the capability to achieve spot sizes in the 5-15 mu m range both applied to high-order laser harmonics and free-electron-laser radiation.

The ultrafast dynamics induced by photo-ionization in atoms and molecules plays an important role in a number of fundamental physical and chemical phenomena [1]. Understanding the coupling of electronic and nuclear degrees of freedom as well as the electron correlations immediately following, or accompanying, optical excitation is particularly important and requires the use of ultrafast methods [2,3].

The attosecond streak camera method is usually implemented to characterize the temporal phase and amplitude of isolated attosecond pulses produced by high-order harmonic generation. This approach, however, does not provide any information about the carrier-envelope phase of the attosecond pulses. We demonstrate that the photoelectron spectra generated by an attosecond waveform and an intense synchronized infrared field are sensitive to the electric field of the attosecond pulse. The dependence on the carrier-envelope phase of the attosecond pulse is understood in terms of the coherent superposition of two photoelectron wave packets. This effect suggests an experimentally feasible method for complete reconstruction of attosecond waveforms.

The introduction of defects in photonic lattices generally allows to control the localization and the propagation of light. While point defects are conventionally used in order to obtain localized photonic states, linear defects are introduced for waveguiding EM waves. In this work we demonstrate the possibility of obtaining localized states also in a waveguiding configuration, by using quasicrystalline lattices. This result opens a new range of possibilities in designing optical circuits, in which the localization-propagation switch is easily obtainable by mechanical or opto-electric methods.

This work presents a study of the XUV-induced ultrafast molecular dynamics of 5XU conducted with unprecedented temporal resolution. A clear dynamics occurring in 35 fs for both 5FU and 5BrU has been identified and assigned to the hydrogen migration from the C6 site to the C5 site of the molecule. Since 5XU are routinely used as radio sensitizers, the present work provides new important insights in the XUV induced structural changes responsible for the DNA breaking when these molecules are embedded in the DNA chain for radiotherapy.

Molecules in the gas-phase can be treated as isolated systems without influence from the environment. Gaining further control over the molecules, such as quantum state or conformer selection, or/and fixing the molecular axis in space, can be highly advantageous or simply necessary for a variety of experiments aiming at, for instance, probing of the molecular structure, or molecular frame dependent properties such as molecular-frame photo angular distributions.

Single-shot Self-Referenced Spectral Interferometry method, with 40-dB dynamic range, was implemented for complete temporal characterization of 4-fs, 1.9-mJ pulses. The experimental results are in excellent agreement with pulse reconstruction from streaking with isolated attosecond pulses.

Generation of few-femtosecond (fs) pulses in the ultraviolet (UV) is important in ultrafast spectroscopy since several bio-relevant molecules, including DNA bases, possess electronic transitions in this spectral region [1]. Exploiting nonlinear processes driven by intense laser pulses has led to several advances to meet this challenge. We developed a source delivering 1.9 fs (2.2 cycles at 255 nm) deep-UV pulses with 150 nJ of energy on target [2].

Electron transfer within a single molecule is the fundamental step of many biological processes and chemical reactions. It plays a crucial role in catalysis, DNA damage by ionizing radiation, photosynthesis, photovoltaics, and for switches based on molecular nano-junctions. The investigation of this process has been the subject of considerable research effort [1-2]. In this work we present the first direct measurement of ultrafast charge migration in a biomolecular building block, the amino acid phenylalanine, using attosecond pulses [3]. Clean plumes of isolated, neutral molecules were produced by laser induced acoustic desorption (LIAD] technique [4]. Phenylalanine molecules were irradiated by a short train of attosecond pulses produced by high-order harmonic generation in Xenon (the train was composed by two attosecond pulses], with a photon energy in the range 16-40 eV, followed at a variable temporal delay by a 6-fs visible/near infrared (500-950 nm, VIS/NIR} probe pulse. The parent and fragment ions produced were then extracted into a linear time of flight device for mass analysis. Figures l(a]-(b] showthe mass spectra obtained individually from the XUV and VIS/NIR pulses. © 2013 IEEE.

We investigated the ultrafast charge-migration in the amino-acid phenylalanine. By measuring the yield of a doubly-charged ion vs. delay between a 1.5-fs XUV pulce and a 6-fs pulse, a 30-fs charge migration process was measured.

Summary form only given. The design of optical systems for micro-focusing of extreme-ultraviolet (XUV) attosecond pulses through grazing-incidence toroidal mirrors is presented. Aim of the configuration is to provide a micro-focused image through a high demagnification M of the XUV source (i.e. M > 10), with almost negligible aberrations.Toroidal mirrors are a cheaper alternative to the use of more expensive Cartesian surfaces (ellipsoidal and paraboloidal), but they give high residual aberrations especially when used to give high demagnification [1]. Furthermore, a configuration with high demagnification using a single mirror has the drawback of the short exit arm q: in fact, once the entrance arm p has been fixed, the higher the demagnification the shorter the exit arm, since q = p/M. The small space available at the exit may be insufficient to accommodate the experimental set-up, therefore an additional mirror to realize a relay section with a suitable length of the exit arm may be required. In addition to this, in case of XUV pump-probe experiments, the beam has to be split in two delayed sections through a plane split-mirror working in parallel beam; this requires to replace the first mirror with a section with a collimating mirror to provide the parallel beam and a condenser mirror to focus and demagnify the two delayed beams. We present two configurations that fulfill these requirements. 1) C1 consists of two mirrors: M1 provides the high demagnification and M2 is the relay section that is required to increase the length of the exit arm. 2) C2 consists of three mirrors: M1 and M2 provide the collimating-focusing section and M3 is the relay section. Both configurations provide a micro-focused image of the XUV attosecond source and a suitable length of the exit arm. Furthermore, C2 provides an intermediate sector with parallel beam where a plane split-mirror may be mounted for XUV pump-probe experiments. The configurations are schematically shown in Fig. 1.The analytical and numerical study of the configurations is discussed. In both cases, the first section provides a stigmatic image of the source in the intermediate plane, that is free from defocusing but has a large third-order aberration, namely coma, due to the high demagnification. The relay mirror is mounted in Z-shaped geometry with respect to the previous one, so that it gives a stigmatic image with a coma that is opposite to that provided by the first section [2]. The mirror geometrical parameters (i.e. the incidence angle and the ratio between its entrance and exit arms) are calculated to give an image that is almost coma-free, since the coma of the second section compensates almost completely for the coma of the first one. Some examples are provided to demonstrate the capability to achieve spot sizes in the 5-15 μm range with a demagnification higher than 10. Finally, the effects of the residual aberrations given by the toroidal mirrors on the sub-femtosecond pulse duration are discussed.

We used velocity-map imaging to measure ultrafast electron dynamics in N 2 initiated by attosecond pulses. A time-to-space mapping of autoionization channel is demonstrated. A sub-cycle oscillatory dynamics related to quantum interference is also observed.

4-fs, 1.9-mJ, pulses measurement with 40dB dynamic on +/- 500-fs temporal range was implemented by single-shot Self-Referenced Spectral Interferometry method. The experimental results agree well with pulse reconstruction from streaking with isolated attosecond pulses.

We investigated the attosecond electronic collisional dynamics in a dielectric nanomaterial, which are of primary importance to fully understand the transport properties in future dielectric-electronic devices with up to petahertz switching speeds.