Search

We demonstrate the spatial separation of a considerable portion of the XUV from the fundamental IR driving beam in high-order harmonic generation by an integrated system of microchannels realized through Femtosecond Laser Micromachining. © 2020 The Author(s)

We describe the implementation of nonlinear time-domain spectroscopy of rotovibrational IR-active modes in methane through broadband Four-Wave Mixing driven by resonant high-energy mid infrared laser pulses. At high driving pulse intensities we observe an efficient vibrational ladder climbing triggered in the molecules. This study opens the possibility to impulsively and selectively excite molecules of biological interest to high-lying vibrational states and to characterize their dynamics.

We report on the application of femtosecond laser micromachining to the fabrication of complex glass microdevices, for high-order harmonic generation in gas. The three-dimensional capabilities and extreme flexibility of femtosecond laser micromachining allow us to achieve accurate control of gas density inside the micrometer interaction channel. This device gives a considerable increase in harmonics&rsquo, generation efficiency if compared with traditional harmonic generation in gas jets. We propose different chip geometries that allow the control of the gas density and driving field intensity inside the interaction channel to achieve quasi phase-matching conditions in the harmonic generation process. We believe that these glass micro-devices will pave the way to future downscaling of high-order harmonic generation beamlines.

We report efficient high harmonic generation and control in glass devices fabricated by femtosecond laser micromachining. This work paves the way to microfluidic HHG beamlines for X-ray spectroscopy with attosecond resolution.

Synopsis We present a high-energy mid-infrared optical parametric amplifier source tunable between 2.8 and 3.8 μm for strong-field applications. We exploited this source in combination with a 800 nm source for generating high-order harmonics in atoms and molecules in a two-color pulse scheme.

We report on the efficient excitation of high-lying rovibrational states in methane by a high-energy mid-IR source and on the time-domain study of the induced dynamics.

We investigate high-order harmonic generation (HHG) in ZnTe crystals driven by a mid-IR optical parametric amplifier as a function of the angle between the polarization direction of the driving laser field and the crystal axis.

We measured the chiral relaxation of photoexcited Fenchone at the Carbon K-edge. Our results demonstrate that ultrafast chiral dynamics can be probed using core level spectroscopy with circularly polarized free-electron laser pulses.

We generated high-order harmonics in ZnTe crystal driven by a mid-IR optical parametric amplifier. The dependence of the harmonic signal as a function of the crystal orientation is investigated and interpreted within the re-collision framework.

We demonstrate efficient high-order harmonic generation in fused-silica chips fabricated by femtosecond laser micromachining. This work provides a route toward the miniaturization of HHG beamlines and the implementation of X-ray spectroscopy with attosecond temporal resolution.

We report efficient high harmonic generation and control in glass chips fabricated by femtosecond laser micromachining. This work paves the way for the implementation of microfluidic HHG beamlines for X-ray spectroscopy with attosecond resolution.

We demonstrate efficient high-order harmonic generation in fused-silica chips fabricated by femtosecond laser micromachining. This work provides a route toward the miniaturization of HHG beamlines and the implementation of X-ray spectroscopy with attosecond temporal resolution.

We present a robust, three-stage optical parametric amplifier driven by a Ti:Sapphire ultrafast laser system that implements passive carrier-envelope phase stabilization and directly generates five-cycle mid-IR pulses by dispersion compensation. The source is based on potassium titanyl arsenate crystals and exploits intra-pulse difference-frequency seed generation in the mid-IR. This source will be particularly suited for applications in strong-field physics, such as high order harmonic generation and photoelectron spectroscopy.

We report on the implementation of time-domain spectroscopy through broadband Four-Wave Mixing in the study of roto-vibrational excitation of hydrocarbons by resonant high-energy mid-IR pulses.

One way to increase the well known low efficiency of high order harmonics generation is to place the gas medium in a hollow core waveguide. The numerical model used to obtain driving and harmonics field configuration along and across the waveguide was developed for an arbitrary gas density profile and arbitrary fiber diameter modulation. The model was tested against experimental measurements and excellent agreement was obtained for the fluorescence emission along the waveguide. We analyse the influence of the diameter modulation which result from the fabrication process on both pulse propagation and on harmonic generation.

Since the first observation of High-order Harmonic Generation (HHG) in gas twenty years ago, the combination of intense research together with technological developments, has led to impressive progress in the field of extreme ultraviolet spectroscopy and attosecond science. Beam lines based on HHG extend over several meters and are based on instrumentation that requires careful alignment and even active stabilization systems. Therefore, a miniaturization of HHG beams will reduce the cost of these light sources and pave the way to their application in numerous new fields. Femtosecond laser micromachining followed by chemical etching (FLICE) has already demonstrated its high potential in the fabrication of fused silica lab-on-a-chip devices; it can directly produce microfluidic networks in a 3D geometry directly buried in the glass substrate. Until now, they have been extensively used for the manipulation of fluids but they are perfectly suitable for the manipulation of gas as well. In this work, we will demonstrate HHG in a gas filled microchannel network fabricated by the FLICE technique. The device structure will be based on hollow waveguides: several inlets will deliver the gas into a central hollow waveguide where the ultrafast laser will be coupled and HHG will take place. The high versatility of the FLICE technique will allow us to fabricate devices with modulated gas concentration and waveguide profile to achieve quasi-phase-matching conditions. Moreover, we will also demonstrate an integrated filtering chip that will allow to geometrically separate the main laser radiation from the XUV generated beam.

We exploit high-order harmonic generation spectroscopy at the caustics of the recombining electron wave-packet as a method for directly comparing experimental spectra with ab-initio theories. Experimental results in xenon and comparison with ab-initio time-dependent configuration-interaction singles calculations allowed to assess the role of the wave-packet enhancement during the giant resonance. Results in argon show that this technique can also be applied to other targets.

We present a tunable, Ti:Sa-pumped mid-IR OPA with CEP-stable, few-cycle output. The pulses are compressed in bulk, resulting in 56.5-fs, 300-µJ pulses at 3.4 micron with 308 mrad CEP noise.

Since the first observation of High-order Harmonic Generation (HHG) in gas twenty years ago, the combination of intense research together with technological developments, has led to impressive progress in the field of extreme ultraviolet spectroscopy and attosecond science. Beam lines based on HHG extend over several meters and are based on instrumentation that requires careful alignment and even active stabilization systems. Therefore, a miniaturization of HHG beams will reduce the cost of these light sources and pave the way to their application in numerous new fields. Femtosecond laser micromachining followed by chemical etching (FLICE) has already demonstrated its high potential in the fabrication of fused silica lab-on-a-chip devices; it can directly produce microfluidic networks in a 3D geometry directly buried in the glass substrate. Until now, they have been extensively used for the manipulation of fluids but they are perfectly suitable for the manipulation of gas as well. In this work, we will demonstrate HHG in a gas filled microchannel network fabricated by the FLICE technique. The device structure will be based on hollow waveguides: several inlets will deliver the gas into a central hollow waveguide where the ultrafast laser will be coupled and HHG will take place. The high versatility of the FLICE technique will allow us to fabricate devices with modulated gas concentration and waveguide profile to achieve quasi-phase-matching conditions. Moreover, we will also demonstrate an integrated filtering chip that will allow to geometrically separate the main laser radiation from the XUV generated beam.

We demonstrate the generation of high-order harmonics in a fused-silica device fabricated through femtosecond laser micromachining. This achievement paves the way for the miniaturization of HHG applications from large-scale laboratories to microstructures.

The use of fast closed-loop adaptive optics has improved the performance of optical systems since its first application. Here we demonstrate the amplitude and carrier-envelope phase stabilization of a high energy IR optical parametric amplifier devoted to Attosecond Science exploiting two high speed adaptive optical systems for the correction of static and dynamic instabilities. The exploitation of multi actuator adaptive lenses allowed for a minimal impact on the optical setup.

We demonstrate the experimental realization of impulsive alignment of carbonyl sulfide (OCS) molecules at the Low Density Matter Beamline (LDM) at the free-electron laser FERMI. OCS molecules in a molecular beam were impulsively aligned using 200 fs pulses from a near-infrared laser. The alignment was probed through time-delayed ionization above the sulphur 2p edge, resulting in multiple ionization via Auger decay and subsequent Coulomb explosion of the molecules. The ionic fragments were collected using a time-of-flight mass spectrometer and the analysis of ion-ion covariance maps confirmed the correlation between fragments after Coulomb explosion. The analysis of the CO+ and S+ channels allowed us to extract the rotational dynamics, which is in agreement with our theoretical description as well as with previous experiments. This result opens the way for a new class of experiments at LDM within the field of coherent control of molecules with the possibilities that a precisely synchronized optical-pump XUV-probe laser setup like FERMI can offer., Comment: 7 pages, 6 figures

High-order harmonic generation is a nonlinear effect appearing when atoms or molecules are exposed to intense laser pulses. It consists in the emission of ultrashort bursts of extreme ultraviolet and soft X radiation, giving rise to harmonics in the spectral domain. This emission encodes a wealth of information about the intimate structure of the targeted species, allowing the reconstruction of the outermost distribution of electrons. We will review here the most important aspects of high-order harmonic generation and we will show how this process can be applied to the reconstruction of molecular orbitals. A critical analysis will illustrate benefits, weaknesses and perspectives of this technique.

We demonstrate the generation of high-order harmonics in a fused-silica chip produced by femtosecond laser micromachining. This achievement paves the way to the miniaturization of HHG applications from large-scale laboratories to microdevices.

We report on the first application of adaptive deformable lenses to the stabilization of a high-energy mid-IR parametric source. Fluctuations of output pulse intensity and CEP were significantly suppressed by the adaptive optics system.

Adaptive Optics (AO) is a key technology for ground-based astronomical telescopes, allowing to overcome the limits imposed by atmospheric turbulence and obtain high resolution images. This technique however, has not been developed for small size telescopes, because of its high cost and complexity. We realized an AO system based on a Multi-actuator Adaptive Lens and a Shack-Hartmann wavefront sensor (WFS), allowing for a great compactness and simplification of the optical design. The system was integrated on a 11” telescope and controlled by a consumer-grade laptop allowing to perform Closed-Loop AO correction up to 400 Hz.

Spectral focusing of the recolliding electron in high-order harmonic generation driven by two-color fields is shown to be a powerful tool for isolating and enhancing hidden spectral features of the target under study. In previous works we used this technique for probing multi-electron effects in xenon and we compared our experimental results with time-dependent configuration-interaction singles calculations. We demonstrate here that this technique can be exploited for reconstructing the enhancement factor of the xenon giant dipole resonance and we discuss the sensitivity of this method to macroscopic effects. We then extend the technique to argon in order to test the applicability of this procedure to other targets.

We demonstrate amplitude and carrier-envelope phase stabilization of a high energy IR optical parametric amplifier designed for Attosecond Science exploiting two high speed adaptive optical systems based on multi actuator adaptive lenses.

Intense ultrafast laser sources in the mid-IR have attracted in the recent years lot of attention in strong-field physics. A possible implementation for such sources relies in: a) the generation of a short IR seed by intra-pulse difference frequency generation (DFG) of a broadband continuum generated in an hollow-core fiber (HCF); b) optical parametric amplification (OPA) of the seed to the mJ level [1]. This approach yields a major advantage, namely the passive stabilization of the carrier-envelope phase (CEP) owing to the DFG process, enabling applications like the generation of isolated attosecond pulses in the soft X-rays. Nevertheless the CEP stability performances are limited with respect to those achievable with active stabilization techniques. Moreover, OPA setups require a very good beam quality as well as a robust stability of the pumping source and this can hinder the scalability towards higher pulse energies.

Over the last few decades, the investigation of ultrafast phenomena occurring in atoms, molecules and solid-state systems under a strong-field regime of light-matter interaction has attracted great attention. The increasing request for a suitable optical technology is significantly boosting the development of powerful ultrafast laser sources. In this framework, Optical Parametric Amplification (OPA) is currently becoming a leading solution for applications in high-power ultra-broadband light burst generation. The main advantage provided by the OPA scheme consists of the possibility of exploring spectral ranges that are inaccessible by other laser technologies, as the InfraRed (IR) window. In this paper, we will give an overview on recent progress in the development of high-power few-optical-cycle parametric amplifiers in the near-IR and in the mid-IR spectral domain. In particular, the design of the most advanced OPA implementations is provided, containing a discussion on the key technical aspects. In addition, a review on their application to the study of strong-field ultrafast physical processes is reported.

We investigated the giant resonance in Xenon by high-order harmonic generation spectroscopy driven by a two-color field. The addition of a non-perturbative second harmonic component parallel to the driving field breaks the symmetry between neighboring sub-cycles resulting in the appearance of spectral caustics at two distinct cut-off energies. By controlling the phase delay between the two color components it is possible to tailor the harmonic emission in order to amplify and isolate the spectral feature of interest. In this paper we demonstrate how this control scheme can be used to investigate the role of electron correlations that give birth to the giant resonance in Xenon. The collective excitations of the giant dipole resonance in Xenon combined with the spectral manipulation associated with the two color driving field allow to see features that are normally not accessible and to obtain a quantitative good agreement between the experimental results and the theoretical predictions.

We studied the dependence of harmonic signal on the ellipticity of the driving field in xenon. We were able to observe trajectories beyond the classical cutoff and interpret the results in the strong-field approximation picture.

We probed the electronic structure of xenon by two-color high-order harmonic spectroscopy. We were able to identify the contribution of electron correlations in the spectral region corresponding to the giant resonance.

Escaping from a complex maze, by exploring different paths with several decision-making branches in order to reach the exit, has always been a very challenging and fascinating task. Wave field and quantum objects may explore a complex structure in parallel by interference effects, but without necessarily leading to more efficient transport. Here, inspired by recent observations in biological energy transport phenomena, we demonstrate how a quantum walker can efficiently reach the output of a maze by partially suppressing the presence of interference. In particular, we show theoretically an unprecedented improvement in transport efficiency for increasing maze size with respect to purely quantum and classical approaches. In addition, we investigate experimentally these hybrid transport phenomena, by mapping the maze problem in an integrated waveguide array, probed by coherent light, hence successfully testing our theoretical results. These achievements may lead towards future bio-inspired photonics technologies for more efficient transport and computation., Studying quantum transport in biological systems is difficult so developing an artificial platform that can be used to understand quantum transport is desirable. Here, Caruso, et al. demonstrate how a quantum walker can quickly reach the output of a maze by partially suppressing the presence of interference.

High order harmonic generation (HHG) has shown its impact on several applications in Attosecond Science and Atomic and Molecular Physics. Owing to the complexity of the experimental setup for the generation and characterization of harmonics, as well as to the large computational costs of numerical modelling, HHG is generally performed and modelled in collinear geometry. Recently, several experiments have been performed exploiting non-collinear geometry, such as HHG in a grating of excited molecules created by crossing beams. In such studies, harmonics were observed at propagation directions different from those of the driving pulses; moreover the scattered harmonics were angularly dispersed. In this work we report on a new regime of HHG driven by multiple beams, where the harmonics are generated by three synchronized, intense laser pulses organized in a non-planar geometry. Although the configuration we explore is well within the strong-field regime, the scattered harmonics we observe are not angularly dispersed.

The aim of this study is probing the multi-electron behavior in xenon by two-color driven high harmonic generation. By changing the relative polarization of the two colors we were able to study different aspects of the multi-electron response.

We demonstrate the generation of high-order harmonics in a fused-silica chip produced by femtosecond laser micromachining. This achievement paves the way for the miniaturization of HHG applications from large-scale laboratories to microstructures.

We report on the efficient generation of high-order harmonics in helium gas inside complex glass micro-devices fabricated by femtosecond laser micromachining. By exploiting the three-dimensional capabilities and extreme flexibility of this fabrication technique we developed fluidic micro-structures in a fused-silica substrate that allowed us to achieve accurate control of the gas density inside a micrometer-sized microchannel. As a result, we achieved a broadband spectrum of extreme ultraviolet (XUV) radiation which extends up to 200 eV and we observed a considerable increase in the harmonics generation efficiency if compared with traditional harmonic generation in gas jets. We foresee that the application of femosecond-laser-micromachined glass devices to high-order harmonics generation can be extended to more complex on-chip systems including different functionalities, thus opening the possibility to future miniaturization of XUV and Attosecond beamlines.