Intense and short soft X-ray light pulses offer unprecedented possibilities for studying ultrafast phenomena in matter at the nanometer scale. Plasma-based soft X-ray lasers (SXRLs) have the advantage of being compact sources. We report recent achievement aiming to demonstrate the control and reduction of duration of a seeded collisional soft X- ray laser induced by the anticipated interruption of the gain lifetime at high densities. By controlling the peak intensity velocity of an ultrashort beam by spatio-temporal couplings we improve the performances of a seeded soft X-ray laser (SXRL), which intrinsically suffers from the group velocity (vg) mismatch between the infrared pump beam used to generate the plasma amplifier and the XUV seed. The energy extraction was measured to raise from 19 to 59% when the pump vg ranges from 0.55c to 1.05c. We also demonstrate that the SXRL pulse duration is governed by the pump beam velocity and can be maintained constant along its propagation, resulting in energetic pulses as short as 450 fs. The measurements, in good agreement with simulations from a 3D Maxwell-Bloch code, have been performed thanks to an original method allowing to recover the temporal profile of any kind of soft X-ray laser pulse in single-shot operation.

The coherence of EUV radiation is extremely important for many experiments based on diffraction or interference and thus knowledge of coherence degree is one of the key parameter of all real partially coherent sources. We present a single shot method based on evaluation of far field diffraction pattern from specially designed diffraction masks. Several measurements of a beam of Ne-like Zn X-ray laser were performed with 1D and 2D masks showing an expected pattern of degree of coherence for this type of source.

Microscopy at extreme ultraviolet (EUV) wavelengths has the potential to transform nanotechnology and materials science. The short wavelengths allow for high resolution, while absorption edges in the EUV range enable element-selective imaging. Because of the complexity of imaging optics at EUV wavelengths, lensless coherent diffractive imaging methods are particularly attractive. Compact and fully coherent EUV sources based on high-harmonic generation (HHG), combined with powerful lensless imaging techniques such as ptychography, form the main ingredients for table-top-scale EUV imaging systems. Ptychography is a particularly powerful concept, based on coherent diffractive imaging combined with translational diversity. It has been shown to allow for wavelength-scale-resolution imaging, and has the unique ability to provide images of both the object under study and the incident light field used for imaging. As such, ptychography can be used as an imaging method, but also as a wavefront sensing technique with unparalleled resolution and sensitivity. Importantly, ptychography allows multiplexed imaging, using for instance beams at multiple wavelengths in parallel. We have used both the imaging and wavefront sensing capabilities of ptychography, using multi-wavelength HHG beams as the light source. Through ptychographic wavefront sensing, we have characterized HHG wavefronts in unprecedented detail, allowing measurements of intrinsic chromatic aberration arising from the HHG process itself, and enabling us to identify how wavefront aberrations are transferred from the fundamental beam to the harmonics. Furthermore, I will present our recent results on ptychographic EUV imaging of complex nanostructures, and the future applications enabled by this work.

We report on upgrades and applications of a versatile and powerful XUV source based on high harmonic generation (HHG) in gases and solids. Our pursuit for better phase-matched, wavelength-tunable and monochromatic XUV source resulted in various methods that take advantage of medium-tailoring by electrical discharges, non-linear crystals phase-matching and IR beam spatial shaping of Gauss-Bessel beams. We have resolved issues with nonlinear propagation effects in long media and monochromatization that alters the XUV wavefront significantly. Such achievements make part of the new capabilities of the HHG beamlines available to users.

ELI Beamlines is a large European laser facility housing state-of-the-art high power lasers that drive secondary sources of photons and charged particles for user applications. The MAC end-station at ELI Beamlines is a Multipurpose station for AMO (atomic, molecular and optical sciences) and CDI (coherent diffractive imaging). It is designed for investigations of ultrafast dynamics in low-density targets (atoms, molecules or nanostructures) employing fs-synchronized EUV and NIR/Vis beams. In this contribution, we introduce experimental capabilities of the MAC station, show few resent scientific outcomes, discuss ongoing user projects and access procedure for the user-community.

High-harmonic generation (HHG) in gaseous media is a workhorse tool in attosecond science. Its description originates from the microscopic scale of a single atom or molecule interacting with a driving IR-laser pulse. A complete macroscopic picture corresponding to usual experimental realizations aggregates all the microscopic emitters and brings novel physical mechanisms that drive the generation. One of the key mechanisms within the macroscopic scale is the shaping of the driving pulse due to the non-linear response of the medium. We present a comprehensive numerical model describing and coupling the physics on both scales. The model consists of different modules that provide different levels of approximation to choose an optimal trade-off between accuracy and computational cost. We then use it to address two generation schemes, for which we provide a detailed picture together with experimental realizations. The first scheme uses a long medium homogeneously pre-ionized by an electrical discharge to optimize the phase-matching of the harmonic signal. This scheme allows, in particular, for optimizing HHG in long media where the control is difficult because the driving pulse undergoes strong re-shaping and defocusing due to the non-linear response after the entrance to the medium. The second scheme is based on the driving-pulse-wavefront shaping that is imprinted in the HHG beam and used to control the harmonic-beam divergence. This mechanism is harmonic dependent and may provide a tunable spectral filter of the harmonic spectrum. The proposed scheme is optics-free and dodges unavoidable losses inherent to the use of optics in the XUV region.

High-order harmonic generation (HHG) is a tabletop source of VUV radiation with many applications limited by a necessity for a specific photon energy and a monochromatized spectrum. The approach of using grating monochromators is not applicable for photon-hungry applications due to the high losses and pulse lengthening. We present experimental results of a wavelength-tunable monochromatic HHG source developed to tackle this challenge. We demonstrate this method using the L1 Allegra broadband OPCPA laser system at ELI-Beamlines and its conversion to UV used to pump the HHG.

High-order harmonic generation (HHG) is an instrumental process enabling the transfer of short infrared pulse coherence properties into the Extreme Ultraviolet (EUV) spectral range. This phenomenon has opened the way to ultrafast pump-probe experiments at the nanoscale level. Recently, HHG has provided a straightforward approach to frequency upconvert beams structured in their phase and/or polarization. An emblematic example is the optical vortex beam, which is characterized by an azimuthally twisting wavefront. From a fundamental point of view, such a beam exhibits a phase singularity on the propagation axis and is carrying orbital angular momentum (OAM). Vector beams denote another structured beam family, exhibiting a spatially varying polarization. In this paper, we will present our recent results on the generation and characterization of EUV vortex beams exhibiting very high topological charges (up to 100). Besides, using a similar HHG up-conversion scheme, we will show the production of so-called EUV vector-vortex beams that present the combined characteristics of the vortex and vector beams. Finally, progress on plasma-based soft x-ray laser amplification of such structured beams will be outlined,

In recent years laser-plasma based accelerators have provided access to GeV electron energies within laboratory scale facilities. This has opened many new research avenues, one of which focuses on the application of the ultrafast (few femtoseconds) X-ray source that is generated by the electron oscillations. A key strength of the X-ray source is its smooth broadband nature which makes it perfect for X-ray absorption spectroscopy; these measurements provide a wealth of information about the structure and state of a sample. XANES (X-ray Absorption Near Edge Structure) and EXAFS (Extended X-ray Absorption Fine Structure) in particular, provide a simultaneous measurement of the temperature and structure of both the electronic and ionic distributions. These techniques have been used with great success over the last few decades at synchrotron facilities worldwide, however, these large-scale facilities are relatively costly to construct, and beamtime slots are highly competitive and generally have a short timeframe. We present high-resolution single-shot K-edge XANES and EXAFS measurements of copper samples from recent experiments using a laser-wakefield accelerator at the laboratory-scale Gemini laser facility (building upon results of [1]). Up to 106 photons/eV per shot at 9 keV were measured. We demonstrate that this source is capable of single-shot simultaneous measurements of both the electron and ion distributions in matter heated to eV temperatures. The unique combination of a high-flux, large bandwidth, few femtosecond duration x-ray pulse synchronised to a high-power laser will enable key advances in the study of ultrafast energetic processes such as electron-ion equilibration and non-thermal phase transitions. Additionally, the development of this laser-plasma accelerator X-ray source will enable high quality laboratory scale XAS facilities to be realised. References [1] B. Kettle et al. “Single-shot multi-keV X-ray absorption spectroscopy using an ultrashort laser-wakefield accelerator source”, Phys. Rev. Lett. 123, 254801, (2019).

Secondary radiation sources using compact laser plasma accelerators, including narrow bandwidth Thomson gamma ray, femtosecond betatron X-rays, and novel x-ray free-electron lasers, have broad scientific and societal applications. The Thomson gamma ray source up to MeV photon energies developed at the Hundred Terawatt (HTW) line of BELLA Center has been applied in recent experiments like 3D gamma tomography and 3D single view gamma lidar, allowing us to gain insight into its application capabilities ranging from spatial resolution, penetration depth, and single-shot acquisition viability. Recent upgrades on the laser system will be presented in context of accelerator and photon source improvements, such as active laser stabilization, laser mode improvements with a deformable mirror, and temporal shaping concepts.

Ultrafast high-brightness X-ray pulses have proven invaluable for a broad range of research. Such pulses are typically generated via synchrotron emission from relativistic electron bunches using large-scale facilities. Recently, significantly more compact X-ray sources based on laser-wakefield accelerated (LWFA) electron beams have been demonstrated. In particular, laser-driven betatron sources, where the radiation is generated by transverse oscillations of electrons within the plasma accelerator structure can generate highly-brilliant ultrashort X-ray pulses using a comparably simple setup. Here, we present experimental and simulation data that demonstrate significant enhancement of and control over the parameters of LWFA-driven betatron X-ray emission. With our novel Transverse Oscillating Bubble Enhanced Betatron Radiation (TOBER) scheme, we show a significant increase in the number of generated photons by specifically manipulating the amplitude of the betatron oscillations. We realize this through an orchestrated evolution of the temporal laser pulse shape and the accelerating plasma structure. This leads to controlled off-axis injection of electrons that perform large-amplitude collective transverse betatron oscillations, resulting in increased radiation emission. Our concept holds the promise for a method to optimize the X-ray parameters for specific applications, such as time-resolved investigations with spatial and temporal atomic resolution or advanced high-resolution imaging modalities, and the generation of X-ray beams with even higher peak and average brightness.

This conference presentation was prepared for SPIE Optics + Optoelectronics, 2023.

Laser-based mass spectrometry techniques allow one to spatially resolve and analyze the molecular, elemental, or isotopic signatures in a solid at a lateral spatial resolution dictated by the laser’s spot size. Typically, UV/Vis/IR wavelength lasers are used with mass spectrometers to map signatures in a solid, but their lateral spatial resolution is limited to ≥1 µm. Short-wavelength lasers in the EUV regime bring new opportunities to laser-based mass spectrometry methods by realizing nanoscale (≤100 nm) ablation due to their high absorptivity in materials (i.e., 10’s of nanometers) as well as their ability to efficiently ionize the removed material in their laser-created plasmas. In this talk, we will discuss how we are using an EUV laser, operating at a wavelength of 46.9 nm, for material ablation and ionization with a time-of-flight mass spectrometer to map isotopic information down to the nanoscale in nuclear and geologic materials. We will also discuss how we are working towards expanding the use of the EUV laser by connecting it to a more sensitive mass spectrometer so that nanoscale analyses can be realized with increased precision and accuracy.

The recent advances in the development and application of laser plasma sources of X-rays and extreme ultraviolet (EUV) based on a double-stream gas puff target are presented. The targets are formed by a system of two solenoid gas valves equipped with a double nozzle setup. Soft X-ray and EUV radiation is emitted from the plasma created by irradiating the gas puff target with a nanosecond laser pulse from the Nd:YAG laser. The results of recent work on the improvement of source parameters and their use in absorption spectroscopy, coherence tomography and plasma studies are presented.

A compact tabletop plasma X-ray source (PXS) generating hard X-ray radiation in the energy range between 3 keV and 30 keV has been installed and commissioned at ELI beamlines, experimental hall E1, utilizing ELI’s high repetition-rate / high pulse-energy fs-laser system L1. Together with the TREX endstation IR-pump / X-ray-probe stroboscopic approaches to time-resolved studies can be conducted.

This conference presentation was prepared for SPIE Optics + Optoelectronics, 2023.

A plasma mirror is an over-dense plasma, created on the surface of a solid target ionized by a high-contrast femtosecond laser. It nonlinearly reflects an ultra-intense laser, resulting in surface high-harmonic generation (SHHG). At relativistic driving intensities, SHHG is a promising candidate for generating intense attosecond pulses, spanning the optical to the EUV spectral ranges. I will present our recent work on the development of such a source, driven by a waveform-controlled 1.5-cycle (< 4 fs, 780 nm) terawatt laser at 1-kHz repetition rate with extremely high temporal contrast. It allows fine control of the plasma density gradient, maximising the efficiency and spectral extent of relativistic SHHG. At optimal driving laser carrier-envelope-phase (CEP), the SHHG-emission is spectrally continuous and reaches beyond 30eV photon energy. This is the first demonstration of controlled and stable generation of such SHHG continua supporting powerful isolated attosecond pulses. Particle-in-cell simulations predict this emission to be compressed to a sub-femtosecond field transient even without any spectral filtering. We will discuss the experimental challenges related to re-focusing these to high intensity. Simultaneously and precisely synchronized with the light, MeV-kinetic-energy electron bunches are emitted through vacuum-laser acceleration. Their simultaneously measured spatio-spectral properties also carry clear CEP signatures.

We report on the measurement of XUV harmonic spectra between 53nm and 17nm wavelength emitted from solid targets driven by a short pulse (30fs FWHM) PW laser with peak intensity up to 6 x 10^21 W/cm2. Experiments were carried with a variety of target materials (metal foils, plastic foils, glass substrates), thicknesses (tens of nm to micron range) and laser parameters. This allowed us to study the influence of these parameters on the harmonic emission and gain insight into the interaction of the pump laser with the target front surface, where most of the energy absorption takes place. We explore the correlation between the dynamics on this target region and the proton acceleration from the laser target interaction by complementing the XUV spectrum measurements with simultaneous proton spectra for the different aforementioned conditions.

This conference presentation was prepared for SPIE Optics + Optoelectronics, 2023.

This conference presentation was prepared for SPIE Optics + Optoelectronics, 2023.

This conference presentation was prepared for SPIE Optics + Optoelectronics, 2023.

This conference presentation was prepared for SPIE Optics + Optoelectronics, 2023.