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Advancements in light engineering have led to the creation of pulsed laser sources capable of delivering high-repetition-rate, high-power few-cycle laser pulses across a wide spectral range, enabling exploration of many fascinating nonlinear processes occurring in all states of matter. High-harmonic generation, one such process, which converts the low-frequency photons of the driver laser field into soft x-rays, has revolutionized atomic, molecular, and optical physics, leading to progress in attosecond science and ultrafast optoelectronics. The Extreme Light Infrastructure, Attosecond Light Pulse Source (ELI ALPS) facility pioneers state-of-the-art tools for research in these areas. This paper outlines the design rationale, capabilities, and applications of plasma- and gas-based high-repetition-rate (1 kHz to 100 kHz) attosecond extreme ultraviolet (XUV) beamlines developed at ELI ALPS, highlighting their potential for advancing various research fields.

Al-doped ZnO (AZO) thin films were deposited on p-Si (100) by pulsed laser deposition from a composite ceramic target (ZnO:Al₂O₃) by using 355 nm laser at different O₂ background pressure and substrate temperature. Upon ablation at laser fluence of 2 Jcm⁻², plasma plume consists of Zn neutrals and ions, Al neutrals and O neutral are formed. As the O₂ background pressure increases from 3 Pa to 26 Pa, the energy of the plasma species are moderated. The results show that the ions density and velocity reduced significantly above 13 Pa. The velocity of the ions reduced from 14 kms⁻¹ to 11 kms⁻¹ at 13 Pa, while the ions energy reduced from 63 eV to 42 eV respectively. Below 13 Pa, crystalline and homogeneous AZO nanostructured films were formed. Above 13 Pa, the process results in low crystallinity films with higher porosity. The resistivity of the films also increases from 0.1 ohmcm to 24 ohmcm as the pressure increased. At fixed O₂ background pressure of 3 Pa, the adatom mobility of atoms on the substrates is altered by substrate heating. The resistivity of the films decreased to 10^–3 ohmcm when the substrates are heated to 100 °C–300 °C during deposition. The films with highest carrier density of 10²⁰ cm⁻³ and carrier mobility of 13 cmV⁻¹ s⁻¹ are achieved at 200 °C.

FemtoLux 3 laser was used as an illumination source in the wide-field second harmonic generation (SHG) microscope. Relatively high laser pulse energy at a medium pulse repetition frequency allowed for a faster single image acquisition compared to that using laser-scanning. It was also possible to acquire images of relatively large sample areas, which paved the way for the rapid imaging of macroscopic sample areas with microscopic resolution.

The black body remains the most prominent source of light for absolute radiometry. Its main alternative, synchrotron radiation, requires costly and large facilities. Quantum optics offers a new radiometric source: parametric down-conversion (PDC), a nonlinear optical process, in which pairwise photon correlations enable absolute calibration of photodetectors. Since the emission rate crucially depends on the brightness of the electromagnetic field, quantum-mechanical fluctuations of the vacuum can be seen as a seed of spontaneous PDC, and their amplitude is a natural radiometric standard. Thus, they allow for the calibration of the spectral radiance of light sources by measuring the ratio between seeded and unseeded PDC. Here, we directly use the frequency spectrum of the electromagnetic vacuum to trigger spontaneous PDC and employ the generated light to infer the spectral response of a spectrometer over a broad spectral range. Then, we deduce the absolute quantum efficiency from the spectral shape of PDC in the high-gain regime, without relying on a seed or reference detector. Our results compare well with the ones obtained with a reference lamp, demonstrating a promising primary radiation standard.

Hydrated singly charged magnesium ions [Mg(H₂O)_n]⁺ are thought to consist of an Mg²⁺ ion and a hydrated electron for n > 15. This idea is based on mass spectra, which exhibit a transition from [MgOH(H₂O)_n−1]⁺ to [Mg(H₂O)_n]⁺ around n = 15–22, black-body infrared radiative dissociation, and quantum chemical calculations. Here, we present photodissociation spectra of size-selected [Mg(H₂O)_n]⁺ in the range of n = 20–70 measured for photon energies of 1.0–5.0 eV. The spectra exhibit a broad absorption from 1.4 to 3.2 eV, with two local maxima around 1.7–1.8 eV and 2.1–2.5 eV, depending on cluster size. The spectra shift slowly from n = 20 to n = 50, but no significant change is observed for n = 50–70. Quantum chemical modeling of the spectra yields several candidates for the observed absorptions, including five- and six-fold coordinated Mg²⁺ with a hydrated electron in its immediate vicinity, as well as a solvent-separated Mg²⁺/e⁻ pair. The photochemical behavior resembles that of the hydrated electron, with barrierless interconversion into the ground state following the excitation.

Mid-infrared (MIR) microscopy provides rich chemical and structural information about biological samples, without staining. Conventionally, the long MIR wavelength severely limits the lateral resolution owing to optical diffraction; moreover, the strong MIR absorption of water ubiquitous in fresh biological samples results in high background and low contrast. To overcome these limitations, we propose a method that employs photoacoustic detection highly localized with a pulsed ultraviolet laser on the basis of the Grüneisen relaxation effect. For cultured cells, our method achieves water-background suppressed MIR imaging of lipids and proteins at ultraviolet resolution, at least an order of magnitude finer than the MIR diffraction limits. Label-free histology using this method is also demonstrated in thick brain slices. Our approach provides convenient high-resolution and high-contrast MIR imaging, which can benefit the diagnosis of fresh biological samples.

Understanding the intrinsic properties of the hydrated carbon dioxide radical anions CO₂^.−(H₂O)_n is relevant for electrochemical carbon dioxide functionalization. CO₂^.−(H₂O)_n (n=2–61) is investigated by using infrared action spectroscopy in the 1150–2220 cm⁻¹ region in an ICR (ion cyclotron resonance) cell cooled to T=80 K. The spectra show an absorption band around 1280 cm⁻¹, which is assigned to the symmetric C−O stretching vibration ν_s. It blueshifts with increasing cluster size, reaching the bulk value, within the experimental linewidth, for n=20. The antisymmetric C−O vibration ν_as is strongly coupled with the water bending mode ν₂, causing a broad feature at approximately 1650 cm⁻¹. For larger clusters, an additional broad and weak band appears above 1900 cm⁻¹ similar to bulk water, which is assigned to a combination band of water bending and libration modes. Quantum chemical calculations provide insight into the interaction of CO₂^.− with the hydrogen-bonding network.

Soft x-ray spectra, in the range from 2 nm to 9 nm, were recorded from strontium plasmas formed by pulses from 20 ps, 170 ps and 5.5 ns Nd:YAG lasers operating at the fundamental wavelength of 1064 nm. Features due to 3d–4p and 3d–4f transitions were identified by comparison with spectra from adjacent ions and atomic structure calculations with both the Cowan code and the Flexible Atomic Code. As in the spectra of ions of other elements in the fifth row of the periodic table, resonant lines 3dⁿ–3dⁿ⁻¹4p¹, 3dⁿ–3dⁿ⁻¹4f¹ and satellite lines 3dⁿ⁻¹4s¹–3dⁿ⁻²4s¹4p¹, 3dⁿ⁻¹4s¹–3dⁿ⁻²4s¹4f¹ of Δn = 1 were observed over the 3.0–8.5 nm region, emitted by 10+ to 19+ ions. These Δn = 1 transitions provide a range of narrow band emission features which may match to specific multi layer combinations for reflective optics in the extreme ultraviolet region of the spectrum.

Despite intense research into the optoelectronic properties of metal halide perovskites (MHPs), sub-bandgap absorption in MHPs remains largely unexplored. Here we recorded two-photon absorption spectra of MHPs using the time-resolved microwave conductivity technique. A two-step upward trend is observed in the two-photon absorption spectrum for methylammonium lead iodide, and some analogues, which implies that the commonly used scaling law is not applicable to MHPs. This aspect is further confirmed by temperature-dependent conductivity measurements. Using an empirical multiband tight binding model, spectra for methylammonium lead iodide were calculated by integration over the entire Brillouin zone, showing compelling similarity with experimental results. We conclude that the second upward trend in the two-photon absorption spectrum originates from additional optical transitions to the heavy and light electron bands formed by the strong spin-orbit coupling. Hence, valuable insight can be obtained in the opto-electronic properties of MHPs by sub-bandgap spectroscopy, complemented by modelling.

The new C-2W Thomson scattering (TS) diagnostic consists of two individual subsystems for monitoring electron temperature (T_e) and density (n_e): one system in the central region is currently operational, and the second system is being commissioned to monitor the open field line region. Validating the performance of the TS’s custom designed system components and unique calibration of the detection system and diagnostic as a whole is crucial to obtaining high precision T_e and n_e profiles of C-2W’s plasma. The major components include a diode-pumped Nd:YAG laser which produces 35 pulses at up to 20 kHz, uniquely designed collection lenses with a fast numerical aperture, and uniquely designed polychromators with filters sets to optimize a T_e ranging from 10 eV to 2 keV. This paper describes the design principles and techniques used to characterize the main components of the TS diagnostic on C-2W, as well as the results of Rayleigh scattering calibrations performed for the whole system response.