ELI-HU Research and Development Non-Profit

Fe-based metallic glasses are ideal candidates to be utilized in transformer cores owing to their outstanding soft magnetic properties. However, they are difficult to machine properly by conventional means due to their mechanical brittleness and poor thermal conductivity. Here, the cutting of Fe91-Si4.5-C4.0-Al0.5 amorphous alloy ribbons is reported with a sub-50 fs laser pulses. A systematic study is performed on local morphological and chemical composition changes to the machined edge in comparison to crystalline metals. It is shown that only the innermost 80 μm wide region of the cut edge shows any detectable modifications, which is much less than for continuous laser machining. Therefore, the proposed method is indeed a valuable approach to overcome the fine machining difficulties of metallic glasses.

Performing ultrafast spectroscopy during nanoparticle synthesis can provide new insights into the kinetics and mechanism of nanoparticle formation. In these experiments, we thoroughly studied the ultrafast decay of the transient absorption signal from reference gold nanoparticles (with well-defined diameters of 5, 20, and 40 nm) and from synthesized gold nanoparticles with 1:1 and 1:4 gold-to-citrate molar ratio. The application of the high repetition rate laser (100 kHz) with short pump pulse duration (10 fs, 470–570 nm) allows the rapid in situ TAS monitoring of the particle growth. Following excitation with femtosecond pulses, the acoustic vibrations of the particles produced periodic oscillations in the transient absorption signal. The decay traces at the selected wavelengths were fitted, and the Fast Fourier Transform (FFT) analysis was used for the determination of the characteristic frequencies of the acoustic vibrations. The frequency of the periodic oscillations decreases with an increasing size. We demonstrate that the formation of monodisperse gold nanoparticles at 75 °C can be monitored during the synthesis, providing direct evidence about their quality and particle size in the 12–55 nm particle diameter range. We concluded that the average primary size of the monodisperse gold nanoparticles increased in the 19–23 min synthesis time range as the frequency of the acoustic vibrations decreased for the Au-Cit 1:4 sample and remained constant in the last phase of the synthesis.

We present the post-compression of 25 fs pulses with a flat-top beam profile in different nonlinear media. Fused silica, sapphire, and YAG plates were tested for spectral broadening and compressibility while measuring the spatio-spectral properties of the broadened pulses. To our best knowledge, such systematic investigation has not yet been carried out. The near- and far-field profiles show that no significant wavefront distortion occurred during the nonlinear propagation but the spatio-spectral homogeneity has a strong correlation with the material characteristics and the accumulated B integral. A series of numerical simulations were also conducted to have deeper insight on the broadening process and the impact of the material properties. The theoretical model also reveals the limitations of compressibility in the single thin plate arrangement and it can support the optimization of future, high-energy experiments. • The spatio-spectral homogeneity depends on the material properties • The maximum compression factor is limited regardless of the material or intensity • Compression quality correlates with the nonlinear propagation length • Input pulse parameters determine the optimal material thickness

We report on the development of a carrier-envelope phase (CEP) stable 1030 nm fiber-based laser system producing 6.2 fs pulses achieved via the multi-pass cell (MPC) post-compression technique with 402 W average power at 100 kHz repetition rate. This system employs an upgraded three-stage MPC compression scheme exhibiting excellent beam quality properties for this intensity region. Active stabilization locks the CEP noise below 430 mrad RMS. This work represents the first demonstration of a coherently combined fiber laser system simultaneously achieving such exceptional average power, CEP stability, and sub-two-cycle pulse durations. Similarly to all other light sources of the Extreme Light Infrastructure Attosecond Light Pulse Source (ELI ALPS), this newly developed system is accessible to the international research community in peer-reviewed open user calls of Extreme Light Infrastructure European Research Infrastructure Consortium (ELI ERIC).

Here, we report THz pulse generation in the organic crystals MNA and BNA in a previously unexplored regime with few-cycle near-infrared pump pulses. Fourier limited pump pulses of 13 fs duration generated the largest bandwidth of 5.5 THz. Negatively chirped pump pulses with a group-delay dispersion of −1200 fs<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (MNA) and −800 fs<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (BNA) gave the highest THz pulse energies, 2 to 3 times higher than the Fourier limited pulses. The THz source is scalable to multi-MV/cm extreme field strengths and can be implemented in attosecond XUV beamlines for a new class of pump-probe studies.

Abstract Non-classical and entangled light states are of fundamental interest in quantum mechanics and they are a powerful tool for the emergence of new quantum technologies. The development of methods that can lead to the generation of such light states is therefore of high importance. Recently, it has been demonstrated that intense laser-matter interactions can serve towards this direction. Specifically, it has been shown how the use of fully quantized approaches in intense laser-matter interactions and the process of high harmonic generation, can lead to the generation of high photon-number non-classical and entangled states from the far-infrared to the extreme-ultraviolet. Here, after a brief introduction on the fundamentals, we summarize the operation principles of these approaches and discuss the recent developments and future directions of non-classical light engineering using strong light fields with the potential application in ultrafast and quantum information science. These findings represent an important step in the development of novel quantum nonlinear spectroscopy methods, based on the interplay between the quantum properties of light and those of quantum matter.

Development trends of high intensity laser systems points in the direction of increasing the repetition rate towards 10 Hz and beyond, while reliability and stability is also greatly improved [1], [2]. Next generation of particle and high harmonic beamlines require stable temporal compression of the driver pulses together with high spatio-temporal quality. Operation of the HFPW laser of the ALPS Facility of ELI ERIC has been recently demonstrated at the 700 TW level at 10 Hz repetition rate [3]. Intensity contrast and spectral stability requirements of experiments push the boundaries of currently available laser frontends. Furthermore, the high repetition rate and consequently the high average power also put a high demand on the final amplifiers, and on the vacuum compressor optical elements.

Recent high repetition rate lasers capable to produce TW peak power, few-cycle laser pulses with 100 W average power at industrial standards. Hence, they may offer an alternative to the PW peak power lasers for applications that need a quasi-continuous source of neutrons. The laser-based neutron source was commissioned using the SEA laser of ELI-ALPS, delivering 21mJ, 12fs laser pulses at 10Hz repetition rate on the target. The system operates for several hours a day, providing a fast neutron yield of 2×10^5 neutron/s with a shot-to-shot stability better than 10%. Further scaling of the neutron source has been recently demonstrated at 1 kHz repetition rate, with the 100mJ, sub-10 fs laser pulses of the SYLOS 3 laser system. The highest neutron yield of 10^8 neutron/s was achieved for several minutes. Current and future development of the neutron source aims at the extension of the kHz operation for several hours.