We demonstrate the scaling of few-cycle post-compression to the multi-TW regime by producing 15 mJ, 6.9 fs pulses through spectral broadening of 800 nm light in a large-bore (circle divide 1 mm) hollow-capillary fiber (HCF) of 5 m in length. The good beam quality allows for focusing of the beam to near diffraction limit to achieve a peak intensity of 6.5 10(18) W/cm(2) for relativistic laser-matter interaction studies. The performance of the helium-filled HCF is characterized under various operating conditions. We find that a reverse pressure gradient allows for operation above the critical power for self-focusing with >88% transmission for input energies of 23 mJ. (c) 2025 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

Scaling spectral broadening to higher pulse energies and average powers, respectively, is a critical step in ultrafast science, especially for narrowband Yb-based solid state lasers which become the new state-of-the-art. Despite their high nonlinearity, molecular gases as the broadening medium inside hollow-core fibers have been limited to 25 W, at best. We demonstrate spectral broadening in nitrogen at ten-fold average powers up to 250W with repetition rates from 25 to 200kHz. The observed ten-fold spectral broadening is stronger compared to the more expensive krypton gas and enables pulse compression from 1.3ps to 120fs. We identified an intuitive explanation for the observed average power scaling based on the density of molecular ro–vibrational states of Raman active molecules. To verify this ansatz, spectral broadening limitations in O2 and N2O are experimentally measured and agree well. On these grounds we propose a new perspective on the role, suitability, and limits of stimulated Raman scattering at high average and peak powers. Finally, high harmonic generation is demonstrated at 200~kHz.

We investigate the enhanced terahertz generation in the organic crystal BNA when pumped by compressed highenergy ytterbium laser pulses. By compressing the pump pulses from 170 fs down to 43 fs using an argon-filled hollowcore fiber and chirped mirrors, the terahertz conversion efficiency is increased by 2.4 times, leading to the generation of multi-microjoule terahertz pulses with a frequency spectrum almost twice as wide, extending up to 19 THz. These findings showcase a simple and efficient way to generate intense and broadband terahertz pulses by means of an amplified ytterbium laser system. (c) 2025 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

Starting from 330fs, we generate 6.1fs (1.8 cycle), 50W, 1.2mJ pulses centered at 1030nm via two subsequent hollow-core fiber compressors with a total transmission efficiency of 60%.

Ultrafast laser science witnesses a transformative change due to the introduction of robust, high repetition rate Yb based solid state lasers. We prove the ability of hollow-core fiber (HCF) post compression to keep pace with the constantly raising average powers and pulse energies provided by state-of-the-art lasers. Over a wide range of input parameters, HCFs can provide high transmissions in the 80%-90% range with greater than 10-fold compression. First, we describe a double stage HCF setup that compresses 80 W, 2 mJ, 338 fs pulses centered at 1030 nm down to sub-two optical cycles (6 fs FWHM) with 56 W output power. This 56-fold pulse compression is paired with an overall throughput of 70% and very good long term stability (1.5% StDev over 8 hours). Next, power scaling to 300 W with variable pulse energy and repetition rate (from 100 kHz, 3 mJ to 25 kHz, 12 mJ) is presented. We compressed 1.3 ps pulses of down to 100 fs in a single HCF at 300 W level. Finally, we reveal the potential of utilizing the ultrabroadband HCF output as a spectroscopy platform that can provide various, simultaneous outputs covering a wavelength range from 430 nm up to 12 mu m.

Starting from a 330fs Yb laser, we generate 50fs femtosecond VIS pulses (340-580 nm) and in the NIR (1600-2500 nm) via frequency mixing of spectral side lobes out of a hollow core fibre continuum.

Upon photoexcitation, molecules break apart, following different dissociation reactions. We can image these dissociation pathways using Coulomb explosion imaging (CEI) and sometimes we can control them using asymmetric laser fields. In the formaldehyde molecule, we can see fragments following the direct, conventional dissociation path, as well as fragments deviating from this minimum energy path. So-called roaming fragments or “roamers” explore the potential energy landscape in a statistical manner and could be directly captured in real-time, despite the signal’s statistical character. This is possible due to the single-molecule sensitivity of CEI and we could show that the onset of roaming occurs actually several orders of magnitude earlier than previously expected. In the polar molecule OCS we go one step further by controlling the fragmentation process using two-color asymmetric laser fields. In addition to expected direct ionization effects, we also see post-ionization contributions, which are usually not visible in heavy polar molecules. We thus show in two different examples that CEI provides the means to extract new, unexpected pathways, which would otherwise remain hidden underneath a strong background.

We demonstrate the production of 1.5 terawatt, few-cycle laser pulses for irradiation of solid targets at relativistic intensities. Pulses of up to 25 mJ are spectrally broadened in a helium-filled hollow-core fiber and recompressed.

Starting from ~50-cycle-long pulses at 1035 nm, we show how gas-filled hollow-core fibers facilitate the generation of intense few-cycle light transients from the terahertz to the visible domain.

We show how gas-filled capillary fibers represent a unique platform to explore ultrafast spatiotemporal nonlinear dynamics. We review our recent results including extreme pulse compression, ultra-broad Raman red-shift, and few-cycle visible light generation.

In this work, we introduce a simplified approach to efficiently extend the high harmonic generation (HHG) cutoff in gases without the need for laser frequency conversion via parametric processes. Instead, we employ postcompression and red-shifting of a Yb:CaF2 laser via stimulated Raman scattering (SRS) in a nitrogen-filled stretched hollow core fiber. This driving scheme circumvents the low-efficiency window of parametric amplifiers in the 1100–1300 nm range. We demonstrate this approach being suitable for upscaling the power of a driver with an optimal wavelength for HHG in the highly desirable XUV range between 200 and 300 eV, up to the carbon K-edge. Due to the combination of power scalability of a low quantum defect ytterbium-based laser system with the high conversion efficiency of the SRS technique, we expect a significant increase in the generated photon flux in comparison with established platforms for HHG in the water window. We also compare HHG driven by the SRS scheme with the conventional self-phase modulation (SPM) scheme.

Large scale laser facilities are needed to advance the energy frontier in high energy physics and accelerator physics. Laser plasma accelerators are core to advanced accelerator concepts aimed at reaching TeV electron electron colliders. In these facilities, intense laser pulses drive plasmas and are used to accelerate electrons to high energies in remarkably short distances. A laser plasma accelerator could in principle reach high energies with an accelerating length that is 1000 times shorter than in conventional RF based accelerators. Notionally, laser driven particle beam energies could scale beyond state of the art conventional accelerators. LPAs have produced multi GeV electron beams in about 20 cm with relative energy spread of about 2 percent, supported by highly developed laser technology. This validates key elements of the US DOE strategy for such accelerators to enable future colliders but extending best results to date to a TeV collider will require lasers with higher average power. While the per pulse energies envisioned for laser driven colliders are achievable with current lasers, low laser repetition rates limit potential collider luminosity. Applications will require rates of kHz to tens of kHz at Joules of energy and high efficiency, and a collider would require about 100 such stages, a leap from current Hz class LPAs. This represents a challenging 1000 fold increase in laser repetition rates beyond current state of the art. This whitepaper describes current research and outlook for candidate laser systems as well as the accompanying broadband and high damage threshold optics needed for driving future advanced accelerators.

Upon photo-excitation of a molecule it will break apart. We can see fragments following direct, conventional dissociation paths, as well as fragments deviating from this minimum energy path. The latter are called roaming fragments and explore the potential energy landscape in a statistical manner. Dissociating and roaming fragments are directly captured using Coulomb Explosion Imaging (CEI) and individual pathways are distinguished based on state-of-the-art theory analysis.

We demonstrate enhanced and broadband terahertz generation in a collinearly pumped BNA organic crystal. Suitably compressed ytterbium laser pulses yield a 75% increase in conversion efficiency and a spectral coverage up to 12 THz.

We investigate the enhanced THz generation characteristics of the organic crystal BNA when pumped by compressed ytterbium laser pulses. When the pump pulses are compressed down to 42 fs using a gas-filled hollow-core fiber and chirped mirrors, the THz conversion efficiency is increased by 75%, and the generated frequency spectrum extends up to 12 THz. These findings demonstrate the benefits of using compressed ytterbium laser pulses for enhancing THz generation in suitable nonlinear crystals for the development of intense and broadband THz sources.

We demonstrate Yb laser (170fs) propagation in large a core hollow-core fiber (HCF) with 97.4% transmission and subsequent pulse compression down to 25fs. The tunable pulse duration between 25fs to 100fs can be used to enhance THz emission of BNA organic crystals for instance. We also demonstrate average power scaling of this approach to 270W paired with pulse compression of a 1.3ps Yb laser down to 100fs. A particular setup feature is its ability to tune the input energy and repetition rate, respectively, over an order of magnitude. Pulse compression is possible for input pulses energies ranging from 1mJ to 10mJ with the same setup.

Ultrashort high-energy visible pulses have enabled unprecedented opportunities in temporally resolving ultrafast dynamics in physics, chemistry, and biology. Until now, high-energy sub-10 fs visible pulses have been mostly obtained through complex non-collinear optical parametric amplification setups, followed by some pulse post-compression technique. Here, we present an alternative approach, which relies on considering the typically-undesired multimode nature of large-core hollow-core capillary fibers (HCFs) as an essential asset. In our experiments, 1 mJ 175-fs-long pulses centered at 1035 nm, emitted by an Yb:KGW (Pharos – Light Conversion) laser, were coupled into a 3-m-long HCF (few-cycle Inc.) filled with Argon gas. At a selected pressure of 2.9 bar, a fast energy transfer from the laser broadened via self-phase modulation towards the arising visible light was observed starting at around 0.8 mJ laser pulse energy. At the maximum pulse energy of 0.94 mJ, a continuous spectrum of visible light between 800 nm and 400 nm was measured, with an overall energy of approximately 30 µJ. To understand this process, we implemented 3D carrier-resolved pulse propagation simulations based on the guided mode theory. The simulations predict the direct formation of a pulse of about 5 fs right at the exit of the fiber, considering the visible spectrum in the range 525 - 750 nm. We found that the presence of higher-order modes is crucial to generate such visible pulses and that the Kerr effect is the dominant nonlinearity enabling the modal energy transfer. Experimentally, we characterized the visible pulses by means of a transient-grating frequency-resolved optical gating setup (TG-FROG). At 0.94 mJ and 2.9 bar, a visible pulse duration of 4.6 fs was measured. We also implemented a cross-correlation TG-XFROG, using the separately-compressed laser light and the visible pulses, which demonstrates the possibility of directly implementing high-energy NIR-pump VIS-probe measurements on a sub-10-fs scale.

Starting from 175-fs-long pulses at 1035 nm, we directly generate 20 µJ, 4.6 fs visible pulses through the nonlinear mixing between the spatial modes of a 3-m-long Ar-filled hollow-core fiber, without any pulse post-compression.

The XUV flux from HHG is limited by the laser to driver and by the driver to XUV conversion efficiency. We demonstrate a driving scheme optimizing both steps when targeting 200-300 eV cut-off.