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Recent developments in attosecond technology led to table-top x-ray spectroscopy in the soft x-ray range, thus uniting the element- and state-specificity of core-level x-ray absorption spectroscopy with the time resolution to follow electronic dynamics in real-time. We describe recent work in attosecond technology and investigations into materials such as Si, SiO2, GaN, Al2O3, Ti, and TiO2, enabled by the convergence of these two capabilities. We showcase the state-of-the-art on isolated attosecond soft x-ray pulses for x-ray absorption near-edge spectroscopy to observe the 3d-state dynamics of the semi-metal TiS2 with attosecond resolution at the Ti L-edge (460 eV). We describe how the element- and state-specificity at the transition metal L-edge of the quantum material allows us to unambiguously identify how and where the optical field influences charge carriers. This precision elucidates that the Ti:3d conduction band states are efficiently photo-doped to a density of 1.9 × 1021 cm−3. The light-field induces coherent motion of intra-band carriers across 38% of the first Brillouin zone. Lastly, we describe the prospects with such unambiguous real-time observation of carrier dynamics in specific bonding or anti-bonding states and speculate that such capability will bring unprecedented opportunities toward an engineered approach for designer materials with pre-defined properties and efficiency. Examples are composites of semiconductors and insulators like Si, Ge, SiO2, GaN, BN, and quantum materials like graphene, transition metal dichalcogens, or high-Tc superconductors like NbN or LaBaCuO. Exiting are prospects to scrutinize canonical questions in multi-body physics, such as whether the electrons or lattice trigger phase transitions.

Recent developments in attosecond technology led to tabletop X-ray spectroscopy in the soft X-ray range, thus uniting the element- and state-specificity of core-level x-ray absorption spectroscopy with the time resolution to follow electronic dynamics in real time. We describe recent work in attosecond technology and investigations into materials such as Si, SiO2, GaN, Al2O3, Ti, TiO2, enabled by the convergence of these two capabilities. We showcase the state-of-the-art on isolated attosecond soft x-ray pulses for x-ray absorption near edge spectroscopy (XANES) to observe the 3d-state dynamics of the semi-metal TiS2 with attosecond resolution at the Ti L-edge (460 eV). We describe how the element- and state-specificity at the transition metal L-edge of the quantum material allows to unambiguously identify how and where the optical field influences charge carriers. This precision elucidates that the Ti:3d conduction band states are efficiently photo-doped to a density of 1.9 x 10^21 cm^-3 and that the light-field induces coherent motion of intra-band carriers across 38% of the first Brillouin zone. Lastly, we describe the prospects with such unambiguous real-time observation of carrier dynamics in specific bonding or anti-bonding states and speculate that such capability will bring unprecedented opportunities towards an engineered approach for designer materials with pre-defined properties and efficiency. Examples are composites of semiconductors and insulators like Si, Ge, SiO2, GaN, BN, quantum materials like graphene, TMDCs, or high-Tc superconductors like NbN or LaBaCuO. Exiting are prospects to scrutinize canonical questions in multi-body physics such as whether the electrons or lattice trigger phase transitions., 5 figures

Recently, imec has installed and commissioned an industrial, ultrafast EUV materials characterization and lithography lab, imec’s AttoLab, with a primary aim to explore limits of photoresist performance and their associated ultrafast chemistries. Here, we demonstrate, for the first time, the use of a table-top, high-harmonic EUV system (KM Labs, XUUS4) to perform interference lithography of sub-22-nm pitch patterns in an Inpria MOx resist via a Lloyd’s mirror interference lithography (IL) tool. Analysis of SEM images enables us to identify potential sources of image blur, which we attribute to out-of-sync vibrations, flare, spectral purity, and laser stability. Nevertheless, these results confirm the ability of table-top, high-harmonic EUV sources to print lithographic patterns below a 22-nm pitch. In future work, we plan to investigate sub-20-nm patterning in different resist formulations, as well as expand the lithographic capabilities in AttoLab to perform IL on full 300-mm wafers.

Imec’s AttoLab is the first industrial laboratory capable of watching the ultrafast dynamics of photoresists following 13.5 nm, EUV exposure, and for emulating high-numerical-aperture (high-NA) exposure on 300-mm wafers using two-beam EUV interference. The two respective beamlines are powered by a laser-based high-harmonic generation EUV source. Its capabilities have recently been proven by imaging 20 nm pitch lines and spaces using Lloyd’s Mirror interference lithography. In parallel, time-averaged and time-resolved techniques for studying the ultrafast dynamics of photoresists after EUV exposure, coherent diffractive imaging to study resist interfaces, and more sophisticated interference lithography techniques for printing sub-22 nm pitches on full 300-mm wafers are being developed. Taking advantage of the bright and short EUV pulses now available at imec, we will be able to contribute to a smooth transition towards next generation high-NA lithography.

A new imaging technique enables nondestructive, 3D characterization of nanostructures, their composition, and interfaces., Next-generation nano- and quantum devices have increasingly complex 3D structure. As the dimensions of these devices shrink to the nanoscale, their performance is often governed by interface quality or precise chemical or dopant composition. Here, we present the first phase-sensitive extreme ultraviolet imaging reflectometer. It combines the excellent phase stability of coherent high-harmonic sources, the unique chemical sensitivity of extreme ultraviolet reflectometry, and state-of-the-art ptychography imaging algorithms. This tabletop microscope can nondestructively probe surface topography, layer thicknesses, and interface quality, as well as dopant concentrations and profiles. High-fidelity imaging was achieved by implementing variable-angle ptychographic imaging, by using total variation regularization to mitigate noise and artifacts in the reconstructed image, and by using a high-brightness, high-harmonic source with excellent intensity and wavefront stability. We validate our measurements through multiscale, multimodal imaging to show that this technique has unique advantages compared with other techniques based on electron and scanning probe microscopies.

An ultra-short pulsed, ultra-broadband (~13nm-~13pm) light-source has been developed to drive atto- to femto- second time-resolved studies on EUV photo-resist materials. The same source will also be used to investigate EUV driven nano-lithography.

Information about the real-time response of carriers to optical fields is paramount to advance information processing or to understand the bottlenecks of light-matter interaction and energy harvesting. Transition-metal dichalcogenide (TMDC) compounds are an emerging class of materials with attractive structural and electronic properties that can be thinned to the 2D limit and TiS 2 is a paradigmatic example for a semi-metallic TMDC, since its electron mobility ranges between that of a metal and a semiconductor.

We present a tabletop-scale complex-imaging EUV reflectometer that uses grazing- incidence ptychographic imaging to non-destructively determine depth-dependent, spatially-resolved composition with high sensitivity to chemical makeup, thin film layer thickness, interface quality and dopant profiles.

Attosecond light pulses in the extreme ultraviolet have drawn a great deal of attention due to their ability to interrogate electronic dynamics in real time. Nevertheless, to follow charge dynamics and excitations in materials, element selectivity is a prerequisite, which demands such pulses in the soft X-ray region, above 200 eV, to simultaneously cover several fundamental absorption edges of the constituents of the materials. Here, we experimentally demonstrate the exploitation of a transient phase matching regime to generate carrier envelope controlled soft X-ray supercontinua with pulse energies up to 2.9±0.1 pJ and a flux of (7.3±0.1) × 107 photons per second across the entire water window and attosecond pulses with 13 as transform limit. Our results herald attosecond science at the fundamental absorption edges of matter by bridging the gap between ultrafast temporal resolution and element specific probing., Attosecond soft X-ray pulses hold promise for probing electronic dynamics in real time, but it is challenging to achieve element sensitivity while maintaining temporal resolution. Teichmann et al. report the cover of carbon, nitrogen and oxygen absorption edges with an isolated pulse supporting 13 as duration.

We present the first ultrafast and all-fiber pumped OPCPA operating at 7 μm and generating 0.55 mJ pulses at 180 fs (7.7 optical cycles).

We present a novel all-fiber pumped optical parametric chirped pulse amplifier (OPCPA) architecture to generate self-carrier-to-envelope-phase stable, sub-eight-optical-cycle duration pulses at 7 μm wavelength approaching millijoulelevel pulse energy at 100 Hz repetition rate. The system yields a peak power of 1.1 GW and, if focused to the diffraction limit, would reach a peak intensity of 7 × 1014 W∕cm2. The OPCPA is pumped by a 2 μm Ho:YLF chirped pulse amplifier to leverage the highly efficient and broadband response of the nonlinear crystal ZGP. The 7 μm seed at 100 MHz is generated via difference frequency generation from an Er:Tm:Ho multi-arm fiber frequency comb, and a fraction of its output optically injects the Ho:YLF amplifier. While the pulse bandwidth at 7 μm is perfectly suited for nonlinear and spectroscopic applications, current parameters offer, for the first time, to the best of our knowledge, the possibility to explore strong-field physics in an entirely new wavelength range with a ponderomotive force 77 times larger than from an 800 nm source. The overall OPCPA system is very compact and provides a new tool for investigations directly in the molecular fingerprint region of the electro-magnetic spectrum or to drive high harmonic generation to produce fully coherent x-rays in the multi-kiloelectron-volt range and possibly zeptosecond temporal waveforms.

Attosecond pulses at photon energies that cover the principal absorption edges of the building blocks of materials are a prerequisite for time-resolved probing of the triggering events leading to electronic dynamics such as exciton formation and annihilation. We demonstrate experimentally the isolation of individual attosecond pulses at the carbon K-shell edge (284 eV) in the soft X-ray water window with pulse duration below 400 as and with a bandwidth supporting a 30-as pulse duration. Our approach is based on spatiotemporal isolation of long-wavelength-driven harmonics and validates a straightforward and scalable approach for robust and reproducible attosecond pulse isolation., Time-resolved probing of electronic dynamics such as exciton formation and annihilation requires attosecond pulses at photon energies covering the absorption edges of materials. Here, Silva et al. experimentally demonstrate spatio-temporal isolation of single-attosecond soft X-ray pulses in the water window.

We generate high order harmonics in the water window with CEP-stable pulses at 1.8 μm at 1 kHz repetition rate. We produce half-cycle cutoffs at 370 eV supporting isolated attosecond pulses of 60 as.

We produce CEP-dependent X-ray continua up to the oxygen edge (543 eV) through high harmonic generation driven by sub-2-cycle 1.85 μm pulses at 1kHz, supporting isolated attosecond pulses of 45 as in the water window.

We report on a compact coherent All-PM fiber laser amplifier system at around 2.03 mm running at 100 MHz delivering broadband pulses at 290 mW average power and pulse duration down to 128 fs.

We demonstrate the generation of temporally clean few-cycle pulses at 2.1 μm by shortening of 6-optical-cycle pulses via cross-polarized wave (XPW) generation in BaF(2), CaF(2) and CVD-Diamond crystals. By combining spectra and single-shot third-order intensity cross-correlation traces in a novel Bayesian pulse retrieval technique, we measured pulse durations of 20 fs, corresponding to 2.8 optical cycles. Our results show that XPW generation in the infrared could provide a high-fidelity source of few-cycle pulses for strong-field physics applications. It could also serve as an injector for high-peak power ultrafast mid-IR wavelength parametric amplifiers.

We observe ring structures in high-order harmonics generated in the loose focusing geometry of a semi-infinite gas cell. Phase matching and absorption considerations indicate that the measured signal is restricted to the harmonics generated in the exit plane. We therefore attribute the ring structure to interferences in the single-atom response in the transverse exit plane of the interaction region. Calculations using the stationary phase approximation were used to analyze the contributions of the long and the short trajectories, respectively, and confirm our experimental findings. The simple setup makes quantum path interference measurements feasible without the need for special filtering mechanisms.

We demonstrate the generation of spectrally clean few-cycle pulses at 2.1 μm by shortening of 40 fs pulses via cross-polarized wave (XPW) generation. Single-shot autocorrelation traces show 20 fs pulse duration.

Ultrashort pulse characterization is sufficiently mature that temporal amplitude and phase profiles are now routinely acquired. However, most implementations either ignore or average over spatial variations. Nontrivial spatiotemporal couplings play a significant role in many ultrafast sources, such as chirped-pulse and optical parametric amplifiers, and can strongly affect many applications, such as high-harmonic generation and materials processing. This motivates the development of methods for full spatio-temporal characterisation [1, 2]. Most current designs involve augmenting an existing temporal characterisation method with additional components such as a spatially resolved interferometer [3]. Such implementations usually complicate usage and it is therefore important to devise a simple setup with a minimum number of components and straightforward usage.

Few-cycle pulses centered at long wavelengths with stable carrier envelope phase are increasingly sought after for a range of strong-field physics and spectroscopic applications. The generation of such pulses at central wavelengths up to 1.8 µm is well-known [1], however at longer wavelengths non-collinear optical parametric amplifiers must be used to maintain bandwidth. Using the idler from such a non-collinear interaction always implies an angularly dispersed pulse, requiring complicated and lossy compensation strategies [2] which limit scalability to higher energies.

We measure the far-field (angle-wavelength) spectrum of high order harmonics from a semi-infinite gas cell. Individual harmonics exhibit ring structures in space-time, which are attributed to the different quantum paths.

We demonstrate a scalable, CEP stable, three-cycle source at 2.1 μm with 180 μJ pulse energy from OPA in bulk BiB3O6 at 3 kHz repetition rate without post-compression.

Nonlinear pulse compression mediated by three-wave mixing is demonstrated for ultrashort Ti:sapphire pulses in a type II phase-matched β-barium borate (BBO) crystal using noncollinear geometry. 170 μJ pulses at 800 nm with a pulse duration of 74 fs are compressed at their sum frequency to 32 fs with 55 μJ of pulse energy. Experiments and computer simulations demonstrate the potential of sum-frequency pulse compression to match the group velocities of the interacting waves to crystals that were initially not considered in the context of nonlinear pulse compression.

We report on a dual output all-PM fiber laser system running at 100 MHz repetition rate offering coherent broadband and narrowband pulses centered at 2.05 µm with a spectral FWHM bandwidth of 60 nm and 1.5 nm at up to 360 mW and 500 mW, respectively. The broadband pulses are compressed down to 135 fs. The multi-stage double-clad amplifier based on Tm/Ho codoping is seeded by a supercontinuum light source, spanning from around 1 µm up to 2.4 µm.

An acousto-optic pulse shaper has been used to characterize few-cycle pulses generated in a hollow-core fiber. A grism pair precompensates for the dispersion of the acousto-optic crystal, allowing the full pulse-shaping window to be used for replica generation rather than self-compensation. A 9.4 fs pulse was measured, the shortest ever measured with an acousto-optic pulse shaper, to our knowledge.

X-ray absorption fine-structure (XAFS) spectroscopy is a well-established technique capable of extracting information about a material’s electronic and lattice structure with atomic resolution. While the near-edge region (XANES) of a XAFS spectrum provides information about the electronic configuration, structural information is extracted from the extended XAFS (EXAFS) spectrum, consisting of several hundreds of eV above the absorption edge. With the advent of high harmonic sources, reaching photon energies in soft x-ray (SXR) region, it now becomes possible to connect the spectroscopic capabilities of XAFS to the unprecedented attosecond temporal resolution of a high harmonic source allowing the observation of electronic and lattice dynamics in real time [1,2]. Layered materials, such the transition-metal dichalcogenide TiS2 or graphite, are an emerging class of materials with attractive structural and electronic properties as they can be thinned to a single atomic layer with electron mobilities resembling that of a metal, semiconductor, or semi-metal. In this work, we utilized broadband water-window-covering attosecond SXR pulses (300 as, ranging from 200 - 550 eV) capable of accessing orbital-specific K- and L-edges of such layered materials to perform transient XAFS with attosecond time resolution [3,4]. [1] Teichmann, S. et al, "0.5-keV soft x-ray attosecond continua", Nat. Commun. 7, 11493 (2016). [2] Cousin S. et al, "Attosecond streaking in the water window: a new regime of attosecond pulse characterization", Phys. Rev. X, 7, 041030 (2017). [3] Buades, B. et al., “Dispersive soft x-ray absorption fine-structure spectroscopy in graphite with an attosecond pulse”, Optica 5 (5), 502 (2018). [4] Buades, B. et al., “Attosecond-resolved petahertz carrier motion in semi-metallic TiS2”, arXiv: 1808.06493 (2018).

We present half-cycle cutoff features in the water window using high-order-harmonic generation (HHG) with two-cycle, carrier-envelope-phase-controlled pulses at 1.85 μm in a high-pressure neon target. A relative carrier-envelope-phase (CEP) shift of the acquired spectra at different pressures is related to an in situ slip of the CEP in the HHG target. A simple model based on the pressure-dependent dispersion of the target gas reveals the importance of the free electrons for this effect. Our analysis also reveals that the effect is relaxed at high target pressures due to plasma defocusing of the driving pulse. We show that as a consequence of the CEP slip mediated by free electrons, moderate-intensity fluctuations can have a detrimental influence on the generation and application of attosecond pulses. Our findings emphasize the potential of combining high target pressures and long driver wavelengths to reveal subtle details of the complex light-matter interaction of HHG.

An acousto-optic pulse shaper has been used to characterise an 8.2 fs pulse generated in a hollow-core fibre. A grism-pair compressor has been used to overcome a dispersion related bandwidth limit of the acousto-optic crystal.

We generate 260 μJ energy optical pulses at 7 μm with an OPCPA pumped by an optically synchronized 2 μm picosecond CPA system. The mid-IR pulses exhibit a bandwidth supporting sub-4 optical cycle duration.

We use attosecond soft X-ray pulses between 284 eV to 543 eV for orbital-selective and real-time probing of the opto-electronic response of semi metallic TiS2.

Phase transitions of solids and structural transformations of molecules are canonical examples of important photo-induced processes whose underlying mechanisms largely elude our comprehension due to our inability to correlate electronic excitation with atomic position in real time. Here, we present a decisive step towards such new methodology based on water-window covering (284–543 eV) attosecond soft x-ray pulses that can simultaneously access electronic and lattice parameters via dispersive x-ray absorption fine-structure (XAFS) spectroscopy. We validate this approach with an identification of the σ* and π* orbital contributions to the density of states in graphite simultaneously with its lattice’s four characteristic bonding distances. This work demonstrates the potential of dispersive XAFS, in combination with attosecond pulses, as a powerful investigative tool that is equally applicable to gas, liquid, and condensed phase.