In this talk, we review the recent developments in machine learning applications to ultrafast photonics with emphasis on the study of complex dynamics and transient instabilities.

We introduce a new approach based on two neural network architectures for mimicking the nonlinear propagation dynamics of ultrashort pulses in optical fibers for supercontinuum generation, allowing for significant memory and speed improvements compared to the conventional approach of numerically integrating the generalized nonlinear Schrödinger equation.

We demonstrate a technique for the programmable generation and multi-millijoule amplification of ultrashort pulse bursts, which can be applied to any master-oscillator regenerative-amplifier system with very low implementation complexity and high stability in burst-mode operation.

Laser-Induced Aerosol Formation (LIAF), driven by UV and near-IR filaments, relies on the nitrogen photo-oxidative chemistry, triggered by photoionization and leading to the production of HNO3, stabilizing the growth of aerosol. Mid-IR filaments were expected to be less efficient due to their lower photoionization rates. However, we observed surprisingly high yields of aerosols, generated by mid-IR laser pulses, which cannot be fully explained by the HNO3-pathway. Therefore, we suggest a new mechanism of LIAF, based on the resonant excitation of volatile organic compounds, enabled by the spectral broadening during filamentation.

Experiments on molecules in solution showed that the first step of vision consists in an ultrafast photo-isomerization that can be coherently controlled by femtosecond pulse shaping. Here, we measure the electric signals fired from the retina of living mice upon femtosecond multi-pulse and single-pulse visual stimulation. We show that the electrophysiological response is sensitive to the manipulation of the pulse spectral-phase and the control mechanism relies on multiple interactions in proximity of the conical intersection, leading to pump-dump and pump/re-pump processes. Our interpretation is supported by quantum dynamics simulations.

In the framework of the Laser Lightning Rod project, we study over 140 m the filaments created by a laser system with J-range pulses of 1 ps duration at 1 kHz repetition rate. We investigate the spatial evolution of the multiple filamentation regime and its ability to control high-voltage discharges at different distance. The measurements were made using both a collimated beam and a focused beam.

Our work contributes to integrate artificial intelligence into laser devices to make them versatile, adaptable and programmable. Within a fiber laser cavity, we incorporate interfaced liquid-crystal components driven by an evolution algorithm that optimizes merit functions leading to user-defined mode-locked regimes. To illustrate the possibility to generate on-demand complex ultrashort-pulse dynamics, we demonstrate the generation of 2-soliton molecules with pre-determined temporal separation.

Built from robust Er:fiber lasers, we describe optical frequency combs generated with pulses approaching a single-cycle of light. When combined with chi-2 and chi-3 nonlinear optics such short pulses efficiently generate multi-octave frequency combs spanning from 350 nm to beyond 25 microns. We further demonstrate straightforward techniques for scaling the energy of the few-cycle pulses, which can then drive non-perturbative nonlinear optics in solids for harmonic generation below 200 nm. Applications of frequency comb spectroscopy across the full coherent spectrum, from the UV to the MIR, are being pursued.

Dual-comb ranging offers high precision and high accuracy distance measurements. However, the application of dual-comb ranging systems is restricted by the complexity of the setup and inherent length ambiguity. Here we present a new and simple approach to increase the ambiguity-free measurement range of dual-comb raining while simultaneously decreasing the complexity by using a single cavity dual-color-fiber laser. By exploiting the intrinsic intensity modulation of our laser we are able to measure distances up to 150 km without ambiguity in a single measurement.

We present a thin-disk laser oscillator generating two asynchronous pulse trains of 240-fs duration at each 6-8 W average power and 97-MHz repetition rate at 1030-nm central wavelength. We confirm its suitability for high-resolution spectroscopy in free-running operation by detecting the absorption spectrum of acetylene within 1 millisecond.

We present frequency up- and down-conversion of an Yb-fiber based ultrafast electro-optic (EO) frequency comb. The repetition rate of the EO comb is continuously tunable across 11-18 GHz and a frequency divider further extends the tunability over multiple octaves down to 1 GHz. Burst-mode operation is also demonstrated, showing the potential for flexible operation in the temporal domain. Furthermore, second- and forth-harmonic generation, as well as an optical parametric oscillator have been realized based on the EO comb, extending the flexible GHz pulses to other spectral regions.

We show that the power-dependent self-frequency shift introduced by cascaded quadratic nonlinearities couples via the intracavity group delay dispersion to the carrier-envelope offset (CEO) frequency, enabling its control over a wide frequency range.

We report on 100-W 132 MHz Yb:fiber amplifier seeded by a low noise all-polarization maintaining (PM) nonlinear amplifying loop mirror (NALM) oscillator, operating in the near zero-dispersion regime. We tune the laser spectrum to match it to different applications while keeping the noise properties and power performance of the system.

We report a novel multiheterodyne relative timing jitter detection measurement and apply it to a single-cavity single-mode-diode pumped dual-comb laser. The inherent passive mutual coherence of the two frequency combs leads to a low relative timing jitter of 7.5 fs [100 Hz, 100 kHz].

We recently demonstrated the coherent synthesis of different phase-stable pulses generated via optical parametric amplifiers (OPAs) with mJ-level energy. The multi-octave spanning bandwidth covered by OPAs, jointly with an advanced phase-control scheme, allow for the synthesis of tailored non-sinusoidal optical waveforms whose duration shrinks below a single optical cycle. Adapting the so-called parametric waveform synthesis (PWS) technology to different pump lasers will allow to further scale energy and average power, making PWS the ideal tool for controlling strong-field light-matter interactions.

We present a non-collinear linear-cavity optical parametric oscillator delivering 53 W around 1030 nm with a 10.2-MHz repetition-rate and sub-picosecond pulses. The system is pumped by a frequency doubled high-power SESAM-modelocked thin-disk laser.

Two optical parametric oscillator systems are introduced that offer ultra-broadband tunability across the visible spectral range with femtosecond pulse durations and substantial output power. Both are based on BBO in the non-collinear phase matching geometry (NOPO). The first one is pumped in the deep blue and emits directly in the visible, the second one is pumped in the green, emits in the NIR and is converted to the visible via an intracavity sum-frequency process.

We review several optical parametric chirped-pulse (OPCPA) systems designed to achieve extreme carrier-envelope phase (CEP) stability and/or spectral tunability in the infrared. The common architecture of these OPCPAs combines a “self-seeded” difference-frequency stage with active CEP stabilization. We demonstrate the compatibility of this architecture with a set of high-power Ytterbium pump lasers based on different amplification technologies (bulk, rod-type, thin-disk, InnoSlab).

Amongst the new engineerable semiconductor nonlinear gain materials, orientation-patterned gallium phosphide (OPGaP) is unique in allowing a 1-um laser to pump an OPO that can produce light across the near- and mid-IR regions. Using OPGaP-on-GaP we have demonstrated the generation of ultrafast optical pulses from 4–13 µm, with applications in the spectroscopy of gases, aerosols and powders. Most recently, new OPGaP-on-GaAs technology has allowed us, using fan-out and multi-grating crystals, to achieve gap-free continuous tuning from 4–12 µm.

Extreme ultraviolet microscopy and wavefront sensing are key challenges in the development of next-generation ultrafast applications. Ptychography offers a single solution to both of the aforementioned challenges. Originally proposed and developed in the electron and synchrotron communities, the increase in flux and stability of high harmonic sources has enabled the transfer of ptychography to the laboratory. Here, we present the status of the PST beamline, a versatile tool for laboratory-scale XUV ptychography in the silicon transparency window, including the latest experimental results demonstrating sub-30nm lateral resolution at 13.5 nm wavelength.

We present an intra-oscillator high harmonic generation source based on a 100-fs Kerr lens mode-locked Yb:YAG thin-disk laser. We generate XUV light with an average power of 10 µW at 30 eV in argon, 12 µW at 25 eV in krypton, and 30 µW at 20 eV in xenon.

In this contribution a fully tunable high harmonic source is presented, which delivers a photon flux of over 1x10^11 photons/s per harmonic line in the range of 50 eV to 70 eV. This table-top waveguide-based XUV source is driven by a 50 W, 1.0 mJ, 36 fs nonlinearly post-compressed fiber laser centered at 1030 nm with a repetition rate of 50 kHz. The tunability of the XUV spectrum is achieved by exploiting the intensity-dependent blueshift of the driving laser field in a noble gas within the waveguide.

We report on carrier-enveloppe phase (CEP) effects on the emission of high-order harmonics and electron beams from plasma mirrors driven by relativistic-intensity near-single-cycle laser pulses at 1 kHz repetition rate.

A Laser Wakefield Accelerator (LWFA) can accelerate electrons up to many GeV energies using the accelerating field structure in the wake of a high-power laser pulse propagating through low-density plasma. Within the accelerating structure, energetic electrons can undergo betatron oscillations, emitting a bright, broadband source of keV X-rays with femtosecond-scale duration. A LWFA can also drive wavelength-tunable pulses of infrared radiation with high focusability through spectral broadening of the laser pulse within plasma waves. In this talk, I will discuss the generation and application of these diverse radiation sources.

Access to local information about material composition and its distribution at the nanoscale is of chief importance for studying functional materials both for biology and materials science, as well as for the fundamental understanding of physical properties. X-ray imaging with high-energy photons, otherwise known as hard X-rays, offers an opportunity for deriving such information in a minimally intrusive procedure. This is due to the high penetration depth of hard X-rays, which allows probing intact representative volumes, and combined with their sub-nm wavelength opens the door to nm-scale imaging. One of the challenges for nm-resolution imaging at these energies lies in the fabrication of lenses of sufficient quality. If the X-ray source is coherent, then imaging lenses can be forgone altogether and instead computational reconstructions can be used, for example via holography or iterative phase retrieval algorithms. In this talk, I will provide an introduction to some of the coherent lensless imaging techniques used in X-ray microscopy for nanoscale imaging: X-ray holography, coherent diffractive imaging, and ptychography. Furthermore, I will show examples from the state of the art methods and how they are used today for nanoscale 3D imaging, imaging of fast dynamics, and chemical characterization of functional materials. I will also introduce the principle, and practical examples, of surveying nanostructure properties on macroscopic-scale samples using scanning small angle X-ray scattering (SAXS). In our group, we have generalized this technique using tensor tomography in order to probe statistical anisotropy of nanostructure in samples on the order of millimeters in linear size.

We present an efficient method for generating frequency combs in the mid-infrared (MIR) spectral range in bulk lithium niobate crystals as well as in waveguides. Our approach is simple and robust, since it is based on single-pass configuration of femtosecond Optical Parametric Generation (OPG) seeded by a telecom continuous-wave laser. Precise and fast tuning of the seed laser allows to rapidly change the offset frequency of the generated MIR comb independent of its repetition rate. The MIR comb’s offset frequency is inherently known, so its direct detection is not required.

Generation of a pair of sub-mJ femtosecond pulses with arbitrary delay control in a single cw-pumped Yb regenerative amplifier is demonstrated. The two pulses drive separate optical parametric amplifiers producing seed for Ho:YAG chirped pulse amplifier and mid-IR optical parametric chirped pulse amplifier. As a result, broadband 40 µJ pulses are generated around 8.6 µm wavelength, which lies in the atmospheric transparency window.

A subharmonic (frequency-divide-by-2) optical parametric oscillator (OPO) is reported as an efficient frequency divider that rigorously both down converts and dramatically augments the spectrum of the pump laser, while maintaining its coherence. Our recent result is a demonstration of a subharmonic system with an unprecedented continuous wavelength span of 3–12 µm that covers most of the molecular ro-vibrational “signature” region. The OPO with a minimally dispersive cavity was pumped by a 2.35-µm Kerr-lens mode-locked oscillator and delivered 245 mW of the average power with the conversion efficiency exceeding 20%.

We demonstrate the direct generation, at a repetition of 250 kHz, of µJ-level, sub-160 fs pulses from 3 to 10 µm in a LiGaS2 (LGS) crystal pumped at 1030 nm.

A new method of seeding χ2 optical parametric converters with χ3 fiber optical parametric sources is introduced. We demonstrate a tuneable mid-infrared (MIR) source around 3 µm with the technique and discuss the potential of this architecture.

We demonstrate dimensional metrology and odometry (detection of change in position over time) with resolution on nanometric to picometric scales by analysing scattering of electrons or topologically structured light from the nanostructures using artificial intelligence. We show how these techniques can be applied to characterization and optimization of nano-opto-mechanical metamaterials and to fundamental studies of the dynamics of thermal motion and the physics of phonons in photonic nanostructures.

The talk addresses recent progress in mid-infrared field-resolved spectroscopy driven by high-power MHz-repetition-rate femtosecond lasers. Intrapulse difference-frequency generation (IPDFG) delivers trains of Watt-level few-cycle mid-infrared optical waveforms with sub-attosecond jitter. Electro-optic sampling (EOS) with multi-Watt short-wave mid-infrared gate pulses allows for recording these waveforms with high fidelity, and with sensitivities close to the fundamental quantum limit. This renders the combination of IPDFG and EOS ideal for tracing light-matter interactions on their native time scales, as well as for broadband vibrational fingerprinting of molecular samples with unprecedented sensitivity and dynamic range.

We report the measurement and assignment of sub-Doppler transitions in the 3ν3 ← ν3 band of methane using optical-optical double resonance spectroscopy with a 3.3 µm continuous wave pump and a 1.67 µm frequency comb probe. We implement an optical cavity for the comb probe that improves the sensitivity by more than two orders of magnitude compared to previous measurements in a single-pass cell.

We present a dual-comb setup operating in the mid-infrared between 4.2µm and 4.85µm based on the frequency conversion of combs generated around 1.56µm by intensity modulation. We show that the spectrometer can be used for high-resolution spectroscopic applications enabling isotopic ratio measurements, but also towards the medical domain.

We use Fourier transform spectroscopy based on frequency combs to measure broadband spectra with resolution limited by the comb mode width. In the near-infrared, we measured mode profiles of a high-finesse cavity over 15 THz of bandwidth with 3 kHz resolution, and derived absorption and dispersion spectra of three CO2 bands from the broadening and shift of the cavity modes. In the mid-infrared, we measured and assigned absorption spectra of CH3I around 3.3 µm, and we retrieved transition frequencies of N2O and CH4 around 7.8 µm with precision <200 kHz.

We demonstrate an Yb:YAG thin-disk laser oscillator operating in the self-phase modulation broadened regime. The laser delivers 100 W of average power in 50-fs pulses at 17-MHz repetition rate with an optical-to-optical efficiency of 25%.

High power ultrafast laser systems directly emitting in the short-wavelength infrared region (1.4-3 µm) has seen strong interest, due to applications in science and technology. Among different laser technologies, the development of 2-µm thin-disk lasers is very promising for power and energy scaling. Recently, we have demonstrated record results with Ho:YAG thin-disk oscillator, delivering 112-W CW power, and 40.5-W modelocked operation with 1.66-ps pulse duration at 52.2-MHz. Here we would like to briefly review the recent achievements of 2-µm thin-disk lasers and discuss the potential development and applications.

We present a novel pumping scheme relying on cross-polarization that overcomes previous bandwidth and efficiency limitations. Implementing this pumping scheme in a soft-aperture Kerr-lens mode-locked laser oscillator based on Yb:CALGO, we demonstrate more than one order of magnitude higher optical-to-optical efficiency compared to previous few-cycle laser oscillators based on Yb-doped gain materials operating in the sub-30-fs pulse duration regime.

We report an approach to generation of femtosecond pulses and optical frequency combs in the 2 – 20 µm spectral range. The laser architecture is based on a combination of laser and nonlinear interactions in polycrystalline Cr:ZnS media that enables simultaneous amplification of ultrashort pulses, nonlinear pulse compression to 2-optical-cycle, and nonlinear broadening of pulses’ spectrum to an optical octave. This has allowed us to implement robust and reliable shoe-box sized middle-IR frequency combs with ultra-low timing jitter of the pulse trains, broad instantaneous spectra, and Watt-level average power.

We present InGaSb/GaSb quantum well based high-quality SESAM at infrared wavelength of 2.4 µm. Using the SESAM we demonstrate self-starting soliton modelocking of Cr:ZnS oscillators delivering 155-fs pulses at record-high 2 GHz repetition rate and short pulses of only 79-fs at 250 MHz repetition rate, both at a high average output power of 0.8 W.

We present a high-precision (<0.03%) nonlinear reflectivity and pump-probe characterization of InGaSb/GaSb quantum-well-based SESAMs for high-power 2.1 μm Ho-doped lasers. The SESAMs have ~1% modulation depth, high saturation fluences and fast recovery times.

Until 2017, all mode-locked lasers essentially operated in a single transverse mode of the laser cavity. In the past few years, the first demonstrations of locking of multiple transverse and longitudinal modes of a fiber laser have appeared. The existence of many different 3-dimensional (spatiotemporal) lasing states opens opportunities for future scientific investigation. Generation of ultrashort pulses in multiple modes may also provide a new route to power scaling in fiber lasers. Basic features of multimode or spatiotemporal mode-locking will be presented along with first steps toward a theoretical treatment.

In this contribution, we present our first results on coherent beam combination of four ultrafast Tm-doped fiber amplifiers. Pulse energies in the mJ-regime with a pulse duration of 123 fs and an average power of 130 W (98 kHz repetition rate) were achieved. This is the highest pulse energy emitted from an ultrafast SWIR fiber laser to date and proves the scaling potential of ultrafast Tm-doped fiber lasers.

In the past few years, the interest in fiber lasers mode-locked with a non-linear amplifying loop mirror has increased due to their robustness and low noise performance. Different amplitude noise characteristics for operation in different intracavity group delay dispersion regimes have been investigated. However, in recently reported laser designs, tuning of the saturable absorber parameters is possible even after achieving mode-locking. We provide systematic amplitude noise measurements and present options for a further optimization of the amplitude noise performance by altering the saturable absorber behavior in mode-locked operation.

The molecular fingerprint region located in the 2-10 um spectral range plays an essential role in scientific research, environmental protection, security, and even searching for signs of life beyond the Earth. Progress in these fields is directly linked to developing stable and versatile laser sources operating in the MIR. This talk will present our recent results on quasi-all-fiber laser systems generating broadband optical spectra with a high-quality frequency comb structure in the MIR spectral range. As a workhorse, a stable and compact femtosecond Er-doped fiber-based platform is used.

We demonstrate a thin-disk based regenerative amplifier system with a maximum pulse energy before compression of 550 mJ at a repetition rate of 1 kHz. Pulse compression was preliminary done with a fraction of the output and led to a pulse duration of 602 fs.

We present a thin-disk multipass amplifier which allows power scaling of ultrafast lasers to the multi-kilowatt and 100 mJ range. With a seed laser including an Innoslab amplifier, 170 W of average power were amplified to 1950 W average power at a repetition rate of 800 kHz with near diffraction-limited beam quality at a stretched pulse duration of 10 ps. In a second experiment, 117 mJ of pulse energy were reached at a stretched pulse duration of 1 ns using a seed laser including a regenerative thin-disk amplifier.

We present a rod-type, ytterbium-doped multicore fiber with 4x4 cores for coherent beam combination of femtosecond pulses. Due to the all-glass structure of the fiber, high average powers of up to 500 W after combination and compression could be achieved. Additionally, a version of this fiber with larger core diameters has been employed for energy extraction experiments resulting in multi 10 mJ energy nanosecond pulses, demonstrating future power scaling opportunities.

We discuss the generation of > 1 J pulses at 1 kHz repetition rate from a cryogenically cooled Yb:YAG active mirror amplifier. After compression 1.1 J pulses of < 4.5 ps duration are obtained with high beam quality and high shot-to-shot stability. In addition, we report the frequency doubling of 1.2 J ns pulses with 78 percent conversion efficiency in LBO to generate 0.94 J, =515 nm pulses. A second LBO crystal generates additional >100 mJ second harmonic from unconverted light reaching a total green average power of 1.04 kW.

Optically resonant dielectric metasurfaces have been established as a versatile platform for manipulating light fields at the nanoscale. While initial research efforts were concentrated on purely passive structures, all-dielectric metasurfaces also hold a huge potential for dynamic control of light fields, as well as for tailoring light emission processes, such as spontaneous emission and nonlinear frequency generation. This talk will review our recent advances in tunable, light-emitting and nonlinear all-dielectric metasurfaces, and outline future research directions for next-generation metasurface architectures.

Using sub-picosecond pulses, we report the first time observation of the formation of highly-stable multidimensional solitary states (MDSS) in molecular-filled hollow-core fibers. The MDSS have broadband red-shifted spectra with an uncommon negative quadratic spectral phase at output, originating from strong intermodal interactions. This approach paves the route to compress sub-picosecond Ytterbium laser systems to few-cycle pulse duration using a compact setup.

We report on the nonlinear temporal compression of mJ energy pulses from a Ti:Sa chirped pulse amplifier system in a multipass cell filled with argon. The pulses are compressed from 30 fs down to 5.6 fs, corresponding to approximately two optical cycles. The post-compressed beam exhibits excellent spatial quality and homogeneity. These results pave the way to robust and energy-scalable compression of Ti:Sa pulses down to the few-cycle regime.

We have experimentally demonstrated the post-compression of a long-wave infrared (9.2 µm) 150-GW peak power pulse from 2 ps to less than 500 fs using a combination of two optical materials with significantly different ratios of the nonlinear refractive index to the GVD coefficient. Such combination allows for optimization of the compression mechanism and promises a viable path to scaling peak powers to supra-terawatt levels.

Generating energetic, few-cycle laser pulses with stabilized Carrier-Envelope Phase at high repetition rate constitutes a first step to access the ultra-fast dynamics underlying the interaction of matter with intense, ultrashort pulses in attosecond science or high field physics. We present here a post-compression stage delivering 3.8fs pulses with 2.5mJ coupled to a Ti: Sa based 1 kHz TW-class laser which can deliver 17.8fs pulses with 350mrad shot to shot CEP noise. This is the first step towards high energy few-cycle post-compression of the FAB laser at ATTOLAB-Orme.

We present the nonlinear pulse compression of an ytterbium-based 4-pulse burst in a gas-filled multipass cell as a scaling approach to increase the supported pulse energy and output peak power. The pulse division and passive recombination is based on birefringent crystals and enables an output pulse energy of 4.5 mJ at a pulse duration of 31 fs while more than doubling the energy limitations set by laser induced damage of the multipass cell mirrors. Overall, a good efficiency and temporal contrast are achieved.

Subwavelength spaced arrays of nanostructures, known as metasurfaces, provide a new basis for

recasting optical components into thin planar elements, easy to optically align and control

aberrations, leading to a major reduction in system complexity and footprint as well as the

introduction of new optical functions. The planarity of flat optics will lead to the unification of

semiconductor manufacturing and lens making, where the planar technology to manufacture

computer chips will be adapted to make CMOS compatible metasurface based optical components

for high volume markets like cell phones. New polarization sensitive and depth cameras will be

discussed. Metasurfaces also offer fresh opportunities for structuring light by wavefront

engineering. I will discuss spin to total orbital angular momentum (OAM) converters and high

OAM lasing, as well as flat devices that enable light’s spin and OAM to evolve, simultaneously,

from one state to another along the propagation direction

Advancements in attosecond pulse generation give access to the electron motion dynamics of matter in real-time. Here, we measured the field-induced electronic delay response of the dielectric system to be in the order of a few hundred attoseconds and increase at higher field strength. Moreover, we demonstrate the attosecond electron motion control using synthesized two-octave light waveforms. This on-demand electron motion control opens the door for establishing ultrafast optical switches and paves the way to extend the frontiers of modern electronics and data information processing technologies into the petahertz realm.

High harmonic generation is particularly sensitive to band structure, making it a tool of choice to study all kind of complex dynamics in strongly correlated materials. We present a table-top all optical technique using high harmonic spectroscopy to probe the time-resolved electronic dynamics of the insulator-to-metal phase transition in vanadium dioxide. Our measurements are in good agreement with previous ultrafast electronic diffraction measurements and theoretical density functional calculations.

We demonstrate femtosecond time–resolved soft–X–ray absorption spectroscopy of liquid samples using table-top high-order harmonic source in the water-window spectral range. The proof-of-principle measurements of dynamics in photoionized liquid alcohols, and UV-excited small heterocyclic hydrocarbons reveal the intermolecular interaction effects on the dynamics. In the time domain, our measurements resolve the gradual appearance of absorption features due to multi-photon induced dynamics in liquid alcohols at carbon K-edge, aqueous solutions at nitrogen K-edge and charge dynamics in TiO2 colloidal suspension probed at Ti L2,3-edge with a temporal resolution of ∼30 fs.

Photo-assisted Ultrafast Scanning Electron Microscopy (USEM) dynamically maps surface photovoltages and local electric fields in semiconducting samples. Photovoltages and their gradients close to the emission at surface affect the yield and the detection efficiency of secondary electrons (SE). In this work, we present a method to characterize the evolution of photo-excited SE 2D patterns up to ultrafast regime. These results reveal the role of surface states in affecting the external field dynamics at picoseconds. Moreover, we show that tiny changes in surface preparation express deeply different photo-excited voltage signals.

We measured the femtosecond evolution of the electronic temperature of laser-excited gold nanoparticles, by means of ultrafast time-resolved photoemission spectroscopy induced by extreme-ultraviolet radiation pulses. The temperature of the electron gas was deduced by recording and fitting high-resolution photoemission spectra around the Fermi edge of gold nanoparticles providing a direct, unambiguous picture of the ultrafast electron-gas dynamics.

We present a real-time measurement technique based on Fourier Transform spectral interferometry coupled with a broadband reference pulse for the full-field characterization of broadband ultrafast complex pulses. With the proposed method we analyse noise-seeded modulation instability inducing soliton fission with a 20 fs resolution. We record the spectral interference between our test and reference pulse and retrieve complete field information using Fourier Transform Spectral interferometry pulse reconstruction. Experimental results are in good agreement with numerical simulations.

Energetic ultrashort pulses with durations below one optical cycle are highly intriguing for attosecond science among other strong-field driven applications. For the generation of such sub-cycle pulses a coherent bandwidth wider than one octave is required. We recently pioneered the generation of such millijoule level sub-cycle pulses using parametric waveform synthesis (PWS). With such pulses, we achieve direct isolated attosecond pulse generation via high-harmonic generation without the need for additional gating techniques. Additionally the PWS offers to manipulate the synthesized waveform, giving precise tuning capability to shape the attosecond pulses.

We present a flexible few-cycle pulsed laser source in the short-wavelength infrared spectral region. It combines a quasi-continuous center wavelength tunability over one octave (1–2 µm) with a millijoule-level output and an exceptional long-term stability (<1.2% rms over >160 h at 1750 nm center wavelength). This is realized by spectral broadening in a 3.2m stretched hollow-core fiber with adaptable focusing optics, few-cycle bulk compression and extensive characterization of the pulses. The 1 kHz repetition-rate source is utilized for soft x-ray high-order harmonic generation and subsequent strong-field transient-absorption experiments.

Attosecond science relies upon the generation, characterization, and control of intense, few-cycle laser pulses with well-controlled electric field waveforms. Generating such pulses has, for decades, relied upon state-of-the-art laser systems accessible in only a few laboratories worldwide, while characterization of their electric field waveforms has required complex pump-probe setups. In this talk, I will show that the delayed rotational nonlinearity of molecular gases can be harnessed for extreme compression and frequency conversion of industrial-grade lasers, and I will present a new technique for single-shot characterization of the generated laser waveforms.

We report on three novel tools to generate and characterize few-cycle pulses in the mid-infrared. This toolbox enables the generation of high mid-infrared fields, and the characterization of their temporal profiles and carrier-to-envelop phase stability.

A new variant of SPIDER (Spectral Phase Interferometry for Direct Electric field Reconstruction) method is presented. The method called DEER-SPIDER for Doppler Effect E-field Replication is based on a non-standard effect, the so-called “rotational Doppler effect”, for producing the frequency shear. It provides a spectral shearing at/near the fundamental wavelength, enabling operation of the technique in the ultraviolet spectral range. The method, evaluated under two different conditions, provide reconstructions of high reliability. Possible improvements and outlook are discussed

Layered materials are solids consisting of crystalline sheets with strong in-plane covalent bonds and weak van der Waals out-of-plane interactions. These materials can be easily exfoliated to a single layer (1L), obtaining two-dimensional (2D) materials with radically novel physico-chemical characteristics compared to their bulk counterparts. The field of 2D materials began with graphene and quickly expanded to include semiconducting transition metal dichalcogenides (TMDs). 2D materials exhibit very strong light-matter interaction and exceptionally intense nonlinear optical response, enabling a variety of novel applications in optoelectronics and photonics. This talk will review our studies on the ultrafast non-equilibrium and nonlinear optical response of 2D materials. We will discuss ultrafast carrier and spin dynamics in 2D semiconductors and their heterostructures. We will also show gate-tunable absorption saturation and third-harmonic generation in 1L-graphene and optical parametric amplification in 1L-TMDs.

We demonstrate two multi-pass cell post-compression stages that are optimized for operation at highest average power. In the first stage the pulse duration of 1-mJ 200-fs pulses with up to 1 kW average power is compressed to 31 fs with 96% efficiency yielding the highest average power for sub-100-fs pulses demonstrated to date. This is followed by a second compression stage employing ultra-broadband reflectivity enhanced silver mirrors on a silicon substrate to minimize heating induced aberrations. The second stage supports further compression of the pulse duration to <7 fs at an average power of 388 W with 82% transmission, again an average power record for few-cycle bandwidth pulses. The output of both stages is characterized and shows essentially no loss in terms of beam quality and spatiospectral homogeneity.

We demonstrate efficient post-compression of a 30 W, 0.46 GW peak power Yb source with 250 fs initial pulse duration, down to 31 fs (FWHM) in a bulk multi-pass cell (MPC). The bulk compression setup is compact, based only on off-the-shelf optics and features a total transmission of about 85 %. To the best of our knowledge, this constitutes the highest peak power in bulk MPC compression to-date, competing with gas-based post-compression solutions such as hollow-core fibers or gas-filled MPCs for a similar laser parameter range.

The soft x-ray Free-Electron Laser (FEL) FLASH is a unique tool to study ultrafast processes and is mostly used for pump-probe experiments in combination with an optical laser. Within the framework of the FLASH2020+ facility upgrade, the currently operating Ti:Sapphire and OPCPA systems will be largely replaced by high-power Yb:YAG lasers combined with nonlinear pulse compression in multi-pass cells (MPCs). This approach offers superior compactness, efficiency and simplicity of the optical laser systems. We here present first example implementations of MPC compression-based pump-probe laser systems.

We developed a high transmission Hollow-core fiber (HCF) with 1mm ID that supports 97% absolute transmission over 1m of propagation when coupled with lower power regenerative amplifiers. By adding appropriate thermal management to the system, we were able to achieve about 30 times spectral broadening of 11mJ, 1.5ps pulses from a 275W, 25 kHz InnoSlab multi-pass amplifier with 90% fiber transmission. The spectrum achieved in 1 bar Kr supports to a 50fs TL bandwidth. At the conference we plan to present first tests towards J level energy and kW level average power handling.

We present post-pulse compression of a 8.6 mJ, 1.2 ps Yb:YAG laser to a pulse duration of 44 fs at 1 kHz repetition rate in a single compression stage employing a 2m long, Ar filled-multi-pass cell reaching a transmission efficiency greater than 93%.

Spectral broadening of 3.2 µm pulses is experimentally demonstrated at 8.2 W average power output through nonlinear propagation in the combination of a thin Si and BaF2 crystal plates. Sub-two-cycle compression was achieved, by compressing up to third order dispersion with the combination of bulk compressor and custom-made dispersive mirrors. Excellent long-term power, spectral and CEP stability was observed for a period of 4 hours.

Accurate 3D imaging is essential for machines to map and interact with the physical world. While numerous 3D imaging technologies exist, each addressing niche applications with varying degrees of success, none have achieved the breadth of applicability and impact that digital image sensors have achieved in the 2D imaging world. A large-scale, two-dimensional focal plane array of coherent detector pixels operating as a light detection and ranging (LiDAR) system could serve as the core of a universal 3D imaging platform. It would enable megapixel resolution, high depth accuracy, immunity to interference from sunlight, as well as the ability to directly measure the velocity of moving objects. This talk will present an overview of architectural implementations of large-scale coherent focal plane arrays, and show results of their operation in a 4D imaging (3D + velocity) system. We will discuss performance characteristics, tradeoffs and design optimization for different applications. Finally, we will discuss future architectural implementations and opportunities for pixel size reduction to enable 10 megapixels and beyond coherent imaging cameras.

Ultrafast laser-driven THz sources for time-domain spectroscopy are a ubiquitous tool in many fields of science and are even starting to penetrate industrial fields. Whereas enormous progress has been achieved in achieving ultra-broadband operation and very high fields in the last decades, average power has for very long remained a bottleneck for many applications in spectroscopy and sensing. this talk, we will review recent progress in the generation and application of high-average power broadband Terahertz pulsed sources at MHz repetition rates for time-domain spectroscopy.

We present the generation of broadband terahertz radiation with the two-color gas plasma scheme. Driven by a multipass cell compressed high-power fiber laser system at a repetition rate of 200 kHz an average power of 94 mW is generated. A measurement based on the air-biased coherent detection scheme is used to characterize the full bandwidth of the generated pulses. By using the full potential of the driving laser further scaling of the generated THz power towards watt-level average power can be expected in the near future.

We report on a direct all optical encoding of a free-space terahertz signal onto an optical signal probing the absorption of CdSe/CdS quantum dots. The ultrafast electro-absorption modulator is based on the quantum confined stark effect. This method demonstrates the ability for high speed modulators with transition rates in the Tbit/s range and extinction ratio exceeding 6 dB. An extreme change in transmission of more than 15% is measured, which is, to the best of our knowledge, the highest value ever reported for solution processed electro-absorption materials at room temperature.

We present the methods for controlled pulse burst amplification in a single and dual femtosecond regenerative amplifier that enable a plethora of third and higher-order nonlinear spectroscopic techniques. High-resolution time-delay scans and narrowband frequency sweeping is obtained without any mechanically moving parts.

Soliton-driven frequency conversion provides an exceptionally versatile source of tuneable pulses for ultrafast science. A simple experimental setup using gas-filled hollow-fibres can continuously tune few-femtosecond pulses from the vacuum ultraviolet (around 100 nm) to the near infrared (750 nm), with high efficiency. This technique can be scaled in repetition rate: so far we have reached 50 kHz (limited by our pump laser). It can also produce circularly polarised ultraviolet pulses. Furthermore, soliton self-compression in the same system can be harnessed to produce terawatt-scale sub-cycle pulses in the infrared spectral region.

We present a new technique for asymmetric spectral broadening of high-peak power pulses, which relies on the continuous red-shift provided by rotational, Stimulated Raman Scattering over the long propagation distance in a nitrogen-filled capillary. As a result, pulses can be compressed with a net shift of their central wavelength in the vicinity of their fundamental with high energy efficiency.

Potential applications include high harmonic generation with extended cut-off, frequency difference generation in the 5-9µm range, and filamentation-induced optical path cleaning for telecommunication in the atmosphere.

We report on a nonlinear compression down to 20 fs in air-filled HCPCF. Novel spectral-temporal dynamic is observed and analysed. The results represent a promising pathway for strong and stable compression of current commercial ultra-short-pulse lasers.

We demonstrate the generation of an octave-spanning supercontinuum from 800 nm to 2800 nm in a tellurite multimode graded-index fiber. Our results show signatures of beam self-cleaning opening the way towards high-power supercontinuum light sources in the mid-infrared.

We report on the efficient external pulse compression of 255 fs, 20 μJ, 2 MHz pulses of a Yb:YAG amplifier to 6.7 fs in two gas-filled photonic crystal fiber; and their broadband down conversion to 2 μm via intra-pulse difference frequency generation. The synchronized, high power, ultrashort pulses, with octave-separated centre frequencies are ideal for advanced near-infrared spectroscopy.

Fluorescence imaging and nonlinear coherent optical microscopy can reveal important spatial properties in nanomaterials, cells and biological tissues from fixed situations to in vivo dynamics. While microscopy can guide interpretation through morphological observations at the sub-micrometric scale, optical imaging cannot directly access the way molecules are organized in specific ulstrastructures, occuring at the molecular scale. This property, which is important in many fields, from material engineering to biomechanics, is today most often studied using electron microscopy (EM) or X ray diffraction, which are not compatible with real time imaging. ... read more https://www.europeanoptics.org/pages/events/eosam2021/program/plenaries.html

We present a new technique for the temporal measurement of intense ultrashort laser pulses directly on target and at full laser power. The setup can be easily added to an existing beamline, providing pulse characterisation at the sample location. This allows pulse optimization and meaningful comparison with theory, while revealing potential pulse distortions occurring in or on the target. We demonstrate the technique by measuring intense 4-fs pulses in conditions optimized for high-harmonic generation and show that it enables measuring pulses at extreme relativistic intensities presently inaccessible to other diagnostics.

By controlling high order harmonic generation in gases and characterizing the XUV beams properties, we observe that high order harmonics are usually not all focused at the same longitudinal position. We show that this focusing can be modified by controling the XUV wavefront directly in the generating medium and achieve optics free focusing of the attosecond XUV beam with micrometer size of the XUV foci. We use this effect to perform broad band XUV spectral filtering with high efficiency and without temporal stretching of the attosecond pulses.

In this contribution, a novel class of extreme ultraviolet (XUV) sources based on high-harmonic-generation (HHG) is presented. The source realized in this work is driven by a frequency doubled and post compressed Yb-fiber laser system, delivering 51μJ, 18.6fs pulses at a central wavelength of 515nm and a repetition rate of 1MHz. Employing this unique laser system for HHG, results in a record high XUV average power of 12.9mW in a single harmonic line at 26.5eV with sub-6fs pulse duration – surpassing previously reported HHG sources by one order of magnitude.

We report efficient, phase-coherent high-harmonic generation in chirped periodically poled lithium niobate waveguides pumped with a watt-scale 3 $\mu$m frequency comb. Simulations support a mechanism of cascaded quadratic nonlinearity and provide insight into spectral optimization.

Propagation of sub-picosecond laser pulses in a gas-filled hollow-core fibre creates red-shifted multidimensional solitary states through intermodal Raman scattering. The pulses, which can be compressed to few-cycle durations by simple transmission through materials with positive dispersion, are used to generate high harmonics in argon. Due to the characteristics of the ultrashort driver pulses, the highest generated photon energy is increased, allowing for the implementation of photon-demanding applications with high photon energy requirements. As a demonstration, the source is used for resonant magnetic scattering measurements at the M2,3 edge of cobalt.

QuTech and Kavli Institute of Nanoscience, Delft Technical University, The Netherlands

Starting with the demonstration of lasing more than 50 years ago, the special properties of rare-earth ion doped crystals and glasses have given rise to the development of numerous solid-state lasers and amplifiers, which are crucial for the functioning of today’s world-wide Internet. As a fascinating generalization of their use in optical communication infrastructure, it became clear during the past decade that, when cooled to cryogenic temperatures of a few Kelvin, rare-earth crystals also promise the creation of technology for quantum communication networks.

I will discuss recent advances in my and other groups towards the development of key ingredients of such networks: the reversible storage of quantum states of light in large ensembles of rare-earth ions, as well as the creation of single photons using individual emitters. This work is interesting from a fundamental point of view, and furthermore paves the path towards a quantum repeater, which will ultimately enable quantum communications over arbitrary distances.

In this talk, I will discuss our recent progress in the context of metasurfaces with tailored nonlocal responses. Based on these principles, I will describe opportunities for augmented reality, secure communications, analog optical computing and a new generation of light-emitting metasurfaces.

When nanostructures are buried underneath optically opaque layers, extremely-high-frequency. laser-induced ultrasound may be used to detect them, which has potential applications for wafer alignment. In this talk, results will be shown on femtosecond generation and detection of ultrasound to detect buried gratings. We show results on home-made samples consisting of gratings buried underneath up to 20 layers, and discuss possible methods to improve signal strength.