We introduce a high-harmonic generation (HHG)-based XUV source that offers a broad photon flux range from 40 eV to 150 eV. This source utilizes an industrial-grade TruMicro 2030 laser system with 20-W average power, delivering up to 100 µJ with pulse durations under 400 fs. A post-compression unit is incorporated to reduce the pulses to approximately 40 fs with just a 10% average power loss. The turnkey source achieves a photon flux exceeding 10^10 photons/s around 70 eV.

We present a highly stable, easy-to-use, table-top coherent XUV source delivering a brightness of >1kW/(mm²sr)/1%BW at 130eV (9.5nm). It is based on high-harmonic generation driven by an ultrastable ytterbium-based fiber laser and a multipass-cell-based post- compression to 35fs.

We present recent developments in high-power fiber-laser-driven frequency conversion allowing for imaging and spectroscopy applications at unprecedented measurement speeds.

We report on our progress in developing a compact laser that uses thulium-based fiber CPA technology emitting >30W at 2 µm and a >100W ultrafast laser for scientific applications based on coherent combination.

We analyse time- and angle-resolved transverse magneto-optical Kerr effect spectroscopy measurements at soft x-ray energies via polarization-dependent magnetic scattering simulations to determine the spatio-temporal and element-specific evolution of femtosecond laser-induced spin dynamics in magnetic nanostructures.

Laboratory based laser driven short pulse X-ray sources like laser produced plasmas (LPP) and high harmonic generation (HHG) exhibit a great potential for spectroscopy in the soft X-ray range. These sources are complementary to large scale facilities like synchrotrons or free electron lasers. For applications of LPP or HHG sources for time-resolved X-ray absorption spectroscopy in the water window or beyond a high photon flux is crucial. The available photon flux strongly depends on energy, pulse duration and repetition rate of the pump laser. Depending on the experimental needs in timeresolved experiments pulse durations of the X-ray pulse ranging from nanoseconds to sub-femtoseconds are required. In our contribution we will present a highly brilliant LPP source emitting soft X-rays in the photon energy range between 50 and 1500 eV based on CPA and thin disk laser technology as well as the high average power thin disk laser based OPCPA system for high photon flux HHG. In addition we present a new generation of reflection zone plates on spherical substrates, that promises a remarkable high resolution over a wide spectral range making it an ideal and highly efficient diffractive optic for time-resolved NEXAFS experiments in the lab.

We developed a high power optical parametric chirped-pulse amplification (OPCPA) system at 2.1 µm harnessing a 500 W Yb:YAG thin disk laser as the only pump and signal generation source. The OPCPA system operates at 10 kHz with a single pulse energy of up to 2.7 mJ and pulse duration of 30 fs. The maximum average output power of 27 W sets a new record for an OPCPA system in the 2 µm wavelength region. The soft X-ray continuum generated through high harmonic generation with this driver laser can extend to around 0.55 keV, thus covering the entire water window (284 eV - 543 eV). With a repetition rate still enabling pump-probe experiments on solid samples, the system can be used for many applications.

Powerful Mid-IR sources are key tools for advanced spectroscopic applications, high field science and conversion to high frequency radiation. In particular, the so-called water window spectral region between 2.3 nm and 4.4 nm attracts a lot of attention, as it covers the K-shell absorption edges of carbon, nitrogen and oxygen and is therefore ideally suited for spectroscopic studies of biomolecules in their natural aqueous environment [1]. On a laboratory scale, pulses with a central wavelength of a few nm can be obtained by generating high harmonics, where the physics of this highly nonlinear process favors the use of driver lasers in the 2 μm wavelength region. However, due to the extremely low conversion efficiency, meaningful soft X-ray photon flux can only be provided by employing high average-power high pulse energy mid-infrared driver lasers [2]. Here we present a 2.1 μm OPCPA delivering 3.3 mJ pulses at a repetition rate of 10 kHz, thus improving our previous results [3] and setting a new record in terms of average power in the 2 μm wavelength region. Our setup starts with a commercially available 500 W Yb:YAG thin disk laser (DIRA 500, Trumpf Scientific Lasers) operating at 10 kHz, serving both as pump and signal generation source. The latter is performed in a front-end developed by Fastlite, and makes use of supercontinuum generation, followed by difference frequency generation. The resulting pulses are centered around 2.1 μm and pre-amplified to an average power of 280 mW. Owing to the system design, the 2 μm pulses should feature passive carrier-envelope phase (CEP) stability. Indeed, first measurements of the single shot CEP noise in our setup yielded results around 200 mrad. However, further improvements are expected since in comparable systems values below 100 mrad have been reported [4]. For power amplification, the pulses are stretched to 1 ps duration with a pair of silicon wedges, so that they fit the pump pulse duration of 2 ps in the two power OPA stages. The first one consists of a 2 mm thick BiBO crystal pumped with 130 W of the DIRA output power. This allows to amplify the 2 μm beam to an average power of 10 W. The second OPA stage is a 5 mm thick YCOB crystal pumped with 320 W, and delivers an output power of 33 W. The amplified pulses are compressed with a 4 cm thick suprasil glass block. We obtain a slightly elliptic beam profile, as shown in Fig. 3(a). The measured spectrum (Fig.3(b)) extends from 1.8 μm to 2.4 μm, with a FWHM of 430 nm. The modulations result from our front-end configuration, which is optimized for the shortest pulses after power amplification. The spectrum would allow for a Fourier transform limited pulse duration of only 22 fs, which is close to the experimental value of 25 fs inferred from an autocorrelation measurement (Fig. 3(c)).

For the last few years, coherent beam combining (CBC) has been drastically increasing the performances of ytterbium-doped femtosecond fiber amplifiers, up to more than 10 mJ output energy and to the multi-kilowatt level [1,2]. CBC consists in coherently adding the output beams of several independent amplifiers seeded by a common source. This method involves both an efficient combination process along with a phase detection and control technique applied on all the beams to combine. However, for femtosecond pulses to reach the Joule level and address applications such as particles acceleration, several thousands of fibers need to be combined. Thus, highly scalable CBC architectures along with adapted phase measurements techniques need to be investigated.

A monolithic OPCPA-system based on an Yb:YAG thin disk laser delivers 30 fs pulses at 2100 nm wavelength with 27 W average power at 10 kHz. Design, pulse characterization, soft X-ray generation and optimization are addressed.

Oral MoA1.2 Monday, 14:45 Auditorium Novel Methods for CEO Stabilization in Fiber Lasers: Opto-Optical Modulation and Cross Gain Modulation— ∙Kutan Gurel, Valentin J. Wittwer, SargisHakobyan, Nayara Jornod, Stephane SchiltThomas Südmeyer— Laboratoire Temps-Fréquence, Université deNeuchâtel,2000Neuchâtel, Switzerland We present the carrier-envelope-offset (CEO) frequency stabilization of a fiber laser using two new methods. The first method is based on cross gain modulation (XGM) of the intra-cavity power. The second is by opto-optical-modulation (OOM) of a semiconductor-absorber chip. Both methods are easy to integrate, yielding tight-lock of the CEO.

We report on the coherent beam combining of seven fiber chirped-pulse amplifiers using a highly scalable architecture. A combining efficiency of 48% is obtained in linear regime, yielding 71 W pump-limited average power after compression, with a phase noise between two fibers as low as λ/38 RMS. The experiment is operated at high B-integral, with only little impact on the combining efficiency as well as on the temporal and spatial properties of the combined beam.

Coherent beam combining in tiled-aperture configuration is demonstrated on seven femtosecond fiber amplifiers using an interferometric phase measurement technique. The residual phase error between two fibers is as low as λ/55 RMS and a combination efficiency of 48% has been achieved. The combined pulses are compressed to 216 fs, delivering 71 W average power at a repetition rate of 55 MHz. Operating the laser system in a nonlinear regime with an estimated B-integral of 5 rad yields a combining efficiency of 45% with the same phase stability. These results pave the way to very large high-power and high energy coherent beam combining systems.

The XCAN project aims at the coherent combination of 61 fiber amplifiers in the femtosecond regime. An important intermediate step towards this goal is the implementation of a seven fiber test setup, which allows to address key scientific and technical challenges which might occur in the scaled version of 61 fibers. This work includes the design and characterization of a support unit able to hold 61 fibers with the high precision required for an efficient coherent combination in tiled aperture configuration. This configuration, in combination with an interferometric phase measurement and active phase control, is particularly well suited for the coherent combination of a very large number of beams. Our first preliminary results with seven fibers include a combination efficiency of 30 % and a residual phase error between two fibers as low as lambda/40 rms. Experiments conducted with three fibers in order to evaluate technical improvements revealed an increase of efficiency to 54 %. The combined beam was temporally compressed to 225 fs, which is Fourier transform limited with respect to the measured spectrum.

The XCAN project aims at the coherent combination of 61 fiber amplifiers in the femtosecond regime. An important intermediate step towards this goal is the implementation of a seven fiber test setup, which allows to address key scientific and technical challenges which might occur in the scaled version of 61 fibers. This work includes the design and characterization of a support unit able to hold 61 fibers with the high precision required for an efficient coherent combination in tiled aperture configuration. This configuration, in combination with an interferometric phase measurement and active phase control, is particularly well suited for the coherent combination of a very large number of beams. Our first preliminary results with seven fibers include a combination efficiency of 30 % and a residual phase error between two fibers as low as λ/40 rms. Experiments conducted with three fibers in order to evaluate technical improvements revealed an increase of efficiency to 54 %. The combined beam was temporally compressed to 225 fs, which is Fourier transform limited with respect to the measured spectrum.

We report on the coherent combination of seven fiber amplifiers in the femtosec-ond regime using an interferometric phase measurement technique. A combination efficiency of 54 % and a compressed pulse length of 225 fs were achieved.

The XCAN project, which is a three years project and began in 2015, carried out by Thales and the Ecole Polytechnique aims at developing a laser system based on the coherent combination of laser beams produced through a network of amplifying optical fibers. This technique provides an attractive mean of reaching simultaneously the high peak and high average powers required for various industrial, scientific and defense applications. The architecture has to be compatible with very large number of fibers (1000-10000). The goal of XCAN is to overcome all the key scientific and technological barriers to the design and development of an experimental laser demonstrator. The coherent addition of multiple individual phased beams is aimed to provide tens of Gigawatt peak power at 50 kHz repetition rate. Coherent beam combining (CBC) of fiber amplifiers involves a master oscillator which is split into N fiber channels and then amplified through series of polarization maintaining fiber pre-amplifiers and amplifiers. In the so-called tiled aperture configuration, the N fibers are arranged in an array and collimated in the near field of the laser output. The N beamlets then interfere constructively in the far field, and give a bright central lobe. CBC techniques with active phase locking involve phase mismatch detection, calculation of the correction and phase compensation of each amplifier by means of phase modulators. Interferometric phase measurement has proven to be particularly well suited to phase-lock a very large number of fibers in continuous regime. A small fraction of the N beamlets is imaged onto a camera. The beamlets interfere separately with a reference beam. The phase mismatch of each beam is then calculated from the interferences’ position. In this presentation, we demonstrate the phase locking of 19 fibers in femtosecond pulse regime with this technique. In our first experiment, a master oscillator generates pulses of 300 fs (chirped at 200 ps). The beam is split into 19 passive channels. Prior to phase locking, the optical path differences are adjusted down to 10 μm with optical delay lines. Interferograms of the 19 fibers are recorded at 1 kHz with a camera. A dedicated algorithm is developed to measure both the phase and the delay between the fibers on a measurement path. The delay and phase shift are thus calculated collectively from a single image and piezo-electric fiber stretchers are controlled in order to ensure compensation of time-varying phase and delay variations. The residual phase shift error is below λ/60 rms. The coherent beam combining is obtained after propagation and compression. The combined pulse width is measured at 315fs. A second experiment was done to coherently combine two amplified channels of the XCAN demonstrator. A residual phase shift error of λ/30 rms was measured in this case.

Architecture évolutive de combinaison cohérente femtoseconde pour amplificateurs à fibre de puissance Allier de fortes puissances moyennes et crêtes donne accès à un champ applicatif très large pour un système laser ultrarapide. Une technique qui s’est avérée capable de satisfaire ces exigences est la combinaison cohérente de faisceaux (CBC). Elle permet de séparer spatialement les faisceaux avant l’amplification pour les recombiner ensuite d’une manière cohérente en un unique faisceau. Afin d’obtenir une recombinaison efficace, les propriétés spatiales et spectrales de tous les faisceaux doivent être parfaitement en accord.Pour des applications comme l’accélération de particules, le recours à plusieurs milliers de fibres doit être envisagé. Il est donc nécessaire d’étudier des architectures CBC fortement évolutives en termes de canaux amplificateurs.Le projet XCAN vise à une première démonstration d’un tel système en réalisant la combinaison cohérente de 61 fibres amplificatrices. Afin d’étudier les défis scientifiques et techniques d’une telle architecture, une version de taille réduite comprenant sept fibres a été mise en place.La conception et la réalisation de ce prototype sont le sujet de cette thèse.Dans un premier temps, des simulations ont été effectués afin d’estimer les désaccords tolérables entre les propriétés spatiales et spectrales des différents faisceaux.Basé sur ce travail de modélisation, un système laser de combinaison cohérente de sept fibres a été ensuite assemblé et caractérisé. Les résultats obtenus sont très prometteurs et montrent que notre architecture est bien adaptée pour accueillir les 61 fibres du démonstrateur final XCAN.