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Coherent soft X-ray (SXR) sources that provide a high photon flux in the water window are essential tools for advanced spectroscopy (e.g. of magnetic materials [1] and organic compounds [2] ) or for lens-less bio imaging with nm-scale resolution [3] . To date, such sources are mostly large-scale facilities like synchrotrons or free electron lasers. A promising alternative are laser-driven sources, based on high harmonic generation (HHG) in noble gases. Current state-of-the-art SXR HHG uses frequency converted Ti:Sa lasers (to ~2 µm wavelength to increase the phase matching cutoff) with multi-mJ pulse energies at 1 kHz repetition rate [1] . Most recently, there has been a strong push towards increasing the repetition rate of the driving lasers, and the SXR HHG, to enable faster data acquisition, space-charge-reduced SXR photoelectron spectroscopy or coincidence detection [4] , [5] . In this contribution, we present an approach to SXR HHG that is based on nonlinear pulse self-compression and HHG in the same helium gas-filled antiresonant hollow-core fiber (ARHCF). Because of the intensity enhancement resulting from temporal pulse self-compression, the experiments can be driven by moderate-energy, multi-cycle laser pulses, which facilitates repetition rate scaling. We coupled 100 fs-, 250 µJ-pulses centered around 1.9 µm wavelength at a 98 kHz repetition rate to the ARHCF ( Fig. 1a ). When the fiber length (~1.2 m) and the gas pressure at its output (~3.8 bar) were chosen appropriately, the pulses close to its end ( Fig. 1b ) were self-compressed to 4×10 14 W/cm 2 . At this point, the gas is partially ionized, and the chosen pressure ensures phase matching between the driving laser and the generated SXR light ( Fig. 1b ). It is the first time that this approach is experimentally realized, and we have generated a photon flux >10 6 Ph/s/eV at the carbon K-edge ( Fig. 1c ). To the best of our knowledge, this is the highest photon flux at 300 eV reported to date at a laser repetition rate >1 kHz.

We report on the generation of GW-class peak power, 35-fs pulses at 2-µm wavelength with an average power of 51 W at 300-kHz repetition rate. A compact, krypton-filled Herriott-type cavity employing metallic mirrors is used for spectral broadening. This multi-pass compression stage enables the efficient post compression of the pulses emitted by an ultrafast coherently combined thulium-doped fiber laser system. The presented results demonstrate an excellent preservation of the input beam quality in combination with a power transmission as high as 80%. These results show that multi-pass cell based post-compression is an attractive alternative to nonlinear spectral broadening in fibers, which is commonly employed for thulium-doped and other mid-infrared ultrafast laser systems. Particularly, the average power scalability and the potential to achieve few-cycle pulse durations make this scheme highly attractive.

Bright, coherent soft X-ray (SXR) radiation is essential to a variety of applications in fundamental research and life sciences. So far, high photon flux in this spectral region can only be delivered by synchrotrons, free electron lasers or high-order harmonic generation (HHG) sources, which are driven by kHz-class repetition rate lasers with very high peak powers. Here, we establish a novel route toward powerful and easy-to-use SXR sources by presenting a compact experiment, in which nonlinear pulse self-compression to the few-cycle regime is combined with phase-matched HHG in a single, helium-filled antiresonant hollow-core fibre (ARHCF). This enables the first 100 kHz-class repetition rate, table-top SXR source, that delivers an application-relevant flux of 2.8*10^6 Photons/s/eV around 300 eV. The fibre-integration of temporal pulse self-compression (leading to the formation of the necessary strong-field waveforms) and pressure controlled phase-matching will allow compact, high repetition rate laser technology, including commercially available systems, to drive simple and cost-effective, coherent high-flux SXR sources., 12 pages, 3 figures

Intense, ultrafast laser sources with an operation wavelength beyond the well-established near-IR are valuable tools for exploiting the wavelength scaling laws of strong-field, light-matter interactions. Such laser systems enable the scaling of the phase matching photon energy cut-off in high-order harmonic generation, which allows for the generation of coherent soft X-ray radiation up to, and even beyond, the water window. Such laser-driven sources enable a plethora of subsequent applications. A number of these applications can significantly benefit from an increase in repetition rate. In that regard, ultrafast thulium-doped fiber laser systems (providing a broad amplification bandwidth in the 2 μm wavelength region) represent a promising, average-power scalable laser concept for driving high-order harmonic generation. These lasers are capable of delivering ~100 fs pulses with multi-GW peak power at hundreds of kHz repetition rate. In this work, we show that combining ultrafast thulium-doped fiber CPA systems with HHG in an antiresonant hollow-core fiber is a promising approach to realize high photon energy cut-off HHG from a compact setup. The realization is based on combining nonlinear pulse self-compression (leading to strong-field waveforms) and phase-matched high-order harmonic generation in a single antiresonant hollow-core fiber. In this demonstration, a photon energy cut-off of approximately 330 eV has been achieved, together with a photon flux >106 ph/s/eV at 300 eV. These results emphasize the great potential of exploiting the HHG wavelength scaling laws with 2 μm fiber laser technology. Improvements of the HHG efficiency, the overall HHG yield and further laser performance enhancements will be the subjects of our future work.

We present the setup of a compact, q-switched, cryogenically cooled Yb:YAG laser, which is capable of producing over 1 J output energy in a 10 ns pulse at 10 Hz. The system’s design is based on the recently published unstable cavity layout with gain shaping of the spatial intra-cavity intensity distribution. Using a hexagonal homogenized pump beam, the laser generated an according hexagonal output beam profile. The suitability of such laser properties for the intended use in a laser shock peening process is demonstrated. In the experiment an aluminum plate was treated and the generated residual stresses in the sample subsequently measured. Other applications of this laser system like laser pumping or surface cleaning are conceivable.

Intense, ultrafast laser sources with an emission wavelength beyond the well-established near-IR are important tools for exploiting the wavelength scaling laws of strong-field, light-matter interactions. In particular, such laser systems enable high photon energy cut-off HHG up to, and even beyond, the water window thus enabling a plethora of subsequent experiments. Ultrafast thulium-doped fiber laser systems (providing a broad amplification bandwidth in the 2 μm wavelength region) represent a promising, average-power scalable laser concept in this regard. These lasers already deliver ~100 fs pulses with multi-GW peak power at hundreds of kHz repetition rate. In this work, we show that combining ultrafast thulium-doped fiber CPA systems with hollow-core fiber based nonlinear pulse compression is a promising approach to realize high photon energy cut-off HHG drivers. Herein, we show that thulium-doped, fiber-laser-driven HHG in argon can access the highly interesting spectral region around 90 eV. Additionally, we show the first water window high-order harmonic generation experiment driven by a high repetition rate, thulium-doped fiber laser system. In this proof of principle demonstration, a photon energy cut-off of approximately 400 eV has been achieved, together with a photon flux

In this contribution, we present a Tm-doped fiber chirped pulse amplifier system delivering 108 W of average output power at 417 kHz repetition rate with 250 fs pulse duration and close to 1 GW of pulse peak power.

We report on soft x-ray HHG driven by a thulium-doped fiber laser. It is the first time that a photon energy cut-off ~400 eV has been demonstrated using this highly scalable laser technology.

Die Hande des medizinischen Personals sind in Krankenhausern der wichtigste Vektor bei der Ubertragung von Erregern. In Grosbritannien wurde daher ein „bare to the elbows“-Dresscode erlassen. Ziel dieser Studie war es, herauszufinden, ob die Kontamination der Arbeitskleidung durch Keime vergleichbar ist mit der Kontamination der Hande des Krankenhauspersonals und ob durch die Arbeitskleidung ein reales Transmissionsrisiko besteht. Insgesamt wurden 54 Abstriche beim Pflegepersonal sowie bei Arzten, Patienten und Krankenhausarbeitsmaterialien abgenommen. Die statistisch signifikant dichteste Besiedlung mit Keimen zeigten die Abstriche der Patienten (Median 73 kolonienbildende Einheiten (= KBE)), gefolgt vom Armel des Arztkittels (Median 36 KBE, p = 0,005), Arbeitskleidung des Pflegepersonals nach Beendigung einer Schicht (Median 23 KBE, p

The latest generation of high-energy-class pulsed laser facilities, under construction or planned, such as EuPRAXIA, require reliable pump sources with high power (many kW), brightness (&gt, 1 MW/cm2/sr) and electro-optical conversion efficiency (&gt, 50%). These new facilities will be operated at high repetition rates (around 100 Hz) and only diode lasers are capable of delivering the necessary performance. Commercial (quasi-continuous wave, QCW) diode laser pulse-pump sources are, however, constructed as low-cost passively cooled stacked arrays that are limited either in brightness, efficiency or repetition rate. Commercial continuous wave diode laser pumps constructed using microchannel coolers (as used in high-value industrial machine tools) can fulfil all requirements, but are typically not preferred, due to their cost and complexity and the challenges of preventing cooler degradation. A custom solution is shown here to fill this gap, using advanced diode lasers in a novel passive side-cooling geometry to realize 100 &hellip, 200 Hz pump modules (10%&ndash, 20% duty cycle) that emit peak power of 6 kW at wavelength = 940 nm. The latest performance of these modules is summarized and compared to literature. We show that a brightness &gt, 1 MW/cm2/sr can be efficiently delivered across a wide range of laser pulse conditions with 10% duty cycle (pulse width: 100 &micro, s &hellip, 100 ms &hellip, cw, repetition rate up to 1 kHz). Furthermore, we describe how these pumps have been used to construct and reliably operate (&gt, 109 pulses without degradation) in high-energy-class regenerative and ring amplifiers at the Max-Born-Institut f&uuml, r Nichtlineare Optik und Kurzzeitspektroskopie (MBI). We also show first results on 100 Hz pumping of cryogenically cooled solid-state Yb:YAG slab amplifiers, as anticipated for use in the EuPRAXIA laser, and note that peak temperature is disproportionately increased, indicating that improved cooling and more detailed studies are needed.

This research aims to provide a more comprehensive, life cycle accounting of two categories of environmental and economic benefits associated with the $3 billion US “Cash for Clunkers” vehicle scrappage program. First, using a life cycle emissions methodology developed in Lenski et al. (2010), we find that about 29,000 metric tons of criteria pollutant emissions were avoided, for a benefit of about $23 million; avoided carbon dioxide emissions, by comparison, provided a benefit worth $90 million. Second, we compare the market value of scrapped vehicles to the rebates provided, calculating the consumer surplus or “gift” to participants to be up to $2 billion (about $2000 to $3000 per vehicle). This is significantly more than offered in previous vehicle scrappage programs, and suggests opportunities to get more environmental and economic “bang for the buck.” Finally, these two categories of benefits are found to be heavily concentrated geographically around urban centers. About 2% of US counties (50 counties) received 50% and 30% of the aggregate benefits from avoided criteria pollutant emissions and consumer surplus from the rebates, respectively.

The hands of medical stuff are the most important vectors for the transmission of pathogens in the hospital. Furthermore a "bare below the elbows dress code" has been introduced in Great Britain.Aim of this study was to investigate whether workwear contamination of the medical stuff by pathogens is similar to the contamination of their hands and whether wearing workwear is associated with increased transmission risk.In total 54 swabs were collected from nursing stuff, medical doctors, patients and hospital work material.Patients had a statistically significant more dense colonization with bacteria (median = 73 colony-forming units (CFU)), than the sleeves of the doctor's coat (median = 36 CFU, p = 0,005), followed by workwear of the nursing stuff at the end of a shift (median = 23 CFU, p0,001) and the hospital work material (median = 15 CFU, p0,001). Isolated pathogens were coagulase-negative staphylococci, Staphylococcus aureus, Enterobacter cloacae and Acinetobacter species.Contaminated work wear presents a relevant risk for the transmission of pathogens. A "bare below the elbow dress-code" or the daily change of the doctor's coat appear both to represent reasonable measures to reduce the transmission risk of pathogens in hospitals.

We report on the properties of a-/ μ c-Si:H and a-SiC:H grown by hydrogen assisted chemical vapour deposition (HACVD) of different gas mixtures depending on various deposition parameters. Silicon films were grown by using gas mixtures of H 2 /SiH 4 and H 2 /Si 2 H 6 , whereas silicon–carbon films were deposited using H 2 /CH 4 /SiH 4 , H 2 /C 2 H 4 /SiH 4 , H 2 /C 2 H 4 /Si 2 H 6 and H 2 /SiH 3 CH 3 . The composition and bulk properties of the deposited films are investigated by FT–IR and Raman, XPS, RBS, SEM, conductivity measurements and UV/VIS. As proved by Raman and conductivity measurements, μ c-Si:H films are obtained using total pressures P tot smaller than 5.5 Torr. Above a certain total pressure P tot (6.5 Torr) a-Si:H films are obtained. As shown by SEM, the amorphous films exhibit a rather smooth surface morphology, whereas the μ c films show a grain structure. In the pressure range from 5.5 to 6.5 Torr, a phase transition occurs. Carbon-rich a-SiC:H-films (up to X C =0.7) are obtained using C 2 H 4 as carbon source, whereas the use of CH 4 leads to films with minor amounts of carbon. Films based on CH 3 SiH 3 exhibit a nearly stoichiometric composition and a high degree of chemical order. The composition is influenced by several gas phase parameters, e.g., total pressure P tot , substrate temperature T s and the mole fraction of the reaction gases. A gas phase kinetic simulation has been carried out and the validation of the model is tested by comparison with experimental results of silicon film deposition. As a result, the pressure P calc , at which the concentration of disilene is a hundred fold higher than that of atomic hydrogen, and the characteristic pressure P * of the μ c-/a-Si:H phase transition plotted as a function of Φ (SiH 4 )/ Φ tot behave very similar. These results were used to extend the model to the deposition of silicon–carbon films in order to correlate and to discuss the material properties of the silicon–carbon system.

We report on the electronic properties, stability and hydrogen content of amorphous hydrogenated silicon films (a-Si:H) grown by hydrogen assisted chemical vapour deposition. The dependence of the dark conductivity and photoconductivity, the optical gap, defect density, Urbach energy, microstructure parameter and hydrogen content on substrate temperature, varied in the range 150–350°C, was investigated. As a result, the defect density, determined by the constant photocurrent method, reaches a minimum value of 5 x 1015 cm−3 at 240°C with an Urbach energy of 45 meV and a hydrogen content of 5 at.%, obtained from analysis of the corresponding IR spectra. After 36 h light soaking, performed with a xenon flash lamp, the defect density is increased to a value of 5 x 1017 cm−3. The observed dependence of the material properties on substrate temperature is discussed in the light of existing growth models.

A 10 Hz, 10 mJ-level Yb:KYW diode-pumped regenerative amplifier for picosecond pulses at 1040 nm was developed. It will be used in front end of the PHELIX petawatt laser system at the Helmholtz-Center GSI to pump an optical parametric amplifier (OPA) for temporal contrast enhancement. In order to achieve a high temporal contrast, this regenerative amplifier is used as the pump source in a chirped-pulse amplification arrangement, which generates picosecond pulses before frequency doubling. For synchronization purposes, the seed pulses are derived from the femtosecond oscillator of the petawatt laser system, frequency shifted and pre-amplified by two fiber amplifiers.

We report on a novel 10 mJ-level diode-pumped Yb:KYW amplifier at 1040 nm, which generates picosecond pulses at a repetition rate of 10 Hz. It will be used in the front end of a petawatt laser system for pumping an optical parametric amplifier (OPA) for contrast enhancement. For synchronization purposes the amplifier is seeded by pulses that are derived from the femtosecond oscillator. After stretching by a volume Bragg grating and amplification in a double stage fiber amplifier the pulses are injected into the Yb:KYW regenerative cavity. Finally, the pulses are compressed to 1 ps before preparing pump pulses for the OPA by second harmonic conversion.

For laser performance simulations, optical properties of applied active materials have to be exactly known. Here we report on temperature dependent emission and absorption cross section measurements for Yb:YAG, Yb:CaF 2 and Yb:FP15-glass. The temperature of the samples was aligned in steps of 20 K between 100 K and room temperature with a liquid nitrogen driven cryostat. Absorption spectra were obtained with a fiber coupled white light source and fluorescence spectra by excitation with a fiber coupled 10W laser diode at 970 nm. All spectral measurements were performed with a scanning spectrum analyzer, providing a spectral resolution down to 0.05 nm. By applying the McCumber relation in combination with the Fuchtbauer-Ladenburg method, we were able to obtain a valid emission cross section over the whole range of interest from the measured data.

It has been shown, that cryogenic cooling of Yb3+-doped media is increasing laser performance significantly[1,2]. The reason for this is the thermal depopulation of the lower laser levels turning the quasi three level extraction scheme into a real four level scheme. By now most of these cryogenic cooled amplifiers aim on liquid nitrogen temperature. For future systems it has to be estimated what is an optimum operation temperature as compromise between laser performance and effort for cooling. This is needed as well from an energetic point of view as from an financial point of view. For this it is necessary to know the basic absorption and emission cross sections in dependence of temperature.

An output energy of 1.1 J of amplified nanosecond pulses was obtained by utilizing a diode-pumped Yb:YAG laser amplifier with the crystal cooled to 125 K. We achieved an unrivaled high total amplifier efficiency of 45 %.

One of the goals of the US Consumer Assistance to Recycle and Save (CARS) Act of 2009, more commonly known as ‘Cash for Clunkers’, was to improve the US vehicle fleet fuel efficiency. Previous studies of the program’s environmental impact have focused mainly on the effect of improved fuel economy, and the resulting reductions in fuel use and emissions during the vehicle use phase. We propose and apply a method for analyzing the net effect of CARS on greenhouse gas emissions from a full vehicle life cycle perspective, including the impact of premature production and retirement of vehicles. We find that CARS had a one-time effect of preventing 4.4 million metric tons of CO2-equivalent emissions, about 0.4% of US annual light-duty vehicle emissions. Of these, 3.7 million metric tons are avoided during the period of the expected remaining life of the inefficient ‘clunkers’. 1.5 million metric tons are avoided as consumers purchase vehicles that are more efficient than their next replacement vehicle would otherwise have been. An additional 0.8 million metric tons are emitted as a result of premature manufacturing and disposal of vehicles. These results are sensitive to the remaining lifetime of the ‘clunkers’ and to the fuel economy of new vehicles in the absence of CARS, suggesting important considerations for policymakers deliberating on the use of accelerated vehicle retirement programs as a part of the greenhouse gas emissions policy.

not Available.

We present HHG results obtained with thulium-doped fiber lasers. It is the first time that a photon energy cut-off close to 400 eV has been demonstrated using this highly scalable laser technology.