KEYWORDS: Physics, Current controlled current source, Laser optics, Free electron lasers, X-ray optics, X-rays, Femtosecond phenomena, X-ray lasers, X-ray sources, High power lasers
The combination of powerful optical lasers and an x-ray free-electron laser (XFEL) provides unique capabilities to study the transient behavior of matter in extreme conditions. The high energy density science instrument (HED instrument) at the European XFEL will provide the experimental platform on which an unique x-ray source can be combined with various types of high-power optical lasers. In this paper, we highlight selected scientific examples together with the associated x-ray techniques, with particular emphasis on femtosecond (fs)-timescale pump–probe experiments. Subsequently, we present the current design status of the HED instrument, outlining how the experiments could be performed. First user experiments will start at the beginning of 2018, after which various optical lasers will be commissioned and made available to the international scientific community.
We present an overview of the cryo-amplifier concept and design utilized in the DiPOLE100 laser system built for use at the HiLASE Center, which has been successfully tested operating at an average power of 1kW. Following this we describe the alterations made to the design in the second generation system being constructed for high energy density (HED) experiments in the HED beamline at the European XFEL. These changes are predominantly geometric in nature, however also include improved mount design and improved control over the temporal shape of the output pulse. Finally, we comment on future plans for development of the DiPOLE laser amplifier architecture.
E. Schleifer, E. Nahum, S. Eisenmann, M. Botton, A. Baspaly, I. Pomerantz, F. Abricht, J. Branzel, G. Priebe, S. Steinke, A. Andreev, M. Schnuerer, W. Sandner, D. Gordon, P. Sprangle, K.W. Ledingham, A. Zigler
Compact size sources of high energy protons (50-200MeV) are expected to be key technology in a wide range of scientific applications 1-8. One promising approach is the Target Normal Sheath Acceleration (TNSA) scheme 9,10, holding record level of 67MeV protons generated by a peta-Watt laser 11. In general, laser intensity exceeding 1018 W/cm2 is required to produce MeV level protons. Another approach is the Break-Out Afterburner (BOA) scheme which is a more efficient acceleration scheme but requires an extremely clean pulse with contrast ratio of above 10-10. Increasing the energy of the accelerated protons using modest energy laser sources is a very attractive task nowadays. Recently, nano-scale targets were used to accelerate ions 12,13 but no significant enhancement of the accelerated proton energy was measured. Here we report on the generation of up to 20MeV by a modest (5TW) laser system interacting with a microstructured snow target deposited on a Sapphire substrate. This scheme relax also the requirement of high contrast ratio between the pulse and the pre-pulse, where the latter produces the highly structured plasma essential for the interaction process. The plasma near the tip of the snow target is subject to locally enhanced laser intensity with high spatial gradients, and enhanced charge separation is obtained. Electrostatic fields of extremely high intensities are produced, and protons are accelerated to MeV-level energies. PIC simulations of this targets reproduce the experimentally measured energy scaling and predict the generation of 150 MeV protons from laser power of 100TW laser system18.
In the present paper it is offered to significantly increase target absorption and to optimize
parameters of a relief and basic part of a target so that an absorbed energy is transferred to an
accelerated particles and reflected (transmitted) energy is radiated as attosecond pulses. The choice
of optimum characteristics of a target is made by means of analytical and multi-dimensional
numerical modeling of a target set with characteristics near to optimum values. It is shown, that at
reflection from a target the laser wave of relativistic intensity is effectively converted in sequence of
electromagnetic pulses of tens nanometer length, the following one after another through the period
of an initial laser wave. Dependence of its parameters on angle of incidence and laser intensity is
investigated.
The effective action of strong electrical fields on a beam of protons passing through a laser irradiated thin foil has been investigated. The energy distribution function of protons propagating along the surface normal changes in a pronounced way, exhibiting a gap in the spectrum accompanied by up to two local maxima. The temporal behavior is set into context with expectations derived from the evolution of strong electrical fields at the plasma-vacuum interface, usually being considered responsible for fast ion acceleration during the initial stage of laser driven plasma expansion. Our investigation reveals complex field effects in thin foils when irradiated with intense and ultra-short pulses with a very high temporal contrast. The experiments were performed with a laser accelerated proton beam, the probe, traversing a “plasma slab” created by ultra-short ( 80fs), high-intensity (~ 1 × 1019 W/cm2) laser irradiation of a 30 nm to 800 nm thick foil. Laser pulses with different temporal contrast and pulse duration have been used, both for the probe and for the plasma slab creation (the pump). An analytical model is discussed to approach an understanding of the observation.
Beams of energetic negative ions and neutral atoms are obtained from water and ethanol spray targets irradiated by high
intensity (5×1019 W/cm2) and ultrashort (50 fs) laser pulses. The resulting spectra were measured with the Thomson parabola spectrometer, which enabled absolute measurements of both: positive and negative ions. The generation of a beam of energetic neutral hydrogen atoms was confirmed with CR-39 track detectors and their spectral characteristics have been measured using time of flight technique. Generation is ascribed to electron-capture and -loss processes in the collisions of laser-accelerated high-energy protons with spray of droplets. The same method can be applied to generate energetic negative ions and neutral atoms of different species.
Polarized X-ray pulses at 0.6 Å have been generated via head-on collision of a laser pulse from the high-field laser
facility at Daresbury with a 30 MeV electron bunch in the ALICE energy recovery linear accelerator. The angular
distribution of the backscattered X rays was obtained in single-shot using a scintillation screen. The temporal profile of
the X ray yield as a function of the time delay between the laser pulse and electron bunch was measured and agreed well
with that expected from the collision point dependence of the laser-electron beam longitudinal overlap.
Inverse Compton is a promising method to implement a high brightness, ultra-short, energy tunable X-ray source at accelerator facilities. We have developed an inverse Co Compton ba mpton backscattering X-ray source driven by the multi 10 TW-L backscattering Laser installed at Daresbury (COBALD). Hard X-rays, with spectral peak ranging from 15 to 30 keV, depending on the scattering geometry, will be generated through the interaction of a laser pulse with an electron bunch delivered by the energy recovery linear accelerator prototype (ERLP) at Daresbury. X-ray pulses containing 9×107 photons per pulse will be created from head on collisions, with a pulse duration comparable to that of the incoming electron bunch. For transverse collisions 8×106 photons per pulse will be generated, where the laser pulse transit time defines the X-ray pulse duration. The peak spectral brightness is predicted to be ~ 1021 photons / s / mm2 / mrad2 / 0.1% ΔE/E, which is
comparable to fourth generation synchrotron light sources.
The present trends in the development work on X-ray lasers are shown and discussed on a background of a brief history of the collisionally pumped X-ray lasers. The presentation is focused on two variants of the transient inversion pump method succesfully applied in the experiments - slab target geometry and single profiled laser pulse. Recently, another scheme referred to as GRIP (GRazing Incidence Pumping) has been proposed and demonstrated. This pump geometry opens the new real possibility to construct a repetitive X-ray laser. Some
aspects of the pump scheme implementation are discussed in detail. Finally, a specific injector-amplifier system giving a new perspective on the future of X-ray lasers is dicussed briefly as well.
Recent development in the field of X-ray lasers is shown and discussed starting from transient inversion scheme in a double-pulse arrangement. Different variants of this scheme are discussed in detail from the point of view of reduction in the pump energy. The discussion is concentrated on the kinetic aspect of the plasma created
and heated by a profiled pulse. Recently, a scheme referred to as GRIP (GRazing Incidence Pumping) has been proposed and demonstrated. This pump geometry opens a new real possibility to construct a repetitive X-ray laser. Some aspects of the pump scheme implementation are analysed. Finally, a specific injector-amplifier system giving a new perspective on the future of X-ray lasers is dicussed briefly as well.
Technological reasons stimulated enormous interest in the spectral range between 10 nm and 15 nm. One of the most important, apart from the potential to be applied in the microlithography, was the existence of the high-efficiency, spectrally highly selective (narrow-band) reflective multi-layer (ML) optics in this spectral range. Applying these optics to plasma based XUV (extreme ultra violett) sources the debris from the plasma is a serious problem. For transmissive multi-layer optics we have additionally the low figures of merit. For example, the best beam splitters have an efficiency of about 30% (energy in both parts of the splitted beam). This type of element is crucial for efficient single-shot interferometry being the main application using table-top soft x-ray lasers.
We applied capillary optical elements, to our knowledge for the first time, to XUV radiation at 13.9 nm. These optical elements help overcome the limits discussed above or at least remarkably reduce the existing difficulties. A capillary beam splitter and a focussing capillary were applied to an incoherent XUV radiation source. For the beam splitter we measured a throughput of about 80%. With the focussing capillary we obtained a spot size of 27 μm (FWHM) with a gain (intensity in the focal spot compared to the intensity behind a pinhole of the focal spot size) of 600. Advantages and disadvantages of these optics in the discussed spectral range are analyzed.
Output characteristics of a transient Ni-like Ag X-ray laser pumped by a single picosecond laser pulse are demonstrated. The small-signal gain coefficient, beam divergence, output pulse profile and beam dimensions in the near-field were measured. The influence of the pump pulse structure on the lasing process and the output signal is analysed theoretically.
Some prospects for development of collisional X-ray lasers with a high repetition rate based on the output characteristics of a transient Ni-like Ag soft X-ray laser pumped by a single picosecond laser pulse are analysed. Such problems as target technology, new driver development and the active medium parameters are discussed.
The state-of-the-art and the trends in development of table-top soft x-ray lasers (XRLs) with a special emphasis on the work of the Max Born Institute (MBI) are presented. Both, basic physics and some features of the output radiation crucial for applications are discussed as well.
Quasi-phasematched (QPM) Second Harmonic Generation (SHG) in poled polymer waveguides has been realized. Rib-waveguide devices were fabricated by lithographic techniques like multilayer spin coating and reactive ion etching, well known from semiconductor technology. Guest-host-systems [Cyanobiphenyl-Polymethylmethacrylat (CN-PMMA)] as well as co-polymers have been used as the NLO-waveguiding layer between Perfluorcyclobutane (PFCB) layers acting as lower refractive index claddings. Cut-off experiments yield waveguide losses of 3 dB/cm and endfire coupling losses of 3 - 5 dB. The QPM-period has been determined experimentally to (Lambda) approximately equals 20 micrometer for a 4 micrometer wide Rib- waveguide by recording Maker fringes. Periodically poled waveguides were realized using Corona poling in combination with corrugated surfaces. The period (Lambda) of the poling structure was varied continuously between 15 micrometer and 30 micrometer using a fan-shaped corrugation structure. SHG tuning curves exhibit a relative acceptance bandwidth of 3.7 times 10-3 which indicates an effective interaction length leff over the full waveguide length of 4 mm.
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