Energy-Spread Preservation and High Efficiency in a Plasma-Wakefield Accelerator

Energy-efficient plasma-wakefield acceleration of particle bunches with low energy spread is a promising path to realizing compact free-electron lasers and particle colliders. High efficiency and low energy spread can be achieved simultaneously by strong beam loading of plasma wakefields when accelerating bunches with carefully tailored current profiles [M. Tzoufras et al., Phys. Rev. Lett. 101, 145002 (2008)PRLTAO0031-900710.1103/PhysRevLett.101.145002]. We experimentally demonstrate such optimal beam loading in a nonlinear electron-driven plasma accelerator. Bunches with an initial energy of 1 GeV were accelerated by 45 MeV with an energy-transfer efficiency of (42±4)% at a gradient of 1.3  GV/m while preserving per-mille energy spreads with full charge coupling, demonstrating wakefield flattening at the few-percent level

“I Look in Your Eyes, Honey”: Internal Face Features Induce Spatial Frequency Preference for Human Face Processing

Numerous psychophysical experiments found that humans preferably rely on a narrow band of spatial frequencies for recognition of face identity. A recently conducted theoretical study by the author suggests that this frequency preference reflects an adaptation of the brain's face processing machinery to this specific stimulus class (i.e., faces). The purpose of the present study is to examine this property in greater detail and to specifically elucidate the implication of internal face features (i.e., eyes, mouth, and nose). To this end, I parameterized Gabor filters to match the spatial receptive field of contrast sensitive neurons in the primary visual cortex (simple and complex cells). Filter responses to a large number of face images were computed, aligned for internal face features, and response-equalized (“whitened”). The results demonstrate that the frequency preference is caused by internal face features. Thus, the psychophysically observed human frequency bias for face processing seems to be specifically caused by the intrinsic spatial frequency content of internal face features

A laser-plasma platform for photon-photon physics : The two photon Breit-Wheeler process

We describe a laser-plasma platform for photon-photon collision experiments to measure fundamental quantum electrodynamic processes. As an example we describe using this platform to attempt to observe the linear Breit-Wheeler process. The platform has been developed using the Gemini laser facility at the Rutherford Appleton Laboratory. A laser Wakefield accelerator and a bremsstrahlung convertor are used to generate a collimated beam of photons with energies of hundreds of MeV, that collide with keV x-ray photons generated by a laser heated plasma target. To detect the pairs generated by the photon-photon collisions, a magnetic transport system has been developed which directs the pairs onto scintillation-based and hybrid silicon pixel single particle detectors (SPDs). We present commissioning results from an experimental campaign using this laser-plasma platform for photon-photon physics, demonstrating successful generation of both photon sources, characterisation of the magnetic transport system and calibration of the SPDs, and discuss the feasibility of this platform for the observation of the Breit-Wheeler process. The design of the platform will also serve as the basis for the investigation of strong-field quantum electrodynamic processes such as the nonlinear Breit-Wheeler and the Trident process, or eventually, photon-photon scattering

Safety and efficacy of a novel calcium sensitizer, levosimendan, in patients with left ventricular failure due to an acute myocardial infarction: A randomized, placebo-controlled, double-blind study (RUSSLAN)

Aims: To evaluate the safety and efficacy of levosimendan in patients with left ventricular failure complicating acute myocardial infarction. Methods and Results: Levosimendan at different doses (0·1-0·4 μg . kg-1 . min-1) or placebo were administered intravenously for 6 h to 504 patients in a randomised, placebo-controlled, double-blind study. The primary end-point was hypotension or myocardial ischaemia of clinical significance adjudicated by an independent Safety Committee. Secondary end-points included risk of death and worsening heart failure, symptoms of heart failure and all-cause mortality. The incidence of ischaemia and/or hypotension was similar in all treatment groups (P=0·319). A higher frequency of ischaemia and/or hypotension was only seen in the highest levosimendan dose group. Levosimendan-treated patients experienced lower risk of death and worsening heart failure than patients receiving placebo, during both the 6h infusion (2·0% vs 5·9%; P=0·033) and over 24 h (4·0% vs 8·8%; P=0·044). Mortality was lower with levosimendan compared with placebo at 14 days (11·7% vs 19·6%; hazard ratio 0·56 [95% CI 0·33-0·951; P=0·031) and the reduction was maintained at the 180-day retrospective follow-up (22·6% vs 31·4%; 0·67 [0·45-1·00], P=0·053). Conclusions: Levosimendan at doses 0·1-0·2 μg . kg-1 . min-1 did not induce hypotension or ischaemia and reduced the risk of worsening heart failure and death in patients with left ventricular failure complicating acute myocardial infarction. © 2002 The European Society of Cardiology. Published by Elsevier Science Ltd. All rights reserved

Post-compression of 8.6 mJ ps-pulses from an Yb:YAG Innoslab amplifier using a compact multi-pass cell

We demonstrate post-compression of a high energy Yb:YAG laser in a 2m long Argon-filled multi-pass cell (MPC). 1.2 ps pulses with 8.6 mJ are compressed to 44 fs with an MPC transmission of 93%

Factor Hundred Compression of Multi-mJ 1.2 ps Pulses at 1030 nm to Few Cycles using Multi-Pass Cells

Multi-pass cells (MPCs) enable the accumulation of a large amount of B-integral while preserving the spatial mode of a laser beam and ensuring a uniform spectral distribution [1], [2]. In addition, MPCs used for post-compression allow achieving very large compression factors, without considerable degradation in temporal quality [3]. These qualities of MPCs, in combination with the high average power and pulse energy that Ytterbium-based lasers can deliver, open up the generation of ultrashort laser pulses with unprecedented properties [4]

Approaching the TW-regime with mJ-class picosecond pulses post-compressed to 13 fs

We demonstrate efficient post compression of 9.45 mJ, 1.2 ps pulses to 13 fs at 1 kHz repetition rate using a two stage gas filled multi pass cell system reaching near terawatt peak power

Post-compression of multi-millijoule picosecond pulses to few-cycles approaching the terawatt regime

Advancing ultrafast high-repetition-rate lasers to shortest pulse durations comprising only a few optical cycles while pushing their energy into the multi-millijoule regime opens a route towards terawatt-class peak powers at unprecedented average power. We explore this route via efficient post-compression of high energy 1.2 ps pulses from a Ytterbium InnoSlab laser to 9.6 fs duration using gas-filled multi-pass cells (MPCs) at a repetition rate of 1 kHz. Employing dual-stage compression with a second MPC stage supporting a close-to-octave spanning bandwidth enabled by dispersion-matched dielectric mirrors, a record compression factor of 125 is reached at 70% overall efficiency, delivering 6.7 mJ pulses with a peak power of about 0.3TW. Moreover, we show that post-compression can improve the temporal contrast at picosecond delay by at least one order of magnitude. Our results demonstrate efficient conversion of multi-millijoule picosecond lasers to high-peak-power few-cycle sources, opening up new parameter regimes for laser plasma physics, high energy physics, biomedicine and attosecond science