An intense laser pulse in a plasma can accelerate electrons [1][2][3][4] to GeV energies in centimetres [5][6][7] . Transverse betatron motion 8,9 in the plasma wake results in X-ray photons with an energy that depends on the electron energy, oscillation amplitude and frequency of the betatron motion [10][11][12] . Betatron X-rays from laser-accelerator electrons have hitherto been limited to spectra peaking between 1 and 10 keV (ref. 13). Here we show that the betatron amplitude is resonantly enhanced when electrons interact with the rear of the laser pulse 14,15 . At high electron energy, resonance occurs when the laser frequency is a harmonic of the betatron frequency, leading to a significant increase in the photon energy. 10 X-ray pulses from synchrotron sources have become immensely useful tools for investigating the structure of matter 17 , which has led to a huge international effort to construct light sources for many different scientific and technological applications. Synchrotrons are usually based on radio-frequency (RF) accelerating cavities that are limited to fields of 10-100 MV m −1 because of electrical breakdown, which results in very large and expensive devices.High-power lasers, on the other hand, have led to the development of many new areas of science, as diverse as inertial confinement fusion and laboratory astrophysics to the study of warm dense matter. However, they now have the potential to transform accelerator and light source technology. In the late 1970s, Tajima and Dawson 1 proposed harnessing the ponderomotive force associated with intense laser fields to excite plasma waves and form wake-like structures 18 (as behind a boat) that travel with a velocity close to the speed of light, c. The electrostatic forces of these charge density structures can rapidly accelerate particles to very high energies 6 ; where momentum is gained analogous to a surfer riding an ocean wave. Recent progress in the development of laser wakefield accelerators (LWFAs) has enabled electron beams to be accelerated with unprecedented acceleration gradients 2-4 , three orders of magnitude higher than in RF cavities, thus reducing a 100 m long GeV accelerator to centimetres in length 6 . The LWFA can now produce high-quality electron beams with low emittance, ε n , of the order 1π mm mrad 19 , small energy spread 20 , δγ /γ 1%, where γ is the Lorenz factor, and high charge 4 , Q = 10-100 pC. At high laser intensities, in the so-called blowout regime 21 , the LWFA structure has an approximately spherical bubble shape with a radius of R ≈ 2 √ a 0 c/ω p , which is primarily determined by the normalized laser vector potential, a 0 = eA/m e c 2 and the plasma frequency, ω p = √ 4π n p e 2 /m e , where n p is the plasma density, e, the electron charge and m e , the electron mass 22 . The plasma wave is efficiently driven when the laser pulse duration is approximately a plasma period. Micrometre-long electron bunches that extend only a fraction of the plasma wavelength, λ p = 2πc/ω p , are self-injected and accelerate...

The application of differential phase contrast imaging to the study of polycrystalline magnetic thin films and nanostructures has been hampered by the strong diffraction contrast resulting from the granular structure of the materials. In this paper we demonstrate how a pixelated detector has been used to detect the bright field disk in aberration corrected scanning transmission electron microscopy (STEM) and subsequent processing of the acquired data allows efficient enhancement of the magnetic contrast in the resulting images. Initial results from a charged coupled device (CCD) camera demonstrate the highly efficient nature of this improvement over previous methods. Further hardware development with the use of a direct radiation detector, the Medipix3, also shows the possibilities where the reduction in collection time is more than an order of magnitude compared to the CCD. We show that this allows subpixel measurement of the beam deflection due to the magnetic induction. While the detection and processing is data intensive we have demonstrated highly efficient DPC imaging whereby pixel by pixel interpretation of the induction variation is realised with great potential for nanomagnetic imaging.

Charge collection properties of particle detectors made in HV-CMOS technology were investigated before and after irradiation with reactor neutrons. Two different sensor types were designed and processed in 180 and 350 nm technology by AMS. Edge-TCT and charge collection measurements with electrons from 90 Sr source were employed. Diffusion of generated carriers from undepleted substrate contributes significantly to the charge collection before irradiation, while after irradiation the drift contribution prevails as shown by charge measurements at different shaping times. The depleted region at a given bias voltage was found to grow with irradiation in the fluence range of interest for strip detectors at the HL-LHC. This leads to large gains in the measured charge with respect to the one before irradiation. The increase of the depleted region was attributed to removal of effective acceptors removal. The evolution of depleted region with fluence was investigated and modeled. Initial studies show a small effect of short term annealing on charge collection.