11,857,789 research outputs found
Pepper-pot emittance measurement of laser-plasma wakefield accelerated electrons
No full textThe transverse emittance is an important parameter governing the brightness of an electron beam. Here we present the first pepper-pot measurement of the transverse emittance for a mono-energetic electron beam from a laser-plasma wakefield accelerator, carried out on the Advanced Laser-Plasma High Energy Accelerators towards X-Rays (ALPHA-X) beam line. Mono-energetic electrons are passed through an array of 52 mu m diameter holes in a tungsten mask. The pepper-pot results set an upper limit for the normalised emittance at 5.5 +/- 1 pi mm mrad for an 82 MeV beam
Chirped pulse Raman amplification in plasma: high gain measurements
No full textHigh power short pulse lasers are usually based on chirped pulse amplification (CPA), where a frequency chirped and temporarily stretched ``seed'' pulse is amplified by a broad-bandwidth solid state medium, which is usually pumped by a monochromatic ``pump'' laser. Here, we demonstrate the feasibility of using chirped pulse Raman amplification (CPRA) as a means of amplifying short pulses in plasma. In this scheme, a short seed pulse is amplified by a stretched and chirped pump pulse through Raman backscattering in a plasma channel. Unlike conventional CPA, each spectral component of the seed is amplified at different longitudinal positions determined by the resonance of the seed, pump and plasma wave, which excites a density echelon that acts as a "chirped'" mirror and simultaneously backscatters and compresses the pump. Experimental evidence shows that it has potential as an ultra-broad bandwidth linear amplifier which dispenses with the need for large compressor gratings
An ultrashort pulse ultra-violet radiation undulator source driven by a laser plasma wakefield accelerator
No full textNarrow band undulator radiation tuneable over the wavelength range of 150–260 nm has been produced by short electron bunches from a 2 mm long laser plasma wakefield accelerator based on a 20 TW femtosecond laser system. The number of photons measured is up to 9 × 106 per shot for a 100 period undulator, with a mean peak brilliance of 1 × 1018 photons/s/mrad2/mm2/0.1% bandwidth. Simulations estimate that the driving electron bunch r.m.s. duration is as short as 3 fs when the electron beam has energy of 120–130 MeV with the radiation pulse duration in the range of 50–100 fs
Wavebreaking as a limit for Raman amplification
No full textThe influence of wavebreaking on Raman amplification is investigated. A phenomenological modification is added to a set of slowly varying envelope equations, and found to give good agreement to particle-in-cell simulations for cold plasma in the wavebreaking regime. For warm plasma, good agreement is not found using the warm wavebreaking limit. However, the PIC simulations show that the decreased wavebreaking limit does have a significant impact on amplification. The limitations of our model are discussed, and possible future work outlined
On the energy-momentum tensor of light in strong fields : an all optical view of the Abraham-Minkowski controversy
No full textThe Abraham-Minkowski controversy is the debate surrounding the "correct" form of the energy-momentum tensor of light in a medium. Over a century of theoretical and experimental studies have consistently produced conflicting results, with no consensus being found on how best to describe the influence of a material on the propagation of light. It has been argued that the total energy-momentum tensor for each of the theories, which includes both wave and material components, are equal. The difficulty in separating the full energy-momentum tensor is generally attributed to the fact that one cannot obtain the energy-momentum tensor of the medium for real materials. Non-linear electrodynamics provides an opportunity to approach the debate from an all optical set up, where the role of the medium is replaced by the vacuum under the influence of a strong background field. We derive, from first principles, the general form of the energy-momentum tensor in such theories, and use our results to shed some light on this long standing issue
Theory of short pulse FEL oscillators
No full textA simple model for the nonlinear low gain evolution of a short pulse Compton free electron laser (FEL) oscillator is derived. An analysis of the small signal regime allows the calculation of the shape of the produced optical pulse. For small excess over threshold, a Landau-Ginzburg equation is obtained, which allows us to show that a strong superradiant efficiency enhancement occurs at small detuning. Furthermore, the knowledge of the eigenfrequencies in the small signal regime allows one to infer a scale law for the period of limit cycles occurring at larger excess over threshold. Theoretical results are compared to experimental results from FELIX
Photon frequency up-shifting by an amplified plasma density wake due to two co-propagating laser pulses
No full textAn analytical study of significant photon acceleration (frequency up-shift) in a plasma density wake produced by two laser pulses in the mildly relativistic and linearized regime is presented. The wake amplitude is amplified and its phase controlled using two coaxially, co-propagating laser pulses, which are considered to be identical but separated by a fixed time. A third probe pulse, with a variable delay, is considered as ``test particle'' or quasi-photon propagating through the amplified density wake, which experiences significant photon acceleration because of the local temporal and spatial variation of the permittivity. The evolution of the ``photon'' is studied using Hamiltonian theory. The significant frequency up-shift is much larger than that produced by the wake of a single relativistic laser pulse in the highly relativistic nonlinear wake regime. Our study demonstrates that the inter-pulse separation between the ``controlling'' pulse and the ``driver'' pulse, producing the amplified density wake, can provide an additional degree of freedom for tuning the maximum up-shift of the probe photon frequency
Practical considerations for the ion channel free-electron laser
No full textThe ion-channel laser (ICL) has been proposed as an alternative to the free-electron laser (FEL), replacing the deflection of electrons by the periodic magnetic field of an undulator with the periodic betatron motion in an ion channel. Ion channels can be generated by passing dense energetic electron bunches or intense laser pulses through plasma. The ICL has potential to replace FELs based on magnetic undulators, leading to very compact coherent X-ray sources. In particular, coupling the ICL with a laser plasma wakefield accelerator would reduce the size of a coherent light source by several orders of magnitude. An important difference between FEL and ICL is the wavelength of transverse oscillations: In the former it is fixed by the undulator period, whereas in the latter it depends on the betatron amplitude, which therefore has to be treated as variable. Even so, the resulting equations for the ICL are formally similar to those for the FEL with space charge taken into account, so that the well-developed formalism for the FEL can be applied. The amplitude dependence leads to additional requirements compared to the FEL, e.g. a small spread of betatron amplitudes. We shall address these requirements and the resulting practical considerations for realizing an ICL, and give parameters for operation at UV fundamental wavelength, with harmonics extending into X-rays
"… von einem ruchlosen Banditen zerfleischt" : der Wiener Kriminalfall Jaroszynski (Frühjahr 1827) in Wirklichkeit und Fiktion : eine publizistische und literarische Spurensuche
No full textBarbara Tumfart beschäftigt sich mit den literarischen Verhandlungen des Raubmordes des polnischen Adligen Severin von Jaroszynski am Geistlichen Johann Conrad Blank in Wien. Die der Untersuchung zugrunde gelegten Texte von Adolph Bäuerle und Carl Haffner bieten allen voran eine sensationslüsterne Darstellung des Verbrechens und fokussieren auch das Privatleben der Wiener Schauspielerin Therese Krones, die mit Jaroszynski befreundet war. Die Schilderung eines Verbrechens entwickelt sich in diesen Texten zu einer skandalösen Geschichte aus dem Milieu des Theaters. Die in den Texten offensichtlichen Mythisierungsstrategien folgen den ästhetischen Prämissen der Unterhaltungsliteratur. Dass die Geschehnisse aufgegriffen werden, belegt andererseits auch, dass die Verkündigung des Urteils und die Hinrichtung Jaroszynskis durch Erhängen an der Spinnerin am Kreuz ein vielbeachtetes gesellschaftliches Ereignis war, das eben auch Eingang in die Unterhaltungsliteratur fand
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