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- Mak, Alan, et al.
(författare)
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Attosecond single-cycle undulator light : a review
- 2019
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Ingår i: Reports on progress in physics (Print). - : IOP Publishing. - 0034-4885 .- 1361-6633. ; 82:2
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Forskningsöversikt (refereegranskat)abstract
- Research at modern light sources continues to improve our knowledge of the natural world, from the subtle workings of life to matter under extreme conditions. Free-electron lasers, for instance, have enabled the characterization of biomolecular structures with sub-angstrom spatial resolution, and paved the way to controlling the molecular functions. On the other hand, attosecond temporal resolution is necessary to broaden our scope of the ultrafast world. Here we discuss attosecond pulse generation beyond present capabilities. Furthermore, we review three recently proposed methods of generating attosecond x-ray pulses. These novel methods exploit the coherent radiation of microbunched electrons in undulators and the tailoring of the emitted wavefronts. The computed pulse energy outperforms pre-existing technologies by three orders of magnitude. Specifically, our simulations of the proposed Soft X-ray Laser at MAX IV (Lund, Sweden) show that a pulse duration of 50-100 as and a pulse energy up to 5 mu J is feasible with the novel methods. In addition, the methods feature pulse shape control, enable the incorporation of orbital angular momentum, and can be used in combination with modern compact free-electron laser setups.
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- Mak, Alan, et al.
(författare)
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Compact undulator line for a high-brilliance soft-X-ray free-electron laser at MAX IV
- 2019
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Ingår i: Journal of Synchrotron Radiation. - : INT UNION CRYSTALLOGRAPHY. - 0909-0495 .- 1600-5775. ; 26, s. 891-898
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Tidskriftsartikel (refereegranskat)abstract
- The optimal parameter space for an X-ray free-electron laser (FEL) in the self-amplified spontaneous emission (SASE) operation mode is examined. This study focuses on FEL operation with a shorter undulator period and higher undulator strength made available through recent developments in in-vacuum, cryogenic and superconducting undulators. Progress on short-period undulator technologies is surveyed and FEL output characteristics versus undulator parameters are computed. The study is performed on a case of the planned soft-X-ray FEL at the MAX IV Laboratory in Sweden. An extension of the SASE mode into the harmonic lasing self-seeded mode is also analysed.
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- Mak, Alan
(författare)
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Efficiency Enhancement Techniques for Free-Electron Lasers
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The central question addressed in this thesis is how to make the free-electron laser (FEL) more efficient. In recent years, coherent diffraction imaging provides an important motivation for efficiency enhancement. This is because a more efficient FEL process enables converting a larger fraction of the electron beam's power into optical power. By increasing the average optical power to the terawatt level, an x-ray FEL will open the door to single-shot, single-molecule imaging with a sufficiently high signal-to-noise ratio.This thesis examines two techniques for efficiency enhancement, namely, undulator tapering and the phase jump method.For undulator tapering, the well-established analytical model by Kroll, Morton and Rosenbluth (KMR) is revisited and modified. With the aid of numerical simulations, it is demonstrated that the modified model results in a further enhancement in FEL efficiency beyond the original model.For the phase jump method, a new physics model is developed to describe the energy extraction mechanism in the longitudinal phase space. The model reveals the possibility to extract energy from electrons outside the ponderomotive bucket, as well as the potential to increase the spectral purity by suppressing the synchrotron sidebands.
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- Mak, Alan, et al.
(författare)
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FEL Operation Modes of the MAX IV Short Pulse Facility
- 2015
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Ingår i: Proceedings of FEL 2015, Daejeon, Korea. - 9783954501342 ; , s. 241-241
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Short Pulse Facility (SPF) of the MAX IV Laboratory in Lund, Sweden features the production of ultrashort, incoherent x-ray pulses. It is driven by a 3-GeV linac and comprises two 5-metre undulator modules. While the SPF is designed for spontaneous radiation, we explore alternative operation modes in which the SPF functions as a simple free-electron laser (FEL). In this article, we characterize two of them in time-dependent numerical simulations. We perform a sensitivity study on the electron beam parameters and examine the technique of single-step tapering.
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- Mak, Alan, et al.
(författare)
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Further Studies of Undulator Tapering in X-Ray FELs
- 2015
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Ingår i: Proceedings of FEL 2015, Daejeon, Korea. - 9783954501342 ; , s. 321-321
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We further the studies of the model-based optimization of tapered free-electron lasers presented in a recent publication [Phys. Rev. ST Accel. Beams 18, 040702 (2015)]. Departing from the ideal case, wherein the taper profile is a smooth and continuous function, we consider the more realistic case, with individual undulator segments separated by break sections. Using the simulation code GENESIS, we apply our taper optimization method to a case, which closely resembles the FLASH2 facility in Hamburg, Germany. By comparing steady-state and time-dependent simulations, we examine how time-dependent effects alter the optimal taper scenario. From the simulation results, we also deduce that the "traditional" empirical method, whereby the intermediate radiation power is maximized after closing every undulator gap, does not necessarily produce the highest final power at the exit of the undulator line.
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