Abstract
A proposal for a self-seeding, tunable free-electron laser amplifier operating in the vacuum ultra-violet (VUV) region of the spectrum is presented. Full three-dimensional (3D) modelling of the free electron laser and the optical feedback system has been carried out. Simulations demonstrate the generation of near transform limited radiation pulses with peak powers in the hundreds of megawatts. Preliminary 1D simulations show that by using a similar system it may be possible to extend such operation beyond the VUV to higher photon energies.
Highlights
PII: S1367-2630(07)48987-X IOP Publishing and Deutsche Physikalische Gesellschaft allowing increased structural resolution and the study of the chemistry of sub-cellular domains in real time of proteins, carbohydrates and nucleic acids; the creation and study of transient, short-lived species such as those created in the upper atmosphere and interstellar dust clouds; the reaction pathways in asymmetric synthesis and of the origins of the homochirality of life; the measurement of ultra-fast charge and spin dynamics in optoelectronic nanomaterials, photovoltaics and magnetic semiconductors; and, when used with the XUV-FEL, the use of quantum chemical control to explore molecular evolution and chemical reactions
The effect of varying the radius of the outcoupling hole and the mirror reflectivity on the saturated output power is plotted as a colour contour plot. (Saturation is defined to occur here after twenty cavity passes by which time actual saturation of the FEL output has occurred except perhaps at some of the extremes of the parameter ranges used in this and in the following simulation results.) The results show that the parameters as defined in the conceptual design report (CDR) [6] and reproduced in table 2 give a satisfactory and stable output
The above results present a specific design for the 3–10 eV photon energy vacuum ultra-violet (VUV)-FEL of the 4GLS project in which the minimum required cavity feedback is of the order of a few percent, potentially more stable output could be obtained for ∼10%
Summary
The VUV-FEL is designed to generate radiation of variable polarization and will use APPLE-II variably polarized undulator modules. The fundamental cold-cavity mode is focused to maximize the transverse overlap, and FEL coupling, between radiation and electron beam over the first two undulator modules. This is achieved with a waist at the end of the first module, ∼12.2 m from the US mirror as shown in figure 5. Propagation of the radiation through the undulator is modelled by Genesis 1.3, while OPC propagates the optical field through the non-amplifying section of the resonator. Running both codes sequentially provides a single pass through the resonator. Cavity detuning is realized through a control parameter already present in the Genesis 1.3 configuration file that controls the synchronization of the radiation pulse with the electron pulse at the entrance to the undulator
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