| Paper | Title | Page |
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| THPLT044 | Measurement of the Transverse Coherence of the TTF Free Electron Laser | 2577 |
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| The transverse coherence is important for many applications of a free electron laser (FEL). It depends on the inner structure of the electron bunch in the undulator, which is difficult to measure. It is therefore essential to determine the coherence properties of the FEL radiation directly. The coherence of the vacuum ultraviolet FEL at the TESLA Test Facility has been measured by recording the diffraction pattern of a double slit and measuring the visibility of the interference fringes. The experimental near field diffraction pattern is compared with a numerical model, taking into account the formation of the FEL radiation, the Fresnel diffraction in the near field zone and effects of the experimental set-up. Diffraction patterns have been recorded at various undulator lengths to measure the evolution of the transverse coherence along the undulator. This is compared to the expected evolution of the transverse radiation modes. |