R. Ischebeck, J. Feldhaus, Ch. Gerth, E. Saldin, P. Schmueser, E. Schneidmiller, B. Steeg, K. Tiedtke, M. Tonutti, R. Treusch, M. Yurkov

Study of the Transverse Coherence at the TTF Free Electron Laser

Double slits with different separations and crossed slits, as well as circular apertures have been used to study the transverse coherence of the VUV light of the SASE free electron laser at the TESLA Test facility at DESY. The resulting diffraction patterns are converted to visible light by a Ce:YAG crystal and imaged by a high resolution CCD camera. The height contrast of the diffraction patterns indicates a high degree of transverse coherence. Measurements have been taken at various operating modes and wavelengths of the FEL.
A numeric simulation code (FAST) has been used to calculate the wavefronts of the FEL light at the exit of the undulator. By propagating the wavefronts through the optical set-up, the diffraction at the double slits is simulated (GLAD) and found to be in good agreement with the measurements.

FEL conference 2002, to be published: Nucl. Instrum. Meth. A