Photon beam characterization of the VUV SASE FEL at DESY

(MO-4-15)

Ch. Gerth, Th. Lokajczyk, R. Treusch, J. Feldhaus  

HASYLAB at DESY, Hamburg

A SASE FEL operating in the Vacuum Ultraviolet region around 100 nm wavelength is currently under test at the TESLA Test Facility at DESY. After first lasing in February 2000 the electron and photon beams have been characterized by different techniques in order to provide experimental evidence for SASE and to compare with numerical simulations. Based on these results, the main goal has been to improve the quality of the electron beam and thus to increase the gain of the FEL. This paper presents the techniques used for the measurement of the photon beam intensity, its angular and spectral distribution, and its statistical properties. It also demonstrates how various electron beam parameters affect the photon beam characteristics. For example, the angular and spectral distribution of the FEL radiation is particularly sensitive to the electron orbit in the undulator. This indicates ways of on-line photon beam diagnostics to enhance the electron beam quality and thus the FEL output.