Magnetic measurements with the FLASH infrared undulator

The FLASH free-electron laser at DESY, Hamburg, has been equipped with an infrared electromagnetic undulator which provides radiation in the mid- and far-infrared range. It will be used both for electron beam diagnostic purposes and as a powerful radiation source synchronized to the VUV and soft X-ray pulses of the FEL. This paper summarizes the undulator construction, the main design features, and the magnetic measurements undertaken to verify the device performance prior to installation.