Spectral distribution of infrared synchrotron radiation by an insertion device and its edges: A comparison between experimental and simulated spectra

The first measurements of the spectral distribution of infrared radiation e mitted by an undulator are reported. They are compared with calculations in cluding both velocity and acceleration terms. Measurements have been perfor med at the beam line SIRLOIN (Spectroscopie en InfraRouge Lointain). The ag reement between the observations and this first exact numerical solution sh ows that the inclusion of the velocity term in the submillimeter frequency range is necessary. Moreover, structures due to undulator edges are observe d in the far infrared and mid-infrared range, while the interference patter n due to redshifted harmonics of the undulator is dominating in the mid-inf rared to near infrared.