Coherence of a near diffraction limited undulator synchrotron radiation source

We present experimental measurements of the coherence of an undulator synchrotron radiation source near to the diffraction limit condition. These measurements have been done following two objectives. The first one is to verify a fundamental point of the theory of synchrotron radiation. To our knowledge, since it has been re-written by Geloni et al. [1], no experimental verification to validate the theory has been performed. Our measurement proves the theory to be valid for the case of a near diffraction limited undulator source. The other objective is to measure the coherence of the synchrotron radiation on the I05 beamline of Diamond, in front of the last focusing element of the beamline. This knowledge can be used to predict the focusing performance of the beamline by means of Fourier Optics.