Transverse Beam Size Diagnostics using Brownian Nanoparticles at ALBA

In this work we describe a novel beam diagnostic method based on coherence characterization of broad-spectrum bending magnet radiation through the Heterodyne Near Field Scattering (HNFS) technique. HNFS is a self- referencing technique based on the interference between the transmitted beam and the spherical waves scattered by each particle of a colloidal suspension. The resulting single-particle interferogram shows circular interference fringes modulated by the spatio-temporal Complex Coherence Factor (CCF) of the radiation. Superposition of a number of these patterns results in a stochastic speckle field, from which spatial and temporal coherence information can be retrieved in near field conditions. Here we describe the basics of this technique, the experimental setup mounted along the hard X-ray pinhole at the ALBA synchrotron light source, and the possibility of transverse electron beam size retrieval from the spatial coherence function of the emitted dipole radiation. We also show preliminary results concern- ing power spectral density of visible synchrotron radiation as obtained from temporal coherence.