Luca Conversi ESA Research Fellow Planck Science Office I work in the Planck Science Office as a research fellow. My research fields are the Cosmic Microwave Background, its polarization, the Sunyaev-Zel'dovich effect and the technology related to these fields, in particular optics and antenna design. The SZ effect arises when the cold CMB photons interact with the hot electron gas present in the galaxy clusters. It has a very peculiar frequency spectrum: it is zero at ~220GHz, it has a minimum around 140GHz and a maximum at ~350GHz. It is redshift-independent, thus it is in principle possible to discover very distant clusters undetectable by X-ray experiments. Nevertheless, it is subdominant at all frequencies, hence it is very important to disentangle it from the other signals (CMB below 220GHz, galactic dust and cosmic infrared background at shorter wavelengths). In order to achieve this objective, multifrequency experiments are mandatory. During my Ph.D. in Astrophysics (obtained in 2007 at the University of Rome 'La Sapienza'), I worked on OLIMPO, a balloon-borne experiment made of a Cassegrain telescope of 2.6m and a 3He crystat, which reaches 300mK, the detectors' working temperature. It will fly in the summer of 2008 from the Svalbard islands (north of Norway), making a circumpolar flight of ~15 days. It will observe a small patch of the sky (~10x10deg) in 4 frequency bands (from 140 to 550GHz) analyzing in detail the 4 main components at these wavelengths: CMB, SZ, galactic dust and cosmic infrared background. I was in charge of the design, realization and test of the cold optics, focal plane and feed horn arrays. I also realized a model to estimate the signals observed by OLIMPO and its capacity in disentangle each other. Planck and OLIMPO share many technologies and scientific goals. I'm mainly involved in the HFI instrument, where I'm studying on-flight calibration techniques to increase our knowledge of the experiment.