Diagnostics of Solar Magnetic fields based on the Hanle effect

Abstract
The Hanle effect was first used in solar physics to determine weak magnetic fields in prominences (see Leroy 1981). More recently the development of a new generation of very accurate spectro-polarimeters has open a new window for the diagnostics of weak magnetic fields in the solar photosphere and chromosphere, based on the Hanle effect. I present here such recent research programs performed with the solar telescope THEMIS and with other polarimeters such as ZIMPOL and the LOCARNO polarimeter.