LABORATORI NAZIONALI DI LEGNARO
In the presence of an external magnetic field in vacuum, both an ellipticity and/or dichroism can be induced on a linearly polarized light beam propagating transversely with respect to the field. Induced ellipticity and dichroism can be linked with photon-photon scattering and with the production of light, neutral, scalar/pseudoscalar particles, which are a good candidate constituents of Cold Dark Matter. A direct ellipticity and dichroism measurement would lead to a determination of mass and coupling constant to two photons of the produced particles. The PVLAS collaboration is operating a high-sensitivity (~10-7 1/ vHz) optical ellipsometer capable of detecting very small changes in the light polarization state induced by a strong transverse magnetic field. The apparatus is based on a high finesse (~10+5), high quality factor, 6.4 m long Fabry-Perot (FP) optical resonator and on a 5.5 T superconducting, 1.1 m long, dipole magnet housed in a rotating cryostat. This ellipsometer is capable of measuring, using the heterodyne technique, both ellipticities and dichroisms in an independent way, down to levels below 10-8 rad, for about one hour of data taking time. At present, all data taking runs have shown the presence of both an ellitpticity and a dichroism signal. Diagnostic tests, and measurements with Nitrogen and Neon gas, indicate that these signals are compatible with a generation within the Fabry-Perot cavity.

DATA: 15-10-2004

Sito Collegato : http://www.lnl.infn.it/~seminari/2004/15Oct_04bis.html