Particle laser production at PVLAS: recent developments

In the PVLAS apparatus a polarised laser beam is used to probe the structure of quantum vacuum when it is perturbed by an external magnetic field. The photon-photon scattering process, taking place in the field region, could result in the production of light scalar/pseudoscalar particles coupled to two photons thought to be dark matter candidates. The photon-photon scattering induces a change in the polarisation state of the laser beam, and can be detected by optical techniques. The PVLAS collaboration has been operating the apparatus for about two years, and the available sets of data show the presence of a signal believed to originate within the magnetic field region. Preliminary results from the data sets will be presented, along with a brief discussion