Spectroscopy of ultralight bosons by photon-boson-photon   conversion-reconversion: experimental aspects
  A conversion-reconversion experimental scheme is proposed where photons stored in a Fabry-Perot cavity (FP) embracing a dipole conversion magnet generate two beams of ultralight bosons emitted in opposite directions. Fractions of the bosons convert in dipole magnets aligned along the two boson beam lines and generate photons of the same energy and directions of the FP grandparent photons. The reconversion photons are detected individually by means of single photon detectors. Such an experiment can determine the bosons parity by measurements with different angles between the polarization vector of linearly polarized light injected into the FP and the direction of the magnetic field Bc of the conversion magnets. It can establish both the bosons mass m and the coupling constant to two photons gmgg by measurements with different lengths Lr of the string of powered regeneration magnets of one boson beam line, while the second boson beam line is left unchanged and used for normalization. The optimal total length Lc of the string of conversion magnets depends on m2 and on the energy E of the laser photons. For E=2.4eV Lc is of the order of 3m if m=10-3eV and of the order of 300m if m=10-4eV. If the signals observed by the PVLAS experiment are due to the existence of ultralight bosons with m=10-3eV and gmgg=10-6GeV-1, these regeneration measurements are feasible with existing tachnology on a site of length below 100m in relatively short periods of data taking time. 
Ugo Gastaldi