Measuring orbital angular momentum superpositions of light by mode transformation

We recently reported on a method for measuring orbital angular momentum (OAM) states of light based on the transformation of helically phased beams to tilted plane waves [Phys. Rev. Lett.105, 153601 (2010)]. Here we consider the performance of such a system for superpositions of OAM states by measuring the modal content of noninteger OAM states and beams produced by a Heaviside phase plate

U, B and r band luminosity functions of galaxies in the Coma cluster

We present a deep multi-colour CCD mosaic of the Coma cluster (Abell 1656), covering 5.2 deg^2 in the B and r bands, and 1.3 deg^2 in the U band. This large, homogeneous data set provides a valuable low redshift comparison sample for studies of galaxies in distant clusters. In this paper we present our survey, and study the dependence of the galaxy luminosity function (LF) on passband and radial distance from the cluster centre. The U, B and r band LFs of the complete sample cannot be represented by single Schechter functions. For the central area, r<245 h_{100}^{-1} kpc, we find best-fitting Schechter parameters of M^{*}_U=-18.60^{+0.13}_{-0.18} and \alpha_U=-1.32^{+0.018}_{-0.028}, M^{*}_B=-19.79^{+0.18}_{-0.17} and \alpha_B=-1.37^{+0.024}_{-0.016} and M^{*}_r=-20.87^{+0.12}_{-0.17} and \alpha_r=-1.16^{+0.012}_{-0.019}. The LF becomes steeper at larger radial distance from the cluster centre. The effect is most pronounced in the U band. This result is consistent with the presence of a star forming dwarf population at large distance from the cluster centre, which may be in the process of being accreted by the cluster. The shapes of the LFs of the NGC 4839 group support a scenario in which the group has already passed through the centre.Comment: Accepted for publication in MNRA

The galaxy population in the Coma cluster

Results from large optical and H t surveys presented in the previous chapters are summarized. We combine the results from the analyses of the separate projects to discuss how these have improved our knowledge of the galaxy population in the Coma cluster. Proposals for future observations are discussed. ... Zie: Summary