  We present a unified picture which studies simultaneously the gamma
gamma-->pi^+ pi^-, pi^0 pi^0, K^+ K^-, K^0 bar{K}^0, pi^0 eta reactions up to
about sqrt(s)=1.4 GeV reproducing the experimental cross sections. The present
work implements in an accurate way the final state interactions of the
meson-meson system, which is shown to be essential in order to reproduce the
data, particularly the L=0 channel. This latter channel is treated here
following a recent theoretical work in which the meson-meson amplitudes are
well reproduced and the f_0, a_0, sigma resonances show up clearly as poles of
the t matrix. The present work, as done in earlier ones, also incorporates
elements of chiral symmetry and exchange of vector and axial resonances in the
crossed channels, as well as a direct coupling to the f_2(1270) and a_2(1320)
resonances. We also evaluate the decay width of the f_0(980) and a_0(980)
resonances into the gamma-gamma channel.
