Measuring the Beam Polarizations and the Luminosity at Photon-Photon   Colliders
  We present methods to measure the beam polarizations and the luminosity of $\gamma \gamma$ colliders at TeV energy scale.   The beam polarizations of a $\gamma \gamma$ collider can easily be monitored by comparing the numbers of events of the processes $\gamma \gamma$ $\rightarrow$ $\ell^+ \ell^-$ and $\gamma \gamma$ $\rightarrow$ $W^+ W^-$, where $\ell$ means $e$ or $\mu$.   The luminosity of a $\gamma \gamma$ collider is also measurable by the event rate of $W$ boson pair productions and the light lepton pair productions. 
Y. Yasui, I. Watanabe, J. Kodaira and I. Endo