Using Back-Scattered Laser Beams to Detect CP Violation in the Neutral   Higgs Sector
  We demonstrate that the ability to polarize the photons produced by back-scattering laser beams at a TeV scale linear $\epem$ collider could make it possible to determine whether or not a neutral Higgs boson produced in photon-photon collisions is a CP eigenstate. The relative utility of different types of polarization is discussed. Asymmetries that are only non-zero if the Higgs boson is a CP mixture are defined, and their magnitudes illustrated for a two-doublet Higgs model with CP-violating neutral sector. 
B. Grzadkowski and J.F. Gunion