The elastic light-light scattering below the threshold of the $e^+e^-$ pair production leads to a variation in polarization of hard $\gamma$-quanta traversing without loss a region where the laser light is focused. This effect can be used to control the $\gamma$-quantum polarization. Equations are obtained which determine the variation of Stokes parameters of $\gamma$-quanta in this case, and their solutions are given. It is pointed out that this effect can be observed in the experiment E-144 at SLAC. It should be taken into account and, perhaps, it can be used in experiments at future $\gamma \gamma$ colliders.
KOTKIN, G.L. and SERBO, V.G. (1998) "A possibility to control the polarization of high-energy photons by means of a laser beam," Turkish Journal of Physics: Vol. 22: No. 7, Article 19. Available at: https://journals.tubitak.gov.tr/physics/vol22/iss7/19