$\gamma\gamma$ Collider – A Brief History and Recent Developments

There is renewed interest in constructing a gg collider following the discovery of the Higgs boson and the formation of an ICFA ( International Committee for Future Accelerators ) – ICUIL ( International Committee on Ultrahigh Intensity Lasers ) collaboration. ICUIL brings state-of-the-art laser technology to build new types of accelerators such as a gg collider.  A recent ICFA mini-workshop on gg colliders investigated the possibility and physics value of a low energy gg collider. This paper uses a 1 MeV (c.m.) gg collider currently under design at IHEP as an example to discuss various aspects of this collider, including the physics case, requirements on the laser beam, the electron beam, the accelerator and detector.