[dspeyer]

The timeline:

    1934: This is predicted
    1997: This is done http://www.nytimes.com/1997/09/16/science/scientists-use-light-to-create-particles.html
    2014: We will "demonstrate the feat within the next 12 months"
    2015: Didn't bother

[TTPrograms]

The 1997 experiment is slightly different, as it involves electrons instead of just photons. See https://en.wikipedia.org/wiki/Schwinger_limit:

"Photon–photon scattering and other effects of nonlinear optics in vacuum is an active area of experimental research, with current or planned technology beginning to approach the Schwinger limit.[5] It has already been observed through inelastic channels in SLAC Experiment 144.[6][7] However, the direct effects in elastic scattering have not been observed. As of 2012, the best constraint on the elastic photon–photon scattering cross section belongs to PVLAS, which reports an upper limit far above the level predicted by the Standard Model.[8] Proposals have been made to measure elastic light-by-light scattering using the strong electromagnetic fields of the hadrons collided at the LHC.[9] Observation of a cross section larger than that predicted by the Standard Model could signify new physics such as axions, the search of which is the primary goal of PVLAS and several similar experiments. Even the planned, funded ELI–Ultra High Field Facility, which will study light at the intensity frontier, is likely to remain well below the Schwinger limit[10] although it may still be possible to observe some nonlinear optical effects.[11] Such an experiment, in which ultra-intense light causes pair production, has been described in the popular media as creating a "hernia" in spacetime.[12]"