Breit–Wheeler γ γ′ → e+ e− pair production with hohlaraum as photon target; is this particular experiment going to be carried out? The IFLScience article Scientists Work Out How To Make Matter From Light describes photon-photon collisions producing pairs of particles, and the Nature Photonics Letter A photon–photon collider in a vacuum hohlraum describes a possible way of doing the experiment.

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* Breit–Wheeler pair production
edit: The Phys.org article The first model for capturing and condensing light under realistic conditions discusses this as well.
Following this proposal, has a hohlaraum now been built or is in the process of being built for the purposes of serving as photon target for such an experiment?
From the abstract:

[...]The simplest mechanism by which pure light can betransformed into matter, Breit–Wheeler pair production $\gamma \gamma' \rightarrow e^+e^-$, has never been observed in the laboratory. Here, we present the design of a new class of photon–photon collider in which a gamma-ray beam is ﬁred into the high-temperature radiation ﬁeld of a laser-heated hohlraum. Matching experimental parameters to current-generation facilities, MonteCarlo simulations suggest that this scheme is capable of producing of the order of 10^5 Breit–Wheeler pairs in a single shot. This would provide the ﬁrst realization of a pure photon–photon collider, representing the advent of a new type of high-energy physics experiment.


 A: Work is in progress. See Experiments underway to turn light into matter on the Imperial website: 

In laser facilities in the UK, Imperial physicists are testing an 84-year-old theory which was once thought impossible to prove. The theory of the Breit-Wheeler process says it should be possible to turn light into matter by smashing two particles of light (photons) together to create an electron and a positron. However, past attempts to do this have required the addition of other high-energy particles. Physicists from Imperial College London, led by Professor Steven Rose, came up with a way of testing the theory that did not rely on these added extras in 2014, and today an experiment is running in the hope of turning light directly into matter for the first time. Professor Rose said: “This would be a pure demonstration of Einstein’s famous equation that relates energy and mass: E=mc², which tells us how much energy is produced when matter is turned to energy. What we are doing is the same but backwards: turning photon energy into mass, i.e. m=E/c²”...

Also see this reportage from Science Alert:

These lasers will be used to create the photons that are going to be smashed together. Inside a target chamber, electrons are fired at a slab of gold to produce a beam of high-energy photons. Next, a second high-energy laser is fired into a tiny gold tube called a hohlraum to create a thermal radiation field. The photon beam is then directed through the hohlraum, and the photons from the two sources collide. If it works, the team will be able to detect charged positrons from those collisions...

