Tabletop Accelerator To Create Ultra-Relativistic Positron Beams? Sure, I'll Take One!

I had just finished reading this new paper that appeared in PRL this week. Using a high-powered laser, they shoot the light beam to a He gas jet to create a beam of high-energy electrons (exceeding 80 MeV). These electrons are then shot at various high-Z material, and this is where the electron-positron pairs are created. The authors stated two separate processes for these pair production:

In these experimental conditions, the positrons inside the high-Z target are mainly generated via either direct electroproduction (trident process), in which pair production is mediated by a virtual photon in the electron field [25], or via a two-step ‘‘cascade’’ process where the electron first emits a real photon (bremsstrahlung) [26], which then produces an electron-positron pair via the Bethe-Heitler process [27].

It looks like the could get positrons with energies in the range of 90 to 120 MeV.

Now, while I'm sure the size of this whole contraption can be considered as "tabletop", it doesn't include the laser source, which is a petawatt laser, something that is not trivia and not easily available to everyone, much less having it fit onto a tabletop size (at least, for now).

Zz.