A laser–plasma platform for photon–photon physics: the two photon Breit–Wheeler process by Kettle, B, Hollatz, D, Gerstmayr, E, Samarin, GM, Alejo, A, Astbury, S, Baird, C, Bohlen, S, Campbell, M, Colgan, C, Dannheim, D, Gregory, C, Harsh, H, Hatfield, P, Hinojosa, J, Katzir, Y, Morton, J, Murphy, CD, Nurnberg, A, Osterhoff, J, Pérez-Callejo, G, Poder, K, Rajeev, PP, Roedel, C, Roeder, F, Salgado, FC, Sarri, G, Seidel, A, Spannagel, S, Spindloe, C, Steinke, S, Streeter, MJV, Thomas, AGR, Underwood, C, Watt, R, Zepf, M, Rose, SJ, Mangles, SPD