I was reading about electron-positron annihilation and I got to the part where it says that this is a reversible process, meaning that an electron and a positron could be created from photons. About this reverse process the article says "In nuclear physics, this occurs when a high-energy photon interacts with a nucleus". But that doesn't sound like the reverse of annihilating an electron and a positron to produce photons. Has ever been observed in the laboratory the creation of a "pair" only from photons? If no, why not? If yes any source to the experiment would be appreciated. Thanks in advance.