Electron-positron pair production in ultrastrong fields

With the rapid development of modern technology, the intensity of ultrastrong lasers has entered the strong relativistic regime and is approaching the Schwinger critical field value for creating electron-positron pairs. This article focuses on the electron-positron pair production from unstable vacuum in ultrastrong fields, and recounts a number of important methods and interesting results from past and present studies. The status of current research and future prospects are reviewed.