Probing the quantum vacuum with petawatt lasers

Due to the bosonic nature of the photon, increasing the peak intensity through a combination of raising the pulse energy and decreasing the pulse duration will pile up more and more photons within the same finite region of space. In the absence of material, this continues until the vacuum is stressed to the point of breakdown and virtual particles become real. The critical intensity where this occurs for electrons and positrons - the so-called Schwinger limit is predicted to be similar to 10(29) W/cm(2). At substantially lower intensities, however, nonlinear aspects of the quantum vacuum associated with polarization of the vacuum can be explored. These studies become viable at the petawatt level where 10(23) W/cm(2) and above can be reached. This is an era into which we are just embarking that will provide critical tests of QED and theories beyond the Standard Model of particle physics.