PULSE PIs study a wide range of strong-field light matter interactions in atoms, molecules, solids, as well as the vacuum itself.
In the optical regime below threshold excitation leads to tunnel ionization and such phenomena as high-harmonic generation and above-threshold ionization, which is the basis of much of attosecond physics. For x-rays, nonlinear interactions have only recently become accessible using free-electron lasers such as the LCLS. At sufficiently high fields, even the vacuum becomes nonlinear. Here tunnel ionization of the vacuum can produce copious electron-positron pairs at field strengths comparable to the electron mass in a Compton wavelength. Such fields are orders of magnitude away from what is possible with even the most intense lasers, but are expected to occur in various astrophysical phenomena as well as in beam-beam collisions in future lepton colliders. Importantly, they can also occur in the collisions of high energy electrons or photons with a strong laser field. This is because the electric field is not a Lorentz invariant and thus an ultrarelativistic particle will see the laser field boosted dramatically in the center of momentum frame. PULSE is leading an international team of researchers to study this regime of strong-field physics on the SLAC FACET-II facility. The experiment, E-320 (Meuren PI) will begin later in 2020 and is expected to measure strong-field QED phenomena including nonperturbative photon emission and tunneling of electron-positron pairs from the vacuum.
For additional information about strong-field quantum electrodynamics, you may be interested in the 3rd International Extremely-High Intensity Laser Physics conference, which PULSE hosted at Stanford in 2019. You may also be interested in a workshop on Physics Opportunities at a Lepton Collider in the Fully Nonperturbative QED Regime, held at SLAC also in 2019.
Under construction. Please contact Sebastian Meuren, Phil Bucksbaum or David Reis for more information. You might also be interested in E-144, which was an experiment that observed multi-photon Compton scattering and Breit-Wheeler pair production below the Schwinger limit.