Ultrahigh-Intensity Lasers: Physics of the Extreme on a Tabletop

Over the past ten years, laser intensities have increased by more than four orders of magnitude to reach enormous intensities of 1020 W/cm2. The field strength at these intensities is on the order of a teravolt per centimeter, or a hundred times the Coulombic field binding the ground state electron in the hydrogen atom. The electrons driven by such a field are relativistic, with an oscillatory energy of 10 MeV. At these intensities, the light pressure, P = I/c, is extreme, on the order of giga- to terabars. The laser interacting with matter—solid, gas, plasma—generates high-order harmonics of the incident beam up to the 3 nm wavelength range, energetic ions or electrons with mega-electron-volt energies (figure 1), gigagauss magnetic fields and violent accelerations of 1021 g (g is Earth's gravity). Finally, the interaction of an ultraintense beam with superrelativistic particles can produce fields approaching the critical field in which an electron gains in one Compton wavelength an energy equal to twice its rest mass. Under these conditions, one observes nonlinear quantum electrody-namical effects. In many ways, this physical environment of extreme electric fields, magnetic fields, pressure, temperature and acceleration can be found only in stellar interiors or close to the horizon of a black hole. It is fascinating to think that an astrophysical environment governed by hydrodynamics, radiation transport and gravitational interaction can be re-created in university laboratories for extremely short times, switching the role of the scientist from voyeur to actor.