Control of Intense Laser- Atom Processes With Strong Static Fields

We analyze the use of strong static electric and magnetic fields for controlling two intense laser-atom processes: laser-assisted x-ray-atom scattering and highorder harmonic generation. We find that x-rays scattered from atoms in the presence of both a strong laser field and a strong static electric field can be boosted in energy many-fold by absorption of energy from the laser field. The spectrum of scattered x-ray intensity vs. the number of laser photons absorbed exhibits a rich plateau structure, whose key features may be understood using a classical analysis. We find also that the intensities of high-order harmonics can be increased by orders of magnitude in the presence of strong static magnetic or parallel electric and magnetic fields and also that the static electric field can introduce additional plateaus and cutoffs. The maximum values of the harmonic intensity correspond to values of magnetic field for which the return time of the ionized electron wave packet to the atomic core under the influence of the laser field (and the static electric field, if present) is an integer multiple of the classical cyclotron period.