We have presented the results from the numerical solution of the time dependent Dirac equation in one dimension. For a free wavepacket, the relativistic Schroedinger equation is equivalent to the Dirac equation. For ionization by a laser pulse, the R equation is also in very close agreement with the D equation. Small differences are visible due to the slight differ- ence in the bound state in the two equations. With proper care, negative energy wavepackets can be identified that are created by the ultrastrong field during the driving process. Such wavepackets occur when the field intensity becomes close to (but still significantly below) the critical vacuum polarization field strength.
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