A femtosecond laser pulse delivers energy within an extremely short time interval. The result is a very high power which can exceed that of all nuclear plants on Earth, for the brief moments of the flash. If this power is concentrated in a focused beam, the resultant extremely high intensity implies very strong electric and magnetic fields in the laser pulse. These exert giant forces on charged particles, such as electrons, which are stripped from their atomic binding nearly instantly, within attoseconds.

The following pages look at how the ultrastrong laser fields along with the fields produced by the liberated electrons separated from the positively charged ions can accelerate the freed electrons to velocities very close to the speed of light. It is conceivable that their relativistic motion can be steered with laser pulses with a controlled wave form. If this control can be extended to a large number of electrons within a small volume, it may open the door for the development of compact, laser-driven ultra-brilliant X-ray sources.