Ultrafast X-ray generation and its application

Isolated bursts of radiation of the order of 1 femtosecond or shorter are required to reliably trace dynamics never before accessed in the time domain. These single bursts need to be carried at substantially shorter wavelengths, preferably in the extreme ultraviolet (EUV) or X-ray regime, if bound atomic electrons are to be accessed in ultrafast spectroscopy. High harmonic generation using few-cycle pulses is ideal for this purpose. High harmonics are generated by electrons removed from the atom by the high laser field and then driven back to their ion of origin. As their recollision energy is greatest when the laser field is largest, the most energetic "harmonic" radiation is produced at the peak of the laser pulse. We select radiation produced only within a fraction of the laser cycle near the peak of the pulse by passing the harmonics through a filter that transmits only the highest frequencies. This method has been predicted to be capable of generating single EUV/X-ray pulses of /spl sim/100-attosecond duration emitted in a collimated, laser-like beam.