GENERATION AND PROPAGATION OF ATTOSECOND X-RAY PULSES IN GASEOUS MEDIA

Using a self-consistent model that solves both the three-dimensional S chrodinger equation and the wave equation ab initio, we study the prop agation of subfemtosecond pulses produced by high harmonic generation in a gas. The presence of a plasma shortens the coherence length for t he harmonics. However, for the case of very short pump pulses, ionizat ion is suppressed, and the coherence length can approach that of a neu tral gas. Thus, the combination of enhanced single-atom harmonic gener ation for short pulses and improved phase matching allows for efficien t amplification of attosecond x-ray pulses, resulting in 100 times hig her output intensity for 5 fs compared to 10-fs pump pulses.