The suggested technique is based on the reflection of ultra-short (5 fs, ~2 cycles) tightly focused ("single mode mirror") relativistically intense laser pulses from near-critical plasma. The tight focus creates strong slopes moving with relativistic velocity within the plasma density. As a result each half-cycle is deflected into a different direction (Fig.1).

The relativistic coherent motion of electrons (Fig.2) towards the reflected pulse (due, to the oblique incidence of the laser pulse on the plasma) compresses the radiation, generating isolated attosecond pulses.

Due to the short pulse duration this interaction is phase sensitive, imposing the need to develop a phase-stable laser system. This technique provides efficient (~10%) generation of relativistic isolated pulses with durations ranging from 500 as to 10 as with state-of-the-art lasers. Well focused, these attosecond pulses could bring us close to the critical field where electron-positron pairs can be torn from vacuum.

References:

1) Relativistic Attosecond Physics

N. M. Naumova, J. A. Nees, and G. A. Mourou

Physics of Plasmas 12, 056707 (2005)

2) Isolated Attosecond Pulse Generation in the Relativistic lambda³ Regime by Reflection/Deflection/Compression

G. A. Mourou, N. M. Naumova, I. V. Sokolov, B. Hou, and J. A. Nees

Ultrafast Optics IV Vol. 95 of Springer Series in Optical Sciences, F. Krausz, G. Korn, P. Corkum, and I. A. Walmsley, eds. (Springer-Verlag, Berlin, 2004), p.303.

3) Relativistic Generation of Isolated Attosecond Pulses in a lambda³ Focal Volume

N. M. Naumova, J. A. Nees, I. V. Sokolov, B. Hou, and G. A. Mourou

Phys. Rev. Lett. 92, 063902 (2004).