HIGH-HARMONIC GENERATION OF ATTOSECOND PULSES IN THE SINGLE-CYCLE REGIME

High-harmonic generation with excitation pulses shorter than 25 fs is studied theoretically using a 3D model. For very short excitation puls es, a new regime of harmonic generation by a ''single-cycle'' of the d river pulse can be reached. In this regime: the temporal coherence of the adjacent harmonic orders is dramatically improved compared with lo nger excitation pulses, even though the discrete harmonic structure in the emission disappears. X-ray pulses as short as 100 attoseconds can be emitted, with increased conversion efficiency of laser-to-harmonic radiation.