Attosecond electron bunches accelerated and compressed by radially polarized laser pulses and soft-x-ray pulses from optical undulators

We present a study of direct laser driven electron acceleration and scaling of attosecond bunch compression in unbound vacuum. Simple analytical expressions and detailed three-dimensional numerical calculations including space charge and non-paraxial laser fields reveal the conditions for compression to attosecond electron sheets. Intermediate emittance minima suitable for brilliant x-ray generation in optical undulators are predicted. We verify a favourable coherent enhancement of the resulting x-ray fields and demonstrate feasibility for realistic laser parameters. (paper)