Generation of attosecond pulses of recombination radiation in two-colour laser fields

The possibility of generation of attosecond pulses of recombination radiation upon the above-threshold tunnel ionisation of atoms (ions) in two-colour laser fields is studied. The method of classical photoelectron trajectories in the continuum is used to determine the laser field parameters minimising the duration of recombination radiation. It is shown that pulses of duration of several tens of attoseconds can be generated in such fields. The principal possibility of generation of coherent electromagnetic pulses of duration $\tau_g\lesssim1$ as is also shown.