  The short wavelength and high peak power of the present generation of
free-electron lasers (FELs) opens the possibility of ultra-short pulses even
surpassing the present (tens to hundreds of attoseconds) capabilities of other
light sources - but only if x-ray FELs can be made to generate pulses
consisting of just a few optical cycles. For hard x-ray operation (~0.1nm),
this corresponds to durations of approximately a single attosecond, and below
into the zeptosecond scale. This talk will describe a novel method to generate
trains of few-cycle pulses, at GW peak powers, from existing x-ray FEL
facilities by using a relatively short 'afterburner'. Such pulses would enhance
research opportunity in atomic dynamics and push capability towards the
investigation of electronic-nuclear and nuclear dynamics. The corresponding
multi-colour spectral output, with a bandwidth envelope increased by up to two
orders of magnitudes over SASE, also has potential applications.
