  We demonstrate the ability to control and shape the spectro-temporal content
of extreme-ultraviolet (XUV) pulses produced by a seeded free-electron laser
(FEL). The control over the spectro-temporal properties of XUV light was
achieved by precisely manipulating the linear frequency chirp of the seed
laser. Our results agree with existing theory, which allows retrieving the
temporal properties (amplitude and phase) of the FEL pulse from measurements of
the spectra as a function of the FEL operating parameters. Furthermore, we show
the first direct evidence of the full temporal coherence of FEL light and
generate Fourier limited pulses by fine-tuning the FEL temporal phase. The
possibility to tailor the spectro-temporal content of intense short-wavelength
pulses represents the first step towards efficient nonlinear optics in the XUV
to X-ray spectral region and will enable precise manipulation of core-electron
excitations using the methods of coherent quantum control.
