Ultrawide
bandwidth of SASE FEL radiation has been observed at the VISA (Visible
to Infrared SASE Amplifier) experiment. This radiation, with bandwidth
as high as 15% relative width, at high gain operations, is obtained
with a strongly chirped electron beam which is longitudinally compressed
through second-order effects in the transport. Start-to-end simulations
are able to reproduce key features of the radiation, namely the large
bandwidth and the characteristic double peak structure. In this paper,
we will report on these measurements and the consequent analyses. We
will also offer a brief description of a state-of-the-art diagnostic
to measure frequency chirped SASE radiation utilizing a modified frequency
resolve optical gating (FROG) method.