Superradiance and nonlinear evolution of a FEL pulse in a single-pass
FEL were experimentally demonstrated at the National Synchrotron Light
Source (NSLS) Source Development Laboratory (SDL). The FEL spectrum,
energy and pulse length along the undulator were measured. FEL saturation
was observed, and gain of more than 200 (relative to seed laser) was
measured. Both FEL spectrum widening and pulse length shortening were
observed. The superradiance and nonlinear evolution were also simulated
using the numerical code GENESIS1.3 yielding good agreement with the
experimental results.