ABSTRACTThis paper reports an experimental study of the shot-to-shot intensity and spectral distribution fluctuations in the femtosecond coherent pulses from the storage ring (SR) based seeded free electron laser (FEL) at DELTA. A unique implementation of a gated ICCD camera coupled to a Czerny-Turner monochromator is utilized to reveal the details of the individual spectra and intensity of femtosecond pulses accompanied by a significant synchrotron background. This technique demonstrates the potential to study the dynamics of the electron bunches in an SR by scanning over a single electron bunch with seeded femtosecond laser pulses at a subharmonic repetition rate. To the best of our knowledge, this picture provides the first direct experimental evaluation of shot-to-shot intensity and spectral fluctuation in seeded SR-based FELs.