Recently, record high accelerating gradients have been demonstrated in dielectric laser accelerator structures. However, the temporal profile and phase of compressed femtosecond laser pulses often deviates from theoretical distributions. In this work, we apply frequency-resolved optical gating to interpret the peak accelerating gradient in experiments with relativistic beams in dielectric laser accelerators, highlight recent experimental results and outline the scope for future increases in accelerating gradient in dielectric laser accelerator structures. Show Partial Abstract