Femtosecond pulse fronts suffer a time delay across the beam when propagating through diffraction gratings or dispersive prisms. A general relation was found describing the tilt angle γ of the pulse front as, tanγ=λdε/dλ where dε/dλ is the angular dispersion of the grating or prism and λ is the central wavelength of the pulse. The expression is valid for any spectral device having angular dispersion (e.g., Fabry-Pérot interferometer, Lummer-Gehrcke plate, and Michelson echelon). The tilt angle is shown to have a close relation to the classical uncertainty principle.
H. A. Hazim,
"Femtosecond pulse front tilt caused by angular dispersion," Optical Engineering 32(10), (1 October 1993). https://doi.org/10.1117/12.145393