ABSTRACT
When light travels through a medium other than vacuum, each frequency component travels at the corresponding velocity of the said frequency in the medium. Because we are dealing with ultrashort pulses that have very broad bandwidth spectra, the difference in velocities experienced by all the frequencies causes the pulse to broaden. A function describing the index of refraction as a function of wavelength, such as Sellmeier's equation, is then used to replicate the variations in the index as a function of wavelengths in one mathematical formula. The formula is needed because as the field travels in a medium that is not a vacuum, the spectral phase accumulated depends on variations in the index of refraction. If the index of refraction is a constant of frequency, then the pulse experiences only a delay proportional to the length of the medium.
