Dispersion compensation for ultrafast lasers is to introducing a negative GDD that cancels out the positive GDD that results from chromatic dispersion. Dispersion compensation is critical for femtosecond ultrafast lasers to preserve the temporal profile and peak power of laser pulses. Chirped mirrors are a special dispersive Bragg mirror coated with alternating dielectric thin films of high and low refractive indices, and the thickness of the thin films becomes thinner towards the surface to provide larger group delay dispersion for longer wavelengths.