 The refractive index of typical materials such as BK7 glass changes only a small amount (0.01 – 0.02) within the few tens of nanometers that are covered by an ultrashort pulse.Within a practical size, a prism compressor can only compensate a few hundred μm of path length differences between the wavelength components.However, by using a large refractive index material (such as SF10, SF11, etc.)