Material Dispersion

Measuring pulses requires the use of certain materials such as silica. A measurement system must have at least one material to obtain a nonlinear effect. T he materials in the measuring system, unfortunately, could cause chirp in the pulse and stretch the pulse to be measured. Although chirp from the materials in a system is generally negligible in long pulses, it is not for some short pulses. Therefore, one must be mindful of the materials used in a measuring system. The table below shows how much chirp is introduced by materials and how much pulses are stretched by the materials.

Transform limited pulse length at 800nm 10fs 25fs 100fs
Bandwidth FWHM 80nm 32nm 8nm
10mm fused silica Chirp 361fs^2/rad
Stretched pulse length 85fs 36fs 102fs
Error (%) 300 % 44 % 2 %
10mm BK7 Chirp 446fs^2/rad
Stretched pulse length 248fs 102fs 103fs
Error (%) 952% 308% 3 %
1mm BBO crystal Chirp 75fs^2/rad
Stretched pulse length 43fs 30fs 100.1fs
Error (%) 132% 20% 0.1%