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%