Wavelength [nm]

B. Refractive Optics The next practical concern is the use of refractive optics to focus and collimate an ultrafast pulse. The most common materials for these optical components are BK7 glass and fused silica. The GVD coefficients for BK7 and fused silica at 800 nm are 45 ps2/km and 36 ps2 /km, respectively [3], while the nonlinear coefficients are 4.4 X 10-16cm2/W and 3.5 X 10-16cm2/W, respectively [8]. Intuitively, one would like to use only thin lenses to minimize the interaction lengths relative to the characteristic lengths of GVD and SPM.