#3. 15 pts Numbers for Pulse Expansion. (a) Given a transform-limited gaussian 100 fs pulse at 800 nm, you are to design a double pass negative GVD grating pair that will expand the pulse to a 1 ns duration, i.e. an expansion of 10000 times. Under the minimum astigmatic conditions, what is the grating spacing if the groove density of the gratings is 1800 lines per mm? (b) Suppose instead that the pulse that you are given is a transform-limited gaussian of 1 ps duration. By what factor will this pulse be expanded by the above system? Did you expect this