FIG. 4.

Structural contributions to the excited state XUV absorption. (a) The predicted effect of an expansion along the [100] direction (light orange) and (b) an isotropic lattice expansion (light blue) on the Si band structure, shown as the resulting change in the theoretically predicted absorption. In each case, a 3% expansion of the relevant axis is used. The k-space directions are marked. Note L is at $\frac{1}{2}$,$\frac{1}{2}$,$\frac{1}{2}$ and the Δ is at ∼0.8,0,0 in the Brillouin zone. The ground state silicon band structure (black line) and ground state absorption (grey area) are shown for reference to the [100] and isotropic expansion calculations (colored lines and colored areas). The top of the valence band is arbitrarily set to zero. Comparison of the experimental (solid black line) and theoretical (color-range or dashed line) differential absorption lineouts at (c) 100 fs and (d) 150 ps after 800 nm excitation. The theoretical differential absorption is calculated using a range of [100] expansions for the 100 fs time slice and a range of isotropic expansions for the 150 ps time slice. In each case, the carrier densities from Table I are used. An isotropic expansion is also shown for comparison for the 100 fs time slice as a grey dotted line. The grey shaded areas show the 95% confidence intervals on the experimental data.