FIG. 5.

The real part of the nonlinear index is given for (a) 10 kV/m, (b) 50 kV/m, and (c) 100 kV/m. The real part of the nonlinear index is given, as calculated (wide dash-dotted black) with the two-level system neglecting saturation (wide dashed orange) with the two-level system including saturation, and (solid green) as recovered from simulated measurements on three detector planes, namely $Z=z/z_R=0.5$, 1, and 2 using PROM with 12 basis functions. An adjustable constant for the green curve was optimized by hand for best agreement.