Nonlinear photoconductivity distortion in pump-probe spectroscopy

Optical pump-probe spectroscopy typically involves a procedure to derive the photoexcited conductivity from the measured changes in the reflection amplitude. Although the photoconductivity depth profile is typically not measured directly, it is commonly assumed that it decays exponentially with depth, over the length scale of the pump penetration depth. Recently we showed that nonlinearity can distort this depth profile at high pump fluence, and that this can introduce large systematic errors in the optical response functions derived from it. I will describe the general features of this systematic error and show how to correct for it.