Ultrafast shadowgraphy utilizes few cycle probe pulses in order to image density gradients in a plasma allowing to probe structures, such as laser-driven wakes, moving close to the speed of light. Here we study the process of shadowgraphic image formation in the interaction of a few cycle probe pulse with a laser-driven wake using particle-in-cell (PIC) simulations. The output of the PIC code is then post-processed by means of Fourier optics in order to take into account the effect of a typical imaging setup. This allows to construct synthetic shadowgrams which can be compared with experimentally recorded ones. This facilitates the correct interpretation of such involved measurements
