  Scattering prevents light from being focused in turbid media. The effect of
scattering can be negated through wavefront shaping techniques when a localized
form of feedback is available. Even in the absence of such a localized
reporter, wavefront shaping can blindly form a single diffraction-limited focus
when the feedback response is nonlinear. We developed and experimentally
validated a model that accurately describes the statistics of this blind
focusing process. We show that maximizing the nonlinear feedback signal does
not always result in the formation of a focus. Using our model, we can
calculate the minimal requirements to blindly focus light through strongly
scattering media.
