  Controlling the propagation and interaction of light in complex media has
sparked major interest in the last few years. Unfortunately, spatial light
modulation devices suffer from limited speed that precludes real-time
applications such as imaging in live tissue. To address this critical problem
we introduce a phase-control technique to characterize complex media based on
the use of fast 1D spatial light modulators and a 1D-to-2D transformation
performed by the same medium being analyzed. We implement the concept using a
micro-electro-mechanical grating light valve (GLV) with 1088 degrees of freedom
modulated at 350 KHz, enabling unprecedented high-speed wavefront measurements.
We continuously measure the transmission matrix, calculate the optimal
wavefront and project a focus through various dynamic scattering samples in
real-time, all within 2.4 ms per cycle. These results improve prior wavefront
shaping modulation speed by more than an order of magnitude and open new
opportunities for optical processing using 1D-to-2D transformations.
