  We describe a fast closed-loop optimization wavefront shaping system able to
focus light through dynamic scattering media. A MEMS-based spatial light
modulator (SLM), a fast photodetector and FPGA electronics are combined to
implement a closed-loop optimization of a wavefront with a single mode
optimization rate of 4.1 kHz. The system performances are demonstrated by
focusing light through colloidal solutions of TiO2 particles in glycerol with
tunable temporal stability.
