  Light scattering is the main limitation for optical imaging. However, light
can be focused through or inside turbid media by spatially shaping the incident
wavefront. Wavefront shaping is ultimately limited by the available photon
budget. We developed a new `dual reference' wavefront shaping algorithm that
optimally uses the available light. Our method allows for multi-target
wavefront shaping, making it suitable for transmission matrix measurements or
transmitting images. We experimentally confirmed the improvement of the focus
intensity compared to existing methods.
