  Propagation of an ultrashort pulse of light through strongly scattering media
generates an intricate spatio-spectral speckle that can be described by means
of the multi-spectral transmission matrix (MSTM). In conjunction with a spatial
light modulator, the MSTM enables the manipulation of the pulse leaving the
medium; in particular focusing it at any desired spatial position and/or time.
Here, we demonstrate how to engineer the point-spread-function of the focused
beam both spatially and spectrally, from the measured MSTM. It consists in
numerically filtering the spatial content at each wavelength of the matrix
prior to focusing. We experimentally report on the versatility of the technique
through several examples, in particular as an alternative to simultaneous
spatial and temporal focusing, with potential applications in multiphoton
microscopy.
