  We developed a 2D Finite-Difference Time-Domain (FDTD) method for modeling a
space-time modulated guidestar targeting wavefront shaping applications in
disordered media. Space-time modulation in general (a particular example being
the acousto-optic effect) is used here as a guidestar for the transverse
confinement of light around the tagged region surrounded by disorder. Together
with the guidestar, the iterative optical phase conjugation (IOPC) method is
used to overcome the diffusion of light due to multiple scattering. A phase
sensitive lock-in detection technique is utilized to estimate the steady-state
amplitude and phase of the modulated wavefronts emerging from the guidestar
region continuously operating in the Raman-Nath regime. As the IOPC scheme
naturally converges to the maximally transmitting eigenchannel profile, one
could use the position of the guidestar within the disorder to channelize the
maximal transmission through the tagged region. The associated code developed
in MATLAB is provided as an open source (MIT license) package. The code package
is referred by the acronym STAR-FDTD where STAR stands for Space-Time modulated
Acousto-optic guidestaR.
