  We show theoretically with an accurate spin Hamiltonian describing the
multiferroic Mn perovskites that the application of the picosecond optical
pulse with a terahertz frequency can switch the spin chirality through
intensely exciting the electromagnons. There are four states with different
spin chiralities, i.e. clockwise and counterclockwise ab/bc-plane spin spirals,
and by tuning the strength, shape and length of the pulse, the switching among
these states can be controlled at will. Dynamical pattern formation during the
switching is also discussed.
