Pump and probe nonlinear transmission experiments with femtosecond res
olution are used to investigate electron tunnelling between the centra
l CdMnTe well and the outer CdTe wells of a CdTe/CdMnTe double barrier
structure. The time dependence of the reduction in oscillator strengt
h resulting from bandfilling at the exciton resonance is used to measu
re population changes in the outer wells. A tunnelling time of 8 ps is
measured when a carrier density of 1 x 10(13) cm(-2) is used. Monte C
arlo simulations show that the timescale of tunnelling via LO phonon s
cattering is 10 ps. A pump induced increase in absorption at energies
smaller than that of the exciton resonance is observed at early times
and assigned to band-gap renormalisation.