  Optical harmonic generation on excitons is found in ZnSe/BeTe quantum wells
with type-II band alignment. Two experimental approaches with spectrally-broad
femtosecond laser pulses and spectrally-narrow picosecond pulses are used for
spectroscopic studies by means of second and third harmonic generation (SHG and
THG). The SHG signal is symmetry-forbidden for light propagation along the
structure's growth axis, which is the [001] crystal axis, but can be induced by
an external magnetic field. The THG signal is detected at zero magnetic field
and its intensity is field independent. A group theory analysis of SHG and THG
rotational anisotropy diagrams allows us to identify the involved excitation
mechanisms.
