  We report on our study of the luminescence spectra of a quantum cascade laser
in the presence of an external magnetic field tilted from the direction
perpendicular to the electron plane. The effect of the tilted field is to allow
novel optical transitions because of the coupling of intersubband-cyclotron
energies. We find that by tuning the applied field, one can get optical
transitions at different energies that are as sharp as the zero-field
transitions.
