Combined intersubband-cyclotron resonances in a $\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}-{\mathrm{Ga}}_{1-x}{\mathrm{Al}}_x\mathrm{As}$ heterojunction

The quasi-two-dimensional electron gas in $\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}-{\mathrm{Ga}}_{1-x}{\mathrm{Al}}_x\mathrm{As}$ heterojunctions is studied with far-infrared Fourier transform spectroscopy in a strip-line configuration that yields nearly perfect light polarization perpendicular to the electron layer. In this configuration, we observe simultaneously diamagnetically shifted intersubband resonance, combined intersubband-cyclotron resonances, and cyclotron resonance in tilted magnetic fields. In particular, this allows us to determine the depolarization shift of the $B=0\mathrm{}$ intersubband resonance.