Optical transmission spectroscopy of the two-dimensional electron gas in GaAs in the quantum hall regime

Optical transmission spectroscopy of a two-dimensional electron gas is shown to be a sensitive probe of the Fermi level and electronic density of states. Results are presented for interband transmission of modulation-doped GaAs multiple quantum wells in high magnetic fields. The appearance of new absorption transitions at even integral filling factors is the optical observation of quantum oscillations of the Fermi level of a two-dimensional electron gas. The broadening of the Landau level density of states is found to be $1.2\sqrt{B}$ meV ${\mathrm{T}}^{\frac{-1\mathrm{}}{2}}$ by fitting the Fermi level oscillations.