Experimental Measurements of $^{69/71}$Ga NMR in Optically-pumped NMR (OPNMR) of AlGaAs/GaAs Quantum Wells

We have conducted photon-energy and helicity-dependent measurements of the $^{69}$Ga and $^{71}$Ga NMR signals that result from optical pumping of states in the conduction band. The sample we have used for these studies is a 60-well multiple quantum well sample of Al$_{0.34}$Ga$_{0.66}$As/GaAs. Our measurements show a particularly strong dependence of the OPNMR signal from the GaAs quantum wells, when irradiating at photon energies consistent with the spin-split light hole within the material. (We use a frequency-stabilized continuous wave Ti:sapphire ring laser, with a very narrow linewidth for these excitation.) The coupling to the light-hole has an important NMR signature which we will discuss in this presesntation. We will show results for multiple external magnetic field strengths (B$_{0})$ and for different laser light intensities. A thorough understanding of the ``fine structure'' observed in the photon energy dependence of these OPNMR signals is afforded through theoretical modeling of these results, which will be shown in a separate presentation.