We report a method for tuning a split-ring resonator (SRR) using infrared light. The SRR unit cells are commonly used in arrays to form a metamaterial that exhibits an effective negative permeability and are often used in negative-refractive-index materials. The region of negative permeability is generally limited to a narrow bandwidth at a fixed frequency. In this work, we use photocapacitance as observed in undoped semi-insulating GaAs to modify the gap capacitance of a SRR. We demonstrate a continuously tunable frequency over the range of 0.1–1.5 GHz using a 975 nm laser diode with a power range of 0–189 mW.

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A general expression for the rms emittance of a multiple beam system is unambiguously derived. The emittances for rectangular and circular arrays of identical beamlets are analyzed and expressed in terms of quantities associated with the beamlet distribution and the array geometry. A few examples relevant to actual experiments are included.

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The epitaxial deposition of (111)-oriented GaAs on substrates consisting of BaF2 (111)/Si (100) heterostructures has been investigated. The temperature dependence (from 575 to 650 °C in 25 °C steps) of the initial stages of deposition was examined. Substrates were exposed to Ga and As fluxes simultaneously during these depositions. In situ x-ray photoelectron spectroscopy and reflection high-energy electron diffraction showed that the GaAs grows epitaxially between 575 and 625 °C. The amount of material adhering to the surface during deposition decreases as the substrate temperature increases. GaAs does not adhere to the surface at 650 °C. Analysis of the Ba 3d5/2 photoelectron peak indicated a surface chemical reaction between Ba and the GaAs. In order to determine which species was reacting with the Ba atoms, a BaF2 (111) surface was exposed separately to Ga and As fluxes at 625 °C and to Ga at 650 °C. No chemical interactions were observed, indicating that the presence of both species is required before the chemical reaction and subsequent epitaxial deposition will occur. A chemical reaction that produces a gaseous GaF byproduct resulting in a Ba “template” layer is proposed. This Ba layer facilitates the epitaxial deposition of the GaAs layer.