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InAs quantum dots at telecommunication wavelengths are desired as single-photon sources, but a growth technique that enables wide control over quantum dot size, density, and morphology is needed. Droplet epitaxy is well suited for this purpose, but InAs nanostructures tend to form as rings on (001) InGaAs, InAlAs, and InP surfaces. In this work, we investigate how surface diffusion can be manipulated to grow quantum dots by molecular beam epitaxy without using high-index substrates or metamorphic buffers. First, surface diffusion characteristics of In on In0.52Al0.48As are compared to In and Ga on In0.53Ga0.47As. Then, a two-step arsenic exposure protocol is applied to modify the droplet crystallization step, resulting in a series of different nanostructure morphologies that have narrow-linewidth emission between 1200 and 1520 nm at 4 K. Ultimately, we show that controlling surface diffusion of the group-III species during growth is critical for achieving quantum dots appropriate for single-photon sources at telecommunication wavelengths. [ABSTRACT FROM AUTHOR]

Establishes a rigorous theoretical connection between measurements of the angular distribution of atomic photofragment alignment and the underlying dynamics of molecular photodissociation. Derivation of laboratory and molecular-frame angular momentum state multipoles; Steps in obtaining a method for analyzing experimental data.

Analyzes the near ultraviolet dissociation dynamics of azomethane. Observation of laser-limited appearance times for both vibrationless and umbrella-excited methyl photofragments; Difference between translational energy distributions and non-state-selective measurements; Background on the complexity of the three-body process.

Focuses on the observation of strong orbital alignment in the ground-state oxygen atom following dissociation of NO[sub 2] at 212.8 nm using ion imaging. Analysis of the results using a rigorous quantum mechanical theory; Dominance of a strong incoherent parallel perpendicular contributions to the excitation of a polyatomic molecule.

The optical quality of site-controlled quantum dots is typically assessed by off-resonant photoluminescence spectroscopy, and emission linewidth is the most common figure of merit. Here, we combine photoluminescence and resonance fluorescence spectroscopy to obtain a more complete picture of site-controlled quantum dots embedded in a charge injection device. Although resonant and non-resonant linewidths are nearly as small as those of randomly nucleated dots, other optical properties show clear evidence of influence from defects introduced by the nanofabrication process. We demonstrate optical spin pumping and spin-flip Raman processes, which are important functions for use in quantum information applications. [ABSTRACT FROM AUTHOR]

We report the effects of tunnel coupling on the Quantum-Confined Stark Effect (QCSE) for excitons in InAs/GaAs coupled quantum dots (CQDs). As the barrier separating the dots is reduced, the zero-field dipole moment and the polarizability are both found to increase. This systematic variation as a function of barrier thickness is due to factors including the formation of molecular wavefunctions, the electron/hole effective masses, and the CQD structural properties. The dipole moment for the interdot exciton is found to be up to 100 times larger than that of the intradot exciton resulting in a predominantly linear shift with field. The ability to control the QCSE of the exciton in a single CQD could be useful for a new class of single photon optical switches and tunable emitters. [ABSTRACT FROM AUTHOR]

Ultrasensitive detection of molecular hydrogen is reported by using Doppler-free (2+1) resonance-enhanced multiphoton ionization through the E,F 1Σ+g state. By using an arrangement with two near-transform-limited counterpropagating laser beams, a single-shot detection efficiency of 6.8×103 molecules/cm3 has been demonstrated. Frequency scans of the two-photon transitions show that the detection efficiency is limited by ac Stark effects. [ABSTRACT FROM AUTHOR]

Presents additional information provided by experimental results for efficient REMPI detection scheme for the detection of N[sub2]. Discussion on laser system used in the experiment; Pulse amplification; Spectral analysis.