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Active mirror structures based on a dielectric high-contrast grating reflector combined with optical gain are proposed. Design parameters are found that work for III-V based compounds on diamond substrates, thus allowing semiconductor disk lasers with kW output power. Preliminary fabrications validates the concept by exhibiting a passive reflectivity ~99%.

Modulation doping is a commonly adopted technique to create two-dimensional (2D) electrons or holes in semiconductor heterostructures. One constraint, however, is that the intentional dopants required for modulation doping are controlled and incorporated during the growth of heterostructures. Using undoped strained germanium quantum wells as the model material system, we show, in this work, that modulation doping can be achieved post-growth of heterostructures by ion implantation and dopant-activation anneals. The carrier density is controlled ex situ by varying the ion fluence and implant energy, and an empirical calibration curve is obtained. While the mobility of the resulting 2D holes is lower than that in undoped heterostructure field-effect transistors built using the same material, the achievable carrier density is significantly higher. Potential applications of this modulation-doping technique are discussed.

We report the preparation, crystallization, and solid-state characterization of the first members of a new family of spiro-bis-(1,9-diamino-substituted-phenalenyl)boron neutral radicals. The crystal structures show that the three radicals are monomeric and without close contacts in the crystal lattice. In all cases magnetic susceptibility measurements confirm the presence of free radicals with one unpaired spin per molecule. Two of the new radical compounds are among the most highly conducting neutral organic solids, with room-temperature conductivities reaching sigma(RT) = 4 x 10(-2) S/cm. The measured conductivities correlate with the closest intermolecular contacts in the solid state and with the calculated band dispersions, even though the bandwidths are much smaller than those found in other organic conductors.

A simple analytical model for the signal acquisition range for a laser guided mortar is presented. The signal consists of a repetitively pulsed laser of fixed pulse duration and fixed pulse repetition frequency. The pulses are detected by a seeker consisting of a quadrant photodiode and a trans-impedance amplifier. Noise is introduced from solar irradiance and from the detector/amplifier electronics. The model maximizes the acquisition range by optimizing trans-impedance amplifier circuit components. A comparison of integrating multiple low energy pulses (MPLD) versus detecting each pulse individually (conventional) is made.