Ultrafast polarization dynamics and noise in pulsed vertical-cavity surface-emitting lasers.

We have measured on ps time scales the temporal behavior of the intensity noise of, and correlations between, orthogonally polarized modes in an optically pumped VCSEL. Measurements were made in both the circular and the linear bases. Sub-ps optical pumping with circular polarization leads to positively correlated intensity noise for emission in orthogonal linear polarizations. Optical pumping with linear polarization leads to anti-correlated intensity noise for emission in orthogonal linear polarizations, due to random orientation of linearly polarized emission. Intensity noise for circularly polarized emission is uncorrelated or anti-correlated depending on spin-flip rates which determine the strength of gain competition. We have generalized the theoretical treatment of San Miguel, Feng, and Moloney to successfully model these phenomena.

Mid-ultraviolet light-emitting diode detects dipicolinic acid.

Dipicolinic acid (DPA, 2,6-pyridinedicarboxylic acid) is a substance uniquely present in bacterial spores such as that from anthrax (B. anthracis). It is known that DPA can be detected by the long-lived fluorescence of its terbium chelate; the best limit of detection (LOD) reported thus far using a large benchtop gated fluorescence instrument using a pulsed Xe lamp is 2 nM. We use a novel AlGaN light-emitting diode (LED) fabricated on a sapphire substrate that has peak emission at 291 nm. Although the overlap of the emission band of this LED with the absorption band of Tb-DPA (lambda(max) doublet: 273, 279 nm) is not ideal, we demonstrate that a compact detector based on this LED and an off-the-shelf gated photodetection module can provide an LOD of 0.4 nM, thus providing a basis for convenient early warning detectors.

Strong coupling in the sub-wavelength limit using metamaterial nanocavities.

The interaction between cavity modes and optical transitions leads to new coupled light-matter states in which the energy is periodically exchanged between the matter states and the optical mode. Here we present experimental evidence of optical strong coupling between modes of individual sub-wavelength metamaterial nanocavities and engineered optical transitions in semiconductor heterostructures. We show that this behaviour is generic by extending the results from the mid-infrared (~10 µm) to the near-infrared (~1.5 µm). Using mid-infrared structures, we demonstrate that the light-matter coupling occurs at the single resonator level and with extremely small interaction volumes. We calculate a mode volume of 4.9 × 10(-4) (λ/n)(3) from which we infer that only ~2,400 electrons per resonator participate in this energy exchange process.

Intracavity frequency doubling of a diode-pumped external-cavity surface-emitting semiconductor laser.

We present a compact, robust, solid-state blue-light (490-nm) source capable of greater than 5 mW of output in a TEM(00) mode. This device is an optically pumped, vertical external-cavity surface-emitting laser with an intracavity frequency-doubling crystal.