Quantum cascade lasers (QCLs) are unipolar semiconductor lasers operating in the mid infrared region. Their emitted wavelength is defined by the separation of intersubband levels which can be tailored by band structure engineering. Due to the fact that the maximum conduction band offset in the GaAs/AlGaAs material system is 380 meV, the lowest directly accessible wavelength is roughly 7 μm. One...

The energy flow lines (field lines of the Poynting vector) of electric dipole radiation exhibit a vortex structure in the near field when the dipole moment of the source is in circular rotation. The spatial extend of this vortex is smaller than a wavelength and may not be observable by a measurement in the near field. We show that the rotation of the field lines close to the source affects the ...

For a connected digits speech recognition task, we have compared the performance of two inexpensive electret microphones with that of a single high quality PZM microphone. Recognition error rates were measured both with and without compensation techniques, where both single-channel and two-channel approaches were used. In all cases the task was recognition at a significant distance (2–6 feet) f...

We overcame the resolution limit of scanning far-field fluorescence microscopy by disabling the fluorescence from the outer part of the focal spot. Whereas a near-UV pulse generates a diffraction-limited distribution of excited molecules, a spatially offset pulse quenches the excited molecules from the outer part of the focus through stimulated emission. This results in a subdiffraction-sized e...

The theoretical diffraction-limit of resolution for ultrasound imaging has recently been bypassed in-vitro and in-vivo. However, in the context of ultrasound therapy, the precision of therapeutic beams remains bound to the half-wavelength limit. By combining acoustic vaporization of composite droplets and rapid ultrasound monitoring, we demonstrate that ultrasound drug-delivery can be restricte...

In this work, we analyze the far-field pattern produced by a grating made of strips with two different random roughness levels. The efficiency and shape of the diffraction orders is obtained, which are shown to depend on the statistical properties of roughness. We assume for the calculations that the grating can be used in a mobile mechanical system. A preliminary experimental approach which pa...