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We report on a novel approach to adjust the emission wavelength of VCSEL devices. By patterning the Fabry-Perot cavity, we can control the effective refractive index of the optical mode and thus adjust the resonant wavelength. We developed a fabrication process based on 2 steps epitaxy and a lithographic cavity patterning to define the emission wavelength at the emitter level. A multiwavelength VCSEL array with a 30 nm wavelength tuning range around 940 nm is demonstrated. [ABSTRACT FROM AUTHOR]

Abstract Background The aim of this study was to assess the distribution of key SNARE proteins in glutamatergic and GABAergic synapses of the adult rat cerebellar cortex using light microscopy immunohistochemical techniques. Analysis was made of co-localizations of vGluT-1 and vGluT-2, vesicular transporters of glutamate and markers of glutamatergic synapses, or GAD, the GABA synthetic enzyme and marker of GABAergic synapses, with VAMP-2, SNAP-25A/B and syntaxin-1. Results The examined SNARE proteins were found to be diffusely expressed in glutamatergic synapses, whereas they were rarely observed in GABAergic synapses. However, among glutamatergic synapses, subpopulations which did not contain VAMP-2, SNAP-25A/B and syntaxin-1 were detected. They included virtually all the synapses established by terminals of climbing fibres (immunoreactive for vGluT-2) and some synapses established by terminals of parallel and mossy fibres (immunoreactive for vGluT-1, and for vGluT-1 and 2, respectively). The only GABA synapses expressing the SNARE proteins studied were the synapses established by axon terminals of basket neurons. Conclusion The present study supplies a detailed morphological description of VAMP-2, SNAP-25A/B and syntaxin-1 in the different types of glutamatergic and GABAergic synapses of the rat cerebellar cortex. The examined SNARE proteins characterize most of glutamatergic synapses and only one type of GABAergic synapses. In the subpopulations of glutamatergic and GABAergic synapses lacking the SNARE protein isoforms examined, alternative mechanisms for regulating trafficking of synaptic vesicles may be hypothesized, possibly mediated by different isoforms or homologous proteins.

We present a directly generated on-chip dual-comb source at terahertz (THz) frequencies. The multi-heterodyne beating signal of two free-running THz quantum cascade laser frequency combs is measured electrically using one of the combs as a detector, fully exploiting the unique characteristics of quantum cascade active regions. Up to 30 modes can be detected corresponding to a spectral bandwidth of 630 GHz, being the available bandwidth of the dual comb configuration. The multi-heterodyne signal is used to investigate the equidistance of the comb modes showing an accuracy of 10-12 at the carrier frequency of 2.5 THz. [ABSTRACT FROM AUTHOR]

This paper reports on the formation of nanoporous Ge in polycrystalline and amorphous Ge thin films, grown by molecular beam epitaxy and implanted with Ge+ ions at 300 keV with different fluences (3×1015–2×1016 Ge/cm2). Implanted polycrystals show a more regular columnar structure with respect to smaller and disconnected voids of amorphous grown films. These results strongly rely on the film properties and mechanism of void nucleation. Our findings represent a goal for the technology transfer of the ion-induced nanoporosity from bulk Ge to Ge thin films and meet the requirements for future applications. [ABSTRACT FROM AUTHOR]

We report a device that provides coherent emission of phonon polaritons, a mixed state between photons and optical phonons in an ionic crystal. An electrically pumped GaInAs/AlInAs quantum cascade structure provides intersubband gain into the polariton mode at λ = 26.3 μm, allowing self-oscillations close to the longitudinal optical phonon energy of AlAs. Because of the large computed phonon fraction of the polariton of 65%, the emission appears directly on a Raman spectrum measurement, exhibiting a Stokes and anti-Stokes component with the expected shift of 48 meV.