Metal-Enhanced Near-Infrared Fluorescence by Micropatterned Gold Nanocages.

In metal-enhanced fluorescence (MEF), the localized surface plasmon resonances of metallic nanostructures amplify the absorption of excitation light and assist in radiating the consequent fluorescence of nearby molecules to the far-field. This effect is at the base of various technologies that have strong impact on fields such as optics, medical diagnostics, and biotechnology. Among possible emission bands, those in the near-infrared (NIR) are particularly intriguing and widely used in proteomics and genomics due to its noninvasive character for biomolecules, living cells, and tissues, which greatly motivates the development of effective and, eventually, multifunctional NIR-MEF platforms. Here, we demonstrate NIR-MEF substrates based on Au nanocages micropatterned with a tight spatial control. The dependence of the fluorescence enhancement on the distance between the nanocage and the radiating dipoles is investigated experimentally and modeled by taking into account the local electric field enhancement and the modified radiation and absorption rates of the emitting molecules. At a distance around 80 nm, a maximum enhancement up to 2-7 times with respect to the emission from pristine dyes (in the region 660-740 nm) is estimated for films and electrospun nanofibers. Due to their chemical stability, finely tunable plasmon resonances, and large light absorption cross sections, Au nanocages are ideal NIR-MEF agents. When these properties are integrated with the hollow interior and controllable surface porosity, it is feasible to develop a nanoscale system for targeted drug delivery with the diagnostic information encoded in the fluorophore.

Physically transient photonics: random versus distributed feedback lasing based on nanoimprinted DNA.

Room-temperature nanoimprinted, DNA-based distributed feedback (DFB) laser operation at 605 nm is reported. The laser is made of a pure DNA host matrix doped with gain dyes. At high excitation densities, the emission of the untextured dye-doped DNA films is characterized by a broad emission peak with an overall line width of 12 nm and superimposed narrow peaks, characteristic of random lasing. Moreover, direct patterning of the DNA films is demonstrated with a resolution down to 100 nm, enabling the realization of both surface-emitting and edge-emitting DFB lasers with a typical line width of <0.3 nm. The resulting emission is polarized, with a ratio between the TE- and TM-polarized intensities exceeding 30. In addition, the nanopatterned devices dissolve in water within less than 2 min. These results demonstrate the possibility of realizing various physically transient nanophotonics and laser architectures, including random lasing and nanoimprinted devices, based on natural biopolymers.

Distributed feedback imprinted electrospun fiber lasers.

Imprinted, distributed feedback lasers are demonstrated on individual, active electrospun polymer nanofibers. In addition to advantages related to miniaturization, optical confinement and grating nanopatterning lead to a significant threshold reduction compared to conventional thin-film lasers. The possibility of imprinting arbitrary photonic crystal geometries on electrospun lasing nanofibers opens new opportunities for realizing optical circuits and chips.

Longitudinal coherence of organic-based microcavity lasers.

We report on the measurement of the longitudinal coherence of organic microcavity lasers based on a conjugated polymer. By using a modified Michelson interferometer configuration enabling single-shot measurements of the coherence length, the transition from spontaneous emission to lasing is investigated. The measured coherence length grows upon increasing the pumping fluence, saturating around 45 microm above threshold. At large fluences, possible thermal and photo-oxidation processes occurring in the gain medium limit the further increase of the coherence length. Our results are important for understanding lasing emission in organic microcavities and optimizing the device design and performances.

Very high-quality distributed Bragg reflectors for organic lasing applications by reactive electron-beam deposition.

We report on the realisation of a few pairs dielectric Distributed Bragg Reflectors fabricated by reactive electron-beam deposition, with state-of-the-art performances, such as very high reflectance (up to about 99.4%), wide stop band (up to 160 nm) in the visible range, and smooth interfaces (roughness as low as 1.5 nm). As a demonstrator of the very high quality of the mirrors we realized a polymer-based vertical microcavity laser by an imprinting-like approach. The device exhibits laser action at 519 nm, indicating low-loss dielectric reflectors grown by electron-beam techniques as promising tools for organic solid-state lasers.