Enhancement of two photon processes in quantum dots embedded in subwavelength metallic gratings

We show a large enhancement of two-photon absorption processes in nanocrystal quantum dots and of light upconversion efficiency from the IR to the near-IR spectral regime, using a hybrid optical device in which near-IR emitting InAs quantum dots were embedded on top a metallic nanoslit array. The resonant enhancement of these nonlinear optical processes is due to the strong local electromagnetic field enhancements inside the nanoslit array structure at the extraordinary transmission resonances. A maximal two-photon absorption enhancement of more than 20 was inferred. Different high field regions were identified for different polarizations, which can be used for designing and optimizing efficient nonlinear processes in such hybrid structures. Combining nanocrystal quantum dots with subwavelength metallic nanostructures is therfore a promising way for a range of possible nonlinear optical devices.Comment: 14 pages, 7 figure

Development of a spatially dispersed short-coherence interferometry sensor using diffraction grating orders

Modern manufacturing processes can achieve good throughput by requiring that manufactured products be screened by better quality control exercised at a quicker rate. This trend in the quality control of manufactured products increases the need for process-oriented precision metrology capable of performing faster inspections and yielding valuable feedback to the manufacturing system. This paper presents a spatially dispersed short-coherence interferometry sensor using diffraction orders of the zeroth and first order for a diffraction grating introduced as a new compact system configuration for surface profile measurement. In this modified design, the diffraction grating acts as the beam splitter/combiner. Diffractions for the zeroth and first orders are represented by the reference and measurement arms, respectively, of a Michelson interferometer, which reduces the optical path length. This innovative design has been proven effective for determining the step-height repeatability in the sensor range from 27 nm to 22 nm for profiles spanning the step heights of the tested specimens

Optothermal nonlinearity of silica aerogel

The authors acknowledge support from EPSRC (EP/J004200/1), the Templeton Foundation (grant number 58277) and the ERC project VANGUARD (grant number 664782).We report on the characterization of silica aerogel thermal optical nonlinearity, obtained by z-scan technique. The results show that typical Silica Aerogels have nonlinear optical coefficient similar to that of glass (≃ 10-12m2/W), with negligible optical nonlinear absorption. The nonlinear coefficient can be increased to values in the range of 10-10m2/W by embedding an absorbing dye in the Aerogel. This value is one order of magnitude higher than that observed in the pure dye and in typical highly nonlinear materials like liquid crystals.PostprintPeer reviewe

Nonlinear optics and saturation behavior of quantum dot samples under continuous wave driving

The nonlinear optical response of self-assembled quantum dots is relevant to the application of quantum dot based devices in nonlinear optics, all-optical switching, slow light and self-organization. Theoretical investigations are based on numerical simulations of a spatially and spectrally resolved rate equation model, which takes into account the strong coupling of the quantum dots to the carrier reservoir created by the wetting layer states. The complex dielectric susceptibility of the ground state is obtained. The saturation is shown to follow a behavior in between the one for a dominantly homogeneously and inhomogeneously broadened medium. Approaches to extract the nonlinear refractive index change by fringe shifts in a cavity or self-lensing are discussed. Experimental work on saturation characteristic of InGa/GaAs quantum dots close to the telecommunication O-band (1.24-1.28 mm) and of InAlAs/GaAlAs quantum dots at 780 nm is described and the first demonstration of the cw saturation of absorption in room temperature quantum dot samples is discussed in detail

[Liber de natura falconum]

Edizione critica a stampa a cura di G. Tilander esportazione in formato TEI XML livello ALIM2_0 effettuata da Chiara Casali Edizione in formato TEI XML, livello ALIM2_1, a cura di Jan Ctibor HomePage del progetto: http://it.alim.unisi.it/il-progetto/ Documentazione: http://alim.unisi.it/documentazion

Sámi Identity across Generations: From Passing for Nordics to Sámi Self-Exposure

Following histories of racism and abuse at the hands of Norwegian and Swedish authorities, many Indigenous Sámi have chosen to disconnect from everything Sámi and instead pass for ethnic Norwegians and Swedes. As a result, their children and grandchildren have grown up with no or little knowledge of their Sámi heritage. In the 2000s, several of these children and grandchildren, who were born after the Second World War, are eager to reconnect with their Sámi identity. This article fleshes out the entangled road back to Sáminess through a close analysis of two Norwegian documentaries—Suddenly Sami (Min mors hemmelighet) (2009) and My Family Portrait (Familiebildet) (2013)—in which the women directors discover their Sámi identity in front of the camera. A central point in the discussion is how the directors use discourses of biology and genetics to recuperate their Sámi identity in the 2000s. The article raises several explanations as to why they retreat to these discourses byputting the two Norwegian documentaries in conversation with the Swedish feature film Sami Blood (Sameblod) (2016)

The virality of Norwegian guilt. How a story of male rape from Norway made international headlines

When a young Norwegian man talked openly about being raped by a Somali asylum seeker and for feeling guilty about the rapist’s deportation, the news went viral not only in Norway, but also abroad. Several British and American tabloid newspapers as well as news and opinion websites from the UK, the US, Russia, Poland, Croatia and the Czech Republic reported about the Norwegian “politician” who felt “guilty” that Norwegian authorities sent his rapist back to Somalia. This article closely investigates the mediation of this story with a focus on how the emotion of guilt was staged in a national televised and digital media context in Norway before it reached the international tabloid media and opinion websites like Breitbart.com. It demonstrates how guilt functions as an affective nodal point at the intersection of many dimensions of identity, such as gender, sexuality, race, able-bodiedness, national identity, and political affiliation. The article also shows how a story of male rape from Norway facilitated an opportunity for tabloid journalists to rally against the Norwegian, and by extension, the European political Left, which they constructed as weak, feminine, and raped from behind by the very immigrants it seeks to protect