Photo‐thermo‐refractive glass containing nanosized NaF crystals embedded in the glassy matrix shows a significant shift of X‐ray diffraction (XRD) lines to lower angles resulting from large residual ...(tensile) stresses within the crystals. This is thus an excellent “model” system to test residual stresses models in glass–ceramics and composites because: the estimated stresses are high—about 1 GPa—the precipitates are nearly spherical, the NaF crystals structure is cubic and their volume fraction is quite small, which eliminates overlap between the stress fields of neighbor crystals. Samples treated at a sufficiently high temperature to develop larger (micrometer size) crystals revealed microcracking of the glassy matrix around the crystals, which partially relieved the residual stresses and decreased the shift of the XRD peaks. The experimental results for the magnitude of the residual stresses and the critical crystal diameter for microcracking agree with theoretical values calculated by the Selsing and the Davidge & Green models, respectively. These results suggest that these two models can be used for stress estimates and as a first approach for the design of tough glass–ceramics.
In this paper we study the wavelength selection process for optical monitoring of thin film filters. We first discuss the technical limitations of monitoring systems as well as the criteria defining ...the sensitivity of different wavelengths to thickness errors. We then present an approach that considers the best monitoring wavelength for each individual layer with a monitoring strategy selection process that can be fully automated. We finally validate experimentally the proposed approach on several optical filters of increasing complexity. Optical interference filters with close to theoretical performances are demonstrated.
Sb2Te3 is a well-known thermoelectric material and a topological insulator and its utilization is foreseen for many applications, such as quantum computing, mode-locking of laser systems, and cooling ...systems. Various methods have been used to grow thin Sb2Te3 films on different substrates, such as molecular beam epitaxy or electrodeposition. Often, such methods require performing laborious and rigid steps in order to optimize film growth and reduce the amount of defects. For this reason, we investigate a simplified growth method: thermal deposition starting from Sb2Te3 lumps followed by annealing. By means of various surface science techniques (LEED, STM, XPS), we show that it is possible to obtain a single crystalline Sb2Te3 film on a Ge(111) substrate. The film, which is amorphous after deposition, undergoes a phase transition and becomes crystalline after annealing at 573 K. This is clearly shown by a 1x1 surface termination typical of a (0001) surface with hexagonal lattices. The presence of several quintuple-layer steps was observed by scanning tunneling microscopy. Photoelectron spectroscopy characterization confirms that the grown chalcogenide film presents the expected stoichiometry (Te/Sb=1.5). The proposed method simplifies the growth phase and seems to reduce the number of defects induced by the growth technique, major advantages for many applications.
In this paper, we investigate the design and the fabrication of an advanced optical interference filter based on metal and dielectric layers. This filter respects the specifications of the 2016 OIC ...manufacturing problem contest. We study and present all the challenges and solutions that allowed achieving a low deviation between the fabricated prototype and the target.
Single-molecule Förster resonance energy transfer (smFRET) is widely used to monitor conformations and interaction dynamics at the molecular level. However, conventional smFRET measurements are ...ineffective at donor-acceptor distances exceeding 10 nm, impeding the studies on biomolecules of larger size. Here, we show that zero-mode waveguide (ZMW) apertures can be used to overcome the 10 nm barrier in smFRET. Using an optimized ZMW structure, we demonstrate smFRET between standard commercial fluorophores up to 13.6 nm distance with a significantly improved FRET efficiency. To further break into the classical FRET range limit, ZMWs are combined with molecular constructs featuring multiple acceptor dyes to achieve high FRET efficiencies together with high fluorescence count rates. As we discuss general guidelines for quantitative smFRET measurements inside ZMWs, the technique can be readily applied for monitoring conformations and interactions on large molecular complexes with enhanced brightness.
Topological insulators, such as the Bi
2
Se
3
material, exhibit significant optical nonlinearities. This work investigates the impact of the pulse duration on the nonlinear optical responses of Bi
2
...Se
3
layers. Scanning electron microscopy studies have been performed to reveal the crystalline structure of the samples. The nonlinear optical performance has been investigated for a wide range of pulse durations, from 400 fs to 10 ps, using 1030 nm laser excitation. The nonlinear absorption coefficients recorded in this study range from -1.45 x10
−7
m/W to -4.86 x10
−7
m/W. The influence of two different mechanisms on optical nonlinearities was observed and discussed. Identical experimental conditions have been employed throughout the studies allowing a direct comparison of the results.
Plasmonic antennas have a profound impact on nanophotonics as they provide efficient means to manipulate light and enhance light–matter interactions at the nanoscale. However, the large absorption ...losses found in metals can severely limit the plasmonic applications in the visible spectral range. Here, we demonstrate the effectiveness of an alternative approach using all-dielectric nanoantennas based on silicon dimers to enhance the fluorescence detection of single molecules. The silicon antenna design is optimized to confine the near-field intensity in the 20 nm nanogap and reach a 270-fold fluorescence enhancement in a nanoscale volume of λ3/1800 with dielectric materials only. Our conclusions are assessed by combining polarization resolved optical spectroscopy of individual antennas, scanning electron microscopy, numerical simulations, fluorescence lifetime measurements, fluorescence burst analysis, and fluorescence correlation spectroscopy. This work demonstrates that all-silicon nanoantennas are a valid alternative to plasmonic devices for enhanced single molecule fluorescence sensing, with the additional key advantages of reduced nonradiative quenching, negligible heat generation, cost-efficiency, and complementary metal–oxide–semiconductor (CMOS) compatibility.
Optical detection of ultrasound for photoacoustic imaging provides a large bandwidth and high sensitivity at high acoustic frequencies. Therefore, higher spatial resolutions can be achieved using ...Fabry-Pérot cavity sensors than conventional piezoelectric detection. However, fabrication constraints during the deposition of the sensing polymer layer require precise control of the interrogation beam wavelength to provide optimal sensitivity. This is commonly achieved by employing slowly tunable narrowband lasers as interrogation sources, hence limiting the acquisition speed. We propose instead to use a broadband source and a fast-tunable acousto-optic filter to adjust the interrogation wavelength at each pixel within a few microseconds. We demonstrate the validity of this approach by performing photoacoustic imaging with a highly inhomogeneous Fabry-Pérot sensor.
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