We developed Hg 2+ -sensing chips by decorating the external surface of metal-clad optical waveguides with a monolayer of Hg 2+ -sensitive fluorescent molecular probes. The emission properties of the original water-soluble form of the molecule were previously found to be selectively quenched in the presence of Hg 2+ ions. The fabricated samples were tested with optical waveguide fluorescence spectroscopy by putting them in contact with a 5-μM water solution of Hg 2+ ions and recording the emission spectra versus incubation time. The estimate of the limit of detection was 150 nM. A preliminary evaluation of the selectivity of the structure was also performed by using Cd 2+ as possible interfering analytes.
KEYWORDS: Near field scanning optical microscopy, Atomic force microscopy, Near field optics, Optical microscopy, Imaging systems, Photodiodes, Atomic force microscope, Liquids, Transmittance, Optical fibers
Fiber-top and ferrule-top cantilevers (FTC) are a new generation of all optical, monolithic, self-aligned microdevices.
They are obtained by carving a cantilever on the cleaved end of an optical fiber (fiber-top) or on a ferrule terminated
fiber (ferrule-top). FTCs rely on Fabry-Perot interferometry to measure the deflection of the cantilever with
subnanometer deflection sensitivity. FTCs specially developed for scanning probe microscopy are equipped with a sharp
tip that has the dual function of probing the topography and collecting/emitting light. We perform the scanning probe
microscopy using these probes in air, liquid and at low temperature (12°K). The light emission/collection functionality of
FTC probes also allows one to combine scanning near field optical microscopy (SNOM) and optical transmission
microscopy with contact and non-contact mode atomic force microscopy (AFM). This makes FTCs ideal for
AFM+SNOM on soft samples, polymers and biological specimen, where bent fiber probes and tuning fork based
systems would not be recommended because of the high stiffness of those probes. We demonstrate here the capability of
fiber-top cantilevers to measure deflection and collect near field optical signal, and also the capability of ferrule-top
cantilevers for simultaneous optical transmission microscopy and topography of SNOM gratings. Thanks to their unique
features, FTCs also open up possibilities for UV nanolithography and on-demand optical excitation at nanoscale.
Spectroscopic investigation of metallic nanostructures of different size and morphology is presented, with particular
focus on the capability of enhancing the Raman response of molecular adsorbates, namely on their SERS properties. In
this framework, we describe recent results obtained with Au/Ag nanocages and Au nanostars, which can be used
conveniently to shift the extinction spectra and the SERS activity up to the near infrared. In the case of nanostars, we
present a synthesis procedure which permits fine tuning of their morphology and extinction, thus allowing preparation of
structures with controlled SERS activity from 500 up to 1500 nm.
A temperature sensor immune to electromagnetic noise is designed and fabricated. The sensor key element is a periodically poled lithium niobate (PPLN) substrate. PPLN allows a direct and efficient frequency conversion of lightwave through the quasi-phase matching (QPM) of the pump radiation propagating at the fundamental and second harmonic wavelengths. For these devices, the efficiency of second harmonic generation (SHG) depends on the QPM condition, and it strongly changes with respect to the wavelength and the temperature. The effect of temperature variation on the SHG in periodically poled lithium niobate annealed proton exchange (APE) channel waveguides (WG) is theoretically modeled via a home-made computer code and experimentally validated via a suitable measurement set-up. A lot of simulations have been performed to test the temperature sensor feasibility and to identify its optimal configuration. Another sensor configuration made by two waveguides with suitable gratings of inverted ferroelectric domains is designed and refined, too. For an optimised PPLN-WG device, which could be fabricated through electric field poling and annealed proton exchange or titanium diffusion, a sensitivity S≡0.03μW/°C for the temperature range equal to 100 °C is demonstrated by using an input power at a fundamental wavelength equal to 40 mW. Similar evaluations and measurements, performed on bulk substrates, allowed us to design a layout of a sensor particularly suited for rugged in-field applications.
In this paper we measure the efficiency of photon pair production from parametric downconversion at the photon counting level, generated in a laboratory prototype of PPLN waveguide at 1572 nm. The aim is to enhance the brightness of an heralded single photon source and to improve compactness for quantum communication applications, namely quantum key distribution. We observed a maximum of the conversion efficiency corresponding to 7.9 106 photon pairs/s for a pump power of 28 μW. This value is compared with the measured pairs production in a classical experiment of difference frequency generation, realized with the same sample by analogue classical detection. We highlight the advantages of using the waveguide versus a bulk PPLN for such applications and we foresee further possible improvements by adopting waveguide in a single photon level experimental setup.
In this work we report on a novel angular and positional sensor based on the phenomenon of attenuated total reflection that occurs at a metal-dielectric interface when the conditions for the excitation of a surface plasma wave in Kretschmann configuration are satisfied. The reflectivity of the metallic surface exhibits a very sharp dip at an angle of incidence corresponding to the phase-matching condition for the coupling of energy from the incident beam to the resonant surface mode. The typical width of the resonance is a few mrad, thus making feasible the direct measurement of small angular movements by just detecting the intensity of the reflected light. By means of a simple optical setup this sensitivity can be exploited to build a position-sensitive detector capable of nanometric resolution. Tests have been carried out on several Ag depositions. The angular resolution obtained has been in the 0.2 to 0.4 arcsecs range; the sensitivity to linear displacements has been tested monitoring the motion of piezoelectric actuators and is better than 5 nm over a range of a few microns. We have verified that the proposed method does not require beams of high optical quality and permits in principle a considerable simplification over interferometric systems. Well-established technological processes might be used for its implementation, keeping its cost at a competitive level with respect to other devices of the same potential sensitivity.
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