We present an optical system which integrates a plasmonic sensing surface and an angular tracking system to enable a compact refractive index measurement. A refractive index change at the surface of the sensing membrane causes a change in the angle at which monochromatic light is transmitted through the membrane. This transmission angle is measured by the angular tracking system. We show good theoretical and experimental agreement of the transmission of the plasmonic sensing surface at different angular illumination of the membranes. Using this compact optical setup the embedded angular tracking system has an accuracy of <10-4 deg. This corresponds to a sensitivity <10-5 refractive index units. Finally we demonstrate this measurement technique using different concentrations of saline solution.

La presente invention concerne un capteur (1) de detection de gaz, en particulier de detection de CO2, qui comprend une face contact (2) qui peut etre dirigee vers un site de mesure. Le capteur comprend (1) au moins une source de rayonnement (3), un volume de mesure (4) pour recevoir le gaz a mesurer et au moins un premier detecteur (5) pour la detection d'un rayonnement transmis par la source (3) au premier detecteur (5) par le volume de mesure (4). Le capteur comprend une trajectoire (6) du rayonnement entre la source de rayonnement (3) et le premier detecteur (5), dans lequel la rayonnement se propage le long de la trajectoire sans imagerie.

Enhanced transmissions at infra-red wavelengths are measured through hole arrays made in gold-covered silicon nitride free-standing membranes. The membranes are made by a standard photolithography batch process. They are cheap to fabricate, reproducible and robust. The optical transmission of the membranes are investigated with varying hole size (down to 1 mu m), period, and thickness. The membranes show enhanced optical transmission. The spectra show good agreement with a very simple mode matching model which can be used for design. Calculations are also shown giving absorption enhancements of 5.7 normalized to the same material on a silicon membrane. Finite difference time domain calculations are also presented to show the spatial distribution of the enhanced field. Field enhancements of 3.3 are calculated. The field enhancements are concentrated in the hole which makes the membranes ideally suited for a microfluidic setup. Hence, this paper shows that through enhanced transmission cheap, disposable membranes in a simplified transmission can be used for measurements for molecular absorption.

Gold membranes with large arrays of sub-μm holes were fabricated and optically characterized. The fabrication is a combination of a bottom-up, self-assembly based patterning technique, Nanosphere Lithography (NSL), and standard microfabrication. This was achieved by 1) up-scaling of the deposition of close-packed bead monolayers to 4" wafer substrates, 2) controlled bead size reduction, 3) etching of high aspect-ratio Si pillar arrays, 4) using the pillar arrays as a lift-off template, and 5) releasing the membranes by dry-etching. In this way, millimeter-size, 200 nm thick gold membranes with dense, short-range ordered hole arrays were fabricated. The array periodicity was either 428 nm or 535 nm, depending on the initial bead size. The hole diameter was tuned in the range of 150 nm to 250 nm. Optical transmission spectroscopy showed surface plasmon mediated extraordinary optical transmission (EOT) with an enhancement factor greater than two.

Enhanced optical transmission (EOT) through a single aperture is usually achieved by exciting surface plasmon polaritons with periodic grooves. Surface plasmon polaritons are only excited by p-polarized incident light, i.e. with the electric field perpendicular to the direction of the grooves. The present study experimentally investigates EOT for s-polarized light. A subwavelength slit surrounded on each side by periodic grooves has been fabricated in a gold film and covered by a thin dielectric layer. The excitation of s-polarized dielectric waveguide modes inside the dielectric film strongly increases the s-polarized transmission. A 25 fold increase is measured as compared to the case without the dielectric film. Transmission measurements are compared with a coupled mode method and show good qualitative agreement. Adding a waveguide can improve light transmission through subwavelength apertures, as both s and p-polarization can be efficiently transmitted.

Enhanced optical transmission (EOT) through subwavelength apertures is usually obtained for p-polarized light. The present study experimentally investigates EOT for s-polarized light. A subwavelength slit surrounded on each side by periodic grooves has been fabricated in a gold film and covered by a thin dielectric layer. The excitation of s-polarized dielectric waveguide modes inside the dielectric film strongly increases the s-polarized transmission. Transmission measurements are compared with a coupled mode model and show good qualitative agreement. Adding a waveguide can improve light transmission through subwavelength apertures, as both s and p-polarization can be efficiently transmitted.

The miniaturization of photodetectors often comes at the expense of a smaller photosensitive area. This can reduce the signal and thus limit the image quality. One way to overcome this limitation is to reduce the photosensitive area but with no reduction of signal i.e. harvest the light. Here we investigate, theoretically and experimentally, light harvesting with nanostructured metals. Nanostructured metals can also give additional functionality such as polarization filtering which is also investigated. After defining the figure of merits used when characterizing light harvesting and polarization filtering structures, we detail the fabrication and measurement process. Structures were made on glass substrate, as a post process step on CMOS fabricated detectors and directly in the CMOS fabrication of the detectors. The optical characterization results are presented and compared with theory. Finally, we discuss the challenges and advantages of integrating metallic nanostructures within the CMOS process.

In this paper, we present the design, fabrication, and characterization of wire grid polarizers. These polarizers show high extinction ratios and high transmission with structure dimensions that are compatible with current complementary metal-oxide-semiconductor (CMOS) technology. To design these wire grids, we first analyze the transmission properties of single apertures. From the understanding of a single aperture, we apply a modal expansion method to model wire grids. The most promising grids are fabricated on both a glass substrate and CMOS photodiode. An extinction ratio higher than 200 is measured.

An enhanced transmission is detected through a single slit of subwavelength width surrounded by grooves in a gold layer that is added as a postprocess to a standard complementary metal oxide semiconductor (CMOS) fabricated detector. The enhanced transmission results from constructive interference of surface waves, which interact with the incident light. The measured enhanced transmission shows strong qualitative agreement with that predicted by the modal expansion method. With the decreasing dimensions available in standard CMOS process, such nanostructures in metals could be used to replace current optical systems or to improve performance by increasing the signal to noise ratio and/or allowing polarization selection.

β+-sensitive probes are useful tools for the measurement of radiotracer kinetics in small animals. They allow the cost-effective development of new PET tracers and offer the possibility to investigate a variety of cerebral processes. The study's main aim was the in vivo evaluation of a probe system for cerebral surface acquisitions. The detector system is a 0.2-mm thick scintillating disk of 3-mm diameter, positioned close to the cerebral surface. The study consists of 4 subparts: (1) simulation of the detection volume, (2) direct comparison with the classic intracortical beta probe regarding its capability to acquire kinetic data, (3) test of the ability to detect local tracer accumulations during infraorbital nerve (ION) electrostimulation and (4) demonstration of the feasibility to measure tracer kinetics in awake animals. Kinetic data acquired with 18F-fluorodeoxyglucose and 15O-H2O were fitted with standard compartment models. The surface probe measurements were in good agreement with those obtained using the intracortical scintillator. ION electrostimulation induced a marked increase in tracer accumulation adequately detected by the surface probe. In the head-fixed animal, a marked change in FDG kinetics was detected between the awake and anesthetized state. The novel surface probe system proved to be a valuable instrument for in vivo radiotracer studies of the cerebral cortex. Its main advantage is the absence of any tissue damage. In addition, serial acquisitions of tracer kinetics in the awake animal turned out to be feasible.

Scanning near-field optical microscopy offers optical imaging with a resolution below the diffraction limit of W. An introduction into the concept is given and its implementation into a real instrument illustrated. The most crucial part of the instrumentation is the optical near-field probe. Our efforts concerning near-field imaging with microfabricated cantilevered probe sare reviewed. The probes are silicon beams with solid quartz tip, which is completely covered with a 60-nm thick layer of aluminum. The demonstrated contrast mechanisms comprise transmission and fluorescence. In the latter case an artifact free 'true' optical resolution of 32 nm is shown. The influence of the polarization on the optical resolution is discussed. Best performance is achieved, when directly transmitted linear polarized is blocked and only components of radial polarized light, which originates from a supported eigenmode of the probe, is detected.

We present an extremely versatile method for the lateral organization of nano-scale objects (NOs) based on the phenomenon of polymer demixing. NOs are suspended in a solution of two immiscible polymers, which is used to form a thin polymer film by spin coating. During spin coating the two polymers separate to give a microphase structure, whose length scale depends on the experimental conditions. The NOs spontaneously partition into one or other of the polymer phases resulting in their lateral organization. In this work, the organization of CdSe nanoparticles and fluorescent organic dyes was studied by fluorescence microscopy. The NOs were organized in the polymer film in stochastic patterns or in ordered designs on substrates pre-patterned by soft-lithography techniques. Single-particle measurements, using confocal microscopy, showed that at low concentrations there was little aggregation of the particles.

The fabrication of silicon cantilever-based scanning near-field optical microscope probes with fully aluminium-coated quartz tips was optimized to increase production yield. Different cantilever designs for dynamic- and contact-mode force feedback were implemented. Light transmission through the tips was investigated experimentally in terms of the metal coating and the tip cone-angle. We found that transmittance varies with the skin depth of the metal coating and is inverse to the cone angle, meaning that slender tips showed higher transmission. Near-field optical images of individual fluorescing molecules showed a resolution < 100 nm. Scanning electron microscopy images of tips before and after scanning near-field optical microscope imaging, and transmission electron microscopy analysis of tips before and after illumination, together with measurements performed with a miniaturized thermocouple showed no evidence of mechanical defect or orifice formation by thermal effects.

A cantilever-based probe is introduced for use in scanning near-field optical microscopy (SNOM) combined with scanning atomic-force microscopy (AFM). The probes consist of silicon cantilevers with integrated 25-mum-high fused-silica tips. The probes are batch fabricated by microfabrication technology. Transmission electron microscopy reveals that the transparent quartz tips are completely covered with an opaque aluminum layer before the SNOM measurement. Static and dynamic AFM imaging was performed. SNOM imaging in transmission mode of single fluorescent molecules shows an optical resolution better than 32 nm.

We demonstrate high resolution imaging with microfabricated, cantilevered probes, consisting of solid quartz tips on silicon levers. The tips are covered by a 60-nm thick layer of aluminium, which appears to be closed at the apex when investigated by transmission electron microscopy. An instrument specifically built for cantilever probes was used to record images of latex bead projection patterns in transmission as well as single molecule fluorescence. All images were recorded in constant height mode and show optical resolutions down to 32 nm.

Microfabrication of probes for near-field optical microscopy is a promising approach to improve probe quality, reproducibility, and availability/cost. We report on cantilevered probes with integrated quartz tips allowing near-field optical imaging of single fluorophores with 32 nm lateral resolution.

We have built a multi-purpose optical microscope by integrating a conventional confocal laser microscope (CLM) and a state of the art scanning near-field optical microscope (SNOM) with a conventional inverted optical microscope. The setup is designed for fluorescence imaging of delicate samples at very low signal levels as found in applications in the Life Sciences. An active-feedback closed-loop x-y-scanner with a scan range of 100 × 100μm enables the instrument to rapidly record large area scans using confocal microscopy. Interesting areas of the samples identified by such a scan can subsequently be investigated with sub-diffraction limited resolution. The near-field part of the instrument is based on standard optical fibre probes and a non-optical, tuning fork shear-force technique for maintaining the probe-sample distance. An extremely sensitive feedback working on the phase rather than the amplitude of the tuning fork response is used in order not to damage delicate biological samples. First results on μ-contact printed rabbit IgG and single molecule fluorescence are reported.

High-resolution near-field optical imaging with microfabricated probes is demonstrated. The probes are made from solid quartz tips fabricated at the end of silicon cantilevers and covered with a 60-nm-thick aluminum film. Transmission electron micrographs indicate a continuous aluminum layer at the tip apex. A specially designed instrument combines the advantages of near-field optical and beam-deflection force microscopy. Near-field optical data of latex bead projection patterns in transmission and of single fluorophores have been obtained in constant-height imaging mode. An artifact-free optical resolution of 31.7±3.6 nm has been deduced from full width at half maximum values of single molecule images.

We present an experimental study of near-field optical interactions between an optical probe and sample objects with different dielectric properties. The interaction strongly affects the radiation emitted at angles beyond the critical angle of total internal reflection in the substrate (the forbidden light regime). Such an effect has been predicted theoretically. Our experimental data show that if a conducting object is close to the optical probe, p-polarized optical fields are deflected away from the object. On the other hand, s-polarized fields are deflected toward dielectric objects. The experimental results show good qualitative agreement with numerical simulations. The described effects have a strong influence on image formation in scanning near-field optical microscopy and thus have to be taken into account for image analysis.