2,473 research outputs found
Photodetectors
In this book some recent advances in development of photodetectors and photodetection systems for specific applications are included. In the first section of the book nine different types of photodetectors and their characteristics are presented. Next, some theoretical aspects and simulations are discussed. The last eight chapters are devoted to the development of photodetection systems for imaging, particle size analysis, transfers of time, measurement of vibrations, magnetic field, polarization of light, and particle energy. The book is addressed to students, engineers, and researchers working in the field of photonics and advanced technologies
CMOS SINGLE-PHOTON AVALANCHE DIODES AND MICROMACHINED OPTICAL FILTERS FOR INTEGRATED FLUORESCENCE SENSING
This dissertation presents a body of work that addresses the two most pressing challenges in the field of integrated fluorescence sensing, namely, the design of integrated optical sensors and the fabrication of high-rejection micro-scale optical filters. Two novel enabling technologies were introduced. They are: the perimeter-gated single-photon avalanche diode (PGSPAD), for on-chip photon counting, and the benzotriazole (BTA)-doped thin-film polymer filter, for on-chip ultraviolet light rejection.
Experimental results revealed that the PGSPAD front-end, fabricated in a 0.5 μm standard mixed-signal CMOS process, had the capability of counting photons in the MHz regime. In addition, it was found that a perimeter gate, a structural feature used to suppress edge breakdown in the diode, also maximized the signal-to-noise-ratio in the high-count rate regime whereas it maximized sensitivity at low count rates.
On the other hand, BTA-doped filters were demonstrated utilizing three commonly used polymers as hosts. The filters were patternable, utilizing the same procedures traditionally used to pattern the undoped polymer hosts, a key advantage for integration into microsystems. Filter performance was analyzed using a set of metrics developed for optoelectronic characterization of integrated fluorescence sensors; high rejection levels (nearing -40 dB) of UV light were observed in films of only 5 μm in thickness. Ultimately, BTA-doped filters were integrated into a portable sensor, and their use was demonstrated in two types of bioassays
Multi-confocal Fluorescence Correlation Spectroscopy : experimental demonstration and potential applications for living cell measurements
We report, for the first time, a multi-confocal Fluorescence Correlation
Spectroscopy (mFCS) technique which allows parallel measurements at different
locations, by combining a Spatial Light Modulator (SLM), with an Electron
Multiplying-CCD camera (EM-CCD). The SLM is used to produce a series of laser
spots, while the pixels of the EM-CCD play the roles of virtual pinholes. The
phase map addressed to the SLM is calculated by using the spherical wave
approximation and makes it possible to produce several diffraction limited
laser spots, either aligned or spread over the field of view. To attain fast
enough imaging rates, the camera has been used in different acquisition modes,
the fastest of which leads to a time resolution of 100 s. We qualified the
experimental set-up by using solutions of sulforhodamine G in glycerol and
demonstrated that the observation volumes are similar to that of a standard
confocal set-up. To demonstrate that our mFCS method is suitable for
intracellular studies, experiments have been conducted on two stable cell
lines: mouse embryonic fibroblasts expressing eGFP-actin and H1299 cells
expressing the heat shock factor fusion protein HSF1-eGFP. In the first case we
could recover, by analyzing the auto-correlation curves, the diffusion constant
of G-actin within the cytoplasm, although we were also sensitive to the complex
network of interactions with F-actin. Concerning HSF1, we could clearly observe
the modifications of the number of molecules and of the HSF1 dynamics during
heat shock
Spatially controlled electrostatic doping in graphene p-i-n junction for hybrid silicon photodiode
Sufficiently large depletion region for photocarrier generation and
separation is a key factor for two-dimensional material optoelectronic devices,
but few device configurations has been explored for a deterministic control of
a space charge region area in graphene with convincing scalability. Here we
investigate a graphene-silicon p-i-n photodiode defined in a foundry processed
planar photonic crystal waveguide structure, achieving visible - near-infrared,
zero-bias and ultrafast photodetection. Graphene is electrically contacting to
the wide intrinsic region of silicon and extended to the p an n doped region,
functioning as the primary photocarrier conducting channel for electronic gain.
Graphene significantly improves the device speed through ultrafast out-of-plane
interfacial carrier transfer and the following in-plane built-in electric field
assisted carrier collection. More than 50 dB converted signal-to-noise ratio at
40 GHz has been demonstrated under zero bias voltage, with quantum efficiency
could be further amplified by hot carrier gain on graphene-i Si interface and
avalanche process on graphene-doped Si interface. With the device architecture
fully defined by nanomanufactured substrate, this study is the first
demonstration of post-fabrication-free two-dimensional material active silicon
photonic devices.Comment: NPJ 2D materials and applications (2018
Addressing the exciton fine structure in colloidal nanocrystals: the case of CdSe nanoplatelets
We study the band-edge exciton fine structure and in particular its
bright-dark splitting in colloidal semiconductor nanocrystals by four different
optical methods based on fluorescence line narrowing and time-resolved
measurements at various temperatures down to 2 K. We demonstrate that all these
methods provide consistent splitting values and discuss their advances and
limitations. Colloidal CdSe nanoplatelets with thicknesses of 3, 4 and 5
monolayers are chosen for experimental demonstrations. The bright-dark
splitting of excitons varies from 3.2 to 6.0 meV and is inversely proportional
to the nanoplatelet thickness. Good agreement between experimental and
theoretically calculated size dependence of the bright-dark exciton slitting is
achieved. The recombination rates of the bright and dark excitons and the
bright to dark relaxation rate are measured by time-resolved techniques
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