With the escalating demands for optical communication network system, the need for broadband gain medium in optical communication has increased. Among them, Cr4+:YAG crystal has shown an exceptionally successful broadband amplified spontaneous emission (ASE) light source that fully cover 1.2-1.6 £gm range (3-dB bandwidth up to 265 nm). More recently, we demonstrated the realization of a waveguiding, low-loss, and low-threshold Cr4+:YAG double-clad crystal fiber (DCF) based ultra-broadband ASE light source, optical amplifier, and laser grown by the co-drawing laser-heated pedestal growth technique. These results demonstrate the potential of the Cr4+:YAG DCF for the replacement of the erbium doped fiber in future optical communications. To further improve the efficiency of Cr4+:YAG DCF based active devices, here we show the difference in thermal expansion coefficients between a YAG core and an inner cladding creates a significant localized strain field by near-field scanning optical microscope (NSOM), which can result in optical confinement and provide the possibility to simultaneously alter the Cr3+ and Cr4+ fluorescence lifetime with varied core dimensions. The results indicate that There exists a nearly zero strain across the entire core with a diameter of ~20 £gm, which is beneficial the higher Cr4+ fluorescence lifetime (+6.43%) and emission cross section (+19.17%) as compared with 11-£gm core. In addition, we have successfully investigated the near-field modal characteristics of Cr4+:YAG DCF laser and ASE by NSOM. The results demonstrate that the Cr4+:YAG DCF laser produced nearly a single-mode (LP01) output with diffraction-limited beam quality of M2 ~1.1; for ASE, the modal weighting of LP01 decreases from 26% to 15% as the number of modes increases from 4 to 7. The results offer a guideline not only for further fabricating Cr4+:YAG DCF tunable lasers, but for efficiently coupling a broadband ASE light source into a single-mode fiber.

In recent years, the demand of the optical fiber communication bandwidth is increasing. Therefore, how to develop gain materials has become an important issue. The composition of a chromium-doped glass CaO-GeO2-Li2O-B2O3-Al2O3 is known to have good optical properties, the Cr-doped glass¡¦s radiation wavelength 1.2-1.5£gm covering entire communication band. The characteristics of a chromium-doped glass have potential to develop width band light source, optical amplifier and tunable wavelength laser. Our laboratory has successfully developed chromium-doped glass with infrared radiation characteristics. In order to improve it¡¦s optical properties. For example, increasing fluorescence intensity and less transmission loss. We shape the chromium-doped glass samples produced to high resolution transmission electron microscope sample, scanning its fluorescence intensity and Raman shift, two-dimensional graphics, comparing the difference between quench and heat treatment glass sample. The nanocrystal with infrared radiation characteristics appear when the heat treatment Raise up to appropriate temperature. To prove the nanocrystal distribution more uniform, higher fluorescence intensity, and smaller size of the nanocrystal to decreasing the transmission loss . We use different composition, or different nucleating agents and different heat treatment ways to analyze its transmission characteristics and internal structural changes. Near-field scanning optical microscope (SNOM) and high-resolution electron microscopy play a very important role in nano research. We also adjust the polarization film Polarizer use to reach the high resolution about 100nm. With this thesis we can analysis whether Cr3+ ion and Cr4+ ion exist in the same phase of nanocrystal and mapping high resolution fluorescence distribution picture to know how the nanocrystal appear by heat treatment, distinguish different nanocrystal by Ramen shift.

This thesis discusses the design and construction of a Near-field Scanning Optical Microscope (NSOM). Basic principles of operation, the characteristics of the hardware components, and the control software are discussed. A unique method of controlling the position of the probe is developed, and scans of a diffraction grating are presented. We show the influence that the surface topology and reflectivity and the interference of direct and reflected light have on the images. A second design of the instrument, for use in a vacuum chamber and with a flexure stage for lateral motion, is accomplished. / text

We have designed and constructed a novel Raman near-field scanning optical microscope (NSOM) and evaluated its performance characteristics with the goal of characterizing the strain in nanoscopic silicon structures. The Raman NSOM was built around a commercial Raman microscope to which a custom built stage was added to provide precise control over the tip position above the sample (z) using shear-force microscopy feedback as well as sample scanning in the x-y plane. The motion control axes were calibrated to better than 1 nm in z and approximately 20 nm in x and y. The NSOM provides both topographical images and Raman mapping with a lateral spectral resolution of 150-300 nm. The experiments described herein were enabled by gold-coated chemically etched NSOM tips with aperture diameters ranging between 60 and 150 nm. The sensitivity of the instrument was demonstrated by the high signal-to-noise ratios observed for Raman scattering by diamond and silicon in reflection mode. Spatial resolution and spectral sensitivity were demonstrated by obtaining well-resolved tip-sample separation curves that provide an accurate estimate of tip aperture size during an experiment. / text

La sonde couramment utilisée en microscopie NSOM consiste en une ouverture sub-longueur d'onde au bout d'une pointe diélectrique métallisée, ce qui permet d'atteindre une résolution optique de l'ordre de la taille de l'ouverture (soit 50 nm). Un concept prometteur consiste à remplacer l'ouverture par un matériau actif de taille sub-longueur d'ondes aussi petit qu'une seule molécule ou une nanoparticule semiconductrice. Dans ce schéma, la sonde active offre la possibilité d'obtenir une très haute résolution définie par la taille du nano-objet actif. Nous avons développé une méthode pour réaliser des pointes optiques actives pour l'optique en champ proche avec l'objectif de faire une nanosource de lumière stable utilisable à température ambiante et potentiellement capable d'offrir une résolution optique d'une dizaine de nanomètres. Une pointe optique métallisée est recouverte d'une fine couche de PMMA dans laquelle sont inclus des nanocristaux ou des nanorods de CdSe en faible densité. Pour ce faire, des pointes optiques spécifiques ont été préparées par attaque chimique suivie d'une métallisation. Elles ont en bout de pointe, une ouverture optique de l'ordre de 200 nm. L'évolution temporelle de la signature spectrale de ces sondes actives, couplée à l'analyse temporelle de leur émission dans un mode comptage de photons démontrent clairement qu'un très petit nombre de nanoparticules -voire une seule- sont actives en bout de pointe pour des taux de dilution de CdSe convenables. L'imagerie de surfaces test utilisant ces sondes actives sont actuellement en cours de réalisation.

This research project entails analyses of both alcoholic route C8S3 J-aggregate bundles and the interactions of a polyethylene glycol additive with alcoholic route C8S3 J-aggregates. First, the C8S3 J-aggregate bundles are characterized by both polarized and non-polarized spectroscopy methods. Orientation of the tubular bundled molecular complex was achieved, depending on the experiment, through a combination of flow cell experiments and cover slip deposited sample analysis. Next, isolated alcoholic route C8S3 J-aggregates were investigated using a polyethylene glycol (PEG) additive which has been shown, through absorbance and fluorescence emission spectroscopy, to selectively and reversibly remove the outer wall of the J-aggregate tubule. Spectroscopic analyses have indicated that the addition of a PEG additive left behind an in-tact inner wall tubule without the use of oxidizing agents, a feat never before accomplished with the C8S3 monomer. / text

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Thin-film inorganic solar cells, such as CdTe, have demonstrated the most promise to date for a viable low-cost renewable energy resource. Their current performance, however, is far from the theoretical limit suffering from significant charge recombination losses due to grain boundaries and point defects. It is likely that the microscopic compositions of grain bulk and grain boundaries are significantly different and not optimal for the overall device performance. Good understanding of charge transport along and across the grain boundaries and other microscopic interfaces is lacking, preventing the development of reliable and predictive device models. The insufficient microscopic understanding hinders efficient characterization of photovoltaic materials and also holds back the development of process control techniques. We first show preliminary results for a novel technique, quantum-dot electron-beam induced current to characterize semiconductors in the near-field. We also propose the use of near-field optical scanning microscopy for high precision optical excitation and for local, high-resolution characterization. These imaging techniques are examined with the goal of synthesizing information obtained by both methods, of material phenomena at the relevant length scales, to other measurement methods. The most important nanoscale phenomena being the separation of compositional and electrical effects.

Controlled patterning of light emitting diodes on semiconductors enables a vast variety of applications such as structured illumination, large-area flexible displays, integrated optoelectronic systems and micro-total analysis systems for real time biomedical screening. We have demonstrated a series of techniques of creating quantum-based (QD) patterned inorganic light emitting devices at room temperature on silicon (Si) substrate. In particular: (I) A combination of QDs self-assembly and microcontact printing techniques were developed to form the light emission monolayer. We expand the self-assembly method with the traditional Langmuir-Schaeffer technique to rapidly deposit monolayers of core: shell quantum dots on flat substrates. A uniform film of QDs self-assembled on water was transferred using hydrophobic polydimethylsiloxane stamps with various nano/micro-scale patterns, and was subsequently stamped. A metal oxide electron transport layer was co-sputtered onto the QDs. The structure was completed by an e-beam evaporating thin metal cathode. Multicolor light emission was observed on application of voltage across the device. (II) We also demonstrate the photolithographic patterning capability of a metal cathode for top emitting QDLEDs on Si substrates. Lithographic patterning technique enables site-controlled patterning and controlled feature size of the electrode with greater accuracy. The stability of inorganic silicon materials and metal oxide based diode structure offers excellent advantages to the device, with no significant damage observed during the patterning and etching steps. Efficient electrical excitation of QDs was demonstrated by both the methods described above. The technique was translated to create localized QD-based light sources for two applications: (1) Three-dimensional scanning probe tip structures for near field imaging. Combined topographic and optical images were acquired using this new class of “self-illuminating” probe in commercial NSOM. The emission wavelength can be tuned through quantum-size effect of QDs. (2) Multispectral excitation sources integrated with microfluidic channels for tumor cell analyses. We were able to detect the variation of sub-cellular features, such as the nucleus-to-cytoplasm ratio, to quantify the absorption at different wavelength upon the near-field illumination of individual tumor cells towards the determination of cancer developmental stage. / text