We demonstrate ultrahigh-resolution optical coherence tomography (OCT) using continuum generation in an air-silica microstructure fiber as a low-coherence light source. A broadband OCT system was developed and imaging was performed with a bandwidth of 370 nm at a 1.3-mu;m center wavelength. Longitudinal resolutions of 2.5 microm in air and ~2 microm in tissue were achieved. Ultrahigh-resolution imaging in biological tissue in vivo was demonstrated. 相似文献
We demonstrate experimentally for what is to our knowledge the first time that air-silica microstructure optical fibers can exhibit anomalous dispersion at visible wavelengths. We exploit this feature to generate an optical continuum 550 THz in width, extending from the violet to the infrared, by propagating pulses of 100-fs duration and kilowatt peak powers through a microstructure fiber near the zero-dispersion wavelength. 相似文献
We analyze the waveguide properties of microstructure optical fibers consisting of a silica core surrounded by a single ring of large air holes. Although the fibers can support numerous transverse spatial modes, coupling between these modes even in the presence of large perturbations is prevented for small core dimensions, owing to a large wave-vector mismatch between the lowest-order modes. The result is an optical fiber that can appear single mode with propagation properties that can be achieved only in multimode waveguides. 相似文献
We demonstrate a great simplification in the long-standing problem of measuring optical frequencies in terms of the cesium primary standard. An air-silica microstructure optical fiber broadens the frequency comb of a femtosecond laser to span the optical octave from 1064 to 532 nm, enabling us to measure the 282 THz frequency of an iodine-stabilized Nd:YAG laser directly in terms of the microwave frequency that controls the comb spacing. Additional measurements of established optical frequencies at 633 and 778 nm using the same femtosecond comb confirm the accepted uncertainties for these standards. 相似文献
We report on the ultraviolet photodissociation (UVPD) chemistry of protonated tyrosine, iodotyrosine, and diiodotyrosine. Distonic loss of the iodine creates a high-energy radical at the aromatic ring that engages in hydrogen/proton rearrangement chemistry. Based on UVPD kinetics measurements, the appearance of this radical is coincident with the UV irradiation pulse (8 ns). Conversely, sequential UVPD product ions exhibit metastable decay on ca. 100 ns timescales. Infrared ion spectroscopy is capable of confirming putative structures of the rearrangement products as proton transfers from the imine and β-carbon hydrogens. Potential energy surfaces for the various reaction pathways indicate that the rearrangement chemistry is highly complex, compatible with a cascade of rearrangements, and that there is no preferred rearrangement pathway even in small molecular systems like these.
Abstract For the first time a systematic study was performed for the phosphorylation of 1,2,3-triols with total amides of phosphorous acid. The initial-matrix-structure dependence of phospholane-phospholane bicyclophosphites was found and investigated. The introducing of terminal substituents into a triol molecule was shown to essentially increase their stability. 相似文献
The level of colloidal stability of a latex coating formulation is governed by the hydrodynamic size of the pigment particle and its aggregates, along with the electrolyte concentration of the coating formulation. Model latex coating films were developed to investigate the effects of pigment aggregate size and the electrolyte concentration in the latex coating formulation on the critical pigment volume concentration (CPVC), as determined by mechanical optical and permeability properties. The poly(styrene) pigment and poly(styrene-butadiene) (60:40) binder particles were characterized for their relative sizes, the surfactant surface coverage and the critical coagulation concentration, in dilute (1.8% solids) and concentrated (42% solids) dispersions, for sodium chloride and calcium chloride. The hydrodynamic diameter of the strong pigment aggregates formed as a function of aging time, after adjusting the electrolyte concentration of the pigment dispersion to the c.c.c. level were characterized by capillary chromatography technique. The Increasing size of the pigment aggregates and the increasing electrolyte concentration of the latex coating formulation were shown to sharply decrease the CPVC values determined by mechanical and optical properties such as tensile strength and contrast ratio of the coating. Their influence on the permeability property of the films such as porosity was limited by the availability of the binder to form smooth surface below 35-40% PVC. The morphological studies of the coating films showed that aggregates cause an increase in the degree of non-uniform distribution of the binder and pigment in the latex coating film 相似文献
We developed a microfluidic analogue of the classic Wheatstone bridge circuit for automated, real-time sampling of solutions in a flow-through device format. We demonstrate precise control of flow rate and flow direction in the "bridge" microchannel using an on-chip membrane valve, which functions as an integrated "variable resistor". We implement an automated feedback control mechanism in order to dynamically adjust valve opening, thereby manipulating the pressure drop across the bridge and precisely controlling fluid flow in the bridge channel. At a critical valve opening, the flow in the bridge channel can be completely stopped by balancing the flow resistances in the Wheatstone bridge device, which facilitates rapid, on-demand fluid sampling in the bridge channel. In this article, we present the underlying mechanism for device operation and report key design parameters that determine device performance. Overall, the microfluidic Wheatstone bridge represents a new and versatile method for on-chip flow control and sample manipulation. 相似文献
We report an integrated microfluidic device for fine-scale manipulation and confinement of micro- and nanoscale particles in free-solution. Using this device, single particles are trapped in a stagnation point flow at the junction of two intersecting microchannels. The hydrodynamic trap is based on active flow control at a fluid stagnation point using an integrated on-chip valve in a monolithic PDMS-based microfluidic device. In this work, we characterize device design parameters enabling precise control of stagnation point position for efficient trap performance. The microfluidic-based hydrodynamic trap facilitates particle trapping using the sole action of fluid flow and provides a viable alternative to existing confinement and manipulation techniques based on electric, optical, magnetic or acoustic force fields. Overall, the hydrodynamic trap enables non-contact confinement of fluorescent and non-fluorescent particles for extended times and provides a new platform for fundamental studies in biology, biotechnology and materials science. 相似文献
We utilize the two-photon conductivity of a fused-silica substrate to produce a photoconductive switch for use in an intensity autocorrelator for ultraviolet ultrashort pulses. We perform measurements at 267 nm with pulse durations in the range of 110-330 fs and with energies as weak as 10 nJ. Based on the bandgap of fused silica, this device can potentially operate in the wavelength range of 140-280 nm. 相似文献