M. L. Myrick

Development of patterns for nanoscale strain measurements: I. Fabrication of imprinted Au webs for polymeric materials

A method is presented for patterning polymers with nanoscale gold networks and using the pattern to measure strain in the polymer. A gold film is first coated on a porous alumina template. After coating, the template is impressed into a polymer, and the template is dissolved to leave a continuous metal network on or slightly below the surface of the polymer. The network has a random structure and is electrically conductive and has potential applicability to structural health monitoring. We show that it can be used as a means of measuring deformation through changes in electrical conductivity and continuity and also as a means to measure local material response during controlled loading.

Fabrication and evaluation of a dimension-reduction fiberoptic system for chemical imaging applications

A novel system for rapid chemical imaging is described and evaluated. The system operates via single-frame spectroscopic chemical imaging with high spectroscopic resolution using a second-generation dimension-reduction fiberoptic array. Images are focused onto a rectangular array of square close-packed 25 μm cross-sectional f/2 optical fibers that are drawn into a linear distal array with serpentine ordering. The distal end is then imaged with an f/2 spectrograph equipped with a holographic grating and a gated intensified charge-coupled device (ICCD) camera for analysis. Software is used to extract the spatial/spectral information contained in a single ICCD image and deconvolute it into wavelength-specific univariate reconstructed images or position-specific spectra that span an 86 nm wavelength space using our present grating. A description of the fabrication of the dimension-reduction array is given as well as a zero-order reconstruction of a binary target and single-wavelength image reconstructions of a laser-induced plasma. The system is evaluated for spatial and spectral resolution, throughput, image brightness, resolving power, depth of focus, and channel cross talk. Treatment of the spectroscopic data obtained from the ICCD images for use in potential chemical imaging applications is discussed.A novel system for rapid chemical imaging is described and evaluated. The system operates via single-frame spectroscopic chemical imaging with high spectroscopic resolution using a second-generation dimension-reduction fiberoptic array. Images are focused onto a rectangular array of square close-packed 25 μm cross-sectional f/2 optical fibers that are drawn into a linear distal array with serpentine ordering. The distal end is then imaged with an f/2 spectrograph equipped with a holographic grating and a gated intensified charge-coupled device (ICCD) camera for analysis. Software is used to extract the spatial/spectral information contained in a single ICCD image and deconvolute it into wavelength-specific univariate reconstructed images or position-specific spectra that span an 86 nm wavelength space using our present grating. A description of the fabrication of the dimension-reduction array is given as well as a zero-order reconstruction of a binary target and single-wavelength image reconstructions of ...

Use of a 2D to 1D Dimension Reduction Fiber-Optic Array for Multiwavelength Imaging Sensors

A dimension reduction fiber-optic array is used to measure the response of a stacked-layer, image-guide CO2/O2 sensor, simultaneously at several different wavelengths. Two different image-guide CO2/O2 sensor configurations are described: a stacked-layer sensor, where luminescence indicators for CO2 and O2 are uniformly coated on the tip of the sensor; and a side-by-side coated sensor where the two indicators are coated on different halves of the fiber tip. It is shown that a single image-guide measurement, made by using the dimension reduction array, can be used to generate response plots, intensity profiles, and reconstructed images at different luminescence wavelengths. The spatial resolution of an image guide sensor is limited by the number of fibers used to construct the dimension reduction array.

Single-Frame Chemical Imaging: Dimension Reduction Fiber-Optic Array Improvements and Application to Laser-Induced Breakdown Spectroscopy

A single-frame approach to chemical imaging with high spectroscopic resolution is described that makes use of a second-generation dimension-reduction fiber-optic array. Laser-induced plume images are focused onto a 17 × 32 rectangular array of square close-packed 25 μm cross-sectional f/2 optical fibers that are drawn into a 544 × 1 distal array with serpentine ordering. The 544 × 1 side of the array is imaged with an f/2 spectrograph equipped with a holographic grating and a gated intensified charge-coupled device (ICCD) camera for spectral analysis. Software is used to extract the spatial/spectral information contained in the ICCD images and de-convolute them into wavelength-specific univariate reconstructed images or position-specific spectra that span an 86 nm wavelength space. Temporal resolution is provided by imaging sequential laser plumes with varying time delays after each laser pulse on the gated intensifier.

Construction, figures of merit, and testing of a single-cell fluorescence excitation spectroscopy system

Characterization of phytoplankton community composition is critical to understanding the ecology and biogeochemistry of the oceans. One approach to taxonomic characterization takes advantage of differing pigmentation between algal taxa and thus differences in fluorescence excitation spectra. Analyses of bulk water samples, however, may be confounded by interference from chromophoric dissolved organic matter or suspended particulate matter. Here, we describe an instrument that uses a laser trap based on a Nikon TE2000-U microscope to position individual phytoplankton cells for confocal fluorescence excitation spectroscopy, thus avoiding interference from the surrounding medium. Quantitative measurements of optical power give data in the form of photons emitted per photon of exposure for an individual phytoplankton cell. Residence times for individual phytoplankton in the instrument can be as long as several minutes with no substantial change in their fluorescence excitation spectra. The laser trap was found to generate two-photon fluorescence from the organisms so a modification was made to release the trap momentarily during data acquisition. Typical signal levels for an individual cell are in the range of 10(6) photons/s of fluorescence using a monochromated 75 W Xe arc lamp excitation source with a 2% transmission neutral density filter.

Multi-Wavelength Raman Imaging Using a Small-Diameter Image Guide with a Dimension-Reduction Imaging Array

A commercially available fiber-optic Raman probe was modified for high-resolution spectral Raman imaging using a 350 μm diameter optical fiber image guide coupled to a dimension-reduction imaging array (DRIA). The DRIA comprised 672 optical fibers, arranged as a square array (21 × 32 fibers) on one end and a linear array (672 × 1 fibers) on the other. An imaging spectrograph was used with the DRIA to acquire multi-wavelength Raman images from −250 to 1800 cm−1 at a spectral resolution of ∼5 cm−1. The utility of this technique for in situ and remote Raman imaging is demonstrated by monitoring the polymerization of a model polymer, dibromostyrene (DBS), while simultaneously measuring the Raman Stokes/anti-Stokes ratio as a function of sample heating time, over a sample area of ∼4 × 1.6 mm.

Description and performance of a highly versatile, low‐cost fiber‐optic confocal Raman microscope

A versatile fiber‐optic confocal Raman microscope has been developed. Fiber optics provide remote capabilities for the microscope and the ability to use multiple excitation sources and detection schemes. The horizontal and vertical resolutions of the instrument have been determined by monitoring spectral changes while scanning known interfaces and microparticles. The mini‐ mum detectable particle size has been determined via the spectroscopic analysis of calibrated polystyrene microspheres. The horizontal resolution has additionally been tested in the imaging of a 10 μm glass fiber embedded in an epoxy matrix.

Asymmetric Versus Symmetric Filter Wheels and Associated Processing Algorithms: Results from Asynchronous Fluorescence Imaging Photometer Measurements of Phytoplankton:

The use of rotating filter wheels is common in photometric applications. Traditional filter wheel designs typically exhibit a number of filter openings spaced evenly about the circumference of the wheel. In this work we examine a number of shortcomings of this traditional filter design in measurements of phytoplankton fluorescence made with our fluorescence imaging photometer (FIP). We present an alternative asymmetric wheel design that offers a number of advantages over the traditional design as well as a new processing algorithm designed to accommodate convolution of signals from adjacent channels inherent in measurements collected with the asymmetric design. This approach eliminates the need for a separate signal to establish timing and wheel position, unambiguously establishes filter order even when the direction of rotation is unknown, allows for better estimates of signal baseline, and is more resilient to effects of vibration and other dynamic processes that could occur on the time scale of wheel rotation. We demonstrate performance improvements for phytoplankton fluorescence measurements associated with the new wheel design and algorithm compared with previously published methods using the FIP. Both the improved image processing algorithm and filter wheel design were found to reduce noise in our measurements significantly.

Fine-Structure Measurements of Oxygen A Band Absorbance for Estimating the Thermodynamic Average Temperature of the Earth's Atmosphere. An Experiment in Physical and Environmental Chemistry

The rotational fine structure observable in a forbidden electronic absorbance of diatomic oxygen in the earths atmosphere can be observed as a series of minima in the solar spectrum near 762 nm wavelength. The relative intensities of these rotational fine-structure lines can be used quantitatively to estimate the average temperature of the atmosphere along the path taken by sunlight to the observer. Measured values for temperature vary from day to day and season to season and are generally far lower than ambient temperatures because of averaging over the depth of the atmosphere. These experimentally determined thermodynamic temperatures can be compared to Web-based atmospheric models for particular locations and times to illustrate the fact that they are average values.