Ocean Optics (United States)

This work introduces a new approach to perform LIBS elemental imaging in the vacuum ultraviolet (VUV) wavelength range by using an argon purged probe coupled to a compact spectrometer.

Abstract Spectroscopy is the study of the interaction of light with matter. By observing how light interacts with matter—through reflection, refraction, elastic scattering, absorbance, inelastic scattering, and emission—it is possible to (1) identify the wavelengths of light that interact with atoms and molecules, and (2) quantify the amount of light being absorbed, reflected, scattered, or emitted at a particular wavelength. This unit describes the background and basic principles of spectrophotometry (the study of the reflection or transmission properties of a substance as a function of wavelength), in particular, absorbance spectrophotometry. Also included is discussion of key spectrophotometer components and their functions, the relationship between absorbance and transmittance, experimental considerations, and the steps necessary in preparing a standard curve for determining absorbance concentration. © 2015 by John Wiley & Sons, Inc.

Surfaces are commonly specified with peak to valley (PV) and root-mean-square (rms) requirements for surface form and roughness, describing surface quality with a few simple numbers. These specs ignore lateral feature sizes between form and roughness (so-called mid-spatial frequencies, or MSFs), however, making them inadequate for many modern optics fabricated with advanced technologies. Specifications sensitive to the lateral feature size, such as such as slope or power-spectral density (PSD), are increasingly employed to fill this void. Having a detailed view of the surface error as a function of lateral feature size can drive fabrication decisions. For example, a large aperture tool tends to correct small features well but performs less well on large features; while subaperture tools tend to do the opposite. Therefore after each fabrication step we want to know how the surface features at different lateral sizes evolved, so that we can optimize the choice of the next fabrication step. A spec like PSD often doesn’t inform the fabricator whether it’s failing because of a localized error (such as edge roll), continuous texture, or an artifact of metrology or computation. So while it may indicate the need for additional fabrication steps, it is not ideal for guiding specifically which fabrication step ought to be undertaken next. We have developed analyses to help determine what surface characteristics are failing spec, and thus optimize the next fabrication step. Finally, we demonstrate an example of how we have applied these techniques to fabricate parts with demanding slope and MSF specifications.

This paper takes a system-wide perspective of electrokinetic energy conversion devices based on an array of microchannels to help understanding their operation. The approach taken was a combination of developing an electrical analogy and conducting experiments. The electrical analogy included current sources for the convection current, resistors for the conduction current, a capacitor for accumulating the partitioned ions, resistors for ion transport in the reservoirs, diodes and capacitors for the electrochemistry and polarization at the electrodes, and a simple external resistive load. The number of parallel channels profoundly affected the summative resistive and capacitive characteristics of the array, and highlights the differences between a single channel and an array of channels, especially in the transient responses and the role of the electrodes. The electrical analogy was solved by Laplace Transforms to demonstrate a rich and varied response that such a system exhibits to a step change in flow i...

A Smart pH Cuvette is developed by coating the inner surface with pH sensitive thin film. The coating is a hydroscopic sol-gel material doped with colorimetric pH indicator dye sensitive to the pH of analyte solutions in biological range. Ocean optics miniaturized spectrometers are used for signal detection and analysis, along with multimode optical fibers. This new pH sensing arrangement yields an inexpensive solution for monitoring the pH of samples for biological applications. The Smart pH Cuvettes provide a resolution of 0.01 pH units, an accuracy of 1% of the reading, and 90% response in less than 10 seconds.

We investigated environmental forcing mechanisms of phytoplankton absorption near the Mississippi River delta using multiyear satellite data. An algorithm for the phytoplankton absorption coefficient (aph) was developed from in situ measurements and applied to ocean color imagery. We employed a suite of chemical and physical forcing variables, including surface currents. For satellite‐derived aph time series (2002–2004), correlation and stepwise regression analyses revealed the most important forcing variables of aph on the Louisiana shelf. Areally, Mississippi River discharge and nitrate concentration ([NO3]) were the two most important predictors of aph over the hypoxic zone (defined by its maximum extent). River discharge was important in a band stretching from the Mississippi River delta to the Louisiana‐Texas border. Riverine [NO3] and wind magnitude best predicted aph in nearshore waters, and solar radiation and SST were most important farther offshore over the hypoxic zone, indicating upwelled nutrient sources to phytoplankton. A multiple linear regression model performed well in resolving seasonal and interannual aph variability in model development years (2002–2004) (mean error of 18%, over all pixels and months) and in predicting shelf‐wide aph patterns in 2005 (mean error of 32%). Our results strongly suggest that in recent years, stratification and vertical mixing, in addition to riverine [NO3], play a primary role in regulating phytoplankton biomass over the hypoxic zone. As well, a springtime model experiment showed that aph over the hypoxic zone can differ by an average absolute 37% from its average scenario owing to changes solely in environmental variables other than NO3 flux.

See also: Physics Today 56 (8), 50See also: Physics Today 55 (6), 48See also: Physics Today 55 (9), 10