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1. Calibration of optical parametric amplifiers for frequency-domain ultrafast coherent multidimensional spectroscopic studies

   https://doi.org/10.1063/5.0271282  

   Kain, Schuyler; Thompson, Blaise J; Kohler, Daniel D; Wright, John C (July 2025, Review of Scientific Instruments)

   Frequency-domain ultrafast coherent multidimensional spectroscopy has made possible a family of fully coherent spectroscopies that can create and interrogate characteristic superpositions of the quantum-mechanical states of a system under investigation. Typical applications include the resolution of couplings and dynamics among multiple electronic states in atoms, molecules, and materials. These methods require scanning the wavelengths of multiple, ultrafast light sources—often optical parametric amplifiers (OPAs). Spectral calibration of the OPA output (a.k.a. wavelength-tuning) involves optimizing the OPA output intensity by adjusting the angles of its component nonlinear crystals and motorized delay stages. When the spectral range addressed in the experiment is large, optimization and control of the one or more OPAs become complex. This work describes an automated calibration strategy that measures the multidimensional configuration-space of a typical 800-nm OPA over all angular and delay degrees-of-freedom in order to create a global tuning curve that spans its dynamic spectral range with optimal power and smooth interpolation. To accomplish this task, the optimization assesses the wavelength-dependent variations to the temporal and spatial characteristics of the OPA output caused by material dispersion so that compensations may be applied during a wavelength scan. 

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2. Quantitative Measurement of Iron-Silicides by EPMA Using the Fe L α and L β X-ray Lines: A New Twist to an Old Approach

   https://doi.org/10.1017/S1431927619000436  

   Moy, Aurélien; Fournelle, John; von der Handt, Anette (June 2019, Microscopy and Microanalysis)

   Abstract The recent availability of Schottky-type field emission electron microprobes provides incentive to consider analyzing micrometer-sized features. Yet, to quantify sub-micrometer-sized features, the electron interaction volume must be reduced by decreasing accelerating voltage. However, the K lines of the transition elements (e.g., Fe) then cannot be excited, and the L lines must be used. The Fe L α 1,2 line is the most intense of the L series but bonding effects change its atomic parameters because it involves a valence band electron transition. For successful traditional electron probe microanalysis, the mass absorption coefficient (MAC) must be accurately known, but the MAC of Fe L α 1,2 radiation by Fe atoms varies from one Fe-compound to another and is not well known. We show that the conventional method of measuring the MAC by an electron probe cannot be used in close proximity to absorption edges, making its accurate determination impossible. Fortunately, we demonstrate, using a set of Fe–silicide compounds, that it is possible to derive an accurate calibration curve, for a given accelerating voltage and takeoff angle, which can be used to quantify Fe in Fe–silicide compounds. The calibration curve can be applied to any spectrometer without calibration and gives accurate quantification results. 

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3. Distributed Volt-Var Curve Optimization Using a Cellular Computational Network Representation of an Electric Power Distribution System

   https://doi.org/10.3390/en15124438  

   Dharmawardena, Hasala; Kumar Venayagamoorthy, Ganesh (June 2022, Energies)

   Voltage control in modern electric power distribution systems has become challenging due to the increasing penetration of distributed energy resources (DER). The current state-of-the-art voltage control is based on static/pre-determined DER volt-var curves. Static volt-var curves do not provide sufficient flexibility to address the temporal and spatial aspects of the voltage control problem in a power system with a large number of DER. This paper presents a simple, scalable, and robust distributed optimization framework (DOF) for optimizing voltage control. The proposed framework allows for data-driven distributed voltage optimization in a power distribution system. This method enhances voltage control by optimizing volt-var curve parameters of inverters in a distributed manner based on a cellular computational network (CCN) representation of the power distribution system. The cellular optimization approach enables the system-wide optimization. The cells to be optimized may be prioritized and two methods namely, graph and impact-based methods, are studied. The impact-based method requires extra initial computational efforts but thereafter provides better computational throughput than the graph-based method. The DOF is illustrated on a modified standard distribution test case with several DERs. The results from the test case demonstrate that the DOF based volt-var optimization results in consistently better performance than the state-of-the-art volt-var control. 

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4. A microfluidic approach for hemoglobin detection in whole blood

   https://doi.org/10.1063/1.4997185  

   Taparia, Nikita; Platten, Kimsey_C; Anderson, Kristin_B; Sniadecki, Nathan_J (October 2017, AIP Advances)

   Diagnosis of anemia relies on the detection of hemoglobin levels in a blood sample. Conventional blood analyzers are not readily available in most low-resource regions where anemia is prevalent, so detection methods that are low-cost and point-of-care are needed. Here, we present a microfluidic approach to measure hemoglobin concentration in a sample of whole blood. Unlike conventional approaches, our microfluidic approach does not require hemolysis. We detect the level of hemoglobin in a blood sample optically by illuminating the blood in a microfluidic channel at a peak wavelength of 540 nm and measuring its absorbance using a CMOS sensor coupled with a lens to magnify the image onto the detector. We compare measurements in microchannels with channel heights of 50 and 115 μm and found the channel with the 50 μm height provided a better range of detection. Since we use whole blood and not lysed blood, we fit our data to an absorption model that includes optical scattering in order to obtain a calibration curve for our system. Based on this calibration curve and data collected, we can measure hemoglobin concentration within 1 g/dL for severe cases of anemia. In addition, we measured optical density for blood flowing at a shear rate of 500 s-1 and observed it did not affect the nonlinear model. With this method, we provide an approach that uses microfluidic detection of hemoglobin levels that can be integrated with other microfluidic approaches for blood analysis. 

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5. The CHARA Array Polarization Model and Prospects for Spectropolarimetry

   https://doi.org/10.3847/1538-3881/ae0648  

   Shuai, Linling; Monnier, John D; Setterholm, Benjamin R; Kraus, Stefan; Anugu, Narsireddy; Gardner, Tyler; Le_Bouquin, Jean-Baptiste; Schaefer, Gail H (November 2025, The Astronomical Journal)

   Abstract Polarimetric data provide key insights into infrared emission mechanisms in the inner disks of young stellar objects (YSOs) and the details of dust formation around asymptotic giant branch (AGB) stars. While polarization measurements are well-established in radio interferometry, they remain challenging at visible and near-infrared wavelengths, due to the significant time-variable birefringence introduced by the complex optical beam train. In this study, we characterize instrumental polarization effects within the optical path of the Center for High Angular Resolution Astronomy (CHARA) Array, focusing on theH-band MIRC-X andK-band MYSTIC beam combiners. Using the Jones matrix formalism, we developed a comprehensive model describing diattenuation and retardance across the array. By applying this model to an unpolarized calibrator, we derived the instrumental parameters for both MIRC-X and MYSTIC. Our results show differential diattenuation consistent with ≥97% reflectivity per aluminum-coated surface at 45° incidence. The differential retardance exhibits small wavelength-dependent variations, in some cases larger than we expected. Notably, telescope W2 exhibits a significantly larger phase shift in the Coudé path, attributable to a fixed aluminum mirror (M4) used in place of deformable mirrors present on the other telescopes during the observing run. We also identify misalignments in the LiNbO₃birefringent compensator plates on S1 (MIRC-X) and W2 (MYSTIC). After correcting for night-to-night offsets, we achieve calibration accuracies of ±3.4% in visibility ratio and $\pm 1\stackrel{°}{.}4$in differential phase for MIRC-X, and ±5.9% and $\pm 2\stackrel{°}{.}4$, respectively, for MYSTIC. Given that the differential intrinsic polarization of spatially resolved sources, such as AGB stars and YSOs, typically greater than these instrumental uncertainties, our results demonstrate that CHARA is now capable of achieving high-accuracy measurements of intrinsic polarization in astrophysical targets. 

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