• Adaptive anatomical preservation optimal denoising for radiation therapy daily MRI

      Maitree, Rapeepan; Perez-Carrillo, Gloria J. Guzman; Shimony, Joshua S.; Gach, H. Michael; Chundury, Anupama; Roach, Michael; Li, H. Harold; Yang, Deshan; Univ Arizona, Dept Radiol; Washington University School of Medicine, Department of Radiation Oncology, St. Louis, Missouri; et al. (SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 2017-09-01)
      Low-field magnetic resonance imaging (MRI) has recently been integrated with radiation therapy systems to provide image guidance for daily cancer radiation treatments. The main benefit of the low-field strength is minimal electron return effects. The main disadvantage of low-field strength is increased image noise compared to diagnostic MRIs conducted at 1.5 T or higher. The increased image noise affects both the discernibility of soft tissues and the accuracy of further image processing tasks for both clinical and research applications, such as tumor tracking, feature analysis, image segmentation, and image registration. An innovative method, adaptive anatomical preservation optimal denoising (AAPOD), was developed for optimal image denoising, i. e., to maximally reduce noise while preserving the tissue boundaries. AAPOD employs a series of adaptive nonlocal mean (ANLM) denoising trials with increasing denoising filter strength (i. e., the block similarity filtering parameter in the ANLM algorithm), and then detects the tissue boundary losses on the differences of sequentially denoised images using a zero-crossing edge detection method. The optimal denoising filter strength per voxel is determined by identifying the denoising filter strength value at which boundary losses start to appear around the voxel. The final denoising result is generated by applying the ANLM denoising method with the optimal per-voxel denoising filter strengths. The experimental results demonstrated that AAPOD was capable of reducing noise adaptively and optimally while avoiding tissue boundary losses. AAPOD is useful for improving the quality of MRIs with low-contrast-to-noise ratios and could be applied to other medical imaging modalities, e.g., computed tomography. (C) 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)
    • Adaptive optics with programmable Fourier-based wavefront sensors: a spatial light modulator approach to the LAM/ONERA on-sky pyramid sensor testbed

      Janin-Potiron, Pierre; Chambouleyron, Vincent; Schatz, Lauren; Fauvarque, Olivier; Bond, Charlotte Z.; Abautret, Yannick; Muslimov, Eduard; El-Hadi, Kacem; Sauvage, Jean-François; Dohlen, Kjetil; et al. (SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 2019-07-08)
      Wavefront sensors (WFSs) encode phase information of an incoming wavefront into an intensity pattern that can be measured on a camera. Several kinds of WFSs are used in astronomical adaptive optics. Among them, Fourier-based WFSs perform a filtering operation on the wavefront in the focal plane. The most well-known example of a WFS of this kind is the Zernike WFS. The pyramid WFS also belongs to this class. Based on this same principle, WFSs can be proposed, such as the n-faced pyramid (which ultimately becomes an axicon) or the flattened pyramid, depending on whether the image formation is incoherent or coherent. To test such concepts, the LAM/ONERA on-sky pyramid sensor (LOOPS) adaptive optics testbed hosted at the Laboratoire d’Astrophysique de Marseille has been upgraded by adding a spatial light modulator (SLM). This device, placed in a focal plane produces high-definition phase masks that mimic otherwise bulk optic devices. We first present the optical design and upgrades made to the experimental setup of the LOOPS bench. Then, we focus on the generation of the phase masks with the SLM and the implications of having such a device in a focal plane. Finally, we present the first closed-loop results in either static or dynamic mode with different WFS applied on the SLM.
    • Advances in multiangle satellite remote sensing of speciated airborne particulate matter and association with adverse health effects: from MISR to MAIA

      Diner, David J.; Boland, Stacey W.; Brauer, Michael; Bruegge, Carol; Burke, Kevin A.; Chipman, Russell; Di Girolamo, Larry; Garay, Michael J.; Hasheminassab, Sina; Hyer, Edward; et al. (SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 2018-07-28)
      Inhalation of airborne particulate matter (PM) is associated with a variety of adverse health outcomes. However, the relative toxicity of specific PM types-mixtures of particles of varying sizes, shapes, and chemical compositions-is not well understood. A major impediment has been the sparse distribution of surface sensors, especially those measuring speciated PM. Aerosol remote sensing from Earth orbit offers the opportunity to improve our understanding of the health risks associated with different particle types and sources. The Multi-angle Imaging SpectroRadiometer (MISR) instrument aboard NASA's Terra satellite has demonstrated the value of near-simultaneous observations of backscattered sunlight from multiple view angles for remote sensing of aerosol abundances and particle properties over land. The Multi-Angle Imager for Aerosols (MAIA) instrument, currently in development, improves on MISR's sensitivity to airborne particle composition by incorporating polarimetry and expanded spectral range. Spatiotemporal regression relationships generated using collocated surface monitor and chemical transport model data will be used to convert fractional aerosol optical depths retrieved from MAIA observations to near-surface PM10, PM2.5, and speciated PM2.5. Health scientists on the MAIA team will use the resulting exposure estimates over globally distributed target areas to investigate the association of particle species with population health effects. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.
    • Angle of linear polarization images of outdoor scenes

      Kupinski, Meredith; Bradley, Christine; Diner, David; Xu, Feng; Chipman, Russell; Univ Arizona, Ctr Opt Sci (SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 2019-06-11)
      Observations from the Ground-based Multiangle SpectroPolarimetric Imager (GroundMSPI) are used to relate angle of linear polarization (AoLP) measurements to material properties and illumination conditions in sunlit outdoor environments. GroundMSPI is a push-broom spectropolarimetric camera with an uncertainty in degree of linear polarization (DoLP) of ±0.005. This polarimetric accuracy yields useful AoLP images even when the DoLP is less than 0.02. AoLP images are reported with respect to dependency on surface texture, surface orientation, albedo, and illumination conditions. Agreement with well-known principles of polarized light scattering is illustrated, and several special cases are described. Expected observations of AoLP tangential to surface orientation and AoLP perpendicular to the scattering plane are reported. Significant changes in the AoLP are observed from common variations in outdoor illumination conditions. Also, simple variants in material properties change the dominant polarized light scattering process and thus the AoLP. Measurement examples that isolate a 90 deg AoLP flip are shown for a sunny and cloudy day as well as an object of high and low albedo.
    • Aspheric/freeform optical surface description for controlling illumination from point-like light sources

      Sasián, José; Reshidko, Dmitry; Li, Chia-Ling; Univ Arizona, Coll Opt Sci; University of Arizona, College of Optical Sciences, 1630 East University Boulevard, Tucson, Arizona 85721, United States; University of Arizona, College of Optical Sciences, 1630 East University Boulevard, Tucson, Arizona 85721, United States; University of Arizona, College of Optical Sciences, 1630 East University Boulevard, Tucson, Arizona 85721, United States (SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 2016-11-25)
      We present an optical surface in closed form that can be used to design lenses for controlling relative illumination on a target surface. The optical surface is constructed by rotation of the pedal curve to the ellipse about its minor axis. Three renditions of the surface are provided, namely as an expansion of a base surface, and as combinations of several base surfaces. Examples of the performance of the surfaces are presented for the case of a point light source. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)
    • Assessing computed tomography image quality for combined detection and estimation tasks

      Tseng, Hsin-Wu; Fan, Jiahua; Kupinski, Matthew A.; Univ Arizona, Coll Opt Sci (SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 2017-11-21)
      Maintaining or even improving image quality while lowering patient dose is always the desire in clinical computed tomography (CT) imaging. Iterative reconstruction (IR) algorithms have been designed to allow for a reduced dose while maintaining or even improving an image. However, we have previously shown that the dose-saving capabilities allowed with IR are different for different clinical tasks. The channelized scanning linear observer (CSLO) was applied to study clinical tasks that combine detection and estimation when assessing CT image data. The purpose of this work is to illustrate the importance of task complexity when assessing dose savings and to move toward more realistic tasks when performing these types of studies. Human-observer validation of these methods will take place in a future publication. Low-contrast objects embedded in body-size phantoms were imaged multiple times and reconstructed by filtered back projection (FBP) and an IR algorithm. The task was to detect, localize, and estimate the size and contrast of low-contrast objects in the phantom. Independent signal-present and signal-absent regions of interest cropped from images were channelized by the dense-difference of Gauss channels for CSLO training and testing. Estimation receiver operating characteristic (EROC) curves and the areas under EROC curves (EAUC) were calculated by CSLO as the figure of merit. The one-shot method was used to compute the variance of the EAUC values. Results suggest that the IR algorithm studied in this work could efficiently reduce the dose by similar to 50% while maintaining an image quality comparable to conventional FBP reconstruction warranting further investigation using real patient data. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.
    • Asymmetries in adaptive optics point spread functions

      Madurowicz, Alexander; Macintosh, Bruce; Chilcote, Jeffrey; Perrin, Marshall; Poyneer, Lisa; Pueyo, Laurent; Ruffio, Jean-Baptiste; Bailey, Vanessa P.; Barman, Travis; Bulger, Joanna; et al. (SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 2019-10-25)
      An explanation for the origin of asymmetry along the preferential axis of the point spread function (PSF) of an AO system is developed. When phase errors from high-altitude turbulence scintillate due to Fresnel propagation, wavefront amplitude errors may be spatially offset from residual phase errors. These correlated errors appear as asymmetry in the image plane under the Fraunhofer condition. In an analytic model with an open-loop AO system, the strength of the asymmetry is calculated for a single mode of phase aberration, which generalizes to two dimensions under a Fourier decomposition of the complex illumination. Other parameters included are the spatial offset of the AO correction, which is the wind velocity in the frozen flow regime multiplied by the effective AO time delay and propagation distance or altitude of the turbulent layer. In this model, the asymmetry is strongest when the wind is slow and nearest to the coronagraphic mask when the turbulent layer is far away, such as when the telescope is pointing low toward the horizon. A great emphasis is made about the fact that the brighter asymmetric lobe of the PSF points in the opposite direction as the wind, which is consistent analytically with the clarification that the image plane electric field distribution is actually the inverse Fourier transform of the aperture plane. Validation of this understanding is made with observations taken from the Gemini Planet Imager, as well as being reproducible in end-to-end AO simulations. (C) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License.
    • Automated data processing architecture for the Gemini Planet Imager Exoplanet Survey

      Wang, Jason J.; Perrin, Marshall; Savransky, Dmitry; Arriaga, Pauline; Chilcote, Jeffrey; De Rosa, Robert J.; Millar-Blanchaer, Maxwell A.; Marois, Christian; Rameau, Julien; Wolff, Schuyler; et al. (SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 2018-01)
      The Gemini Planet Imager Exoplanet Survey (GPIES) is a multiyear direct imaging survey of 600 stars to discover and characterize young Jovian exoplanets and their environments. We have developed an automated data architecture to process and index all data related to the survey uniformly. An automated and flexible data processing framework, which we term the Data Cruncher, combines multiple data reduction pipelines (DRPs) together to process all spectroscopic, polarimetric, and calibration data taken with GPIES. With no human intervention, fully reduced and calibrated data products are available less than an hour after the data are taken to expedite follow up on potential objects of interest. The Data Cruncher can run on a supercomputer to reprocess all GPIES data in a single day as improvements are made to our DRPs. A backend MySQL database indexes all files, which are synced to the cloud, and a front-end web server allows for easy browsing of all files associated with GPIES. To help observers, quicklook displays show reduced data as they are processed in real time, and chatbots on Slack post observing information as well as reduced data products. Together, the GPIES automated data processing architecture reduces our workload, provides real-time data reduction, optimizes our observing strategy, and maintains a homogeneously reduced dataset to study planet occurrence and instrument performance. (c) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)
    • Characterizing the responses of vegetation to climate change in the Tibet Plateau using remote sensing data

      An, Chunchun; Fan, Jianrong; Zhang, Yanfen; Yan, Dong; Univ Arizona, Sch Nat Resources & Environm (SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 2018-03)
      It is of great significance to investigate the changes in vegetation and its response to climate change in Tibet due to the sensitivity and vulnerability of the area to climate change. The spatiotemporal pattern of the normalized difference vegetation index (NDVI) and its trends between 2001 and 2015 were depicted using NDVI from the moderate resolution imaging spectroradiometer (MODIS). The responses of vegetation to climatic variables were analyzed through linear regression and correlation analysis with tropical rainfall measuring mission precipitation data and MODIS land surface temperature (LST) data. The results showed that (1) the average annual NDVI gradually decreased from the southeast to the northwest in accordance with the variations in LST and precipitation, (2) the annual NDVI increased from 2001 to 2015 at a rate of 0.3 x 10(-3) per year. The LST exhibited an average annual increase of 0.05 degrees C while precipitation remained relatively stable, (3) the correlation between NDVI and precipitation was positive in the central region, whereas it became negative in the southeast and northeast. The correlation between NDVI and LST was opposite of that between NDVI and precipitation, and (4) the increases in NDVI in the tropical monsoon rain forest and rain forest, subalpine coniferous forest, and alpine meadow vegetation types in the southeast depended more on LST than precipitation. In contrast, the increases in NDVI responded strongly to precipitation in the alpine bush and meadow, alpine grassland, alpine desert, and alpine desert steppe vegetation types in the northwest. (c) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)
    • Colorado Ultraviolet Transit Experiment data simulator

      Sreejith, Aickara Gopinathan; Fossati, Luca; Fleming, Brian T.; France, Kevin C.; Koskinen, Tommi T.; Egan, Arika; Rüdisser, Hannah T.; Steller, Manfred; Univ Arizona, Lunar & Planetary Lab (SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 2019-01)
      The Colorado Ultraviolet Transit Experiment (CUTE) is a 6U NASA CubeSat carrying on board a low-resolution (R similar to 2000 to 3000), near-UV (2500 to 3300 A) spectrograph. It has a rectangular primary Cassegrain telescope to maximize the collecting area. CUTE, which is planned for launch in spring 2020, is designed to monitor transiting extra-solar planets orbiting bright, nearby stars, aiming at improving our understanding of planet atmospheric escape and star-planet interaction processes. We present here the CUTE data simulator, which we complemented with a basic data reduction pipeline. This pipeline will be then updated once the final CUTE data reduction pipeline is developed. We show here the application of the simulator to the HD209458 system and a first estimate of the precision on the measurement of the transit depth as a function of temperature and magnitude of the host star. We also present estimates of the effect of spacecraft jitter on the final spectral resolution. The simulator has been developed considering also scalability and adaptability to other missions carrying on board a long-slit spectrograph. The data simulator will be used to inform the CUTE target selection, choose the spacecraft and instrument settings for each observation, and construct synthetic CUTE wavelength-dependent transit light curves on which to develop the CUTE data reduction pipeline. (C) 2019 Society of Photo-Optical Instrumentation Engineers (SPIE)
    • Colorado Ultraviolet Transit Experiment: a dedicated CubeSat mission to study exoplanetary mass loss and magnetic fields

      Fleming, Brian T.; France, Kevin; Nell, Nicholas; Kohnert, Richard; Pool, Kelsey; Egan, Arika; Fossati, Luca; Koskinen, Tommi; Vidotto, Aline A.; Hoadley, Keri; et al. (SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 2018-01)
      The Colorado Ultraviolet Transit Experiment (CUTE) is a near-UV (2550 to 3300 angstrom) 6U CubeSat mission designed to monitor transiting hot Jupiters to quantify their atmospheric mass loss and magnetic fields. CUTE will probe both atomic (Mg and Fe) and molecular (OH) lines for evidence of enhanced transit absorption, and to search for evidence of early ingress due to bow shocks ahead of the planet's orbital motion. As a dedicated mission, CUTE will observe greater than or similar to 100 spectroscopic transits of hot Jupiters over a nominal 7-month mission. This represents the equivalent of >700 orbits of the only other instrument capable of these measurements, the Hubble Space Telescope. CUTE efficiently utilizes the available CubeSat volume by means of an innovative optical design to achieve a projected effective area of similar to 28 cm(2), low instrumental background, and a spectral resolving power of R similar to 3000 over the primary science bandpass. These performance characteristics enable CUTE to discern transit depths between 0.1% and 1% in individual spectral absorption lines. We present the CUTE optical and mechanical design, a summary of the science motivation and expected results, and an overview of the projected fabrication, calibration, and launch timeline. (c) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)
    • Compact, unit magnification, reflective imaging relay using freeform surfaces

      Sasian, Jose; Gao, Weichuan; Univ Arizona, Wyant Coll Opt Sci (SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 2020-09-07)
      We present a design for a unit magnification imaging relay that is compact. The design uses two mirrors, and one is used by light twice for a three-reflection system. The mirrors are specified with freeform surfaces. There are several tradeoffs of performance depending on field of view, F/#, and wavelength range. One example provides a 30-mm circular field of view at F/2.8, and another example provides a circular field of view of 40 mm in diameter at F/4 for a length of similar to 400 mm. Adding a third nearly flat mirror allows a system to provide a 50-mm field of view at F/4 for a length of 420 mm. A last example includes a beam splitter cube to allow accessing the full field of view. These systems are diffraction limited at 550 nm.
    • Computed tomography imaging system design for shape threat detection

      Masoudi, Ahmad; Thamvichai, Ratchaneekorn; Neifeld, Mark A.; Univ Arizona, Elect & Comp Engn Dept; Univ Arizona, Coll Opt Sci; University of Arizona, Electrical and Computer Engineering Department, 1230 East Speedway Boulevard, Tucson, Arizona 85719, United States; University of Arizona, Electrical and Computer Engineering Department, 1230 East Speedway Boulevard, Tucson, Arizona 85719, United States; University of Arizona, Electrical and Computer Engineering Department, 1230 East Speedway Boulevard, Tucson, Arizona 85719, United StatesbUniversity of Arizona, College of Optical Sciences, 1630 East University Boulevard, Tucson, Arizona 85721, United States (SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 2016-12-08)
      In the first part of this work, we present two methods for improving the shape-threat detection performance of x-ray computed tomography. Our work uses a fixed-gantry system employing 25 x-ray sources. We first utilize Kullback-Leibler divergence and Mahalanobis distance to determine the optimal single-source single-exposure measurement. The second method employs gradient search on Bhattacharyya bound on error rate (P-e) to determine an optimal multiplexed measurement that simultaneously utilizes all available sources in a single exposure. With limited total resources of 10(6) photons, the multiplexed measurement provides a 41.8x reduction in P-e relative to the single-source measurement. In the second part, we consider multiple exposures and develop an adaptive measurement strategy for x-ray threat detection. Using the adaptive strategy, we design the next measurement based on information retrieved from previous measurements. We determine both optimal "next measurement" and stopping criterion to insure a target P-e using sequential hypothesis testing framework. With adaptive single-source measurements, we can reduce P-e by a factor of 40x relative to the measurements employing all sources in sequence. We also observe that there is a trade-off between measurement SNR and number of detectors when we study the performance of systems with reduced detector numbers. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)
    • Curl-free ray mapping in three dimensions for freeform illumination design

      Gannon, Caleb; Liang, Rongguang; Univ Arizona, Ctr Opt Sci (SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 2019-02-08)
      An illumination design method that incorporates the entire 3-D geometry between the optical surface and target plane into the ray mapping calculation has been developed. The resulting mapping relationship is integrable along the specific contours of the optical surface instead of a 2-D plane. The method is capable of creating extremely high performance, off-axis designs (97% uniformity at 54-deg off-axis), and since it explicitly accounts for system geometry, appears to be easily generalizable. (C) 2019 Society of Photo-Optical Instrumentation Engineers (SPIE)
    • Daylight operation of a sodium laser guide star for adaptive optics wavefront sensing

      Hart, Michael; Jefferies, Stuart M.; Murphy, Neil; Univ Arizona, Coll Optic Sci; University of Arizona, College of Optical Sciences, 1630 East University Boulevard, Tucson, Arizona 85721, United StatesbUniversity of Hawai’i, Institute for Astronomy, 34 Ohia Ku Street, Pukalani, Hawaii 96768, United States; University of Hawai’i, Institute for Astronomy, 34 Ohia Ku Street, Pukalani, Hawaii 96768, United StatescGeorgia State University, Department of Physics and Astronomy, 25 Park Place, Atlanta, Georgia 30303, United States; Jet Propulsion Laboratory, Mail Stop 180 600, 4800 Oak Grove Drive, Pasadena, California 91109, United States (SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 2016-10-26)
      We report contrast measurements of a sodium resonance guide star against the daylight sky when observed through a tuned magneto-optical filter (MOF). The guide star was created by projection of a laser beam at 589.16 nm into the mesospheric sodium layer and the observations were made with a collocated 1.5-m telescope. While MOFs are used with sodium light detecting and ranging systems during the day to improve the signalto- noise ratio of the measurements, they have not so far been employed with laser guide stars to drive adaptive optics (AO) systems to correct atmospherically induced image blur. We interpret our results in terms of the performance of AO systems for astronomy, with particular emphasis on thermal infrared observations at the next generation of extremely large telescopes now being built. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)
    • Delta-doped electron-multiplying CCDs for FIREBall-2

      Kyne, Gillian; Hamden, Erika T.; Nikzad, Shouleh; Hoadley, Keri; Jewell, April; Jones, Todd; Hoenk, Michael; Cheng, Samuel; Martin, D. Christopher; Lingner, Nicole; et al. (SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 2020-03-12)
      We present the status of on-going detector development efforts for our joint NASA/Centre National d'Etudes Spatiales balloon-borne UV multiobject spectrograph, the Faint Intergalactic Redshifted Emission Balloon (FIREBall-2;1 13-2). FB-2 demonstrates a UV detector technology, the delta-doped electron-multiplying CCD (EMCCD), in a low-risk suborbital environment, to prove the performance of EMCCDs for future space missions and technology readiness level advancement. EMCCDs can be used in photon-counting mode to achieve extremely low readout noise (<1 electron). Our testing has focused on reducing clock-induced-charge (CIC) through wave shaping and well-depth optimization with a Nuvu V2 CCCP controller, measuring CIC at 0.001 e(-)/pixel/frame. This optimization also includes methods for reducing dark current, via cooling, and substrate voltage levels. We discuss the challenges of removing cosmic rays, which are also amplified by these detectors, as well as a data reduction pipeline designed for our noise measurement objectives. FB-2 flew in 2018, providing the first time an EMCCD, was used for UV observations in the stratosphere. FB-2 is currently being built up to fly again in 2020, and improvements are being made to the EMCCD to continue optimizing its performance for better noise control. (C) 2020 Society of Photo-Optical Instrumentation Engineers (SPIE)
    • Design and fabrication of cascaded dichromate gelatin holographic filters for spectrum-splitting PV systems

      Wu, Yuechen; Chrysler, Benjamin; Kostuk, Raymond K.; Univ Arizona, Dept Elect & Comp Engn, Tucson, AZ 85721 USA; Univ Arizona, Coll Opt Sci, Tucson, AZ USA (SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 2018-01)
      The technique of designing, optimizing, and fabricating broadband volume transmission holograms using dichromate gelatin (DCG) is summarized for solar spectrum-splitting applications. The spectrum-splitting photovoltaic (PV) system uses a series of single-bandgap PV cells that have different spectral conversion efficiency properties to more fully utilize the solar spectrum. In such a system, one or more high-performance optical filters are usually required to split the solar spectrum and efficiently send them to the corresponding PV cells. An ideal spectral filter should have a rectangular shape with sharp transition wavelengths. A methodology of designing and modeling a transmission DCG hologram using coupled wave analysis for different PV bandgap combinations is described. To achieve a broad diffraction bandwidth and sharp cutoff wavelength, a cascaded structure of multiple thick holograms is described. A search algorithm is then developed to optimize both single-and two-layer cascaded holographic spectrum-splitting elements for the best bandgap combinations of two-and three-junction spectrum-splitting photovoltaic (SSPV) systems illuminated under the AM1.5 solar spectrum. The power conversion efficiencies of the optimized systems are found to be 42.56% and 48.41%, respectively, using the detailed balance method, and show an improvement compared with a tandem multijunction system. A fabrication method for cascaded DCG holographic filters is also described and used to prototype the optimized filter for the three-junction SSPV system. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)
    • Design form classification of two-mirror unobstructed freeform telescopes

      Trumper, Isaac; Anderson, Alexander Q.; Howard, Joseph M.; West, Garrett; Kim, Dae Wook; Univ Arizona, Wyant Coll Opt Sci; Univ Arizona, Dept Astron & Steward Observ (SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 2020-02-27)
      We present a general optical design survey of two-mirror unobstructed plane-symmetric freeform (FF) telescopes to provide a standardized framework and reference for further developments in the field of FF optics. We find that there are fundamentally two main design forms: those that use a positive tilt of the secondary and those that employ a negative rotation to achieve the unobstructed condition. Utilizing this survey, results can be categorized into simple groups of two-mirror unobstructed FF telescopes, analogous to the distinction between a Gregorian-type telescope and Cassegrain-type telescope. Allowing FF surfaces in optical design can enable more compact telescopes while potentially improving the image quality and allowing wider fields of view (FOVs). We define a FF optic as a nonrotationally symmetric mirror or lens, typically with large departures from a best- fit spherical surface (many microns or even millimeters). New manufacturing and testing methods have enabled the production of these types of surfaces. The telescopes we present maintain a 4:1 aspect ratio of the FOV and utilize X-Y polynomials for mirror surface description. We impose a plane symmetric constraint on the system and an accessible entrance pupil. We generate charts documenting the relationship between FOV and F/# for the presented optical design forms. We also compare our results to a baseline rotationally symmetric system. These results provide a general method of evaluating baseline designs for two-mirror unobstructed FF telescopes. (C) 2020 Society of Photo-Optical Instrumentation Engineers (SPIE).
    • Design of a practical model-observer-based image quality assessment method for x-ray computed tomography imaging systems

      Tseng, Hsin-Wu; Fan, Jiahua; Kupinski, Matthew A.; Univ Arizona, Coll Opt Sci; The University of Arizona, College of Optical Sciences, Tucson, Arizona 85721, United StatesbCT Engineering, GE Healthcare, Waukesha, Wisconsin 53188, United States; CT Engineering, GE Healthcare, Waukesha, Wisconsin 53188, United States; The University of Arizona, College of Optical Sciences, Tucson, Arizona 85721, United States (SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 2016-07-28)
      The use of a channelization mechanism on model observers not only makes mimicking human visual behavior possible, but also reduces the amount of image data needed to estimate the model observer parameters. The channelized Hotelling observer (CHO) and channelized scanning linear observer (CSLO) have recently been used to assess CT image quality for detection tasks and combined detection/estimation tasks, respectively. Although the use of channels substantially reduces the amount of data required to compute image quality, the number of scans required for CT imaging is still not practical for routine use. It is our desire to further reduce the number of scans required to make CHO or CSLO an image quality tool for routine and frequent system validations and evaluations. This work explores different data-reduction schemes and designs an approach that requires only a few CT scans. Three different kinds of approaches are included in this study: a conventional CHO/CSLO technique with a large sample size, a conventional CHO/CSLO technique with fewer samples, and an approach that we will show requires fewer samples to mimic conventional performance with a large sample size. The mean value and standard deviation of areas under ROC/EROC curve were estimated using the well-validated shuffle approach. The results indicate that an 80% data reduction can be achieved without loss of accuracy. This substantial data reduction is a step toward a practical tool for routine-task-based QA/QC CT system assessment. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)
    • Detection properties of photoconductive antennas fabricated on low-temperature-grown GaAs and ErAs:GaAs at subterahertz band

      Zhang, Jitao; Tuo, Mingguang; Liang, Min; Xin, Hao; Univ Arizona, Dept Elect & Comp Engn (SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 2020-01-25)
      Terahertz (THz) spectroscopy with high sensitivity is essential for biological application considering the strong absorption and scattering effects therein. As the most commonly used THz detector, the photoconductive antenna's (PCA) response greatly relies on the properties of the substrate's material. THz detection properties of the PCAs fabricated on low-temperature-grown GaAs (LT-GaAs) and ErAs:GaAs superlattices were compared at the sub-THz band. The detection efficiency of the PCAs with regard to incident laser power was characterized. In addition, using the PCAs as detectors, the signal-to-noise ratio (SNR) and dynamic range (DR) of a terahertz time-domain spectroscopy were quantified. The result indicates that the PCA detector with LT-GaAs has higher efficiency than the one with ErAs:GaAs. Consequently, the corresponding THz spectrometer has better SNR and DR. This result is contrary to the previous report, in which enhanced detection efficiency was observed with ErAs:GaAs-based PCA, which is probably due to the different structures of ErAs:GaAs superlattices used in the experiment. (C) 2020 Society of Photo-Optical Instrumentation Engineers (SPIE)