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A study of crosstalk in a 256 x 256 photon counting imager based on silicon Geiger-mode avalanche photodiodes

April 1, 2015
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Journal Article
Author:
Brian F. Aull
…
Published in:
IEEE Sens. J., Vol. 15, No. 4, April 2015, pp. 2123-32.
Topic:
photonics
R&D area:
R&D group:

Summary

We demonstrate a 256 x 256 passive photon counting imager based on hybridization of back-illuminated silicon Geiger-mode avalanche photodiodes to an all-digital CMOS counting chip. Photon detection efficiencies in the 10%-20% are observed at visible wavelengths. The detection efficiency is currently limited by optical crosstalk that leads to elevation of dark count rates as the bias voltage on the photodiodes is increased. Both the time dependence of dark count activity during a gate time and the spatial structure of dark images were successfully explained using crosstalk-based models.
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Summary

We demonstrate a 256 x 256 passive photon counting imager based on hybridization of back-illuminated silicon Geiger-mode avalanche photodiodes to an all-digital CMOS counting chip. Photon detection efficiencies in the 10%-20% are observed at visible wavelengths. The detection efficiency is currently limited by optical crosstalk that leads to elevation of...

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A study of crosstalk in a 256 x 256 photon counting imager based on silicon Geiger-mode avalanche photodiodes

Detection statistics in Geiger-mode avalanche photodiode quad-cell arrays with crosstalk and dead time

April 1, 2015
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Journal Article
Author:
Brian F. Aull
…
Published in:
IEEE Sens. J., Vol. 15, No. 4, April 2015, pp. 2133-43.
Topic:
optics
R&D area:
R&D group:

Summary

The detection statistics of Geiger-mode photodetector subarrays with a combination of reset-time blocking loss and optical crosstalk are investigated. Closed-form expressions are obtained for the means and covariances of the numbers of counts in 2 x 2 subarrays (quad cells) used in Shack-Hartmann wavefront sensors. The predicted wavefront sensing precision is compared with that obtained with a charge-coupled device-based wavefront sensor with readout noise. The results of the theory are also used to predict photon transfer curves for the Geiger-mode device and these are compared with experiment.
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Summary

The detection statistics of Geiger-mode photodetector subarrays with a combination of reset-time blocking loss and optical crosstalk are investigated. Closed-form expressions are obtained for the means and covariances of the numbers of counts in 2 x 2 subarrays (quad cells) used in Shack-Hartmann wavefront sensors. The predicted wavefront sensing precision...

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Detection statistics in Geiger-mode avalanche photodiode quad-cell arrays with crosstalk and dead time

Development and application of spherically curved charge-coupled device imagers

April 1, 2015
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Journal Article
Author:
James A. Gregory
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Published in:
Appl. Opt., Vol. 54, No. 10, 1 April 2015, pp. 3072-82.
Topic:
optics
R&D area:
R&D group:

Summary

Operation of a CCD imager on a curved focal surface offers advantages to flat focal planes, especially for lightweight, relatively simple optical systems. The first advantage is that the modulation transfer function can approach diffraction-limited performance for a spherical focal surface employed in large field-of-view or large-format imagers. The second advantage is that a curved focal surface maintains more uniform illumination as a function of radius from the field center. Examples of applications of curved imagers, described here, include a small compact imager and the large curved array used in the Space Surveillance Telescope. The operational characteristics and mechanical limits of an imager deformed to a 15 mm radius are also described.
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Summary

Operation of a CCD imager on a curved focal surface offers advantages to flat focal planes, especially for lightweight, relatively simple optical systems. The first advantage is that the modulation transfer function can approach diffraction-limited performance for a spherical focal surface employed in large field-of-view or large-format imagers. The second...

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Development and application of spherically curved charge-coupled device imagers

Measurement of ion motional heating rates over a range of trap frequencies and temperatures

April 1, 2015
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Journal Article
Author:
Colin D. Bruzewicz
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Published in:
Phys. Rev. A, At. Mol. Opt. Phys., Vol. 91, No. 4, April 2015, 041402.
Topic:
quantum
R&D area:
R&D group:

Summary

We present measurements of the motional heating rate of a trapped ion at different trap frequencies and temperatures between ~0.6 and 1.5 MHz and ~4 and 295 K. Additionally, we examine the possible effect of adsorbed surface contaminants with boiling points below ~105 degrees C by measuring the ion heating rate before and after locally baking our ion trap chip under ultrahigh vacuum conditions. We compare the heating rates presented here to those calculated from available electric-field noise models. We can tightly constrain a subset of these models based on their expected frequency and temperature scaling interdependence. Discrepancies between the measured results and predicted values point to the need for refinement of theoretical noise models in order to more fully understand the mechanisms behind motional trapped-ion heating.
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Summary

We present measurements of the motional heating rate of a trapped ion at different trap frequencies and temperatures between ~0.6 and 1.5 MHz and ~4 and 295 K. Additionally, we examine the possible effect of adsorbed surface contaminants with boiling points below ~105 degrees C by measuring the ion heating...

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Measurement of ion motional heating rates over a range of trap frequencies and temperatures

Cryptographically secure computation

April 1, 2015
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Journal Article
Author:
Emily H. Shen
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Published in:
Computer, Vol. 48, No. 4, April 2015, pp. 78-81.
Topic:
cryptography
R&D area:
R&D group:

Summary

Researchers are making secure multiparty computation--a cryptographic technique that enables information sharing and analysis while keeping sensitive inputs secret--faster and easier to use for application software developers.
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Summary

Researchers are making secure multiparty computation--a cryptographic technique that enables information sharing and analysis while keeping sensitive inputs secret--faster and easier to use for application software developers.

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Cryptographically secure computation

Permittivity evaluation of multilayered hyperbolic metamaterials: ellipsometry vs. reflectometry

March 14, 2015
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Journal Article
Author:
T. Tumkur
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Published in:
J. Appl. Phys., Vol. 117, No. 10, 14 March 2015, 103104.
Topic:
advanced materials
R&D area:
R&D group:

Summary

Metal-dielectric nanolaminates represent a class of hyperbolic metamaterials with uniaxial permittivity tensor. In this study, we critically compare permittivity extraction of nanolaminate samples using two techniques: polarized reflectrometry vs. spectroscopic anisotropic ellipsometry. Both Au/MgF2 and Ag/MgF2 metal-dielectric stacks are examined. We demonstrate the applicability of the treatment of the multilayered material as a uniaxial medium and compare the derived optical parameters to those expected from the effective medium approximation. We also experimentally compare the effect of varying the material outer layer on the homogenization of the composite. Additionally, we introduce a simple empirical method of extracting the epsilon-near-zero point of the nanolaminates from normal incidence reflectance. The results of this study are useful in accurate determination of the hyperbolic material permittivity and in the ability to tune its optical properties.
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Summary

Metal-dielectric nanolaminates represent a class of hyperbolic metamaterials with uniaxial permittivity tensor. In this study, we critically compare permittivity extraction of nanolaminate samples using two techniques: polarized reflectrometry vs. spectroscopic anisotropic ellipsometry. Both Au/MgF2 and Ag/MgF2 metal-dielectric stacks are examined. We demonstrate the applicability of the treatment of the multilayered...

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Permittivity evaluation of multilayered hyperbolic metamaterials: ellipsometry vs. reflectometry

Hyperspectral Microwave Atmospheric Sounder (HyMAS) - new capability in the CoSMIR/CoSSIR scanhead

March 7, 2015
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Conference Paper
Author:
Lawrence M. Hilliard
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Published in:
2015 IEEE Aerospace Conf., 7-14 March 2015.
Topic:
sensing
R&D area:
R&D group:

Summary

MIT Lincoln Laboratory and NASA's Goddard Space Flight Center have teamed to adapt an existing instrument platform, the CoSMIR/CoSSIR system for atmospheric sensing, to develop and demonstrate a new capability in a hyperspectral microwave atmospheric sounder (HyMAS). This new sensor comprises a highly innovative intermediate frequency processor (IFP), that provides the filtering and digitization of 52 radiometric channels and the interoperable remote component (IRC) adapted to CoSMIR, CoSSIR, and HyMAS that stores and archives the data with time tagged calibration and navigation data. The first element of the work is the demonstration of a hyperspectral microwave receiver subsystem that was recently shown using a comprehensive simulation study to yield performance that substantially exceeds current state-of-the-art. Hyperspectral microwave sounders with ~100 channels offer temperature and humidity sounding improvements similar to those obtained when infrared sensors became hyperspectral. Hyperspectral microwave operation is achieved using independent RF antenna/receiver arrays that sample the same area/volume of the Earth's surface/atmosphere at slightly different frequencies and therefore synthesize a set of dense, finely spaced vertical weighting functions. The second, enabling element is the development of a compact 52-channel Intermediate Frequency processor module. A principal challenge of a hyperspectral microwave system is the size of the IF filter bank required for channelization. Large bandwidths are simultaneously processed, thus complicating the use of digital back-ends with associated high complexities, costs, and power requirements. Our approach involves passive filters implemented using low-temperature co-fired ceramic (LTCC) technology to achieve an ultra-compact module that can be easily integrated with existing RF front-end technology. This IF processor is applicable to other microwave sensing missions requiring compact IF spectrometry. The unit produces 52 channels of spectral data in a highly compact volume (
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Summary

MIT Lincoln Laboratory and NASA's Goddard Space Flight Center have teamed to adapt an existing instrument platform, the CoSMIR/CoSSIR system for atmospheric sensing, to develop and demonstrate a new capability in a hyperspectral microwave atmospheric sounder (HyMAS). This new sensor comprises a highly innovative intermediate frequency processor (IFP), that provides...

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Hyperspectral Microwave Atmospheric Sounder (HyMAS) - new capability in the CoSMIR/CoSSIR scanhead

The 2013 Buffalo Area Icing and Radar Study (BAIRS)

March 6, 2015
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Project Report
Author:
Earle R. Williams
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Published in:
MIT Lincoln Laboratory Report ATC-419
Topic:
radar
R&D area:
R&D group:

Summary

The Next Generation Weather Radar (NEXRAD) network completed a dual polarization upgrade in 2013. The radars now can be used to sense the type of scatterers that cause the radar returns. The scatterers can be hydrometeors, biologicals, or earth-sourced. The ability to reliably interpret the radar-sensed thermodynamic phase of the hydrometeors (solid, liquid, mix) in the context of cloud microphysics and precipitation physics makes it possible to assess the icing hazard potential to aviation. That assessment for Federal Aviation Administration (FAA) purposes would necessarily be performed by automated algorithms based in hydrometeor classification terms. The truth as to the icing hazard aloft (where the radar scans) is required to ascertain the value of such algorithms. The Buffalo Area Icing and Radar Study (BAIRS) of 2013 was a partnership between MIT Lincoln Laboratory (LL) and the National Research Council of Canada (NRC) to perform in situ icing missions within the surveillance range of the dual polarization NEXRAD in Buffalo, NY. The goal of these 2013 missions, and the subject of this report, was to target specific winter weather scenarios known to exhibit an aviation icing hazard for the purpose of quantifying the microphysical properties of the target zones and verifying the presence of supercooled liquid water (SLW) to support validation of hydrometeor classification algorithms. These are the first such missions to execute in situ measurements within a NEXRAD's surveillance range running with the fielded, operational NEXRAD hydrometeor classifier. NRC's Convair-580 instrumented research plane was used for three icing missions covering 14 hours. Three distinctly different winter weather scenarios were encountered. This document details the analysis of in situ data such as particle type and liquid water content (LWC) with NEXRAD dual polarization parameters for the three missions. The BAIRS analysis identified these key findings: -NEXRAD radar returns are prevalent in conditions of supercooled water, -NEXRAD classification shows positive results based on particle imagery, -NEXRAD "dry snow" class masks the presence of mixed phase potential icing hazard, -NEXRAD "unknown" class contains diverse regions of icing hazard potential, and there are methods to classify some of these regions, and -In situ aircraft observations are an important tool to both verify algorithm performance and guide further development.
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Summary

The Next Generation Weather Radar (NEXRAD) network completed a dual polarization upgrade in 2013. The radars now can be used to sense the type of scatterers that cause the radar returns. The scatterers can be hydrometeors, biologicals, or earth-sourced. The ability to reliably interpret the radar-sensed thermodynamic phase of the...

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The 2013 Buffalo Area Icing and Radar Study (BAIRS)

Nanochannel fabrication based on double patterning with hydrogen silsesquioxane

March 1, 2015
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Journal Article
Author:
Kenneth A. Diest
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Published in:
J. Vac. Sci. Technol. B, Microelectron. Process. Phenon., Vol. 33, No. 2, March 2015, 020601.
Topic:
microelectronics
R&D area:
R&D group:

Summary

A double patterning process is presented to pattern sub-35 nm wide channels in hydrogen silsesquioxane with near 100% pattern densities. Using aligned electron beam lithography, each side of the nanochannel structure is patterned as a separate layer. A 50000 uC/cm^2 high-dose anneal is applied to the first layer after exposure. Channels with widths below ~60 nm are shown to exhibit footing with standard tetramethyl ammonium hydroxide developers. This problem is resolved by adding surfectant during the development of the final channel structure. The resulting process produced channels
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Summary

A double patterning process is presented to pattern sub-35 nm wide channels in hydrogen silsesquioxane with near 100% pattern densities. Using aligned electron beam lithography, each side of the nanochannel structure is patterned as a separate layer. A 50000 uC/cm^2 high-dose anneal is applied to the first layer after exposure...

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Nanochannel fabrication based on double patterning with hydrogen silsesquioxane

Measurements of differential reflectivity in snowstorms and warm season stratiform systems

March 1, 2015
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Journal Article
Author:
Earle R. Williams
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Published in:
J. Appl. Meteor. Climatol., Vol. 54, No. 3, 2015, pp. 573-95.
Topic:
aviation weather
R&D area:
R&D group:

Summary

The organized behavior of differential radar reflectivity (ZDR) is documented in the cold regions of a wide variety of stratiform precipitation types occurring in both winter and summer. The radar targets and attendant cloud microphysical conditions are interpreted within the context of measurements of ice crystal types in laboratory diffusion chambers in which humidity and temperature are both stringently controlled. The overriding operational interest here is in the identification of regions prone to icing hazards with long horizontal paths. Two predominant regimes are identified: category A, which is typified by moderate reflectivity (from 10 to 30 dBZ) and modest +ZDR values (from 0 to 13 dB) in which both supercooled water and dendritic ice crystals (and oriented aggregates of ice crystals) are present at a mean temperature of -13 degrees C, and category B, which is typified by small reflectivity (from -10 to +10 dBZ) and the largest +ZDR values (from +3 to +7 dB), in which supercooled water is dilute or absent and both flat-plate and dendritic crystals are likely. The predominant positive values for ZDR in many case studies suggest that the role of an electric field on ice particle orientation is small in comparison with gravity. The absence of robust +ZDR signatures in the trailing stratiform regions of vigorous summer squall lines may be due both to the infusion of noncrystalline ice particles (i.e., graupel and rimed aggregates) from the leading deep convection and to the effects of the stronger electric fields expected in these situations. These polarimetric measurements and their interpretations underscore the need for the accurate calibration of ZDR.
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Summary

The organized behavior of differential radar reflectivity (ZDR) is documented in the cold regions of a wide variety of stratiform precipitation types occurring in both winter and summer. The radar targets and attendant cloud microphysical conditions are interpreted within the context of measurements of ice crystal types in laboratory diffusion...

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Measurements of differential reflectivity in snowstorms and warm season stratiform systems
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