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NASA NTRS2010

Hypersonic Laminar Boundary Layer Velocimetry with Discrete Roughness on a Flat Plate

Laminar boundary layer velocity measurements are made on a 10-degree half-angle wedge in a Mach 10 flow. Two types of discrete boundary layer trips were used to perturb the boundary layer gas. The first was a 2-mm tall, 4-mm diameter cylindrical trip. The second was a scaled version of the Orbiter Boundary Layer Transition (BLT) Detailed Test Objective (DTO) trip. Both 1-mm and 2.5-mm tall BLT DTO trips were tested. Additionally, side-view and plan-view axial boundary layer velocity measurements were made in the absence of these tripping devices. The free-stream unit Reynolds numbers tested for the cylindrical trips were 1.7x10(exp 6)/m and 3.3x10(exp 6)/m. The free-stream unit Reynolds number tested for the BLT DTO trips was 1.7x10(exp 6)/m. The angle of attack was kept at approximately 5-degrees for most of the tests resulting in a Mach number of approximately 8.3. These combinations of unit Reynolds numbers and angle of attack resulted in laminar flowfields. To study the precision of the measurement technique, the angle of attack was varied during one run. Nitric-oxide (NO) molecular tagging velocimetry (MTV) was used to obtain averaged axial velocity values and associated uncertainties. These uncertainties are as low as 20 m/s. An interline, progressive scan CCD camera was used to obtain separate images of the initial reference and shifted NO molecules that had been tagged by the laser. The CCD configuration allowed for sub-microsecond sequential acquisition of both images. The maximum planar spatial resolution achieved for the side-view velocity measurements was 0.07-mm in the wall-normal direction by 1.45-mm in the streamwise direction with a spatial depth of 0.5-mm. For the plan-view measurements, the maximum planar spatial resolution in the spanwise and streamwise directions was 0.69-mm by 1.28-mm, respectively, with a spatial depth of 0.5-mm. Temperature sensitive paint (TSP) measurements are provided to compliment the velocity data and to provide further insight into the behavior of the boundary layers. The experiments were performed at the NASA Langley Research Center 31-Inch Mach 10 Air tunnel.

Bathel, Brett↗

NASA NTRS2004

Challenging Issues for On-orbit Calibration in the VIS and NIR

On-orbit calibration of Earth-observing sensors in the VIS and NIR spectral regions is usually performed using the sensors on-board devices such as internal lamp(s) or solar diffuser plate(s) to provide calibration parameters. For sensors with no (or with less reliable) on-board calibrators, lunar calibration or ground validation approaches are often used. Each of these has its own set of problems that need to be fully addressed in order to support high quality on-orbit calibration and characterization. Some science products, such as Ocean color, may impose more stringent requirements that demand greater calibration precision. This paper uses MODIS as an example to illustrate challenging issues involved in VIS and NIR on-orbit calibration. It focuses on the solar diffuser (SD) calibration approach, including the effects due to SD BRF, SD attenuation screen(s), and earthshine. The impact of optics (solar diffuser and scan mirror) on-orbit degradation, including changes in the sensor s response versus scan angle (RVS), on the calibration and subsequent data quality is also discussed.

Xiong, X.↗

NASA NTRS2005

Automated Extraction of Flow Features

Computational Fluid Dynamics (CFD) simulations are routinely performed as part of the design process of most fluid handling devices. In order to efficiently and effectively use the results of a CFD simulation, visualization tools are often used. These tools are used in all stages of the CFD simulation including pre-processing, interim-processing, and post-processing, to interpret the results. Each of these stages requires visualization tools that allow one to examine the geometry of the device, as well as the partial or final results of the simulation. An engineer will typically generate a series of contour and vector plots to better understand the physics of how the fluid is interacting with the physical device. Of particular interest are detecting features such as shocks, re-circulation zones, and vortices (which will highlight areas of stress and loss). As the demand for CFD analyses continues to increase the need for automated feature extraction capabilities has become vital. In the past, feature extraction and identification were interesting concepts, but not required in understanding the physics of a steady flow field. This is because the results of the more traditional tools like; isc-surface, cuts and streamlines, were more interactive and easily abstracted so they could be represented to the investigator. These tools worked and properly conveyed the collected information at the expense of a great deal of interaction. For unsteady flow-fields, the investigator does not have the luxury of spending time scanning only one "snapshot" of the simulation. Automated assistance is required in pointing out areas of potential interest contained within the flow. This must not require a heavy compute burden (the visualization should not significantly slow down the solution procedure for co-processing environments). Methods must be developed to abstract the feature of interest and display it in a manner that physically makes sense.

Dorney, Suzanne↗

NASA NTRS1996

Two-Photon Ghost Image and Interference-Diffraction

One of the most surprising consequences of quantum mechanics is entanglement of two or more distance particles. The two-particle entangled state was mathematically formulated by Schrodinger. Based on this unusual quantum behavior, EPR defined their 'physical reality' and then asked the question: 'Can Quantum-Mechanical Description of Physical Reality Be Considered Complete?' One may not appreciate EPR's criterion of physical reality and insist that 'no elementary quantum phenomenon is a phenomenon until it is a recorded phenomenon'. Optical spontaneous parametric down conversion (SPDC) is the most effective mechanism to generate an EPR type entangled two-photon state. In SPDC, an optical beam, called the pump, is incident on a birefringent crystal. The pump is intense enough so that nonlinear effects lead to the conversion of pump photons into pairs of photons, historically called signal and idler. Technically, the SPDC is said to be type-1 or type-2, depending on whether the signal and idler beams have parallel or orthogonal polarization. The SPDC conversion efficiency is typically on the order of 10(exp -9) to 10(exp -11), depending on the SPDC nonlinear material. The signal and idler intensities are extremely low, only single photon detection devices can register them. The quantum entanglement nature of SPDC has been demonstrated in EPR-Bohm experiments and Bell's inequality measurements. The following two experiments were recently performed in our laboratory, which are more closely related to the original 1935 EPR gedankenezperiment. The first experiment is a two-photon optical imaging type experiment, which has been named 'ghost image' by the physics community. The signal and idler beams of SPDC are sent in different directions, so that the detection of the signal and idler photons can be performed by two distant photon counting detectors. An aperture object (mask) is placed in front of the signal photon detector and illuminated by the signal beam through a convex lens. Surprisingly, an image of this aperture is observed in the idler beam, by scanning the idler photon detector in the transverse plane of the idler beam, if we are sure that the idler photon detector 'catches' the 'twin brother' of the signal, which can be easily performed by a coincidence measurement. This effect is even more striking when we found that the object-lens-image relationship satisfies the Gaussian thin lens equation. The second experiment demonstrates two-photon 'ghost' interference-diffraction. The experimental set up is similar to the image experiment, except that rather than a lens and an aperture it is a Young's double-slit (or a single-slit) inserted into the path of the signal beam. We could not find any interference (or diffraction) pattern behind the slit. Surprisingly, an interference (or diffraction) pattern is observed when scanning the detector in the idler beam, if we are sure that the idler photon detector 'catches' the 'twin brother' of the signal.

Shih, Y. H.↗

NASA NTRS2011

NASA Tech Briefs, September 2011

Topics covered include: Fused Reality for Enhanced Flight Test Capabilities; Thermography to Inspect Insulation of Large Cryogenic Tanks; Crush Test Abuse Stand; Test Generator for MATLAB Simulations; Dynamic Monitoring of Cleanroom Fallout Using an Air Particle Counter; Enhancement to Non-Contacting Stress Measurement of Blade Vibration Frequency; Positively Verifying Mating of Previously Unverifiable Flight Connectors; Radiation-Tolerant Intelligent Memory Stack - RTIMS; Ultra-Low-Dropout Linear Regulator; Excitation of a Parallel Plate Waveguide by an Array of Rectangular Waveguides; FPGA for Power Control of MSL Avionics; UAVSAR Active Electronically Scanned Array; Lockout/Tagout (LOTO) Simulator; Silicon Carbide Mounts for Fabry-Perot Interferometers; Measuring the In-Process Figure, Final Prescription, and System Alignment of Large; Optics and Segmented Mirrors Using Lidar Metrology; Fiber-Reinforced Reactive Nano-Epoxy Composites; Polymerization Initiated at the Sidewalls of Carbon Nanotubes; Metal-Matrix/Hollow-Ceramic-Sphere Composites; Piezoelectrically Enhanced Photocathodes; Iridium-Doped Ruthenium Oxide Catalyst for Oxygen Evolution; Improved Mo-Re VPS Alloys for High-Temperature Uses; Data Service Provider Cost Estimation Tool; Hybrid Power Management-Based Vehicle Architecture; Force Limit System; Levitated Duct Fan (LDF) Aircraft Auxiliary Generator; Compact, Two-Sided Structural Cold Plate Configuration; AN Fitting Reconditioning Tool; Active Response Gravity Offload System; Method and Apparatus for Forming Nanodroplets; Rapid Detection of the Varicella Zoster Virus in Saliva; Improved Devices for Collecting Sweat for Chemical Analysis; Phase-Controlled Magnetic Mirror for Wavefront Correction; and Frame-Transfer Gating Raman Spectroscopy for Time-Resolved Multiscalar Combustion Diagnostics.

Source record↗

NASA NTRS2005

Carbon nanotubes and nanowires for biological sensing

This chapter reviews the recent development in biological sensing using nanotechnologies based on carbon nanotubes and various nanowires. These 1D materials have shown unique properties that are efficient in interacting with biomolecules of similar dimensions, i.e., on a nanometer scale. Various aspects including synthesis, materials properties, device fabrication, biofunctionalization, and biological sensing applications of such materials are reviewed. The potential of such integrated nanobiosensors in providing ultrahigh sensitivity, fast response, and high-degree multiplex detection, yet with minimum sample requirements is demonstrated. This chapter is intended to provide comprehensive updated information for people from a variety of backgrounds but with common interests in the fast-moving interdisciplinary field of nanobiotechnology.

Review↗

NASA NTRS1999

Morphology and Structure of ZnO Films Synthesized by Off-Axis Sputtering Deposition

ZnO is a wide-band-gap oxide material that has many applications. A new potential application of ZnO material is for light emitting devices since its structure and electrical properties are similar to that of the GaN material (a blue laser candidate). It also is a good substrate for fabricating GaN-based devices. Off-axis sputtering technique has revealed great potential in synthesizing excellent oxide materials because the negative ion bombardment is greatly reduced when adatoms condense on substrates. The surface of films grown by off-axis sputtering will be much smoother than that produced in a regular sputtering configuration. A growth mechanism is studied by investigating the morphology and structure of ZnO films under different growth conditions and orientations. ZnO films are deposited on (0001) sapphire and quartz substrates by off- axis sputtering deposition at various oxygen/argon mixture ratios and pressures and at different temperatures. All films reveal highly textured structures on quartz substrates and epitaxial growth on sapphire substrates. Two off-axis configurations, vertical and horizontal orientations are conducted to study the process of film growth, surface morphology, and film structure. X-ray diffraction, scanning probe microscopy, and electrical measurements are used to characterize these films. Detailed results will be discussed in the presentation. Keywords: ZnO, Photonic material, Off-axis sputtering, Growth mechanism

Zhu, Shen↗

NASA NTRS1994

N2 Lyman-Birge-Hopfield dayglow from ATLAS 1

Spectral measurements of the far ultraviolet dayglow were made from the ATLAS 1 shuttle mission using an intensified charge coupled device (CCD) imaging spectrometer array. The instrument imaged relatively large (177 A) segments of the spectrum simultaneously and had the capability to image altitude in the second dimension of the two-dimensional focal plane detector when the entrance slit of the instrument was oriented perpendicular to the limb of the Earth. The far ultraviolet (FUV) channel of the instrument used a CsTe photocathode rather than the more conventionally used and more solar blind CsI photocathode material. As a result, the spectra were also measured with good sensitivity at FUV wavelengths longer than 1500 A. In this paper, data are selected of specific interest to a study of the N2 Lyman-Birge-Hopfield system using two shuttle attitudes: In the first the field of view was held at a fixed tangent ray height of approximately 140 km while scanning in wavelength, providing repeated FUV spectra over a range of latitudes and allowing comparison with our thermospheric airglow model. In the second observing sequence the line of sight of the instrument was scanned down through the atmosphere but covered about 75% of the full wavelength range. This sequence allows comparison of height dependence,including O2 absorption effects, with the thermospheric model. In all cases, relatively good agreement is obtained with the model (run strictly in a predictive mode) in comparisions in which the line of sight must be intergrated along a path that spans a considerable range of conditions (height, local time, latitude, solar zenith angle). In the case of the data sets examined in this study the vibrational population distributions show mixed results. In one case the distribution agrees well with a theoretical model based on direct electron impact excitation without a significant cascade contribution. A second case indicated a lower population in nu' = 3 and a higher population in nu' = 6 than would be expected from direct impact excitation alone. This supports previous indications that conditions resulting in the cascade mechanism may not always be operative.

Torr, Marsha R.↗

NASA NTRS1994

Long path monitoring of tropospheric O3, NO2, H2CO and SO2

Concentrations of tropospheric O3, NO2, H2CO, and SO2 have been measured on the Campus of the 'Universite Libre de Bruxelles' on a routine basis since October 1990. The long path system consists of a source lamp, a first 30 cm f/8 Cassegrain type telescope which collimates the light onto a slightly parabolic mirror placed on the roof of a building situated 394 m away from the laboratory. The light is sent back into a second 30 cm Cassegrain telescope. This telescope has been modified so that the output beam is a 5 cm diameter parallel beam. This beam is then focused onto the entrance aperture of the BRUKER IFS120HR fourier transform spectrometer. The two telescopes are mounted on alignment devices and the external mirror is equipped with a driving system operated from the laboratory. The choice of the light source (either a 1000 W high pressure 'ozone free' xenon lamp or a 250 W tungsten filament) and of the detector (either a solar blind UV-diode or a silicon diode) depended on the spectral region studied. These regions lie respectively from 26,000 cm(exp -1) to 30,000 cm(exp -1) (260-380 nm) and from 14,000 cm(exp -1) to 30,000 cm(exp -1) (330-700 nm). The spectra have been recorded at the resolution of 16 cm(exp -1) and with a dispersion of 7.7 cm(exp -1). They have been measured during the forward and the backward movements of the mobile mirror, in double sided mode; each spectrum is an average of 2000 scans. The time required to record a spectrum is about 45 minutes. The shape of the raw spectra in the two investigated regions are represented.

Vandaele, A. C.↗

NASA NTRS1991

Calibration of passive remote observing optical and microwave instrumentation; Proceedings of the Meeting, Orlando, FL, Apr. 3-5, 1991

Various papers on the calibration of passive remote observing optical and microwave instrumentation are presented. Individual topics addressed include: on-board calibration device for a wide field-of-view instrument, calibration for the medium-resolution imaging spectrometer, cryogenic radiometers and intensity-stabilized lasers for EOS radiometric calibrations, radiometric stability of the Shuttle-borne solar backscatter ultraviolet spectrometer, ratioing radiometer for use with a solar diffuser, requirements of a solar diffuser and measurements of some candidate materials, reflectance stability analysis of Spectralon diffuse calibration panels, stray light effects on calibrations using a solar diffuser, radiometric calibration of SPOT 23 HRVs, surface and aerosol models for use in radiative transfer codes. Also addressed are: calibrated intercepts for solar radiometers used in remote sensor calibration, radiometric calibration of an airborne multispectral scanner, in-flight calibration of a helicopter-mounted Daedalus multispectral scanner, technique for improving the calibration of large-area sphere sources, remote colorimetry and its applications, spatial sampling errors for a satellite-borne scanning radiometer, calibration of EOS multispectral imaging sensors and solar irradiance variability.

Guenther, Bruce W.↗

NASA NTRS1995

ZnO Films on {001}-Cut <110>-Propagating GaAs Substrates for Surface Acoustic Wave Device Applications

A potential application for piezoelectric films on GaAs substrates is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Knowledge of the SAW properties of the layered structure is critical for the optimum and accurate design of such devices. The acoustic properties of ZnO films sputtered on {001}-cut <110> -propagating GaAs substrates are investigated in this article, including SAW Velocity effective piezoelectric coupling constant, propagation loss. diffraction, velocity surface, and reflectivity of shorted and open metallic gratings. The measurements of these essential SAW properties for the frequency range between 180 and 360 MHz have been performed using a knife-edge laser probe for film thicknesses over the range of 1.6-4 micron and with films or different grain sizes. The high quality of dc triode sputtered films was observed as evidenced by high K(exp 2) and low attenuation. The measurements of the velocity surface, which directly affects the SAW diffraction, on the bare and metalized ZnO on SiO2, or Si3N4 on {001}-cut GaAs samples are reported using two different techniques: 1) knife-edge laser probe, 2) line-focus-beam scanning acoustic microscope. It was found that near the <110> propagation direction, the focusing SAW property of the bare GaAs changes into a nonfocusing one for the layered structure, but a reversed phenomenon exists near the <100> direction. Furthermore, to some extent the diffraction of the substrate can be controlled with the film thickness. The reflectivity of shorted and open gratings are also analyzed and measured. Zero reflectivity is observed for a shorted grating. There is good agreement between the measured data and theoretical values.

Kim, Yoonkee↗

NASA NTRS2001

Carbon Nanotubes Grown By CVD in Various Conditions

Since the superior properties of multi-wall carbon nanotubes (MWCNT) could be used in numerous devices such as electronics and sensors, many efforts have been engaged in synthesizing particular structural or dimensional MWCNT. This presentation will illustrate MWCNT synthesized on silicon substrates by thermal CVD. On the substrate, an array of catalysts is coated using sputtering deposition. A thin Ti buffer layer is also coated on some Si substrates prior to depositing catalyst particles. Nickel, cobalt or iron transition metals are used as catalysts for the MWCNT growth. Since the diameter of MWCNT depends on the size of catalyst particles, the catalyst particle size is investigated after annealed at various temperatures. MWCNT are grown on the substrate in the temperature range of 700 to 1000 C and the pressure range of 100 torr to one atmosphere. Methane and hydrogen gases with methane content of 10% to 100% are used for the MWCNT synthesis. Morphology, length and diameter of these MWCNT are determined by scanning electron microscopy and Raman spectroscopy. The detailed results of syntheses and characterizations will be discussed in the presentation.

Zhu, S.↗

NASA NTRS2001

Carbon Nanotubes Growth by CVD in Various Conditions

Since the superior properties of multi-wall carbon nanotubes (MWCNT could be used in numerous devices such as electronics and sensors, many efforts have been engaged in synthesizing particular structural or dimensional MWCNT. This presentation will illustrate MWCNT synthesized on silicon substrates by thermal CVD. On the substrate, an array of catalysts is coated using sputtering deposition. A thin Ti buffer layer is also coated on some Si substrates prior to depositing catalyst particles. Nickel, cobalt or iron transition metals are used as catalysts for the MWCNT growth. Since the diameter of MWCNT depends on the size of catalyst particles, the catalyst particle size is investigated after annealed at various temperatures. MWCNT are grown on the substrate in the temperature range of 700 to 1000 C and the pressure range of 100 torr to one atmosphere. Methane and hydrogen gases with methane content of 10% to 100% are used for the MWCNT synthesis. Morphology, length and diameter of these MWCNT are determined by scanning electron microscopy and Raman spectroscopy. The detailed results of syntheses and characterizations will be discussed in the presentation.

Zhu, S.↗

NASA NTRS1994

Holographic interferometric tomography for reconstructing flow fields

Holographic interferometric tomography is a technique for instantaneously capturing and quantitatively reconstructing three-dimensional flow fields. It has a very useful application potential for high-speed aerodynamics. However, three major challenging tasks need to be accomplished before its practical applications. First, fluid flows are mostly unsteady or at least non repeatable. Consequently, a means for Instantaneously recording three-dimensional flow fields, that is, a simple holographic technique for simultaneously recording multi-directional projections, needs to be developed. Second, while holographic interferometry provides enormous data storage capabilities, expeditious data extraction from complicated interferograms is very important for timely near real-time applications. Third, unlike medical applications, flow tomography does not provide complete data sets but instead involves ill-posed reconstruction problems of incomplete projection and limited angular scanning. During this summer research period, new experimental techniques and corresponding hardware were developed and tested to address the above mentioned tasks. The first task was achieved by diffuser illumination. This concept allows instantaneous capture of many projections with a conventional setup for single-projection recording. For the second task, a phase-shifting technique was incorporated. This technique allows one to acquire multiple phase-stepped interferograms for a single projection and thus to extract phase information from intensity data almost at real-time. For the third task, the research that has been extensively conducted previously was utilized. In this research period, a complete experimental setup that provides the above three major capabilities was designed, built, and tested by integrating all the techniques. A simple laboratory experiment for simulating wind-tunnel testing was then conducted. A test flow was produced by employing a relatively simple device that generated a gravity-driven flow. The flow was then experimentally investigated to check the viability of the holographic interferometric tomographic technique before wind-tunnel application.

Cha, Soyoung S.↗

NASA NTRS1988

CCD camera system for cometary research

The objective is to upgrade the NASA/GSFC 36 inch telescope instrumentation, primarily with a new charge coupled device (CCD) camera system, to permit an effective monitoring program of cometary activity by means of narrowband imaging and spectroscopic techniques. Researchers have twice taken delivery of the CCD camera system from Princeton Scientific Instruments and twice returned it within six weeks for repair. During the times they had the camera system in the lab, they measured the instrumental performance of the TEK 512 x 512 CCD chip (e.g., readout noise, dark current, etc) and developed the complete operational software for the camera system plus several useful observing and data reduction routines for use at the telescope. The CCD camera system is controlled by an IBM-AT computer. The peripheral equipment and software to permit the efficient transfer of large amounts of data to the LASP's computers (VAXs) and subsequent timely reductions are also in place. The Io torus (S II) emission was monitored with a Fabry-Perot scanning spectrometer, in conjunction with the International Jupiter Watch. The CCD camera system will be coupled to a narrowband interference filter imager and a long-slit spectrograph to provide regular and well-calibrated spatial and spectral observations of comets.

Oliversen, R. J.↗

NASA NTRS2001

Synthesis of Carbon Nanotubes Array by CVD

Since the properties of multi-wall carbon nanotubes (MWCNT) are superior in many devices such as electronics and sensors, many efforts have been involved in synthesizing particular structural or dimensional MWCNT. Uniform aligned MWCNT array is one of the prototype structures for devices such as filed emission device and microelectromechanical systems in which a large length to diameter ratio may also be required. Most aligned MWCNT recently synthesized by plasma enhanced chemical vapor deposition (CVD) have cone shaped structures. This presentation will illustrate aligned MWCNT array synthesized on silicon substrates using thermal CVD that could produce MWCNT with uniform diameter. An array of nickel particles was used as catalyst for MWCNT growth. A thin Ti or Au buffer layer was coated on the substrate prior to depositing nickel particles. Because the MWCNT size depends on the catalyst particle size, the nickel particle size annealed at various temperatures was investigated. MWCNT were grown on the substrate in the temperature range of 700 C - 1000 C and the pressure range of 1 to 300 torr. Methane and hydrogen gases with methane content of 1 - 10 % were used for the MWCNT synthesis. Morphology, length and diameter of MWCNT were determined by scanning electron microscopy and Raman spectroscopy. The detailed results of synthesis and characterizations will be discussed in the presentation.

Zhu, S.↗

NASA NTRS1995

ZnO films on /001/-cut (110)-propagating GaAs substrates for surface acoustic wave device applications

A potential application for piezoelectric films substrates is the monolithic integration of surface acoustic wave (SAW) devices with GaAs electronics. Knowledge of the SAW properties of the layered structure is critical for the optimum and accurate design of such devices. The acoustic properties of ZnO films sputtered on /001/-cut group of (110) zone axes-propagating GaAs substrates are investigated in this article, including SAW velocity, effective piezoelectric coupling constant, propagation loss, diffraction, velocity surface, and reflectivity of shorted and open metallic gratings. The measurements of these essential SAW properties for the frequency range between 180 and 360 MHz have been performed using a knife-edge laser probe for film thicknesses over the range of 1.6-4 micron and with films of different grain sizes. The high quality of dc triode sputtered films was observed as evidenced by high K(sup 2) and low attenuation. The measurements of the velocity surface, which directly affects the SAW diffraction, on the bare and metalized ZnO on SiO2 or Si3N4 on /001/-cut GaAs samples are reported using two different techniques: (1) knife-edge laser probe, (2) line-focus-beam scanning acoustic microscope. It was found that near the group of (110) zone axes propagation direction, the focusing SAW property of the bare GaAs changes into a nonfocusing one for the layered structure, but a reversed phenomenon exists near the (100) direction. Furthermore, to some extent the diffraction of the substrate can be controlled with the film thickness. The reflectivity of shorted and open gratings are also analyzed and measured. Zero reflectivity is observed for a shorted grating. There is good agreement between the measured data and theoretical values.

Hickernell, Frederick S.↗

NASA NTRS2019

Maturing Electron Multiplying Charge Coupled Device Photon-Counting with Variable Multiplication Gain Imaging for a Coronagraphic Instrument

This is an introduction to a US Government Program that conducted high-contrast imaging experiments with an Electron Multiplying Charge Coupled Device (EMCCD) in an interferometric coronagraph. This report will introduce the concepts of “Charge Blooming” and “Starlight Saturation” in the context of high-contrast astronomical imaging. These phenomena adversely affect the performance of high-contrast photon-counting instruments that do not use a mask to physically block starlight in the science channel of the coronagraph. The problems will be presented with the help of images taken with a commercial EMCCD camera in the Visible Nulling Coronagraph at the Goddard Space Flight Center (GSFC). A new clocking scheme for EMCCDs – Variable Multiplication Gain Clocking – will be proposed as a means for suppressing horizontal blooming and starlight saturation in an astronomical camera. This opening report from the program will conclude with an introduction to a new controller for high-contrast imaging with EMCCDs in coronagraphs. This controller is being designed to allow a single frame from an EMCCD to be scanned in multiple modes – photon counting and digitization – to enable direct imaging of an exo-planet and wavefront control of a coronagraph, simultaneously.

Udayan Mallik↗