Concept Study Report Preparation for SPHEREx MIDEX Phase A
SPHEREx is a planned NASA mid-range explorer (MID EX) that will perform an all-sky spectral survey of the in near-infrared bands. SPHEREx was recently selected for a Phase A study, and work is required to refine the instrument concept before a concept study report is due to NASA in mid-2018. This program funds activity at RIT to help refine details of the instrument, observation strategy, and to support publishing them as reports for NASA and the community.
THz Modeling and Testing
A group consisting of Harris engineers, RIT scientists, University of Rochester engineers and scientists designed and manufactured a room temperature silicon Complementary
metal–oxide–semiconductor (CMOS) imager for terahertz (THz) frequencies using metal-oxide semiconductor field effect transistors (MOSFETs). THz frequencies have been largely
unexplored due to high absorption within water, however there has been an increase in interest with the rise in high-altitude and space-based telescopes. Emission lines in
spectra within the THz regime exhibit cool molecular gas which traces protoplanetary disks and star formation rates within galaxies. This technology also has other applications
within the medical and security fields because of the nonionizing, non-harmful nature of THz radiation.
Enhancing the UV/VUV Sensitivity of CMOS Image Sensors
Charge-coupled devices (CCDs) and CMOS arrays have limitations in spectral sensitivity as delivered from the foundry. The front-side gate structure of a CCD is absorptive at
ultraviolet (UV) wavelengths. For high efficiency, CCDs are back illuminated, which is expensive to do, and unfortunately the Si substrate is highly reflective. Additionally,
UV photons have a very short absorption length in silicon. The electron–hole pairs produced by the photon interaction are trapped at the back surface and therefore never reach
the accumulation phase gate. These issues have resulted in difficulty in producing efficient CCD-based UV/Far UV (FUV) detectors. Delta doped back illuminated CCDs are the best
solution to this problem. Anti-reflection (AR) coating the CCD is difficult in this spectral region as the coatings available only provide improvement over a narrow spectral region.
This is especially concerning for application in UV/FUV spectroscopy where a wide spectral range needs to be recorded simultaneously (e.g., in UV plasma spectroscopy).
Imaging Polarimetry with Microgrid Polarizers
Polarization is an intrinsic property of light, like frequency or coherence. Humans have long benefited from our ability to distinguish light of different frequency based on its color.
However, our eyes are not sensitive to the polarization of light. Devices to measure polarization are relatively rare and expertise in polarimetry even more so. Polarization sensors
based on micropolarizer arrays appear to be the first devices capable of bringing polarimetric capability to a wide range of applications. Whereas previous polarimeters were built to
perform very specific measurements, the same micropolarizer-based camera can be used on a telescope, a microscope, or with a conventional camera lens.
The Development of Digital Micromirror Devices for use in Space
This project is developing a commercially-available Digital Micromirror Device (DMD) with an ultraviolet transparent window suitable for use in a multi-object spectrograph (MOS) in a future
NASA Explorer Mission (Figure 9). A large spectroscopic survey requires a MOS capable of recording the spectra of hundreds of galaxies in a single exposure. The MOS must have adjustable slits
to eliminate confusion with nearby sources and to block out unwanted zodiacal background, which would otherwise swamp the light from these faint galaxies. The MOS should have access to the
far-ultraviolet (120-200 nm) radiation emitted by a z~1 galaxy because this spectral region has a rich set of diagnostics of stars, gas, and dust in the galaxy. Access to the blue-red spectral
regions (200-800 nm) is also essential for determining the precise redshift of a galaxy, its stellar mass, abundances of the elements, and for characterizing dust extinction. Because the light
from a z~1 galaxy is redshifted before reaching us, a large spectroscopic survey should be sensitive over the spectral interval, 200-1600 nm.
Integrated Quantum Photonics for Photon-Ion Entanglement
The primary objective of this project is the realization of an integrated photonics platform compatible with photon-ion entanglement. The platform will consist of photon sources and entangling
circuits that interface with the visible/UV wavelengths of ion (such as Yb+, Ca+, Be+, Mg+, Sr+, Ba+, Zn+, Hg+ and Cd+) transitions. The challenge with realizing such a platform is that integrated
photonic chips are not well developed at visible wavelengths because of the traditional focus on telecom wavelength compatibility. We are developing a platform that does operate at short wavelengths
by using Aluminum Nitride (AlN), which is a large bandgap semiconductor that is transparent to the deep-UV (see Figure 14). In parallel, we are leveraging our successes in quantum integrated photonics
in telecom-compatible platforms, particularly silicon photonics. This will allow rapid validation of high performance photon sources, entanglement circuits and quantum sensors. These circuits will then
be transitioned to the new visible/UV platform, or interfaced with ions directly by using frequency conversion
Quantum Optical Resonators: a building block for quantum computing and sensing systems
The overall goal of this project is to experimentally demonstrate the quantum optical response of ring resonators and use them as a robust building block for quantum information processing. We have
shown that ring resonators operating in the quantum regime exhibit a resonant response that depends on the photon state. Unlike beam splitters, which operate with maximum fidelity with only one set
of parameters, the unique passive feedback in ring resonators ensures high fidelity quantum interference over effectively an infinite device parameter space. The devices compact size and ability to
be reconfigured dynamically with low energy requirements ensures that ring resonators are the ideal building block for realizing complex quantum optical circuits.
Bifacial III-V Nanowire Array on Si Tandem Junctions Solar Cells
Escalating trends in global energy consumption, mandates for increased national energy independence, and mounting alarm regarding anthropogenic climate change all demand improved sustainable energy
solutions. While the theoretical power generation potential of solar photovoltaics (PV) in the United States is greater than the combined potential of all other renewable resources, substantial market
penetration of PV sand realization of grid-parity have been obstructed by high materials and manufacturing costs, as well as limitations in solar power conversion efficiencies (PCE). A pressing need
exists for tandem solar cells utilizing two dissimilar materials (TDM) or more that are capable of PCE values beyond the ~30% Shockley-Queisser limit. In this program we explore a transformative,
bifacial solar cell design that employs arrays of TDM III-V compound semiconductor nanowires in tandem with a thinned, intermediate Si sub-cell. The use of epitaxial nanowire arrays overcomes the
lattice matching criteria and enables direct III-V on Si monolithic integration. This design eliminates the need for high-cost wafers, growth of graded buffer layers, and anti-reflection coatings,
while permitting ideal solar spectrum matching and capture of albedo radiation. The high risk-high payoff and exploratory research fits the NSF EAGER program, as it involves a radically unconventional
approach with transformative potential to enable cost-effective manufacturing of high-efficiency TDM solar cells.
High Performance Integrated InAs Quantum Dot Laser Based Si Photonics Optical Transceiver
The project is focused on the realization of high performance optical transceivers integrated onto a silicon chip using robust InAs quantum dot lasers. Specifically, this project will overcome one of
the largest challenges in silicon photonics, which is the seamless integration of robust and low-powered lasers with other silicon photonics devices, where the lasers need to operate at relatively high
ambient temperatures (70-80 °C) and the emission wavelengths need to be varied to achieve a multichannel laser array with large transmission bandwidth. Our approach is to bond III-V heterostructures that
contain quantum dots onto silicon substrates. Quantum dots (QD) possess 3D confinement and delta-function like density-of-states (DOS), and as a result, and unlike their quantum well counterparts, have
good temperature stability, low power consumption, high differential gain, and zero chirp and a-factor. In addition, they are spectrally broad due to large size distribution of the quantum dots, and as
a result can be used to realize broadband laser sources. Furthermore, in order to realize high gain, and as a result low threshold power, we are uniquely aiming to directly integrate the lasers to
waveguides through a butt-joint waveguide coupling scheme, as seen in Figure 16. This will enable all of the transceiver components to be integrated into the same plane, significantly increasing
performance and decreasing the overall footprint – in turn, allowing denser integration for overall higher bandwidth at lower powers.
Multi-Color Anisotropy Measurements of Cosmic Near-Infrared Extragalactic Background Light with CIBER2
The Rochester Institute of Technology team is responsible for the delivery of a cryogenically-operable star tracking camera for attitude control of the CIBER-2 payload.
RIT is building, testing, and delivering this camera to Caltech for integration into the full experiment by the beginning of Year 2.
RIT is also responsible for delivering the associated documentation and interface information to both Caltech and NASA by the end of Year 2.
The RIT team is also responsible for assisting with: (1) overall instrument design; (2) integration of the payload system; (3) laboratory testing and characterization;
(4) flight planning and logistical requirements; (5) deployment and flight efforts; (6) data reduction and calibration; and (7) science extraction.
Understanding and Engineering Valence Band Structures of III-Nitride Semiconductors for High-Efficiency Ultraviolet Lasers and Emitters
The Center for Detectors is developing solutions to key challenges in achieving high-efficiency single-mode GaN-based ultraviolet (UV) lasers with wavelength ranging from 220 nm up to 300 nm.
Particularly, the research focuses on the fundamental physics understanding of the valence band structure of lll-Nitride wide bandgap gain active region,
and develop promising solutions on nanostructured quantum wells and fabrication approach of large area GaN-based UV laser arrays.
These lasers are a promising candidate for various naval applications in sensing and communication.
MRI: Acquisition of an Inductively Coupled Plasma Reactive-Ion Etching System for Research and Education in Nanophotonics, Nanoelectronics and Nano-Bio Devices
This Major Research Instrumentation (MRI) funding is supporting the acquisition of an inductively coupled plasma reactive-ion etching (ICP-RIE) system
to enable fundamental research and education in nanophotonics, nanoelectronics and nano-bio devices. The objective of this MRI acquisition is to facilitate new and existing multidisciplinary research
in science and engineering, enable educational curriculum development, and promote outreach activities at Rochester Institute of Technology (RIT).
The ICP-RIE system has the capability for photonic, electronic and bio device fabrication that does not exist presently at RIT and Rochester region.
The ICP-RIE system provides dry etching capability for various material systems such as compound semiconductors, dielectric materials, and metals with fast etching rate, well-controlled selectivity, and promising uniformity. The instrument is essential to enable fundamental research and education on III-Nitride based light emitting diodes (LEDs) and lasers, seamless integration of robust and low-powered III-V quantum dot (QD) lasers with silicon photonics, III-V tunneling field effect transistor, memory devices for computing, QD and nanowire photovoltaics, III-Nitride photodetectors for inertial confinement fusion research, nanoplasmonic devices, and nan-bio devices for efficient biomolecule transfer. The instrument will be the first ICP dry etcher tool at RIT, which will be shared by research groups across all disciplines in science and engineering with students trained from Microsystems Engineering Ph.D. program and Ph.D. in Engineering program. The tool will also be shared by external research groups in Rochester region to enhance research and collaborations between RIT and other colleges, national labs, and small businesses in the region.
The ICP-RIE system will be designated as a shared user facility, available to new curriculum and lab section development on device fabrications for both undergraduate and graduate students at RIT, whom can be trained for next-generation scientists and engineers. The fabrication capability provided by the proposed instrument benefits curriculum development at RIT for several fundamental courses and lab sections focused on nanofabrication and semiconductor devices. Demonstration experiments on photonic and electronic devices can also be designed to K-12 students and teachers through RIT outreach activities by the use of the dry etcher, which can stimulate K-12 students' interest to pursue science, technology, engineering, and mathematics (STEM) disciplines in the future. Connectivity with such demonstration experiments will also be promoted to train existing women and underrepresented minority students at RIT.
AIM Academy Photonic Integrated Circuit Design and Test Education Curricula
This project's long-term objective is the creation of a workforce of proficient integrated photonic circuit designers.
There is a clear industry need for designers that are able to utilize Electronic Photonic Design Automation (EPDA) methodologies to effectively design functional photonic-electronic circuitry
to drive the integrated photonics industry into the future. The primary goal of this project is to meet this need with the creation of integrated photonic circuit design/test content
to enable educators to teach students and industrial practitioners the principles, methodologies and practical knowledge of integrated photonic circuit design.
AIM Photonics TAP004 and TAP005 (Test Assembly and Packaging Hub Planning)
Planning activities and start up for Rochester Hub for test, assembly and packaging.
Selective Area Epitaxy on Foreign Substrates
The growth of various nanostructures, including nanowires and nanofins, by metal-organic chemical vapor deposition (MOCVD) is investigated through a unique crystal synthesis process
known as selective area epitaxy (SAE). The SAE method relies on an oxide template with predefined windows that specify the location of preferential epitaxial atomic assembly.
Growth rate enhancement, as defined by the oxide template, allows for the controlled epitaxy of arrays of vertical, III-V compound semiconductor nanostructures
without the use of foreign catalytic or seeding agents. Based on the SAE technique, the EINS lab has demonstrated growth of InAs, InGaAs, GaAs, GaAsP, and GaP nanowire and nanofin arrays
on Si substrates with 100% yield over large, wafer-scale areas. Our current projects aim to understand the growth kinetics of III-V nanosystems interfaced with Si and 2-dimensional nanomaterials
such as graphene and monolayer transition metal dichalcogenides; to characterize the novel material properties offered by these hybrid nanosystems;
and to demonstrate their utility in innovative photovoltaics and optoelectronics solutions.
MacEtch of III-V Compounds Using Alternative Catalysts
Metal-assisted chemical etching (MacEtch) is an anisotropic, solution-based nanofabrication process that combines the benefits of conventional wet-etching and plasma-based ion etching.
The MacEtch process relies on site-specific, catalytic oxidation of a semiconductor surface by a patterned noble metal layer, followed by preferential dissolution of the selectively oxidized regions.
Continuous repetition of oxidation-dissolution cycles in a single MacEtch bath results in the metal layer sinking into the semiconductor such that vertical nanostructures are left in the path of the metal layer,
having geometries that are complementary to the geometry of the patterned metal. In the EINS lab, we are interested in exploring the fabrication of III-V semiconductor nanostructures
using non-conventional metallic catalysts composed of carbon-nanotubes and graphene. In this manner we define novel nanofabrication paradigms that enable low-cost and clean alternatives to conventional
ion-based etching procedures, offering high-aspect ratio features with atomically-abrupt sidewall termination. Novel device applications in high-efficiency solid-state lighting
and tri-gated nanofin-based field effect transistors have already been demonstrated using on MacEtch fabrication.
Cosmic Radiation Damaged Image Repair project (CRDIR)
RIT has embarked on the Cosmic Radiation Damaged Image Repair project (CRDIR) involving Dr. Donald Pettit, NASA Astronaut & International Space Station astrophotographer.
This project is being conducted by graduate and undergraduate student researchers under the guidance of Dr. Donald Figer, Director of CfD.
Students have a unique opportunity to communicate with an active American astronaut in the process of solving a significant image processing issue. The scientific process these students follow toward a solution provide valuable experience that these students will carry with them in their professional lives.
RIT is providing a sophisticated “image enhancement” software program which specifically addresses degraded images taken by astronauts “on orbit”, extending the useful lives of cameras, and in many cases making unacceptable “noisy” images visually acceptable.
Characterization of Inter-Pixel Capacitive Coupling in Hybridized HgCdTe Arrays
Inter-Pixel Capacitance (IPC) is a mechanism for deterministic electronic cross talk that results from coupling fields between adjacent pixels as a signal is collected and stored. Simulation of small arrays from first principles using software which simultaneously solves Poisson's equation and the Drift Diffusion equations allows for characterization of this coupling across a broad range of design parameters as well as across various environment parameters. Due to the deterministic nature of this cross-talk characterization results in correction.
This project is currently working on characterization of HgCdTe arrays hybridized using indium bumps to H2RG readout circuits akin to those to be used in the James Webb Space Telescope's (JWST) NIRcam. Successful characterization across environment parameters will result in an increase in final image quality from JWST's NIRcam and any device using a similar detector while also introducing new design considerations for future generations of sensor.
Development of Si-MOSFET CMOS Technology for Terahertz Detection
RIT is developing a silicon MOSFET CMOS imager to detect terahertz (THz) frequencies in a collaboration with the Center for Emerging and Innovative Sciences (CEIS) at the University of Rochester and Exelis Geospatial Systems. Creating an asymmetrical design within the FETs, increases the THz response. The current device being tested was designed with 15 individual test transistors with varying design dimensions and antennas along with an array of transistors for an imager. These test structures are being evaluated at RIT to determine the best design for terahertz detection for future imager designs. An advantage of this detector technology is that these MOSFETs do not have to be cooled to extreme temperatures like microbolometers. This project's goal is to advance knowledge of the detection mechanism, lead to the creation of an integrated imaging system, and has many different applications.
THz frequencies have been largely unexplored due to high absorption within water, however there has been an increase in interest with the rise in high-altitude and space-based telescopes. Emission lines in spectra within the THz regime exhibit cool molecular gas which traces protoplanetary disks and star formation rates within galaxies. This technology also has other applications within the medical and security fields because of the non ionizing, non-harmful nature of THz radiation.
Phase II: New Infrared Detectors for Astrophysics
This program will have a profound impact across ground-based and space-based astronomy by dramatically reducing the cost of infrared detectors for existing facilities,
as well as the next generation of extremely large telescopes. The project is continuing development of a new material system for use in astronomical infrared array detectors.
The devices use HgCdTe grown on Silicon using Molecular Beam Epitaxy. In Phase I of this project, the NSF ATI program funded two cycles of design, fabrication, and testing.
The devices made in this phase of the project show that the technology can meet the astronomy requirements pending further development.
Testing shows that there are several challenges that prevent the devices in hand from satisfying these requirements. In this second phase, the Center for Detectors
is developing a series of devices with improved design and processing. The approach is to reduce the number of material defects while maintaining high short-wavelength quantum efficiency
by using proven designs. Given that these previous designs have successfully been used to address the observed non-idealities, it is believed that the new activities will be successful.
The work includes: growth of new material using a thick buffer layer design, fabrication of twelve FPAs in two designs, and extensive testing between the fabrications of the two designs.
This project is advancing the knowledge of a material system that has great promise for infrared detector technology. It is also enhancing the capabilities of infrared instrumentation in astronomy by reducing cost and potentially improving performance when compared to what is available with existing technology. The technical approach has great merit because it was developed over the past 15 years and during Phase I of the project. The plan features a tight connection between design at Raytheon Vision Systems (RVS) and testing in the Center for Detectors at the Rochester Institute of Technology, continuing over 15 years of collaboration between RVS and the PI.
Measuring the Pixel Response Function of Kepler CCDs to Improve the Kepler Database
Stellar images taken with telescopes and detectors in space are usually undersampled, and to correct for this, an accurate pixel response function is required.
The standard approach for HST and KEPLER has been to measure the telescope PSF combined ("convolved") with the actual pixel response function,
super-sampled by taking into account dithered or offset observed images of many stars. This combined response function has been called the "PRF".
However, using such results has not allowed astrometry from KEPLER to reach its full potential. Given the precision of KEPLER photometry,
it should be feasible to use a pre-determined detector pixel response function (PRF) and an optical point spread function (PSF) as separable quantities to more accurately correct photometry
and astrometry for undersampling. Wavelength (i.e. stellar color) and instrumental temperature should be affecting each of these differently.
Discussion of the PRF in the "KEPLER Instrument Handbook" is limited to an ad-hoc extension of earlier measurements on a quite different CCD. It is known that the KEPLER PSF typically has a sharp spike in the middle, and the main bulk of the PSF is still small enough to be undersampled, so that any substructure in the pixel may interact significantly with the optical PSF.
Both the PSF and PRF are probably asymmetric. The Center for Detectors is measuring the PRF for an example of the CCD sensors used on KEPLER at sufficient sampling resolution to allow significant improvement of KEPLER photometry and astrometry, in particular allowing PSF fitting techniques to be used on the data archive.
Quantum Silicon Photonics Measurement System
The Center for Detectors received funds for a measurement system to enable Quantum Silicon Photonics research. The system consists of a low-noise tunable laser and single photon detectors.
Integrated Photonics Education at RIT
The objective of this project is to support AIM Academy (the education arm of AIM Photonics) by providing education modules for integrated photonics design,
manufacturing, packaging and testing. We are also working to educate students, workforce, veterans and the community with: short courses, degree courses, establish an integrated photonics practice facility,
assess workforce needs and develop an ME degree in Integrated Photonics Manufacturing in collaboration with MIT.
A Cryogenic Optical Camera for Attitude Control of Low-Temperature Sub-Orbital Payloads
Charge coupled detectors (CCDs) are inoperable below 120K due to electron freeze-out effects and therefore, problematic in cryogenic applications.
An alternative optical sensing technology, the scientific complementary metal-oxide-semiconductor (sCMOS) detector, offers the possibility of mega-pixel science-grade optical cameras operable to - IOK.
The promise of a fully cryogenic optical detector is a compelling technology for NASA because it does not require active heating in the space environment.
Such a detector enables instruments ranging from actively-cooled star trackers for sounding rockets to low-temperature deep space cameras.
As a first step, The Center for Detectors is developing and flying an attitude-sensing camera employing a low noise, high quantum efficiency cryogenic sCMOS detector on a Black Brant IX sub-orbital vehicle.
Images from the T=77K 5.5 mega-pixel sensor is processed by on-board software and pointing information is used to dynamically control the attitude of the payload with gyroscopes.
The instrument design, fabrication, flight operations and data analysis is being performed by a diverse, multi-disciplinary team of undergraduate students to provide hands-on experience on a flight project
under the leadership of a graduate student mentor and an experienced PI. The students are responsible for mechanical, optical, and electronic engineering activities; firmware and algorithm development;
flight planning and operations; and project management, documentation control, and reporting. Following a successful initial flight, this system will fly on a NASA astrophysics payload to measure extragalactic light
from the cosmic infrared background.
A Data Analysis Pipeline Simulator for a Millimeter-Wavelength Imaging Spectrometer
The Center for Detectors is conducting a design study for software and data analysis for the Tomographic Ionized-carbon Mapping Experiment (TIME-Pilot) instrument,
which is designed to make pioneering measurements of the redshifted 157.7 micron line of singly ionized carbon [CIIJ from the Epoch of Reionization (EoR).
The EoR is the period in the Universe's history during which the first stars and galaxies formed, and whose intense ultra-violet (UV) radiation fields ionized the intergalactic medium.
The New Worlds, New Horizons 2010 Astrophysics Decadal Report recognized the EoR as one of five scientific discovery areas where "new technologies, observing strategies, theories, and computations open
. . . opportunities for transformational comprehension". This investigation is breaking ground for future investment from government and private funding agencies
by improving our understanding of the instrument design and expected performance.
Air Force STTR Phase 1 AF16-AT01: "Wafer-Level Electronic-Photonic Co-Packaging"
This program is developing flexible, low-cost packaging techniques for largescale, integrated optoelectronic systems based on heterogeneously integrated photonic and electronic chips.
Ultracompact Graphene Optical Modulators
The objective of this research is to explore ultracompact graphene optical modulators for future on-chip optical communications.
The approach is to systematically explore the unique electro-optic properties of graphene, and to greatly enhance the interaction of graphene with light based on novel waveguides and platforms.
In particular, graphene in a waveguide can be tuned with anomalous optical properties with a suitable gate voltage, which is being employed to develop the modulators.
This project is systematically exploring novel graphene-sandwiched optical waveguides based on the unique properties of graphene. This research is one of the first experimental attempts to demonstrate optical modulators at nanoscale, and one of the first systematic explorations of graphene for all-optic modulation. The research results may revolutionize nanophotonic technology and on-chip optical interconnects, and contribute to the fundamental theory and techniques for newly developed Graphene Optoelectronics and Graphene and 2D Semiconductor Physics.
Graphene is a topic that is of great interest to the general public. The outreach activity, "From Graphite to Graphene", is helping STEM education by introducing K-12 students to the science and fabrication of nanotechnology for a wide range of applications. The students involved in this research are participating in nanotechnology development, and the results developed from the research activities will be incorporated into several college courses. Collaboration with external companies may commercialize valuable products for industrial and military applications. Under-represented students from Women in Engineering and North Star Program are involved in this project.
Single Photon Counting Detectors for NASA Astronomy Missions
Single photon counting detectors have the potential to be the next big advancement for NASA astronomy missions. The ability to count single photons facilitates science goals that are impossible even with current state-of-the-art detectors. Single photon counting detectors are the future, and many different implementations are in development. In the next 20 years, many NASA missions requiring single photon counting will be proposed, but which single photon counting detector implementations best suit the performance needs of NASA’s astronomy programs? The goal of the proposed research is to characterize (theoretically and physically) three unique implementations of single photon counting detectors, benchmark their operation over a range of performance characteristics, and provide comprehensive justification for the superiority of one of the implementations for each of these NASA astronomy applications: exoplanet detection, high-contrast imaging, adaptive optics, and array-based LIDAR.
The research plan in this project includes simulation, characterization, and evaluation of the performance of three types of semiconductor photon counting detectors for use in NASA astronomy missions: Geiger-mode (GM) APDs, linear-mode (LM) APDs, and Electron Multiplying (EM) CCDs.
The main goal of this project is to provide the basis of comparisons for several types of fundamentally different single photon counting detectors by producing a table of comparisons and recommendations for various applications. All detectors must be sensitive to single photons, be scalable to large array formats, and have high QE (in the visible, UV, NIR, IR, and Far-IR wavelengths). This research is advancing preliminary work by adding new characterization methods and performance benchmarks, and by comparing the different devices at predetermined milestones during the project. The recommended detector(s) should function well at high readout frequencies without significant read noise (leading to improved temporal sampling), have very low noise for increased SNR at low fluence levels, and be implemented (or able to be in the near future) on large arrays. Even though single-photon counting detectors share a common performance benchmark (discerning individual quanta), differences between various implementations make some more efficient than others.
New Infrared Detectors for Astrophysics
Infrared arrays with HgCdTe as the light-sensitive layer, such as have been developed up to sizes 2048x2048 pixels for the James Webb Space Telescope, are near-ideal detectors for imaging and spectroscopy in the region ~1-5 microns. However current construction requires fabrication on CdZnTe substrates, which are expensive and limited in availability. The key to making larger (up to 14,000x14,000 pixels) and less expensive infrared detectors lies in using silicon wafer substrates, since large silicon wafers are common in the high volume semiconductor industry and their coefficient of thermal expansion is well-matched to that of the silicon readout circuits.
While the use of silicon substrates has been a major goal in the field of developing infrared detectors, the main limitation over the past 15 years has been the large lattice spacing mismatch between silicon and commonly-used infrared light-sensitive materials. The mismatch causes defects that can result in higher dark current, or valence holes that lead to reduced quantum efficiency and image persistence.
Enlisting the expertise and fabrication capabilities of Raytheon Vision Systems, detector expert Dr. D. Figer of the Rochester Institute of Technology plans to deposit the HgCdTe light-sensitive layer on silicon using the very promising technique of Molecular Beam Epitaxy (MBE). By maintaining vacuum during MBE processing, defect density has been shown to be reduced and the resulting prototype devices have achieved the anticipated performance. Very large, affordable infrared arrays is essential for making optimum use of the proposed ~30m class ground-based telescopes and their availability has clear implications for fields beyond astronomy, including medical imaging and remote sensing.
A Zero Read Noise Detector for Thirty Meter Telescope (TMT)
The key objective of this project is to develop a new type of imaging detector to enable the most sensitive possible observations with the world’s largest telescopes, i.e. the TMT. The detector will effectively quadruple the collecting power of the TMT, compared to detectors currently envisioned in TMT instrument studies, for the lowest light level observations. It would have fundamental importance in ground-based and space-based astrophysics, Earth and planetary remote sensing, exo-planet identification, consumer imaging applications, and homeland safety, among many others. Measurable outcomes include being able to see further back into the infancy of the Universe to taking a better picture (less grainy) of a smiling child blowing out the candles at her birthday party. The detector will be quantum-limited (zero read noise), be resilient against the harsh effects of radiation in space, consume low power, operate over an extremely high dynamic range, and be able to operate with exposure times over one million times faster than typical digital cameras. The RIDL is teaming with MIT/Lincoln Laboratory to leverage their Geiger-mode Avalanche Photodiode technology for developing the imaging detector. The project is funded through the Gordon and Betty Moore Foundation.
A Photon Counting Detector for Exoplanet Missions
The objective of this project is to advance photon-counting detectors for NASA exoplanet missions. A photon counting detector can provide zero read noise, ultra-high dynamic range, and ideal linearity over the relevant flux range of interest. It could be the best realizable detector for a planet finding spectrograph, and it would have outstanding properties as a wavefront sensor or detector in the imaging focal plane. The benefit of this device is that it dramatically improves the sensitivity beyond what is capable with non-photon counting detectors, thereby increasing science return for a fixed mission life; for low-light-level cases, such as spectroscopy, the device can reduce the necessary exposure time for detecting planetary features by 50-80%. The device always operates in photon counting mode and is thus not susceptible to excess noise factor that afflicts other technologies. It continues operating with shot-noise limited performance up to extremely high flux levels. Its performance is expected to be maintained at a high level throughout mission lifetime in the presence of the expected radiation dose.
LIDAR Imaging Detector
In collaboration with MIT/Lincoln Laboratory, the RIDL is developing an imaging Light Detection and Ranging (LIDAR) detector for NASA planetary space misisons. The device will have a pixelated array of independent Geiger-mode Avalanche Photodiodes that can asynchronously measure laser light time of flight. The output will be three-dimensional images providing distance measurements for each pixel. The device will have a timing accuracy of ~100 picoseconds, thus enabling a ranging accuracy ~1 cm, or roughly two orders of magnitude better than existing LIDAR instruments.
The nature of GLIMPSE 81: a star cluster to rival Westerlund 1
This project uses Chandra/ACIS observations of a young star cluster. The X-ray emission from this cluster, already observed in previous low-resolution observations, will be resolved by Chandra into many components. Analysis will include separation of the diffuse X-ray emission from the point-sources, and a spectral analysis of each source. The data from this project will be combined with those from other observations in order to perform a multiwavelength analysis.
Clumping in OB-star winds
Massive stars, their nature and evolution, play a important role at all stages of the Universe. Through their radiatively driven winds they influence on the dynamics and energetics of the interstellar medium. The winds of OB stars are the most studied case. Commonly, the mass-loss rates of luminous OB stars are inferred from several types of measurements, the strengths of UV P Cygni lines, H-alpha emission and radio and FIR continuum emission. Recent evidence indicates that currently accepted mass-loss rates may need to be revised downwards when small-scale density inhomogeneities (clumping) are taken into account. This project uses Herschel Space Telescope data to consistently treat ALL possible diagnostics, scanning different parts of the winds, and analyzed by means of ‘state of the art’ model atmospheres, will permit the determination of true mass-loss rates.
Guide Detector Evaluation for the Large Synoptic Survey Telescope (LSST)
The RIDL is testing prototype optical guide detectors for LSST. We have developed a guider testbed that simulates the expected image motion that the LSST focal plane will experience. The testbed will be used to validate guide detector performance against LSST requirements.
In collaboration with the University of Rochester, the RIDL is developing very low noise CMOS imaging detectors for NASA space astrophysics and planetary missions. These devices promise sub-electron read noise in a direct-readout architecture that is resilient against the transient and long-term effects of radiation. The novel readout circuit uses a one-bit sigma-delta oversampling comparator design developed by Zeljko Ignjatovic and Mark Bocko (University of Rochester). The light-sensitive silicon wafer is being designed and fabricated by RIDL and the RIT Semiconductor & Microsystems Fabrication Laboratory. NASA/JPL will delta-dope the backside of the detector for enhanced ultraviolet sensitivity. The wafer and the readout will be bump bonded together to produce a hybrid detector with good sensitivity from the ultraviolet through near-optical infrared.
A NICMOS survey of newly-identified young massive clusters
We are on the cusp of a revolution in massive star research triggered by 2MASS and Spitzer/GLIMPSE, and now is the ideal time to capitalize on these projects by performing the first survey of massive stars in young stellar clusters throughout the Galactic plane. A search of the 2MASS and GLIMPSE surveys has produced over 450 newly-identified massive stellar cluster candidates in the Galactic plane which are hidden from our view at optical wavelengths due to extinction. In this project, we are using 29 HST orbits to image the most promising candidate clusters in broad and narrow band filters using NICMOS. The observations will be complemented with approved Spitzer and Chandra programs, numerous approved and planned groundbased spectroscopic observations, and state-of-the-art modelling. We expect to substantially increase the numbers of massive stars known in the Galaxy, including main sequence OB stars and post-main sequence stars in the Red Supergiant, Luminous Blue Variable and Wolf-Rayet stages. Ultimately, this program will address many of the fundamental topics in astrophysics: the slope to the initial mass function (IMF), an upper limit to the masses of stars, the formation and evolution of the most massive stars, gamma-ray burst (GRB) progenitors, the chemical enrichment of the interstellar medium, and nature of the first stars in the Universe.
Mid-Infrared Spectroscopy of the Most Massive Stars
The most massive star that can form is presently defined by observations of a class of very rare stars having inferred initial masses of ~200 solar masses. There are only a few such stars in the Galaxy, including the Pistol Star, FMM362, and LBV 1806-20, the first two being located near the Galactic center, and third located in the disk near W31. Each has only recently been identified as so massive within the past 10 years through the analysis of infrared observations, but they are otherwise too faint, due to extinction, to observe at shorter wavelengths. These stars appear to be very luminous (L>10^6.3 solar luminosities), "blue" (T>10000 K), and variable (delta K~1 mag.), and the Pistol Star has ejected 10 solar masses of material in the past 10000 years. In addition, these stars have near-infrared spectra similar to those of prototypical Luminous Blue Variables, i.e. Eta Car and AG Car. Given their apparent violation of the Humphries-Davidson limit, they are presumably in a short-lived phase of stellar evolution that is often associated with rapid mass-loss through episodic eruptions of their outer atmospheres. We propose to determine the physical properties of these stars and the velocity and ionization structure in their winds by using spectra obtained with the high resolution modes of the Infrared Spectrograph (IRS) on the Spitzer Space Telescope. The 10 to 40 micron wavelength region is ideally suited for accessing a variety of lines from transitions of hydrogen, helium, iron, silicon, sulfur, among others; indeed, through our models, we predict that sufficiently sensitive spectra will yield over 300 spectral lines. In addition, we predict that the mid-infrared continuum will be dominated by free-free emission generated in the thick winds associated with these stars, an effect that should be clearly detectable in the spectra.
Sandia FPGA Imaging Acquisition Software Development
RIDL developed HDL (Hardware Description Language) software for a FPGA (Field Programmable Gate Array) evaluation board for Sandia National Laboratories. The HDL software programs the FPGA chip to transfer digital video rate image data from the evaluation board to a windows based PC using the Camera Link data transfer format. Once the Camera Link data format became available, data acquisition software for the PC was developed to capture and display the imagery on the PC.
The Pre-Supernova Mass-Loss Behavior of Red Supergiants
The mass lost by massive stars as they pass through the Red Supergiant (RSG) phase is a crucial determinant in the terminal mass of the star, the nature of the resulting supernova explosion and the stellar end-state. However, up until now studies of this quantity have been problematic, owing to the low numbers of known RSGs and the difficulty of observing in the mid-IR. Here, we capitalize on the recent discoveries of two remarkable Galactic clusters containing unprecedented numbers of RSGs, and use the capabilities of Spitzer to undertake a comprehensive and unique study of the pre-SN mass-loss of massive stars. We will use Spitzer/IRS observations in conjunction with state-of-the-art dust models to provide the first quantitative investigation of the mass and composition of the pre-SN ejecta as a function of age and metallicity. This study is vital in determining the mass-loss behaviour of RSGs in particular, and the nature of supernova progenitors in general.
A Very Low Noise CMOS Detector Design for NASA
The purpose of this project is to design, fabricate, and test a novel new detector having many advantages over present CCD and CMOS devices. The hybrid CMOS detector is expected to have low noise, radiation tolerance, low power dissipation, low mass and robust electronics. Its low noise is derived from a novel on-die digitization circuit based on a sigma-delta feedback loop.
The Most Massive Stars
Until the Spitzer Space Telescope, there was no wide area survey that could identify massive stars at all distances in the Galaxy. Indeed, the sample of known O-stars is woefully incomplete, as it has largely been generated using optical observations that suffer from the absorption produced by dust in the disk. We will find and measure the physical properties of the most massive stars in the Galaxy using HST, Spitzer, Chandra, SOFIA, and ground-based observatories, using a survey technique that probes the majority of the Galaxy. This program addresses fundamental questions whose answers are basic requirements for studying many of the most important topics in Astrophysics: the formation and evolution of the most massive stars, the effects of massive stars on lower mass protostellar/protoplanetary systems, gamma-ray burst progenitors, nature of the first stars in the Universe, chemical enrichment of the interstellar medium, Galactic gas dynamics, star formation in starbursts and merging galaxies (particularly in the early Universe). The results of our program will influence the science programs for future NASA projects, i.e. JWST, SOFIA, SIM, TPF-C, and TPC-I.