With the next generation observatories such as GMT, TMT, and E-ELT looming, the astronomy community is in need of unprecedented number of infrared pixels. To address the affordability of the next generation of infrared instruments, the Center for Detectors (CfD) at the Rochester Institute of Technology (RIT) and Raytheon Vision Systems (RVS) are developing large format, short-wave infrared HgCdTe focal plane arrays grown on silicon (Si) wafers for observational astronomy. The use of silicon wafers offers significant savings and a path to very large format (>; 8K×8K, 15 μm) focal plane arrays. This paper presents the latest results from the detector development effort and its suitability for use in observational astronomy. Currently, the HgCdTe/Si technology is competitive with the state-of-the-art HgCdTe/CZT technology in many performance metrics, and it has the promise to meet stringent performance requirements posed by observational astronomy. A full suite of characterization results, including for dark current, read noise, spectral response, persistence, linearity, full well, and crosstalk probability, will be presented.
Radiation testing results for a Geiger-mode avalanche photodiode (GM-APD) array-based imager are reviewed. Radiation testing is a crucial step in technology development that assesses the readiness of a specific device or instrument for space-based missions or other missions in high-radiation environments. Pre- and postradiation values for breakdown voltage, dark count rate (DCR), after pulsing probability, photon detection efficiency (PDE), crosstalk probability, and intrapixel sensitivity are presented. Details of the radiation testing setup and experiment are provided. The devices were exposed to a total dose of 50 krad(Si) at the Massachusetts General Hospital’s Francis H. Burr Proton Therapy Center, using monoenergetic 60 MeV protons as the radiation source. This radiation dose is equivalent to radiation absorbed over 10 solar cycles at an L2 orbit with 1-cm aluminum shielding. The DCR increased by 2.3 e−/s/pix/krad(Si) at 160 K, the afterpulsing probability increased at all temperatures and settings by a factor of ∼2, and the effective breakdown voltage shifted by +1.5 V. PDE, crosstalk probability, and intrapixel sensitivity were unchanged by radiation damage. The performance of the GM-APD imaging array is compared to the performance of the CCD on board the ASCA satellite with a similar radiation shield and radiation environment.
The Center for Detectors at Rochester Institute of Technology and Raytheon Vision Systems (RVS) are leveraging RVS capabilities to produce large format, short-wave infrared HgCdTe focal plane arrays on silicon (Si) substrate wafers. Molecular beam epitaxial (MBE) grown HgCdTe on Si can reduce detector fabrication costs dramatically, while keeping performance competitive with HgCdTe grown on CdZnTe. Reduction in detector costs will alleviate a dominant expense for observational astrophysics telescopes. This paper presents the characterization of 2.5μm cutoff MBE HgCdTe/Si detectors including pre- and post-thinning performance. Detector characteristics presented include dark current, read noise, spectral response, persistence, linearity, crosstalk probability, and analysis of material defects.
The ability to count single photons is necessary to achieve many important science objectives in the near future. This paper presents the lab-tested performance of a photon-counting array-based Geiger-mode avalanche photodiode (GMAPD) device in the context of low-light-level imaging. Testing results include dark count rate, afterpulsing probability, intra-pixel sensitivity, and photon detection efficiency, and the effects of radiation damage on detector performance. The GM-APD detector is compared to the state-of-the-art performance of other established detectors using Signal-to-noise ratio as the overall evaluation metric.
Single-photon imaging detectors promise the ultimate in sensitivity by eliminating read noise. These devices could
provide extraordinary benefits for photon-starved applications, e.g., imaging exoplanets, fast wavefront sensing, and
probing the human body through transluminescence. Recent implementations are often in the form of sparse arrays that
have less-than-unity fill factor. For imaging, fill factor is typically enhanced by using microlenses, at the expense of
photometric and spatial information loss near the edges and corners of the pixels. Other challenges include afterpulsing
and the potential for photon self-retriggering. Both effects produce spurious signal that can degrade the signal-to-noise
ratio. This paper reviews development and potential application of single-photon-counting detectors, including highlights
of initiatives in the Center for Detectors at the Rochester Institute of Technology and MIT Lincoln Laboratory.
Current projects include single-photon-counting imaging detectors for the Thirty Meter Telescope, a future NASA
terrestrial exoplanet mission, and imaging LIDAR detectors for planetary and Earth science space missions.
This paper summarizes progress of a project to develop and advance the maturity of photon-counting detectors for
NASA exoplanet missions. The project, funded by NASA ROSES TDEM program, uses a 256×256 pixel silicon Geigermode
avalanche photodiode (GM-APD) array, bump-bonded to a silicon readout circuit. Each pixel independently
registers the arrival of a photon and can be reset and ready for another photon within 100 ns. The pixel has built-in
circuitry for counting photo-generated events. The readout circuit is multiplexed to read out the photon arrival events.
The signal chain is inherently digital, allowing for noiseless transmission over long distances. The detector always
operates in photon counting mode and is thus not susceptible to excess noise factor that afflicts other technologies. The
architecture should be able to operate with shot-noise-limited performance up to extremely high flux levels,
>106 photons/second/pixel, and deliver maximum signal-to-noise ratios on the order of thousands for higher fluxes. Its
performance is expected to be maintained at a high level throughout mission lifetime in the presence of the expected
We obtained 960,200 22-by-22-pixel windowed images of a pinhole spot using the Teledyne H2RG CMOS detector
with un-cooled SIDECAR readout. We performed an analysis to determine the precision we might expect in the position
error signals to a telescope's guider system. We find that, under non-optimized operating conditions, the error in the
computed centroid is strongly dependent on the total counts in the point image only below a certain threshold,
approximately 50,000 photo-electrons. The LSST guider camera specification currently requires a 0.04 arcsecond error
at 10 Hertz. Given the performance measured here, this specification can be delivered with a single star at 14th to 18th
magnitude, depending on the passband.
We describe a CMOS image sensor with column-parallel delta-sigma (ΔΣ) analog-to-digital converter (ADC). The
design employs three transistor pixels (3T1) where the unique configuration of the ΔΣ ADC reduces the noise
contribution of the readout transistor. A 128 x 128 pixel image sensor prototype is fabricated in 0.35μm TSMC
technology. The reset noise and the offset fixed pattern noise (FPN) are removed in the digital domain. The
measured readout noise is 37.8μV for an exposure time of 33ms. The low readout noise allows an improved low
light response in comparison to other state-of-art designs. The design is suitable for applications demanding
excellent low-light response such as astronomical imaging. The sensor has a measured intra-scene dynamic range
(DR) of 91 dB, and a peak signal-to-noise ratio (SNR) of 54 dB.
This paper is a progress report of the design and characterization of a monolithic CMOS detector with an on-chip ΣΔ
ADC. A brief description of the design and operation is given. Backside processing steps to allow for backside
illumination are summarized. Current characterization results are given for pre- and post-thinned detectors.
Characterization results include measurements of: gain photodiode capacitance, dark current, linearity, well depth,
relative quantum efficiency, and read noise. Lastly, a detector re-design is described; and initial measurements of its
photodiode capacitance and read noise are presented.
The Rochester Imaging Detector Laboratory, University of Rochester, Infotonics Technology Center, and Jet Process
Corporation developed a hybrid silicon detector with an on-chip sigma-delta (ΣΔ) ADC. This paper describes the process
and reports the results of developing a fabrication process to robustly produce high-quality bump bonds to hybridize a
back-illuminated detector with its ΣΔ ADC. The design utilizes aluminum pads on both the readout circuit and the
photodiode array with interconnecting indium bumps between them. The development of the bump bonding process is
discussed, including specific material choices, interim process structures, and final functionality. Results include
measurements of bond integrity, cross-wafer uniformity of indium bumps, and effects of process parameters on the final
product. Future plans for improving the bump bonding process are summarized.
We report on long exposure results obtained with a Teledyne HyViSI H2RG detector operating in guide mode. The sensor simultaneously obtained nearly seeing-limited data while also guiding the Kitt Peak 2.1 m telescope. Results from unguided and guided operation are presented and used to place lower limits on flux/fluence values for accurate centroid measurements. We also report on significant noise reduction obtained in recent laboratory measurements that should further improve guiding capability with higher magnitude stars.
We present the first astronomical results from a 4K2 Hybrid Visible Silicon PIN array detector (HyViSI) read out
with the Teledyne Scientific and Imaging SIDECAR ASIC. These results include observations of astronomical
standards and photometric measurements using the 2.1m KPNO telescope. We also report results from a test
program in the Rochester Imaging Detector Laboratory (RIDL), including: read noise, dark current, linearity,
gain, well depth, quantum efficiency, and substrate voltage effects. Lastly, we highlight results from operation of
the detector in window read out mode and discuss its potential role for focusing, image correction, and use as a
telescope guide camera.
We compare a more complete characterization of the low temperature performance of a nominal 1.7um cut-off
wavelength 1kx1k InGaAs (lattice-matched to an InP substrate) photodiode array against similar, 2kx2k HgCdTe
imagers to assess the suitability of InGaAs FPA technology for scientific imaging applications. The data we present
indicate that the low temperature performance of existing InGaAs detector technology is well behaved and comparable
to those obtained for state-of-the-art HgCdTe imagers for many space astronomical applications. We also discuss key
differences observed between imagers in the two material systems.
Precision near infrared (NIR) measurements are essential for the next generation of ground and space based instruments. The SuperNova Acceleration Probe (SNAP) will measure thousands of type Ia supernovae up to a redshift of 1.7. The highest redshift supernovae provide the most leverage for determining cosmological parameters, in particular the dark energy equation of state and its possible time evolution. Accurate NIR observations are needed to utilize the full potential of the highest redshift supernovae. Technological improvements in NIR detector fabrication have lead to high quantum efficiency, low noise detectors using a HgCdTe diode with a band-gap that is tuned to cutoff at 1.7 μm. The effects of detector quantum efficiency, read noise, and dark current on lightcurve signal to noise, lightcurve parameter errors, and distance modulus fits are simulated in the SNAPsim framework. Results show that improving quantum efficiency leads to the largest gains in photometric accuracy for type Ia supernovae. High quantum efficiency in the NIR reduces statistical errors and helps control systematic uncertainties at the levels necessary to achieve the primary SNAP science goals.
We present the results of a study of the performance of InGaAs detectors conducted for the SuperNova Acceleration
Probe (SNAP) dark energy mission concept. Low temperature data from a nominal 1.7um cut-off wavelength 1kx1k
InGaAs photodiode array, hybridized to a Rockwell H1RG multiplexer suggest that InGaAs detector performance is
comparable to those of existing 1.7um cut-off HgCdTe arrays. Advances in 1.7um HgCdTe dark current and noise
initiated by the SNAP detector research and development program makes it the baseline detector technology for SNAP.
However, the results presented herein suggest that existing InGaAs technology is a suitable alternative for other future
Sensors for the LSST camera require high quantum efficiency (QE) extending into the near-infrared. A relatively large thickness of silicon is needed to achieve this extended red response. However, thick sensors degrade the point spread function (PSF) due to diffusion and to the divergence of the fast f/1.25 beam. In this study we examine the tradeoff of QE and PSF as a function of thickness, wavelength, temperature, and applied electric field for fully-depleted sensors. In addition we show that for weakly absorbed long-wavelength light, optimum focus is achieved when the beam waist is positioned slightly inside the silicon.
Large format (1k × 1k and 2k × 2k) near infrared detectors manufactured by Rockwell Scientific Center and Raytheon Vision Systems are characterized as part of the near infrared R&D effort for SNAP (the Super-Nova/Acceleration Probe). These are hybridized HgCdTe focal plane arrays with a sharp high wavelength cut-off at 1.7 μm. This cut-off provides a sufficiently deep reach in redshift while it allows at the same time low dark current operation of the passively cooled detectors at 140 K. Here the baseline SNAP near infrared system is briefly described and the science driven requirements for the near infrared detectors are summarized. A few results obtained during the testing of engineering grade near infrared devices procured for the SNAP project are highlighted. In particular some recent measurements that target correlated noise between adjacent detector pixels due to capacitive coupling and the response uniformity within individual detector pixels are discussed.
The LSST project has embarked on an aggressive new program to develop the next generation of silicon imagers for the visible and near-IR spectral regions. In order to better understand and solve some of the technology issues prior to development and mass-production for the huge LSST focal plane, a number of contracts have been written to imager firms to explore specific areas of technology uncertainty. We expect that these study contracts will do much toward reducing risk and uncertainty going into the next phase of development, the prototype production of the final large LSST imager.
Wide-Field Camera 3 (WFC3) has been built for installation on the Hubble Space Telescope (HST) during the next servicing mission. The WFC3 instrument consists of both a UVIS and an IR channel, each with its own complement of filters. On the UVIS side, a selectable optical filter assembly (SOFA) contains a set of 12 wheels that house 48 elements (42 full-frame filters, 5 quadrant filters, and 1 UV grism). The IR channel has one filter wheel which houses 17 elements (15 filters and 2 grisms). While the majority of UVIS filters exhibited excellent performance during ground testing, a subset of filters showed filter ghosting; improved replacements for these filters have been procured and installed. No filter ghosting was found in any of the IR filters; however, the new IR detector for WFC3 will have significantly more response blueward of 800 nm than the original detector, requiring that two filters originally constructed on a fused silica substrate be remade to block any visible light transmission. This paper summarizes the characterization of the final complement of the WFC3 UVIS and IR filters, highlighting improvements in the replacement filters and the projected benefit to science observations.
The Near-Infrared Spectrograph (NIRSpec) is the James Webb Space Telescope’s primary near-infrared spectrograph. NASA is providing the NIRSpec detector subsystem, which consists of the focal plane array, focal plane electronics, cable harnesses, and software. The focal plane array comprises two closely-butted λco ~ 5 μm Rockwell HAWAII-2RG sensor chip assemblies. After briefly describing the NIRSpec instrument, we summarize some of the driving requirements for the detector subsystem, discuss the baseline architecture (and alternatives), and presents some recent detector test results including a description of a newly identified noise component that we have found in some archival JWST test data. We dub this new noise component, which appears to be similar to classical two-state popcorn noise in many aspects, “popcorn mesa noise.” We close with the current status of the detector subsystem development effort.
The James Webb Space Telescope (JWST) will be a segmented, deployable,
infrared-optimized 6.5m space telescope. Its active primary segments
will be aligned, co-phased, and then fine-tuned in order to deliver image quality sufficient for the telescope's intended scientific goals. Wavefront sensing used to drive this fine tuning will come from
the analysis of defocussed phase diverse images taken with its
near-IR science camera, NIRCam. Here we concentrate on routine maintenance of the JWST primary, as might be expected to occur on a more or less monthly timescale after the telescope is commissioned.
We carry out an end-to-end optical and wavefront sensing simulation,
starting from the primary mirror figure, calculating a noiseless point-spread function as it would appear on the detector, inject noise sources due to photon statistics, as well as detector and electronics characteristics (as measured in Rockwell HAWAII-2RG detectors in the lab), and reduce the data with a simple scheme to create one realization of a full wavefront sensing operation. We generate JWST point-spread functions for a given OPD map on a JWST pupil with -6, -3, 3, and 6 waves of focus, and simulate three realizations of the same exposure. We start with a mirror figure that provides a point-spread function (PSF) that is just under the acceptable specification for JWST's Strehl ratio, which is 80% at 2 microns in NIRCam. We do not include zodiacal light, diffuse sources, or contamination by other stars in our simulation. Our up-the-ramp exposures include a model of cosmic ray contamination of the data.
We calibrate the image to account for dark current and flat field variation, and process the images with an implementation of the Misell-Gerchberg-Saxton algorithm assuming a known pupil support function. Our entire process is described here, to document a tool that helps to verify our intended method of maintaining the JWST PSF within specificatiuons during routine science operations.
We present the science case, design overview and sensitivity estimate for the design study for the WIYN High Resolution Infrared Camera (WHIRC). The WIYN telescope is an active 3.5 m telescope located at an excellent seeing site on Kitt Peak and operated by University of Wisconsin, Indiana University, Yale University and National Optical Astronomical Observatory (NOAO). As a dedicated near-infrared (0.8-2.5 micron) camera on the WIYN Tip-Tilt Module (WTTM), WHIRC will provide near diffraction limited imaging, i.e. FWHM~0.25" typically and 0.12" on exceptional nights. The optical design goal is to use a 2048x2048 HgCdTe array with a plate scale of 0.09" per pixel, resulting in a field of view (FOV), 3'x3', which is a compromise between the highest angular resolution achievable and the largest FOV correctable by WTTM. WHIRC will be used for high definition near-infrared imaging studies such as star formation, proto-planetary disks, galactic dust enshrouded B clusters, dust enshrouded stellar populations in nearby galaxies, and supernova and gamma-ray burst searches.
The Independent Detector Testing Laboratory (IDTL) is jointly operated by the Space Telescope Science Institute (STScI) and the Johns Hopkins University (JHU), and is assisting the James Webb Space Telescope (JWST) mission in choosing and operating the best near-infrared detectors. The JWST is the centerpiece of the NASA Office of Space Science theme, the Astronomical Search for Origins, and the highest priority astronomy project for the next decade, according to the National Academy of Science. JWST will need to have the sensitivity to see the first light in the Universe to determine how galaxies formed in the web of dark matter that existed when the Universe was in its infancy (z~10-20). To achieve this goal, the JWST Project must pursue an aggressive technology program and advance infrared detectors to performance levels beyond what is now possible. As part of this program, NASA has selected the IDTL to verify comparative performance between prototype JWST detectors developed by Rockwell Scientific (HgCdTe) and Raytheon (InSb). The IDTL is charged with obtaining an independent assessment of the ability of these two competing technologies to achieve the demanding specifications of the JWST program within the 0.6-5 μm bandpass and in an ultra-low background (<0.01 e-/s/pixel) environment. We describe results from the JWST Detector Characterization Project that is being performed in the IDTL. In this project, we are measuring first-order detector parameters, i.e. dark current, read noise, QE, intra-pixel sensitivity, linearity, as functions of temperature, well size, and operational mode.
The Independent Detector Testing Laboratory (IDTL) has been established by the Space Telescope Science Institute (STScI) and the Johns Hopkins University (JHU), and it will assist the Next Generation Space Telescope (NGST) mission in choosing and operating the best near-infrared detectors. The NGST is the centerpiece of the NASA Office of Space Science theme, the Astronomical Search for Origins, and the highest priority astronomy project for the next decade, according to the National Academy of Science. NGST will need to have the sensitivity to see the first light in the Universe to determine how galaxies formed in the web of dark matter that existed when the Universe was in its infancy (z ~10-20). To achieve this goal, the NGST Project must pursue an aggressive technology program and advance infrared detectors to performance levels beyond what is now possible. As part of this program, NASA has selected the IDTL to verify comparative performance between prototype NGST detectors developed by Rockwell Scientific (HgCdTe) and Raytheon (InSb). The IDTL is charged with obtaining an independent assessment of the ability of these two competing technologies to achieve the demanding specifications of the NGST program within the 0.6-5 μm bandpass and in an ultra-low background (<0.01 e-/s/pixel) environment. We describe the NGST Detector Characterization Project that is being performed in the IDTL. In this project, we will measure first-order detector parameters, i.e. dark current, read noise, QE, intra-pixel sensitivity, linearity, as functions of temperature, well size, and operational mode.
Intra-Pixel Sensitivity (IPS) is defined as the spatially varying response of the pixel to incoming flux. IPS plays a crucial role when the Point-Spread Function (PSF) is critically, or under-, sampled. Variations in IPS lead to photometric and astrometric errors. The Next Generation Space Telescope (NGST) requires high quality photometry and astrometry, so an accurate estimation of the IPS function is necessary for a successful NGST mission. Photo-electrons generated in a pixel may be detected in the depletion region (detection of the flux) of the same pixel, or might diffuse and end up in the microstructure of the detector, the electric field distribution therein, wavelength of the incident radiation, and diffusion processes of the excess charge carriers generated determines the IPS function of a pixel that can vary from pixel to pixel. The total detected flux is proportional to the convolution of the PSF and the IPS function. If we approximate the profile of the PSF, then the problem of determining the IPS function reduces to deconvolving using the experimentally obtained Sensitivity variation profile and the calculated PSF. We aim to obtain a highly undersampled PSF, scan it over a single pixel on a grid of 10 x 10 points, and retrieving IPS function using deconvolution. We present our results, experiment design, and the scope of further work, using an NGST detector, to estimate the IPS function at various wavelengths.
The Next Generation Space Telescope (NGST) will be a segmented, deployable, infrared-optimized 6.5m space telescope. Its active primary segments will be aligned, co-phased, and then fine-tuned in order to deliver image quality sufficient for the telescope's intended scientific goals. Wavefront sensing used to drive this tuning will come from the analysis of focussed and defocussed images taken with its near-IR science camera, NIRCAM. There is a pressing need to verify that this will be possible with the near-IR detectors that are still under development for NGST. We create simulated NIRCAM images to test the maintenance phase of this plan. Our simulations incorporate Poisson and electronics read noise, and are designed to be able to include various detector and electronics non-linearities. We present our first such simulation, using known or predicted properties of HAWAII HgCdTe focal plane array detectors. Detector effects characterized by the Independent Detector Testing Laboratory will be included as they become available. Simulating InSb detectors can also be done within this framework in future. We generate Point-Spread Functions (PSF's) for a segmented aperture geometry with various wavefront aberrations, and convolve this with typical galaxy backgrounds and stellar foregrounds. We then simulate up-the-ramp (MULTIACCUM in HST parlance) exposures with cosmic ray hits. We pass these images through the HST NICMOS `CALNICA' calibration task to filter out cosmic ray hits. The final images are to be fed to wavefront sensing software, in order to find the ranges of exposure times, filter bandpass, defocus, and calibration star magnitude required to keep the NGST image within its specifications.
The Next Generation Space Telescope (NGST) Project is developing a new generation of near-infrared (NIR; λ=0.6-5 μm) array detectors optimized for ultra-low space-based backgrounds. NASA has selected the Independent Detector Testing Laboratory (IDTL) at the Space Telescope Science Institute (STScI) and the Johns Hopkins University to assist in testing and characterizing NGST's near-infrared detectors. In the IDTL, we have begun to explore how reference pixels might be used to calibrate infrared array data. Here we report some early results from these studies. Results to date are very encouraging, particularly with regard to techniques using temporal or spatial averaging to compute low-noise reference levels before making row-by-row reference pixel corrections. We explored the effectiveness of four potential calibration strategies using a shorting resistor installed where the detector would normally mount and are currently validating the techniques presented here using candidate NGST detectors.
This paper describes the performance of NIRSPEC, the cryogenic cross-dispersed IR echelle spectrograph for the Keck II telescope on Mauna Kea. NIRSPEC employs a 1024 by 1024 InSb array, diamond-machined metal optics and closed- cycle refrigeration on achieve high throughput and low backgrounds. The instrument operates directly at the f/15 Nasmyth focus, but can also be used in conjunction with the Keck adaptive optics system. First Light was obtained on April 25, 1999. As expected, the performance is detector- limited at short wavelengths and background-limited at longer wavelengths. All of the design goals have been met and result illustrating the optical performance and sensitivity are reported.
We report NIRSPEC/Keck observations of the Galactic Center obtained in both low and high resolution modes under excellent seeing conditions. The data were obtained as part of the NIRSPEC commissioning program and will be used to determine: 1) the nature of the stars in the central 0.02 pc, 2) the velocities and accelerations of stars around the central black hole, 3) the velocities of ionized gas in the central parsec, 4) the extent of the main sequence population and star formation history in central parsec, 5) the mass magnitude relation and initial mass function in the Arches cluster, 6) the nature of the MIR sources in the central parsec and Quintuplet clusters, 7) the physical parameters of stellar atmosphere/winds of super luminous stars, and 8) the metallicity in the GC as inferred from observations of red supergiants, red giants, and hot stars. We present a sample of these data, including a high resolution slit scan movie of the central parsec, and show how they can be used to vastly improve the current state of the art in the related science topics. Further, we discuss preliminary results concerning the nature of the central cusp stars and the resultant implications for star formation near a supermassive black hole.
The NIRSPEC Brown Dwarf Spectroscopic Survey is a project to obtain a consistent set of high-quality near-IR spectra for each spectral class and sub-class of low-mass and/or sub- stellar objects to provide a new data base for models of the atmosphere of brown dwarfs and extra-solar giant planets. Most of the current targets are L-dwarfs and T-dwarfs discovered by the 2MASS. The survey is begin performed with the recently-commissioned near-IR spectrometer, NIRSPEC, a 1-5 micrometers cryogenic spectrograph at the WM Keck Observatory on Mauna Kea, using resolving powers of R equals 2,500-25,000. Preliminary results for four sources, three L-dwarfs and one T-dwarf, are presented here. Spectra from 1.13-2.33 micrometers at an average resolution of R equals 2,500 illustrate the development of deep steam bands and the weakening of FeH through the L-sequence, and the emergence of methane bands in the T-dwarfs. Complex detail in the spectra are the result of blending of numerous unresolved molecular transitions.
The design and development of NIRSPEC, a near-IR echelle spectrograph for the Keck II 10-meter telescope is described. This instrument is a large, facility-class vacuum-cryogenic spectrometer with a resolving power of R equals 25,000 for a 0.4 inch slit. It employs diamond-machined metal optics and state-of-the-art IR array detectors for high throughput, together with powerful user-friendly software for ease of use.
The cryogenic optical performance of an all aluminum three mirror anastigmat re-imager developed for the NIRSPEC instrument is reported. Details pertaining to the optical and mechanical design, structural/thermal modeling, initial performance projections, optical/mechanical fabrication, optical alignment, and optical testing procedures are all presented. The operational performance of the optical system at ambient and at cryogenic temperatures is presented and compared with initial performance projections. The optical subsystem has been delivered to UCLA for integration into the NIRSPEC instrument, final installation will be done at the Keck Observatory.
We describe the requirements, constraints, and goals for FLITECAM, the first light IR test experiment camera being built at UCLA for SOFIA. The camera must allow testing of the testing of the telescope/observatory and provide first- light images for public outreach and publicity. In addition, the camera should become a facility-class instrument for use by the general SOFIA user community. The camera is relatively simple and inherits many of the designs from previous instruments built in the IR Imaging Detector Laboratory at UCLA. It will offer wide-field imaging, high- resolution imaging for observing diffraction-limited images at >= 3 micrometers , low-resolution grism spectroscopy, and pupil-viewing. FLITECAM will be delivered for observatory tests in early 2001. The project will not formally start until NIRSPEC is delivered and commissioned at the Keck Observatory.
We present the wavefront error budget and optomechanical tolerance analysis for NIRSPEC, a high-resolution near-IR echelle spectrograph for the Keck II telescope. The error budget accounts for aberrations induced by optical design residual, manufacturing error, cryogenic degradation, mounting effects, and misalignments. The allowed errors due to misalignments are used with boresighting and vignetting requirements in an optomechanical tolerance analysis.
NIRSPEC is a recently funded, high-resolution, 1 - 5 micrometers cryogenic spectrograph for the Keck II telescope. The design of this new instrument is based on 1024 X 1024 InSb arrays and provides resolving powers of R equals 2,000 in non-cross-dispersed mode and R equals 25,000 in echelle mode with typically 5 to 6 orders on the array covering 60 - 90% of the selected waveband, J, H, K, or L, in a single observation. Later, even higher resolution can be achieved by using the proposed adaptive optics facility at Keck II and replacing some of the internal modules of NIRSPEC. This paper gives a brief description of the proposed design concepts, and a discussion of the detector and system constraints required to achieve the scientific goals of the instrument.
This paper describes the performance of a unique new IR array camera system which provides simultaneous imaging at two wavelengths in the near IR. Two-color imaging is achieved with a dichroic beam splitter which yields two independent beams, one short-wave (SW) from 1 to 2.5 micrometers and one long-wave (LW) from 2 to 5 micrometers . A Rockwell NICMOS 3 256 by 256 HgCdTe array is used in the SW channel and the LW channel has an InSb 256 by 256 array from SBRC. The instrument, which is designed for the University of California's Lick Observatory 3-m telescope and for the f/15 focus of the 10-m W.M. Keck telescope, employs a closed cycle refrigerator and a compact array control/data acquisition system based on transputers with a host 486 PC. On the Lick 3-m telescope the pixel size is 0.7' which gives a field of view of about 180' by 180'. Facilities are also provided for spectroscopy and polarimetry. Recent observational results are reported to illustrate the performance of this system.
This paper describes a new infrared imaging system being developed at UCLA for use on both the Lick Observatory 3-m telescope and the W.M. Keck 10-m telescope. The instrument has a relatively wide field of view on each telescope and is intended for infrared surveys and deep imaging. To enhance efficiency, the new instrument incorporates a dichroic beam splitter to provide two simultaneous imaging systems, one short-wave (SW) from 1 - 2.5 micrometers and one long-wave (LW) from 2 - 5 micrometers . Each wavelength channel is independently optimized. The SW channel contains a Rockwell NICMOS3 256 X 256 HgCdTe array and the LW channel has an SBRC 256 X 256 InSb array. The thermal design employs a closed cycle cooler. A control and data acquisition system based on transputers and high speed analog electronics is being developed to handle the high data rates.