We describe the on-orbit characterization of the HgCdTe detectors aboard NICMOS. The flat-field response is strongly wavelength dependent, and we show the effect of this on the photometric uncertainties in data, as well as the complications it introduces into calibration of slitless grism observations. We present the first rigorous treatment of the dark current as a function of exposure time for HgCdTe array detectors, and show that they consist of three independent components which we have fully characterized - a constant component which is the true dark current, an 'amplifier glow' component which results from operation of the four readout amplifiers situated near the detector corners and injects a spatially dependent signal each time the detector is non-destructively read out, and finally the 'shading', a component well known in HgCdTe detectors which we show is simply a pixel dependent bias change whose amplitude is a function of the time since the detector was last non-destructively read out. We show that with these three components fully characterized, we are able to generate 'synthetic' dark current images for calibration purposes which accurately predict the actual performance of the three flight detectors. In addition, we present linearity curves produced in ground testing before launch. Finally, we report a number of detector related anomalies which we have observed with NICMOS some of which have limited the observed sensitivity of the instrument, and which at the time of writing are still not fully understood.
This paper describes the results of a test program to evaluate four Rockwell HAWAII and two PICNIC near IR array detectors with a view to their application in imaging, spectroscopy and in fast telescope tracking and interferometer fringe detection. Results of the laboratory test of the arrays are presented, together with a guide for their general operation.
This paper is a review of current astronomy projects at Raytheon/SBRC in the near-IR band. Another paper in this same session (3354-11) covers astronomy projects in longer wavelengths. For ground-based astronomy, InSb arrays with formats of 256 X 256, 512 X 512, and 1024 X 1024 have been developed and tested. For space-based astronomy, four projects are discussed with array formats ranging from 256 X 256 to 2K X 2K. The space projects support instruments on the SIRTF, IRIS, NGST, and Rosetta missions. Representative data are presented from 1024 X 1024 and 256 X 256 arrays obtained by test facilities at NOAO and the University of Rochester.
Four ALADDIN Type II 1024 X 1024 InSb arrays have been tested in the NOAO IR Detector Lab for use in the Gemini IR instruments; the Gemini Near-IR Spectrometer, and the near IR imager. Santa Barbara Research Center has been able to successfully deliver science devices. The best of which will be selected for use at Mauna Kea and Cerro Pachon. These results are reported to show the progress in the development of these arrays.
A high performance, bias tunable, p-GaAs homojunction interfacial work function internal photoemission far-IR (FIR) detector has been demonstrated. A responsivity of 3.10 +/- 0.05 A/W, a quantum efficiency of 12.5 percent, and a detectivity D* of 5.9 X 1010 cm (root) Hz/W, were obtained at 4.2K, for cutoff wavelengths form 80 to 100 micrometers . The bias dependences of quantum efficiency, detectivity, and cutoff wavelength have been measured and are well explained by the theoretical models. The cutoff wavelength is modeled by a modified high density theory, and the quantum efficiency is predicted by scaling the free carrier absorption coefficient linearly with the doping concentration. The effect of the number of layers on detector performance and the uniformity of the detectors have been discussed. A comparison with Ge:GA photoconductive detectors suggests that a similar or even better performance may be obtainable.
Ge:Ga far-IR photoconductor 2D direct hybrid arrays are being developed for application in the focal-plane detectors of the far-IR surveyor, one of the two main instruments of the IR imaging surveyor satellite. The arrays are composed of Ge:Ga photoconductor arrays fabricated on one chip, Si- pMOS readout integrated circuits, and a hybridization of them done by using indium bump technology.
We describe the design, construction, and performance of the 32 X 32 Ge:Ga imaging array being built at the University of Arizona for the Multiband Imaging Photometer for SIRTF (MIPS). The array will support a number of operational modes in the MIPS instrument including natural background-limited mapping at 70 micrometers , super-resolution observations at 70 micrometers , and spectral energy distribution measurements between 50 and 100 micrometers . The array is constructed in a modular manner using eight 4 X 32 pixel building blocks. To meet the sensitivity and stability requirements, the array must have excellent photometric repeatability, low noise, and robustness to the effects of the ionizing radiation environment in space. Key elements in attaining this level of performance are the Ge:Ga detectors materials and the cryogenic CRC-696 readout electronics. We present laboratory data for a 16 X 32 prototype of the array, and describe the plans for the construction of the qualification and flight units.
The HAWAII-2 is an IR 20482 focal plane array (FPA) that is being developed for next-generation IR astronomy. It will supplant our HAWAII 10242 as the largest high- performance imaging array available for IR astronomy. As with our prior IR sensor, the flip-chip hybrid will consist of a low-capacitance HgCdTe detector array mated to a low- noise CMOS silicon multiplexer via indium interconnects. In order to accommodate reasonable telescope optics and fabrication of the large sophisticated readout using world- class submicron CMOS, the FPA has 18 micrometers pixel pitch. We anticipate > 5 percent yield of defect-free multiplexers using 0.8 micrometers CMOS. The HgCdTe detector arrays will be fabricated on large wafers including sapphire and silicon. Though the first FPAs will have 2.5 micrometers cut-off, the readout will be able to support longer wavelengths. Also reported are the latest 1024 X 1024 FPA results with 2.5 micrometers HgCdTe detectors.
Rockwell Science Center has developed a double layer planar heterostructure (DLPH) detector array fabrication process with significant advantages over the PACE-1 process now being used to produce 256 X 256 and 1024 X 1024 FPAs for low background IR astronomy. The DLPH detectors are p- on-n photodiodes fabricated in a double layer of wide and narrow bandgap HgCdTe grown by molecular beam epitaxy on CdZnTe substrates. The double layer structure provides superior surface passivation while the lattice matched CdZnTe substrate reduces the defect density. DLPH FPAs have been fabricated in array sizes up to 640 X 480 and with cutoff wavelengths as long as 15 micrometers . Quantum efficiencies are typically in the 0.5 to 0.8 range. For a 256 X 256 array DLPH detectors with 5.3 micrometers cutoff wavelength at 50K, the median dark current was 0.39 e-/sec at 0.5V reverse bias. For 7 of 17 individual DLPH detector with 10.6 micrometers cutoff at 30K, the dark current was less than 104 e-/sec at 20 mV bias. For long cutoff wavelengths, the detector breakdown voltage is too low to permit signal integration directly on the reverse biased detector capacitance. Such detectors require a readout circuit that maintains the detector near zero bias and provides a separate capacitor to store the integrated signal.
Instrument platforms like the VLT represent a new challenge to IR focal plane technology. Since the large telescope diameter and the improved image quality provided by adaptive optics reduce the pixel scale, larger array formats are needed. To meet this challenge ESO is participating in development programs for both InSb and HgCdTe large format arrays. To cover the spectral region of 1 to 5 micron ESO has funded a foundry run at SBRC to produce 1024 X 1024 InSb arrays, which will be installed in ISAAC, the IR Spectrometer and Array Camera built for the VLT. Since the delivery of the 1K X 1K InSb array is delayed, the test results obtained with a 256 X 256 InSb array and the application of off chip cryogenic amplifiers to InSb detectors will be discussed. Results obtained with a (lambda) c equals 2.5 micrometers Rockwell 1024 X 1024 HgCdTe array will be presented, where an off chip cryogenic operational amplifier was used yielding a rms read noise of 3 electrons. Sensitivity profiles of individual pixels have been measured with a single mode IR fiber. Limitations of PACE 1 technology, such as persistence, will be discussed. First results with the 1K X 1K array, which was installed in SOFI, an IR focal reducer providing 1-2.5 micron imaging and long slit grism spectroscopy at the NTT telescope, will be presented. Advanced techniques of real time image sharpening will also be included. An outlook to the development of (lambda) c equals 2048 X 2048 HgCdTe array formats will be given. The optical layout of NIRMOS, a multi-object spectrograph for the VLT telescope, is base don the availability of 2K X 2K HgCdTe arrays.
Raytheon/SBRC has demonstrated high quality Si:As IBC IR FPAs for both ground-based and space-based Mid-IR astronomy applications. These arrays offer in-band quantum efficiencies of approximately 50 percent over a wavelength range from 6 micrometers to 26 micrometers and usable responses from 2 micrometers to 28 micrometers . For high background, ground-based applications the readout input circuit is a direct injection (DI) FET, while for low background, space-based applications a source follower per detector (SFD) is used. The SFD offers extremely low noise and power dissipation, and is implemented in a very small unit cell. The DI input circuit offers much larger bucket capacity and better linearity compared with the SFD, and is implemented in a 50 micrometers unit cell. SBRC's Si:As IBC detector process results in very low dark current sand our Raytheon/MED readout process is optimized for very low redout noise at low temperature operation. SBRC is committed to achieving still better performance to serve the future needs of the IR astronomy community.
High performance 128 X 128 Si:As and Si:Sb blocked- impurity-band hybrid arrays have been developed for ground- based and airborne astronomy. These devices cover the 5-25 (Si:As) and 15-40 micrometers (Si:Sb) portions of the spectrum. The peak detective quantum efficiencies quantum efficiencies exceed 50 percent for Si:As and 30 percent for Si:Sb. An anti-reflection coat is used to increase responsivity and to reduce internal reflections for the Si:As detectors. The multiplexer yields a linear output response vs. integrated charge. A special design feature of the multiplexer is a changeable nodal capacitance that allows dynamic switching of the well depth between 1.8 X 106 and 1.8 X 107 electrons. The single-sample read noises for the two states are approximately 75 and approximately 760 electrons respectively. These devices have been used successfully to perform astronomical observations in a number of instruments.
Manufacturing specifications of IR transmitting crystalline optical components for wavelengths >= 0.7 microns should be important to the IR astronomer when designing imaging systems especially where cost and delivery are also major program concerns.
The ESO IR detector high speed array control and processing electronic IRACE is designed as a modular system and supports readout and data processing of arrays with four as well as multiple output channels. In addition the system can handle multiple separate arrays and the data re routed to multiple processing chains. Detector front-ends are galvanically separated form data processing and system administration with fiberoptic links. Interfaces to different data processing systems for on-line data handling are implemented. The paper describes principles of system operation, and the achieved readout and on-line processing speeds.
The NASA IRTF is building a multiple digital signal processor (DSP) based array electronics control system for SpeX, an NSF funded 1 to 5 micron medium resolution spectrograph. SpeX will use a 1024 X 1024 InSb array for spectroscopy and one 512 X 512 quadrant of another 1024 X 1024 InSb array for slit field viewing and IR guiding. An additional system is also being produce at the Institute for Astronomy for the SUBARU IR camera and spectrograph (IRCS). Plans for IRCS include the use of a 1024 X 1024 InSb array for spectroscopy and one 1024 X 1024 InSb array for IR imaging. This document will provide the instrument derived requirements, an overall system description, and some of the tradeoffs and technical choices made. The design for both system is an evolutionary upgrade of the current IRTF array control electronics system used in a 256 X 256 InSb based imager, a 256 X 256 InSb and 512 X 512 CCD in an echelle spectrograph, an 800 X 800 CCD based tiptilt correction system and a non-IRTF 128 X 128 Si:As BIB array based imager.
An overview on the use of grisms from high refractive index optical materials is given. When using grisms manufactured from silicon or germanium two IR focal-reducers of the European Southern Observatory (ESO) can serve as medium resolution echelle spectrometers. A silicon echelle grism allowing for a spectral resolution of 5000 for a 1 arcsec slit is being developed for SOFI, a near IR instrument featuring a 1024 Rockwell HgCdTe detector at ESO's 3.5m New Technology Telescope. For TIMMI2, ESO's new 10/20 micrometers instrument for the 3.6m telescope a germanium echelle grism is being built. For TIMMI a 10 micrometers camera featuring a 64 X 64 detector a low resolution germanium grism yielding a spectral resolution (lambda) /(Delta) (lambda) equals 200 for a 1 arcsec slit has already been successfully commissioned. The manufacturing process, the status and performances will be presented. Moreover we show some astronomical results.
Linear variable filters have found increasing applicability in spectrally selective optical instruments. They serve as moderate resolution spectral discriminators in astronomical instruments and in reconnaissance equipment. They perform extremely well as 'sliding out-of-band blocking filters' when used in conjunction with grating spectrometers.
We describe a grism suitable for low-resolution, slitless spectroscopy in the IR region between 3.0 and 5.0 micrometers . The grism is fabricated in silicon using a three-mask, photolithographic process, resulting in an eight-step binary approximation to the normal sawtooth grating profile. Desirable features of this approach include the ability to incorporate aberration correction in the gratin and a gentle ruing relief profile permitting a conformal anti-reflection coating for improved efficiency. To demonstrate the performance of this grism in a practical applications, we have constructed a slitless spectrograph system using an off-the-shelf InSb camera and simple, uncooled, refractive optics. This system is well suited to observing compact, bright, transient phenomena without good a priori knowledge of their positions. We present examples of present instrument performance. An upgrade currently under construction will increase sensitivity by cooling more of the optical path and increasing the aperture of the collecting optics. We plan to use the improved instrument to observe the Leonid Meteor shower in November 1998.
In order to increase throughput and maximize sensitivity the next-generation of astronomical instrumentation is moving toward cryogenic, all-reflective, off-axis optical design solutions. These off-axis systems require mirrors which are produced with complex conic sections, demand a thermal optical performance at cryogenic temperatures, and must support lifetimes on the order of 5-10 years. SSG specializes in the design, development, fabrication and testing of off-axis, all-reflective optical systems, having produced > 40 such systems over the last 20 years. The majority of these system have been produced using nickel plated aluminum mirror substrates and aluminum metering structures in order to obtain a passively systems has long been a point of debate. In this paper we demonstrate the long term stability of nickel plated aluminum optics by presenting interferometric test data obtained on > 10 optical elements over a period of 10 years. Cryogenic stability is demonstrated by presenting system level wavefront data obtained over a wide thermal range down to 115K. In addition, we will present thermal test data obtained from a number of alternate metal optical materials: beryllium, bare aluminum, and aluminum/beryllium alloys.
The new design of image slicer developed at Durham University for 2D area spectroscopy is described. The unit acts as a coupler between the telescope and a spectrograph to reformat a square or rectangular field into a long slit. Its advantages over previous designs of image slicers and other methods using fibers, lenses or narrow-band filtering are discussed, mainly: large field, high spatial resolution, large number of spectral resolution elements, high transmission, and the small size of the instrument. The system is also easy to cool and is then well suited for IR spectroscopy. The proposed design is a new type of image slicer in which the original 2D image is sliced into narrow sub-images that are re-imaged side by side to form a long 1D image at the spectrograph input. The flexibility of the concept at the base of this new design is highlighted through the description of 5 different slicer designs. Three of these are for future instruments now at the design phase: the CGS4 slicer, the UIST slicer and the GNIRS slicer; the two others are studies for possible future slicers on GMOS and NGST. These designs show how easily our slicer can be added to an existing instrument, how it can be incorporated to the slit wheel of future instruments, and how multi-slit reformatting permits a much larger field of view.
Micromachined silicon gratings offer two great advantages to astronomical spectroscopy in the IR: (1) Photolithographic processing techniques permit the production of gratings with much larger groove constants than are possible with conventional wavelength coverage, despite the relatively small format of IR arrays. (2) One can use anisotropic etching to form gratings on dielectric wedges. By illuminating the grating through the dielectric, we can achieve higher spectral resolution for a given grating size or a smaller grating for a given desired resolution. We discuss the technical challenges involved in micromachining large grating grooves over large areas while holding positional accuracy to very tight tolerances. Manufacturing issues include material choices, surface preparation, and chemical and physical effects during processing. We also discuss our program for evaluation of the finished products, show result of measurements we have made on front-surface and immersion devices, and use these result to assess the potential of these devices for real-world astronomical applications.
SPIFFI is an integral field spectrograph with an HAWAII array that enables us to simultaneously take near IR spectra of 1024 spatial pixels in a hexagonal field of view on the sky. It can be used on 4 to 8 meter class telescopes with a maximum pixel scale of 0.5 arcsec and with adaptive optics pixel scales, Nyquist sampling the point spread function of the telescope. A fiber bundle of 1024 silica/silica fibers rearranges the 2D field of view into the 1D entrance slit of the spectrometer. A novel technique involving flared fibers is used to achieve a high filling factor and coupling efficiency. Each fiber tip in the bundle is flared to increase the fiber core diameter by a factor of 15. The tapered end is polished to form a spherical micro-lens with a hexagonal cross-section to couple light into the fiber core. Apart from yielding a high coupling efficiency and a high geometrical filling factor, the monolithic micro- lens/fiber system can be used at a working temperature of 77K without loosing positioning accuracy. The spectrometer optics is achromatic from 1.1 to 2.5 microns and use four reflection gratings on a wheel as dispersing elements with a resolving power from 2000 to 4500. The fore-optics includes the filter wheel, the cold pupil stop and a scale changing mechanism to switch between three different image scales according to observing and seeing conditions. The spectrometer collimator is a f/4.3 three lens achromat, the spectrometer camera is a f/1.2 folded Schmidt camera. The optical design of the spectrometer is distortion free to get straight, equidistant spectra that match the columns of the detector, thus minimizing cross-talk form adjacent spectra to less than 5 percent.
We are constructing a fully cryogenic near-IR multi-object spectrometer for use from 9000 angstrom to 2.4 micrometers . When completed in the summer of 1999, FLAMINGOS will be the first fully cryogenic near-IR multi-object spectrometer and will thus allow efficient background limited operation through the entire H and K windows. Due to its very fast, wide field optical design FLAMINGOS is also an excellent survey imager being more than an order of magnitude more efficient than current and planned near-IR cameras. When used for multi- slit spectroscopy FLAMINGOS will be a factor of 50 to 100 more efficient than current near-IR spectrometers. FLAMINGOS can accept nay input beam slower than f/6. This makes it extremely versatile allowing use on a large number of telescopes. FLAMINGOS will have a large collimated space with a grism wheel and a filter wheel, providing multiple object near-IR survey spectroscopy at resolutions of 600 up to 2000. It will have a small separate cryogenic dewar with a cycling time less than 6 hours, which will hold 11 cryogenic multi-slit plates that are fabricated outside the dewar. This will allow multi-slit spectroscopy 50-100 objects simultaneously.
The MDM/Ohio State/ALADDIN IR Camera (MOSAIC) is a general purpose near IR imaging camera and medium-resolution long- slit spectrometer in use on the MDM 1.3-m and 2.4-m telescopes and the Kitt Peak 2.1-m and 4-m telescopes. In cooperation with NOAO and USNO, MOSAIC is one of the first general-purpose near-IR instruments available to the astronomical community that uses a first-generation 1024 X 512 ALADDIN InSb array, with the capability to use a full 1024 X 1024 array once one becomes available. MOSAIC provides tow imaging plate scales, and a variety of long- slit grism spectroscopic modes. This paper describes the general instrument design and capabilities, and presents representative scientific results.
The SMIRFS prototype near IR fiber system has been designed to provide a multi-object capability in the J, H and K bands and an integral field capability from 1 to 2 micrometers in conjunction with the cooled grating spectrograph CGS4 at the UKIRT. In multi-object mode there are 14 fibers covering a 12 arcmin2 field and in integral field mode there are 72 fibers covering a 6 X 4 arcsec field with spatial sampling of 0.63 arcsec. Both modes use fibers that are coupled to the telescope and spectrograph using lenslets. The information gleaned from these devices should benefit the next generation of IR spectrographs that will take full advantage of the larger chip formats that are now coming on line.
We have built a panoramic wide field near infrared imaging camera based on 4 Rockwell HAWAII 1024 X 1024 detectors. The baseline survey instrument operates in the region 0.8 to 1.8 micrometers on non-IR optimized telescopes with an upgrade at K band in 1999. The instrument was commission on the 2.5m INT and 4.2m WHT telescopes in December 1997 and January 1998. The main design goals in this project were to produce a highly productive astronomical instrument in a very short space of time and for low cost. Survey instruments are by their nature very versatile and CIRSI will support the wide range of astronomical interests at the Institute of Astronomy. Furthermore, since CIRSI is a traveling instrument and we are able to operate at a number of different telescopes to take opportunity of a range of image sizes and scales.
A new mid-IR spectrograph, the Texas Echelon Cross Echelle Spectrograph (TEXES) is under construction. The primary motivation for TEXES is to observe interstellar molecules at very high resolution. TEXES will operate at 7-25 micrometers wavelength with three spectrographic modes: a high resolution cross-dispersed mode, with R approximately equals 100,000, a mid-resolution long-slit mode, with R approximately equals 14,000, and a low resolution long-slit mode, with R approximately equals 2000. In hi-res mode, the primary disperser is a 36 inch long, R10 grating with a 7 mm groove spacing. The echelon is cross-dispersed with a 7 in long R2 echelle. In mid-res mode, the echelon is by-passed with an Offner relay, and the echelle is used by itself. In lo-res mode, a first-order grating is inserted over the echelle. For initial test, TEXES will use a Hughes Aircraft 20 X 64 pixel Si:As impurity-band array, which covers only two echelon orders. It will later be replaced with a 256 X 256 pixel array, which will Nyquist sample approximately 10 orders. The spectrograph has been assembled and tested with a partially complete echelon, demonstrating the soundness of the design. When we began this project, we were unable to find a vendor capable of machining or ruling a diffraction grating with the very coarse ruling required. Consequently, we attempted to hand-fabricate the echelon. We have not succeeded in assembling the echelon with the required precision, missing by about a factor of two. Fortunately, Hyperfine, Inc. is now capable of diamond machining the echelon. We are purchasing a machined echelon, and hope to complete the spectrograph by the end of summer 1998.
The Instituto de Astrofisica de Canarias (IAC) is undertaking the design and construction of a common-user near IR spectrograph (LIRIS) for the Cassegrain focus of the 4.2 m William Herschel Telescope sited at the Observatorio del Roque de Los Muchachos. LIRIS will be a near IR intermediate-resolution spectrograph designed to operate over a spectral resolution range between 1000 and 5000, with added capabilities for coronographic, multiproject and polarimetric observations. The instrument allows the combination of an adequate spatial resolution with a large useful field of view across the slit, thanks to the use of the new 1024 X 1024 pixel HgCdTe Hawaii detector manufactured by Rockwell. All the optics and mechanisms situated inside the cryostat will be cooled to below 100 K. The detector will operate at 77 K. Calibration and tracking will be made with the existing Cassegrain A and G Box, into which a near IR calibration system will be incorporated.
An imaging spectrometer is being designed to take advantage of recent improvements in the image quality achieved at the UK Infrared Telescope. The realization of near-diffraction limited imaging at two microns brings with it the possibility of significant improvements in sensitivity to IR observations. UIST will provide a versatile facility for high spatial resolution imaging and spectroscopy in the 1-5 micrometers wavelength range. We will present the opto-mechanical design of this new instrument, highlighting the innovative features. These include provision of multiple pixel scales within the camera and polarimetry via a Wollaston prism. One of the most challenging areas of the design is the inclusion of a cryogenic integral field unit for area spectroscopy over a 5 inch field. The spectroscopic modes include cross- dispersed spectroscopy over the complete 1-2.5 micrometers wavelength ranges and moderate resolution long slit or area spectroscopy over the complete 1-5 micrometers range. A higher resolution mode will also the included. This will allow USTI to take advantage of the very low backgrounds to be found between OH sky lines. The instruments will incorporate a 1024 X 1024 Indium Antimonide array from SBRC. The development of the IR array controller for UIST will also be discussed.
SpeX is a medium-resolution 0.8-5.5 micrometers cryogenic spectrograph being built at the Institute for Astronomy, University of Hawaii, for the NASA IR Telescope Facility on Mauna Kea. SpeX was funded by the National Science Foundation in July 1994. First-light is expected in 1999. The primary scientific driver of the instrument is to provide maximum simultaneous wavelength coverage at a spectral resolving power which is well-matched to many planetary, stellar and galactic features, and which adequately separates sky emission lines and disperses sky spectral resolutions of R approximately 1000-2000 simultaneously across 0.9-2.5 micrometers , 2.0-4.2 micrometers , or 2.4- 5.5 micrometers . SpeX will use an Aladdin II 1024 X 1024 InSb array in its spectrograph and an Aladdin II 512 X 512 InSb array in its IR slit-viewer.
The South Pole Imaging Fabry-Perot Interferometer (SPIFI) is a direct detection, imaging, submillimeter spectrometer. The spectral resolving elements are a pair of cryogenic, scanning Fabry-Perot interferometers which use a free- standard Ni mesh for the etalon mirrors. The detectors for SPIFI are a 5 X 5 array of bolometers coupled to the focal plane with Winston cones. An adiabatic demagnetization refrigerator cools the bolometers to approximately 60 mK while a 3He system operates simultaneously as a thermal guard. SPIFI is intended to operate on the ASO/RO submillimeter telescope at the South Pole and on the JCMT telescope on Mauna Kea and will be used to study the gas- phase reservoirs of carbon in star-forming regions in our own and near-by galaxies. SPIFI takes advantage of three things: (1) Advanced bolometers that achieve background limited performance at very high resolving powers. (2) The imaging capability and high spectral resolving power of Fabry-Perot interferometers. (3) The superb atmospheric transmission in submillimeter bands possible from the South Pole. The SPIFI uses state-of-the-art monolithic silicon bolometers fabricated at the NASA Goddard Space Flight Center. The cryogenic, scanning Fabry-Perots in SPIFI were designed and built at Cornell and are an evolution of the design used with great success for the Kuiper Wide Field Camera. The 1.7 m Antarctic Submillimeter Telescope/Remote Observatory exploits what is thought to be the best submillimeter observing site in the world.
Omega Cass is the new MPIA multi-mode camera for imaging and spectroscopy at near IR wavelengths between 1.0 and 2.5 micrometers . The Camera is equipped with an 1024 X 1024 HAWAII HgCdTe focal plane array from Rockwell. The cryogenic re- imaging optics are designed to cover a wide variety of observing conditions. The imaging scales can be changed during observations, allowing the observer to react to changing conditions. Three different lens sets provide scales of 0.3, 0.2 and 0.1 arcsec/pixel at the f/10 Cassegrain focus of the 3.5m telescope. In combination with a laser based adaptive optics system, available at the same telescope, these imaging scale correspond to 0.12, 0.08 and 0.04 arcsec/pixel, which double samples the diffraction limit at the shortest operation wavelength. A set of grisms allow low to medium resolution long slit spectroscopy up to R equals 1000. In addition, sensitive polarimetry can be done with Wollaston prisms and wire grid analyzers. Omega-Cass is mainly designed for the 3.5m telescope on Calar Alto, although it may be used at any other telescopes with a focal ratio slower than f/8, including the MPIA's 2.2m telescopes on Calar Alto and La Silla.
Two wide field, multiple beam, near IR cameras are being developed for the MMT and Whipple Observatories. For the MMT a triple beamed, 1024 X 1024 pixel camera for the 6.5-m f/5 is being designed. As a prototype for the MMT and for use on the Whipple Observatory 1.2-m telescope, a dual beamed, 256 X 256 InSb array camera with three selectable magnifications has been built and in use for the past year.
A 1-5 micrometers IR camera and spectrograph (IRCS) is described. The IRCS will be a facility instrument for the 8.2 m Subaru Telescope at Mauna Kea. It consists of two sections, a spectrograph and a camera section. The spectrograph is a cross-dispersed echelle that will provide a resolving power of 20,000 with a slit width of 0.15 arcsec and two-pixel sampling. The camera section serves as a slit viewer and as a camera with two pixel scales, 0.022 arcsec/pixel and 0.060 arcsec/pixel. Grisms providing 400-1400 resolving power will be available. Each section will utilize an ALADDIN II 1024 X 1024 InSb array. The instrument specifications are optimized for 2.2 micrometers using the adaptive optics and the tip-tilt secondary systems of the Subaru Telescope.
The following capabilities have been identified as high priority for future Gemini instrumentation. (1) A natural guide star/laser beacon adaptive optics (AO) system at Cerro Pachon, and laser beacon capability for the Mauna Kea AO system. (2) A near IR coronagraph/imager for Cerro Pachon. (3) 1-2.5 micrometers multi-object spectroscopic capability, including IFU and multi-slit capability for use with AO corrected images, and wide field multi-object capability over at least 5 arcmin field of view. (4) Polarization modulators for optical and IR wavelengths at both Mauna Kea and Cerro Pachon. (5) A high stability lab optical spectrometer for Cerro Pachon, with resolutions around 120K and >= 300K.
The University of Florida is developing the mid-IR imager, called GatirCam, to be used primarily, but not solely, at the southern hemisphere Gemini telescope at Cerro Pachon, Chile. Key features of GatirCam are its fully reflective optics, its very high mechanical rigidity, and the fact that the associated electronics are very similar to those is in use successfully on similar instrumentation. Design studies for GatirCam indicate that it will meet or exceed all critical requirements of image quality and performance. A low-resolution spectroscopic mode is also currently under consideration for implementation in GatirCam.
We discuss the main design features of the Gemini Near-IR Imager (NIRI) and its scientific capabilities. NIRI is designed to fully exploit the excellent image quality and low telescope emissivity expected from the Gemini telescope on Mauna Kea. It offers a range of pixel scales matched to different scientific objectives and has spectroscopic as well as polarimetric capabilities. One of its main design features is the use of a near-IR 2 X 2 Shack-Hartmann wavefront sensor for tip-tilt and focus control.
The design of a near-IR spectrometer for the Gemini 8m telescopes is described. This instrument, GNIRS, provides coverage from 0.9 to 5.5 micrometers at several spectral resolutions and two pixel scales. Capabilities include an imaging mode intended primarily for acquisition, a cross- dispersed mode covering wavelengths from 0.9 to 2.5 micrometers , and provisions for an integral field unit. The design of the GNIRS is conservative, as it must meet tight schedule and resource constraints; it nonetheless provides high throughput and operational efficiency, minimal flexure, and the flexibility needed to support queue observing. The optics are a combination of diamond-turned metal optics for the fore-optics and collimator, and refractive optics for the cameras. The mechanism include a two-axis grating turret; all mechanism are deposited by means of internal detents. The instrument achieves low flexure within its weight budget by the use of a modular structure composed of cylindrical light-weighted sections into which individual mechanisms and optics modules are mounted. Extensive analyses of mechanical and optical performance have been performed. The GNIRS has passed its critical design review, and fabrication is now underway.
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.
We present a technical description, and up-to-date status report, of the mid-IR imaging Fabry-Perot interferometer system (MIRFI) currently under development by the IR Astronomy Group at the University of California, Irvine. MIRFI, which is designed primarily for operation with the new Keck 10-m telescopes, will facilitate diffraction- limited imaging at extremely high spectral resolution in a variety of important mid-IR ionic and molecular spectral lines. The unique design goals of MIRFI, namely its high spectral resolving power and diffraction-limited imaging capability, are ideally suited for studying the dynamics of extended, optically obscured regions of ionic or warm molecular gas. Such regions include, but are not restricted to, (1) HII regions associated with young OB star clusters, (2) molecular cloud shocks associated with young stellar outflows, (3) photodissociation regions, (4) the Galactic Center, and (5) galactic nuclei and extragalactic HII regions.
The long wavelength IR camera is a facility instrument for the Keck Observatory designed to operate at the f/25 forward Cassegrain focus of the Keck I telescope. The camera operates over the wavelength band 7-13 micrometers using ZnSe transmissive optics. A set of filters, a circular variable filter, and a mid-IR polarizer are available, as are three plate scales: 0.05 inch, 0.10 inch, 0.12 inch per pixel. The camera focal plane array and optics are cooled using liquid helium. The system has been refurbished with a 128 X 128 pixel Si:As detector array. The electronics readout system used to clock the array is compatible wit both the hardware and software of the other Keck IR instruments NIRC and LWS. A new pre-amplifier/A-D converter has been designed and constructed which decreases greatly the system susceptibility to noise.
The instrument ensemble at ESO's Very Large Telescope will be extended by a high-resolution echelle spectrograph for the 1-5 micrometers wavelength range. Primary design goals are high spectral resolution, wide coverage and high sensitivity. Several novel features are introduced with this instrument. At the same time, development time and risk will be minimized through the use of concepts available from earlier ESO VLT instruments.
A high resolution near IR camera (CONICA) for the firs VLT unit is under development, which will provide diffraction limited spatial resolution being combined with the adaptive optics system NAOS. CONICA serves as a multi-mode instrument for the wavelength region between 1.0 and 5.0 micrometers , offering broad band, narrow band or Fabry Perot direct imaging capabilities, polarimetric modes using Wollaston prism or wire grid analyzers and long slit spectroscopy up to a spectral resolution of about 1000 per two pixel. We presented a first concept of CONICA in 1995. In the mean time, large parts of the instrument have been manufactured, the cryostat and the adapter have been finished and first cryogenic test have been performed. This paper describes the actual design and status of development of CONICA focusing on those aspects which have not been described in detail before or the design of which have been changed in the mean time.
In this paper, we present VISIR, the mid-IR instrument to be installed in 2001 on the telescope unit number 3 or the European Very Large Telescope program. The instrument combines imaging capabilities over a field up to about 1 arcmin at the diffraction limit of the telescope, and long- slit grating spectroscopy capabilities with various spectral resolutions. The contract to design and build VISIR was signed in November 1996 between ESO and a French-Dutch consortium of institutes. One year after the signature of the contract, VISIR has successfully passed the preliminary design review. The results of the first year of studies are presented here.Emphasis is put on the optical design which is in its final form.
The imaging photopolarimeter ISOPHOT on-board the European satellite ISO houses 144 background detectors of Si:Ga, Si:P, Ge:Ga and stressed Ge:Ga, all sampled by newly developed cold read-out electronics. There is large temporal radiation damage to most of these detectors on the daily passage through the earth's radiation belts. In addition the Ge:Ga detectors exhibit a continuous responsivity increase caused by the cosmic radiation far off the earth. Effective curing procedure shave been developed to heat out these effects. The in-flight sensitivities achieved are close to the pre-flight predictions for most channels. At 100-200 micrometers cirrus confusion is a serious limit for the detection of faint objects on large parts of the sky. The cold filter wheel carrying 56 optical elements, such as filters, apertures and polarizers, as well as the focal plane chopper, operate with high precision and very low power consumption. Due to an effective cold internal baffle system the measured near-field straylight was close to the pre- flight theoretical prediction based on APART simulations. THe sun and moon straylight at 25 and 175 micrometers was measured during several solar eclipses. Drift and transients of the detectors, non-linearities of the preamplifiers, ionizing radiation effects and a complex optical path make the photometric calibration of this instrument challenging. Because most of these effects are reproducible, a calibration accuracy of < 30 percent is already available for most photometric modes. Examples of observations, including the 175 micrometers Serendipitous Sky Survey, will highlight the capabilities of the instrument.
The long wavelength spectrometer on-board the European Space Agency IR Space Observatory (ISO) uses a grating and one of two Fabry-Perot interferometers to make medium and high resolution spectroscopic observations in the 43-196.9 micrometers wavelength range. The instrument has been in continuous use since the launch of ISO in November 1995. In this paper we describe the calibration of the instrument and its performance, both spectroscopic and photometric, over the two years of instrument operations.
The telescope system of a Japanese IR Astronomical Space Mission, 'IR Imaging Surveyor (IRIS)', is described. The IRIS is a cryogenically-cooled telescope, being planned to be launched in 2003. It will make astronomical observations from near-IR to far-IR regions. The IRIS telescope system is a Ritchey-Chretien type, whose primary mirror size ins 700mm in diameter and whose system F ratio is 6. In order to share the focal plane with two scientific instruments and a focal- plane star sensor, it has a clear field of view of 38 arcminutes in radius. It is being designed to achieve the diffraction-limited performance at 5 micrometers for temperatures below 10K. The IRIS telescope will use light-weight silicon carbide (SiC) mirrors. The current estimate of the primary mirror weight is 9 kg and the goal of total weight of the telescope system is less than 27 kg. Preliminary tests of small size SiC mirrors at 4.2K suggest that slight distortion of the surface figure detected at low temperatures can be reduced by improved CVD processes. The telescope system is designed to meet the launch conditions of the M-V rocket and to have the fundamental frequencies above 100 Hz.
The far-IR Surveyor (IRS) is one of the two focal plane instruments of the IR Imaging Surveyor, IRIS, which is a Japanese IR astronomical satellite. FIS is designed primarily to perform an all-sky survey with several photometric bands like IRAS. Advantages of FIS to IRAS are its high detectivity of point sources and its longer wavelength capability. These features are gained by remarkable improvement in detector technology. FIS adopts currently developed unstressed and stressed Ge:Ga array detectors to cover 50 to 200 micrometers in wavelength. Due to highly sensitive detector system, it is expected to detect over 10 million objects by the all-sky, including a lot of high-z objects. FIS also has spectroscopic capability by a Fourier spectrometer covering 50 to 200 cm-1 in wave number with spectral resolution of 0.5 cm-1. The same detector arrays of the scanner are used and these two functions are switched. As a result of combining a spectroscopic function with the scanner, FIS becomes a unique instrument. The basic observation mode of the FIS is an all-sky survey using the scanner. The spectroscopic function is operated in the pointing mode in which it can take longer integration time. Spectral information can be used to estimate the redshifts of strange objects detected by the all-sky survey. The spectrometer is also a powerful instrument to reveal the physical properties of galactic and nearby sources.
Basic design and current development status of IRC: an IR camera on-board the IRIS is presented. IRC is one of the focal-plane instruments of the 70cm cooled telescope of the IRIS. IRC utilizes recently developed large-format IR arrays for imaging and low-resolution spectroscopy at wavelength 1.8-26 micrometers . IRC consist of 3 camera channels: NIR, MIR-S, and MIR-L. These 3 channels simultaneously observe different fields of the sky, with diffraction-limited spatial resolution. One critical component limiting the performance of the IRC is the performance of large-format arrays: 512 X 412 format InSb and 256 X 256 format Si:As IBC arrays operation at very low temperature. Performance test of the Si:As array manufactured by the Hughes/SBRC is under way, and the preliminary results is presented. Design of the camera optics and the optical components is also presented. IRC is operated under the pointing observation of about 500 sec exposure time, and the development goal is to achieve high point-source detectivity limited nearly by the confusion due to faint astronomical sources.
The joint US and German SOFIA project to develop and operate a 2.5 meter IR airborne telescope in a Boeing 747-SP is now in its second year. The Universities Space Research Association , teamed with Raytheon E-Systems and United Airlines, is developing and will operate SOFIA. The 2.5 meter telescope will be designed and built by a consortium of German companies led by MAN. Work on the aircraft and the preliminary mirror has started. First science flights will begin in 2001 with 20 percent of the observing time assigned to German investigators. The observatory is expected to operate for over 20 years. The sensitivity, characteristics, US science instrument complement, and operations concept for the SOFIA observatory, with an emphasis on the science community's participation are discussed.
SOFIA will permit observations not possible from ground based telescopes, while retaining a number of their major advantages for observers. These include the opportunity to change focal plane instruments frequently, and continuous access to the instrument while observing. SOFIA is being designed to maximize the benefits of these features and to assure optimum performance of the instruments, within the constraints of available resources. This paper describes the top level optical, mechanical, and electronic interface parameters and configuration issues foreseen for Science Instruments on SOFIA.
NASA's Stratospheric Observatory for IR Astronomy (SOFIA) will enable unprecedented IR acuity at wavelengths obscured from the ground. To help open this new chapter in the exploration of the IR universe, we are developing the Airborne IR Echelle Spectrometer (AIRES) as a facility science instrument. Full funding was awarded for a four year development in October, 1997. The instrument is scheduled to come on-line with the observatory in the Fall of 2001. It will be used to investigate a broad range of phenomena that occur in the interstellar medium. AIRES will use a 1200 mm long, 76 degree blaze angle echelle to combine high resolution spectroscopy with diffraction-limited imaging in the cross-dispersion direction. Its three 2D detector arrays will prove good sensitivity over a decade in wavelength. An additional array will be used as a slit viewer for (lambda) <EQ 28 micrometers to image source morphology and to verify telescope pointing. Our scientific motivation, preliminary optical design and packaging, focal plane configuration, echelle prototyping, and cryostat layout are described.
The spectral-photometric IR camera SPICA is proposed as one of the German science instruments of the Stratospheric Observatory for IR Astronomy (SOFIA). It will cover a wavelength range of 20-220 micrometers with three large area detector arrays. With the 2.5 m SOFIA telescope, SPICA will provide unprecedented diffraction limited spatial resolution in the far-IR. In addition, low resolution 3D-imaging spectroscopy is planned. While the silicon array will be commercially available, the germanium arrays are being developed, including their cryogenic multiplexers. The overall instrument concept, its camera optics and the status of the detector development will be presented. The instrument is being developed by the DLR Institute of Space Sensor Technology in Berlin with support of several German and US partners.
To study narrow features in quiescent molecular clouds, a high spectral resolution, high sensitivity instrument is required. We present the design and capabilities of a mid-IR spectrograph being built as a PI instrument for the Stratospheric Observatory for IR Astronomy. The Echelon- Cross-Echelle Spectrograph (EXES) will operate from 5.5-28.5 micrometers in three spectroscopic modes: R approximately 105, 104, and 1500. EXES is similar in concept to our ground based instrument, TEXES. EXES consists of three chambers. The first chamber contains focal-reducing optics. The second chamber houses the high resolution grating, an echelon. Discussion of the echelon can be found elsewhere in this volume. The third chamber contains an echelle grating and a first order grating mounted back-to-back. A flip mirror selects operating mode by either directing light into the echelon chamber or allowing the light to pass through to the grating chamber. Re-imaging optics upstream of the detector provide two plate scales. The detector, a 256 by 256 pixel Si:As IBC, is in a baffled subsection of the third chamber. Finally, the low resolution grating serves as a slit positioning camera when it is rotated face on.
We describe our design for an imaging far-IR spectrometer for NASA/DARA's SOFIA observatory. The design of the instrument is driven by the goal of maximizing observing efficiency. Since the sensitivity of well designed FIR instruments is limited by the thermal background of telescope and atmosphere, observing efficiency can only be increased by increasing the throughput of the spectrometer and the number of simultaneous data channels. Our instrument will feature two separate medium resolution grating spectrometers with common fore-optics feeding two large Ge:Ga arrays. The two Littrow spectrometers operate between 45-110 micrometers , and 110-210 micrometers , resp., in 1st and 2nd order. Multiplexing takes place both spectrally and spatially. An image slicer redistributes 5 by 5 pixel fields-of-view along the 1 by 25 pixel entrance slits of the spectrometers. Anamorphic collimator mirrors help keep the spectrometer compact in the cross-dispersion direction. The spectrally dispersed images of the flits are anamorphically projected onto the detector arrays, to independently match spectral and spatial resolution to detector size. We will thus be able to instantaneously cover a velocity range of approximately 1500 km/s around a selected FIR spectral line, for each of the 25 spatial pixels. For calibration and flatfielding we use blackbody calibrators internal to the instrument, at signal levels comparable to the thermal background of the telescope. An image rotator compensates field rotation during long integrations. Estimated sensitivity of the spectrometer is approximately 2 by 10-15W/(root)Hz/pixel.
FIRST and SOFIA are both future IR observatories with 3m class main mirrors having sophisticated instrumentation aboard. The present design of the FIRST imaging spectrometer PACS requires two large far-IR photoconductor arrays of 25 X 16 pixels each, the baseline material is stressed and unstressed Ge:Ga. A gallium arsenide photoconductive detector which is sensitive in the far IR (FIR) wavelength range from about 60 micrometers to 300 micrometers might offer the advantage of extending considerably the long wavelength cut- off of presently available photodetectors. FIRGA is an ESA sponsored detector development program on this matter involving international partners. The aim is a monolithic 4 X 32 demonstrator array module with associated cryogenic read-out electronics. Recent progress in material research has led to the production of Te-doped n-type GaAs layers using liquid phase epitaxy. We prepared sample detectors from those material and investigated their electrical and IR characteristics. First measurements indicate that GaAs has in principle considerable potential as a FIR photon detector. Theoretical modeling of GaAs detectors can help with the detector design and allows the prediction of response transients as a function of detector parameters. Present development activities are mainly concentration on material research, i.e. the production of GaAs:Te with improved FIR characteristics. Results of the current test and measurements are reported. The FIRGA study is intended to prepare the technology for large 2D GaAs detector arrays for far IR astronomy.