Large-format infrared detectors are at the heart of major ground and space-based astronomical instruments, and the HgCdTe HxRG is the most widely used. The Near Infrared Spectrometer and Photometer (NISP) of the ESA’s Euclid mission launched in July 2023 hosts 16 H2RG detectors in the focal plane. Their performance relies heavily on the effect of image persistence, which results in residual images that can remain in the detector for a long time contaminating any subsequent observations. Deriving a precise model of image persistence is challenging due to the sensitivity of this effect to observation history going back hours or even days. Nevertheless, persistence removal is a critical part of image processing because it limits the accuracy of the derived cosmological parameters. We will present the empirical model of image persistence derived from ground characterization data, adapted to the Euclid observation sequence and compared with the data obtained during the in-orbit calibrations of the satellite.
The Large Interferometer For Exoplanets (LIFE) is a proposed space mission that enables the spectral characterization of the thermal emission of exoplanets in the solar neighborhood. The mission is designed to search for global atmospheric biosignatures on dozens of temperate terrestrial exoplanets and it will naturally investigate the diversity of other worlds. Here, we review the status of the mission concept, discuss the key mission parameters, and outline the trade-offs related to the mission’s architecture. In preparation for an upcoming concept study, we define a mission baseline based on a free-formation flying constellation of a double Bracewell nulling interferometer that consists of 4 collectors and a central beam-combiner spacecraft. The interferometric baselines are between 10–600m, and the estimated diameters of the collectors are at least 2m (but will depend on the total achievable instrument throughput). The spectral required wavelength range is 6–16μm (with a goal of 4–18.5μm), hence cryogenic temperatures are needed both for the collectors and the beam combiners. One of the key challenges is the required deep, stable, and broad-band nulling performance while maintaining a high system throughput for the planet signal. Among many ongoing or needed technology development activities, the demonstration of the measurement principle under cryogenic conditions is fundamentally important for LIFE.
PRIMA addresses questions about the origins and growth of planets, supermassive black holes, stars, and dust. Much of the radiant energy from these formation processes is obscured and only emerges in the far infrared (IR) where PRIMA observes (24–261 um). PRIMA’s PI science program (25% of its 5-year mission) focuses on three questions and feeds a rich archival Guest Investigator program: How do exoplanets form and what are the origins of their atmospheres? How do galaxies’ black holes and stellar masses co-evolve over cosmic time? How do interstellar dust and metals build up in galaxies over time? PRIMA provides access to atomic (C, N, O, Ne) and molecular lines (HD, H2O, OH), redshifted PAH emission bands, and far-IR dust emission. PRIMA’s 1.8-m, 4.5-K telescope serves two instruments using sensitive KIDs: the Far-InfraRed Enhanced Survey Spectrometer (continuous, high-resolution spectral coverage with over an order of magnitude improvement in spectral line sensitivity and 3-5 orders of magnitude improvement in spectral survey speed) and the PRIMA Imager (hyperspectral imaging, broadband polarimetry). PRIMA opens new discovery space with 75% of the time for General Observers.
KEYWORDS: Calibration, Coronagraphy, Simulations, Observational astronomy, Data processing, Exoplanets, Equipment, Analog electronics, Space telescopes, Signal processing
The Nancy Grace Roman Space Telescope’s Coronagraph Instrument will for the first time demonstrate active wavefront sensing and control for a space-based coronagraph, and may image the first planet in reflected light. The Community Participation Program has been initiated to engage members of the broader scientific community in the preparation for its planned launch in late 2026/early 2027. Here we will present the on-going work of the Data Reduction and Simulations working group, one of the four working groups within the Community Participation Program. The working group is charged with the development of the data reduction and postprocessing pipeline for the on-sky data and the development of a simulation suite to aid in the preparation and planning of Roman Coronagraph observations.
In preparation for the operational phase of the Nancy Grace Roman Space Telescope, NASA has created the Coronagraph Community Participation Program (CPP) to prepare for and execute Coronagraph Instrument technology demonstration observations. The CPP is composed of 7 small, US-based teams, selected competitively via the Nancy Grace Roman Space Telescope Research and Support Participation Opportunity, members of the Roman Project Team, and international partner teams from ESA, JAXA, CNES, and the Max Planck Institute for Astronomy. The primary goals of the CPP are to prepare simulation tools, target databases, and data reduction software for the execution of the Coronagraph Instrument observation phase. Here, we present the current status of the CPP and its working groups, along with plans for future CPP activities up through Roman’s launch. We also discuss plans to potentially enable future commissioning of currently-unsupported modes.
The Coronagraphic Instrument onboard the Nancy Grace Roman Space Telescope is an important stepping stone towards the characterization of habitable, rocky exoplanets. In a technology demonstration phase conducted during the first 18 months of the mission (expected to launch in late 2026), novel starlight suppression technology may enable direct imaging of a Jupiter analog in reflected light. Here we summarize the current activities of the Observation Planning working group formed as part of the Community Participation Program. This working group is responsible for target selection and observation planning of both science and calibration targets in the technology demonstration phase of the Roman Coronagraph. We will discuss the ongoing efforts to expand target and reference catalogs, and to model astrophysical targets (exoplanets and circumstellar disks) within the Coronagraph’s expected sensitivity. We will also present preparatory observations of high priority targets.
The Nancy Grace Roman Space Telescope, NASA's next flagship mission in astrophysics, is due for launch in May 2027 with an onboard Coronagraph Instrument (CGI) which will serve as a technology demonstrator for exoplanet direct imaging. The Roman Coronagraph will be capable of detecting and characterizing exoplanets and circumstellar disks in visible light at an unprecedented contrast level of ~108 or better at small separations. The instrument is equipped with six precision alignment mechanisms (PAMs) which enable ultra-stable, sub-micrometer positioning of optical elements such as coronagraphic masks, optical filters and polarizers. In order to achieve contrast level, which are 2 to 3 orders of magnitude better than state-of-the-art visible or near-infrared coronagraphs, the mechanisms need to be stable at sub-microradian levels during a typically 10 hour long science observation. We report here about the development of these mechanisms and present their performance test results from the qualification/flight acceptance test program. All PAM flight models were delivered in the year 2022 and integrated into the CGI flight instrument. Meanwhile CGI has successfully completed all testing at JPL and was shipped to NASA GSFC in May 2024 for final integration into the Roman spacecraft.
Euclid, the M2 mission of the ESA’s Cosmic Vision 2015-2025 program, aims to explore the Dark Universe by conducting a survey of approximately 14 000 deg2 and creating a 3D map of the observable Universe of around 1.5 billion galaxies up to redshift z ∼ 2. This mission uses two main cosmological probes: weak gravitational lensing and galaxy clustering, leveraging the high-resolution imaging capabilities of the Visual Imaging (VIS) instrument and the photometric and spectroscopic measurements of the Near Infrared Spectrometer and Photometer (NISP) instrument. This paper details some of the activities performed during the commissioning phase of the NISP instrument, following the launch of Euclid on July 1, 2023. In particular, we focus on the calibration of the NISP detectors’ baseline and on the performance of a parameter provided by the onboard data processing (called NISP Quality Factor, QF) in detecting the variability of the flux of cosmic rays hitting the NISP detectors. The NISP focal plane hosts sixteen Teledyne HAWAII-2RG (H2RG) detectors. The calibration of these detectors includes the baseline optimization, which optimizes the dynamic range and stability of the signal acquisition. Additionally, this paper investigates the impact of Solar proton flux on the NISP QF, particularly during periods of high Solar activity. Applying a selection criterion on the QF (called NISP QF Proxy), the excess counts are used to monitor the amount of charged particles hitting the NISP detectors. A good correlation was found between the Solar proton flux component above 30 MeV and the NISP QF Proxy, revealing that NISP detectors are not subject to the lower energy components, which are absorbed by the shielding provided by the spacecraft.
The mid/far infrared hosts a wealth of spectral information that allows direct determination of the physical state of matter in a large variety of astronomical objects, unhindered by foreground obscuration. Accessing this domain is essential for astronomers to much better grasp the fundamental physical processes underlying the evolution of many types of celestial objects, ranging from protoplanetary systems in our own milky way to 10-12 billion year old galaxies at the high noon of galaxy formation in our universe. The joint ESA/JAXA SPICA mission will give such access for the astronomical community at large, by providing an observatory with unprecedented mid- to far-infrared imaging, polarimetric and spectroscopic capabilities.
Measurements in the infrared wavelength domain allow us to assess directly the physical state and energy balance of cool matter in space, thus enabling the detailed study of the various processes that govern the formation and early evolution of stars and planetary systems in the Milky Way and of galaxies over cosmic time. Previous infrared missions, from IRAS to Herschel, have revealed a great deal about the obscured Universe, but sensitivity has been limited because up to now it has not been possible to fly a telescope that is both large and cold. Such a facility is essential to address key astrophysical questions, especially concerning galaxy evolution and the development of planetary systems.
SPICA is a mission concept aimed at taking the next step in mid- and far-infrared observational capability by combining a large and cold telescope with instruments employing state-of-the-art ultra-sensitive detectors. The mission concept foresees a 2.5-meter diameter telescope cooled to below 8 K. Rather than using liquid cryogen, a combination of passive cooling and mechanical coolers will be used to cool both the telescope and the instruments. With cooling not dependent on a limited cryogen supply, the mission lifetime can extend significantly beyond the required three years. The combination of low telescope background and instruments with state-of-the-art detectors means that SPICA can provide a huge advance on the capabilities of previous missions.
The SPICA instrument complement offers spectral resolving power ranging from ~50 through 11000 in the 17-230 µm domain as well as ~28.000 spectroscopy between 12 and 18 µm. Additionally, SPICA will be capable of efficient 30-37 µm broad band mapping, and small field spectroscopic and polarimetric imaging in the 100-350 µm range. SPICA will enable far infrared spectroscopy with an unprecedented sensitivity of ~5x10-20 W/m2 (5σ/1hr) - at least two orders of magnitude improvement over what has been attained to date. With this exceptional leap in performance, new domains in infrared astronomy will become accessible, allowing us, for example, to unravel definitively galaxy evolution and metal production over cosmic time, to study dust formation and evolution from very early epochs onwards, and to trace the formation history of planetary systems.
The Habitable Exoplanet Imaging Mission (HabEx) concept has been designed to enable an extensive suite of science, broadly put under the rubric of General Astrophysics, in addition to its exoplanet direct imaging science. General astrophysics directly addresses multiple NASA programmatic branches, and HabEx will enable investigations ranging from cosmology, to galaxy evolution, to stellar population studies, to exoplanet transit spectroscopy, to Solar System studies. This poster briefly describes one of the two primary HabEx General Astrophysics instruments, the HabEx Workhorse Camera (HWC). HWC will be a dual-detector UV-to-near-IR imager and multi-object grism spectrometer with a microshutter array and a moderate (3' x 3') field-of-view. We detail some of the key science we expect HWC to undertake, emphasizing unique capabilities enabled by a large-aperture, highly stable space-borne platform at these
wavelengths.
The far-infrared (FIR) regime is one of the few wavelength ranges where no astronomical data with sub-arcsecond spatial resolution exist yet. Also medium-term satellite projects like SPICA, Millimetron or OST will not resolve this malady. For many research areas, however, information at high spatial and spectral resolution in the FIR, taken from atomic fine-structure lines, from highly excited CO and especially from water lines would open the door for transformative science. These demands call for interferometric concepts. We present here first results of our feasibility study IRASSI (Infrared Astronomy Satellite Swarm Interferometry) for an FIR space interferometer. Extending on the principal concept of the previous study ESPRIT, it features heterodyne interferometry within a swarm of 5 satellite elements. The satellites can drift in and out within a range of several hundred meters, thereby achieving spatial resolutions of <0.1 arcsec over the whole wavelength range of 1–6 THz. Precise knowledge on the baselines will be ensured by metrology employing laser frequency combs, for which first ground-based tests have been designed by members of our study team. In this contribution, we first give a motivation how the science requirements translated into operational and design parameters for IRASSI. Our consortium has put much emphasis on the navigational aspects of such a free-flying swarm of satellites operating in relatively close vicinity. We hence present work on the formation geometry, the relative dynamics of the swarm, and aspects of our investigation towards attitude estimation. Furthermore, we discuss issues regarding the real-time capability of the autonomous relative positioning system, which is an important aspect for IRASSI where, due to the large raw data rates expected, the interferometric correlation has to be done onboard, quasi in real-time. We also address questions regarding the spacecraft architecture and how a first thermomechanical model is used to study the effect of thermal perturbations on the spacecraft. This will have implications for the necessary internal calibration of the local tie between the laser metrology and the phase centres of the science signals.
Roy van Boekel, Björn Benneke, Kevin Heng, Renyu Hu, Nikku Madhusudhan, Sascha Quanz, Yan Bétrémieux, Jeroen Bouwman, Guo Chen, Leen Decin, Remco de Kok, Adrian Glauser, Manuel Güdel, Peter Hauschildt, Thomas Henning, Sandra Jeffers, Sheng Jin, Lisa Kaltenegger, Franz Kerschbaum, Oliver Krause, Helmut Lammer, Armin Luntzer, Michael Meyer, Yamila Miguel, Christoph Mordasini, Roland Ottensamer, Theresa Rank-Lueftinger, Ansgar Reiners, Timo Reinhold, Hans Martin Schmid, Ignas Snellen, Daphne Stam, Zhao Sun, Bart Vandenbussche
We present EclipseSim, a radiometric model for exoplanet transit spectroscopy that allows easy exploration of
the fundamental performance limits of any space-based facility aiming to perform such observations. It includes
a library of stellar model atmosphere spectra and can either approximate exoplanet spectra by simplified models,
or use any theoretical or observed spectrum, to simulate observations. All calculations are done in a spectrally
resolved fashion and the contributions of the various fundamental noise sources are budgeted separately, allowing
easy assessment of the dominant noise sources, as a function of wavelength. We apply EclipseSim to the Exoplanet
Characterization Observatory (EChO), a proposed mission dedicated to exoplanet transit spectroscopy that is
currently in competition for the M3 launch slot of ESA’s cosmic vision programme. We show several case studies
on planets with sizes in the super-Earth to Jupiter range, and temperatures ranging from the temperate to the
≈1500K regime, demonstrating the power and versatility of EChO. EclipseSim is publicly available.*
The Exoplanet Characterisation Observatory (EChO) is a medium class mission candidate within ESA's Cosmic Vision
2015-2025 program on space science. EChO will be equipped with a visible to infrared spectrometer covering the
wavelength range from 0.4 - 11 μm (goal: 16 μm) at a spectral resolving power between 30 and 300 in order to
characterize the atmospheres of known transiting extrasolar planets ranging from Hot Jupiters to Super Earths. In this
paper we will present first results from the dedicated study of the EChO science payload carried out by our EChO
Instrument Consortium during the assessment phase of the mission.
KEYWORDS: Cryogenics, Fermium, Frequency modulation, James Webb Space Telescope, Sensors, Reliability, Position sensors, Data modeling, Space telescopes, Aerospace engineering
The high reliability of the mechanisms of any space instrument is one of the most critical and challenging requirements.
This is even more pronounced in the case of cryogenic instruments, such as the Mid-Infrared Instrument (MIRI) to be
flown on the James Webb Space Telescope (JWST) – which will be cooled down to below 7 K. MIRI hosts three wheel
mechanisms for filter, grating and dichroic selection. All of them have an open loop torque drive and thus the precise
characterisation of the mechanisms and their motors is fundamental to achieve minimum heat load and maximum
reliability of the mechanism movements over the lifetime.
In this paper we present the overview of the characterisation and verification of the MIRI wheel mechanisms. Our
method is based on measuring back EMF voltages generated by the two phase cold redundant motors of the wheel
mechanisms after they had been fully integrated into the MIRI optical module. We present the analysis of the data and
the resulting performance increase. We discuss the optimisation of the open loop drive, as well as the verification of the
measurement results and the physical model of the motors and mechanisms.
We present two designs of a filter mounting structure for the Near-Infrared Imaging Photometer (NIP) planned
for the Euclid dark energy space mission. The three large near-infrared filters - with a 127 mm diameter, 12 mm
thickness and a 330 g mass per element - are challenging to mount. We present the design considerations,
finite element analysis and results from the first prototyping campaign of these structures. The rationale behind
the down-selection between the two designs is detailed and we conclude with recommendations on future
developments of mounts of this type. The results presented here are based on work performed during the Euclid
Assessment Study.
The Euclid dark energy mission is currently competing in ESA's Cosmic Vision program. Its imaging instrument,
which has one visible and one infrared channel, will survey the entire extragalactic sky during the 5 year mission.
The near-infrared imaging photometer (NIP) channel, operating in the ~0.92 - 2.0 μm spectral range, will be
used in conjunction with the visible imaging channel (VIS) to constrain the nature of dark energy and dark
matter. To meet the stringent overall photometric requirement, the NIP channel requires a dedicated on-board
flat-field source to calibrate the large, 18 detector focal plane.
In the baseline concept a 170 mm Spectralon diffuser plate, mounted to a pre-existing shutter mechanism
outside the channel, is used as a flat-field calibration target, negating the need for an additional single-point-failure
mechanism. The 117 × 230 mm focal plane will therefore be illuminated through all of the channel's
optical elements and will allow flat-field measurements to be taken in all wavelength bands. A ring of low power
tungsten lamps, with custom reflecting elements optimized for optical performance, will be used to illuminate
the diffuser plate.
This paper details the end-to-end optical simulations of this concept, a potential mechanical implementation
and the initial tests of the proposed key components.
The NIP is a near infrared imaging photometer that is currently under investigation for the Euclid space mission
in context of ESA's 2015 Cosmic Vision program. Together with the visible camera (VIS) it will form the basis of
the weak lensing measurements for Euclid. The NIP channel will perform photometric imaging in 3 near infrared
bands (Y, J, H) covering a wavelength range from ~ 0.9 to 2 μm over a field of view (FoV) of ~ 0.5 deg2. With
the required limiting point source magnitude of 24 mAB (5 sigma) the NIP channel will be used to determine
the photometric redshifts of over 2 billion galaxies collected over a wide survey area of 20 000 deg2. In addition
to the photometric measurements, the NIP channel will deliver unique near infrared (NIR) imaging data over
the entire extragalactic sky, enabling a wide variety of ancillary astrophysical and cosmological studies. In this
paper we will present the results of the study carried out by the Euclid Imaging Consortium (EIC) during the
Euclid assessment phase.
The Euclid mission is currently being developed within the European Space Agency's Cosmic Vision Program.
The five year mission will survey the entire extragalactic sky (~ 20 000 deg2) with the aim of constraining the
nature of dark energy and dark matter. The spacecraft's payload consists of two instruments: one imaging
instrument, which has both a visible and a near-infrared channel, and one spectroscopic instrument operating in
the near-infrared wavelength regime. The two channels of the imaging instrument, the Visible Imaging Channel
(VIS) and the Near-Infrared Imaging Photometer Channel (NIP), will focus on the weak lensing science probe.
The large survey area and the need to not only image each patch of sky in multiple bands, but also in multiple
dithers, requires over 640 000 operations of the NIP channel's filter wheel mechanism. With a 127 mm diameter
and a mass of ~ 330 g per element, these brittle infrared filters dictate highly demanding requirements on this
single-point-failure mechanism. To accommodate the large filters the wheel must have an outer diameter of
~ 400 mm, which will result in significant loads being applied to the bearing assembly during launch.
The centrally driven titanium filter wheel will house the infrared filters in specially designed mounts. Both
stepper motor and brushless DC drive systems are being considered and tested for this mechanism. This paper
presents the design considerations and details the first prototyping campaign of this mechanism. The design and
finite element analysis of the filter mounting concept are also presented.
The Mid Infrared Instrument (MIRI) aboard JWST is equipped with one filter wheel and two dichroic-grating wheel
mechanisms to reconfigure the instrument between observing modes such as broad/narrow-band imaging, coronagraphy
and low/medium resolution spectroscopy. Key requirements for the three mechanisms with up to 18 optical elements on
the wheel include: (1) reliable operation at T = 7 K, (2) high positional accuracy of 4 arcsec, (3) low power dissipation,
(4) high vibration capability, (5) functionality at 7 K < T < 300 K and (6) long lifetime (5-10 years). To meet these
requirements a space-proven wheel concept consisting of a central MoS2-lubricated integrated ball bearing, a central
torque motor for actuation, a ratchet system with monolithic CuBe flexural pivots for precise and powerless positioning
and a magnetoresistive position sensor has been implemented. We report here the final performance and lessons-learnt
from the successful acceptance test program of the MIRI wheel mechanism flight models. The mechanisms have been
meanwhile integrated into the flight model of the MIRI instrument, ready for launch in 2014 by an Ariane 5 rocket.
The Mid-Infrared Instrument (MIRI) of the James Webb Space Telescope, scheduled for launch in 2013, will provide a
variety of observing modes such as broad/narrow-band imaging, coronagraphy and low/medium resolution
spectroscopy. One filter wheel and two dichroic-grating wheel mechanisms allow to configure the instrument between
the different observing modes and wavelength ranges. The main requirements for the three mechanisms with up to 18
positions on the wheel include: (1) reliable operation at T ~ 7 K, (2) optical precision, (3) low power dissipation, (4)
high vibration capability, (5) functionality at 6 K < T < 300 K and (6) long lifetime (5-10 years). To meet these stringent
requirement, a space-proven mechanism design based on the European ISO mission and consisting of a central bearing
carrying the optical wheels, a central torque motor for wheel actuation, a ratchet system for precise and powerless
positioning and a magnetoresistive position sensor has been selected. We present here the detailed design of the flight
models and report results from the extensive component qualification.
The Grating and Filter Wheel Mechanisms of the JWST NIRSpec instrument allow for reconfiguration of the
spectrograph in space in a number of NIR sub-bands and spectral resolutions. Challenging requirements need to be met
simultaneously including high launch loads, the large temperature shift to cryo-space, high position repeatability and
minimum deformation of the mounted optics. The design concept of the NIRSpec wheel mechanisms is based on the
ISOPHOT Filter Wheels but with significant enhancements to support much larger optics. A well-balanced set of design
parameters was to be found and a considerable effort was spent to adjust the hardware within narrow tolerances.
KEYWORDS: Sensors, Electronics, Quantum efficiency, Temperature metrology, Signal detection, Black bodies, Bolometers, Bandpass filters, Monochromators, Camera shutters
We report first results of laboratory tests of Si:As
blocked-impurity-band (BIB) mid-infrared (4 to 28 μm) detectors developed
by IMEC. These prototypes feature 88 pixels hybridized on an integrated cryogenic readout electronics (CRE). They
were developed as part of a technology demonstration program for the future Darwin mission. In order to be able to separate
detector and readout effects, a custom build TIA circuitry was used to characterize additional single pixel detectors.
We used a newly designed test setup at the MPIA to determine the relative spectral response, the quantum efficiency, and
the dark current. All these properties were measured as a function of operating temperature and detector bias. In addition
the effects of ionizing radiation on the detector were studied. For determining the relative spectral response we used a dualgrating
monochromator and a bolometer with known response that was operated in parallel to the Si:As detectors. The
quantum efficiency was measured by using a custom-build high-precision vacuum black body together with cold (T ~ 4K)
filters of known (measured) transmission.
The Photodetector Array Camera and Spectrometer (Pacs) instrument aboard the Herschel space observatory
contains an integral field spectrometer with two camera channels which consist of 25 linear arrays of 16
stressed Gallium doped Germanium crystals (Ge:Ga) each. The space radiation environment induces changes in
the detector performance. Therefore, testing the Ge:Ga detectors under space radiation environment during the
commissioning phase (CP) is important for optimization of later detector operation in orbit. The test program
for Ge:Ga detector tuning during this phase has been designed according to findings obtained in laboratory
experiments: Protons as well as a 137Cs-γ-source have been used to simulate the space radiation environment
and to induce the radiation impacts on the photoconductor arrays. From comparison of the performance of
the detectors during CP versus laboratory tests the best strategy for operating the detectors during scientific
observations will be derived. This includes annealing, proposals for on-board data reduction algorithms and the
best estimated strategy for well-calibrated scientific measurements.
The present paper describes the different steps leading to the Flight Model integration of the Mid-Infra Red IMager
Optical Bench MIRIM-OB which is part of the scientific payload of the JWST. In order to demonstrate a space
instrument capability to survive the challenging space environment and deliver the expected scientific data, a specific
development approach is applied in order to reduce the high level of risks. The global approach for MIRIM-OB, and the
principal results associated to the two main models, the Structural Qualification Model for vibration and the Engineering
and Test Model for optical performance measured in the infra red at cryogenic temperature will be described in this
paper.
The photoconductors used in the integral field spectrometers of the PACS instrument onboard the Herschel
space observatory consist of stressed gallium doped germanium crystals featuring cut-off wavelengths of 127μm
and 205μm. The measured transient responses of these Ge:Ga photoconductors to a step change in the incident
photon flux level as well as a test setup that allows creation of transients by different methods are presented in
this paper. The transient response of extrinsic photoconductors is caused by charge carriers drifting or diffusing
to a contact region and recombining. This limits the initial gain of the device. Because of potentially long time
constants, the transient behavior presents a serious challenge to high-sensitivity, low-temperature extrinsic semiconductors.
In particular at low IR photon fluxes it usually is impossible for the detector to reach steady-state
behavior during a reasonable observation time.
However, since the time constants depend on the inverse photon flux, theory suggests the transient times for the
high thermal background levels anticipated for PACS to be of the order of tens of milliseconds. Experimentally
we find the response time to be limited by the transition time between the different infrared fluxes. The experimental
studies on the transients are accompanied by numerical calculations. The results support the prediction
that transients are not expected to play a major role for the low signal regime in PACS.
This paper reports on the fabrication and characterization of a linear array of Blocked Impurity Band (BIB) far infrared detectors and of the related Cryogenic Readout Electronics (CRE). It is part of the ESA DARWIN project which aims at the study of exoplanets by means of null interferometry and requires high performance infrared detector arrays in the 6 18μm range. Si:As BIB detectors have been fabricated on an infrared transparent Silicon substrate enabling backside illumination. The buried contact, the active and the blocking layers are deposited by epitaxy; the doping profile is controlled by adjusting the growth parameters. Access to the buried contact is provided by anisotropic silicon etch of V-grooves in the epi layers. Spray coating of photoresist is used for the lithography of the wafers with high topography. The CRE is composed of an input stage based on an integrating amplifier in AC coupled feedback with selectable integrator capacitors, of a sample and hold stage which provides isolation between input and sampling capacitance, and of an output buffer with multiplexing switch. The readout is optimized for low noise with minimum operating temperature of 4K. Linear arrays made of 42 and 88 detectors and having 30μm pixel pitch with various active areas are fabricated. Detector arrays are coupled to the CRE by Indium bumps using flip-chip technology. Measurements on the readout show reduced noise, good linearity and dynamic range. First detector characterization results are presented.
Following a warm launch in 2013 the MIRI instrument aboard JWST will be operated for a lifetime of 5-10 years in the L2-orbit at a temperature of ~6 K. The main requirements for its three wheel mechanisms include: (1) reliability, (2) optical precision, (3) low power dissipation, (4) high vibration capability, (5) functionality at 4 < T < 300 K. The filter wheel carries broad and narrow band spectral filters, coronographic masks and a prism on its 18 positions. Each of the two spectrometer wheels is equipped with two disks on both sides of a central torque motor, one of them carries 6 gratings, the other a dichroic/mirror arrangement. The optical positions are defined by a ratchet mechanism. No closed loop control is required; therefore the long time average heat dissipation is negligible. A new ratchet mechanism had to be developed to satisfy a 120° increment of only three positions for the spectrometer wheels.
Extensive cold and warm tests were performed on the development models of the filter and spectrometer wheels at
MPIA. These results stimulated numerous improvements in the mechanical and thermal design which are now to be
implemented in the qualification and flight models developed jointly with Carl Zeiss. Synergies are expected from a
similar development of the NIRSPEC wheels, in which MPIA and Carl Zeiss are involved.
HERSCHEL's 3.5 m primary mirror will be passively cooled to T ~ 80 K in the L2 orbit. In order to reduce the effects of the remaining high thermal background on the sensitive far infrared detectors (60..210 μm), a focal plane chopper is a vital element in the entrance optics of the imaging and spectroscopic instrument PACS. A gold coated 32 × 26 mm2 plane mirror, suspended by two flexural pivots and driven by a linear motor, allows for precise square wave chopping with up to 9° throw at a frequency 10 Hz with a position accuracy of 1 arcmin. The power required at T ~ 4 K is about 1 mW. The chopper has undergone an extensive qualification programme, including 650 million cold chop throws, 15 cold-warm-cold thermal cycles, 3-axis 26 G-vibration at T ~ 4 K etc. Five models were built and thoroughly tested; the flight model of the chopper is now integrated into the flight model of PACS, ready for the HERSCHEL/PLANCK launch in 2008 by an ARIANE5 rocket and the following 5-year mission.
The Near-Infrared Spectrograph (NIRSpec) onboard the James Webb Space Telescope can be reconfigured in space for astronomical observation in a range of filter bands as well as spectral resolutions. This will be achieved using a Filter wheel (FWA) which carries 7 transmission filters and a Grating wheel (GWA) which carries six gratings and one prism. The large temperature shift between warm launch and cryogenic operation (30K) and high launch vibration loads on the one hand side and accurate positioning capability and minimum deformation of optical components on the other hand side must be consolidated into a single mechanical design which will be achieved using space-proven concepts derived from the successful ISO filter wheel mechanisms which were manufactured and tested by Carl Zeiss. Carl Zeiss Optronics has been selected by Astrium GmbH for the implementation of both NIRSpec wheel mechanisms. Austrian Aerospace and Max-Planck-Institut fur Astronomie Heidelberg (MPIA) will contribute major work shares to the project. The project was started in October 2005 and the preliminary designs have been finalized recently. Critical performance parameters are properly allocated to respective hardware components, procurements of long-lead items have been initiated and breadboard tests have started. This paper presents an overview of the mechanism designs, discusses its properties and the approach for component level tests.
The characterization and calibration of far-infrared (FIR) detectors is a delicate task that requires good knowledge of the
incident flux and its spectral composition. In many test setups the FIR flux to the detectors is provided by means of an
external or internal black body and a set of cold attenuation, band pass, and blocking filters. For scientific instruments (e.g.
PACS aboard ESA's Herschel satellite) band pass and blocking filters are used to achieve the desired spectral throughput
either as order sorting filters in spectrometers or for selecting a wavelength range in imaging cameras. In all cases a detailed
knowledge of the spectral transmittance of the used filters is mandatory for an accurate calibration of the system. We have
build a test platform that allows to measure the transmission of cold (T ~ 4K) filters in the far-infrared. The setup uses
a dual grating monochromator with excellent spectral purity and a resolution up to 800, which is operated under a dry
nitrogen atmosphere to eliminate water vapor absorption bands. An Si-bolometer is used as detector and is read out by a
cryogenic low noise trans-impedance amplifier circuit with common mode rejection and a warm electronics using a lock-in
amplifier and a 22 bit analog-to-digital converter. A cryogenic filter slider in the setup allows for differential measurements
between filters and the use of cold order sorting filters. We present initial results for FIR cut-on and attenuation filters,
demonstrating that our setup is suited to measure transmissions as low as 10-4 over the covered wavelength range.
The Photodetector Array Camera and Spectrometer (PACS) is one of three science instruments on board the
Herschel space observatory to be launched in 2008. It will perform imaging photometry and spectroscopy in
the wavelength range from 57 μm to 210 μm. The integral field spectrometer contains two 25 x 16 pixel cameras
of Gallium doped Germanium crystals (Ge:Ga). By stressing these crystals, cutoff wavelengths of 127 μm
(low-stressed, 200 N) and 205 μm (high-stressed, 800 N) are reached. The characterization of these detectors
(responsivity, noise equivalent power (NEP), dark current,...) is carried out at the Max-Planck-Institutes for Astronomy
(MPIA, Heidelberg) and Extraterrestrial Physics (MPE, Garching). Both test facilities allow simulation
of the in-flight operational conditions of the arrays and provide accurate IR fluxes by means of external/internal
black bodies and calibrated cold attenuation filters. A radioactive 137Cs source is used at MPIA to simulate the
steady cosmic radiation impact on the photoconductor arrays in order to study the radiation induced changes
in responsivity, noise, and the transient behavior. The goal is to determine the optimal operating parameters
(temperature, bias, integration time,..) for the operation at the L2 orbit, the best curing method, curing frequency
and calibration procedure for high photometric accuracy. The "lessons learned" on operating, curing,
deglitching and calibrating stressed Ge:Ga detectors during the ISO mission are applied as well as the relevant
reports from IRAS and Spitzer.
KEYWORDS: Mirrors, James Webb Space Telescope, Actuators, Prototyping, Optical filters, Space telescopes, Spectrographs, Linear filtering, Sensors, Astronomical imaging
In 2011 NASA and ESA plan to launch the James Webb Space Telescope (JWST) as dignified successor of the Hubble Space Telescope. Three scientific instruments will cover the wavelength regions in the near-infrared (0.6-5μm, NIRCam and NIRSpec) and in the mid-infrared (5-28μm, MIRI), respectively. The ESA-led multi-object spectrograph NIRSpec as major European contribution is presently entering the detailed design phase in a collaboration between European space industries, scientific institutes, ESA and NASA. To allow for various operational modes in the instrument’s optical train several cryo-mechanisms are required, i.e. wheels for exchanging optical elements like filters and gratings as well as linear actuators on refocusing mirrors. We will give an overview on the detailed design, the prototyping and the testing of those mechanisms comprising highest reliability in the cryo-vacuum (~ 35K) combined with minimal power dissipation (~ 5mW on average), ultimate position accuracy (~ 0.5 - 1arcsec) combined with high launch vibration capability (ARIANE 5, ~ 60g) and a very long lifetime (~ 15 years) for ground tests and space operation under various environmental conditions. To reach this goal in a low cost and risk approach we rely on the heritage from ESA's earlier infrared missions, i.e. ISO and HERSCHEL.
KEYWORDS: Galactic astronomy, Databases, Stars, Sensors, Calibration, Temperature metrology, Field emission displays, Surface conduction electron emitter displays, Data analysis, Far infrared
The ISOPHOT C200 stressed Ge:Ga array aboard the Infrared Space Observatory was used to carry out scientific observations while the telescope was moved from one target to the next. These strip scanning measurements of the sky in the far-infrared (FIR) at 170 μm comprise the ISOPHOT Serendipity Survey, the first slew survey designed as an integral part of a space observatory mission. The ISOPHOT Serendipity Survey is the only large scale sky survey in the unexplored wavelength region beyond the IRAS 100 μm limit to date. Within nearly 550 hours more than 12000 slew measurements with a total slew length of more than 150000 degrees were collected, corresponding to a sky coverage of about 15%. The slew data analysis has been focused on the detection of compact sources, which required the development of special algorithms. A severe problem at 170 μm is the confusion of genuine compact sources with foreground galactic cirrus knots and ridges. The selection and identification of objects therefore necessarily requires a multi-wavelengths approach, which makes use of a broad variety of additional data from databases and other surveys. Known galaxies were identified by cross-correlating the Serendipity Survey source positions with galaxy entries in the NED and Simbad databases and a subsequent cross-check of optical images from the Digital Sky Survey. A large catalogue with 170 μm fluxes for ≈2000 galaxies is being complied. The particularly interesting rare galaxies with very cold dust and very large dust masses further require additional FIR data from the IRAS survey as well as measured redshifts. A large fraction of the compact galactic structures are prestellar cores inside cold star forming regions. Early stages of medium and high mass star forming regions are identified by combining compact bright and cold Serendipity Survey sources with the near-infrared 2MASS and MSX surveys, the combination of which indicates large dust masses in conjunction with embedded young stars of early spectral types. In all the studied samples of different object classes the 170 μm flux provides the crucial data point for a complete characterization of the FIR spectral energy distributions and the derivation of total dust masses. Follow-up observations are underway to study selected objects in more detail.
The imaging photometer and spectroscopic camera PACS, one of the three scientific instruments aboard the European 3.5 m infrared space telescope FIRST, will apply a tilting mirror mechanism for optical beam switching. The development of this focal plane chopper, capable of operation under cryovacuum conditions, is reported here. In order to meet the stringent requirements with respect to power dissipation and positional accuracy, special drive coils and a new position sensor had to be developed. A simulation model including electromagnetic analysis by the 3D code MAFIA, verified by extensive cold testing of the prototype hardware, was used for the optimization of the system and led to the advanced prototype of the chopper. Closed loop control of the mirror deflection allows square wave modulation in the frequency range 0 - 15 Hz (80% duty cycle) with amplitudes of +/- 9 degree(s) with high positional accuracy of less than 30'. The power dissipation at operating temperature of 4 K is below 500 (mu) W.
The array camera and spectrometer PACS to be flown aboard the European 3.5 m infrared space telescope FIRST will apply a cold focal plane chopper. Its development has to meet ambitious goals, such as large chopper throws, high operational accuracy in several modes, very low heat dissipation in the cryogenic environment, sufficient rigidity to meet the ARIANE5 launch conditions and a long lifetime thereafter. The prototype development of such a chopper and test results under cryovacuum conditions are reported here.
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