Mélanie Leclerc

The VISTA IR camera

The VISTA IR Camera has now completed its detailed design phase and is on schedule for delivery to ESO’s Cerro Paranal Observatory in 2006. The camera consists of 16 Raytheon VIRGO 2048x2048 HgCdTe arrays in a sparse focal plane sampling a 1.65 degree field of view. A 1.4m diameter filter wheel provides slots for 7 distinct science filters, each comprising 16 individual filter panes. The camera also provides autoguiding and curvature sensing information for the VISTA telescope, and relies on tight tolerancing to meet the demanding requirements of the f/1 telescope design. The VISTA IR camera is unusual in that it contains no cold pupil-stop, but rather relies on a series of nested cold baffles to constrain the light reaching the focal plane to the science beam. In this paper we present a complete overview of the status of the final IR Camera design, its interaction with the VISTA telescope, and a summary of the predicted performance of the system.

Image slicers: design for manufacturability

This paper describes our approach to the design of reflective, image-slicing Integral-Field Units. The first IFU built at the UK ATC (Ramsay-Howat et al 2004) has been successfully commissioned and is in routine use on the UKIRT. This IFU uses all diamond-turned optics and close attention was paid in the design to the manufacturability of the individual components, their alignment into groups and the overall alignment and integration of the IFU into the spectrometer. Building on this experience we are designing and making four IFUs for the MIRI on JWST where constraints on mass and launch survivability have led us to use monolithic arrays of slicing and re-imaging mirrors. This paper describes the ways in which the optical design and the manufacturing methods have each been adapted to: (a) achieve image quality, pupil alignment and mass requirements (b) ensure components can be reliably manufactured to the tolerances needed so that the IFUs can be aligned without adjustment and (c) ensure that performance is maintained after launch and cooling to 7 K. We also show that, although designed specifically for a space instrument, such a compact and reproducible IFU is well suited to instruments where multiple IFUs are required.

Performances of the SAC-D NIRST flight model radiometer

Aquarius/SAC-D is a cooperative international mission conducted jointly by the National Aeronautics and Space Administration of the United States of America and the Comisión Nacional de Actividades Espaciales of Argentina. Jointly developed by CONAE and the Canadian Space Agency, the New IR Sensor Technology (NIRST) instrument will monitor high temperature events. NIRST has one band in the mid-wave infrared and two bands in the thermal infrared. The baseline design of the NIRST is based on microbolometer technology developed jointly by INO and the CSA. This paper will first present an overview of the design of the NIRST camera module. The manufacturing and qualification activities for the Flight Model will be described and key performance parameters, as measured during the verification campaign, will be reported.

Design, manufacturing, and qualification of an uncooled microbolometer focal plane array–based radiometric package for space applications

Uncooled microbolometer detectors are well suited for space applications due to their low power consumption while still exhibiting adequate performance. Furthermore, the spectral range of their response could be tuned from the mid- to the far-infrared to meet different mission requirements. If radiometric measurements are required, the radiometric error induced by variation of the temperature of the detector environment must be minimized. In a radiometric package, the detector environment is thermally stabilized by means of a temperature-controlled radiation shield. The radiation shield must be designed to prevent stray radiation from reaching the detector. A radiometric packaging technology for uncooled microbolometer FPAs is presented. The selection of materials is discussed and the final choices presented based on thermal simulations and experimental data. The radiometric stability with respect to stray light and variation of the temperature of the environment as well as the different noise components studied by means of the Allan variance are presented. It is also shown that the device successfully passed the prescribed environmental tests without degradation of performance.

Design of the SAC-D/NIRST camera module

Aquarius/SAC-D is a cooperative international mission conducted jointly by the National Aeronautics and Space Administration (NASA) of the United States of America (USA) and the Comisión Nacional de Actividades Espaciales (CONAE) of Argentina. The overall mission targets the understanding of the total Earth system and the consequences of the natural and man-made changes in the environment of the planet. Jointly developed by CONAE and the Canadian Space Agency (CSA), the New IR Sensor Technology (NIRST) instrument will monitor high temperature events on the ground related to fires and volcanic events, and will measure their physical parameters. Furthermore, NIRST will take measurements of sea surface temperatures mainly off the coast of South America as well as other targeted opportunities. NIRST has one band in the mid-wave infrared centered at 3.8 um with a bandwidth of 0.8 um, and two bands in the thermal infrared, centered respectively at 10.85 and 11.85 um with a bandwidth of 0.9 um. The temperature range is from 300 to 600 K with an NEDT < 0.5 K for the mid-infrared band and from 200 to 400 K with an NEDT < 0.4 K for the thermal bands. The baseline design of the NIRST is based on micro-bolometer technology developed jointly by INO and the CSA. Two arrays of 512x3 uncooled bolometric sensors will be used to measure brightness temperatures. The instantaneous field-of-view is 534 microradians corresponding to a ground sampling distance of 350 m at the subsatellite point. A pointing mirror allows a total swath of +/− 500 km. This paper describes the detailed design of the NIRST camera module. Key performance parameters are also presented.

Aspects of concurrent design during the VISTA IR camera detailed design phase

As detailed instrument design progresses, judgements have to be made as to what changes to allow and when models such as thermal, stray-light and mechanical structure analysis have to be re-run. Starting from a well-founded preliminary design, and using good engineering design when incorporating changes, the design detailing and re-run of the models should bring no surprises. Nevertheless there are issues for maintaining the design and model configuration to a reasonably concurrent level. Using modern modeling software packages and foresight in setting up the models the process is made efficient, but at the same time the level of detail and number of cases now needed for instrument reviews is also large in order to minimise risks. We describe examples from the detailed instrument design of the VISTA IR Camera to illustrate these aspects and outline the design and analysis methods used.

The SCUBA-2 polarimeter

A polarimeter is built to be used with the SCUBA-2 camera of the James Clerk Maxwell Telescope to study polarized sub-millimeter radiations. We simulated the effect of the polarimeter on image quality and polarization measurements.

Optomechanical tolerancing of the VISTA field corrector

VISTA is a 4m class survey telescope designed to perform pre-planned, ground-based astronomy surveys of the Southern sky in the visible and infrared spectrum. The telescope includes a Cassegrain mounted infrared (IR) camera with a field of view of 1.65 degrees. The camera has no cold stop, and therefore the three lenses constituting the field corrector are positioned inside the cryostat of the camera. A window of 950mm diameter closes the cryostat. The lenses have a diameter of approximately 600 mm, and the third lens have its first surface with an aspheric profile. The large cryostat window and the aspheric surface of the third lens are the most difficult components to manufacture and test. To our knowledge, they are the largest Infrasil 302 components to be mounted and used inside a cryostat at 100K up to this date.

Overcoming the challenges of active THz/MM-wave imaging: an optics perspective

Imaging in the Terahertz (THz) and millimeter-wave (mm-wave) bands offer advantages over doing do in other conventional bands, such as the visible, infrared (IR). The THz band ranges from 300 GHz to 3 THz or in wavelength, 1 mm to 100 μm. These longer wavelengths allows THz radiation to pass unobscured through some materials allowing for imaging hidden threats or defects within such materials. Going further, millimeter-waves cover the spectral band of 30 – 300 GHz, or 10 cm to 1 mm. In addition to passing through denser materials, they also have much less atmospheric absorption, thus are ideal for imaging in adverse weather conditions. In the THz/mm-wave, the greatest challenge to real-time active imaging was previously the lack of compact sensor arrays. INO has overcome this by optimizing its microbolometer focal plane array (originally developed for the infrared) for the longer wavelengths, covering both the THz and mm-wave bands. The remaining challenge for active imaging is how to obtain useful imagery using coherent sources. INO has been working on improving the quality of the illumination beam over the past few years, as well as designing high quality fast imaging optics. This paper will focus on the different techniques that have been tested across the THz and into the mm-wave bands in both transmission and reflection imaging modes. The impact on image quality will be demonstrated, and their implications to developing useful systems for different applications will be discussed.

Radiometric packaging of uncooled bolometric infrared focal plane arrays

INO has a wide experience in the design and fabrication of different kinds of microbolometer focal plane arrays (FPAs). In particular, a 512x3 pixel microbolometer FPA has been selected as the sensor for the New Infrared Sensor Technology (NIRST) instrument, one of the payloads of the SACD/Aquarius mission. In order to make the absolute temperature measurements necessary for many infrared Earth observation applications, the microbolometer FPA must be integrated into a package offering a very stable thermal environment. The radiometric packaging technology developed at INO presents an innovative approach since it was conceived to be modular and adaptable for the packaging of different microbolometer FPAs and for different sets of assembly requirements without need for requalification of the assembly process. The development of the radiometric packaging technology has broadened the position of INO as a supplier of radiometric detector modules integrating FPAs of microbolometers inside a radiometric package capable of achieving the requirements of different space missions. This paper gives an overview of the design of INO’s radiometric package. Key performance parameters are also discussed and the test campaign conducted with the radiometric package is presented.