LLNL diamond machined a ZnSe grism for spectroscopy of transiting exoplanets on NIRISS, a Canadian instrument that
will fly on the James Webb Space Telescope. The grism operates over the wavelength range of 0.6 to 2.5 μm. It is cross-dispersed
by a ZnS prism and has a resolving power in first order of ~700. The surface error over the full 29 x 30 mm
grating aperture is 0.03 wave rms at 633nm. We measured a diffraction efficiency at 633 nm of 56% (nearly 88% after
accounting for Fresnel reflection). The diffraction pattern is clean with no discernible ghosts.
An instrument concept called the Birefringent Imaging Doppler Wind Interferometer (BIDWIN) is being validated in the
Atmospheric and Space Physics Lab at the University of New Brunswick in collaboration with COM DEV Ltd (Ottawa,
Canada) to determine its capabilities for measuring Doppler wind fields in the Earth’s nightglow. The instrument is
adapted from a similar approach used to obtain two dimensional images of high speed (~1000 m/s) flow fields in
plasmas at the Australian National University. For that application the precision of the wind measurements was not
explored in detail. With BIDWIN, the intent is to obtain ~ 5 m/s precision on each bin of a CCD image of the wind
field. An examination of the instrument concept and sensitivity of the wind measurements made using this approach is
undertaken to determine the feasibility of this criterion. The BIDWIN has the advantage over other instruments that can
be used for a similar purpose (such as the field widened Michelson interferometer and Fabry-Perot interferometer) in that
it has no moving parts, has a large throughput, is light weight and is relatively cheap to construct. In this paper, the
instrument concept is presented and the ideal and non-ideal instrument effects are explored. Calibration measurements
conducted using a proto-type of the instrument are used to verify the instrument concept and confirm the feasibility of
the approach for making atmospheric wind measurements.
The Fine Guidance Sensor (FGS) is one of the four science instruments on board the James Webb Space Telescope (JWST). FGS features two modules: an infrared camera dedicated to fine guiding of the observatory and a science camera module, the Near-Infrared Imager and Slitless Spectrograph (NIRISS) covering the wavelength range between 0.7 and 5.0 μm with a field of view of 2.2' X 2.2'. NIRISS has four observing modes: 1) broadband imaging featuring seven of the eight NIRCam broadband filters, 2) wide-field slitless spectroscopy at a resolving power of rv150 between 1 and 2.5 μm, 3) single-object cross-dispersed slitless spectroscopy enabling simultaneous wavelength coverage between 0. 7 and 2.5 μm at Rrv660, a mode optimized for transit spectroscopy of relatively
bright (J > 7) stars and, 4) sparse aperture interferometric imaging between 3.8 and 4.8 μm enabling high
contrast ("' 10-4) imaging of M < 8 point sources at angular separations between 70 and 500 milliarcsec. This
paper presents an overview of the FGS/NIRISS design with a focus on the scientific capabilities and performance offered by NIRISS.
The Tunable Filter Imager of the James Webb Space Telescope will be based on blocking filters and a tunable Fabry-
Perot etalon with an average resolution of about 100. It will operate in two wavelength bands from 1.6 μm to 2.5 μm and
from 3.1 μm to 4.9 μm at a cryogenic temperature of about 35K. It will respectively be used to study the First Light and
re-ionization of the universe by surveying Lyman-alpha sources and to provide an in-depth study of proto-planetary
systems as well as giant planets of nearby stars.
The Tunable Filter Imager (TFI) is designed to image a sky field of view of 2.2' by 2.2' (magnified to 4.6 deg. x 4.6 deg.
at the etalon). Its tunable etalon has an aperture of 56 mm. It operates at low orders 1 and 3 for the two wavelength bands
which reduces the number of blocking filters to a number of eight. The etalon gap tuning between 2.5 μm and 5.5 μm is
provided by piezoelectric actuators and will be servo controlled by using capacitive displacement sensors.
In this paper, we present the etalon's opto-mechanical design that allows us to achieve the stringent requirements in
terms of resolution over a wide infrared wavelength band, and operation at low gap at cryogenic temperature. Cryogenic
test results will be shared as well.
Previous publications for the JWST-FGS-TFI instrument described the design and fabrication of mirror coatings for
scanning Fabry-Perot etalons. Since that time, we have extended the fabrication process using ellipsometry analysis over
the full operational bandwidth from 1.0 to 5.0 microns for both mirror and anti-reflection coatings. This paper will
present single and multiple layer ellipsometry analysis of the a-Si/SiO2 optical properties. Analysis improvement came
from a-Si/SiO2 interface consideration and simultaneous use of ellipsometric data from Woollam V-VASE and IRVASE
instruments. Simulations of reflectance and transmittance based on the ellipsometric analysis results will also be
compared to spectrophotometric measurements for witness pieces.
KEYWORDS: Fabry–Perot interferometers, Electrochemical etching, Ferroelectric materials, James Webb Space Telescope, Sensors, Electronics, Tunable filters, Control systems, Reflectivity, Imaging systems
The Fine Guidance Sensor (FGS) on the James Webb Space Telescope (JWST) has a science observing capability
provided by the Tunable Filter Imager (TFI). The TFI incorporates dielectric coated Fabry-Perot etalon plates with a
small vacuum gap. The separation of the plates is controlled by the Etalon Control Electronics (ECE) board, using
piezoelectric actuators (PZTs) and capacitive displacement sensors (CDS). The TFI measures over the wavelength range
of 1.6 to 4.9 microns with a spectral resolution of R~100. We present the key components of the etalon system and the
approach for characterizing and testing the system. Initial results from assembly-level testing are also presented.
The Fine Guidance Sensor (FGS) of the James Webb Space Telescope (JWST) features a tunable filter imager (TFI)
module covering the wavelength range from 1.5 to 5.0 μm at a resolving power of ~100 over a field of view of
2.2'×2.2'. TFI also features a set of occulting spots and a non-redundant mask for high-contrast imaging. This paper
presents the current status of the TFI development. The instrument is currently under its final integration and test phase.
Earlier publications described a novel approach to the design of mirror coatings for scanning Fabry Perot etalons[1],[2]. Since that time, we have extended the design process, fabricated mirror coatings and used them to build etalons.
One design process improvement is the minimization of off-axis de-tuning. It can be significantly worse with a real mirror coating than the normal "blue shift" associated with the basic Fabry-Perot geometry. This option provides for the control of de-tuning in optimization. Another improvement is optimization for multiple-order operation of the etalon. This technique reduces etalon mirror travel while allowing tunability over a broad spectral range.
The focus of this paper, however, is the experimental results obtained for coatings and etalons built for the Fine Guidance Sensor-Tunable Filter Imager (FGS-TFI) - a Canadian Space Agency funded science instrument for the James Web Space Telescope (JWST). We present measured data for both the coating and the etalon performance.
We present the prototyping results and laboratory characterization of a narrow band Fabry-Perot etalon flight model
which is one of the wavelength selecting elements of the Tunable Filter Imager. The latter is a part of the Fine Guidance
Sensor which represents the Canadian contribution to NASA's James Webb Space Telescope. The unique design of this
etalon provides the JWST observatory with the ability to image at 30 Kelvin, a 2.2'x2.2' portion of its field of view in a
narrow spectral bandwidth of R~100 at any wavelength ranging between 1.6 and 4.9 μm (with a gap in coverage
between 2.5 and 3.2 μm). Extensive testing has resulted in better understanding of the thermal properties of the
piezoelectric transducers used as an actuation system for the etalon gap tuning. Good throughput, spectral resolution and
contrast have been demonstrated for the full wavelength range.
The Fine Guidance Sensor (FGS) of the James Webb Space Telescope (JWST) features a tunable filter imager (TFI)
module covering the wavelength range from 1.6 to 4.9 μm at a resolving power of ~100 over a field of view of
2.2'x2.2'. TFI also features a set of 4 occulting spots for coronagraphy. A review of the current design and development
status of TFI is presented along with two key TFI science programs: the detection of first light, high-redshift Lyα
emitters and the detection/characterization of exoplanets.
This is a progress report on the realization of a compact and transportable frequency standard at 1556 nm based on a two-photon transition in rubidium at 778 nm. These hyperfine transitions present great metrological interest. They have a narrow theoretical linewidth of 150 kHz when observed with a 1556 nm laser, and their absolute frequency is known with an uncertainty of 5.2 X 10-12. In this experiment, we use a high power 1556 nm DFB laser and reduce its linewidth to the 10 kHz level using optical feedback from a confocal cavity. We generate its second harmonic in a periodically poled LiNbO3 crystal and use this signal to injection-lock a Fabry-Perot laser emitting 42 mW at 778 nm. The slave laser is used to observe the Doppler-free two- photon transitions: two counter-propagating beams excite rubidium atoms which emit a blue fluorescence on resonance. This 420 nm light is detected on the side of the Rb cell with a photomultiplier. Such an optical frequency standard at 1556 nm, standing in the multiwavelength telecommunications systems window, becomes an attractive source for absolute frequency calibration of WDM components, optical spectrum analyzers and wavemeters.
Raymond Felder, D. Touahri, Ouali Acef, L. Hilico, Jean-Jacques Zondy, Andre Clairon, Beatrice de Beauvoir, Francois Biraben, Lucile Julien, Francois Nez, Yves Millerioux
The absolute frequency measurement of each hyperfine component of the 5S3/2 and 5S5/2 levels in rubidium was done at ENS more than one year ago using Ti-Sa lasers. We built two devices based on diode lasers to study some metrological properties. We measure the frequency differences between hyperfine components of the 5S5/2 level and we calculate the corresponding hyperfine constants. We also measure the frequency interval between the 5S3/2 and 5S5/2 levels using a Schottky diode. The measured stability in terms of Allan variance is 3*10-13t-1/2 up to 2000 s. The light shift is investigated and the difference between our two systems is 1.7 kHz. The repeatability of one system is better than 10-12 and will allow the absolute frequency measurement at this level via the LPTF frequency synthesis chain.
Jean-Jacques Zondy, D. Touahri, Ouali Acef, L. Hilico, M. Abed, Andre Clairon, Yves Millerioux, Raymond Felder, Beatrice de Beauvoir, Francois Nez, Francois Biraben, Lucile Julien
A frequency chain, derived from the one used to measure the absolute frequency ((nu) $= 473 THz) of the He-Ne/I2 optical standard, is currently being implemented in order to measure the frequency of a diode laser stabilized on the two-photon transition of rubidium vapor. The measurement scheme is based on the comparison of the frequency of this near-IR potential secondary standard to the 13th harmonic frequency of the R(12)-CO2/OsO4 LPTF secondary standard at (nu) equals 29.096 THz. Recent results on the frequency synthesis are reported, enabling the testing of long-term stability of this Rb-locked system with respect to the IR reference standard.
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