While radial velocity and transit techniques are efficient to probe exoplanets with short orbits, the study of long-orbit planets requires direct imaging and coronagraphic techniques. However, the coronagraph must deal with planets that are 104 to 1010 fainter than their hosting star at a fraction of arcsecond, requiring efficient coronagraphs at short angular separation. Phase masks proved to be a good solution in monochromatic or limited spectral bandwidth but expansion to broadband requires complex phase achromatization. Solutions use photonic crystals, subwavelength grating or liquid crystal polymers but their manufacturing remains complex. An easier solution is to use photolithography and reactive ion etching and to optimize the azimuthal phase distribution like achieved in the six-level phase mask (SLPM) coronagraph (Hou et al. 2014). We present here the laboratory results of two SLPM coronagraphs enabling high-contrast imaging in wide-band. The SLPM is split in six sectors with three different depths producing three levels of optical path difference and yielding to uniform phase shifts of 0, π or 2π at the specified wavelength. Using six sectors instead of four sectors enables to mitigate the chromatic effects of the SLPM compared to the FQPM (Four-Quadrant Phase Mask) while keeping the manufacturing easy. Following theoretical developments achieved by University of Shanghai and based on our previous experience to fabricate FQPM components, we have manufactured SLPM components by reactive ion etching at Paris Observatory and we have tested it onto the THD2 facility at LESIA. The THD2 bench was built to study and compare high-contrast imaging techniques in the context of exoplanet imaging. The bench allows reducing the starlight below a 10−8 contrast level in visible/near-infrared. In this paper, we show that the SLPM is easy to fabricate at low cost and is easy to implement with a unique focal plane mask and no need of pupil apodization. Detection of a planet can be achieved at small inner working angle down to 1 λ/D. The on-axis attenuation of the best SLPM component reaches 2 × 10−5 at λ = 800 nm and is better than 10−4 in intensity over a 10% spectral bandwidth. Along the diagonal transition, we show that the off-axis transmission is attenuated by less than 3% over a 10% bandwidth and will need to be calibrated. Any etching imperfections can affect the SLPM performance, by lowering the on-axis attenuation and by changing the optimal wavelength. Despite few nanometers of uncertainty for etching the depths, we show that this first component can provide a high-contrast attenuation in laboratory
The goal of a coronagraph is to reduce the flux of a bright object (e.g. a star) in order to distinguish its faint neighborhood (e.g. exoplanets and disks). In this context, we proposed one coronagraph that uses a four quadrant phase mask (FQPM). Since 2000, we fabricated several monochromatic FQPM working in visible and near-infrared light at the Paris Observatory. We have developed systematic procedures for fabrication and characterization of the phase masks. Visual inspections with an optical microscope are performed for every component and a coronagraphic performance measurement based on inclination of the component is done on a dedicated bench that is set up in a clean room. This procedure gives a quick feedback on the quality and performance of the component. Depending on the results, images of the central transition can be recorded with an electron microscope to understand the limitations of the fabrication process. This procedure allowed us to understand the influence of various parameters such as the width of the transitions between the quadrants, the alignment of the transitions or the step depth. Based on these results, we modified the mask design and the fabrication process to improve our success rate to nearly 100% when building a FQPM for any given optimal wavelength in visible or near-infrared. Moreover, we improved the performance of the components, reaching attenuations of more than 20,000 on the central peak in raw images for most coronagraphs. The best of these components are now used on the THD bench, an optical/NIR bench developed for the study of high contrast imaging techniques, reaching 10-8 contrast level routinely.
Direct imaging of exoplanets is very attractive but challenging and specific instruments like Sphere (VLT) or GPI (Gemini) are required to provide contrasts up to 16-17 magnitudes at a fraction of arcsec. To reach higher contrasts and detect fainter exoplanets, more-achromatic coronagraphs and a more-accurate wavefront control are needed. We already demontrated contrasts of ~10-8 at ~4 λ/D at 635nm using a four quadrant phase mask and a self-coherent camera on our THD bench in laboratory. In this paper, we list the different techniques that were tested on the THD bench in monochromatic and polychromatic lights. Then, we present the upgraded version of the THD bench that includes several deformable mirrors for correcting phase and amplitude simultaneously and obtain a field-of-view covering the complete 360 degrees arouns the star with contrasts down to ~10-8 -10-9.
We report on tunable submillimeter-wave radiation sources based on micrometer-sized superconducting tunnel junction
arrays optimized within a bandwidth of 350-520 GHz. The arrays consist of 10, 20 and 40 Superconductor-Insulator-
Superconductor (SIS) parallel-connected Nb/AlOx/Nb junctions embedded in superconducting microstrip lines. A SIS
twin-junction is integrated along with each array to detect output signals. The pumped detector’s I-V characteristic
exhibits clearly photon-assisted quasiparticule steps when the arrays are biased upon corresponding Josephson
resonances ranging from 370 to 520 GHz.
We report on the development of waveguide-based mixers for operation beyond 2 THz. The mixer element is a
superconducting hot-electron bolometer (HEB) fabricated on a silicon-on-insulator (SOI) substrate. Because it is beyond
the capability of conventional machining techniques to produce the fine structures required for the waveguide embedding
circuit for use at such high frequencies, we employ two lithography-based approaches to produce the waveguide circuit:
a metallic micro-plating process akin to 3-D printing and deep reactive ion etching (DRIE) silicon micromachining.
Various mixer configurations have been successfully produced using these approaches. A single-ended mixer produced
by the metal plating technique has been demonstrated with a receiver noise temperature of 970 K (DSB) at a localoscillator
frequency of 2.74 THz. A similar mixer, produced using a silicon-based micro-machining technique, has a
noise temperature of 2000 K (DSB) at 2.56 THz. In another example, we have successfully produced a waveguide RF
hybrid for operation at 2.74 THz. This is a key component in a balanced mixer, a configuration that efficiently utilizes
local oscillator power, which is scarce at these frequencies. In addition to allowing us to extend the frequency of
operation of waveguide-based receivers beyond 2 THz, these technologies we employ here are amenable to the
production of large array receivers, where numerous copies of the same circuit, precisely the same and aligned to each
other, are required.
Observation and analysis of submillimeter-wave radiation
(300GHz-3THz) in astronomy and atmospheric sciences requires
increasingly performant receivers. The most sensitive receivers
working in this range of electromagnetic spectrum use
superconductor-insolator-superconductor (SIS) junctions.
In order to increase the bandwidth and the sensitivity, we are
developing a quantum-noise limited heterodyne receiver
based on several parallel SIS junctions with broad
(larger than 30%) fixed tuned bandwidth. These circuits can be
viewed as passband filters which have been optimized by
varying the spacings between junctions.
We have designed such 5-junction arrays for operation in the
range 480-640 GHz. Fabrication and heterodyne characterization
of these devices has been done. The 1 μm2 junctions current density
ranges from 4 to 13 kA/cm2, using optical lithography and
Nb/Al2Nb5/Nb trilayer sputtering technology. The fabrication
process and yield are presented in this paper, along with
We report on the status of the development of a 30% bandwidth tunerless SIS double-sideband mixer for the “Band 1” (480 GHz-630 GHz) channel of the heterodyne instrument (HIFI) of ESA’s Herschel Space Observatory, scheduled for launch in 2007. After exposing the main features of our mixer design, we present the performance achieved by the demonstration mixer, measured via Fourier Transform Spectroscopy and heterodyne Y factor calibrations. We infer from a preliminary mixer analysis that the mixer has very low, quantum-limited noise and low conversion loss. We also report on some pre-qualification tests, as we currently start to manufacture the qualification models and design the last iteration of masks for SIS junction production.