The imaging search for exoplanets is mainly limited by quasi-static speckle noise that have lifetimes between milliseconds and hours. Attempts to remove this noise using post-processing by building a point spread function (PSF) model from diversity in time, wavelength, and so-forth are limited to a small improvement due to the evolution of the noise along these same axes. The Calibration 2 (CAL2) system, being built by an international team, is a National Research Council of Canada (NRC) funded facility-class focal plane wavefront sensor for the Gemini Planet Imager 2 (GPI2) upgrade. The project consists of a complete rebuild of the GPI calibration (CAL) system. Based on the self-coherent camera concept and the FAST focal plane mask, a fraction of the near-infrared (NIR) science bandpass is extracted using a new dichroic wheel to perform focal plane wavefront sensing, with the goal to do science while also improving the contrast for the GPI2 IFS, up to a factor of 100x on bright stars. The project is at the final design review stage, and construction is expected to start summer/fall 2024, with assembly late fall 2024, and shipping to the Gemini North observatory middle of 2025.
Facility-class high-contrast exoplanet imaging systems are currently limited by non-common path quasi-static speckles. Due to these aberrations, the raw contrast saturates after a few seconds. Several active wavefront correction techniques have been developed to remove this noise, with limited success. The NRC Canada is funding two projects, the SPIDERS pathfinder at the Subaru telescope (ETA 2023), and the CAL2 upgrade of the Gemini Planet Imager-2 (ETA 2024), to deploy a modified self-coherent camera (based on FAST) to measure the focal plane electric field, and to apply wavefront corrections in a closed-loop down to 10s of ms in a narrow band. The CAL2 project will focus on developing a facilityclass focal plane & Lyot-stop Low-order sensors using a CRED2 and a SAPHIRA-based camera, reaching up to a gain of 100x in contrast for bright stars. The SPIDERS pathfinder will have a similar configuration with the addition of an imaging Fourier transform spectrograph, allowing the acquisition of a 3.3” diagonal FOV to up to R-20,000 in the NIR to perform advanced spectral differential imaging at a high-spectral resolution to search and characterize exoplanets. These projects will serve as the foundation to develop similar systems for future ground-/space-based telescopes, and be an important step toward the development of instruments to search for life signatures in the atmosphere of exoplanets.
The new high precision polarimeter for the “Observatoire du Mont Mégantic” (POMM) is an instrument designed to
observe exoplanets and other targets in the visible and near infrared wavebands. The requirements to achieve these
observation goals are posing unusual challenges to structural and mechanical designers.
In this paper, the detailed design, analysis and laboratory results of the key mechanical structure and sub-systems are
presented.
First, to study extremely low polarization, the birefringence effect due to stresses in the optical elements must be kept to
the lowest possible values. The double-wedge Wollaston custom prism assembly that splits the incoming optical beam is
made of bonded α-BBO to N-BK-7 glass lenses. Because of the large mismatch of coefficients of thermal expansion and
temperatures as low as -40°C that can be encountered at Mont-Mégantic observatory, a finite element analysis (FEA)
model is developed to find the best adhesive system to minimize stresses.
Another critical aspect discussed in details is the implementation of the cascaded rotating elements and the twin rotating
stages. Special attention is given to the drive mechanism and encoding technology. The objective was to reach high
absolute positional accuracy in rotation without any mechanical backlash.
As for many other instruments, mass, size and dimensional stability are important critera for the supporting structure.
For a cantilevered device, such as POMM, a static hexapod is an attractive solution because of the high stiffness to
weight ratio. However, the mechanical analysis revealed that the specific geometry of the dual channel optical layout
also added an off-axis counterbalancing problem. To reach an X-Y displacement error on the detector smaller than 35μm
for 0-45° zenith angle, further structural optimization was done using FEA. An imaging camera was placed at the
detector plane during assembly to measure the actual optical beam shift under varying gravitational loading.
A polarimeter, to observe exoplanets in the visible and infrared, was built for the “Observatoire du Mont Mégantic”
(OMM) to replace an existing instrument and reach 10-6 precision, a factor 100 improvement. The optical and
mechanical designs are presented, with techniques used to precisely align the optical components and rotation axes to
achieve the targeted precision. A photo-elastic modulator (PEM) and a lock-in amplifier are used to measure the
polarization. The typical signal is a high DC superimposed to a very faint sinusoidal oscillation. Custom electronics
was developed to measure the AC and DC amplitudes, and characterization results are presented.
The alignment method of a fast catadioptric optical module with very large field of view is presented in this paper. The
module is made of three aspheric optical components: a primary mirror, a secondary mirror and a field lens. To achieve
the 22.6 degrees field of view, the secondary mirror makes a large obscuration requiring an F/0.75 working f-number to
achieve the effective F/1.05. The catadioptric optical module was integrated with the IRXCAM-640 uncooled camera
module made by INO. System spatial resolution is improved with the use of a 4-position microscan mechanism.
Loïc Le Noc, Bruno Tremblay, Anne Martel, Claude Chevalier, Nathalie Blanchard, Martin Morissette, Luc Mercier, François Duchesne, Lucie Gagnon, Patrick Couture, Frédéric Lévesque, Nichola Desnoyers, Mathieu Demers, Frédéric Lamontage, Hubert Jerominek, Alain Bergeron
The needs of surveillance/detection operations in the infrared range, for industrial, spatial and military applications
continuously tend toward larger field of view and resolution while maintaining the system as compact as possible. To
answer this need, INO has developed a 1280x960 pixel thermal imager, said HRXCAM, with 22.6° field of view. This
system consists in the assembly of a catadioptric optics with microscan mechanism and a detection electronic module
based on a 640x480 25μm pitch pixel bolometric detector. The detection module, said IRXCAM, is a flexible platform
developed for fast prototyping of varied systems thanks to its ability to support a large range of infrared detectors. With
its multiple hardware and software functionalities, IRXCAM can also be used as the complete electronic module of a
finalized system. HRXCAM is an example of fast prototyping with IRXCAM and an optical lens that fully demonstrates
the imaging performance of the final system. HRXCAM provides 1280x960 pixel images at a nominal 5-15 Hz
frequency with 60 mK NETD. It can also be used in the 640x480 mode at 58 Hz with the same sensitivity. In this paper,
the catadioptric optics with integrated microscan and IRXCAM architecture and specifications are reviewed. Some
typical examples of image obtained with HRXCAM in outdoor conditions are presented.
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