Exoplanet Detection and Characterization: Development and Results of a New Generation Imaging Fourier Transform Spectrometer

Adam B Johnson (1, 2) , William Thompson (2) , Kris Caputa (2) , Frédéric Grandmont (3) , Christian Marois (1, 2) , Tim Hardy , Joeleff Fitzsimmons , Olivier Lardière , Colin Bradley

1 UVIC - University of Victoria [Canada]
2 NRC - National Research Council of Canada
3 ABB, Inc. (Canada)

Spectroscopy in exoplanet imaging has been used to characterize exoplanets in astronomy for the last two decades. To optimize new and promising techniques, such as using very high-spectral resolution to identify exoplanet molecules in a speckle-limited image, new imaging spectrograph technologies are needed. These new techniques are difficult to implement as they require both a large field-of-view (FOV) to search for hidden exoplanets, and a high-resolution spectrum for every resolution element of the FOV. The Subaru Pathfinder Instrument for Detecting Exoplanets & Retrieving Spectra (SPIDERS) will showcase a new generation imaging spectrograph, using an imaging Fourier transform spectrometer (IFTS) to acquire a wide FOV from low R40 to high R20,000 spectral resolution. Off-the-shelf devices have few options for scan speed and shape control as typical applications can provide a bright light source to take advantage of faster scan speeds with a high spectral signal-to-noise ratio. Implementing new imaging methods and faster techniques, SPIDERS requires an IFTS that can scan much slower than usual to minimize the impact of detector read noise whilst prioritizing scan stability. Using an off-the-shelf Michelson interferometer, a custom PCB was developed and implemented to facilitate a voice coil driving and metrology feedback circuit that will provide complete control over scan speed, length, and shape. A helium-neon laser provides fringe quadrature feedback that is used to determine Angstrom-level positional feedback for closed-loop control. The C-based controller generates a 16-bit current command at 100kHz to provide stable scanning and accurate positioning. Preliminary results are proving the success of the drive and metrology circuit design, the quadrature algorithm, and the closed-loop control. This paper will present the controller design and implementation, along with its performance and initial results on the bench.

Keywords: Imaging Fourier transform spectrometer Michelson interferometer fringe quadrature closed-loop voice coil control exoplanet imaging and characterization adaptive optics; Imaging Fourier transform spectrometer; Michelson interferometer; fringe quadrature; closed-loop voice coil control; exoplanet imaging and characterization; adaptive optics

Domains: Sciences of the Universe [physics]

Adam B Johnson, William Thompson, Kris Caputa, Frédéric Grandmont, Christian Marois, et al.. Exoplanet Detection and Characterization: Development and Results of a New Generation Imaging Fourier Transform Spectrometer. Adaptive Optics for Extremely Large Telescopes 7th Edition, Jun 2023, Avignon, France. ⟨10.13009/AO4ELT7-2023-130⟩. ⟨hal-04461426⟩