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Laboratory validation of the dual-zone phase mask coronagraph in broadband light at the high-contrast imaging THD testbed
摘要： Context. Speci?c high-contrast imaging instruments are mandatory to characterize circumstellar disks and exoplanets around nearby stars. Coronagraphs are commonly used in these facilities to reject the di?racted light of an observed star and enable direct imaging and spectroscopy of its circumstellar environment. One important property of the coronagraph is to be able to work in broadband light. Aims. Among several proposed coronagraphs, the dual-zone phase mask coronagraph is a promising solution for starlight rejection in broadband light. In this paper, we perform the ?rst validation of this concept in laboratory. Methods. First, we consider the principle of the dual-zone phase mask coronagraph. Then, we describe the high-contrast imaging THD testbed, the manufacturing of the components, and the quality control procedures. Finally, we study the sensitivity of our coronagraph to low-order aberrations (inner working angle and defocus) and estimate its contrast performance. Our experimental broadband light results are compared with numerical simulations to check agreement with the performance predictions. Results. With the manufactured prototype and using a dark hole technique based on the self-coherent camera, we obtain contrast levels down to 2 × 10?8 between 5 and 17 λ0/D in monochromatic light (640 nm). We also reach contrast levels of 4 × 10?8 between 7 and 17 λ0/D in broadband (λ0 = 675 nm, ?λ = 250 and ?λ/λ0 = 40%), which demonstrates the excellent chromatic performance of the dual-zone phase mask coronagraph. Conclusions. The performance reached by the dual-zone phase mask coronagraph is promising for future high-contrast imaging instruments that aim to detect and spectrally characterize old or light gaseous planets.
关键词： techniques: high angular resolution,instrumentation: high angular resolution,planets and satellites: detection
更新于2025-09-04 15:30:14
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A High-precision Technique to Correct for Residual Atmospheric Dispersion in High-contrast Imaging Systems
摘要： Direct detection and spectroscopy of exoplanets requires high-contrast imaging. For habitable exoplanets in particular, located at a small angular separation from the host star, it is crucial to employ small inner working angle (IWA) coronagraphs that ef?ciently suppress starlight. These coronagraphs, in turn, require careful control of the wavefront that directly impacts their performance. For ground-based telescopes, atmospheric refraction is also an important factor, since it results in a smearing of the point-spread function (PSF), that can no longer be ef?ciently suppressed by the coronagraph. Traditionally, atmospheric refraction is compensated for by an atmospheric dispersion compensator (ADC). ADC control relies on an a priori model of the atmosphere whose parameters are solely based on the pointing of the telescope, which can result in imperfect compensation. For a high-contrast instrument like the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system, which employs very small IWA coronagraphs, refraction-induced smearing of the PSF has to be less than 1 mas in the science band for the ?rst on-sky measurement and correction of residual optimum performance. In this paper, we present atmospheric dispersion. Atmospheric dispersion is measured from the science image directly, using an adaptive grid of arti?cially introduced speckles as a diagnostic to feedback to the telescope’s ADC. With our current setup, we were able to reduce the initial residual atmospheric dispersion from 18.8 mas to 4.2 in broadband light (y- to H-band) and to 1.4 mas in the H-band only. This work is particularly relevant to the upcoming extremely large telescopes (ELTs) that will require ?ne control of their ADC to reach their full high-contrast imaging potential.
关键词： atmospheric effects,planets and satellites: detection,instrumentation: adaptive optics
更新于2025-09-04 15:30:14