Abstract
The direct detection and imaging of exoplanets requires the use of high-contrast adaptive optics (AO). In these systems quasi-static aberrations need to be highly corrected and calibrated. In order to achieve this, a high-sensitivity wavefront sensor, the pupil-modulated point-diffraction interferometer (m-PDI), is presented. This sensor modulates and retrieves both the phase and the amplitude of an incoming electric field. The theory behind the wavefront reconstruction, the visibility of fringes, chromatic effects and noise propagation are developed. Results show this interferometer has a wide chromatic bandwidth. For a bandwidth of Δλ = 50% in units of central wavelength, the visibility of fringes and the response of the WFS to low and high-order aberrations are almost unaffected with respect to the monochromatic case. The WFS is, in contrast, very sensitive to variations in the size of its pinhole. The size of the pinhole is shown to affect the sensor's linearity, the dynamic range and the amount of noise. Larger pinholes make the sensor less sensitive to low-order aberrations, but in turn also decrease the effects of misalignments.
Highlights
In astronomical adaptive optics (AO) the application of high-contrast techniques, including extreme adaptive optics (XAO), has a particular focus towards the direct detection and imaging of exoplanets
The direct detection and imaging of exoplanets requires the use of high-contrast adaptive optics (AO)
For a bandwidth of ∆λ = 50% in units of central wavelength, the visibility of fringes and the response of the WFS to low and high-order aberrations are almost unaffected with respect to the monochromatic case
Summary
In astronomical adaptive optics (AO) the application of high-contrast techniques, including extreme adaptive optics (XAO), has a particular focus towards the direct detection and imaging of exoplanets. Because the aberrations are long lived, they do not average out over time and are more difficult to deal with In their first approach, systems like VLT-SPHERE [3] and Subaru-SCExAO [4] relied respectively on methods such as phase-diversity [5] and speckle-nulling [6]. Systems like VLT-SPHERE [3] and Subaru-SCExAO [4] relied respectively on methods such as phase-diversity [5] and speckle-nulling [6] For the latter, it has been estimated the converging time needs to be under 15-20 minutes to leave time for the science acquisition (this is only a requirement and converging times can be much lower).
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