The twinkling of stars, while beautiful for the eye, is a serious problem for all ground-based telescopes. It is caused by Earth’s atmosphere distorting the light from stars before arriving at the telescope. These distortions smear out the light of the star, creating a halo of star light much brighter than the signal of exoplanets. To this end, high-contrast imaging systems are equipped with adaptive optics systems that measure the distortions of the atmosphere and correct it close to real-time.
The adaptive optics system consists of three subsystems. The first system is the wavefront sensor that measures the distortion of the light. The second is the deformable mirror which can be reshaped to cancel the distortion of the light. The third subsystem is the control system, which uses the input of the wavefront sensor to calculate the optimal shape of the deformable mirror. Together they form a loop that can correct the aberrations introduced by the atmosphere of the Earth.
The AO system is placed before the coronagraph and imaging systems. Therefore it is not possible to measure aberrations introduced by these optics that are placed after the wavefront sensor. These aberrations are called non-common path aberrations and are currently a limiting factor for imaging exoplanets close to the star.
The LEOPARD works on improving the adaptive optics system and mitigating these non-common path aberrations. To this end, the LEOPARD has developed several systems that are implemented or are in the process of being implemented.
Wavefront sensors:
– The vector-Zernike wavefront sensor (vZWFS)
– The generalized optical differentiation wavefront sensor (g-OD WFS)
– The modal coronagraphic wavefront sensor (cMWFS)
– Fast & Furious
– The Asymmetric Pupil vAPP (APvAPP)
– Spatial linear dark field control (LDFC)
– Polarization-encoded self-coherent camera (PESCC)
Control:
– Predictive control
– Nonlinear wavefront reconstruction with convolutional neural networks