Developing technologies to image and characterize exoplanets
The ET Lab focuses on high-contrast imaging and spectroscopy of exoplanets. Beyond taking striking pictures, the technique promises to yield the most detailed measurements of distant planetary systems, including spectroscopy of planet atmospheres and time-resolved astrometry of their orbital motion. Direct imaging of exoplanets requires separating the signal of a relatively small, faint, and cooler object seemingly very close to a bright host star. Imaging a faint object at small angular separation and high contrast requires a three-pronged approach: use the biggest available optical telescope; use a device called a coronagraph to reject the blinding starlight; correct the blurring effect of Earth's turbulent atmosphere as much as possible by using an adaptive optics system.
Adaptive optics is a sophisticated technique that effectively removes the twinkle from the stars. By means of a dedicated sensor, it measures the corrugation of the incoming waves of starlight upon propagation through the 100 km of Earth's turbulent atmosphere more than 1000 times per second. Almost simultaneously, the adaptive optics system imposes the inverse corrugation upon reflection from a small deformable mirror with a few hundred actuators, flattening the wavefront and restoring the image quality and finesse of the scope in real time. Adaptive optics systems have been used on ground-based telescopes for more than 20 years, and has now fully become of age. Coronagraphy is a mature technique too, first developed by French astronomer-instrumentalist Bernard Lyot to study the Solar corona outside of natural eclipses (Lyot, 1931, 1939). Lyot's original concept to block out the on-axis stellar light with a physical opaque mask, and mitigate diffraction using a stop in the relayed downstream pupil, still forms the foundation of modern stellar coronagraphy and exoplanet imaging. Mask technologies have greatly evolved, benefiting from advances in optical modeling, beam shaping, micro-optics, photonics, and material sciences.