Collaborative Research: Development of a Green-Orange Astro-comb for Exoplanet and Cosmology Research

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The high-dispersion optical spectrographs that have thus far enabled the discovery of more than 400 extrasolar planets have a common susceptibility: the need for ultrastable, broadband, high-line-density, bright, and continuous wavelength calibration so that the small reflex velocities of the host stars can be precisely characterized over periods of weeks to years. One crucial technology for these investigations utilizes a mode-locked femtosecond pulsed laser - which produces a bright, regularly spaced set of emission features in frequency space - together with a Fabry-Perot filtering cavity to create the appropriate line-density, all locked to an atomic clock for long-term stability. These so-called "laser combs" have the potential for enabling radial velocity measurements to a precision 10 cm/s; thus the determination of the mass of Earth-like exoplanets should eventually be possible.Dr. Ronald Walsworth of the Harvard-Smithsonian Center for Astrophysics and Dr. Franz Kaertner of the Massachusetts Institute of Technology are planning to construct such a laser comb for the orange-green spectrum, a region well-suited to the detection of solar-type stars and therefore of stars in which a planet with an orbital period of ~1 yr would exist in the "life-zone", where surface water would be in liquid form. The team of investigators has an excellent track record in this area, having developed laser combs for the optical red and blue spectral regions. The new comb will be tested at the 1.5-m Whipple Observatory telescope on Mt. Hopkins, Az, and, when proven reliable, applied to an ongoing project at the 1.5-m telescope at Cerro Tololo Interamerican Observatory that is searching for exo-Earths orbiting stars in the very nearby alpha/beta-Centaurus star system. The activity will involve both women as both scientists and students, and the resulting time-controlled laser technology should have application well beyond astronomy. Funding for this work is being provided by NSF's Division of Astronomical Sciences through its Advanced Technologies and Instrumentation program.