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Demonstration on starlight in 1999 at Lick Observatory
Externally dispersed interferometry was first brought to a telescope and demonstrated on starlight by Erskine and Ge in Dec 1999, at the 1 meter Nickel telescope at Lick Observatory (Ref. 3). During the summer of 1999 they modified the first EDI apparatus by adding cylindrical lenses to the input optics and a cavity laser stabilization system (with LabView code written by Mike Rushford). The cylindrical optics allow more light to pass through the slit from a round fiber, and the cavity stabilization prevents the interferometer delay from wandering more than a quarter wave during the temperature changes of a long time exposure. Jian Ge designed and built the fiberoptic interface for the 1-meter Nickel telescope at Lick Observatory and operated the telescope. Erskine designed the algorithms, wrote the computer codes and did all the velocity data analyses for the project's publications, including the Lick 1999 data and the earlier sunlight 1998 data.
Moving on
With the end of project funding in early 2000, Ge left for Penn. State Univ. to build his own EDI, with which he has successfully detected planets at the Kitt Peak Observatory. In 2003 he moved his group to Univ. of Florida.
Sabbatical year at UC Berkeley Space Sciences
In 2001, Erskine took a year sabbatical hosted by Jerry Edelstein at UC Berkeley's Space Sciences lab. There he developed a first principles theory of the EDI instrument behavior (Ref. 4, 7 & 11), conducted laboratory demonstrations of the spectral astrometry application (Ref 6.), and developed computer algorithms for implementing the high resolution spectroscopy application of EDI (Ref. 7). This required a solid understanding of the role of heterodyning in the production of moire fringes, and how the instrument modifies the input signal expressed as spatial frequencies along the dispersion axis (the Fourier domain). He invented and demonstrated new algorithms for processing uniphase phase stepped data, required for echelle spectrographs where the beam height is too small to allow any phase variation of the fringe along the slit, and where the phase steps can be unknown and irregular. Since echelle spectrographs are the most important astronomical type due to their very wide bandwidth, this was a major advance toward practical observatory application.
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