DISPERSION IN STELLAR INTERFEROMETRY - SIMULTANEOUS-OPTIMIZATION FOR DELAY TRACKING AND VISIBILITY MEASUREMENTS

In long-baseline optical stellar interferometry, it is necessary to ma intain optical path equality between the two arms of an interferometer in order to measure the fringe visibility. There will be errors in ma tching the optical paths because of a number of factors, and it is des irable to use an automatic system to monitor and correct such path err ors. One type of system is a delay tracker, based on imaging of the ch anneled spectrum. The tracking algorithm is designed to maintain a fix ed number of fringes, ideally linearly spaced, across the observed spe ctral band. This results in a constant optical path difference, which may be incompatible with the requirement of path equality for the meas urement of fringe visibility. In a practical interferometer that uses an optical path-length compensator operating in air, there is a compli cation since air paths introduce differential dispersion. This dispers ion can be compensated for by including dispersion correction. By modi fying the operation of an appropriately designed dispersion corrector, we show that it is possible to make the optical path difference zero at the measurement wavelength and, at the same time, to produce linear ly spaced channel fringes across the tracking band. (C) 1998 Optical S ociety of America.