SIM PlanetQuest white-light fringe modeling: Picometer accuracy calibration and estimation algorithms

SIM PlanetQuest will perform narrow-angle astrometry with microarcsecond accuracy using starlight interferometry requiring tens of picometers accuracy in estimating the optical path difference change between observing two stars. One challenge is to accurately model the white-light fringes and calibrate the required model parameters. Previous studies have developed algorithms based on a CCD-pixel-level calibration scheme assuming slowly varying phase-dispersion functions. However, recent measurements from the SIM PlanetQuest Spectral Calibration Development Unit (SCDU) showed that wavefront aberrations caused the phase-dispersion functions to vary by tens of nanometers across the bandwidth of a CCD pixel, making the previous CCD-pixel-based calibration scheme inadequate. We present a white-light fringe model including the extra phase dispersions caused by the wavefront aberrations together with a calibration and estimation scheme using long-stroke fringe measurements to resolve the bandwidth of pixels. Using simulated data, we show that the total systematic errors in the calibration and estimation scheme are less than a picometer. With SCDU experimental data, we demonstrate that the end-to-end accuracy of the calibration and estimation algorithm is better than 20 pm, achieving the SIM PlanetQuest Engineering Milestone 4.