Presentation #102.169 in the session Poster Session.
Modern astrophysics demands extremely stable wavelength measurements, such as few cm/s scale Doppler radial velocimetry for Earth-like planet detection and multi-year cosmic redshift drift measurements. Placing an interferometer in series with a spectrograph forms an Externally Dispersed Interferometer (EDI). We propose to significantly improve the wavelength accuracy of EDI by measuring spectra with pairs of similar interferometer delays (pathlength differences) measured simultaneously or more rapidly than the wavelength drift, in a technique called “Crossfading.” Fringing spectra for high and low delays, at a spatial frequency overlapped by both, will counter-rotate under a wavelength drift. This counter-rotation can be cancelled by strategic weighting of the fringe signals during analysis. Calculations using multiple delay EDI measurements of a ThAr lamp at Mt. Palomar Obs. show the wavelength stability is improved 1000 times*. However, there is a dearth of EDI data where pairs of delays were taken under identical offsets. We are constructing a crossfaded EDI testbed to measure multiple simultaneous fringing spectra under the same wavelength offset. We also describe crossfading that occurs in a single delay EDI between the fringing and native spectrograph spectral components, when the delay is low enough that the fringing sensitivity overlaps with the native sensitivity, as drift offsets to both components are naturally the same. Crossfading using re-analyzed single delay EDI data taken at Mt. Palomar Obs. in 2010 demonstrates wavelength stabilization of ~500x. *David J. Erskine, J. Astr. Tele. Instrum. Sys., 7(2):025006, June 2021. Prepared by LLNL under Contract DE-AC52-07NA27344.