An approach to upgrading the beam transport system at the Navy Precision Optical Interferometer

James H. Clark, F. Ernesto Penado, Sergio R. Restaino, Henrique Schmitt

Research output: Chapter in Book/Report/Conference proceedingConference contribution


We present an approach to upgrading the beam transport system at the Navy Precision Optical Interferometer. These upgrades together will provide consistent beam transport, improve fringe contrast by preserving beam wavefront, reduce tracking errors by increasing the frequency response of the tracker, and automatically realign the entire transport train after thermal drift over the course of nightly observations. The beam transport system passively redirects stellar light from the telescope output to the fast delay line through a train of flat mirrors. This multi-mirror transport train reduces wavefront preservation due to stack-up of surface flatness errors. We demonstrated previously by using a contour-conformable mirror instead of one of the flats in the train that a 63% improvement in wavefront flatness is achievable. Also, the 25 Hz tracker is replaced by a 100 Hz tracker to further stabilize the trajectory during observations. Finally, we include an auto-aligner to systematically realign the entire beam transport system from thermal drifts. This is necessary for long baseline interferometry with short drift time constants. The beam transport system is common to all front ends (telescopes and siderostats), beam delay, and back-ends (beam combiners and detectors). These three upgrades expand the utility of the NPOI from a relatively short 97 m baseline interferometer to its full reconfigurable 437 m baselines and allow consistent beam transport with various potential experimental telescope front ends and beam combiner back-ends. In this paper, we describe our three-pronged upgrade approach, experimental method and results, and recommendations.

Original languageEnglish (US)
Title of host publicationOptical System Alignment, Tolerancing, and Verification XIII
EditorsJose Sasian, Richard N. Youngworth
ISBN (Electronic)9781510637825
StatePublished - 2020
EventOptical System Alignment, Tolerancing, and Verification XIII 2020 - Virtual, Online, United States
Duration: Aug 24 2020Sep 4 2020

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X


ConferenceOptical System Alignment, Tolerancing, and Verification XIII 2020
Country/TerritoryUnited States
CityVirtual, Online


  • Angle tracker
  • Auto-aligner
  • Beam transport
  • Compliant mirror
  • Ground based optical interferometry
  • NPOI
  • Optical train
  • Wavefront correction
  • Wavefront flatness

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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