A conceptual design for a Cassegrain-mounted high-resolution optical spectrograph for large-aperture telescopes

Cynthia S. Froning, Steven Osterman, Eric Burgh, Matthew Beasley, Paul Scowen, Todd Veach, Steven Jordan, Dennis Ebbets, Michael Lieber, James DeCino, Bruno Vaz Castilho, Clemens Gneiding, Antonio César De Oliveira

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

1 Scopus citations


We present a conceptual design for a high-resolution optical spectrograph appropriate for mounting at Cassegrain on a large aperture telescope. The design is based on our work for the Gemini High Resolution Optical Spectrograph (CUGHOS) project. Our design places the spectrograph at Cassegrain focus to maximize throughput and blue wavelength coverage, delivering R=40,000 resolving power over a continuous 320-1050 nm waveband with throughputs twice those of current instruments. The optical design uses a two-arm, cross-dispersed echelle format with each arm optimized to maximize efficiency. A fixed image slicer is used to minimize optics sizes. The principal challenge for the instrument design is to minimize flexure and degradation of the optical image. To ensure image stability, our opto-mechanical design combines a cost-effective, passively stable bench employing a honeycomb aluminum structure with active flexure control. The active flexure compensation consists of hexapod mounts for each focal plane with full 6-axis range of motion capability to correct for focus and beam displacement. We verified instrument performance using an integrated model that couples the optical and mechanical design to image performance. The full end-to-end modeling of the system under gravitational, thermal, and vibrational perturbations shows that deflections of the optical beam at the focal plane are <29 μm per exposure under the worst case scenario (<10 μm for most orientations), with final correction to 5 μm or better using open-loop active control to meet the stability requirement. The design elements and high fidelity modeling process are generally applicable to instruments requiring high stability under a varying gravity vector.

Original languageEnglish (US)
Title of host publicationOptomechanical Engineering 2013
StatePublished - 2013
EventOptomechanical Engineering 2013 - San Diego, CA, United States
Duration: Aug 26 2013Aug 29 2013

Publication series

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


OtherOptomechanical Engineering 2013
Country/TerritoryUnited States
CitySan Diego, CA


  • Cassegrain mount
  • Optical spectroscopy
  • flexure control
  • integrated modeling

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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