Stiffening an off-axis beam compressor mount for improved performance

F. Ernesto Penado, James H. Clark, Frank Cornelius

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

3 Scopus citations


The Navy Prototype Optical Interferometer (NPOI) near Flagstaff, Arizona, makes use of separate smaller optical elements spaced along a Y-array and used simultaneously to simulate an equivalent single large telescope. The instrument is useful in generating and upgrading existing astronomical catalogues and investigating synthetic aperture optical imaging techniques. The NPOI is a joint collaboration between the US Naval Observatory and Naval Research Laboratory in collaboration with the Lowell Observatory. Stellar radiation (visible light) reflects off 35 cm diameter flat mirrors, also known as siderostats, toward a tilt-tip mirror, which reflects a 12 cm diameter beam through a multi-reflection relay transport system. To maximize the reflective area of the siderostat optics and achieve an increase by a factor of 8.5 in light collecting area, a beam compressor is to be installed between the siderostat and fast tip/tilt mirror. However, the present configuration of a prototype beam compressor mount (BCM) vibrates at unacceptable amplitudes, which makes it nearly impossible to optically align the mirrors. This paper presents the results of finite element analyses conducted to quantify the design limitations of the prototype beam compressor mount. The analyses indicated that the current configuration is too soft, with very low fundamental frequencies, which verified the difficulties encountered during alignment tests. Based on these results, design modifications have been proposed to increase the overall structural stiffness of the mount and increase its fundamental frequency of vibration. These modifications will mechanically stabilize the structure for the alignment of the optics, and allow integration of the compressor into the interferometer. The interferometer will then have the capability to capture more light from each siderostat and allow observations of fainter stellar targets. More generally, the results can be useful as a guide for engineers and scientists involved in the design of similar optomechanical structures.

Original languageEnglish (US)
Title of host publicationOptical System Alignment, Tolerancing, and Verification IV
StatePublished - 2010
EventOptical System Alignment, Tolerancing, and Verification IV - San Diego, CA, United States
Duration: Aug 1 2010Aug 2 2010

Publication series

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


OtherOptical System Alignment, Tolerancing, and Verification IV
Country/TerritoryUnited States
CitySan Diego, CA


  • Beam compressor alignment
  • Finite element analysis
  • Fundamental frequency
  • Light collimation
  • NPOI
  • Vibration analysis

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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