Past OSL Spectrograph Projects

UCL Echelle Spectrograph

The first major project was the conceptual design, development, fabrication and commissioning of the UCL Echelle Spectrograph (UCLES) for the coude focus of the 3.9m Anglo Australian Telescope (AAT).

The UCLES Echelle Spectrograph

The UCLES project was won against international tender, and the revolutionary instrument that resulted was commissioned in 1988. Its key innovation was the use of large fused silica prisms, rather than gratings, for cross dispersion. This led to major advantages in throughput, low stray light and large wavelength coverage in an exposure. The instrument also led the field in its methods of computer control and graphical user interface. With separate funding from the UK's Science and Engineering Research Council as it then was, OSL also originated the data reduction software for processing the echellograms from UCLES.

UCLES was the most heavily subscribed of all the AAT instruments for over a decade, until the recent advent of the telescope's wide-field capability. To this day, UCLES remains a front-rank instrument at the observatory, used for an enormous range of observational projects by the international community..

Utrecht Echelle Spectrograph

The Utrecht Observatory, under scientific guidance and with the manufacturing involvement of OSL, subsequently built a close copy of UCLES (optically identical) - the Utrecht Echelle Spectrograph (UES). This was commissioned at the Nasmyth focus of the 4.2m William Herschel Telescope at La Palma, and provides in the north the capability of UCLES in the south.

Ultra High Resolution Facility

After UCLES, OSL built the Ultra High Resolution Facility (UHRF) with support from the UK Science and Engineering Research Council (as it then was). UHRF was equally successful and has produced the highest resolving power spectra ever, providing new insights into the interstellar medium.


UHRF Ultra High Resolution Facility and echelle spectrogram of the Sun

Active Compensation of Flexure

The gravity-induced flexure of Cassegrain spectrographs has become an increasing challenge as instruments have become larger and more massive, and tolerances on image-degradation more stringent. Looking forwards to 8-m class telescopes, it was clear that the passive methods used up to the 1980's would no longer be adequate, given the likely performance expectations and mass budgets.

OSL was commissioned by the Gemini Project to undertake a design study into this problem in 1992, and presented a major report. The main thrust of the argument was that a hierarchical approach should be explored embodying:

  1. passive compensation of flexure using truss-type methods
  2. open-loop active compensation using a steerable element controlled from a look-up table
  3. closed-loop active compensation using feedback from an optical (or preferable infra-red) reference propagated through the spectrograph in real-time.

This work led to the development of an active PZT-actuated collimator that was implanted in the ISIS spectrograph on the 4.2m WHT on La Palma. The collimator, shown below, was controlled by a look-up table of flexure measured by moving the spectrograph into different altitude / Cassegrain-rotator configurations. The method proved successful, hysteresis being the chief limitation.

The active collimator

The active-compensation methodology has since been taken up by other spectrograph projects, including OSL's High Resolution Optical Spectrograph for Gemini. Interestingly, the idea of using an optical reference was also utilized in the development of a profilometer for testing large optics.


Examples of Other Instrument Design and Fabrication Projects

  • development and supply of image slicers

  • folded Schmidt camera for Mexico

  • lens collimating system for India

  • spectrograph components for Caltech/Keck

  • synchrotron light monitor for Oxford Instruments


Examples of Other Commissioned Conceptual and/or Detailed Design Studies

  • UV echelle spectrograph for proposed Lyman mission

  • Keck Medium and Low Resolution Imaging Spectrographs

  • high resolution echelle spectrograph for Harvard Smithsonian Center for Astrophysics

  • high resolution optical spectrograph for Gemini

  • multi-object spectrograph for Gemini

  • multi-object spectrograph for Columbia University of New York

  • wide-field corrector with atmospheric dispersion compensation for the CTIO 4m telescope

  • assessment of flexure in the ISIS spectrograph on the WHT at La Palma

  • finite element analysis of large lenses for Keck DEIMOS spectrograph

  • optical spectrograph for the Next Generation Space Telescope, with MSSL and Paris Observatory

  • optical spectrograph for Next Generation Space Telescope - study with MSSL sub-contracted from Matra Marconi


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