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A new Generation of Spectrometer Calibration Techniques Based on Optical Frequency Combs

  • P. O. Schmidt
  • S. Kimeswenger
  • H. U. Käufl
Part of the ESO Astrophysics Symposia European Southern Observatory book series (ESO)

Abstract

Typical astronomical spectrographs have a resolution λ/°λ ranging between a few hundred to 200,000. Deconvolution and correlation techniques are being employed with a significance down to 1/1000th of a pixel. HeAr and ThAr lamps are usually used for calibration in low and high resolution spectroscopy, respectively. Unfortunately, the emitted lines typically cover only a small fraction of the spectrometer’s spectral range. Furthermore, their exact position depends strongly on environmental conditions. A problem is the strong intensity variation between different lines1 (intensity ratios >300). In addition, the brightness of the lamps is insufficient to illuminate a spectrograph via an integrating sphere, which in turn is important to calibrate a long-slit spectrograph, as this is the only way to assure a uniform illumination of the spectrograph pupil.

Laboratory precision laser spectroscopy has experienced a major advance with the development of optical frequency combs generated by pulsed femto-second lasers. These lasers emit a broad spectrum (several hundred nanometers in the visible and near infra-red) of equally-spaced “comb” lines with almost uniform intensity (intensity ratios typically <10). Self-referencing of the laser establishes a precise ruler in frequency space that can be stabilized to the 10-18 uncertainty level, reaching absolute frequency inaccuracies at the 10-12 level per day when using the Global Positioning System’s (GPS) time signal as the reference. The exploration of the merits of this new technology holds the promise for broad-band, highly accurate and reproducible calibration required for reliable operation of current and next generation astronomic spectrometers. Similar techniques are also proposed in[5, 6].

Keywords

Global Position System Frequency Shift Transmission Maximum Cavity Resonance Frequency Comb 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer-Verlag Berlin Heidelberg 2008

Authors and Affiliations

  • P. O. Schmidt
    • 1
  • S. Kimeswenger
    • 2
  • H. U. Käufl
    • 3
  1. 1.Institute of Experimental PhysicsAustria
  2. 2.Institute of Astro- and Particle PhysicsAustria
  3. 3.ESO85748 GarchingGermany

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