MEUDON - VUV Observatory

The 10 meter high resolution vacuum spectrograph of the Paris-Meudon Observatory is open to all European and non-European researchers. For access to the instrument, contact the Department of LERMA (see below). Direct and indirect operational costs will be determined with the parties involved.


The instrument is a normal incidence vacuum spectrograph equipped with a reflective concave grating of radius equal to 10.7 m which is the focal length and the diameter of the Rowland circle. It has an Eagle in-plane mounting where the slit and the plate holder for detection are in the same plane while the grating and the plate holder have to be rotated and displaced to keep the image in focus when the wavelength range is varied.

The plate holder was designed to house two 18" x 2" photographic plates. Unfortunately only 15"x 2" Q plates from ILFORD are still available for the VUV region. The spectrograms can be measured using a semi-automatic comparator. FUJI image plates have a maximum useful length of 38 cm and have a linear response in intensities over five orders of magnitude. They have to be read on a specific scanner which provides a digitized spectrum with a given sample step.

The spectrograph generally operates in integrating mode so that unstable or pulsed emission light sources can be used.

Absorption spectra can be also recorded using a continuum light source and absorption cell.

The following table summarises the characteristics of the spectrograph:

Grating holographic (Jobin-Yvon)
Radius of the grating 10.685 m
Number of lines/mm 3600
l of maximum efficiency 1200 Å
Plate factor (linear dispersion on the plate) ~ 0.25 Å/mm
Practical resolution ~150 000 (0.008 Å)
Wavelength range 250 - 2200 Å with image plates 500 - 3000 Å with photographic plates
Maximum range covered in one exposure ~ 200Å with available plates
Mechanical fittings ISO-KF, ISO-CF

Measuring devices

  • For image plates
    • Scanner Cyclone Plus Storage Phosphor System (Perkin-Elmer)
      The image plates are scanned by the system's laser focused to less than 50 microns, and the latent image is detected by its optics to create a high resolution digitized image with quantitative data in the form of an image file. The image is displayed on the screen for analysis with OptiQuant TM software and can be printed, exported, and archived for future reference.

  • For photographic plates:
    • Optical scanner iQSmart 1
      This high resolution (2540 dpi) scanner provides a digitized image of spectrogrammes for further treatment.
    • Semi-automatic comparator of Grant type
      A comparator with photoelectric setting device (F.S. Tomkins & M. Fred, J. Opt. Soc. Am. 41, 641 (1954)) and optical reading of line positions to ±1 m m, connected to a PC computer.

Emission light sources

  • Low pressure Penning discharge source for gases
    The presence of a magnetic field of 0.1 T makes it possible to run the source at pressures as low as a few Pa (10 -2 Torr) with reduced self-absorption.
  • Copper hollow cathode, water cooled, for calibration spectrum

Continuum light sources for absorption studies

  • BRV source
    This source is a vacuum spark with extremely low inductance which is triggered by an auxiliary sliding spark. Under various configurations it is capable of producing a fairly smooth continuum from about 50Å to the visible range. (G. Ballofet, J. Romand and B. Vodar, C.R. Acad. Sci. 252, 4139 (1961), T.B. Lucatorto, T.J. McIlrath and G. Mehlman, Applied Optics 18, 2016 (1979))
  • Deuterium lamp (HERAEUS)
    This source provides a continuum above 1600Å up to 4000Å.

Scientific applications

  • High resolution VUV spectroscopy of complex atomic ions
    Examples :
    Survey of Recent Laboratory Studies of Multiply Charged Ion Spectra Using High Resolution VUV Spectrographs
    W.-Ü L. Tchang-Brillet and V.I. Azarov , Physica Scripta T100 , 104-113, (2002)
    Analysis of the free ion Nd3+ spectrum (Nd IV)
    Jean-François Wyart et al, J. Phys. B: At. Mol. Opt. Phys. 40 , 3957-3972 (2007)
  • Rotationally resolved electronic transitions of small molecules
    High resolution absorption spectrum of CO2 between 10 and 14 eV
    C. Cossart-Magos, M. Jungen, F. Launay, Mol. Phys. 61 , 1077 (1982)
    Atlas of the vacuum ultraviolet emission spectrum of molecular hydrogen
    J.-Y. Roncin and F. Launay, J. Phys. Chem. Ref. Data Monogr. 4 , 1, (1994)
    Tables of vacuum ultraviolet emission band systems of molecular nitrogen from 82.6 to 124.2 nm
    J.-Y. Roncin and F. Launay , Astron. and Astrohys. Suppl. 128 , 361 (1998),
    An Atlas of the Intersystem Transitions of CO
    M. Eidelsberg and F. Rostas, Astrophys. J. Suppl. 145 89 (2003)
    High resolution vacuum uv emission spectrum of D2 from 78 to 103 nm: the D1 Πu→ X1Σ+gand D1 Πu→ X1Σ+gband systems
    M. Roudjane, F. Launay, W.-Ü L. Tchang-Brillet , J. Chem. Phys. 125 , 214305, (2006)
  • Measurement of transmission coefficients for VUV filters


Professor Lydia Tchang-Brillet
Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique (LERMA)
Observatoire de Paris-Meudon
5, Place Jules Janssen
92195 Meudon
Tel + 33 1 45 07 75 76 (sec. 7557)

Last update: 23 January 2012

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