Active Optics Methods

Prof. Gérard René Lemaitre
Astronome CE – Emeritus Professor AMUGerard_Lemaitre
Laboratoire d’Astrophysique de Marseille (LAM)
Aix Marseille Université (AMU)

LAM – Technopole Château Gombert
38 rue Frédéric Joliot Curie
F-13388 Marseille Cedex 13, France

Phone :  +33 (0)4 9504 4138
Mobile :  +33 (0)6 2565 3644
Email :  gerard.lemaitre « (at) »


Curriculum vitae
Gérard René Lemaitre was born in Paris in 1943. Presently émeritus professor at LAM, Aix Marseille Université, he received a degree of engineer from the Ecole d’Arts et Métiers, Paris, in 1967, and focused on researches in astronomical optics. In 1974, he earned the degree of Docteur d’Etat es Sciences Physiques at the Université de Provence for his dissertation entitled Astronomical Optics and Elasticity.

His research concentrates on optical design and elasticity theory for improving the performances of telescopes and spectrographs by use of a minimum number of optical surfaces. Astronomical instruments often include aspherical surfaces which are difficult to obtain with high accuracy and free from discontinuities (ripple errors). From Bernhard Schmidt idea that an elastic deformation could provide an efficient method for generating aspherics, G. R. Lemaitre elaborated Active Optics and related theoretical boundary conditions which are required for developing these methods. Holder of 13 patents in several countries, he developed active optics to generate axisymmetric aspheric optical surfaces by stress figuring or replication technique – corrector plates, telescope mirrrors, reflective aspherized gratings – as well as methods to generate in-situ varying surface shapes – variable curvature mirrors of ESO/VLTI delay lines – or non-axisymmetric surfaces – toroid diffraction gratings from replication of deformable substrates. He investigated and built new wide-field astronomical telescope and reflective spectrograph designs.

Some of his contributions are the followings

  • Establishment of the best shape of the two mirrors of any all-reflective Schmidt system – Telescopes and aspheric grating spectrographs
  • Discovery of variable curvature mirrors – or zoom mirrors – by elastic bending satisfying accurate optics criteria – Application to ESO VLTI
  • Inventions of stress-figuring methods and in-situ-stressing methods for the aspherization of refractive, reflective or diffractive surfaces
  • Elaboration of active optics for obtaining aberration corrected diffraction gratings by two-stage replication or active compensator recording
  • Optical design of faint object spectrographs equipped with plane-aspheric gratings or concave toroid gratings obtained by active replications.
  • Elaboration of an elasticity theory of weakly conical shells – Application to the active aspherization and control of X-ray telescope mirrors

Direction and Expertise
G. R. Lemaitre was leader of the optical laboratory of the Marseille Observatory – LOOM – from 1975 to 2005, and an international member of many optical design committees for large telescopes and astronomical instruments. His general result on the best figure to be given to mirrors or diffraction gratings of reflective Schmidt systems was retained for the giant segmented telescope LAMOST (Chinese Academy of Sciences) which started operations in Xinglong Observatory in 2008 ( He was an member of the international ESE committee of the 39m telescope project E-ELT of European Southern Observatory. The E-ELT started construction in 2014.

 Some selectected papers

Publications and Patents


Astronomical Optics and Elasticity Theory – Active Optics Methods, Astronomy and Astrophysics Library, Springer, 2009

Full CV

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