Science Pictures

Aberration detector

copyright © Phasics 2007 - Tous droits réservés
Analysis by multi-lateral shift interferometry of a light beam exhibiting a spherical aberration.

This image was obtained from a quadri-lateral shift interferometer¹ for analyzing a light beam exhibiting a defect very well known to opticians: spherical aberration.

Spherical aberration is characteristic of a spherical mirror, which is easy to make instead of a parabola, for observing a source at infinity. It has thus been described and studied since the eleventh century by Arab scientists, Ibn Sahl in particular.

This interferometer, invented at Onera, is currently used for checking hyper-intensity lasers², and has regularly contributed to surpassing power frontiers since 2000. It is thus installed on laser chains at:

• Luli [laboratory for the use of intense lasers] of the Ecole Polytechnique in Palaiseau
• Cuos [Center for Ultrafast Optical Science] at the University of Michigan
• Lawrence Livermore National Lab, University of California
• Rutherford Lab in the UK
• and in some ten countries worldwide.

The interferogram is analyzed by harmonic analysis (Fourier technique) by which the shift of each of the spots with respect to an origin position (perfect beam) can be referenced. Considering the very large amplitude of the aberration analyzed here, the grid is especially deformed, which gives it this Vasarely-style abstract character.

copyright © Phasics 2007 - Tous droits réservés
Interferogram of a light beam without aberration defect.

Images: Phasics company [www.phasics.com]

Text: Jérôme Primot, researcher in Onera's Theoretical and Applied Optics department

Glossary

1. Quadri-Lateral Shift Interferometer
   An optical analysis instrument recently developed by Onera. The principle was proposed in 2000, based on the use of four replicas of the light wave to be analyzed, shifted and slightly inclined, of the incident wave. The intensity figure generated by the interference of these four replicas is simply composed of bright spots arranged in a Cartesian grid. If the replicated wave phase is not flat, the interferogram will then be subjected to deformations that can be studied to obtain the derivatives of the incident wave surface. The derivatives thus obtained can then be numerically combined to reconstruct the analyzed wave surface. 
   What use is it?
2. Hyper-intense laser
   A hyper-intense laser is a pulsed laser source that can generate very large powers (from a gigawatt to petawatt³), often used for metrics or the analysis of matter. [Laser pointer pens have powers of the order of a milliwatt.]
3. Giga, Peta
   Giga=10⁹ or a billion; Peta = 10¹⁵ or a million billion.

Last Update: April 2, 2007 - © ONERA 2009 - Terms of use