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Accelerator Seminar


"Laser Beams and Optics Characterization.
New Zoom-Type Optical Systems for Extended Laser Applications

George Nemes,


The talk contains two parts: 1- Laser beams and optics characterization, and 2- New zoom-type optical systems for extended laser applications.

The first part is a survey of the results obtained in the field of laser beam characterization and propagation. These results rely on the ABCD-type matrix description of optical system, and on the so-called method of second-order moments, allowing the definition of a beam matrix, to describe the laser beams. Depending on the optical system and on the beam symmetry, the matrices involved are 2x2 or 4x4. We introduce the terminology and the definitions of stigmatic (ST), aligned simple astigmatic (ASA), rotated simple astigmatic (RSA), and general astigmatic (GA) optical systems and beams and analyze their general properties. We proceed gradually from 2x2 to 4x4 matrix treatment discussing several systemic concepts related to optical systems and to beams: analysis, identification, classification, synthesis of optical systems, and beam transformations, including beam generation and beam measurements. General synthesis theorems for any matrix able to represent an optical system are given. The widely used M2 propagation parameters and their usefulness and limitations are explained. Their generalization to any kind of beams, i.e., the new beam invariants named the intrinsic astigmatism, a, and the effective propagation ratio Meff4, which recently were introduced in ISO standards, are defined and discussed. A formal definition of the beam concept is given in the end.

The presentation is intended for people involved in laser beam optics, but it could be of interest for people working in charged-particle beam optics as well, due to the obvious analogy between light optics and charged-particle beam optics, in spite of the different convention of writing the matrices in the two different fields.      

In the second part, based on the results presented in the first part, the new family VariSpot® of zoom-type optical systems for lasers, designed and manufactured by ASTiGMATTM, are introduced and discussed. They are based on a new, patented zoom principle, involving rotating cylindrical lenses, rather than translational movement of spherical lenses. Their advantages in comparison to classical zoom systems, i.e., a larger dynamic range of spot sizes, a better resistance to high power laser-fields, and a simpler zoom mechanism, are emphasized. Some potential applications in material processing, materials characterization, biology, and beam diagnostics, are discussed. An experimental demonstration with a VariSpot® system will be performed in real time.    


Thursday, October 29, 2009

10:30 a.m. - 4:30 p.m.
CEBAF Center, F113

Talk Slides: (Slides)

Dr. Alex Bogacz or Anne-Marie Valente.