Divergence and Strehl ratios of L-G multimode beams

David R. Whitehouse

doi:10.1117/12.143842

22 April 1993 Divergence and Strehl ratios of L-G multimode beams

David R. Whitehouse

Proceedings Volume 1834, Laser Energy Distribution Profiles: Measurement and Applications; (1993) https://doi.org/10.1117/12.143842
Event: Applications in Optical Science and Engineering, 1992, Boston, MA, United States

Abstract

At present, the quality of a laser beam is defined by the parameter M² or divergence ratio. It is the ratio of the actual far-field divergence of a beam to that of an ideal TEM₀₀ Gaussian beam with the same size waist. It is important because it provides information on beam size for the design of beam delivery systems and on beam focusability for the design of applications which require a small spot size. This parameter, however, relates to the beam size which contains no information on energy distribution within the beam. By defining an additional parameter called the intensity or Strehl ratio which is related to the on-axis, far-field intensity of the beam, one has further information on the smoothness or sharpness of the beam. From an analysis of multimode beams composed of pure Laguerre-Gaussian (L-G) modes, this paper shows that the divergence ratio and Strehl ratio are independent and concludes that both ratios would be beneficial in specifying the `quality' of a beam. For specific cases, these two ratios uniquely determine the energy distribution of a multimode beam, even though the combination of L-G modes is not unique.

Citation Download Citation

David R. Whitehouse "Divergence and Strehl ratios of L-G multimode beams", Proc. SPIE 1834, Laser Energy Distribution Profiles: Measurement and Applications, (22 April 1993); https://doi.org/10.1117/12.143842

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