Phase Aberrations And Laser Output Beam Quality

C. J. Knight; G. W. Sutton; R. Berggren

doi:10.1117/12.932322

30 December 1981 Phase Aberrations And Laser Output Beam Quality

C. J. Knight, G. W. Sutton, R. Berggren

Proceedings Volume 0293, Wavefront Distortions in Power Optics; (1981) https://doi.org/10.1117/12.932322
Event: 25th Annual Technical Symposium, 1981, San Diego, United States

Abstract

This paper presents a theoretical study relating a general measure of laser beam quality to the amplitude and scale size of phase aberrations at the output aperture. Laser output beam quality has frequently been stated in terms of the Strehl ratio, S, which is the ratio of the far-field centerline intensity with arbitrary phase aberration at the output aperture to the centerline intensity with uniform phase and amplitude at the output aperture. This is based on the belief that the focal spot diameter with aberrations should be roughly l/ig times larger than the spot size for a diffraction limited beam. This need not be the case, especially for a beam which is several times diffraction limited. A more meaningful definition is based on the beam divergence angle within which a certain fraction of the total power flux (e.g., 83%) is contained. Aberrations that arise from ordered disturbances as well as random disturbances (e.g., turbulence) with the laser are examined, using both Fraunhofer and geometric optics whose results are compared to each other. When the far field is calculated for lower order aberrations, tilt and refocus are incorporated, for two strategies: maximizing the Strehl ratio, or maximizing the encircled power. For large aberrations, the former requires a different correction than just minimizing the rms phase aberration. The latter increases the encircled power by 50% as compared to the former for lower ordered aberrations. The results indicate that for a highly aberrated phase distribution at the output aperture, the beam divergence angle may still be small enough to be useful, particularly for small laser wavelengths.

Citation Download Citation

C. J. Knight, G. W. Sutton, and R. Berggren "Phase Aberrations And Laser Output Beam Quality", Proc. SPIE 0293, Wavefront Distortions in Power Optics, (30 December 1981); https://doi.org/10.1117/12.932322

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