Abstract

The beam radius along a focused, unapertured Gaussian beam was measured and used to calculate the dependence of the geometrical Fresnel number on the effective Fresnel number of the beam as it emerged from the focusing lens. The resulting data clearly demonstrate a focal shift away from the focal plane given by geometrical optics. The data agree very well with a theory due to Carter. This theory indicates that a significant focal shift occurs in these beams if the focusing lens is placed within the near field of the focal plane.

© 1984 Optical Society of America

Focal shift and concept of effective Fresnel number for a Gaussian laser beam

William H. Carter
Appl. Opt. 21(11) 1989-1994 (1982)

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Oscillations and discontinuity in the focal shift of Gaussian laser beams

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