FRESNEL Quick Guide

Example 4. Diffraction of an Elliptical Beam

This example is given to show how sensitive the diffraction is to the shape of the beam. It demonstrates also that the aspect ratio (ellipticity) of the beam as small as 0.999 can be detected. User can reproduce these results with a Flat-topped beam (file ellipt.pls) that has next parameters: points=512; scale 1.28 cm; beam size (diameter)= 0.8 cm; ellipticity = 0.99; rotation angle 60 degree; softening = 0.003 cm; wavelength 1066.7 nm.
Results of the elliptical beam propagation at the distance 120 cm ellipt.scm are given in the next figure with various magnifications. Pictures are contrasted using Range Selection Controls (on the right side of the Beam Window). The asymmetry in the center of the picture can be detected visually in the case of ellipticity 0.99.

Magnification=8 Magnification=8, Zoom=4

Next figure shows results for the ellipticity 0.999. You can reproduce this result editing the input beam parameters (changing the ellipticity and setting rotation angle equal to 0). In this case the asymmetry can be detected only if two profile cuts are taken along X- and Y-axes through the center of the diffraction pattern. These profiles are shown in the right figure below.

Magnification = 8, Zoom = 4

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