An investigation is made of a perturbation in the vicinity of focal points
over a laboratory path of a laser beam used in the processing of materials.
The following situations are considered: a beam emerges from a focal point
and expands; horizontal and vertical beams focused on a control surface. R
igorous numerical solutions are obtained of the aero-optics equations descr
ibing beam perturbations in front and behind the focal plane. The results a
re compared with the experimental data.