Influence of symmetry breaking on the inner core of a structured laser beam

The inner core (IC) of a structured laser beam (SLB) can serve as a straight reference line for optical measurements. However, obstructions near the beam may disrupt the beam symmetry and cause the IC to bend. This study presents numerical simulations and experimental validation of the symmetry breaking of an SLB for distances up to 140 m. We find IC displacements of more than 2 mm if the obstruction occurs within the near zone of about 1.9 m from the generator, and up to about 0.3 mm if the obstruction occurs in the far zone. These values are orders of magnitude above the noise level of the measurements. Symmetry breaking is a potential accuracy limitation when using SLBs for alignment purposes. The present investigation corroborates that symmetry breaking can be analyzed using numerical simulations and does not require extensive physical testing. This is a crucial prerequisite for designing SLB-based highly accurate alignment systems. Additionally, the numerical results provide insights useful for roughly predicting the clear space required around SLBs to ensure straight reference lines.