Optical alignment influenced aberrations in laser beam delivery systems and their correction

Abstract

Industrial high power laser systems are often evaluated based upon spatial profile of the beam before they are brought to focus for processing materials. It is therefore often assumed that if the raw beam profile is good that the focus is equally as good. The possibility of having good optics and poor alignment or bad optics and good alignment and therefore not achieve a good focal spot is quite high due to the fact that a raw beam spatial profile does not manifest third order aberrations. In such instances the focal spot will contain aberrations when there are slightly misaligned, poor quality, high power optics in the system such as a beam expander or eye piece and objective of a 3-axis galvo. Likewise, if the beam itself is not on axis, the third order aberrations of astigmatism and coma are likely to appear but again not be seen in the unfocused beam's spatial profile. The third order aberrations of astigmatism, coma and spherical aberration can significantly alter both the size and spatial profile at the focus resulting in out of spec performance. The impact of beam and zoom expanders and their alignment in beam delivery systems is investigated by measuring both the far field unfocused and the far field focus beams using an all passive beam waist analyzer system.

Optoelectronic Device for Measuring the Power of Laser Radiation

“…When designing the optical system (OS) of the laser, it is assumed that the source of radiation is at infinity and its angular dimensions are determined by the divergence of the beam [3], [4], [12], [13], [14]. In order to achieve optimal coordination between the laser and the optical system it is necessary to place the entrance pupil of the optical system in the area of the beam waist [1], [7], [10], [15].…”