1μm adjustment-tolerance for high-precision helical laser drilling

High-precision micro laser drilling with high aspect ratios requires laser imaging effects such as optical double rotation. Optical double rotation is an effect where the laser beam is guided through any optical elements with a total amount of reflections that remains uneven. Those optical elements need to be mounted in a rotary stage that spins the elements with a certain velocity. In an ideal case the optical axis is identically with the rotational axis. Few optical elements such as the Dove-prism show the effect that the beam is rotated in itself while it is moving on a helical path. That offers an independency of the beam profile. However the Dove-prism alone can not be adjusted in a way that the two axis match. This is based on geometrical errors of the Dove-prism due to manufacturing technologies. Certain deviation in length and angle lead to a helical error. Additional optical elements can compensate this effect. Alignment that only takes place in one 2D plane (e.g. the focal plane) leads most likely to a cross-over of both axes (x-alignment) in that one plane. In order to match both axes the alignment needs to be done at least in two 2D planes. That requires the opportunity to both influence the optical angle and the optical position (parallel shift) in both planes. The highly complex optical alignment method as well as the mechanical storage of the optical elements will be shown in this paper.