Real-time laser focusing system for high-precision micromachining using diffractive beam sampler and advanced image sensor

In this manuscript, a system for the real-time detection of the focal position on a target sample's surface during laser micromachining is presented. This system utilizes the advantages of diffractive beam samplers, double-hole masks, and two laser sources, including a diode laser for detection and a high-powered laser for fabrication. Moreover, this system can simultaneously detect the focal position and examine the defocusing direction during fabrication. This ability gives it an advantage over conventional methods that can only conduct a single task. The off-axis detection beams generated by the diffractive beam sampler that are examined during the detection process create various configurations of the beam spots on the advanced image sensor that are enhanced to read the sizes and separation of the beam spots simultaneously. Furthermore, the analytical relationship between the beam spot spacing and the specimen-objective-lens distance is used to support the calibration process and compared with experimental results. According to the changes in the distance between beam spots, the focal point and defocusing direction can be identified with the highest precision, which is indicated by the similarity between the theory and the experimental results. In addition, images of microholes fabricated by a fabrication laser are shown as a test of the focal detection system that is consistent with theory. The resolution of the system is optimized to polish the images obtained by the image sensor. Therefore, it is demonstrated that this technique provides the most accurate focusing conditions with a high numerical aperture as well as inexpensive laser fabrication and processing.