Experimental Investigation of Laser Micro-Structure Ablation Under Oblique Incidence

Laser processing is an effective and precise micro-structure fabrication technique. At present, micro-structure processing is primarily applied to planar surfaces. However, for curved surfaces, variations in the incident angle of the laser beam lead to distortions in micro-structural morphology. In this study, an experimental investigation was conducted to characterize micro-structural ablation under oblique laser incidence. Initially, a single-factor parametric study was performed on the surface of stainless steel. The results indicate that grooves measuring 45 μm in width and 43 μm in depth were achieved under the conditions of a single-pulse energy of 10 μJ, a laser frequency of 70 kHz, a scanning speed of 10 mm/s, and 20 processing cycles. Subsequently, the influence of the laser incidence angle on groove morphology was further examined. The results demonstrate that for incidence angles below 11°, the groove removal rate approaches 1, and the root mean square of shape error (RMS) remains below 1.5 μm. To reduce the deformation of the micro-structure at oblique incidence, a curve-guided surface projection (CGSP) method was developed, and the micro-dimples were fabricated at laser incidence angles of 10° and 14°. Compared with the conventional direct projection (DP) method, the CGSP approach significantly mitigates structural distortion resulting from oblique incidence. Finally, the CGSP method was applied to fabricate the micro-dimples at various locations on a spherical surface. The removal rates of 0.988 and 0.936 were closer to unity than those achieved via direct projection, while the RMS values were reduced by 56.4% and 76.2%, respectively. These findings offer a promising solution to the challenge of oblique laser incidence in curved micro-structuring and further broaden the application scope of laser processing technology.