Direct laser interference patterning via scanning optics using the Michelson-Morley configuration

Abstract

Direct Laser Interference Patterning (DLIP) is a promising method to realize patterns on surfaces, based on two or more beams, interference. Compared with the traditional direct laser writing approach, DLIP allows control of the features’ shape and size below the size of the laser beam. The standard configuration of a DLIP system is based on fixed optical elements and the movement of the sample via a motorized axis. This work proposes a new optical setup for two-beam DLIP. A Michelson-Morley interferometer was used, realizing the interference of a split beam. A nanosecond pulsed green laser was used to realize the interference phenomenon. The innovative concept combines the interferometer with an industrial scanner head for beam steering. The work explores possibility to use the galvanometric mirrors in DLIP to expand the process capabilities towards larger areas without moving the workpiece. Moreover, the concept is adaptable for different laser wavelengths and optical solutions permitting a degree of flexibility in the pattern period. An optical model is proposed for the first time to describe the design requirements and the pattern period for scanning optics. The developed prototype was used to pattern a biodegradable magnesium alloy with known difficulties for nanosecond pulse ablation. Two strategies namely point by point and continuous scanning were investigated. Periodic linear patterns were produced with periodicity equal to 23 µm and with a productivity up to 6.5 cm2/min.