Investigation of laser-assisted micromachining of NiTi SMA bimorph based actuators toward developing optical shutters

This work explores laser-assisted micromachining for the precision cutting of NiTi shape memory alloy (SMA)-based bimorph in a single-pass laser scan. SMA thin film based optical shutters were developed with this method, which can generate the opening and closing via Joule's heating rather than mechanical components. NiTi SMA bimorph was fabricated using the e-beam evaporation technique followed by micromachining using a 1064 nm fiber laser. The influence of laser power (LP), laser speed (LS), spot diameter (SP), and laser travel direction on kerf width and heat-affected zone after micromachining was studied using the design of experiments. The optimized parameter for micromachining was at LP 5 W with 5 mm s-1 LS and 50 mu m SP. Various shapes were cut at the optimized parameter, including an optical shutter of a diameter of 30 mm. A LS of 6 mm s-1 has produced microchannels in the bimorph due to NiTi film removal only. The SEM analysis of the shutter reveals the formation of refined grains at micromachined edges compared to the center of the actuator. Fabricated optical shutter shows negligible optical transmittance in the 450-700 nm wavelength range.