Microstructuring in metals using a UV laser microspot scanning system

We report the experimental studies of UV laser ablation with a microspot scanning system comprising of a 10 ps, 355nm ultrashort pulse laser in combination with a standard galvoscanner employing a Microscan MSE-G2-UV extension from Pulsar Photonics. The UV wavelength provides the first step in downscaling the feature size and the microscan extension allows the laser beam to be tightly focused down to a very small diameter of < 1.5 μm. The small focal spot size allows highly precise ablation of microstructures. Laser ablation characteristics with the microscan objective is investigated in steel and copper for different laser repetition rates. The threshold fluence and the energy penetration depth for steel and copper were found to be comparable for repetition rates from 200 kHz-2 MHz. The advantages and also the limitations of laser ablation using the microscan objective is discussed, especially with respect to its small Rayleigh range of ~ 5 μm. The sample positioning tolerances and maximum achievable ablation depths count among the latter. Initial experiments on laser drilling in 10 μm steel foils is also reported, with the exit hole diameter of the order of the focused laser beam diameter.