Dynamics of double-pulse laser printing of copper microstructures.

Highlights • A laser-induced forward transfer (LIFT) strategy combining quasi-continuous (QCW) and femtosecond (fs) lasers is successfully applied for high resolution printing from a 1 µm copper donor film. • Influences of copper film temperature, and especially diameter of the melted metal area, on the printing dynamics are revealed. • By simply adjusting the synchronization between the QCW and fs pulses, droplets with different shapes are printed. The reproducibility is demonstrated by printing two-dimensional arrays. • Double-pulse LIFT prints debris-free microstructures with controllable dimensions. Abstract Laser induced forward transfer process can be implemented in a double-pulse scheme where a solid thin film deposited on a transparent donor substrate is irradiated by two synchronized lasers. In a recently demonstrated methodology, a long pulse is first applied to melt the film and an appropriately delayed ultrashort laser pulse initiates material transfer in the liquid phase toward a receiver substrate. This provides a versatile method to print high-resolution (<2 µm) patterns with a long working distance (>40 µm). In this paper we focus on the study of the dynamical aspects associated with these printing performances. The temperature evolution of the thin copper film during irradiation with a quasi-continuous wave (QCW) pulse is calculated. By combining the calculations with time-resolved imaging experiments, we reveal the influence of the copper film temperature and molten metal diameter on the ejection dynamics. Characterization of the transferred materials shows that the delay between the two laser pulses is a control parameter for the shape and volume of the printed structures. This is finally exploited to demonstrate high-precision printing of different debris-free microstructures onto a Si receiver substrate set as far as 60 µm away from the donor film. [ABSTRACT FROM AUTHOR]