Femtosecond laser-induced forward transfer of thin layers studied by time-resolved shadowgraphy

Laser-induced forward transfer (LIFT), a laser-assisted direct-write method, has been explored for the fabrication and repair of electronic and photonic devices. Besides LIFT with nanosecond (ns) and picosecond (ps) sources, femtosecond pulses (fs-LIFT) has also been investigated since the use of a fs-laser was expected to reduce the interfacial thermal damage of the material to be transferred (referred to as the donor), when compared to LIFT employing ps or ns pulses. In order to further establish the feasibility of LIFT as a valuable tool for micro-fabrication, we studied the dynamics of fs-LIFT (~ 100 fs) of solid donors via a time-resolved shadowgraphy technique with an aim of identifying the velocity of the transferred product, the behaviour and integrity of the donor in transfer (the flyer), and the role of the creation of shock waves. The experiments were carried out with the help of an 800 nm Ti:Sapphire laser and a flash-lamp-illuminated shadowgraph imaging system. Thereby we observed transfer of flyers in intact state at transfer velocities as low as 34 m/s for ~ 1.1 µm thick bismuth selenide donors, and 48 m/s for ~1.8 µm thick lead zirconate titanate. For a ~0.5 µm thick donor of a third alloy we measured a velocity for non-intact transfer of ~ 140 m/s. Contrary to what has been observed so far in time-resolved studies of LIFT, no shock-wave has been observed during the experiments