Controllable fabrication of unidirectional liquid spreading surface through confining plasma eruption and femtosecond laser double pulses

The efficient and simple fabrication of a self-driven, continuous, and controllable unidirectional liquid spreading surface is an enormous challenge. In this paper, we present a maskless, one-step, and controllable method to fabricate unidirectional high-speed liquid spreading surfaces. The method confines the eruption of plasma by using oblique glass and femtosecond (fs) laser double pulses. The oblique glass is used to regulate plasma density via plasma confinement, and the double-pulse is used to control the final processing energy by changing pulse delay. The gradient structure size can be controlled by adjusting the laser energy, pulse delay and the tilted glass angle. Moreover, It has even can both achieved a high-speed and unidirectional spreading. A 1 μL droplet flows approximately 7 mm in 640 ms with no increase of the corresponding width using the gradient grating structure fabricated under double pulses with a pulse delay of 1 ps. Using different gradient channel assembly, a selective flow along designed direction can be achieved. The selective flow phenomenon is observed through customized liquid diode. By manufacturing continuous and adjustable gradient structure, the method is potential to control liquid flow in microsystem.