Tilting Behaviors of Metal Microjet in Laser-Induced Forward Transfer

Laser-induced forward transfer (LIFT) is proposed as a highly efficient and high-resolution printing technique. Tilting of the microjet in the LIFT process affects the deposition deviation, lowering the printing resolution. In this paper, the tilting behaviors of the metal microjet in the nanosecond LIFT process are investigated based on a high-speed observation. Experiments were conducted on the copper film under different laser fluences. Observations based on the pump-probe method were performed to capture the ejection behavior of microjets. It is found that the tilting direction is isotropic, and the tilting angle follows Gaussian distribution. The tilting behavior originates from the disturbance of residual stress within the film during jet generation because the statistical result of the tilting angle hardly varies with the propagation time. In addition, the tilting angle is found to decrease linearly with the laser fluence due to the ejection velocity increasing at a higher rate than the lateral velocity. The lateral offset of the tilting microjet at different flight distances matches well with the position deviations, verifying the tilting behavior of the microjet. This study provides essential comprehension of the tilting behavior of metal microjet in the LIFT process.