Nanoscale ultra-high-resolution non-destructive detection by correlated double femtosecond laser pulses

In this report, ultra-high spatial and temporal resolution non-destructive detection has been demonstrated using correlated double femtosecond laser pulses for the time. Owing to the residual thermal relaxation, our modal system ZnO thin film exhibits an interference between the two correlated femtosecond-laser-induced ultrasonic waves, and sound pressure enhancement has been observed. In comparison, only slight or negligible wave interference/pressure improvement for non-correlated double picosecond and nanosecond laser pulses could be identified. We demonstrate the capability of the correlated femtosecond laser to be used in ultra-precise thickness detection, which has a spatial measurement error as low as 1 nm, however, the errors for both the picosecond and nanosecond laser pulse are > 1 μm, three magnitudes worse than that of their femtosecond counterpart. Correlated femtosecond laser-induced waves presented ultra-high temporal resolution of ps level, which shows advantages over that (ns level) of non-correlated picosecond and nanosecond counterpart. Our results open the opportunities to achieve atomic resolution detection through ultrafast laser technology in the future.