Fig. 3: Positive and negative optical forces and the nanoscale Leidenfrost effect.
a The calculated Fz on an Au NP with a nanobubble along the central axis (z-direction) of the Gaussian beam. A beam waist and intensity at the focal plane (z = 0) are 6 μm and 12 mW μm−2, respectively. The red line represents the positive force for rnb = 130 nm, θ = 180o, and the blue line represents the negative force rnb = 130 nm, θ = 0o. The insets illustrate (left top) the positive motion and (right bottom) the negative motion. b Schematic illustration of a supercavitating ballistic Au NP. Under the laser illumination, the plasmonic Au NP is intensely heated to generate a nanobubble which encapsulates it. When the Au NP moves forward, it keeps evaporating water and maintaining a vapor cushion in front of it, which effectively makes the NP moving in a virtually frictionless environment, like the Leidenfrost effect. In the meantime, vapor at the trailing end of the bubble cools and condenses back to liquid as the hot NP moves forward. c Nanoscale Leidenfrost effect of a hot moving NP simulated by molecular dynamic (MD) simulations. The hot NP is thermostated at 1000 K (Supplementary Note 9 for justification), and the blue contour visualizes the isosurface of the critical density of liquid argon (0.536 g cm−3), which represents the nanobubble surface. The NP moves in the positive x-direction with a speed of 13 m s−1.
