Figure 7.
UV-vis spectra of 30 nm HGN with different LSPR peaks at 700 nm (black line), 800 nm (red line) and 900 nm (blue line). The nanobubble threshold fluence is proportional to the difference between the LSPR peak and the irradiation wavelength. Black circles refer to the threshold fluence for HGN with λmax = 700 nm, red stars refer to HGN with λmax = 800 nm, blue triangles refer to HGN with λmax = 900 nm as a function of irradiating wavelength. The minimum fluence for picosecond pulsed irradiation at various wavelengths given by the individual symbols is ~ 2 mJ/cm2 for all three sets of HGN of the same size when irradiated at their resonance wavelength. However, irradiating at wavelengths off the particular HGN LSPR peak (such as irradiating a HGN with λmax = 700 nm at 900 nm) requires a significantly different fluence to initiate nanobubble generation. The order in which nanobubbles form with increasing fluence is reversed at 730 nm compared to 800 nm compared to 900 nm.