Figure 1: Principle of optical generation and detection of: (A) a standard PNB induced with a single laser pulse around a mono-NP cluster, and (B) a rainbow PNB induced with several simultaneous laser pulses (shown with green and purple arrows) and a multi-NP cluster (yellow and purple NPs with different plasmon resonances); (C) thermal energy released by a single NP, mono-NP clusters and multi-NP cluster under identical optical excitation with two laser pulses, like in case (B): only simultaneous excitation of two plasmon resonances in one multi-NP cluster delivers thermal energy sufficient for a PNB. Red arrows in (A) and (B) show PNB detection through optical scattering of an additional probe laser beam.