As shown in Figure , when the power is greater than 19 mW (i.e., 24 mW/μm 2 ), the estimated global temperature of the Au nanoparticle reaches the bulk boiling temperature, ~ 2800 ºC. The melting enthalpy (1.22 ×10 9 J m -3 ) at 1044 ºC was added to the estimation. This temperature increase is an order of magnitude higher than the increase due to the self-heating at the plasmonic resonance. The collective temperature increase is about 1 K per 0.005 mW/μm 2 . At such a high particle temperature, it is unsurprising that we observed the formation of small (~ 3 nm) Au NPs, which were expected from the surface evaporation of the plasmonic Au NPs. This observation was similar to the surface evaporation of the Au NPs at the air/glass interface observed by Setoura et al. Orders of magnitude higher temperatures than the estimated self-heating temperature were observed in the case of water boiling when solar light illuminated a solution of highly concentrated gold NPs. Bauton et al. suggested that collective thermal effects must be considered to account for the contradiction between the experimental observation of water boiling and the small temperature increase estimated using self-heating. At low Au NP density (~75/μm 2 ) with 30 nm Au NPs, the estimation (Figure ) shows that the power that could reach the melting temperature of the TiO2 is higher than 50 mW. However, the power has a considerable variation depending on the particle size and the particle density. The global temperature can reach the melting temperature of TiO2 with a slightly larger average particle size (40 nm) and slightly larger particle density (~120/μm 2 ) at 35 mW. This makes it reasonable to observe the melting of TiO2 on the sample with low Au NP density, as the particle size and the particle dispersion on the surface at low Au NP density (Figure ) were not as uniform as the sample with a high Au NP density. The local variation in NP size and density makes it difficult to compare the estimated global temperature directly with the experimental observation. The collective heating due to plasmonic absorption impacts various applications, including plasmon photochemistry, which has become a hot topic, and powder-bed additive manufacturing (AM), which has yet to be explored. The relative thermal and non-thermal contribution (e.g., hot carriers) in the plasmon-drive process has been under extensive debate regarding the application of photocatalysis. The distinguishment requires accurately measuring the actual temperature of the plasmonic particle and the surrounding matrix (e.g., TiO2). From shape-changing and surface evaporation, it is known that the temperature of the Au NPs and other plasmonic particles can reach melting temperature and boiling temperature under moderate laser irradiance. Theory simulations predicted these high temperatures. However, the impact of the plasmonic heating on the surrounding catalysts and the photocatalytic reaction is still unclear. Different approaches have been developed to measure the temperature accurately. Most of the developed techniques are based on optical measurements, including Raman spectroscopy, fluorescence anti-stokes emission of metal NPs , and quadriwave shearing interferometry. The time needed to take a spectrum is about 10-100 ms, which is longer than the 𝜏 (~ 0.2 μs) for a focused CW laser beam and the 𝜏 (~ 130 μs) for an unfocused CW laser beam (e.g. Theory simulations predicted these high temperatures. However, the impact of the plasmonic heating on the surrounding catalysts and the photocatalytic reaction is still unclear. Different approaches have been developed to measure the temperature accurately. Most of the developed techniques are based on optical measurements, including Raman spectroscopy, fluorescence anti-stokes emission of metal NPs 90 , and quadriwave shearing interferometry. The time needed to take a spectrum is about 10-100 ms, which is longer than the 𝜏 (~ 0.2 μs) for a focused CW laser beam and the 𝜏 (~ 130 μs)