Linear and nonlinear excitation induced ultrafast absorption dynamics in laser ablated and chemically synthesized gold nanoparticle colloids

Abstract Study of excited state electron dynamics on gold nanoparticles produced by femtosecond laser ablation and chemical synthesis routes are conducted through the pump-probe technique under nonlinear (800 nm, two-photon region) and linear (350 nm, one-photon region) excitations. The temporally delayed broadband probe in the plasmonic region signifies the occurrence of dominant ground state bleach and photo-induced absorption. The excited state electrons, specifically those corresponding to below-resonant excitation, undergo relaxation as a brisk tapering curve due to electron-electron coupling followed by a gradual rise attributed to electron-phonon coupling events. The gold colloids show longer duration of electron-phonon process at 350 nm excitation than at 800 nm with an almost linear dependence of decay time with increasing excitation energy. The resonant excitation regime of chemically synthesized sample shows a visible red-shift compared to their laser ablated counterparts. This study proves efficient in better understanding energy dependent electron dynamics at different excitation wavelengths.