Nonlinear Absorption and Ultrafast Dynamics of Ag Nanoparticle

Resonant nonlinear optical absorption of silver nanoparticles was studied experimentally via open aperture Z-scan using 130 fs, 400 nm laser pulses. Experimental results show that, at low laser intensity, silver nanoparticles can exhibit saturated absorption. While at high laser intensity, it shows reverse saturated absorption. The saturable absorption is explained in terms of ground state plasmon bleaching, while the reverse saturable absorption is believed to be from two-photon absorption. Saturable optical intensity and two-photon absorption coefficient were obtained to be 1.3 x 10(-10) W/m 2 and 3.3 x 10(-10) m/W, respectively. The energy relaxation process of Ag nanoparticles after laser excitation was studied via pump-probe technique at 400 nm. Experimental results demonstrated that energy relaxation included electron-phonon coupling process with time constant tau(1) = (713 +/- 50) fs, and phonon-phonon coupling process with time constant tau(2) = (25.2 +/- 3) ps, respectively.

Automated summary

Experimental results reveal that silver nanoparticles exhibit saturated absorption and reverse saturated absorption, caused by ground state plasmon bleaching and two-photon absorption, respectively. The energy relaxation process of silver nanoparticles after laser excitation involves electron-phonon coupling and phonon-phonon coupling processes.