Picosecond self-induced thermal lensing from colloidal silver nanodisks

The optical and nonradiative relaxation dynamics of 5 unit thick silver nanodisks with a 25 nm diameter have been investigated in an organic solvent by continuous wave (cw) and femtosecond pump-probe time-resolved spectroscopies. Several surface plasmon absorption bands are observed due to the disk shape of these particles. In the time-resolved experiments, the time dependence of the bleach resulting from femtosecond pulsed excitation is studied. On the 1-3 ps time scale, a decay resulting from electron-phonon relaxation is observed. On a longer time scale (>20 ps), a rise father than a further decay of the bleach intensity is observed. This is shown to result from the formation of a thermal lens due to the induced thermal gradients produced from heating the organic solvent by the phonon-phonon relaxation processes of the photoexcited nanodisks.