Laser-Induced Spectral Hole-Burning through a Broadband Distribution of Au Nanorods

Nanorods are amenable to laser-induced reshaping, a process that can dramatically modify their shape and therefore their plasmonic properties. Here we show that when a broadband spectral distribution of nanorods is irradiated with a femtosecond-pulsed laser, an optical transmission window is formed in the extinction spectrum. Surprisingly, the transmission window that is created does not occur at the laser wavelength but rather is consistently shifted to longer wavelengths, and the optical extinction on the short-wavelength side of the transmission window is increased by the hole-burning process. The laser irradiation results in a wavelength-dependent partial reshaping of the nanorods, creating a range of unusual nanoparticle morphologies. We develop a straightforward theoretical model that explains how the spectral position, depth, and width of the laser-induced transmission window are controlled by laser irradiation conditions. This work serves as an initial example of laser-based processing of specially designed nanocomposite media to create new materials with "written-in" optical transmission characteristics.