Picosecond pulsed laser-assisted reshaping of metallic nanoparticles embedded in a glass matrix

Summary form only given. Modification of silver nanoparticles embedded in a glass substrate with femtosecond pulsed laser sources has recently been of great interest. These studies were fuelled by the observation of unique optical properties in terms of femtosecond pulsed laser-induced optical dichroism in these materials, leading to modification of the surface plasmon resonance (SPR) band of the embedded nanoparticles [1, 2].We present the results of our investigations on the picosecond pulsed laser irradiation of these materials. Picosecond sources are reliable, industrially friendly and adaptable. Our samples were made by Ag-Na ion exchange, resulting in the formation of metallic clusters 30-40 nm in diameter embedded in a thin surface layer approximately 10µm thick. Figure 1 shows the extinction spectrum of the original sample. Samples were then exposed to a linearly polarized 10 ps laser beam at 532 nm with a repetition rate of 200 kHz. The beam spot diameter on the sample was measured to be - 7µm. Dichroism was observed as a result of elongation of the previously spherical silver nanoclusters (Fig. 2). The modification threshold for the process was established to be - 0.05 J/cm2. The sample depicted in Fig. 2 was irradiated at a laser fluence of - 0.26 J/cm2. In addition to the shape modification, separation of the SPR band was observed as a result of changing the number of pulses per spot irradiating the material.Various applications have been identified for this class of nanocomposite materials, ranging from fabrication of embedded optical elements and filters [3], to long-lasting optical storage devices [2], and to materials for ultrashort relativistic electron bunch diagnostics [4]. In this work we have demonstrated a method for selective modification of the nanocomposites which is more affordable than those previously employed involving femtosecond lasers. This is a proof of concept study showing the possibility of modifying silver nanopa- ticles with much longer laser pulses.