S.E. Imamova

Ablation of metals by ultrashort laser pulses

Ablation of Fe by ultrashort laser pulses with durations 0.1, 1, and 5 ps were investigated experimentally. The laser fluence varied from the ablation threshold up to 100 J cm−2. Above 1 J cm−2, the ablation rate depended on the laser pulse duration, with the shortest pulse producing the highest value. A change in the ablation rate as the laser fluence increased was also observed. These results were analysed using molecular dynamics simulations. We show that the change in the ablation rate is connected to an overheating of the material above the critical point, which results in a steep rise of the pressure developed. Furthermore, due to the electron heat diffusion, the overheated volume increases and involves material located deeper than the skin depth. An increase in the pulse duration results in a decrease in the degree of overheating.

Gold nanoparticles as nanoheaters and nanolenses in the processing of different substrate surfaces

We present results of our recent study on the heating process and near field localization arising when gold nanoparticles are irradiated by ultrashort laser pulses at wavelength of 800 nm. The system under consideration consists of Au nanoparticles with diameter of 40, 80, or 200 nm in vacuum or deposited on different substrates. Substrate materials with different dielectric properties are used in order to sense and visualize the nanoparticle heating and near field electromagnetic distribution. The theoretical analysis is based on the optical properties obtained by the Mie scattering theory. The absorption coefficients calculations are implemented in a two-temperature heat model for estimation of the nanoparticle temperature. The near field distribution in the vicinity of the particles is calculated by the finite difference time domain (FDTD) method. It is found that at even moderate laser fluences the temperature of the particle can reach a value sufficient for bubble formation in biological tissues. The analysis of the near field distribution shows that when the particle is deposited on a substrate surface, the dielectric properties of the substrate define the spatial distribution and the enhancement of the near field intensity. The observed localization and field enhancement may result in a precise modification of the substrate with a resolution defined only by the nanoparticle size. Such modifications are experimentally observed in different substrates.

Optical parameters of silicon carbide and silicon nitride ceramics in 0.2–1.3 μm spectral range

The optical properties—reflectance, absorptance, and transmittance—of silicon carbide (SiC) and silicon nitride (Si3N4) ceramics in the 0.2–1.3 μm spectral range were estimated by means of Monte Carlo simulation using single-crystal macroscopic optical constants assumed to remain uniform over a small unit of ceramic volume. The data obtained are in good agreement with the measurements made by other authors.