Emission of molecular nitrogen at tight focusing of femtosecond laser pulses in air

A numerical model describing the dynamics of plasma particle density upon filamentation of femtosecond radiation in the air is presented. The simulation results are in good agreement with the experimental data. The pumping processes of the N2 and N2+ radiative levels are investigated. The model predicts a sharp drop in electron temperature and density within 1 ns. For the first positive nitrogen system, an excess of the population of the upper radiation level over the population of the lower one is observed for 550 ps.

Superradiance pulse duration by molecular nitrogen ions in air laser plasma

The results of study of superradiance pulse duration by molecular nitrogen ions in air for various focusing conditions of femtosecond radiation pulse with a wavelength of 950 nm are presented. Parameters of active medium are analyzed and mechanism for the formation of picosecond superradiance pulse at femtosecond seed duration is proposed.

Laser-induced methods for obtaining carbon nanomaterials in liquid nitrogen under femtosecond radiation

The paper presents the experimental results of nanostructures formation under the influence of femtosecond laser radiation on carbon samples at liquid nitrogen temperatures. Two femtosecond laser systems were used to study the processes of laser action on highly oriented pyrolytic graphite and glassy carbon samples in liquid nitrogen: titanium-sapphire laser system with wavelength 800 nm, pulse duration 50 fs, energy 1 mJ, and repetition frequency of 1 kHz; ytterbium laser system with wavelength 1030 nm, pulse duration 280 fs, energy 150 µJ, and repetition frequency of 10 kHz. Cryostats, including those with the possibility of observing the laser action process, were collected for the experiments. As a result of laser action on the surface of the processed carbon samples, sheets of exfoliated graphene of various sizes and shapes (sheets, tapes, crumpled graphene), as well as nanostructures in the form of nanopeaks, were obtained. The mechanisms of graphene exfoliation under femtosecond laser action in liquid nitrogen, consisting in intercalation and further heating of nitrogen molecules in the interplanar space of graphite, were proposed. The possibilities of further research and development of technologies for graphene formation using laser radiation are presented.