33 research outputs found
On the focusing limit of high-power femtosecond laser pulse propagation in air
Focused propagation of high-power femtosecond laser radiation in air is
considered. Based on numerical solution of the nonlinear Schrödinger
equation for complex envelope of light wave electric field, evolution of the
beam effective radius is studied. The dependence of the effective (rms) size
of a focal spot and the maximally achievable intensity of laser radiation at
focal waist on the initial pulse power is established. It is shown that
focal spot of tightly focused intensive ultrashort laser radiation can
change its size during the pulse passage through the beam waist. This is the
consequence of pulse intensity clamping in region of beam focusing caused by
gas photoionization and plasma producing. This may prevent laser intensity
from its further growth in the focal region and arrest the transversal
compression of the beam in the linear focus as a whole
Peculiarities of the formation of photonic nanojets by a matrix of dielectric microtoroids
Energy deposition in air by moderately focused femtosecond laser filaments
Filamentation of high-power femtosecond laser pulses in air is accompanied by a fairly strong release of optical energy into the propagation medium due to laser-induced ionization of air molecules and production of an underdense plasma of charged species. We present the results of our laboratory experiments and numerical simulations aimed to the estimation of energy deposition amount by laser filament upon propagation in air depending on the conditions of spatial focusing, pulse energy, and radiation wavelength. For the first time to our knowledge, our study reveals a more than 50% decrease in the filament energy deposited in air in the range of moderate numerical aperture values, approximately from 0.003 to 0.007, at the carrier wavelengths of 740 nm and 470 nm. We attribute such a considerable reduction in the laser pulse energy release for femtosecond plasma to the competing effects of Kerr self-focusing and geometric divergence of focused laser pulse