D. S. Sitnikov

Determination of the Transport and Optical Properties of a Nonideal Solid-Density Plasma Produced by Femtosecond Laser Pulses

Experimental data on the amplitude and phase of the complex reflection coefficient of a laser pulse from a non-ideal solid-density plasma, which is produced on the surface of a metallic target by intense femtosecond laser radiation, have been obtained using femtosecond interference microscopy. A theoretical model developed for the interaction of intense femtosecond laser pulses with solid targets on the basis of the two-temperature equation of state for an irradiated substance allows the description of the dynamics of the formation and scattering of the plasma. Comparison of the experimental data with the simulation results provides new information on the transport coefficients and absorption capacity of the nonideal plasma.

Femtosecond optical diagnostics and hydrodynamic simulation of Ag plasma created by laser irradiation of a solid target

A combined experimental‐theoretical method of diagnostics of the plasma created on a surface of Ag target irradiated by intense femtosecond laser pulses is proposed. The method is based on semiempirical wide-range models of optical, transport and thermodynamic properties of Ag plasma. Numerical coefficients in these models are chosen so as to ensure the best accordance of simulations to measurements of a complex absorption coefficient of Ag plasma by means of femtosecond interference microscopy. A two-temperature hydrodynamic modelling of non-stationary laser-produced Ag plasma is carried out; calculated results are presented in comparison with experiments. Unexpectedly high values of the phase of the complex reflection coefficient at short (200 fs) time delay between pump and probe laser pulses are obtained experimentally; possible explanations of this phenomenon are discussed. (Some figures in this article are in colour only in the electronic version)

Study of opto-mechanical characteristics of interaction of ultrashort laser pulses with polymer materials

The opto-mechanical characteristics, such as the specific mechanical recoil momentum, the specific impulse, and the energy efficiency, of the laser ablation of flat polymer targets ((C2F4)n, (CH2O)n) have been determined experimentally for the first time for the case of excitation with femtosecond pulses (τ ∼ 45–70 fs) of UV-IR (λ ∼ 266, 400, 800 nm) laser radiation (I0 up to 1015 W/cm2) under normal atmospheric and vacuum (p ∼ 10−4 mbar) conditions. The efficiency of mechanical recoil momentum generation is analyzed for various regimes of the laser irradiation.

Gas-plasma flows under femtosecond laser ablation for metals in vacuum

New information on particle distribution over velocities, the mean-mass velocity, and the degree of monochromaticity of gas-plasma flow under femtosecond (τ ∼ 45 fs, λ ∼ 800 nm) laser ablation is obtained for several metals (Ti, Zr, Mo, Nb, Cu) in vacuum (p ∼ 5 × 10−2 Pa) by means of combined interferometry.

Experimental and theoretical study of Al plasma under femtosecond laser pulses

The amplitude and phase of the complex reflection coefficient of a weak probe laser pulse from strongly coupled Al plasma created on the surface of a metallic target by pump femtosecond laser pulses with intensities I ≤ 10 15 W cm ―2 were measured using femtosecond interference microscopy. A theoretical model developed for the interaction of intense ultrashort laser pulses with solid targets on the basis of a two-temperature equation of state for an irradiated substance was used for numerical simulations of the dynamics of the formation and expansion of the plasma. A comparison of the experimental data with the simulated results shows that the model is suitable up to I ∼ 10 14 W cm ―2 . At higher intensities of the heating laser pulse, lower values of the reflection coefficient amplitude of Al plasma are observed in the experiment.

Laser microsurgery of cells by femtosecond laser scalpel and optical tweezers

This paper provides a brief overview of the current state of research in the field of laser microsurgery of preimplantation embryos. The combined system femtosecond laser tweezers-scalpel developed in JIHT RAS is described. A scheme of device and peculiarities of functioning its nodes as well as the ground for the choice of their parameters are presented. The results of the development of methodology for noncontact polar body biopsy of the preimplantation embryo are also presented to demonstrate the potentials of the combined multi-purpose system femtosecond laser tweezers-scalpel.

Experimental study of polymers femtosecond laser ablation opto-mechanical characteristics at ambient and vacuum conditions

Values of the momentum coupling coefficient, spectral energy thresholds for laser ablation, and efficiency of the laser radiation energy conversion into kinetic energy of a gas-plasma flow during femtosecond pulsed laser ablation of condensed (polymeric) targets under vacuum and atmospheric conditions have been determined. Methods are developed for measuring the recoil momentum in a sub-nanonewton range to within ΔIM < 10−11 N s and for high-precision combined pulsed laser microinterferometry of the surface of targets and radiative-erosive gas-plasma flows.

An investigation of the optical-and-thermophysical and gasdynamic characteristics of femtosecond laser ablation of structural materials of the polymer series

A description is made of the experimental-diagnostic module with femtosecond terawatt laser complex (τ0.5 ∼ 45–70 fs, λ = 266, 400, and 800 nm) and of the pioneering procedure of combined ultrahighspeed interferometry and interference microscopy (Michelson and Mach-Zehnder schemes) of the processes of interaction between ultrashort laser pulses and condensed media in vacuum. Results are given for the first time of the investigation of spectral-energy thresholds and rates of laser ablation of a number of solidstate media using elements of the polymer series (C2F4)n, (CH2O)n in the UV-NIR wavelength range of laser radiation in atmospheric conditions and in vacuum p ∼ 10−2 Pa.

Application of femtosecond laser scalpel and optical tweezers for noncontact biopsy of late preimplantation embryos

We demonstrate that one of the key steps of preimplantation genetic diagnosis called embryo biopsy can be successfully performed in noncontact mode by means of femtosecond laser scalpel and optical tweezers. Embryo biopsy was carried out in late-stage mouse preimplantation embryos. Femtosecond laser pulses were applied to detach the desired amount of trophectoderm cells from the blastocyst, while the optical tweezers trapped the cells and moved them out of the embryo. The parameters of laser radiation were optimized so as to efficiently perform embryo biopsy and preserve the viability of the treated embryos.

Application of femtosecond laser pulses in biomedical cell technologies

The results are presented of the works in the field of development of equipment, investigation techniques, and technologies for biology and medicine performed in the Joint Institute for High Temperatures of the Russian Academy of Scienses (JIHT RAS). On the base of the new generation infrared femtosecond lasers, the experimental models are developed and manufactured of laser tweezers, scalpel, and the “tweezers-scalpel” combined system. The results are presented of the experimental studies on the noncontact mammalian cell fusion (blastomeres of mouse embryos on day 1.5 of development) by means of the femtosecond laser pulses.