Yu. Yu. Protasov

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.

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.

Experimental investigation on spectral-energy efficiency of femtosecond laser ablation of metals

Results of investigation on spectral-energy thresholds, rates, and mass flow rates of laser ablation of structural materials (Cu, Ti, Zr, Nb, Mo) of high-energy photonics are presented. The data were obtained by means of an experimental diagnostic module developed for study of multifactor interaction processes between UV-near IR femtosecond laser pulse radiation and condensed media in vacuum.

Experimental study of the dynamics and macrostructure of laser-induced high-pressure dust gas-plasma flows

We propose and for the first time experimentally carry out a method of laser-induced generation of high-pressure dust gas-plasma flows with complex chemical and ionization composition under UV laser ablation of a polymer matrix containing the dust component. The method uses the difference in the spectral-energy threshold of laser ablation and optical properties of polymer materials and dust components in the short-wavelength region of the spectrum. We present the results of an experimental study of the dynamics and macrostructure of laser-induced high-pressure dust gas-plasma flows under UV (λ1 = 213 nm, λ2 = 266 nm, λ3 = 355 nm) laser ablation of condensed targets based on a (C2F4)n polymer matrix with a dust component (SiO2, Al2O3, CeO2). Using laser interferometry and shadowgraphy, we determined the spectral-energy thresholds and conditions for generating dust structures in ionized pairs of the target matrix and their spatiotemporal localization in a gas-dust flow up to spatial division of the evaporated substance of the target matrix and the dust-component cloud. We determine the lifetimes of heterophase flows as a function of the parameters of laser action on a condensed target and the charge of dust particles.

A Technique for Experimental Determination of the Condensed Media Laser Ablation Momentum Coupling Coefficient in Vacuum

An experimental technique for measuring the recoil momentum with an accuracy of ΔI < 10−11 N s during femtosecond laser ablation of condensed media has been developed. The technique is based on combined microinterferometry of the surface of an ablating target and near-surface photoerosion gasplasma flows. The results of experimental determination of the momentum coupling coefficient and the efficiency of the laser-radiation energy conversion into the kinetic energy of a gas-plasma flow under the action of short laser pulses on condensed media in atmospheric and vacuum conditions are presented.

Complex processing of interferograms of light-erosion gas-plasma streams in vacuum

A technique for automated processing of the results of interferometry of light-erosion gas-plasma flows using the local thermodynamic equilibrium approximation and data on the mass flow rate of the target substance was developed. The application of this technique allowed evaluation of the spatiotemporal distributions of the optical (refraction and absorption coefficients), thermophysical (temperature, density, and electron concentration), gas-dynamic (velocity distribution of particles, average-mass velocity, and pressure), and optomechanical (momentum coupling coefficient) characteristics of light-erosion gas-plasma flows. The features of application of frequency filters at various stages of automatic processing of measurement results are considered. Examples of processing the experimental results that were obtained under the impact of ultrashort laser pulses on condensed media are presented.

Efficiency of the conversion of radiation energy into kinetic energy of a gas-plasma flow during femtosecond laser ablation of metals in vacuum

Using the methods of combined interferometry, we obtained new data on the momentum coupling coefficient and conversion efficiency of radiation energy into kinetic energy of a gas-plasma stream during femtosecond laser ablation (τ ∼ 45 fs, λ ∼ 800 nm) of several metals (Ti, Zr, Mo, Cu) in vacuum (p ∼ 5 × 10−2 Pa).

Experimental Diagnostic Module for Ultrafast Combined Interferometry of the Processes of Interaction of Ultrashort Laser Pulses with Condensed Media in Vacuum

An experimental diagnostic module based on a femtosecond laser system (τ0.5 ∼ 45-70 fs, 7n = 266, 400, and 800 nm) and the experimental technique for ultrafast combined interferometric investigation of the interaction of ultrashort laser pulses with condensed media in vacuum are described. A combined interferometric microscope built according to the Michelson and Mach-Zehnder schemes allows studies of the dynamics of optico-thermophysical and gas-dynamic proc esses at the surface of a target (the crater depth and diameter, optical properties) and in a plasma plume (velocity of expanding particles, electron density, optical characteristics) at a time resolution of 5 - 10-14 s in the range of delays 10-13-10-7 susing two probing wavelengths (7n = 400, 800 nm) in vacuum (to 5 - 10-5 mbar). Setting a mechanical shutter in the reference arm of the interferometer also allows obtaining of shadow photographs without changing the optical scheme.

Experimental investigation of the dynamics of laser-induced gas-plasma flows under femtosecond laser ablation of copper in vacuum

Thermophysical and gas-dynamic characteristics of gas-plasma flows induced by ultrashort laser pulses interacting with a thin-film copper target in vacuum were studied experimentally. Using combined laser interferometry and complex processing of experimental data, we estimated the momentum coupling coefficient and the efficiency of laser-energy conversion to kinetic energy, spatiotemporal distributions of the number density and velocities of particles, pressure, and temperature in the gas-plasma flow. We provide comparative analysis of presented data with those found in the literature, which were obtained by other methods.