Alexandre M. Zabelin

High-power CW CO2 lasers for material processing

Strict requirements of modern industry and medicine to laser beam quality, stimulated to fulfil a lot of special researches have been undertaken concerning: a) gas discharge stability and uniformity; b) enhancement of active medium optical nonuniformities in the presence of laser generation; c) new concepts of optical resonators; beam power modulation with a controllable coupling mirror. As the result of these investigations, several series of fast-flow and of diffusion-cooled waveguide industrial CO2 lasers in 0.5 to 10.0 kW beam power range have been designed in the IPLIT RAN.

Laser decommissioning of RBMK nuclear reactor fuel channels

A justification of laser decommissioning of nuclear reactor of Kursk Nuclear Power Plant. The main reason of laser beam application in this case is the marked decrease of radioactive radiation exposure of the service personnel. The use of a high power laser beam provided to realize laser cutting and welding processes of a distance up to 35m between the laser and the workstation placed behind a contre-radiation shield. By application of laser cutting gas and dust contamination is tenfold decreased. Some result of decommissioning application of a stationary laser workstation based upon a 5kw fast-transverse-flow discharge CW-CO2 laser TL-5M installed of a nuclear reactor site are presented. A special high-beam-quality model of the laser was developed to satisfy the needs of decommissioning. Laser cutting process was applied to decommissioning of fuel channels of RBMK-1000 reactor, after their extraction from the reactor active zone during the procedure of channels replacement.

Physical and technical factors, determining beam quality of high-power industrial fast transverse flow CO2 lasers

The results of the investigation of the beam quality in the high-power industrial carbon-dioxide laser generating in the 10 kW range are presented. As a result of this investigation, a scheme of the modified stable-unstable resonator is proposed, that uses only reflective mirrors. In this scheme, the plane of the unstable telescopic resonator is transverse to the flow in the discharge chamber. In the plane parallel to the electrodes this scheme represents a single-mode stable resonator. High efficiency of this resonator and high beam quality have been pointed out.

Study of plasma formation in CW CO2 laser beam-metal surface interaction

An interaction of the cw CO2 laser beam and a moving metal surface has been studied. The pulsed and thermodynamical parameters of the surface plasma were investigated by optical and spectroscopical methods. The subsonic radiation wave propagation in the erosion plasma torch has been studied.

Beam quality of cw fast-flow CO2 lasers

The analysis has been performed of main sources of wave front aberrations in industrial CO2 lasers, which have an effect upon beam quality. Nonlinear optical inhomogeneities caused by thermal self-action have been studied.

Interaction of cw CO2 laser radiation with plasma near-metallic substrate surface

Optical and spectroscopic methods were used in studying near-surface plasma that is formed under the effect CW CO2 laser of (2- 5)x106W/cm2 power density upon stainless steel in He and Ar shielding gases. The variation of plume spatial structure with time has been studied, the outflow of gas-vapor jets from the interaction area has been characterized. The spectra of plasma plume pulsations have been obtained for the frequency range Δf = 0-1 MHz. The temperature and electron concentration of plasma plume have been found under radiation effect upon the target of stainless steel. Consideration has been given to the most probable mechanisms of CW laser radiation-metal non-stationary interaction.

Decommissioning of nuclear reactor fuel channels using laser technology

Decommissioning of nuclear reactors using laser remote dismounting and welding was experimentally proved at a nuclear reactor of Kursk Nuclear Power Plant. The main reason of laser beam application in this case is the marked decrease of radioactive exposure of the service personnel. The use of a high-power laser beam provided for laser cutting and welding processes realization at a distance up to 35 m between the laser and the workstation placed behind a radiation shield. By application of laser cutting gas and dust contamination is ten-fold decreased. Some results of decommissioning application of a stationary laser workstation based upon a 5 kW fast-transverse-flow discharge CW CO2 laser TL-5M installed at a nuclear reactor site are presented. A special high-beam- quality model of the laser was developed to satisfy the needs of decommissioning. Laser cutting process was applied to decommissioning of fuel channels (FC) of RBMK-1000 reactor, after their extractor from the reactor active zone during the procedure of channels replacement.

Polarization characteristics of a high-power industrial CO2 laser

The polarization characteristics of radiation of the industrial transverse-flow 5 kW CO2 laser have been studied. The conditions for generation of radiation with linear polarization and for the regime of random change of its direction have been determined. The interrelation of radiation polarization characteristics with the parameters of the laser of this type has been established.

Nonstationary plasma-thermo-fluid dynamics and transition in processes of deep penetration laser beam-matter interaction

A qualitative analysis of the role of some hydrodynamic flows and instabilities by the process of laser beam-metal sample deep penetration interaction is presented. The forces of vapor pressure, melt surface tension and thermocapillary forces can determined a number of oscillatory and nonstationary phenomena in keyhole and weld pool. Dynamics of keyhole formation in metal plates has been studied under laser beam pulse effect ((lambda) equals 1.06 micrometers ). Velocities of the keyhole bottom motion have been determined at 0.5 X 105 - 106 W/cm2 laser power densities. Oscillatory regime of plate break- down has been found out. Small-dimensional structures with d-(lambda) period was found on the frozen cavity walls, which, in our opinion, can contribute significantly to laser beam absorption. A new form of periodic structure on the frozen pattern being a helix-shaped modulation of the keyhole walls and bottom relief has been revealed. Temperature oscillations related to capillary oscillations in the melt layer were discovered in the cavity. Interaction of the CW CO2 laser beam and the matter by beam penetration into a moving metal sample has been studied. The pulsed and thermodynamic parameters of the surface plasma were investigated by optical and spectroscopic methods. The frequencies of plasma jets pulsations (in 10 - 105 Hz range) are related to possible melt surface instabilities of the keyhole.

Investigation of nonlinear properties of high-power industrial CO2 lasers stable resonator

Industrial transverse flow cw CO2 laser irradiance parameters were investigated experimentally and theoretically in the single mode beam ultimate power region. It was shown that the semitransparent mirror reflecting surface curvature variation under the irradiance heat effect and the active medium linear optical inhomogeneities result in Gaussian beam power saturation effect.