Yu. N. Zavalov

Evaluation of speed of melt evacuation in the technology of laser cutting of metals by the optical correlation method

A multichannel pyrometer was used to determine the speed of melt evacuation from an irradiated zone in laser-cutting technology with auxiliary gas. Local pulsations of brightness temperature were measured in four areas of ∼0.1 mm in diameter each spaced by 0.6 mm along the cutting front. A method is described for measuring the displacement rate of temperature heterogeneities during melt motion by mutual correlations of brightness-temperature pulsations calculated in neighboring areas. The necessity of preliminary frequency filtration of the measurement data may be due to propagation of a nonlinear wave in the melt on a metal surface under the impact of a gas jet.

Estimation of output beam characteristics of laser with unstable resonator and turbulent active medium

In this paper we present calculations of the three-dimensional mode structure and output beam characteristics of unstable resonator with turbulent active medium. The calculations of the output beam are carried out in the Fresnel approximation using the well-known iterative method [1]. The active medium is modeled as a series of phase screens with Kolmogorov statistics. The dependence of output radiation parameters of the gas flow laser with unstable resonator on the strength of turbulence in active medium and parameters of resonator is under consideration.

The development of turbulence in the active medium of a fast-flow gas-discharge laser

The effect of pump nonequilibrium on the heat generation and the parameters of turbulent flow in the active medium of a fast-flow gas-discharge laser is studied. It is shown that the amplitudes of the turbulent pulsations of the density and refractive index of the active medium depend on the pump method and the degree of saturation by laser radiation and grow with the pump level. Criteria for estimating the effect of turbulence on the quality of the active medium are presented. A model is proposed that relates the build-up of the turbulent pulsations of the gas density and refraction to the heterogeneous heat release in the nonequilibrium active medium. The effect is determined by both the growth of the isobar local temperature pulsations and the ionization-overheating instability. In the case of dc-discharge pumping, the optical inhomogeneity of the active medium may substantially exceed that for the high-frequency discharge pumping.

Using optical diagnostics to determine the melt temperature field in layer-by-layer laser alloying of metal powder

The results of application of optical diagnostics in the estimation of the temperature field at the melt surface in layer-by-layer laser alloying of metal powder are presented. It is demonstrated that surface concavity induced by the thermocapillary effect upon nonuniform heating may distort pyrometry data considerably. The use of external illumination provides an opportunity to determine the shape of the melt surface. The obtained minimum estimate of the temperature gradient in the metal region affected by laser radiation is 2.8 × 104 K/cm.

Optical correlation method for assessing the parameters of melt flow in the laser technology of metal cutting

Processes that occurring at the front of laser irradiation in the gas-laser cutting of 6 mm-thick mild steel are investigated. It shown that at identical parameters of cutting, the speed of melting changes considerably over time. Surface waves with wavelengths of 2.5–4 mm are observed.

Numerical investigation of unstable resonator for generating radially or azimuthally polarized beams

We present the calculations of intracavity radiation for a confocal positive-branch unstable resonator with a radially or azimuthally selective mirror. We carried out beam propagation in the resonator by the fox-li iterative method using jones vector calculus for the polarization state. The optimization of the resonator for generating a high-power radially or azimuthally polarized beam is discussed.

Influence of nonuniform heat-releasing on optical inhomogeneities of active medium turbulent flow in high power CO 2 laser

The enhancement of optical inhomogeneities of active medium of high-power fast-axial flow CO2 laser is coupled with increasing of the isobaric fluctuations of temperature and density in turbulent flow due to nonuniform heat-releasing.

The determination of transverse pulsations of turbulent flow velocity in fast-axial flow CO2 laser by phase-conjugation method

The scheme of intracavity four-wave mixing is used to measure the spectrum of turbulent pulsation of velocity of ative-medium flow in fast-axial flow CO2 laser. The coefficient of transverse turbulent diffusion and viscous size of turbulent pulsations are also obtained.

The investigation of quality of active medium of FAF RF CO2 laser by luminescent method

The luminescent method was used to measure the spectrum of turbulent pulsations of gas density in fast- axial flow CO2 laser with radio-frequency discharge input. It is shown that gas density pulsations increase through gas discharge along gas flow axes. In continuous-wave fast-axial flow (FAF) CO2 laser there is subsidiary deterioration of quality of active medium due to intrinsic turbulence intensified by gas discharge energy input.

The determination of a turbulent parameters of active-medium flow of a CO 2 laser by method of intracavity four-wave mixing

The degenerate intra-cavity four-wave mixing on nonlinearity of gain of active medium of cw CO2 laser was used for determination of turbulent parameter of active medium flow.