With the purpose of producing the multikilowatt high-beam-quality industrial lasers, the
Institute has carried out the basic research of the instabilities and self-organization
of current structures in the gas discharge. The role of nonlinear phase inhomogeneities
of the active medium has been studied; the new effective optical components and systems
(polarization transformers, diffraction mirrors, and optical resonators) have been
developed; the principles of adaptive correction of high-power laser radiation have
been elaborated. The high-efficient processes of laser cutting of perspective materials
(graphite, ceramics, special steels) and laser welding of oil-and-gas pipes, parts from
aluminum alloys, titanium and high-strength steels have been mastered. The methods
of stamping tool surfaces processing with a laser have been devised. Relying on this
research work, the pilot department of the Institute and the innovation industrial
enterprises set up under ILIT RAS have developed and are manufacturing the processing
lasers and laser systems to perform cutting, welding and surface treatment of materials.
To date, more than 150 lasers and systems have been produced, which are operated both
in Russia and abroad.
The theoretical and experimental research has been conducted in the following lines.
(1) For the sake of producing gaseous lasers showing high beam quality offered by the spatially
homogeneous discharge, a fundamental theoretic investigation on modeling the processes of spatial
self-organization of current structures in the gas discharge has been pursued. A closed
analytical model of the processes of current spots self-organization in a self-sustained glow
discharge has been constructed. It has been shown that the formation of spatial current structures
is a consequence of Turing-type instability in the bistable system having the S-shaped volt-ampere
characteristic. The structures were found capable of emerging under the originally uniform
distribution of current in the absence of any intentional initiating disturbances.
It has been determined that the spontaneous formation of anode spots becomes impossible
when some critical value of current density is exceeded.
(2) The role of nonlinear phase inhomogeneities of the active medium in high-power lasers has
been studied both theoretically and experimentally. It has been shown that in the gas-discharge
lasers with fast turbulent flow of the working mixture, the light induced heat release gives birth
to small-scale nonlinear nonuniformities of active medium refraction. This effect constrains the
beam quality of the multikilowatt industrial lasers.
The characteristics of turbulent fluctuations of density and velocity, as well as the value of
optical structural turbulence parameter Cn2 of the fast-axial-flow
CO2 laser gas mixture have been investigated by the luminescent and interference
methods, as well as by the four-wave-mixing method. The effect of the gas discharge and of the
laser generation process on the amplitudes of the turbulent small-scale optical nonuniformities
of the active medium has been investigated. It was shown that in the presence of a gas discharge
and during the laser generation these amplitudes begin to build up noticeably under the nonlinear
influence of local heat release in the thermodynamically unbalanced turbulent gas mixture.
The frequency characteristics of turbulence are in good agreement with the theory of uniform
isotropic turbulence at low energy inputs. With an increase in the input power, due to
emergence of filamentation in the gas discharge, the regularities predicted by this theory
are violated. The data obtained are essential to the understanding of the physics of turbulence
in the thermodynamically nonequilibrium flows of the gas mixture. Relying on these data it is
recommended to make use of the adaptive optics systems in order to achieve high optical quality
of multikilowatt laser radiation.
(3) The new highly efficient optical components and systems have been developed in an effort to
control the energy, spatial and polarization parameters of the industrial laser radiation:
- interference polarization transformers, which permitted the quality of material processing to
be upgraded;
- diffraction mirrors with the strong anisotropy of reflection of the mutually orthogonal radiation
components, which first allowed obtaining radially polarized radiation in a kilowatt-class
CO2 laser. The use of such radiation practically doubles laser cutting efficiency, and holds
promise in other applications;
- new-kind optical resonators (mode-selective; stable-unstable), which enabled reaching the
diffraction limit (M2 = 1.1–1.2) of the optical quality of the laser beam with the power to 6kW.
(4) The analytical diffraction theory has been elaborated, and the experimental research of
high-efficient (92 to 97%) transformation of linearly polarized laser radiation to a specular
reflected wave of a predetermined polarization (circular or linear with the polarization plane
turning at an arbitrary angle) under resonance excitation of SEW on metallic diffraction gratings
(Wood polarization anomaly) has been conducted. The developed 90? polarizers have found use in the
CO2 laser system for cutting metals. A number of diffraction methods of linearly polarized
incident radiation transformation to a radially or azimuthally (over beam cross-section) polarized
wave have been developed and experimentally realized.
(5) The noncontact methods and devices to detect subsurface flaws have been developed (thermal
wave spectroscopy method; laser optothermoacoustic diagnostics). These devices permit detection
of defects at the depth to 100mm with the resolution of 50 mm
