The quantitative model for the continuous-wave laser cutting of metals without chemical reactions is presented. The cutting gas flow is investigated experimentally using a geometrically similar model. Gas pressure and velocity distribution over the cutting front have been measured. Simplified mathematical algorithms for the heat problem have been developed and the maximum depth and cutting speed have been calculated depending on the laser beam parameters. The possible nonstationarities in motion of the melt and the cutting front have been considered. A thermal mechanism for regular cut ripple formation is suggested. The mechanism involves a balance of the capillary forces and those caused by the gas flow and acting on the melt near the upper edge of a cutting front. The simple formulae have been obtained for the magnitude and period of the ripples.

The melt surface oscillations during the nonpenetrating cw CO₂ laser welding of metals are studied. It is assumed that the concurrence between the melt expelling from the keyhole bottom by the vapor pressure and the capillary and the gravity forces tendency to fill the keyhole is the main cause of building up the oscillations. Assuming that the radiation flux being transported to the bottom is unstable, the possibility of parametric inducing melt oscillations on its bottom is investigated.

Dynamics of keyhole formation in metal plates of Mo, W, Ni, stainless steel have been studied under the solid-state laser pulse effect ((lambda) equals 1.06 micrometers ). Velocities of the keyhole bottom motion have been determined for these metals in the (0.5 (DOT) 10⁵ - 10⁶) W/cm² range of irradiated power densities. A pulse regime of plate breakdown has been found out. Small-dimensional structures with d is congruent to 1 micrometers period were found on the keyhole walls, which, in our opinion, can contribute significantly to laser beam absorption. A new form of periodic structure has been revealed, being a helix-shaped modulation of the keyhole walls and bottom relief. Temperature variation were discovered in the keyhole, related to capillary waves propagation in the melt layer.

Results of the experimental studies of dynamics and optical properties of laser-induced plasmas are presented. Lasers with microsecond pulse width at (lambda) equals 0.308 and 10.6 micrometers were used. Spatially and temporally resolved plasma emission spectroscopy and laser beam absorption measurements were used to reveal plasma plume structure. It has been shown that in the case of low absorption at the plasma front, a two component plasma is formed with gas plasma temperature above 3 eV and electron number density in both gas and target vapor plasma in the range 10¹⁸ - 3 (DOT) 10¹⁹ cm^-3. Comparison of the experimental data with computer model predictions is presented.

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.

A combined mode as superposition of continuous pulsed radiation for laser cutting, pulsed seam laser welding, and fiber optical track for laser marking of distant and large-sized blanks are realized on the basis of radiator of batch-produced JITH-103 laser with regard to structural and technological features of steel and alloys treatment with solid laser beam for aviation industry.

Some peculiarities of interaction between laser radiation and dielectric matter are discussed in this paper from the point of view of their technological applications. As has been shown, laser technologies of processing of dielectric materials with low heat conduction have essential advantage. Among them the impulse-periodical TEA CO₂ laser technology excels in the quality of processing. The original experimental plant is described in the paper. The results of comparison of quality of processing of different dielectric plates by ultrasound and pulse- periodical laser technologies are presented.

The paper presents the review of major results of the NICTL activities in the field of welding, cutting, hardening, alloying with CO₂ lasers, as well as the survey of the work on the development of laser technological systems for these processes application in industry.

An investigation has been undertaken on stainless steel's tendency toward hot cracking during laser welding over a wide range of regimes. It has been found that laser welds feature a high safety factor, excellent service properties, and the optimum structure of cast metal. The obtained results were used on introduction of high-efficiency laser welding in industrial production of straight-weld pipes made in stainless steels.

The retained austenite fraction in the surface remelted layer of the steels and cast irons after heating by the surface heat source is determined by the degree of the carbide phase dissolution at the end of the heating stage. The amount of the retained austenite correlates with the highest temperature at the end of the heating stage. There is an optimum value of the retained austenite fraction in the surface remelted layer, the said optimum value corresponds to the highest values of the resistance to the wear, contact fatigue and anodic dissolution of the steels and cast irons.

Comparative investigations of fretting-resistance of laser coatings applied on high-strength steel and nickel alloys were carried out over a wide range of temperatures under conditions approximate to operating ones at dynamic vibrocontact loading. At 1000 degree(s)C carbide- containing coats were demonstrated to be correlated according to wear resistance with cast heat-resistant alloys. They are several times superior to carbideless coatings, including an argon-arc coat used during repair of turbine engine blades. At 1200 degree(s)C carbide- containing coats maintain their strength as opposed to cast materials and coats based on nickel. Tests performed at room temperature show that coatings of self-fluxing alloy powders increase 2.3 to 3.5 times the fretting resistance of 30X(Gamma) CA volume-hardened steel and as a mixture with carbide powder nearly by an order, whereas laser hardening by both continuous and pulse-periodic beam raises fretting resistance only 1.4 times. The obtained results indicate that application of laser coatings on friction pairs operating under the discussed conditions is advisable.

The paper presents the results of theoretical and experimental investigation on the process of metal boiling initiated by pulsed laser beam, with a transparent layer on the metal surface that provides the impedance acoustic load. The theoretical analysis shows that with the squeezed surface, when the energy thresholds of metal boiling essentially depend on laser pulse shape and duration, considerable overheating of metal is possible in the course of laser pulse. In the experiments on mercury, nonlinear variations in the photoacoustic signal were registered that are due to vapor pressure contribution under the excess of boiling thresholds. The experimental values of mercury boiling thresholds under pulse laser heating agree well with theoretical estimates.

Consideration has been given to the laser thermal-wave microscopy method of nondestructive inspection that relies upon thermal wave excitation with flying laser spot and IR-radiometry registration of thermal waves. The theoretical analysis disclosed that contrast and amplitude of thermal image depend heavily on the relative position of the thermal beam and observation point, as well as on scanning velocity. The location of the thermal wave recording point at a distance of 1 or 2 thermal beam diameters ahead of the moving laser beam is optimum. The use of laser-scanning heat source and thermal wave recording with IR detector array improves greatly the inspection efficiency over the point-by-point technique of thermal wave recording.

The paper presents the results on investigations and development of multichannel CO₂ lasers with diffusion cooling of active medium excited by the discharge of an audio-frequency alternating current. Various methods of improving the laser beam quality and energy efficiency have been considered and experimentally tested.

A variety of industrial technological laser systems with 1.5, 2.5 - 3.5, 8 - 10 kW power have been developed around the multibeam diffusion-cooled CO₂ lasers. A number of technological processes of parts hardening and reconditioning (sleeves made in cast iron, cylinder of diesel locomotive engines, crankshafts and camshafts of tractor engines, parts of car and tractor running gears, rings of drilling bearings, lead screws, machine guides), that employ the LTS have been developed and introduced at various industries.

The performance of a 3 kW CO₂ transverse flow laser using a self-filtering unstable resonator configuration is presented. The output beam quality is the same as TEM₀₀ mode stable resonator. The resonator contains nontransmitting optical elements. A facility for Q- switching and line tuning has been developed on the basis of this resonator and the results of preliminary experiments are given.

Results of studies of an EB-controlled discharge in a pulse-periodic CO₂ laser are given. A conclusion on the expediency of the change in the traditional transverse scheme of the gas mixture circulation through the discharge region for the longitudinal one is reached. It is shown that a laser with the longitudinal circulation scheme offers a 1.5-fold efficiency over that of a laser with the transverse scheme and a 1.8-times higher beam brightness on the polar diagram axis in the far field. Based on the obtained data, an experimental prototype of the technological CO₂ laser providing an average output power of more than 10 kW in the pulse-periodic mode at the beam divergency of not more than 0.42 mrad is constructed.

The paper presents the results of estimating the characteristics of a CO₂ laser with a fast axial flowing of the working mixture, developed at the Scientific Research Center for Technological Lasers. Particular attention has been given to the investigation into methods of production and parameters of this laser pulse-periodical operation.

The high power (10 MW beam power) compact laser system with average beam power up to 300 W and a pulse repetition rate to 1 kHz is discussed. Pulse energy is up to 0.8 J at low pulse repetition rate and up to 0.5 J at maximum pulse repetition rate. The results of gas dynamic testing of closed circuit are obtained, comparison of them with calculated parameters is performed, working mixture temperature dependencies on the energy input into discharge volume are noted, dependencies of the beam energy and beam pulse duration on different operating parameters are shown, and data on far field beam divergency and service life are considered.

The aim of this work was to investigate the influence of plasma-chemical reactions products, heat processes on the electrode surface, and the degree of coordination of pump pulse generator on the forming conditions of volume discharge in the working mixtures of sealed-off TEA CO₂ laser. The main factors limiting the pulse repetition rate were determined. Some versions of sealed-off TEA CO₂ lasers with the pulse repetition rate of 1 - 5 kHz and the pulse radiation energy of 10 - 50 mJ were realized.

A self-consistent calculation of voltage fall on the anode film as a function of its resistance has been performed in the presence of anode current spots under elevated-pressure glow discharge in nitrogen and N₂:He equals 1:1 mixture. It has been shown that resistance of anode oxide films in industrial lasers with continuous copper anode can reach the values when total suppression of anode current structures takes place.

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.

The generation regimes of cw-pumped CO₂ laser with the controllable base Fabry-Perot interferometer (FPI) as the resonator output mirror were investigated. The pulse-periodical radiation regime over the frequency range 0 - 5 kHz and pulse length range 0.1 - 10 ms with the modulation depth 100% were obtained. The FPI-based method of power control and stabilization was realized.

A quantitative investigation of the excited CO₂ molecules diffusion display in industrial lasers was done. It is shown that in the diffusively cooled lasers diffusion results in an additional gain on the tube axis which depends on the gas mixture contents and pressure, beam sizes, and energy input. It was found that in the fast transverse flow lasers the influence of turbulent diffusion was significantly smaller than the convective bringing the excited particles in the laser beam region.

The purpose of this paper is a quantitative analysis of the diffusively cooled laser discharge characteristics effect on the optical quality and the signal gain in the active medium.

The paper presents the original results obtained by the authors on investigation of lasers operating by the 3 p - 3 s Ne transitions ((lambda) equals 585 nm; 703 nm; 725 nm), by the first negative ((lambda) equals 391 nm; 428 nm) and second positive ((lambda) equals 358 nm; 381 nm) systems of N₂, by d-p argon ((lambda) equals 1.79 micrometers ) and xenon ((lambda) equals 2.03 micrometers ) transitions, as well as on the study of multifrequency simultaneous lasing due to several of the above-mentioned transitions.

The characteristics of pulse repetitive rate nitrogen lasers with longitudinal excitation PGL- 505, PGL-504A, PGL-511 are investigated. The data about dependence of energy and average power of laser radiation on repetition rate are represented. The possibility of obtaining laser generation with average power of 95 mW at a high repetition rate up to 5 kHz is demonstrated. A compact nitrogen laser with air cooling and average power of 10 mW is developed.

Wavefront aberrations, arising due to active medium optical inhomogeneities and mirrors thermal deformations, influence on the self-filtrating unstable resonator parameters of industrial cw CO₂ lasers were investigated theoretically. The output radiation amplitude- phase performance in the diffractional approximation and the resonator losses were calculated.

A simple design of an unstable laser resonator with a continuous rectangular aperture of an output beam is proposed. A mathematical model was developed to simulate the discharge laser cavity and it was used to study numerically the performance of a fast-flow technological CO₂ laser with such type of resonator that, as it has been shown, possesses good perspectives.

A resonator with a `cat-eye' mirror (CEM) has been experimentally studied. The laser beam output characteristics are considered against the corresponding beam properties in a standard stable resonator. The prospects of the CEM resonators use in technological lasers are shown.

The solution method of a diffraction problem for a multilayer diffraction structure enabling us to analyze the diffraction coupler (DC) with an efficiency of 80% in the first order is discussed. The DC of 62% efficiency in the first order has been manufactured by the photolithography method in conjunction with ion-beam surface treatment. A resonator with DC as an output mirror has been investigated experimentally. The beam output has been performed through the zero order of DC. The stepped change in generation in the range from 9.18 to 10.82 mm has been obtained. A condition for concurrent generation on several neighboring lines has been investigated.

We report the new method of highly efficient transformation of linear polarized laser beam into another beam, with any required polarization performed by reflection grating. The parameters of this grating were calculated theoretically. The grating converters with a reflectivity of R >= 96% for transformation of linearly polarized CO₂ laser beam into a circular polarized beam have been fabricated. The efficiency of these converters included in a 1.5 kW CO₂ laser technological system for metal cutting is demonstrated.

Some peculiarities of a process of non-polarized radiation diffraction on ultrasonic waves in uniaxial crystals are examined. Particular calculations are made to single-crystals of paratellurite. The experimental design of an acousto-optical modulator operating with non- polarized multimode laser radiation is reported. Basic parameters of the device are presented as well.

A new approach to the measurement of high-level laser radiation characteristics based on a tertiary pyroelectric effect that manifests itself during nonuniform heating of [111]- oriented crystals of 43 m symmetry within their transparent region has been developed. The proposed procedure allows the functions of the laser output window and the radiation detector to be combined.

One of the properties of surface plasmon-polariton (SPP) waves is that their excitation takes place only when appropriate relations between wave vectors of incident electromagnetic and SPP waves are fulfilled for a given frequency. In addition the incident wave has to be p- polarized. Due to the aforementioned peculiarities SPP waves may be applied for the development of some devices such as detectors of angular shifts, wide-band polarizers of light, or frequency discriminators. It is necessary to say that such devices have small sizes that offer an opportunity to use them with opto-electronic equipment. It is important to have an opportunity to induce SPP waves for different frequencies but the same relations exist between wave vector of incident electromagnetic and SPP waves. The technique of deposition of a monolayer of oriented molecules with necessary properties and thickness on the boundary of two mediums where SPP waves spread is used to get such an opportunity.

To measure the power and energy of wide-aperture high power laser beams, thermoelectric mirror-detectors have been designed, combining the functions of high-reflective mirror and thermal converter. The paper presents the technical data and schemes of potential applications in actual technological laser systems.

Definite axial and radial temperature gradients created in the directed growth zone of zinc selenide single crystals lead to the formation of substructures. Such crystals may be used for manufacturing piezoresonators, special optical elements for measuring the power of transmitted laser radiation and modulating the latter.

A reduction of the divergence of a laser beam by a factor of 2 - 2.5 was achieved in a multimode regime of laser generation using an intracavity controlled mirror. It is shown that various radiation mode structures may be formed at the laser output and in the far-field zone. The correspondence between the shape of a deformed flexible mirror and the configuration of a generated mode has been detected.