The common design of CO lasers for materials processing is founded upon a fast, mechanially enhanced gas flow to remove the heat released by the electrical discharge for laser excitation. The blower and the gas handling devices limit the compactness of this system on principle. In this paper a diffusion cooled rf-excited CO laser in stationary gas is described that works according to th stripline laser concept. Because this laser needs no gas circulation, it can be built essentially more compact and of less weight than common systems. With a modified cooling cycle it can act as a high power CO laser as well. Experimental investigations concerning discharge and laser parameters are described. The beam quality achieved with a stableunstable waveguide hybrid resonator is compared with theoretical calculations. Technological concepts for high lifetime sealed off lasers are presented.

Excitation of C02-N2-He gas mixtures by means of microwave discharges (ii = 2.45 GHz) leading to powerful laser action has been reported to work successfully. Experiments with fast axial flow systems were carried out using three different discharge tube diameters d at a fixed discharge length of L =0.3 m. In the case of d = 0.016 m an optimum cw output of PL = 400 W in the TEM01 mode at a discharge pressure of p = 3.8 kPa for cw excitation or p = 4.2 kPa for pulsed excitation was reached. Calculations of the electrical field within the waveguide filled with plasma and dielectric are compared with the results of invasive probe measurements. Using d = 0.024 m a cw laser output of more than 1 kW at a discharge pressure of p = 5 kPa was achieved. The design of a CO2 laser amplifier requires large and homogeneously excited discharge cross sections to minimize saturation effects and to enlarge the energy stored per length in the discharge volume. Therefore a discharge tube diameter of d = 0.051 m was chosen. One discharge unit was carefully studied with respect to the small signal gain 7o and the saturation intensity 1s using different types of cw or pulsed power supplies for magnetron operation.

The electrical and optical characteristics of a 12 kW transverse flow C02-laser with rf excitation will be discussed. The rf discharge with its bulk plasma and the electric boundary layers covering the ceramic electrodes are analysed on the basis of refined measurements of the complex discharge impedance. The dissipative influence of the electrical boundary layers on the electrodes is deduced from heat balances. The phase distribution in the discharge zone measured with a Mach Zehnder interferometer characterizes the optical effect of the gas density gradient in flow direction. Measured small signal gain distributions give the optimum location of the double pass unstable resonator. The overall performance of the system will be demonstrated by the measured output power and the far field intensity distribution.

The CO2 decomposition caused by a transverse rf excited discharge has been investigated in a waveguide laser with a square bore in alumina and in a slab waveguide device formed by electrodes of various metals. The discharge was sustained in a 3He:1N2:1C02 +5 % Xe fresh gas mixture at a pressure of 100 mbar. As shown by spectroscopic measurements in the discharge of the square waveguide the equilibrium of the CO formation is attained within 0.3 s at a rf power density of 71 W/cm". The attendant steadystate CO2 decomposition degree of 52 % was determined with a mass spectrometer taking the gas sampies from the gas bllast volume. The addition of 1-2 % hydrogen to the gas mixture reduced the CO2 decomposition and enhanced the laser output power by 25 %. Measurements on the slab waveguide showed that the CO2 degradation depends on the type of electrode materials. For aluminium the observed CO2 decomposition degree of 45 % did not alter remarkably with pressure and rf power density in the range of 70-150 mbar and 50-120 W/cm3, respectively.

The effects of hard apertures on the transversal mode distribu- tion and on the output near and far field distributions are investig- ated both theoretically and experimentally. Wavefronts propagating in different directions inside a C02 laser cavity were measured at the same plane and found to have different transversal amplitude prof 1- les. The influence of intracavity aperture's location and diameter on the near field distribution and on far field beam quality were measured and calculated. Quantitative figures of merit are introduced to evaluate the departure of the transversal mode patterns from ideal gauss ians.

A repetitively pulsed e-beam controlled CO laser has been constructed. The laser system is a completely seled off unit with an active volume of 12 liters outlined to laser pulse energies up to 100 Joules. The electron beam source has been designed and built up to produce electron pulses of 120 key energy, current densities of about 100 mA/cm2 behind a window area of > 1000 cm2 and repetition rates up to 100 Hz. Principal design features and typical measurements of multimode operation are presented.

Fluctuations of the active medium thermodinamical parameters can influence strongly the final quality of industrial processes accomplished by laser devices. In this paper, the effects produced on the emitted radiation by active medium parameter variations, are analyzed, through numerical methods, for some situations of interest for oscillator-amplifier configuration based systems.

The design and operation of a laser based on an M-mode radiation distribution is described. A thin rectangular gain region (whkh normally generates an elongated strip output) is matched to a hemiconfocal optical cavity with a stop at the center of the spherical mirror, producing a narrow Gaussian beam traveling parallel to the optical axis. For suitable electrode dimensions, more than 85% of the total extractable power is present in the beam, which is identical in its waist to that of a laser four times as long. Computer simulations of the cavity yielded results conforming to experiment regarding the sensitivity of the mode to deviations in the hemiconfocality of the cavity. The possibility of extending the folding to higher multiplicities is discussed.

Very strong and efficient emission from a TEA CO2 laser utilizing nonconventional ternary C02/N2/H2 gas mixture is obtained. Output pulse energy and power up to 240 mJ and 1.2 MW (multimode operation) were registered respectively from only 14 cm3 of active discharge volume.

Change of focus length due to CO2 laser beam absorption in ZnSe lens was analyzed by the thermal conduction theory and the physical optics. Temperature distribution was calculated in ZnSe lens where the thermal conductivity varies with temperature. Transient focus position was determined within an accuracy of by a diagnostic system where laser beam passing through a rotating slit probe moving along the beam axis is detected by a pyroelectric detector. Focus length was found to be shortened quickly in the initial 10-20 sec, reaching steady state in 60-90 sec in ZnSe lens of 2 inch-diameter. At absorbed power density wab<5 W/cm2, the focus shift is proportional to wab, and increases more rapidly at wab>S W/cm2 with accompanying aberration. The measured focus shift was found to agree well with calculated values. Effect of lens-to-holder contact on the transient focus shift are also discussed.

A laserrobot cell consisting of an industry robot, a fast axial flow COz-Laser with 5 kW output power and an external beam delivery system (BDS) is presented. The CAD-/CAM-interface named USIS (Universal SImulation System) enables off-line programming and simulation ofthe robot. A scanning lasersensor has been integrated in order to enable keeping the right focus distance to the surface and to follow the welding path.

Laser material processing has found new applications, e.g. in treating spatially formed workpieces. The aim to get the high working qualities, which on principle can be reached by cutting and welding of sheet metals with C02-lasers even in case of manufacturing spatially formed parts, lead to the development of convenient machine systems. Meanwhile there exist many solutions to realize a three dimensional movement between the working tool laser beam and the workpiece'. A fundamental distinction can be made between robot and gantry systems. Robots have a greater freedom of movement but are not as accurate in guidance as gantry systems. Mostly robot systems are equipped with an external beam guidance system, which diminishes the working area and raises the danger of collisions between workpiece and machine system. Therefore recent developments of robot systems for laser material processing integrate the beam in the handling system in such a manner that the optical axis of the laser beam lies in the mechanical axis of the robot system. Despite of this improvements there are still laser material processing operations which better or exclusively can be executed with gantry machine systems. Gantry machine systems have a high frame stability, an accurate guiding behaviour even at high process velocities and large working areas. Especially when processing large workpieces, where heavy clamping devices are necessary, the use of a gantry machine system is advisable. A typical set up of a gantry machine system is given in figure 1.

A compact 550 watt slow flow RF excited CO2 laser directly attached to a Yaskawa Motoman robot is used to cut three dimensional patterns in 1 mm thick curved steel sheets. The quality and speed of the cutting is identical to that of cuts made with a static laser, since movement of the laser does not degrade its mode quality in any way. The light weight laser head is rigidly attached to the five-axis robot and is flexibly connected to its power/gas/cooling sources. It can be manipulated through a 2r spherical angle at dynamic accelerations of up to at least (3.4g. This laser-robot system implements the ultimate precision capability of the robot. Its potential for manufacturing flexibility will be reviewed.

Plastic hollow fibers and the layers deposited on their walls were analyzed. FITR analysis showed that the fiber is transmitting similar IR spectral range as air (2.5 - 12 pm). Employing Auger analysis it was shown that the upper layer consists of the compound AgI (x&square;1) where x varied with the depth of the layer. SEM analysis showed that the fiber that got layers which have finer grains structure transmits more CO2 laser energy (A = 10.6 pm) than the fiber with layers which have coarse grain structure.

We present here a comparison between the calculated propagation parameters, the power threshold, the root mean square (RMS) output pulse width and pulse shape for 10.6 itm laser propagation through hollow circular metallic waveguides and infrared (IR) optical fibers. Initially reported experimental results indicate that hollow metallic waveguides exhibit 1O times smaller loss than optical fibers at 10.6 rn and this is in good agreement with the calculated results. On the other hand, compared to common communication fibers at 1.5rn, hollow waveguides have an attenuation coefficient 10 210L1 larger and therefore are not suitable for infrared communications.

Instability of metal mirrors in C02-lasers is caused by the thermal load layed on such mirror surfaces which relieves the strain in the individual grain brought in to it by the deforination of the cutting and polishing process. A solution to this problem was sought and found in a single crystal, grown to its final form as a laser mirror, which had a one sided careful conventional polish for CW-lasers and for pulsed lasers no polish at all, but the crystal was grown against a replica of optical quality.

In order to minimize the mass flow rate and the optical distortion of aerodynamic windows, a novel type with a pump cavity and a supersonic as jet has been deve- loped. Prototypes of this window with an aperture of 4x4 mm have been designed and fabricated. With it, a 80 mbar laser cavity can be sealed up using a gas jet of 5 g/s mass rate at 5.4 bar while the pressue in pump cavity is about 600 mbar and the volume to be pumped is less than 7.2 m /h. It can be operated stably if the pressure variation is less than 25 mbar. A wide range of operation pressure of the laser cavity can be realized easily by adjusting the supply pressure for the gas jet and the pressure in the pump cavity.

The new generation of automated laser machine tools poses problems for those responsible for setting safety standards. While traditional safeguarding will frustrate full exploitation of this hybrid technology, wholesale abandonment of effective containment in favour of safety monitoring and control systems is unlikely to be acceptable. Long term, quantitative risk assessment will resolve this dilemma. Short term, guide lines will have to be derived from practical considerations of the laser facility design, materials, primary safety devices and procedures. Earlier risk assessments are reviewed relative to the emerging perspective of high average power laser installations. Aspects of extended beam delivery systems and equipment utilization and maintenance are examined to assess possible interaction with operational safety and in particular the potential to adversely influence errant laser beam occurrances (ELBO). To satisfy international safety standards for a laser enclosure which offers flexibility and is cost effective a detection system is described which continuously surveys the inside of the enclosure. Extensive trials have been carried out with high average power lasers (up to 10kW) where a range of engineering materials has been exposed to a laser beam. It is shown that the ratio of detection and shut down time to the burn through time can be an acceptable risk and thus indicate which materials will prove adequate.

A novel beam shaping optics, Linear-polarized Shape Variable (LSV) optics for high power CO2 laser beam has been developed, which provides a beam spot with variable beam shape in terms of different aspect ratios, and negligible shaping loss of 5% with high beam absorptivity of 50% in non-coated steel, which is as high as carbon coated steel, The high efficiencies both in shaping and metal heating are attained by utilizing linear-polarized CO2 laser beam. In laser hardening, the case depth larger than 2mm (width=l5mm) was obtained without any absorption coating. By changing the beam width in the direction of beam motion, D, in accordance with the traveling speed, hardened depth from 0.3mm to 2.5mm (width=l5mm) was obtained at constant surface temperature of 1400 C at 3kW power level. LSV optics was also used for local heating up to 1100 C in brazing Si3N4 ceramics with insertion of Al foil, and joint strength as high as 400 MPa was obtained in an irradiation time of about 20 sec without any preheating.

The patented "Acoustic Mirro?' has previously been used to investigate weld quality in laser welding. A good correlation was observed between the acoustic signal and weld quality. This success led the authors to investigate the use of the acoustic mirror in gas assisted laser cutting. A piezoelectric transducer mounted on the rear of the final mirror of the beam path was used to observe high frequency vibration due to reflected energy from the cutting process. Off-line inspection of the cut samples enabled the determination of cut quality. A correlation was obtained between the RMS value of the acoustic signal and full penetration of the laser beam, a decrease in signal corresponding to penetrating. Dross adhesion was also indicated by an increase in the level. Changes in the low frequency modulation showed some correlation to cut quality. Guidelines for the use of the acoustic signal as an indicator of fault cutting are discussed.

The high reflection and the high thermal conductivity of aluminum make it difficult to transfer the laser energy into the workpiece. For high energy transfer efficiencies a multikilohertz repetition rate laser system with high average power and high peak power is required. By using a Q-switched CO2 laser oscillator amplifier system laser pulses of 70 mJ energy, 0.2 ps half width and 250 kW peak power with a repetition rate of 20 kllz, an average power of 1.4 kW and TEM00 mode quality are available. The pulsed laser system allows the cutting of aluminum plates with a higher velocity and a better quality than it can be reached with a cw laser at comparable average power. Using laser pulses burr free cutting of aluminum up to 10 mm thickness at moderate average laser power level is possible, because a laser-induced plasma is ignited within the gap by each laser pulse. For welding of aluminum plates the laser pulses of the Q-switched laser system can be shaped to achieve an optimized energy transfer into the material and a good welding quality. The electron density of the welding plasma plays an important role for the energy transfer. The spatial and temporal distribution of the electron density in a laser-induced plasma is measured by a beam deflection technique. The electron density can be influenced by the working gas and the laser pulse form. Typical values 1.2 mm above the aluminum surface are for example 3 . 1023 m3 in case of argon as working gas and 1 . 1023 m3 in case of helium.

The authors investigate the results attainable by laser welding steel with high carbon content ('TX) to sintered diamond in a cobalt matrix, supplied by an Italian Company producing disk saws for granite quarries, Different laser resonator configurations are tested in order to obtain acceptable results while decreasing manufacturing costs, Physical properties of the weld joint are tested and overall results are compared to those already obtained in the same application basing on steels with lower carbon content (3",),

For this paper laser beam cutting-experiments at the grain refined steel T StE 960 V and Q StE 690 TM and at the aluminium alloys AA 2024, 6061, 7474, 8090 were carried out. The hardness profile in the area near the cut edge and the change of the alloy composition were analysed. The measurements of the resulting residual stresses are connected with the observed fatigue properties. The results are compared to those of specimens prepared by plasma-, flame-, and jetcutting.

A mathematical model for deep penetration laser welding has been developed that considers only main phenomena. A moving linesource describes the net energy input given by the difference between laser power entering the keyhole and evaporation loss. Energy flow continuity yields the dependence of welding speed on the wall temperature of the keyhole. Since it is generally assumed that the keyhole is held open by the vapour pressure, a second condition for the keyhole wall temperature is obtained.

A C02-Heterodyne Laser Radar-System for detection of wires and obstacles encountered by helicopters flying at low altitudes is being developed. The main requirement is to detect wires of 3 mm diameter at distances greater than 3oo m under good weather condition and 5o m at low visibility. The sensor field of view is 600 azimuth by 300 elevation with a frame rate of 5 Hz. A scanner configuration using counter- rotating pairs of optical wedges for azimuth and elevation scanning in conjunction with a fast scanning micro scanner allows a good spatial coverage of the field of view. A Q-switched CO2 waveguide laser delivering a 2oo ms pulse at a pulse repetition frequency of approximately loo kHz provides a relatively large number of returns from thin wires per scan. Range measurement is determined by the time of flight of the emitted laser pulse. Together with the corresponding scanner position the range data is processed to give a rough three-dimensional representation of the scenario.

The results of a theoretical and simulated study of an infrared two dimensional time integrating spectrum analyser using a crystal of tellurium with infrared photorecievers time integration are presented. Spectrum analysis of the modulated input infrared laser radiation has been carried out with a very efficient single element two dimensional acoustooptic (2DAO) tellurium deflector. A simulated multifrequency spectrum analysis of radio signals has been performed. The frequency resolution can be scaled to cover a few hertz to tens of kilohertz. A minimum detectable input radio signal power at least two orders of magnitude higher, using Te as well as a wide banwidth can be obtained compared to other AO spectrum analysers which operate at lower wavelengths and utilize other materials than Te. Our previously reported experimental data is in good agreement with some of the simulated tests.

A limitation of heterodyne C02-laser radars results from the statistical properties of speckle effects. Suppression of speckle influence by adding uncorrelated speckle pattern was experimentally studied. Using a space separation technique involving a quadrant detector allows to 'look' at different parts of the laser spot on the target at the same time. By choosing the proper diameter of the receiver optics nearly uncorrelated signals are seen with the four detector elements. The signal statistics was measured for direct and heterodyne detection. The achieved improvement in the signal probability distribution and in the contrast were compared with theory. The measurements were done with both a laboratory setup and with the Ff0 Laser-Radar-System BASIS 2.

Pulsed high average power C02-lasers allow for a most efficient conversion of coherent IR-laser radiation into thermal and mechanical energies. This paper is concerned with investigations using a specially developed repetitively pulsed high energy C02-laser. This powerful device provides mean powers of several kW and peak powers of the individual pulses in the multi-MW range. Studies were performed to obtain information on the transient behaviour of the fast energy transfer mechanisms that occur at peak power densities near or above the surface plasma ignition thresholds. As shown, these plasma waves are periodically building up, expanding and recombining during the short time intervals between subsequent pulses, even in case of the highest repetition rates that are presently limited to 100 Hz. Besides the efficient thermal energy transfer through plasma-enhanced thermal coupling mechanisms, the simultaneously induced mechanical pressure waves are providing an additional impulsive loading of the targets. These pressures were investigated by using PVDF gauges. The experiments reveal that these effects too are responsible for improvements, concerning the energy balance, in most manufacturing processes such as in cutting or in drilling, where these fast thermo-mechanically coupled processes, for example, contribute to increase the mass removal rates.

A float zone crystal growth apparatus was developed. The heat source was a 3.5 kW CO2 Trumpf laser with a long term stability of 2 %. The original laser beam was divided, in the beam delivery system, into three equivalent focusable beams. The vacuum vessel is equipped with two equivalent rotation - translation systems with a maximum translational speed of 1 mm/minute. The vessel is also pierced with five windows, three of which serve the three incoming beams, one for observation with a television camera, one for an optical pyrometer or for direct observation. The three beam windows are protected by a laminar gas curtain. A heat shield system with an after heater is planned, in order to enable growth of high temperature oxides. The system was tested in the growth of small sapphire crystals (0 4 mm) and in the growth of silicon whose dimensions were 0 10 mm x 70 mm. * On leave from the Weizmann Institute, Rehovot, Israel

The demands made by modern technology on components can only be fulfilled if sophistical materials are used eg composite materials, surface treated materials or graduated materials. The component is subjected to different types of stresses at different parts and hence different properties are required to withstand the loading. Lasers are high technology tools which can be applied to locally modify the surface properties. In the last ten years laser cutting and laser welding have established themselves as reliable industrial processes. Laser surface treatment has been shown to be a viable process although it is much more complex than cutting and welding. Apart from isolated applications laser surface treatment has yet to become an accepted process. The different working processes require different laser charcteristics eg beam size, energy density etc. I shafl concentrate on applications undertaken y CO2 lasers although NdIAG lasers are serious2contenders for many applications and excimer lasers are gaining in importance

The purpose of this paper is more to stimulate a discussion than to set out well proven and undisputed facts. A great many papers are being published on the subject of diffracting optics and these usually fall into one of two classes: those concerned with bulk or with surface relief components. In most cases the authors have experience with one or other technology and often tend to describe the benefits of their own advances without fully putting them into the context of what is offered by alternative technologies. When comparing different forms of diffracting component it is also necessary to compare them with the equivalent conventional ones and to compare all relevant aspects of performance and cost. This critique is intended to be as impartial as possible but it must be admitted that the author's main experience is with surface relief technology.

To utilize the advantages of surface treatment with laser radiation for modifying the proper metallurgical structures or achieving the required processing geometries the use of optical systems for beam guiding and shaping is necessary to guarantee the required power density distribution and interaction time for an unique materials processing effect as hardening, remelting, alloying, dispersing, cladding and gla.- zing. Simple beam guiding and shaping techniques using static and moving optical components are described evaluating their reliability for an industrial environment with applications for processing of areas hardly to access and of complex workpiece geometries.

For many applications it is necessary to generate wear resistant, hard surface layers. These layers should consist of hard particles embedded in a ductile matrix. These hard particles are choosen appropriate to the wear conditions and wear partners like minerals, carbides in an iron base material or coked particles in motor oils. For protective layers it is important to use low cost hard phase materials, however, some tools require diamonds, the hardest material known. These have then to be fixed onto the surface. One way of generating such layers is the application of surface treatments with CO2-lasers. The selection of the hard particles as well as the process control is furthermore dependent on the boundary conditions like chemical resistivity, desired layer thickness, maximum lagging and price. The generation and deposition of hard phases is possible by a dispersion of additives into the melt, by forming a hard phase in the pool or by their precipitation, respectively. In the present paper examples are outlined and some of the current problems are discussed.

There is significant industrial interest in methods to improve the surface properties of cast iron. This paper describes investigations of laser treatments to enhance cast iron surfaces by alloying with the elements chromium, nickel or cobalt, or a cobalt/chromium mixture. The coatings achieved are of high integrity, low porosity and uniform in composition, microstructure and hardness. Alloyed surfaces have been subjected to corrosion testing in a range of acids and to wear and cavitation erosion in distilled and salt waters. The data show substantial improvements over those obtained from unalloyed material. Results are presented and discussed including the response of the microstructure to the testing environments.

The melting of sandcast and chillcast A1Si1OMg alloys with CO laser radiation is investigated as a function of processing variables to improve tñe surface properties with respect to wear resistance by self-quenching and rapid solidification. To overcome the high reflectivity of aluminium alloys graphite coatings were used to increase the energy coupling. In order to avoid any chemical reactions with the amblent, shielding gases such as C02, He, Ar and N2 have been used. The results of microstructural refinement are discussed in view of processing variables, melt dynamics, improvement in wear and efficiency of energy coupling in combination with calculations of the processing geometry via diffusive and convective heat transfer.

For many years the C02-Iaser is the most common laser in materials processing. However, in recent years new technologies require lasers which are most suitable for a specific task. In a feasibility study the authors investigated metal processing with Copper vapor lasers. The lasers used had a repetition rate of 7kHz and an output power of 4W and 23W, respectively. It was found that the surface could be modified in a similar manner as it is known from the Excimer laser processing. In the paper the authors present preliminary results of the beam/ substrate interaction and the observed drilling velocity for different substrates. Narrow holes with a diameter to width ratio of about 1:30 could be drilled.

The problem of determining stresses, phase compositions and temperature distributions during the transformation hardening of steel with a CO-laser beam is investigated. To model the different phases in each material point a parallel fraction model is used, in which each fraction represents one phase. The description of phase transformations is obtained by an incremental formulation of the Avrami-equation for isothermal transformation. A model is developed to describe the superheating of ferrite and pearlite. The model is demonstrated by a detailed computation of stresses, deformations and phase compositions in the case of a stationary laser flash.

The stationary energy current density associated with the transmission of light through a metal-vacuum surface is analysed. Combining the Maxwell equations and Boltzmann's transport equation, a generalized Poynting vector of the coupled system of light and conduction electrons is obtained. Within the framework of nonlocal optics, the structure of the electromagnetic and material parts of the Poynting vector is investigated. Dividing the electric field into divergence-free (T) and rotational-free (L) parts, explicit expressions are derived for the o-ca1led TT and TL-parts of the electromagnetic Poynting vector, and for the TT, TL, and LL-parts of the Poynting vector associated with the kinetic energy flow in the electron system. Analytical expressions are derived for the third rank nonlinear response tensor describing the kinetic energy flow for oblique incident light. Special emphasis is devoted to a study of the contributions to the energy current density from collective plasmon and polariton excitations in the frequency range between the longitudinal and transverse plasma edges. A comparison of the present work with previous ones based on the so-called hydrodynamic description is given.

The absorption coefficient of the C02 laser light has been measured when metallic target of steel (35 NCD 16) and pure iron are irradiated with laser intensities varying from i03 to lO7Watt/cm 2 with helium gas shielding. The diagnostic used consists of an integrating sphere which collects all the laser light reflected by the target. This set-up allows a temporal resolution of this measurement of about 0. 1 ms. As the laser intensity increases, a clear correlation between the time-dependance of the increase of absorption and of the appearance of the plasma luminosity is evidenced. For higher intensities, when a keyhole regime is reached, this correlation disappears and the absorption reaches 95 %. This very high level of absorption is interpreted as a result of the geometrical trapping of the laser light inside the keyhole and a low contribution of plasma plume absorption to this process.

This paper presents an upgrading technique using anisotropic-resistive (AR) electrodes and radionucide pre-ionization for discharge pumping of pulsed high-pressure gas lasers. Plutonium-238, polonium-210 and krypton-85 radionucide alpha and beta radiation sources were effectivelyused for pre-ionization in the volumetric discharge setup. These sources feature high stability, versatility and simplicity as compared to traditional UV irradiation and electron beam ionization techniques. The use of AR electrodes makes it possible to suppress efficiently electrode instabilities in volumetric discharges with various power modes of operation and to increase energy input in an active medium by a factor of 2-3 due to extended discharge duration in the volumetric phase. With the use of the AR cathode as an alternative to a metal one, a commercially available photo-ionization 2 laser gained two-fold increase in generation energy. It also showed a stable operation of the volumetric discharge in Ar, Kr, Xe mixtures with He at atmospheric pressure and allowed us to obtain generation in An, Kr!, Xe! spectral lines.

An investigation was made determining the parameters affecting the phase conjugate reflectivity in a four-wave mixing scheme using a pulsed TEA CO2 laser and gaseous sulfur hexafluoride (SF6) as the nonlinear medium. With a low energy CO2 laser (60 mJ pulse energy) an optimum energy reflectivity of 20 % was achieved at a pump-probe angle of 30 mrad, a SF6 pressure of 50 hPa at the lOiim P(1O) laser transition for exactly aligned counterpropagating pump waves. In addition, the reflectivity showed a substructure when enlarging the angular mismatch between the pump waves. A simulation of the phase conjugate intensity distribution was carried out solving the Kirchhoff- Fresnel integral equation.

A new class of compact C02-lasers in the kilowatt range uses radial compressors for circulating the laser gas through resonator and laser head 1 , The highest degree of a compact, modular design is achieved when the turbo blower is integrated directly into the laser head 2 At the Technologie Zentrum Nord a prototype of a new compact C02-laser with 2.5 kW CW-output power and a volume of only 0.6 m3 has been developped in the past two years . The results of our work reveal the necessity of a special design of the laser head when using turbo blowers in fast axial flow, rf-excited C02-lasers. First it is obviously appropriate to integrate the blower into the laser head, and second, the gas flow has to be optimized by specially shaped parts in the laser head to reduce pressure losses. Further we report on the performance of the turbo compressor with different gas mixtures, derived from measuring gas velocities and mass flow rates. These results are correlated to laser output power and efficiency. Cw output power of more than 2.5 kW has been achieved with our laboratory prototype. Efficiencies between 18% and 23% have been measured for the pumping process.

The computer information system combines the features of a data base management system (DBMS), some artificial intelligent (A.I.) techniques and the computer language C into one integrated system capable of handling a variety of data and knowledge types available in the area of laser materials processing (LMP). Experimental data and general guideline data and knowledge are stored in data bases using the DBMS. Models for parameter prediction and process simulation are implemented in the computer language C. Some heuristic reasoning rules are implemented to handle the searching of general knowledge and experimental data from the data bases. A so-called "control center", which is implemented in Prolog, functions as a shell, providing an interactive user environment and guiding the user in accessing different parts of the system.