High-power multibeam CO2 laser for industrial applications

Multibeam CO₂ lasers consist of a large number of closely packed parallel glass discharge tubes, all sharing a common plane parallel resonator. This paper describes construction and operation of a CW multibeam CO₂ laser consisting 20 discharge tubes and cooled length of 1500 mm, delivering 1 kW power. A high-frequency pulser is used for producing preionization in all discharge sections for initiating the main DC discharge simultaneously in all discharge tubes. Plane parallel resonator consists of a plane ZnSe mirror of 90 mm diameter having 60% reflectivity and a gold-coated copper mirror of same diameter. This laser operates in waveguide regime and laser power is not critically sensitive to mirror misalignment.     

High-power transverse flow CW CO2 laser for material processing applications

A transverse flow transversely excited (TFTE) CW CO₂ with a maximum output power about 15 kW has been developed. This is excited by pulser sustained DC discharge applied between a pair of multi-pins anodes and a common tubular cathode. Though the laser power in convective cooled CO₂ laser scales proportionally with the volumetric gas flow, it did not increase in this laser when the volumetric gas flow was increased by increasing the electrode separation keeping the flow velocity constant. The discharge voltage too remained almost unchanged with increase of the electrode separation. These observations are explained considering the electrical discharge being controlled by ionization instability. Laser materials processing applications often demand programming facilities for laser power modulation. A four-stage cascaded multilevel DC–DC converter-based high-frequency switch mode power supply has been developed to modulate the output power of the laser. Laser was operated up to 15 kW output power in four different modes viz. continuous wave mode, pulse periodic mode, single shot mode and processing velocity-dependent power mode with 1.2 kHz modulation bandwidth. We describe briefly the laser system, the SMPS, and the temporal behavior of laser beam.     

Design considerations and scaling laws for high power convective cooled CW CO2 lasers

Various criteria for designing high power convective cooled CO₂ lasers have been discussed. Considering the saturation intensity, optical damage threshold of the optical resonator components and the small-signal gain, the scaling laws for designing high power CW CO₂ lasers have been established. In transverse flow CO₂ lasers having discharge of square cross-section, the discharge lengthL and its widthW for a specific laser powerP (Watt) and gas flow velocityV (cm/s) can be given byL = 1.4 x 10⁴ p ^1/2 V ^-1 cms andW = 0.04P ^1/2 cms. The optimum transmitivity of the output coupler is found to be almost constant (about 60%), independent of the small signal gain and laser power. In fast axial flow CO₂ lasers the gas flow should be divided into several discharge tubes to maintain the flow velocity within sonic limit. The discharge length in this type of laser does not depend explicitly on the laser power, instead it depends on the input power density in the discharge and the gas flow velocity. Various considerations for ensuring better laser beam quality are also discussed.     

Theoretical prediction on the wavelength-temperature shift in pulsed TE CO2 lasers

The wavelength-temperature shift observed in pulsed TE CO₂ lasers is discussed theoretically by means of Six-temperature model rate equations for tunable TE CO₂ lasers. Numerical calculations of the temperature-wavelength shift in a pulsed TE CO₂ laser with a simple plano-concave stable resonator, whether excited by conventional low-inductance fast-discharge scheme or by a long-pulse Pulser/sustainer discharge scheme, show that the laser output wavelengths are within the 10P branch as the ambient temperature varies from 228 to 338 K, but will change as the ambient temperature varies. The laser output wavelengths will move to the transition lines with longer wavelengths in the 10P branch as the ambient temperature increases and vice versa. The calculated results also illustrate that near the ambient temperature of 310 K, the laser is more likely to operate on multi-transition lines. Considering this wavelength-temperature shift, the chilling device adopted in high-power high repetition rate TE CO₂ lasers is important in maintaining a stable laser output spectra as well as a stable laser output power. The numerical results also suggest that a frequency agile resonator is highly recommended if stable laser output spectra are required in TE CO₂ lasers.     

Diffractive scanning mechanism for laser marker

We present a new idea of marking based on spectral properties of CO₂ laser radiation. The idea has been illustrated on RF excited waveguide CO₂ lasers in different configurations: single channel, multi-waveguide and slab-waveguide ones. The pulse operation of the laser has been considered as well. The advantage of the presented diffraction marker is avoiding complicated and fallible mechanical elements. The only executive elements of the marker are a diffraction grating and a piezoceramic transducer. It has been shown that the slab-waveguide configuration of the RF excited CO₂ laser equipped with an unstable resonator is the most promising configuration for application to the diffraction marker.     

Angular spectrum theory to calculate coupling efficiency in rectangular waveguide resonators

Coupling efficiency of the rectangular waveguide resonators are discussed in terms of the method of angular spectrum theory. Under the condition given in the paper, the coupling coefficients for the EH₁₁ mode in the rectangular waveguide resonator are presented as a function of mirror curvature and position. It is shown that there exist two special geometries to provide low coupling efficiency. The method can be applied to the other modes.     

Optical resonator for high-power transverse flow CO2 lasers

A new design of the U-type resonator is described. In this way, a laser beam with symmetrical intensity profile (regarding to a symmetry plane) can be extracted from an active medium that exhibits gain asymmetry along one of the transverse directions. The whole area of the active medium cross-section can be used, and consequently the laser efficiency will be increased. This resonator structure was applied for efficiency power extraction (as a low order TEM modes laser beam) from a DC excited transverse flow CO₂ laser with cylindrical geometry. Although the cross-section area of the discharge was entirely used (including the cathode fall region), a symmetrical intensity profile of the laser beam (regarding to the two orthogonal symmetry planes) was obtained in the near field as well as in the far field; the gain asymmetry along the flow direction was compensated by the gas circulation fluidodynamical circuit with two counterflowing discharge channels. A double-U optical resonator was introduced in order to provide a laser beam with axial symmetry.For the practical construction of these two types of optical resonators we have developed two new types of 90° deflection elements: the first one, which does not reverse the image (and which has the properties of the pentaprism), and the second one, which rotates the image with 90° angle. Both elements exhibit good focusability if they are equipped with two concave mirrors.     

Mode structure of hollow dielectric waveguide lasers

The mode structure of hollow dielectric waveguide lasers with free space sections and flat mirrors is studied theoretically and experimentally. The study covers the fundamental mode and the three most important higher order modes, and graphs are given which identify regions of high mode discrimination in the parameter space. Calculated coupling losses are verified experimentally by detailed studies of the output power of CO₂ lasers as a function of resonator geometry. The intensity profile inside and outside the resonator is calculated, and the profile outside the resonator is compared with experiments for the fundamental mode as well as for the higher order modes. It is shown that in general the fundamental mode is non-Gaussian, and that drastically different output characteristics are obtained for different choice of output plane. The paper identifies design criteria for obtaining single line and single mode oscillation over a wide tuning range, even in the densest region of the CO₂ laser line spectrum, and this is exemplified by a spectroscopic application.Supported by the Danish Science Research Councils under grants no. 5.17.4.6.19 and 5.17.4.1.23 and by FLS airloq     

Theoretical and experimental investigation of a waveguide CO2 laser with radio-frequency excitation

A comprehensive experimental and theoretical study of the optimization of a continuous-wave radiofrequency (rf) excited CO₂ waveguide laser is presented. The numerical simulation includes the modelling of the gas-discharge plasma parameters like the plasma impedance and energy deposition, the laser kinetics and finally the influence of the resonator feedback on the lasing process. Along with this theoretical study, an extensive experimental research program enabled us to optimize the laser performance of the CO₂ waveguide laser. As a result, a total output power of 42 W and a specific output power of 1.1 W/cm were obtained.     

An efficient,RF excited,waveguide CO2 laser

A CW waveguide CO₂ laser excited by a transverse radiofrequency discharge is described. An efficiency of 8.5% (laser power/RF power from supply) has been achieved and an output power of up to 4.6 W.     

Design and experimental characterisation of a DC-excited CW/repetitively pulsed sealed off CO2 laser

This paper reports the design procedure and experimental study of a sealed off CO₂ laser. Simple algorithms for threshold and steady state excitation voltage calculation, resonator design and its temperature dependent operation are presented. The sealed off CO₂ laser was operated both in CW and pulsed modes and found stable both thermodynamically and optically. Frequency limits for pulsed operation regarding maximum and minimum output energy ranges are determined. Different aspects of CO₂ laser studied include threshold excitation voltages, temperature dependent efficiency, optical power saturation limitations, pulsed and steady state discharge currents for optimum gases mixture combinations. The laser has successfully been constructed, operated and tested for different applications within the limits of its maximum output power of 14 W.     

Operational characteristics and power scaling of a transverse flow transversely excited CW CO<Subscript>2</Subscript> laser

Transverse flow transversely excited (TFTE) CO₂ lasers are easily scalable to multikilowatt level. The laser power can be scaled up by increasing the volumetric gas flow and discharge volume. It was observed in a TFTE CW CO₂ laser having single row of pins as an anode and tubular cathode that the laser power was not increasing when the discharge volume and the gas volumetric flow were increased by increasing the electrode separation keeping the gas flow velocity constant. The discharge voltage too remained almost constant with the change of electrode separation at the same gas flow velocity. This necessitated revision of the scaling laws for designing this type of high power CO₂ laser. Experimental results of laser performance for different electrode separations are discussed and the modifications in the scaling laws are presented.     

Design of CW High-Power Discharge-Pumped DCN Laser

This paper describes a CW sub-millimeter waveguide dischargepumped DCN laser operating on 190 and 195 mu m lines. The laser discharge length is 3 m, and the resonator length is 3.4 m. The resonator cavity consists of a pyrex tube of 54 mm diameter and two plane reflectors against its ends, one is a plane mirror, the other is a metal mesh. After optimization of various parameters, such as the N₂:CD₄:He gas mixture, the pressure and the discharge current, the wall temperature and the output couple, this laser delivers 200 and 220mW on the 190 and 195 mu m lines, respectively, for EH₁₁ mode.     

A waveguide CO2 laser operating in a Gaussian mode: Experimental analysis

An experimental analysis of the dielectric waveguide laser modes has been carried out and it has been shown that the maximum power output is related to the EH₁₁ or TEM₀₀ mode oscillation. Gaussian mode operation is discussed and practical consequences of this type of operation are demonstrated.     

封离式He-N$lt;sub$gt;2$lt;/sub$gt;-CO$lt;sub$gt;2$lt;/sub$gt;激光器横模特性的测量与分析

利用激光光束分析仪,实时在线测量了一根He-N₂-CO₂封离式激光管的横模分布特性,得到了激光模式随放电电流的变化关系.实验表明该激光器在最佳工作电流时,容易形成低阶模运转,但很难获得基模运转,通过改善对称性以及加快冷却水流速可以获得基模运转.通过激光动力学过程分析了模式变化的形成原因,为大功率激光器模式控制与改善提供了一定的理论和实验借鉴. 关键词： 2激光')" href="#">CO₂激光 横模 激光模式分析 光束质量     

Study of a Waveguide CO_2 Laser with Two Parallel Tubes

ＳｔｕｄｙｏｆａＷａｖｅｇｕｉｄｅＣＯ２ＬａｓｅｒｗｉｔｈＴｗｏＰａｒａｌｅｌＴｕｂｅｓＨＵＡＮＧＹｕａｎｇｑｉｎｇ（Ｄｅｐｔ．ｏｆＳｃｉ．Ｉｎｓｔｒ．ａｎｄＰｒｅｃｉｓｉｏｎＭｅｃｈ．ｏｆＸｉａｍｅｎＵｎｉｖ．，Ｘｉａｍｅｎ，３６１００５，Ｃｈｉｎ...     

A new grating tuning compound unstable resonator

A proposal of new grating tuning compound unstable resonator is presented. This new type of unstable resonator is profitable for generating single transverse mode, high energy, high-average power tunable laser radiation from TEA CO₂ laser and other gas lasers.     

A CW DCN waveguide laser of high volumetric efficiency

This paper describes a CW submillimeter waveguide laser operating on 190 and 195 μm DCN lines with high volumetric efficiency. The laser cavity is a 3.2 cm inner diameter, 70 cm long, Pyrex tube with plane reflectors (one of them is a copper mesh) against its ends. After optimization of various parameters (such as the N₂:CD₄:He gas mixture, the pressure and the discharge current, the wall temperature and the output coupling), this laser, with only 57 cm long active discharge, delivers 8.4 and 7.6 mW on the 190 and 195 μm lines, respectively, for the EH₁₁ mode. This represents volumetric powers of 75 and 65 μW cm^-3. The free space propagation of the EH₁₁ fundamental mode was found to be as for a gaussian beam, and the absorption of the laser beam in the atmosphere was also measured.     

Theory of a waveguide laser

The role of diffusion of the components of the gas mixture is the generation mechanism of a waveguide CO₂ laser is analyzed. A method is proposed for reducing the multicomponent problem of linear diffusion with dissipation to a one-component problem. The superposition of relaxation modes for a cylindrical waveguide is considered. The diffusion contribution to the loss of electromagnetic energy is estimated for the case of the field hybrid mode EH₁₁ of a dielectric waveguide. The rapid increase in the loss for a SiO₂ waveguide tube and the observation of the filtration properties of the laser in conditions when the diffusion is taken into account are noted.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 17–21, July, 1975.