Fast Axial Flow Research Articles

1.5 kW radially polarized beam irradiated from a FAF CO2 laser based on an intracavity triple-axicon retroreflector and quarter wave phase retarders.

In this paper, a three folds spatial resonator composed of a triple-axicon retroreflector and four pieces of quarter wave phase retarder is demonstrated to directly output radially polarized beams in a fast axial flow (FAF) CO2 laser system. The triple-axicon retroreflector serves as the azimuthally polarized beams' selective element, and the quarter wave phase retarders convert the azimuthally polarized beams to radially polarized beams. Finally, a stable 1.5 kW radially polarized beam is generated in this laser system.

Vectorial eigenvector method for simulating the polarization dependent resonator.

Derived from the eigenvector method (EM), a vectorial eigenvector method (VEM) for the mode calculation of polarization dependent resonator is presented. New transfer matrices of laser resonant cavities with polarization-selective devices are built by using Jones matrix representation. The eigenvectors computed by solving the matrix eigenequation manifest the mode characteristics of resonators, including cylindrical vector (CV) modes. Comparing with EM, the VEM inherits EM's superiorities and extends scalar models to vector models. Then, an example utilizing VEM to simulate axicon mirror resonator was given, which proved the VEM feasible and efficacious. Finally, upon a fast axial flow (FAT) CO2 laser with an axicon mirror as rear mirror, we experimentally corroborated the validity of the VEM and a working-stable 1.5 kW radially polarized beam was obtained.

Generation of azimuthally polarized beams in fast axial flow CO2 laser with hybrid circular subwavelength grating mirror

A hybrid circular subwavelength grating mirror is proposed and fabricated as a rear mirror in a fast axial flow CO2 laser system to generate azimuthally polarized beams (APBs). This grating mirror, with particular gold-covered ridges and nanopillar-stuffed grooves, performs wideband TE wave reflectivity and high polarization selectivity. It shows that the polarization selectivity mechanism lies in the gold ridge's high reflectivity to the TE wave and the lower TM wave reflectivity, which are the result of the mode leaking into substrate through the dielectric-like nanopillar layer. Finally, a high-quality 550 W APB is obtained in subsequent experiments, which provides potential applications in drilling and welding.

Impedance matching in RF excited fast axial flow CO2 laser: The role of the capacitance due to laser head

Impedance matching in an indigenously developed 2kW RF-excited fast axial flow (RF-FAF) CO2 laser was seen to be significantly influenced by the capacitance formed between the laser head and the electrodes. We find in the published literature that this capacitance is generally assumed to be negligible while designing the matching network in the RF-FAF CO2 lasers. It is shown that this capacitance could have a significant value and consequently would modify the design of the matching network remarkably for a specific laser design studied in the present case. The widely used discharge load model for capacitively coupled RF (CCRF) discharge excited CO2 laser plasma is extended to include this capacitance. The method of measurement of this capacitance using a bridge and the ANSYS software based simulation of its formation due to the laser head structure are discussed.

Formation of transverse mode in axially symmetric lasers

The developed iteration algorithm for simulation of lasers with an open resonator was employed in the study of transverse mode formation. The simulations of an axially symmetrical resonator rely on an analytical description of radiation diffraction from a narrow ring. Reflection of an incident wave with a specified amplitude-phase distribution from the mirror is calculated by the Green-function method. The model also includes an active medium homogeneous along the resonator axis that is represented by the formula for saturating gain. The calculations were performed for two types of lasers: with on-axis and off-axis gain maximum. In the first type of laser one can obtain either a principal mode or "multimode" generation. The latter means quasi-stationary generation with regular or chaotic oscillations. In the second type of laser high order single-mode generation is possible. Experimental results obtained on a fast axial flow 4 kW CO(2) laser are also presented. They are in good agreement with the calculations.

Optimization of gas pressures ratio in a fast-axial-flow CO2 laser with genetic algorithm

In this paper, the laser output power of a fast-axial flow CO2 laser was optimized with gas pressures ratio of CO2:N2:He using a genetic algorithm technique. The power of laser was increased from 500W (un-optimized case) to 2200W (simulated case), also experimentally the power has achieved the value of 700W (optimized case).

Effect of argon on the performance of a fast-axial flow CO2 laser

The performance characteristics of a fast-axial flow (FAF) cw CO2 laser are described. The dependences of the output power, efficiency, and discharge voltage on the discharge current of a FAF cw CO2 laser with optimised composition of the CO2:N2:He=1:4.4:7.6 gas mixture with a small amount of argon are studied experimentally at two pressures of 50 and 60 mbar in open and closed cycle regimes of the laser system.

单折叠腔轴快流CO2激光器双折反镜结构方案设计

单折叠腔轴快流CO₂激光器双折反镜结构方案设计

高功率轴快流CO2激光器气体循环系统的研究进展

高功率轴快流CO₂激光器气体循环系统的研究进展

高功率轴快流CO2激光器的流体动力学模拟

To increase the photoelectronic conversion efficiency of the single discharge tube and to meet the requirements of the laser cutting system, optimization of the discharge tube structure and gas flow field is necessary. We present a computational fluid dynamic model to predict the gas flow characteristics of high-power fast-axial flow CO2 laser. A set of differential equations is used to describe the operation of the laser. Gas flow characteristics, are calculated. The effects of gas velocity and turbulence intensity on discharge stability are studied. Computational results are compared with experimental values, and a good agreement is observed. The method presented and the results obtained can make the design process more efficient.

Indigenous development of a 2 kW RF-excited fast axial flow CO2 laser

RF-excited fast axial flow CO2 lasers in kilowatt regime are presently being used for various new scientific applications in addition to laser material processing because of its versatility and superior beam quality. We have indigenously developed a compact 2 kW RF-excited fast axial flow CO2 laser with moderate beam quality. In this paper the key design features of the laser and the associated high power capacitively coupled RF excitation technique are discussed in detail. Operational characteristics of this system are described along with the experimental findings.

Gas laser for efficient sustaining a continuous optical discharge plasma in scientific and technological applications

A stable high-power laser is developed for the study and technical applications of a continuous optical discharge (COD). The laser based on the technology of a combined discharge in a scheme with a fast axial gas flow emits 2.2 kW at 10.6 μm per meter of the active medium in continuous and repetitively pulsed regimes with the electrooptical efficiency 20%. The sustaining of the COD plasma in argon and air is demonstrated at the atmospheric pressure. The emission properties of the COD plasma are studied and its possible applications are discussed.

Optimization of the operational parameters in a fast axial flow CW CO 2 laser using artificial neural networks and genetic algorithms

This paper presents an artificial intelligence approach for optimization of the operational parameters such as gas pressure ratio and discharge current in a fast-axial-flow CW CO 2 laser by coupling artificial neural networks and genetic algorithm. First, a series of experiments were used as the learning data for artificial neural networks. The best-trained network was connected to genetic algorithm as a fitness function to find the optimum parameters. After the optimization, the calculated laser power increases by 33% and the measured value increases by 21% in an experiment as compared to a non-optimized case.

Disk Lasers Enable Industrial Manufacturing – What Was Achieved and What Are the Limits?

AbstractIn the past few years, CO2 lasers as well as lamp‐pumped solid‐state lasers have become established solutions for industrial cutting and welding applications. Due to its high beam quality and output powers up to 20 kW the RF excited fast axial flow CO2 laser has enabled the largest single laser application in the world: Cutting of steel up to one inch thickness. So far, these lasers are also the preferred industrial choice for deep penetration welding of thick plate and narrow seam geometries.

Numerical modeling of a fast-axial-flow CW–CO 2 laser

A four-temperature model has been applied on a fast axial flow, longitudinal discharge CO 2 laser. Using Runge–Kutta method, a set of differential equations of the model is numericaly solved. These equations describe the operation of the laser with certain ratio 1:3:6 of the mixture CO 2:N 2: He and average output power of 550 W. The temporal behaviour of the output power and photon density was obtained. The effects of kinetic temperature, coupled mirror reflectivity, gas flow speed, and cavity loss on the output power were studied. Calculated output power was compared with its measured value taken from experiment and a good agreement was observed.

High frequency pulser-sustainer for preionization in dc excited continuous wave CO2 lasers

Slow flow diffusion cooled CO2 lasers mostly use dc electrical discharge for excitation. Preionization in the discharge tubes of such a laser helps to initiate and maintain the dc discharge at voltages below breakdown voltage. A high frequency pulser using an insulated gate bipolar transistor as switching device is developed for preionization of the 20 discharge tubes of the 1 kW multibeam CO2 laser that we have developed. This pulser produces positive pulses of 10 kV peak voltages; frequency variable from 1 to 5 kHz and its pulse width is variable from 1 to 10 μs. The rise time of the pulses is between 600 and 700 ns. Preionization allows dc discharge excitation simultaneously in all discharge tubes of the multibeam CO2 laser even at high operating pressures. Other advantages of the preionization technique, such as the discharge stability at lower discharge currents with lower ballast resistance and the shorter inactive zone in the discharge tubes, are discussed. This pulser can also be used with dc excited fast axial flow CO2 lasers and other discharge devices.

Microstructure and microhardness study of laser bent Al-2024-T3

Microstructure and microhardness profile of laser bent AA 2024-T3 sheets were obtained to determine the effects of such a process on this material. A fast-axial flow CO2 laser unit (TEM00) was used at 250, 500, and 800 W continuous wave to bend the samples; scanning velocities ranged from 10 to 80 mm/s while laser spot diameters used were 1, 5, and 10 mm. Characterization techniques included light microscopy, scanning electron microscopy, and Vickers microhardness. Laser bending process variables were arranged into a parameter called accumulated energy density (AED) in J/mm2. Light microscopy observations and microhardness results revealed that there was no damage to the microstructure for AED values less than 25 J/mm2. At these AED values, the microhardness level across the depth is closer to the average value of the as-received material (150.9+/−2.7 Hv). However, some AED values resulted in samples with microhardness above and below that number. Higher microhardness levels were attributed to a small grain size and a localized T6 temper while the lower values were associated with grain growth. For AED values between 25 and 125 J/mm2 subgrain structures and dispersoids at grain boundaries were observed under scanning electron microscopy. Partial melting at recrystallized grain boundaries was the principal form of damage. Remelting of the upper region of the sheet underneath the alclad layer took place leaving a cast structure. For AED values of 125 and 250 J/mm2, the alclad layer fused to the substrate. For AED values that caused partial melting and a considerable fusion drop in the microhardness value was observed.

Experimental Verification of Revised Roles Played by Helium and Nitrogen in CO2 Lasers

In one of our previous papers we presented a fast axial flow CO2 laser excited by 150 kHz resonant silent discharge. The optimized gas mixing ratio of this setup was CO2 : N2 : He = 1 : 22 : 5. This ratio was very peculiar but the laser efficiency thus achieved was optimized and comparable to that of other fast axial flow CO2 lasers. We have already put forth some preliminary postulations explaining the reason for this particular result; nevertheless in order to obtain a clearer insight into this laser we designed and carried out a series of experiments. The data collected were helpful for understanding why N2 is more important than He, and what roles they play in such a laser system.

A new helical coupling microwave antenna excited high-power CO/sub 2/ laser using a cylindrical resonant cavity

A new helical coupling antenna which was installed into a cylindrical microwave cavity (2.45 GHz) has been investigated to obtain high-power CO/sub 2/ laser operation. Laser experiments using a system of swirling fast axial gas flow parallel to the beam have been performed. The geometric properties of the helical antenna and the gas flow structures were optimized by using numerical codes analyzing the electric fields and gas flow dynamics. The swirling flow of the laser gas mixtures of CO/sub 2/-N/sub 2/-He=0.7-5-19 was caused in the discharge tube by an 8-slit nozzle. It is shown that the electric field obtained by the proper design of the helical coupling coil yields homogeneous discharges. The maximum output power and the efficiency (RF to laser power conversion ratio) was obtained as 1010 W and 15%, respectively, at a gas pressure of 45 torr and a gas flow rate of 57 kg/h.

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.