Slab CO2 lasers excited by switching power

In this paper we present a new discharge technique to excite slab CO₂ lasers. A uniform stable glow discharge has been obtained in a volume of 3 × 30 × 446 mm³. Output power is 10 W, and a gain of 0.26% cm⁻¹ has been obtained.     

CO2 laser cutting of slate

Slate is a natural stone which has the characteristic that shows a well-developed defoliation plane, allowing to easily split it in plates parallel to that plane which are particularly used as tiles for roof building. At present, the manufacturing of slate is mostly manual, being noisy, powdery and unsafe for the worker. Thus, there is a need to introduce new processing methods in order to improve both the working conditions and the quality of the products made of slate.Following the previous work focused on the drilling and cutting of slate tiles using a Nd : YAG laser, we present in this paper the results of the work carried out to explore the possibilities to cut slate plates by using a CO₂ laser. A 1.5 kW CO₂ laser was used to perform different experiments in which, the influence of some processing parameters (average power, assist gas pressure) on the geometry and quality of the cut was studied. The results obtained show that the CO₂ laser is a feasible tool for a successful cutting of slate.     

In-process high power CO2 laser beam position sensing

The case for in-process sensing is one of the strengths of laser materials processing, both in the variety of signals obtainable from the process and the range of techniques for beam guidance. It is known that beam/nozzle alignment is of importance for high quality laser cutting. Thus, an in-process beam position sensing system was devised in this study as one of the potential tools for automation of the cutting process. Further, if the beam could be stabilized at a given location automatically this would be equivalent to relocating the laser beam. Laser beam position sensing is the first step towards this goal. The aim of this study is to create a beam position sensing system. This work presents a new approach using a rotating slit, a focusing lens and a photodetector. An automatic alignment procedure is also investigated.     

On the modelling of the power extraction problem from a gas-dynamic CO2 laser considering the variations of intensity

In this paper a new simple model for investigation of the power extraction process from a gas-dynamic laser (GDL) is presented. This analysis consists of a numerical solution of non-equilibrium supersonic flow in the laser cavity and, simultaneously, point-by-point numerical integration of the laser intensity in the beam direction. The simplest cavity, that is a Fabry-Perot with parallel mirrors, is used. This model gives the variation of intensity in the flow direction, without any specific assumptions. The behaviours of all interesting quantities are obtained and compared with other existing models.     

Pulse behaviour of a compact RF discharged CO2 slab laser

We present the measurements made on a medium power, 35 cm long, radio-frequency discharge CO₂ slab laser operated in a pulsed regime obtained by switching the RF discharge. In this way, pulses with peak power up to 480 W at pulse repetition frequencies in the range 1 to 10 kHz have been obtained. Pulse energy and average extracted power have been experimentally characterized with respect to the pulse repetition frequency and to the pulse duration, and the pulse shape and characteristic times have been measured. We also investigated the propagation properties of the beam emerging from our laser.     

Thermal processes taking place in the bone during CO2 laser irradiation

The present study examines the drilling and heating of a bone due to pulsed CO₂ laser irradiation. To obtain temperature profiles inside and at the surface of the bone, electron-kinetic and Fourier theories are used. The study is extended to include an experimental investigation into the measurement of the penetration speed. This is achieved using a fibre-optic system. In order to reduce the degree of burning around the hole side, helium was used as the assisting gas during drilling. It is found that the penetration speeds predicted from the theory are in good agreement with the experimentally obtained values.     

Short single-mode CO2 laser pulse generation by pulsed Q-switching

A simple method for the generation of short, single-mode CO₂ laser pulses produced by applying two voltage gates (of amplitude 3U_λ/4 and U_λ/4) to an electro-optic Q-switch placed in a three-mirror cavity is proposed. Single, single-mode, well-synchronizable pulses of 3 ns duration and of 3 mJ energy have been experimentally achieved from a TEA CO₂ laser with an intracavity Pockels cell with 3 ns switching time. Using a numerical simulation it is shown that with shorter switching time (≈1 ns) the method enables one to obtain, from such a laser, a single, megawatt pulse of 1 ns duration.     

A compact TEA CO2 laser for field-based spectrochemical analysis of geological samples

A compact capacitor-transfer TEA CO₂ laser of 180 mJ output energy and 50 ns pulse duration in half width was designed and constructed for field use. This laser is suitable for laser microprobe spectrochemical analysis on geological and mining samples. Experiments show that the use of helium as a surrounding gas suppresses the continuous emission spectrum of the plasma, thus increasing the S/N ratio. Using glass as standard samples, the minimum detectable concentrations are estimated with Zn neutral line and F ionic line to be 60 ppm and 500 ppm, respectively.     

Gain and saturation intensity parameters in a transverse-flow CO2 laser

Details of an experimental investigation of the output characteristics of the 1.2 kW cw transverse-flow, electrically excited CO₂ laser are presented. They were used for estimation of the saturation intensity and the laser cavity loss values, as they follow from the Rigrod-type model of laser operation. The saturation intensity parameter was calculated from measurements of the output power and small signal gain performed with the same experimental conditions. Measurements of the small signal gain were conducted at different points along the gas flow direction for several laser operational parameters described by gas pressure and input electrical power.     

Spectroscopic comparison of aluminium welding plasmas produced by high power CO and CO2 lasers

Welding tests on the aluminium alloy AlMgSi1 (6082) by the use of a high power CO laser with good beam quality show higher penetration depths and better weld seam quality compared with the results obtained with a commercial industrial CO₂ laser. Spectroscopy of the laser-induced welding plasma shows a strong decrease of the intensities of Al(II) lines and no appearance of Al(III) lines in CO laser aluminium welding compared with CO₂ laser welding at the same process parameters. This is a consequence of the shorter 5 to 5.6 μm wavelength of the CO laser leading to reduced beam-plasma interaction.     

Collimation testing of a CO2 laser beam with a shearing interferometer

A shearing interferometer based on a Michelson interferometer is proposed for collimation testing of a CO₂ laser beam. The shear and tilt between the interfering wavefronts is obtained by replacing one or both mirrors of the Michelson interferometer with double mirrors arranged to act as 90 ° or near 90 ° prisms in retroreflecting mode. Detailed analysis for two experimental configurations of this system are presented.     

A power ramped pulsed mode laser piercing technique for improved CO2 laser profile cutting

Laser piercing is one of the inevitable requirements of laser profile cutting process and it has a direct bearing on the quality of the laser cut profiles. We have developed a novel power ramped pulsed mode (PRPM) laser piercing technique to produce much finer pierced holes and to achieve a better control on the process parameters compared to the existing methodology based on normal pulsed mode (NPM). Experiments were carried out with both PRPM and NPM laser piercing on 1.5-mm-thick mild steel using an in-house developed high-power transverse flow continuous wave (CW)-CO₂ laser. Significant improvements in the spatter, circularity of the pierced hole and reproducibility were achieved through the PRPM technique. We studied, in detail, the dynamics of processes involved in PRPM laser piercing and compared that with those of the NPM piercing.     

Surface roughness analysis and improvement of PMMA-based microfluidic chip chambers by CO2 laser cutting

For the microfluidic chip, the surface roughness of the chamber sidewall is an important parameter in estimating its quality. In this work, the chambers of the polymethyl methacrylate (PMMA)-based microfluidic chip were fabricated by CO₂ laser cutting, and then the surface roughness of the sections cut using different laser parameters and ambient temperature was studied by a non-contact 3D surface profiler. Our observation shows that the surface roughness results primarily from the residues on the laser-cut edge, which are produced by the bubbles bursting. To reduce the surface roughness of the cut section, a new approach is proposed, that is preheating the PMMA sheet to a suitable ambient temperature during laser processing. The results indicate that at a preheat temperature of 70-90 °C, the surface roughness resulting from the cut would be reduced. In our experiment, the best result was that the arithmetical mean roughness is R_a = 100.86 nm when the PMMA sheet was heated to 85 °C.     

Optically pumped submillimeter laser lines from CD2Cl2 using a large tunability CW CO2 laser

Twenty-five new laser lines have been obtained in the wavelength region from 155 to 830 μm by optically pumping the CD₂Cl₂ (deuterated dichloromethane) molecule with a CW CO₂ laser having a tunability range of 300 MHz. The wavelength, polarization relative to that of CO₂ pumping radiation, and offset relative to the CO₂ center frequency were determined for all of the new lines and some other already known laser emissions. For all of them we give also the relative intensity and the optimum pressure of operation. Permanent address: Depto de Física e Química da FEIS — UNESP 15.378-000 Ilha Solteira-SP, Brazil     

Temperature distribution along oversized hollow-core waveguides for CO2 laser radiation

Temperature distributions along various hollow waveguides are fully analysed experimentally when the waveguides are excited by CO₂ laser light. It is shown that the temperature decreases in an oscillatory manner along the waveguides due to the interference effect of guided modes. The distributors are well explained by a theory developed previously.     

A compact, highly stable CW CO2 laser without brewster windows

We describe an open resonator, quasi sealed-off; 70cm cavity length CO₂ laser with very high stability of power and frequency, which lases on 96 lines from 9R42 (2W) to 10P52 (5W) with a power of >11W on 9R20, 9P20, 10R20 and 10P20, plus on 18 hotband lines with ≈2W. This laser was used successfully to pump an FIR ring laser [1] enabling an FIR power stability of ΔP/P ≈ 10⁻⁴ by use of a simple PI control loop, thus demonstrating its superb frequency stability.     

A 3 kW average power tunable TEA CO2 laser

A high average power line-tunable TEA CO₂ laser is described. Average output power up to 3 kW is achieved at repetition rate of 180 Hz. The maximum output power is almost equal among the four spectrum bands of CO₂ laser (the P and R branches of 00°1–10°0 and 00°1–02°0 transition bands). Several special technologies including rotating spark gap switching, PCB (printed circuit board) preionization and zeroth-order grating coupling are employed.     

Thermal and efficiency analysis of the CO2 laser cutting process

In CO₂ laser gas-assisted cutting process, modeling of the interaction mechanism is important. Consequently, the present study treats the complete problem of the interaction of the melting surface with the boundary layer and describes the behavior of the melting layer. In the analysis, gas–liquid interface parameters are developed and relationships between the parameters influencing the cutting action are identified theoretically. To achieve this, effects of momentum and gas–liquid interface shear stress, due to the assisting gas jet, are considered. The approximate magnitude of the heat absorbed is estimated and melting layer thickness is predicted. An experiment is carried out and the theoretical predictions are compared with the experimental findings. First and second law efficiencies of the cutting process are predicted, which may, then, be used to improve the process. It is found that the assisting jet velocity increases the first and second law efficiencies of the CO₂ laser cutting process.     

Investigation of cutting of engineering ceramics with Q-switched pulse CO2 laser

In this paper, the cutting of Si₃N₄ engineering ceramics with Q-switched pulse CO₂ laser is studied. Considering the influence of the cut front shape on the absorption of the laser beam, a simplified 2D mathematic model is developed based on a pulsed laser vaporization cut process. This model is based on the conservation of energy. The experimental results show that it would realize crack-free cutting by using high-speed and multi-pass feed cutting process.     

Far infrared stimulated emissions from CO2 laser excited dichloromethane

Six new far-infrared laser frequencies have been obtained in CO₂-laser excited dichloromethane. Competing transitions have enabled assignments to be made to the v₇ band.