Pulsed CO2 Laser Radiation Research Articles

Efficient two-stage laser enrichment up to 99% of carbon-13 isotope by IR multiphoton dissociation of Freon molecules

A new method for two-stage laser enrichment of carbon-13 (13C) by isotope-selective IR multiphoton dissociation of Freon molecules is considered, which makes it possible to achieve a concentration of 13C up to 99 % or higher with high productivity. At the first stage, as a result of the selective dissociation of CF2HCl (Freon-22) molecules, it is expected to obtain a C2F4 dissociation product enriched in 13C up to 30 % – 50 %. At the second stage, CF2Br2 (Freon-12B2) is proposed to be used as a working substance, which is synthesised from enriched C2F4, and the enrichment process is carried out by selective deep ‘burning-out’ of the 12C-containing component. Experiments on multiphoton dissociation of Freon-12B2 with an initial 13CF2Br2 concentration of 30 % in a mixture with oxygen by pulsed CO2 laser radiation are performed. It is shown that reaching a 13CF2Br2 concentration of no lower than 99 % is possible at high values of the elementary separation act parameters: 15 % – 18 % dissociation yield and 40 – 75 selectivity for 12CF2Br2 molecules.

Investigation on laser beam figuring of fused silica using microsecond pulsed CO2 laser radiation

A laser-based process chain is a possible solution to increase precision and reduce production time in optics manufacturing of components with complex shaped surfaces. A new high-precision laser ablation process was investigated using CO2 laser radiation and microsecond laser pulses. An average ablation depth of approx. 0.1 nm per laser pulse indicates that material ablation on an atomic/molecular scale was achieved. Four characteristic laser processing regimes and their related dominant physical process mechanisms were identified. The effect of crucial process parameters such as pulse energy, pulse duration and fluence on ablation depth and spatial resolution was empirically investigated. Ablation depths smaller than 5 nm per layer and a spatial resolution of less than 50 μm were achieved in areal laser ablation. The potential use of this high-precision laser ablation process was studied for an iterative process cycle (laser beam figuring - LBF) consisting of contactless surface measurement and subsequent laser ablation. The feasibility of LBF for form correction of fused silica components was successfully demonstrated, while a reduction in average surface roughness from Sa = 10.3 nm to 3.5 nm was achieved. High stability in pulse energy is the key requirement for high precision in ablation depth.

Synthesis of Fe:MgAl2O4 nanopowders by laser ablation

The features of production of Fe:MgAl2O4 nanopowders by evaporation of targets made from a simple oxide mixture (Fe2O3, MgO, Al2O3) by repetitively pulsed CO2 laser radiation with I = 1.8 MW/cm2 peak power density and Paver = 600 W average radiation power as well as by ytterbium fiber laser radiation (I = 0.4 MW/cm2 and Paver = 300 W) were studied. It was demonstrated that the nanopowder produced with the use of the CO2 laser has the specific surface of 56 m2/g and contains two crystalline phases, i.e. MgAl2O4 (98.2 wt%) and MgO (1.8 wt%), with Fe ions dissolved in them. At the average radiation power of 600 W, the output of the nanopowder was 16 g/h. For the nanopowder produced using the ytterbium fiber laser, a twofold increase of the specific surface (105 m2/g) was observed. This nanopowder contains four phases, i.e. MgAl2O4 (67.5 wt%), γ-Al2O3 (24.8 wt%), Fe3O4 (3.2 wt%) and MgO (4.5 wt%). In this case, the output of the nanopowder was 2.7 g/h due to high transparency of initial target and the formation of a “forest-like” array of 4–5-mm-high spikes covered with a semitransparent melt layer. Significant differences in the phase compositions of the nanopowders obtained using these lasers are associated with a higher rate of the laser plume cooling for the ytterbium fiber laser.

Fabrication of multiscale structures on polymethylmethacrylate following pulsed CO2 laser irradiation

Different micro- and nanostructures are formed on the surface of the polymers following laser irradiation. The formation of these structures, which is dependent on the irradiation parameters and the material properties, affects the functionality and the efficiency of the polymers for a desired application. We investigate nano- and microstructure formation on the surface of polymethylmethacrylate polymer following pulsed CO2 laser irradiation at the wavelength of 9.55 μm in vacuum. Three different multiscale structures including nano- and microspheres, microholes, and ripples are formed on the surface after irradiation at various fluences below and above the ablation threshold. The possible mechanisms for the formation of these structures are explained. Melting, thermal waves, and internal stresses supposed to be the most important phenomena affect the shape and the size of the structures. The effect of irradiation on the UV–Vis spectra of the samples is also investigated.

The influence of pulsed CO2-laser radiation on the transport of powder during laser cladding of metal

The problem of measurement of the in-flight velocity and temperature of particles in the light field of a pulsedperiodic laser was solved using contactless detection methods. The solution of the problem is based on using a spectrometer and a complex of laser and optical means. The diagnostic technique combines two independent methods for measuring the in-flight particle velocity: a passive one, based on the registration of the natural radiation emitted by the heated particles in the gas flow, and an active one, using the effect due to laser-beam scattering. Histograms of the statistical distributions of particle velocities for two operating modes of a coaxial nozzle were presented. There is no laser radiation in the first mode. There is pulsed laser radiation in the second mode. In the experiments, various powders (Al2O3, Mo, Ni, Al) with particle size distributions typical of laser deposition technology and various working gases (air, nitrogen, argon) were used. СО2-laser works in pulse-periodic mode with a mean power up to 2 kW. Pulsed power reaches several ten/hundred kilowatts. It is shown that in the field of laser radiation, powder particles acquire additional acceleration due to the evaporation and the appearance of a reactive force due to the recoil pressure of the vapors emitted from the irradiated part of the particle surface. It is shown that laser radiation can significantly affect the velocity and temperature of powder particles being transported by a gas jet. At the maximum carrier-gas velocity of up to 30 m/s, the velocities of single particles due to the laser-induced acceleration can reach the values of the order of 120 m/s.

The influence of pulsed CO2 laser irradiation on the optical properties of PMMA

Views In this paper, effect of the pulsed CO2 laser irradiation on optical properties and surface morphology of PMMA was investigated. The samples were irradiated by a CO2 pulsed laser with the wavelength of 9.55 micron and the pulse duration of about 100 ns. UV-Visible spectroscopy and Scanning Electron Microscopy (SEM) were used for investigating the change in absorption, reflection, refractive index and surface morphology, respectively.

Laser-based surface patterning of composite plates for improved secondary adhesive bonding

The effects of laser irradiation surface pretreatments on the mode I fracture toughness of adhesively bonded composite joints were evaluated. First, pulsed CO2 laser irradiation was uniformly deployed on carbon fiber reinforced polymer (CFRP) substrates. Next, double cantilever beam (DCB) tests were performed to assess the effects of surface pretreatments on the mode I fracture toughness of the adhesive joints. Then, a thoughtful combination of the proposed surface pretreatments was deployed to fabricate DCB specimens with patterned interfaces. A wide range of techniques, including X-ray photoelectron spectroscopy (XPS), contact profilometry, and optical and scanning electron microscopy (SEM) were used to ascertain the effects of all investigated surface pretreatments. It is shown that patterning promoted damage mechanisms that were not observed in the uniformly treated interfaces, resulting in an effective fracture toughness well above that predicted by a classical rule of mixture.

Numerical model and experimental demonstration of high precision ablation of pulse CO2 laser

To reveal the physical mechanism of laser ablation and establish the prediction model for figuring the surface of fused silica, a multi-physical transient numerical model coupled with heat transfer and fluid flow was developed under pulsed CO2 laser irradiation. The model employed various heat transfer and hydrodynamic boundary and thermomechanical properties for assisting the understanding of the contributions of Marangoni convention, gravitational force, vaporization recoil pressure, and capillary force in the process of laser ablation and better prediction of laser processing. Simulation results indicated that the vaporization recoil pressure dominated the formation of the final ablation profile. The ablation depth increased exponentially with pulse duration and linearly with laser energy after homogenous evaporation. The model was validated by experimental data of pulse CO2 laser ablation of fused silica. To further investigate laser beam figuring, local ablation by varying the overlap rate and laser energy was conducted, achieving down to 4 nm homogenous ablation depth.

Propulsion of a flat tin target with pulsed CO2 laser radiation: measurements using a ballistic pendulum

The recoil momentum transfer produced by irradiation of a flat tin (Sn) target with pulses of high-power CO2 laser with intensity ranging from 107 to 10 W has been studied. Momentum measurements were performed using a ballistic pendulum, capable of measuring momenta as small as g · cm . It has been established that the recoil momentum monotonically increases with the laser energy and asymptotically reaches the power scaling law with . Results are compared with previously published theoretical studies.

Pulsed TEA CO2 Laser Irradiation of Titanium in Nitrogen and Carbon Dioxide Gases

Surface changes created by interaction of transversely excited atmospheric carbon dioxide (TEA CO2) laser with titanium target/implant in nitrogen and carbon dioxide gas were studied. TEA CO2 laser operated at 10.6 μm, pulse length of 100 ns and fluence of ∼17 J/cm2 which was sufficient for inducing surface modifications. Induced changes depend on the gas used. In both gases the grain structure was produced (central irradiated zone) but its forms were diverse, (N2: irregular shape; CO2: hill-like forms). Hydrodynamic features at peripheral zone, like resolidified droplets, were recorded only in CO2 gas. Elemental analysis of the titanium target surface indicated that under a nitrogen atmosphere surface nitridation occurred. In addition, irradiation in both gases was followed by appearance of plasma in front of the target. The existence of plasma indicates relatively high temperatures created above the target surface offering a sterilizing effect.

Glass processing with pulsed CO2 laser radiation.

Recent results of processing fused silica using a high-power Q-switched CO2 laser source with a maximum output power of 200 W are presented. Compared to the processing with continuous wave laser radiation, the main advantage of pulsed laser radiation is the influence of the light-matter interaction with high laser peak power at small average laser power. An application for the approach presented in this paper is the flexible manufacturing and form correction of optics. This laser-based process is nearly independent of the surface geometry and can even be enhanced by laser polishing and expanded to other glass materials. Hence, the high-power Q-switched CO2 laser source is used to ablate glass material with an ablation rate up to 2.35 mm3/s and also for ablating glass material locally in a vertical dimension down to 3 nm.

STUDYING PHOTOKINETICS OF THE IR LASER RADIATION EFFECT ON MIXTURE OF THE CO2-N2-H2O GASES FOR DIFFERENT ATMOSPHERIC MODELS

A kinetics of energy exchange in the mixture of the atmosphere CO2-N2-H2O gases under passing the powerful CO2 laser radiation pulses within the three-mode model of kinetical processes is studied. More accurate data for the absorption coefficient are presented.

Sensitive ablation of brittle materials with pulsed CO2 laser radiation

The interaction process between pulsed CO2 laser radiation and glass was studied systematically. The concept of the structuring process is related to an absorption-controlled ablation of small elementary material volumes with reduced melt formation, the so-called elementary volume ablation (EVA). For this purpose, suitable pulse parameters were predicted on the basis of the optical and thermal materials properties. These pulses with durations as low as 10 μs and a peak power of up to 600 W were generated using a specific arrangement consisting of a commercially available continuous CO2 laser of high beam quality and a cascade of two interference laser beam modulators. Optical microscopy, scanning electron microscopy, white light interferometry, and tactile profilometry were used to investigate the influence of the CO2 laser pulse parameters on the processing quality. The results obtained from the ablation of borosilicate glass (Borofloat33) and 100 μm thick sheets of cerium doped borosilicate glass demonstrate that the EVA method is a suitable approach to select an appropriate range of processing parameters for a high precision thermal ablation of glass without microcrack formation.

CO2 Laser irradiation of GeO2 planar waveguide fabricated by rf-sputtering

We present a fabrication protocol combining radio frequency sputtering technique and CO2 laser annealing for GeO2 based planar optical waveguides. The effects of pulsed CO2 laser irradiation on the optical and structural properties of pure GeO2 planar waveguide are evaluated by different techniques as m-line and micro-Raman spectroscopy and AFM measurements. Amorphous GeO2 planar waveguide was fabricated by Radio Frequency magnetron sputtering system on v-SiO2 substrate. An increase of the refractive index of approximately 0.04 at 1.5 μm and a decreasing of the attenuation coefficient from 0.9 to 0.5 dB/cm at 1.5 μm have been observed after pulsed CO2 laser annealing. Raman spectroscopy and AFM results showed that after an adapted pulsed CO2 laser annealing, the resulting materials showed a crystalline environment in which the phase of the crystalline GeO2 varies with varying irradiation time.

Influence of molecular absorption of a ground atmospheric path on characteristics of filamentation region of high-power CO2 laser radiation

Theoretical aspects of self-focusing and filamentation in air of high-power pulsed CO2 laser radiation with a carrier wavelength of 10.6 μm are considered. The frequency-differential molecular absorption of atmospheric air is included in a theoretical model. The super-broad pulse spectrum is shown to be strongly affected by atmospheric absorption that destabilizes the filamentation process and considerably reduces the length of a plasma channel formed in a beam channel under the conditions of pulse self-phase modulation.

The Spectroscopical and Microstructural Investigations of Nanoclusters and Micron-Sized Periodic Structures Created at the Surface of the Crystal and Amorphous Silica by Resonant CO2Laser Irradiation

The action of pulsed CO2 laser radiation (pulse energy of 1 J, pulse time of 70 ns) at the surface of silica (crystal quartz and fused quartz ) have been investigated. By means of spectroscopical and microstructural investigations it has been established the appearrance of two kind of structures – periodical micron-sized structures with the period length close to wave length of CO2 laser irradiation and nanoclusters with size close to 50-100 nanometers.

Slicing-response model for ablation mass removal of polyformaldehyde irradiated by pulsed CO2 laser in vacuum

The interaction between CO2 laser and polyformaldehyde (POM) is quite important in the research of laser irradiation effects and mechanisms. At this time, the accuracy of the existing mass-ablation models for POM irradiated by CO2 laser is poor compared with the experimental data. Based on the energy distribution deposited in the POM target, the active area excited by laser is divided into four slices, the ablation slice (the temperature-rising slice, the perturbation slice, and the undisturbed slice), and a slicing response model for the mass ablation of POM induced by pulsed CO2 laser irradiation in vacuum is developed. A formula is deduced to predict the ablated mass areal density from the model and is verified with data from several studies and our own experiments. The results show that our model fits the experimental data quite well before the shielding effect of ablation products becomes notable. The applicability of the model to other materials and the mass ablation in atmosphere are also briefly explored.

A Novel Q‐switched CO2 Laser and its Applications

AbstractFor the efficient treatment of a broad variety of materials, pulsed CO2 laser radiation is well‐suited. But nevertheless, CO2 lasers are well established in industrial processes, a significant disadvantage of all previously basicavailable commercial systems, which are suitable for material processing, is their restricted pulsability. This is not caused by the amplification properties of the active medium, but by the wavelength of about 10 μm. In this region the spectrum of optical materials, which can be used for modulation, especially Q‐switching, is rather limited. In principle for acousto‐optic modulation only Ge and for electro‐optic modulation only CdTe are suitable materials. But both semiconductors are relatively power‐sensitive and therefore Q‐switching of conventional CO2 lasers is typically limited to less than 100 W of average power. This problem can be solved by the new resonator concept described below [1]. The aim is the optimum transformation of the potentially available power (cw up to the kW range) into average power of the pulsed radiation.

Third-harmonic and fourth-harmonic generations of CO 2 laser radiation in a GaSe crystal

Tunable third-harmonic and fourth-harmonic generations of pulsed CO2 laser radiation in a GaSe crystal were demonstrated. The optical properties of GaSe and phase-matching conditions in harmonic generations were investigated. The output peak powers for 3.2 μm and 2.4 μm were measured to be 1500 W and 320 W, with corresponding conversion efficiency from 9.6 μm of 0.1% and 0.02%, respectively.

Second harmonic oscillation produced by pumping GaSe and GaSe0.7S0.3 crystals with 10.6-μm pulsed CO2 laser radiation

Second harmonic oscillation produced by pumping GaSe and GaSe0.7S0.3 crystals with 10.6-μm pulsed CO2 laser radiation