Pulsed CO2 Laser Research Articles

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 effect of composition on photoconductivity and nonlinear optical properties in the acentric Ag2In2AB6 (A = Si, Ge, B = S, Se) crystals

Complex studies of the photoconductivity, photoinduced second harmonic generation (SHG) and linear electrooptic for four quaternary chalcogenide crystals Ag2In2GeSe(S)6 and Ag2In2SiSe(S)6 that crystallize in the monoclinic structure have been done in the infrared spectral range. As a photoinduced beam we have used a bicolor coherent 9400/4700 nm laser beam of microsecond pulsed CO2 laser. The electrooptical effect was probed by continuous wave He-Ne laser at wavelength 3390 nm and second harmonic generation by nanosecond pulse Er:glass laser at wavelength 1540 nm. The relation between the energy gap, output electrooptic efficiency and the photo stimulated SHG has been done. The detailed kinetics of the photoconductivity show that there occurs significant re-distribution of photoexcited carriers between the defects. This factor also may play a crucial role both for the photoinduced electrooptic as well as for second harmonic generation. It was experimentally shown that there exists an increase of the second-order susceptibility with enhanced electronic energy gap which contradicts compared to the generally adopted approach. Such extraordinary behavior is a consequence of the significant contribution of anharmonic phonons in the infrared spectral range spectrally situated near the nonlinear optical resonances. Additional role here may also belong to the space re-distribution of carriers between the defects that was established following the photoconductivity kinetics studies.

Plasma induced by a pulsed CO2 laser from powder samples mixed with silicone on metal subtarget and its possibility for detecting difficult salts of Cl, B, and S

Emission spectrum from plasma produced by a transversely excited atmosphere (TEA) carbon dioxide (CO2) laser from pure powder samples mixed with silicone grease attached to a nickel plate was studied. The pulsed CO2 laser operating at wavelength of 10.6 μm with energy and duration of the laser pulse is 2.5 J and 200 ns, respectively. The plasma was produced by focusing the laser beam onto the sample using a focusing lens (f = +200 mm) under air and helium surrounding gas at atmospheric pressure alternatively. The plasma emission spectrum was detected using an optical multichannel analyser (OMA) system equipped with a 0.32-m-focal length spectrograph. The spectrograph consists of a grating of 1200 graves/mm and a 1024-channel photodiode detector array with a micro-channel plate intensifier. The samples used this work are pure chemical powder samples. This technique was used to investigate emission spectral lines due to important salts but difficult to detect such as boron (B), chlorine (Cl) and sulphur (S) from powder samples. It was found that emission intensity detected from the produced plasma is remarkably higher in case using He as ambient gas compared with that using air. It was found that emission spectral lines due to B, Cl, and S can clearly be detected. Even though concentration of the salts (B, Cl, S) is very high since the samples used are pure chemical powder, however several emission spectral lines theoretically expected to appear with strong relative intensity displays relatively low intensity in the detected spectrum. This result confirms the difficulty for detecting the salts, especially chlorine (Cl) and sulphur (S). This technique basically promises a potential application for direct detection of B, Cl and S from powder samples, however new approaches must be developed to realise a high sensitive detection especially for Cl and S.

Theoretical Investigation of Z-Pinch Ar-Plasma Waveguide in a Millimeter-Scale Cross Section Capillary

Theoretical investigation of the transient Z-pinch Ar-plasma waveguide was conducted on CO2-laser pulse with a central wavelength of $10.6~\mu \text{m}$ and an input peak intensity of $1.3\times 10^{15}$ W/cm2. The main plasma variables of the fast Z-pinch discharge were obtained from a 1-D magnetohydrodynamic model. Simulation showed that the guiding channel exists for only a few nanoseconds and occurs far from capillary wall, which makes possible pure plasma guiding. In terms of laser-driven plasma wakefield accelerators, the Z-pinch waveguide is able to extend the acceleration length over the whole capillary, assuming that a single-mode transmission takes place. In order to quantify such ability of the channel, a correlation coefficient was introduced and computed at different input beam spot sizes. As a result, an optimal beam spot size was determined by taking maximum of time average of correlation coefficient over the channel lifetime. At the end of the channel existence, a repetitive focusing and defocusing pattern was observed with significant intensity increase at the focal points. This property offers an alternative regime of waveguiding.

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.

Material Characterisation with New Indentation Technique Based on Laser-Induced Shockwaves

Conventional material development of new compositions is expensive and time consuming. Thus, for material characterisation there is a demand to enable high through-put experimentation to analyse and develop new materials in a short time. In this context, a new experimentation method is presented, which is based on TEA CO2 laser-induced shockwaves. First, plasma is created with a nanosecond pulsed TEA CO2 laser on top of a spherical indenter. Further interactions of the plasma with the high intensity laser beam result in a shockwave. The pressure of the shockwave is used to force the indenter penetrate inside the test material. Indentations are created on different aluminium alloys and correlated with hardness. The influence of environmental conditions, indenter material and diameter are investigated. Additionally, an energy model is introduced, which describes the possible indentation strain energy in dependence of the indenter diameter and the shockwave energy transferred to the indenter. The experiments reveal that smaller indenter diameters are recommendable for higher impact efficiencies. Best indentation results are achieved in terms of reproducibility and depth with a 3 mm indenter.

Generation of high-average-power ultra-broadband infrared radiation

High-average-power ultra-broadband mid-IR radiation can be generated by illuminating a nonlinear medium with a multi-line laser radiation. Propagation of a multi-line pulsed CO2 laser beam in a nonlinear medium, e.g., gallium arsenide or chalcogenide, can generate directed broadband IR radiation in the atmospheric window (2–13 μm). A 3D laser code for propagation in a nonlinear medium has been developed to incorporate extreme spectral broadening resulting from the beating of several wavelengths. The code has the capability to treat coupled forward and backward-propagating waves, as well as transverse and full linear dispersion effects. Methods for enhancing the spectral broadening are proposed and analyzed. Grading the refractive index radially or using a cladding will tend to guide the CO2 radiation and extend the interaction distance, allowing for enhanced spectral broadening. Nonlinear coupling of the CO2 laser beam to a backward-propagating reflected beam can increase the rate of spectral broadening in the anomalous dispersion regime of a medium. Laser phase noise associated with the finite CO2 linewidths can significantly enhance the spectral broadening, as well. In a dispersive medium, laser phase noise results in laser intensity fluctuations. These intensity fluctuations result in spectral broadening due to the self-phase modulation mechanism. Finally, we present propagation through a chalcogenide fiber as an alternative for extreme spectral broadening of a frequency-doubled CO2 multi-line laser beam.

Pulsed CO2 laser-induced gas plasma spectroscopy based on single beam splitting for trace metal analysis on a material surface

ABSTRACTLaser-induced gas plasma spectroscopy based on pulsed CO2 laser beam splitting has been applied to the problem of trace film analysis on the silicon surface. In this study, 2.1 J of laser energy (70% of the laser beam) was focused at a 10-degree incidence on a metal mesh attached to a sample surface containing trace metal elements in order to produce a gas plasma. The remaining part of the laser beam (approximately 30% or 0.9 J) was employed to vaporize a film which had been deposited on the material by focusing the laser beam 3 cm under the surface. In this scheme, the vaporized metal film moves into the gas plasma region, in which the dissociation and excitation takes place. Our measurements show that the detection of Cr on the silicon surface can be made with high sensitivity. The limit of detection of Cr in the silicon material was approximately 7.5 × 1012 atom/cm2.

Q-switched repetitively pulsed cryogenic slab RF discharge CO laser with active medium comprising air

Q-switched repetitively pulsed cryogenic slab RF discharge CO laser output characteristics (its spectrum, peak power and pulse duration) were studied for various active medium compositions and pump pulse energies. It was found that small addition of N2 increased output peak power at the same other parameters. The highest peak power of this CO laser facility ~ 4 kW was obtained for gas mixture CO:O2:N2:He with O2:N2 concentration ratio 1:4 as about in the atmospheric air. It was shown that the atmospheric air as the active gas mixture component can be applied instead of pure nitrogen and oxygen without the laser peak power loss.

Nonlinear interaction of femtosecond laser pulses with a CO2-laser-induced air spark

We observe a dramatic enhancement in third harmonic generation (THG) when intense femtosecond laser pulses travel through CO2-laser-induced spark in air. By further investigating the dependence of the enhancement factor on the delay between the femtosecond laser pulse and CO2 laser pulse in various gases at different pressures, we reveal that the enhancement in THG results from the suppression of Gouy-phase-induced destructive interference, which can be attributed to a fast and a slow process. Our analyses show that the plasma generated in CO2 laser field plays the dominant role in the fast process whereas hydrodynamics of the gas heated by the CO2 laser contributes to the slow process.

Reducing the Energy Consumption of a Laser Photo-Acoustic SF6 Gas Analyzer

Experimental studies of the operating modes of a laser photo-acoustic SF6 gas analyzer that were aimed at reducing its energy consumption were carried out. It was shown in the experiments that an average power of CO2 laser radiation of at least 100 mW is required for the assured detection of low SF6 concentrations (less than 100 ppb). To reduce the energy consumption of the gas analyzer, it is proposed to decrease the repetition frequency of CO2 laser pulses by several times and operate on subharmonics of the resonance frequency of the photo-acoustic detector. The experimental results made it possible to reduce the energy consumption of the gas analyzer to ~15 V A and use a Li-ion battery from a laptop to power it. The duration of the continuous operation of the gas analyzer on one battery charge was at least 6 h.

Three-stage frequency conversion of sub-microsecond multiline CO laser pulse in a single ZnGeP2 crystal.

Broadband three-stage frequency conversion of multiline sub-microsecond CO laser radiation in a single sample of ZnGeP2 crystal was experimentally and numerically studied for the first time, to the best of our knowledge. As a result, the hybrid laser system emitted more than 200 narrow spectral lines within the 2.4-6.2μm spectral range. The measured conversion efficiencies of the first, second, and third stages were about 4.8%, 0.4%, and 0.05%, respectively. Our numerical simulation demonstrated that the third stage of this frequency conversion can extend the laser system spectrum toward the shorter wavelength of 2.2μm.

Theoretical and experimental investigations of the influence of overlap between the laser beam tracks on channel profile and morphology in pulsed laser machining of polymers

Pulsed laser machining is a method used for the fabrication of microchannels in different materials. There are various laser parameters and material properties which affect quality and dimension of the manufactured channel. The pulse overlapping is a process parameter which has significant effect on the resultant channel depth and morphology. In spite of many investigations on the effect of the pulse overlapping on laser machining, there is no theoretical equation for predicting the channel depth and profile, which involves this parameter explicitly as a function of the scanning velocity and the pulse repetition rate. In this paper, CO2 pulsed laser was used for the fabrication of channels in polymethylmethacrylate (PMMA). The temporal shape of the laser pulse and the corresponding overlap of each pulse over the spot area were added as two processing parameter to the theoretical equation. The influence of pulse overlapping on the morphology at the bottom of the channels is also studied. The results offer a simple way to predict the channel depth, profile and morphology for pulsed laser machining of polymeric materials which has good absorption at the laser wavelength.

Rapidly tunable pulsed CO2 laser based on Acoustic-optic Modulator

A rapidly tunable pulsed CO2 laser intended for use in DIAL lidar system has been developed. For achievement of short tuning time, the system of laser based on two oppositely placed Acoustic-optic Modulators has been created. In this laser system, a fixed reflector and a rotating grating were used as rear mirrors of two oscillation paths to select wavelengths, and two AOMs were served as a switcher between two paths. Under the control of time sequence of two AOMs, two wavelengths emitted from different oscillation paths with time interval of 1 ms were obtained from the single output mirror of CO2 laser, and the pulse duration was 220 ns and 280 ns for two paths, respectively.

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.

Aplicación de wavelets en la detección fotoacústica de gases traza con señales ruidosas

En este trabajo se muestra que la utilización de filtros basados en la transformada wavelet discreta (DWT) mejora la sensibilidad de sistemas fotoacústicos para medición de gases traza bajo condiciones de relación señal a ruido (SNR) desfavorables. Para lograr este objetivo se diseñó un filtro basado en la DWT de Meyer y se lo probó con senales simuladas y medidas. Para las mediciones se implementó un sistema para la detección de trazas de hexafluoruro de azufre en nitrógeno usando un láser pulsado de CO2. A partir de los resultados se obtuvo que el uso de DWT tuvo un muy buen desempeño para señales generadas con bajas energías láser (< 100 uJ) corrompidas con ruido impulsivo electromagnético.

Rapid identification of macro nutrients in pharmaceutical medicine using laser-induced plasma spectroscopy

Identification of macro nutrients in medicine is really necessary for healthy purpose. In this study, identification of macro elements in pharmaceutical products was carried out by laser-induced plasma spectroscopy (LIPS). A comparative study was made by employing different types of laser, namely an Nd:YAG laser and a pulse TEA CO2 laser. Experimentally, the laser beam was directed and focused by a convex lens on a mineral supplement tablet. A luminous plasma was induced on the tablet’s surface. Sharp and high-intensity emission spectra of macro elements including Ca and Mg were detected both in LIBS using Nd:YAG and pulse CO2 lasers. However, the intensities of Ca and Mg spectra are much higher for the LIBS using CO2 laser. Based on the analysis, the plasma temperature plays important role in the spectra. Namely, the plasma induced by a TEA CO2 laser is much higher than that of Nd:YAG laser; the plasma temperature for the case of TEA CO2 laser and Nd:YAG laser were 6400 K and 4500 K, respectively.

Experimental investigation of machinability in laser-assisted machining of fused silica

Fused silica is difficult to machine through conventional machining at room temperature, mainly due to high brittleness, low fracture toughness, high strength, and poor plastic deformation. In this study, we demonstrated experimentally that we are able to machine fused silica with improved efficiency and precision with laser-assisted machining (LAM) by heating workpiece locally in front of the cutting tool utilized a pulse CO2 laser beam. Then, the machinability of fused silica was evaluated. The surface roughness tests with a Taguchi orthogonal array indicated that the pulse duty ratio was the main factor for a minimum Ra value achievement. The experimental results demonstrated a considerable improvement in the machinability of fused silica through the improved surface quality, high material removal rate, low rate of tool wear, as well as the cutting force reduction. The material removal mechanism was a hybrid of quasi plastic deformation and brittle fracture during the LAM of fused silica, which was inferred from the machined surface quality and chip morphology changes compared to the conventional machining.

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.

Large-area uniform periodic microstructures on fused silica induced by surface phonon polaritons and incident laser

A simple and convenient means to self-organize large-area uniform periodic microstructures on fused silica by using multiple raster scans of microsecond CO2 laser pulses with beam spot overlapping at normal incidence is presented, which is based on laser-induced periodic surface structures (LIPSS) attributed to the interference between surface phonon polaritons and incident CO2 laser. The evolution of fused silica surface morphologies with increasing raster scans indicates that the period of microstructures changed from 10.6 µm to 9 µm and the profiles of microstructures changed from a sinusoidal curve to a half-sinusoidal shape. Numerical simulation results suggest that the formation of the half-sinusoidal profile is due to the exponential relationship between evaporation rate and surface temperature inducing by the intensive interference between surface phonon polaritons and incident laser. The fabricated uniform periodic microstructures show excellent structural color effect in both forward-diffraction and back-diffraction.