Pulsed TEA CO2 Laser Research Articles

Optimization of some input parameters of a pulsed TEA CO2 laser based on the generalized Landau-Teller equations

Optimization of some input parameters of a pulsed TEA CO2 laser based on the generalized Landau-Teller equations

The role of multi-photon dissociation of high pressure SF6 gas in TEA CO2 lasers pulse shaping

High pressure SF6 gas has been irradiated by intense TEA CO2 laser pulses with different wavelengths around 10.6μm and then, temporal variations of the transmitted laser pulses have been characterized at different energy fluences and gas pressures. It has been shown that for every fluence above the multi-photon dissociation threshold of SF6 molecules, there is a certain cut-off pressure at which the pulse spike is completely quenched. While, the pulse tail escapes with an appreciable fraction of its initial energy. FTIR spectra of the irradiated gases together with other experimental evidences have clearly revealed the occurrence of laser induced multi-photon dissociation of SF6 molecules, that should be considered as the main responsible for the observed pulse shaping effects.

Analytical model to determine the relevant parameters governing the transferred momentum to spherical indenters by laser-induced shock waves

Rapid material development is a new approach to reduce the time and cost intensity. It is based on small and simple sample geometries. Many conventional test methods such as hardness measurements or tensile tests are not suitable for this approach, because they either require a sample geometry adapted to the test method or they are time-consuming. Thus, research is being conducted on a novel impact-based method, which allows short time indentations and correlations with mechanical material properties such as hardness and tensile strength: With a high intensity pulsed TEA-CO2 laser, a shock wave is generated on top of a spherical indenter. The momentum of the shock wave pushes the indenter inside a sample. From the induced indentations, characteristic values such as indentation depth and indentation diameter are extracted, which correlate well with the material hardness and tensile strength. Still, the process dynamics are not fully understood. Thus, a model is developed to determine the main parameters that govern the interaction between laser-induced shock wave as well as indenter and accordingly, significantly affect the forming energy. The model is validated by experimental results. From the findings of the analytical model and the conducted experiments, fundamental correlations with respect to the available forming energy are determined. The main parameters influencing the available forming energy are pulse energy, pulse duration, laser spot area, density of the ambient medium and indenter mass.

Numerical simulation and experimental study of pulsed CO2 laser-induced micro-channels on poly-ether sulfone (PES) polymer

TEA CO2 laser pulses were used to create micro-channels on PES samples with various low fluences and scanning speeds in 16–50 J/cm2 and 23–45 µm/s ranges, respectively. Different micro-channels were created with 142–342 µm widths and 85–440 µm depths which has been 3-dimensionally simulated using ABAQUS software based on the finite element method and CIN heat source. The sharp spike (~85 ns FWHM) and long tail (~3.8 µs) parts of the laser pulses were mathematically modeled with individual Gaussian profiles. A good agreement has been found between the simulated and experimental results. Namely, the maximum relative errors of the depth and opening width of the grooves remain below 11.5% and 12.3%, respectively. However, the corresponding mean values of these relative errors do not exceed 4.1% and 7.5%, respectively.

Emission Characteristics of Hydrogen and Carbon in Various Ambient Gases using Pulsed-CO2 Laser-Induced Breakdown Spectroscopy

Background:Hydrogen (H) and Carbon (C) are major elements that occur in various materials, including organic matter. The identification and analysis of C and H are necessary for several fields. LIBS is an excellent method for such analysis because it is rapid, and can be conducted remotely. The technique has been employed for the analysis of H in zircaloy metals. However, few studies on the emission characteristics of H and C in various gases have been undertaken because of the difficulty of identifying H and C using standard LIBS techniques. In this work, the emission characteristics of H and C were studied using pulsed CO2 LIBS. H and C elements were obtained from ethanol vapor. Various gas environments were employed, including Nitrogen (N2), Argon (Ar), and Helium (He) gases, in order to study the stability of the laser-induced plasma, the plasma lifetime, and the excitation mechanisms of H and C.Methods:The LIBS system used in this work consisted of a pulsed TEA CO2 laser (Shibuya SQ 2000), pulse generator, and optical multichannel analyzer. In this work, the laser with a wavelength of 10.6 µm, pulse duration of 200 ns, and pulse energy of 3 J, was used as the irradiation source. The laser energy used was 1.5 J. The laser was irradiated, and focused, using a 200 mm zinc selenide (ZnSe) lens, onto a metal surface in order to initiate and induce a luminous plasma. The sample used in this study was ethanol vapor, obtained from ethanol (99.5%, Merck). For this purpose, 10 mL ethanol was poured into a glass beaker, and this was placed into a closed chamber that could be evacuated by ambient gases including N2, Ar, and He gases.Results:Identification of H emission line has been successfully carried out using this present technique demonstrated in various gases including N2, Ar, and He. From the results, it was observed that in N2 gas, the Hα I 656.3 nm emission line was clearly expressed, with a wide, full-width halfmaximum, and quite a low emission intensity.Conclusion:The emission characteristics of H and C in laser-induced plasma, produced in various ambient gases, including N2, Ar, and He, were studied. The emission spectra of Hα and Hβ were expressed clearly, with high intensity and low background emission, in He, while they were broad and had high background emissions in N2 and Ar. Based on the time-resolved emissions, the Hα emission had a longer lifetime in Ar and He. It was assumed that the metastable atoms of Arand He were predominant in the excitation process of H and C. The characteristics of the H and C emissions in various gases are important in selecting a suitable ambient gas for the study of light atomic emission in the medical field, which mostly deals with organic materials containing H, C, and oxygen.

An innovative method for plasma characterization of the spark pre-ionization pulsed TEA-CO2 laser

In this study, the electron density of plasma discharge has been obtained using the innovative combination of a basic theoretical relation and measured current–voltage characteristics of a uniform glow discharge of a spark array TEA-CO2 laser. The maximum values of electron densities have been obtained as and cm−3, respectively, for charging voltage of discharges at 18, 20 and 22 kV. The drift velocity of electrons has been obtained in the different conditions versus the reduced electric field (E/N) and gas mixtures in the discharge tube. Furthermore, the efficiency in energy conversion and the behavior of electrical energy density versus reduced electric field has been studied.

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.

Energy of Laser Induced Shockwaves

High throughput experimentation is a possibility to develop new materials in a short time in order to meet the demands of efficient characterisation of compositions. Thus, fundamentals of a new hardness measurement method are investigated based on laser-induced shockwaves. In this study, plasma is created with a nanosecond pulsed TEA CO2 laser on top of an indenter. Further interactions of the plasma with the high intensity laser beam result in a shockwave. The pressure of the shockwave is used to push an indenter inside a material surface. So far, the energy transfer of the shockwave on indenters is not fully understood. Therefore, pendulum experiments are conducted to calculate how much energy can be transferred from the shockwave into the indenter. For these experiments, a bob, which geometry is equal to the indenter geometry, is connected to a thread pendulum and maximum deflection angles are recorded with a high-speed camera. Under standard conditions and the assumption of a spherical expansion of the shockwave, the experiments show that with a 6 J pulse energy a shockwave energy of up to 9 μJ can be used for indentation tests.

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.

Infrared multiphoton dissociation of tetramethoxygermane

Infrared multiphoton dissociation of Ge(OCH3)4 molecules by irradiation with a pulsed TEA CO2 laser has been studied. The basic characteristics of the process have been experimentally investigated. The spectral characterization of the dissociation has been made. The product composition of the dissociation has been analyzed, and possible dissociation pathways have been proposed.

Simulation and initial experiments of a high power pulsed TEA CO2 laser

In this paper, the output characteristics of a UV pin array pre-ionized TEA CO2 laser have been simulated and compared with the associated experimental data. In our simulation, a new theoretical model has been improved for transient behavior analysis of the discharge current pulse. The laser discharge tube was modeled by a nonlinear RLC electric circuit as a real model for electron density calculation. This model was coupled with a six-temperature model (6TM) in order to simulation dynamic emission processes of the TEA CO2 laser. The equations were solved numerically by the fourth order Runge–Kutta numerical method and some important variables such as current and voltage of the main discharge, resistance of the plasma column and electron density in the main discharge region, were calculated as functions of time. The effects of non-dissociation factor, rotational quantum number and output coupler reflectivity were also studied theoretically. The experimental and simulation results are in good agreement.

Experimental study on laser produced tin droplet plasma extreme ultraviolet light source

Extreme ultraviolet lithography (EUVL), which uses the extreme ultraviolet radiation at a wavelength of 13.5 nm, is the leading candidate of next generation lithography addressing not only the 10 nm half-pitch nodes, but several nodes beyond that. Among all the methods for getting EUV radiation, laser-produced plasma (LPP) light source is the most promising EUV light source because of its high conversion efficiency (CE), large collect angle and low debris output. In this paper, pulsed TEA-CO2 laser and Nd:YAG laser are used to irradiate tin droplets to obtain plasma EUV emission, and the properties of EUV radiation from the plasma are studied. Results show that the EUV emission spectra induced by Nd:YAG laser have an obvious blueshift as compared with those by CO2 laser. In addition, the LPP sources are point light sources, so that the angular distribution of EUV emission from LPP can be described by Lambertian distribution.

Second harmonic conversion of 10 µm emissions of pulsed and CW CO2 lasers in ZnGeP2

The paper reports on the satisfactory performance of a ZnGeP2 crystal towards second harmonic conversion of a pump beam at 10 μm wavelength and thus establishes its utility in the generation of coherent radiation not only around 4.5 μm but also in the neighbourhood of the 5 μm region of mid-infrared. Experimental results comparing performance of a thin crystal when pumped alternately with the emissions of continuous wave (CW) and TEA CO2 lasers are presented. The performance was also studied as a function of the duration of the pump TEA CO2 laser pulse and the observed anomaly is qualitatively explained. The significant increase in conversion efficiency in the case of pulsed operation is attributed to the much higher irradiating intensity to which the crystal is subjected to in comparison with the CW case. Of particular interest is the finding that the pump intensity below which the second harmonic generation process ceases is lower by almost 3 orders of magnitude in case of the CW operation.

RIR MAPLE procedure for deposition of carbon rich Si/C/H films

We applied the resonant infrared matrix assisted pulsed laser evaporation (RIR MAPLE) technique to demonstrate a new approach to a controlled deposition of carbon rich amorphous Si/C/H film. In absence of radicals and accelerated species commonly generated in PECVD and sputtering setups, the RIR MAPLE method does not decompose precursor molecules. Moreover, unlike the standard MAPLE procedure, in which solvent molecules absorb laser energy from excimer or near infrared lasers, we applied the pulsed TEA CO2 laser to excite the dendrimer precursor molecules in a frozen target. In this manner we achieved just cross-linking of the starting precursor on substrates and the deposition of carbon rich Si/C/H film. The film was analyzed by Fourier Transformed Infrared (FTIR), UV/VIS, Raman and X-ray Photoelectron (XPS) spectroscopy and Atomic Force Microscopy (AFM) technique. According to analyses the film retained the precursor elemental composition free of graphitic (sp2) clusters. In course of reaction only the peripheral allyl groups containing C=C bonds were opened to achieve cross-linking. Whereas annealing to 300°C was necessary for the elimination of =C–H1, 2 bonds in the films prepared at 200°C, those bonds vanished completely for the films prepared at substrate temperature 255°C. The film posseses a smooth surface with root mean square (RMS) parameter up to 10nm within scanned distance 2.5μm.

Effect of CO2 pulsed laser irradiation on improving the biocompatibility of a polyethersulfone film

In this paper a 200 ns pulsed TEA CO2 laser is used for treatment of polyethersulfone (PES) films surface. The laser induced structures and chemical compositions on the surface upon irradiation are studied. The hydrophilicity and biocompatibility of the irradiated surfaces are examined by contact angle and platelet adhesion measurements, respectively. The optimum number of pulses and fluence for improving the surface biocompatibility are found.

High power 4.65 μm single-wavelength laser by second-harmonic generation of pulsed TEA CO2 laser in AgGaSe2 and ZnGeP2

A high power 4.65 μm single-wavelength laser by second-harmonic generation (SHG) of TEA CO2 laser pulses in silver gallium selenide (AgGaSe2) and zinc germanium phosphide (ZnGeP2) crystals is reported. Experimental results show that the average output power of SHG laser is not only restricted by the damage threshold of the nonlinear crystals, but also limited by the irradiated power of fundamental-wave laser depending on the operating repetition-rate. It is found that ZnGeP2 can withstand higher 9.3 μm laser irradiation intensity than AgGaSe2. As a result, using a parallel array stacked by seven ZnGeP2 crystals, an average power of 20.3 W 4.65 μm laser is obtained at 250 Hz. To the best of our knowledge, it is the highest output power for SHG of CO2 laser by far.

Surface modification of the titanium implant using TEA CO2 laser pulses in controllable gas atmospheres – Comparative study

Interaction of a TEA CO2 laser, operating at 10.6μm wavelength and pulse duration of 100ns (FWHM), with a titanium implant in various gas atmospheres was studied. The Ti implant surface modification was typically studied at the moderate laser beam energy density/fluence of 28J/cm2 in the surrounding of air, N2, O2 or He. The energy absorbed from the TEA CO2 laser beam is partially converted to thermal energy, which generates a series of effects, such as melting, vaporization of the molten material, shock waves, etc. The following titanium implant surface changes and phenomena were observed, depending on the gas used: (i) creation of cone-like surface structures in the atmospheres of air, N2 and O2, and dominant micro-holes/pores in He ambient; (ii) hydrodynamic features, most prominent in air; (iii) formation of titanium nitride and titanium oxide layers, and (iv) occurrence of plasma in front of the implant. It can be concluded from this study that the reported laser fluence and gas ambiences can effectively be applied for enhancing the titanium implant roughness and creation of titanium oxides and nitrides on the strictly localized surface area. The appearance of plasma in front of the implants indicates relatively high temperatures created above the surface. This offers a sterilizing effect, facilitating contaminant-free conditions.

Optimization performance of a CO2 pulsed tuneable laser

In this paper, a procedure is presented that will allow (i) the power and (ii) the energy of a pulsed and tuneable TEA CO2 laser to be optimized. This type of laser represents a significant improvement in performance and portability. Combining a pulse mode with a grating tuning facility, it enables us to scan the working wavelength between 9.2 and 10.8 µm instead of the typical 1064 nm for other infrared lasers. Along the way, the study proved that there are many factors which could be improved in order to get even better results. Following an adequate procedure, the energy values could be optimized in intensity and stability, and therefore indirectly laser power. In addition, the same procedure allowed us to check the wavelengths of the laser emission lines in the absence of a spectrometer, using a previously established conversion table of the grating position versus line designation. This work is mainly intended for graduate and experimental physicists. This experimental work is being performed in our Physics Group at the New University of Lisbon, targeting physics students at the graduation level, in the aim of Bologna Master's degree.

Infrared multiphoton dissociation of 1,2-dichloroethyltrifluorosilane

Infrared multiphoton absorption and dissociation of 1,2-dichloroethyltrifluorosilane molecules under the action of pulsed TEA CO2 laser were experimentally studied. The composition of dissociation products was analyzed. The only products of dissociation have been found to be stable molecules: chloroethylene and trifluorochlorosilane. Dissociation proceeds via chlorine atom transfer from carbon to silicon. The silicon isotope-selective infrared multiphoton dissociation was performed at different wavelengths of the CO2-laser radiation. High degrees of silicon isotope separation have been achieved.

CrossRef Listing of Deleted DOIs

A pulsed CO2-TEA laser was used to melt the surface of plasma-sprayed coatings. An analysis of the laser parameters on the heat transfer is made: the melt depth and the surface temperature were calculated for different laser inputs. It was found that the pulse length must be in the range of 20 to 40 µ s in order to fill up the pores of the coating and to keep the surface temperature below the boiling range. Experimental results on surface modification are explained in terms of power density.