Transversely Excited Atmospheric CO2 Research Articles

The effects of focusing power on TEA CO2 laser-induced gas breakdown and the consequent pulse shaping effects

Transversely Excited Atmospheric (TEA) CO2 laser pulses were used in order to generate an optical breakdown in a variety of mono- and polyatomic molecules using different focusing powers. The dependence of the spark kernel geometry and the transmitted pulse shapes on the focusing power as well as the pressure, molecular weight, and ionization energy of the gases was investigated in detail. Partial removal of the transmitted pulse tail in the 0.05–2.6 μs range together with shortened spikes in the 10–60 ns range has been observed by applying a 2.5 cm focal length lens for all the gases. At higher focal lengths, this effect is only incompletely observed for He gas. Spatial-temporal analyses of the laser beams and the relevant plasma plumes indicate that this behavior is due to the drop in the plasma density below the critical level, before the laser pulse tail is completed.

Transversely Excited Atmospheric CO2 Laser-Induced Plasma Spectroscopy for the Detection of Heavy Metals in Soil

A rapid detection of heavy metals in soil was presented by the metal-assisted gas plasma method using specific characteristics of a pulsed, transversely excited atmospheric (TEA) CO2 laser. The soil particles were placed in a hole made of acrylic plate. The sample was covered by a to prevent the soil particles from being blown off. The mesh also functioned to initiate a luminous plasma. When a TEA CO2 laser (1500 mJ, 200 ns) was focused on the soil sample, passing through the metal mesh, some of the laser energy was used to generate the gas plasma on the mesh surface, and the remaining laser energy was employed to ablate the soil particles. The fine, ablated soil particles moved into the gas plasma region to be dissociated and excited. Using this technique, analysis can be made with reduced sample pretreatment, and therefore a rapid analysis can be performed efficiently. The results proved that the signal to noise ratio (S/N) of the emission spectral lines is much better for the case of the present method (mesh method) compared to the case of standard laser-induced breakdown spectroscopy using the pellet method. Rapid detection of heavy metal elements in soil has been successfully carried out. The detection limits of Cu and Hg in soil were estimated to be 3 and 10 mg/kg, respectively. The present method has good potential for rapid and sensitive detection of heavy metals in soil samples.

LIBS Analysis of Geomaterials: Comparative Study of Basalt Plasma Induced by TEA CO2 and Nd:YAG Laser in Air at Atmospheric Pressure

We present a study of the plasma generated by transversely excited atmospheric (TEA) CO2 laser irradiation of a basalt sample. The plasma was induced in air at atmospheric pressure. The same sample was also analyzed using a commercial LIBS system based on Nd:YAG laser and time-gated detection. The main plasma parameters, temperature, and electron number density were determined and analytical capabilities of the two systems compared. Despite differences in laser wavelength, pulse duration, applied fluence, and signal detection scheme, the two systems are comparable in terms of element detectability and limits of detection. In both cases, all elements usually present in geological samples were identified. The estimated limits of detection for most elements were below 100 ppm, while for Cu, Cr, and Sr they were around or below 10 ppm. The obtained results led to the conclusion that simple, cost-effective TEA CO2 LIBS system can find applications for geological explorations.

Optical Emission Studies of Copper Plasma Induced Using Infrared Transversely Excited Atmospheric (IR TEA) Carbon Dioxide Laser Pulses.

Spatially resolved, time-integrated optical emission spectroscopy was applied for investigation of copper plasma produced by a nanosecond infrared (IR) transversely excited atmospheric (TEA) CO2 laser, operating at 10.6 μm. The effect of surrounding air pressure, in the pressure range 0.1 to 1013 mbar, on plasma formation and its characteristics was investigated. A linear dependence of intensity threshold for plasma formation on logarithm of air pressure was found. Lowering of the air pressure reduces the extent of gas breakdown, enabling better laser-target coupling and thus increases ablation. Optimum air pressure for target plasma formation was 0.1 mbar. Under that pressure, the induced plasma consisted of two clearly distinguished and spatially separated regions. The maximum intensity of emission, with sharp and well-resolved spectral lines and negligibly low background emission, was obtained from a plasma zone 8 mm from the target surface. The estimated excitation temperature in this zone was around 7000 K. The favorable signal to background ratio obtained in this plasma region indicates possible analytical application of TEA CO2 laser produced copper plasma. Detection limits of trace elements present in the Cu sample were on the order of 10 ppm (parts per million). Time-resolved measurements of spatially selected plasma zones were used to find a correlation between the observed spatial position and time delay.

Comparative study of Nd:YAG laser-induced breakdown spectroscopy and transversely excited atmospheric CO2 laser-induced gas plasma spectroscopy on chromated copper arsenate preservative-treated wood

Taking advantage of the specific characteristics of a transversely excited atmospheric (TEA) CO(2) laser, a sophisticated technique for the analysis of chromated copper arsenate (CCA) in wood samples has been developed. In this study, a CCA-treated wood sample with a dimension of 20 mm × 20 mm and a thickness of 2 mm was attached in contact to a nickel plate (20 mm × 20 mm × 0.15 mm), which functions as a subtarget. When the TEA CO(2) laser was successively irradiated onto the wood surface, a hole with a diameter of approximately 2.5 mm was produced inside the sample and the laser beam was directly impinged onto the metal subtarget. Strong and stable gas plasma with a very large diameter of approximately 10 mm was induced once the laser beam had directly struck the metal subtarget. This gas plasma then interacted with the fine particles of the sample inside the hole and finally the particles were effectively dissociated and excited in the gas plasma region. By using this technique, high precision and sensitive analysis of CCA-treated wood sample was realized. A linear calibration curve of Cr was successfully made using the CCA-treated wood sample. The detection limits of Cr, Cu, and As were estimated to be approximately 1, 2, and 15 mg/kg, respectively. In the case of standard LIBS using the Nd:YAG laser, the analytical intensities fluctuate and the detection limit was much lower at approximately one-tenth that of TEA CO(2) laser.

Direct analysis of powder samples using transversely excited atmospheric CO2 laser-induced gas plasma at 1 atm

A novel method for the direct and sensitive analysis of powder samples has been developed by utilizing the characteristics of a transversely excited atmospheric (TEA) CO(2) laser. In this study, a powder sample was placed in a container and covered by a metal mesh; the metal mesh functions to control the blowing-off of the powder. The container was then perpendicularly attached on a metal surface. When a TEA CO(2) laser (1.5 J, 200 ns) was focused on the metal surface, a large hemispherical gas plasma (radius of around 8 mm) with long emission lifetime (several tens of microseconds) was produced without ablating the metal surface. The high-speed expansion force of the gas plasma samples the powder covered by the metal mesh and fine powder particles are sent into the gas plasma region to be dissociated and excited. Sensitive semi-quantitative analysis was made on organic powder samples such as powdered rice, starch, seaweed (agar), and supplements. The detection limit of heavy metals of Cr in powdered mineral supplement was approximately 0.55 mg/kg.

A unique technique of laser-induced breakdown spectroscopy using transversely excited atmospheric CO 2 laser for the sensitive analysis of powder samples

A sensitive analysis of powder samples has successfully been conducted using a strong gas breakdown plasma induced by assisting a metal mesh and a metal subtarget utilizing a transversely excited atmospheric (TEA) CO 2 laser; the metal mesh and the metal subtarget were placed on the front side and backside of the sample, respectively. The experiment was made at high pressure of air surrounding gas. In this study, the TEA CO 2 laser (1.5 J, 200 ns) was focused on the sample surface through the metal mesh. At the initial stage, a strong gas breakdown plasma was initiated by the assist of the metal mesh and finally enhanced by the metal subtarget after the laser beam struck on the metal subtarget’s surface through a hole inside the sample. The strong gas breakdown plasma can effectively be applied to completely dissociate and excite the ablated atoms from the sample. Using this technique, an excellent calibration curve with zero intercept has been made using herb medicine powder sample containing different concentrations of Zn. For sensitive analysis, a detection of hazard element of Cr in commercial supplement was also carried out. The detection limit of Cr was estimated to be around 0.6 mg/kg. This present technique has high possibility to realize the analysis of powder samples with high precision and high sensitivity.

New Technique for the Direct Analysis of Food Powders Confined in a Small Hole Using Transversely Excited Atmospheric CO2 Laser-Induced Gas Plasma

Taking advantage of the differences between the interactions of transversely excited atmospheric (TEA) CO(2) lasers with metal and with organic powder, a new technique for the direct analysis of food powder samples has been developed. In this technique, the powder samples were placed into a small hole with a diameter of 2 mm and a depth of 3 mm and covered by a metal mesh. The TEA CO(2) laser (1500 mJ, 200 ns) was focused on the powder sample surfaces, passing through the metal mesh, at atmospheric pressure in nitrogen gas. It is hypothesized that the small hole functions to confine the powder particles and suppresses the blowing-off of sample, while the metal mesh works as the source of electrons to initiate the strong gas breakdown plasma. The confined powder particles are then ablated by laser irradiation and the ablated particles move into the strong gas breakdown plasma region to be atomized and excited; this method cannot be applied for the case of Nd:YAG lasers because in such case the metal mesh itself was ablated by the laser irradiation. A quantitative analysis of a milk powder sample containing different concentrations of Ca was successfully demonstrated, resulting in a good linear calibration curve with high precision.

Surface modifications of TiN coating by pulsed TEA CO 2 and XeCl lasers

Interactions of a transversely excited atmospheric (TEA) CO 2 laser and an excimer XeCl laser, pulse durations ∼2 μs (initial spike FWHM ∼100 ns) and ∼20 ns (FWHM), respectively, with polycrystalline titanium nitride (TiN) coating deposited on high quality steel AISI 316, were studied. Titanium nitride was surface modified by the laser beams, with an energy density of 20.0 J/cm 2 (TEA CO 2 laser) and 2.4 J/cm 2 (XeCl laser), respectively. The energy absorbed from the CO 2 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 energy from the excimer XeCl laser primarily leads to fast and intense target evaporation. The calculated maximum temperatures on the target surface were 3770 and 6300 K for the TEA CO 2 and XeCl lasers, respectively. It is assumed that the TEA CO 2 laser affects the target deeper, for a longer time than the XeCl laser. The effects of the XeCl laser are confined to a localized area, near target surface, within a short time period. Morphological modifications of the titanium nitride surface can be summarized as follows: (i) both lasers produced ablation of the TiN coating in the central zone of the irradiated area and creation of grainy structure with near homogeneous distribution; (ii) a hydrodynamic feature, like resolidified droplets of the material, appeared in the surrounding peripheral zone; (iii) the process of irradiation, in both cases, was accompanied by appearance of plasma in front of the target. Target color modifications upon laser irradiation indicate possible chemical changes, possibly oxidation.

Surface modifications of TiN coating by the pulsed TEA CO 2 and KrCl laser

Interaction of a transversely excited atmospheric (TEA) CO 2 and excimer-KrCl laser, pulse duration ∼2 μs (FWHM of initial spike ∼100 ns) and ∼12 ns (FWHM), respectively, with polycrystalline titanium nitride (TiN) coating deposited on high quality steels, was studied. The results have shown that the titanium nitride was surface modified by the laser beam, with an energy density (ED) of 43.0 J/cm 2 (TEA CO 2 laser system) and 3.3 J/cm 2 (KrCl system), respectively. The energy absorbed from the CO 2 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 energy from the excimer-KrCl laser primarily leads to a fast and intense target evaporation. Calculated maximal temperatures, on the target surface, were 3940 and 8000 K for the TEA CO 2 and the KrCl lasers, respectively. It is assumed that TEA CO 2 laser affects the target deeper, during a longer time than the KrCl laser. The effects of the KrCl laser are confined to a localized area, near target surface, in the course of short time. The following morphological changes of titanium nitride surface were observed: (i) both types of laser caused ablation of the TiN coating in the central zone of the irradiated area, (ii) appearance of a hydrodynamic feature like resolidified droplets of material in the surrounding outer zone (cracking) in the case of the TEA CO 2 laser, and (iii) appearance of wave-like microstructures (consisting of periodic parallel fringes with a period of about 20 microns) in the case of KrCl laser. Formation of the wave-like microstructures is discussed in the context of laser-induced periodic surface structure (LIPSS) effects and diffraction phenomena. The process of the CO 2 and KrCl laser interaction with titanium nitride were typically accompanied by plasma formation. Plasma appeared above the target after about 40 and 1 laser pulse, respectively.

Surface modification of stainless steels by TEA CO 2 laser

The interaction of a transversely excited atmospheric (TEA) CO 2 laser with austenitic stainless AISI 316 and high-speed tool AISI M2 steel is considered. The results have shown that both types of steel were surface modified by the laser beam, for the laser energy densities used. Morphological features on the AISI M2 were more prominent in comparison to a AISI 316 steel. On the AISI M2 steel crater like forms, solidified boundary and hydrodynamical modifications were observed, while on the AISI 316 one, corrugation, cracking and resolidified areas were registered. The morphology changes of steel surfaces in dependence of laser pulse temporal shape were analyzed especially. The pulse with a tail for difference of a tail-free pulse, for the same incident peak power density, as a rule caused higher level of damage.

Direct writing of conductive aluminum line on aluminum nitride ceramics by transversely excited atmospheric CO2 laser

The fabrication of very low resistance aluminum conductor line on the aluminum nitride (AlN) by transversely excited atmospheric (TEA) CO2 laser writing was demonstrated. A minimum electrical resistance was measured to be less than 0.1 Ω/mm with a linewidth of 500 μm. The electrical resistance measured is lower than those of conventional conductor lines used for electronic circuits. The x-ray photoelectron spectroscopy depth profile analysis of aluminum layers can explain the resistance of the metallic aluminum layer formed. Compared to the experimental data by KrF laser, TEA CO2 laser writing is found to be a more effective process for fabricating a low resistance conductor line on AlN than the KrF excimer laser.

Investigation of gas chemistry in the sealed TEA CO 2 laser

A general view on the plasma chemistry of lasers, which primarily includes the changes of CO 2, CO and O 2 species, and the corresponding influence on the operation of the sealed transversely excited atmospheric (TEA) CO 2 laser, utilizing a corona discharge preionized system, has been given. Decomposition process of CO 2, especially in the case of standard CO 2/N 2/He gas mixture, was observed. The addition of H 2 as well as CO/H 2 gases extends the total number of stable discharge pulses in the system. Hydrogen improves the plasma stability and the output energy, while carbon monoxide significantly reduces decomposition of CO 2. The CO 2/N 2/He(/CO/H 2) has shown itself as the most convenient gas mixture of achieving long-life operation. An increase of CO 2 concentration in this mixture, when the initial content of CO was 10% has been recorded.

Studies in laser safety of new high-output systems: 2. TEA CO2 laser impacts

The new TEA (transversely excited atmospheric pressure) CO 2 laser can produce ionization of air. No information is as yet available of the effect of this new high-power output laser on man. Repeated impacts of 30 mJ pulses with 100 kW, which produced ionization of air, caused non-specific superficial coagulation necrosis which healed promptly.

WA2--Comparison of theory and experiment for a transversely excited high-pressure CO2laser

Small-signal gain and laser output power have been measured as a function of time for a pin-resistor transversely excited atmospheric (TEA) CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> laser gain device. Both fixed-mirror and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> -switched rotating-mirror laser cavities were studied. A set of coupled differential equations describing the mechanisms underlying gain and lasing behavior are presented. Electrical excitation of the CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> and N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> vibrational modes, collisional relaxation of vibrational energy, and interaction with TEM <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">00</inf> and plane-wave laser radiation are explicitly treated. Electrical excitation is calculated using the measured time-resolved voltage and current input to the TEA CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> gain tube in conjunction with a simple model of the discharge geometry. A single adjustable parameter relating to the physical extent of the electrical discharge enters the calculations. Direct comparisons are made between the measured quantities and the numerical predictions of the model. The value of the adjustable parameter that gives close waveform fits is consistent with the results of other experiments. Use of the rotating-mirror <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> -switched cavity resulted in laser pulses with enhanced peak power for one set of the device parameters studied. An explanation of the phenomenon is presented and a limitation on the applicability of the technique in terms of gas mixtures is discussed.

Selection of a Single Pulse from a Mode-Locked TEA CO2 Laser

The isolation of a single pulse from a transversely excited atmospheric (TEA) CO2 laser, actively mode-locked by an acoustic loss modulator, is described. The single pulse selection has been achieved with the aid of a GaAs electrooptic shutter located either inside or outside the laser resonator. Pulses of 1 MW peak power and 2 ns duration have been recorded with instrument-limited precision. The availability of such pulses uncovers new possibilities for the investigation of laser–matter interactions at 10.6 μm.