TEA CO2 Research Articles

A new grating tuning compound unstable resonator

A proposal of new grating tuning compound unstable resonator is presented. This new type of unstable resonator is profitable for generating single transverse mode, high energy, high-average power tunable laser radiation from TEA CO 2 laser and other gas lasers.

Fourier-wavelet regularized deconvolution (ForWaRD) for lidar systems based on TEA–CO 2 laser

Lidar is an efficient tool for remotely measuring physical quantities or detecting targets. To improve the range resolution in long pulse lidars, such as lidar systems based on TEA–CO 2 lasers, deconvolution methods were used by previous investigators. Deconvolution is a noise sensitive process. In order to avoid noise amplification during the deconvolution process, the Fourier–wavelet regularized deconvolution method is used to deconvolve and denoise the back-scattered lidar signal simultaneously. This method is applied to lidar systems based on the TEA–CO 2 laser and the results are compared to nitrogen tail clipping method. Numerical simulation shows, in comparison to the clipping nitrogen tail technique, by using the ForWaRD method; the range resolution and working distance of the lidar is improved and the clipping tail apparatus is also eliminated.

Numerical solution of Boltzmann tranport equation for TEA CO 2 laser having nitrogen-lean gas mixtures to predict laser characteristics and gas lifetime

Selective laser isotope separation by TEA CO 2 laser often needs short tail-free pulses. Using laser mixtures having very little nitrogen almost tail free laser pulses can be generated. The laser pulse characteristics and its gas lifetime is an important issue for long-term laser operation. Boltzmann transport equation is therefore solved numerically for TEA CO 2 laser gas mixtures having very little nitrogen to predict electron energy distribution function (EEDF). The distribution function is used to calculate various excitation and dissociation rate of CO 2 to predict laser pulse characteristics and laser gas lifetime, respectively. Laser rate equations have been solved with the calculated excitation rates for numerically evaluated discharge current and voltage profiles to calculate laser pulse shape. The calculated laser pulse shape and duration are in good agreement with the measured laser characteristics. The gas lifetime is estimated by integrating the equation governing the dissociation of CO 2. An experimental study of gas lifetime was carried out using quadrapole mass analyzer for such mixtures to estimate the O 2 being produced due to dissociation of CO 2 in the pulse discharge. The theoretically calculated O 2 concentration in the laser gas mixture matches with experimentally observed value. In the present TEA CO 2 laser system, for stable discharge the O 2 concentration should be below 0.2%.

TEA CO 2 Laser Simulator: A software tool to predict the output pulse characteristics of TEA CO 2 laser

“TEA CO 2 Laser Simulator” has been designed to simulate the dynamic emission processes of the TEA CO 2 laser based on the six-temperature model. The program predicts the behavior of the laser output pulse (power, energy, pulse duration, delay time, FWHM, etc.) depending on the physical and geometrical input parameters (pressure ratio of gas mixture, reflecting area of the output mirror, media length, losses, filling and decay factors, etc.). Program summary Title of program: TEA_CO2 Catalogue identifier: ADVW Program summary URL: http://cpc.cs.qub.ac.uk/summaries/ADVW Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Computer: P.IV DELL PC Setup: Atomic Energy Commission of Syria, Scientific Services Department, Mathematics and Informatics Division Operating system: MS-Windows 9x, 2000, XP Programming language: Delphi 6.0 No. of lines in distributed program, including test data, etc.: 47 315 No. of bytes in distributed program, including test data, etc.:7 681 109 Distribution format:tar.gz Classification: 15 Laser Physics Nature of the physical problem: “TEA CO 2 Laser Simulator” is a program that predicts the behavior of the laser output pulse by studying the effect of the physical and geometrical input parameters on the characteristics of the output laser pulse. The laser active medium consists of a CO 2–N 2–He gas mixture. Method of solution: Six-temperature model, for the dynamics emission of TEA CO 2 laser, has been adapted in order to predict the parameters of laser output pulses. A simulation of the laser electrical pumping was carried out using two approaches; empirical function equation (8) and differential equation (9). Typical running time: The program's running time mainly depends on both integration interval and step; for a 4 μs period of time and 0.001 μs integration step (defaults values used in the program), the running time will be about 4 seconds. Restrictions on the complexity: Using a very small integration step might leads to stop the program run due to the huge number of calculating points and to a small paging file size of the MS-Windows virtual memory. In such case, it is recommended to enlarge the paging file size to the appropriate size, or to use a bigger value of integration step.

Theoretical and experimental study of V– I characteristics of UV pre-ionized TEA CO 2 laser for variety of laser gas mixtures

Experimental and theoretical study of V– I characteristics of UV pre-ionized TEA CO 2 laser has been carried out for a variety of gas mixtures emitting different optical pulse shapes suitable for various applications. Coupled differential equations have been solved to model the pulse excitation circuit using the numerically calculated values of ionization coefficient ( α ), attachment coefficient ( β ) and drift velocity ( U d ) as functions of E/N (i.e. electric field to neutral particle density ratio) for chosen gas mixture. Calculated and experimental V–I characteristics for gas mixtures (CO 2:N 2:He::1:2:3, 1:1:4, 1:1:5 and 1:0:4.7) show a good agreement. It has been shown that gas mixture has a dominant effect on the delay between pre-ionization and main discharge; thus, determining the long-term stability of discharge. The excitation pulse duration increases with increase in molecular content of gas mixture (i.e. amount of CO 2 and N 2 in gas mixture).

System of pulsed photoacoustics based on a TEA CO2laser applied to SF6-N2mixtures

A transversal single-mode TEA CO 2 laser, whose cavity design is a diffraction coupled resonator, tuned at the 10P(16) line, is used for photoacoustic detection of SF 6 traces in N 2 . The acoustic cavity, resonant at a longitudinal mode, is designed on the basis of an electric analog model of a one-dimensional resonator. The acoustic signal from SF 6 -N 2 and the signal from a laser energy detector enter simultaneously into a PC through its sound port. The photoacoustic signal, proportional to the average number of absorbed photons per molecule, is found to increase with the laser energy as a power of 0.5. The constant of the setup, previously measured from pulsed photoacoustics on NO 2 -N 2 mixtures excited with the second harmonic of a Q-switched Nd:YAG laser, allows to quantitatively determine the SF 6 absorption cross section as a function of the CO 2 laser fluence. The calibration of this system is performed down to 150 ppbV of SF 6 in N 2 at atmospheric pressure for different values of laser energy.

Pulsed photoacoustic detection of isotopic mixtures of chloroform

Photoacoustic spectroscopy is applied to the detection of small concentrations of CDCl 3 in CHCl 3 -N 2 using a TEA CO 2 laser tuned at the 10P(48) line. At this laser line both species H/D are excited but the ratio betweenabsorbances is such that a relatively higher excitation of the deuterated species is expected compared to other available laser wavelengths. The photoacoustic signal is digitized by an oscilloscope and, at the same time, acquired through the sound port of a PC, pulse by pulse, for comparison of both acquisition methods. The signal processing is performed through the calculation of the standard deviation of each transient. For a fixed mixture the processed signal shows a very good linear dependence on laser energy around 1 mJ. Different mixtures of CDCl 3 in a fixed proportion of CHCl 3 /N 2 are prepared for studying the capability of the photoacoustic technique of distinguishing the deuterated component from the hydrogenated background. The results show that the sensitivity of this setup allows to measure smaller quantities of CDCl 3 in CHCl 3 than those corresponding to natural abundance (150 ppmV).

Improved pulsed photoacoustic detection by means of an adapted filter

We present a numerical and experimental study of two adapted filters devised to the quantitative analysis of weak photoacoustic signals. The first one is a simple convolution-type one and the other is based on neural networks of the multilayer perceptron type. The theoretical signal used as one of the inputs in both filters is derived from the solution of the transient response of the acoustic cell modeled with a simple transmission-line analogue. The filters were tested numerically by using the theoretical signal corrupted with white noise. After 500 iterations it was possible to define an average error for the returned value of each filter. Since the neural network outperformed the convolution-type, we assessed its performance by measuring SF 6 traces diluted in N 2 and excited by tuned TEA CO 2 laser. The results show the use of the neural network filter allows recovering a signal with poor signal-to-noise ratio without resorting to extensive averaging, thus reducing the acquisition time while improving the precision of the measurement.

Atomic Hydrogen Emission Induced by TEA CO2 Laser Bombardment on Solid Samples at Low Pressure and its Analytical Application

Hydrogen emission has been studied in laser plasmas by focusing a TEA CO(2) laser (10.6 microm, 500 mJ, 200 ns) on various types of samples, such as glass, quartz, black plastic sheet, and oil on copper plate sub-target. It was found that H(alpha) emission with a narrow spectral width occurs with high efficiency when the laser plasma is produced in the low-pressure region. On the contrary, the conventional well-known laser-induced breakdown spectroscopy (LIBS), which is usually carried out at atmospheric air pressure, cannot be applied to the analysis of hydrogen as an impurity. By combining low-pressure laser-induced plasma spectroscopy with laser surface cleaning, a preliminary quantitative analysis was made on zircaloy pipe samples intentionally doped with hydrogen. As a result, a good linear relationship was obtained between H(alpha) emission intensity and its concentration.

Characterization of deposits produced by TEA CO 2 pulsed laser ablation of silicon mono- and dioxide

Silicon based deposits were prepared by TEA CO 2 pulsed laser ablation (PLA) of SiO and SiO 2 targets in the atmosphere of selected gases (N 2, He, Ne, Ar, Kr). These deposits possess high specific area of several hundreds m 2 per gram. Owing to the high specific area, some chemical groups and hydrogen related radical were detected by means of FTIR and EPR analyses and theoretical calculations: silyl (E′ center) Si , silylen Si:, silanon Si O, POL (peroxy linkage) SiOOSi and/or NBOHC (non-bridging oxygen hole center) SiO , POR (peroxy radical) SiOO and dioxysilirane Si(O) 2. In SiO 2 deposits the concentration of silyl Si resp. POR SiOO was determined to be 5.8 × 10 18/g resp. 6.2 × 10 19/g. In SiO deposits the ratio [ Si:]:[ Si ] = (3.1–5.7) × 10 19/g: (5.3–9.8) × 10 19/g was measured. Estimated concentration of [ Si ] in deposits was increased nearly five times in comparison with SiO target. After exposure of the SiO deposits to H 2 EPR doublet with hyperfine splitting of 7.7 mT was observed. The best agreement between calculated theoretical and experimental values was found for the model [(HO) 3SiO] 2HSi . FTIR measurements and calculations of the silanol theoretical model clusters enabled us to discuss the chemical surroundings of the silanol and to determine the defects in the deposits.

A 3 kW average power tunable TEA CO 2 laser

A high average power line-tunable TEA CO 2 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 CO 2 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.

Carbon Analysis for Inspecting Carbonation of Concrete Using a TEA CO2 Laser-Induced Plasma

It has been demonstrated that a spectrochemical analysis of carbon using the laser plasma method can be successfully applied to inspect the carbonation of concrete by detecting carbon produced in aged concrete by a chemical reaction of Ca(OH)2 with CO2 gas in environmental air, turning into CaCO3, which induces degradation of the quality of building concrete. A comparative study has been made using a TEA CO2 laser (500-1000 mJ) and a Q-switched Nd-YAG laser (50-200 mJ) to search for the optimum conditions for carbon analysis, proving the advantage of the TEA CO2 laser for this purpose. Also, it was clarified that laser irradiation with suitable defocusing conditions is a crucial point for obtaining high sensitivity in the detection of carbon. Practical experiments on the inspection of carbonation were carried out using both a concrete sample that had been intentionally carbonated by exposure to high concentrations of CO2 gas and a naturally carbonated concrete sample. As a result, good coincidence was observed between the laser method and the ordinary method, which uses the chemical indicator phenolphthalein, implying that this laser technique is applicable as an in situ quantitative method of inspection for carbonation of concrete.

IR laser decomposition of 1,3-disilacyclobutane in presence of carbon disulfide: chemical vapour deposition of polythiacarbosilane

TEA CO 2 laser irradiation of gaseous mixtures of 1,3-disilacyclobutane – carbon disulfide affords chemical vapour deposition of solid polythiacarbosilane films that possess Si–S–X (X = Si, C), S–H and Si–H bonds and undergo slow hydrolysis in air to polyoxothiacarbosilanes containing Si–H, Si–O–Si and (C)S–H bonds. The formation of the polythiacarbosilane is proposed to take place via polymerization of transient silene and incorporation of CS 2 into growing polysilene network.

Modification of Carbon Cloth by Interaction with Pulsed TEA CO<sub>2 </sub>Laser

Modification of Carbon Cloth by Interaction with Pulsed TEA CO<sub>2 </sub>Laser

Comparative study of dentine permeability after apicectomy and surface treatment with 9.6 microm TEA CO2 and Er:YAG laser irradiation.

Failure of apicectomies is generally attributed to dentine surface permeability as well as to the lack of an adequate marginal sealing of the retrofilling material, which allows the percolation of microorganisms and their products from the root canal system to the periodontal region, thus compromising periapical healing. The purpose of this study was to evaluate dentine and the marginal permeability after apicectomy and surface treatment with 9.6 micro m TEA CO(2) or Er:YAG 2.94 micro m laser irradiation. Sixty-five single rooted human endodontically treated teeth were divided into five experimental groups: group I (control), apicectomy with high speed bur; group II, similar procedure to that of group I, followed by dentinal surface treatment with 9.6 micro m CO(2) laser; group III, similar procedure to group I followed by dentinal surface treatment with Er:YAG laser 2.94 micro m; group IV, apicectomy and surface treatment with CO(2) 9.6 micro m laser; and group V, apicectomy and surface treatment with Er:YAG laser 2.94 micro m. The analysis of methylene blue dye infiltration through the dentinal surface and the retrofilling material demonstrated that the samples from the groups that were irradiated with the lasers showed significantly lower infiltration indexes than the ones from the control group. These results were compatible with the structural morphological changes evidenced through SEM analysis. Samples from groups II and IV (9.6 micro m CO(2)) showed clean smooth surfaces, fusion, and recrystallized dentine distributed homogeneously throughout the irradiated area sealing the dentinal tubules. Samples from groups III and V (Er:YAG 2.94 micro m) also presented clean surfaces, without smear layer, but roughly compatible to the ablationed dentine and without evidence of dentinal tubules. Through the conditions of this study, the Er:YAG 2.94 micro m and the 9.6 micro m CO(2) laser used for root canal resection and dentine surface treatment showed a reduction of permeability to methylene blue dye.

Power scaling of printed-circuit-board preionized TEA CO 2 laser up to [formula omitted

A high average power, high-repetition-rate TEA CO 2 laser employing printed-circuit-board preionizer is described. The power scaling of this preionization configuration has been demonstrated. The average output power reaches 3.6 kW at pulse repetition rate of 180 pps . Furthermore, the scaling-up ability of the rotating spark gap as high-voltage switch for high-average-power gas laser has been validated.

The structure of multi-electrode-pair pulse laser and discharge pulse time selection

Applying multi-electrode-pair pulse TEA CO 2 laser to one optical resonance cavity will have several advantages over traditional method, including higher gain, shorter pulse discharge time interval, and in particular, continuous adjustable time interval of multi-pulse laser output can be achieved without high vacuum condition. To improve laser's working stabilization, we proposed new approaches to optimize laser structure design and discharge pulse time interval selection.

IR laser ablation of silicon monoxide in gaseous methanol and hydrocarbons: deposition of polyoxocarbosilane

TEA CO 2 laser-induced (thermal) ablation of amorphous silicon monoxide in gaseous methanol and hydrocarbon (ethane, ethene, ethyne) results in chemical vapour deposition of solid nano-structured polyoxocarbosilane coatings. The coatings analyzed by FTIR spectroscopy and X-ray photoelectron spectroscopy (XPS) are revealed as composed of different Si k O l H m C n configurations and containing SiOCH x , SiCH x and SiH bonds (ablation in methanol) or SiH and SiCH x bonds (ablation in hydrocarbons). The enrichment by H and CH x groups is dependent on methanol and hydrocarbon pressure. The incorporation of carbon during the SiO ablation in hydrocarbons grows in the series ethane<ethene<ethyne.

Confinement effect in enhancing shock wave plasma generation at low pressure by TEA CO 2 laser bombardment on quartz sample

An experimental study on the pre-irradiation effect observed on quartz sample when TEA CO 2 laser pulse (550 mJ, 200 ns) was focused repeatedly at a fixed point of quartz sample under surrounding gas of air at 2 torr was made. The disappearance of this effect at later stages was found to be connected with the appearance of a crater of appropriate depth created by repeated irradiation on the sample surface. Analysis of the experimental data imply that the pre-irradiation effect is due to the confinement of the fast electron and by the confinement of the electrons, laser absorption takes place effectively to induce localized hot plasma from which atoms can gush with supersonic speed. Hydrodynamic confinement also takes place after several tens of shots of the laser irradiation due to the geometrical focusing of gushed atoms flow in the crater with effective enhancement of the shock wave generation.

Efficient spiker-sustainer excitation scheme for transversely excited gas lasers

An efficient spiker-sustainer excitation scheme wherein a single source power and a single switch controls all the three discharges viz., the pre, the spiker, and the sustainer is reported. The delay between the discharges can be controlled by the usage of a simple wire wound inductance of appropriate value. The isolation element between the spiker and the sustainer discharges, an integral part of the conventional spiker-sustainer excitation scheme, is dispensed with here. The performance of this scheme has been tested in the operation of a TEA CO 2 laser, which produced energy of 2.1 J per pulse at an operating efficiency of 18%.