Transversely Excited Atmospheric Research Articles

Thermo-optic dispersion properties of CdSe for parametric nonlinear interactions

Temperature tuning of CdSe optical parametric oscillators (OPO’s) is studied by pumping with the 1.8645-µm signal and 2.4793-µm idler outputs of a Nd:YAG laser-pumped CsTiOAsO4 (CTA) OPO. The measured temperature-dependent phase-matching conditions are used to construct new Sellmeier and thermo-optic dispersion formulas for CdSe, which are verified via temperature-tuned sum-frequency generation (SFG) between the fundamental and second harmonic of a transversely excited atmospheric (TEA) CO2 laser operating at 10.2466, 9.5525, and 9.2714 µm.

Development of Low-Cost Prototype N<sub>2</sub> Laser System and Laser-Induced Fluorescence of Pyranine

This work aims to a detailed description of the development of a prototype Transversely Excited Atmospheric (TEA) nitrogen laser and its high-tension electrical pump source, along with its application study of Laser-Induced Fluorescence (LIF). The high-tension pump source is designed and simulated by using NI Multisim to study the voltage behavior at different points. The high-tension pump source is constructed using the flyback transformer. The open-air laser cavity is designed and simulated by using Zemax Optic Studio. Blumlein transmission line equivalent of nitrogen laser is designed in NI Multisim, voltage and current behavior across laser cavity and spark gap are simulated. The air is used as a lasing medium, as it contains 78% molecular nitrogen. The L-shaped electrodes are used as a cavity in the construction of this N₂ laser system. An ignition system in the form of the low inductance spark gap is built using the two bolts. Generally, the current passes through gas either by transverse or longitudinal discharge; in this work, the transverse discharge technique is used. Nitrogen laser produces a beam with a center wavelength of 337.1nm. Laser-induced fluorescence spectrum of the Pyranine is taken which shows its fluorescence in the green region with a maximum peak at the wavelength of 567.5nm. Pyranine is made up of a mixture of C₁₆H₇Na₃O₁₀S₃ so some other peaks can also be seen in the fluorescence spectrum with low intensity.

TEA CO2 Laser – Polymethyl Methacrylate Interaction: LIBS Hydrogen Analysis

The interaction of a Transversely Excited Atmospheric (TEA) CO2 laser with a polymer polymethyl methacrylate (PMMA) sample in a vacuum ambiance was studied. The main goal was to demonstrate the feasibility of laser-induced breakdown spectroscopy (LIBS) to detect hydrogen. The generation of plasma over the PMMA surface, using a low laser intensity of ∼ 48 MW/cm2 and fluence of ∼ 16.5 J/cm2, required the application of a metal sub-target. Besides hydrogen, the recorded spectra were dominated by atomic lines of carbon and oxygen and band emission of the C2 and CN molecules. The electron number density and temperature (ionic, vibrational, and rotational) were evaluated to characterize the laser-induced plasma. In addition, PMMA micro-damages (diameter ∼ 45 µm) created by a multipulse laser ablation could find potential applications in sensor technologies.

Laser-Induced Plasma as a Method for the Metallic Materials Hardness Estimation: An Alternative Approach

The application of an alternative laser-induced breakdown spectroscopy (LIBS) method based on transversely excited atmospheric (TEA) CO2 laser was investigated for the first time for estimating the hardness of metallic materials. The human eye-safe (TEA) CO2 laser, operating at 10.6 µm, was used for plasma generation. The LIBS spectra were recorded by employing a cost-effective CCD camera for the time-integrated and spatial resolved measurements. The cast iron and aluminum alloys samples with different hardness have been tested. The ratio between the magnesium ionic and neutral lines in LIBS spectra was applied for estimating the material hardness. In addition, the hardness of all samples included in this study was determined using the conventional method for material hardness determination, i.e. Vickers hardness test. The linear dependence of magnesium lines intensity ratio on the sample’s hardness was obtained for both kinds of materials. Profilometric measurements were used to verify that the newly-introduced method is almost nondestructive for the investigated metals. The results obtained in the present work confirmed the potential of using this original LIBS system not only for the fast elemental analysis but also for the direct estimation of the hardness of metals and alloys.

Energy dependence of Cl emission lines in CO2 laser induced breakdown spectroscopy

Chlorine (Cl) detection using laser induced breakdown spectroscopy (LIBS) techniques in geology and environment samples is still challenging since the experimental conditions greatly influence the analytical performance of LIBS. Cl emission in LIBS must be studied carefully to find the optimum condition to allow Cl detection. In the present study, Cl emission was studied from polyvinyl chloride (PVC) sample containing Cl as major element. A Transversely Excited Atmosphere (TEA) carbon dioxide (CO2) laser was used for inducing plasma from the sample. Cl emission was investigated by varying the experimental conditions, especially energy of the laser pulse. The emission spectrum from the consequent plasma was detected using an Optical Multichannel Analyzer (OMA) system. It was found that Cl emission lines only can be obtained when helium was used as the surrounding gas. The strongest emission line of Cl I 837.59 nm in the infrared region cannot be detected even under helium surrounding gas. Instead, many ionic emission lines of Cl in ultraviolet regions including the strong ionic lines (Cl II 479.45 nm, Cl II 481.00 nm, Cl II 481.94 nm and the weak lines (Cl II 476. 86 nm, Cl II 478.13 nm, Cl II 489.67 nm, Cl II 490.47 nm and Cl II 491.77 nm) can unequivocally be detected. It was also found that the intensity of Cl emission lines critically depends on the energy of the laser pulse, namely the emission intensity of Cl lines increases sharply with energy. In present work, the highest intensity of Cl emission lines was obtained when the energy of the laser pulse was about 2500 mJ, giving strong and clear Cl emission lines with low background and relatively high signal to background ratio of more than 3.

EUV spectroscopy of optically thin Ge VI-XI plasmas in the 9-18 nm region

Identification of previously unclassified emission features in the extreme ultraviolet (EUV) spectra of Ge VI to XI has been carried out by recording emission from laser-produced plasmas created using a high-powered Transversely Excited Atmospheric (TEA) CO2 laser. The analysis was carried out using the Cowan suite of atomic structure codes with the aid of the unresolved transition array (UTA) statistical approach to determine the extent of the transition arrays, lines in Ge VI to Ge XI have been identified.

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.

Power broadening and its effects in TEA CO2 lasers

In this paper, a new mechanism which limits extracted peak power in transversely excited atmospheric (TEA) CO2 lasers is introduced. This mechanism is power broadening that we considered it as a saturation term here. A comprehensive model has been developed and used to study the influence of the proposed mechanism on the gain switched pulse in TEA CO2 lasers. We have demonstrated that output peak power will be reduced whenever power broadening dominates collision broadening. Also, it has been found that power broadening is more effective than rotational coupling. The numerical simulations well reproduce the experimental gain switched pulse and exactly predict the laser peak power.

Detection of salts in soil using transversely excited atmospheric (TEA) carbon dioxide (CO2) laser-induced breakdown spectroscopy (LIBS) by the aid of a metal mesh

In this work, a nickel metal mesh was used to allow a direct detection of salt in soil sample by LIBS utilizing unique characteristics of a TEA CO2. The metal mesh is placed in the front of the soil sample to prevent the soil sample from blowing off upon focusing the high pulsed laser beam irradiation. LIBS apparatus used in this work is a TEA CO2 laser operated at wavelength of 10.6 μm with pulse energy and duration of 3J and 200 ns, respectively. The laser beam was focused using a ZnSe lens (f = 200 mm) onto soil sample after passing through the metal mesh. The emission spectrum from the induced plasma was detected using an optical multichannel analyzer (OMA) system consisting of a 0.32-m-focal length spectrograph with a grating of 1200 graves/mm and a 1024-channel photodiode detector array with a micro-channel plate intensifier. The soil sample used is a standard soil and ordinary soil containing several salts such as Ca, Mg at high concentration. The LIBS experiment was carried out at high pressure surrounding gas of 1 atmosphere. It was observed that by the aid of the metal mesh, strong breakdown gas plasma can be produced just after TEA CO2 laser irradiation on soil sample without significant sample blowing off. It was found that emission lines from salts, Ca (Ca II 393. 3 nm, Ca II 396.3 nm, Ca I 422.5 nm), and also other salts including Mg and Na can clearly be detected with strong emission intensity and narrow spectral width. This result implies that a TEA CO2 LIBS assisted by the metal mesh (metal mesh method) can be used for direct analysis several salts such as Ca, Mg, and Na in soil sample.

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.

Mode transition of plasma expansion for laser induced breakdown in Air

High-speed shadowgraph visualization experiments conducted using a 10 J pulse transversely excited atmospheric (TEA) CO2 laser in ambient air provided a state transition from overdriven to Chapman–Jouguet in the laser-supported detonation regime. At the state transition, the propagation velocity of the laser-supported detonation wave and the threshold laser intensity were 10 km/s and 1011 W/m2, respectively. State transition information, such as the photoionization caused by plasma UV radiation, of the avalanche ionization ahead of the ionization wave front can be elucidated from examination of the source seed electrons.

Elemental analysis of aluminum alloys by Laser Induced Breakdown Spectroscopy based on TEA CO2 laser

The applicability of nanosecond infrared Transversely Excited Atmospheric (TEA) CO2 laser induced plasma for spectrochemical analysis of aluminum alloys was investigated. The plasma was generated by focusing a pulsed TEA CO2 laser that emits at 10.6 μm on the Al target in ambient air at atmospheric pressure. The temporal profile of the laser pulse is composed of a 100 ns peak followed by a slowly decaying tail of about 2 μs. The output pulse energy was approximately 160 mJ, thus the peak output power was estimated to be around 1.6 MW. Time-Integrated Space-Resolved Laser Induced Breakdown Spectroscopy (TISR-LIBS) was employed to obtain the emission spectra. The maximum intensity of emission, with sharp and well resolved spectral lines that were almost free of the background continuum, was obtained from plasma region 2 mm from the target surface. Linear calibration curves for Mg, Cr, Cu and Fe were obtained using aluminum alloy spectrochemical standards. The limits of detection for the investigated elements were in the 2–73 ppm range. Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) was used as a reference technique to estimate the accuracy of LIBS determination by use of control samples with known compositions. Comparison of the obtained results with those available in the literature confirms that LIBS system based on TEA CO2 laser, in combination with TISR spectral measurements, can be successfully applied to qualitative and quantitative determinations of minor elements in aluminum based alloys.

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.

Metal-Assisted Laser-Induced Gas Plasma for the Direct Analysis of Powder Using Pulse CO2 Laser

Analysis of powder samples available in small quantities has been carried out using metal-assisted gas plasma by utilizing a transversely excited atmospheric (TEA) CO2 laser. The powder was homogeneously mixed with Si grease, and the mixed powder was painted on a metal subtarget. When a TEA CO2 laser was directly focused on the metal subtarget at atmospheric pressure of He gas, a high-temperature He gas plasma was induced. It is assumed that the powder particles were vaporized to be effectively atomized and excited in the gas plasma region. This method has been employed in the rapid analyses of elements in organic and inorganic powder samples present in small quantities. Detection of trace elements of Cr and Pb has been successfully made by using the supplement powder and loam soil, respectively. The detection limits of Pb in loam soil were approximately 20 mg/kg.

Moderation of near-field pressure over a supersonic flight model using laser-pulse energy deposition

The impact of a thermal bubble produced by energy deposition on the near-field pressure over a Mach 1.7 free-flight model was experimentally investigated using an aeroballistic range. A laser pulse from a transversely excited atmospheric (TEA) CO2 laser was sent into a test chamber with 68 kPa ambient pressure, focused 10 mm below the flight path of a conically nosed cylinder with a diameter of 10 mm. The pressure history, which was measured 150 mm below the flight path along the acoustic ray past the bubble, exhibited precursory pressure rise and round-off peak pressure, thereby demonstrating the proof-of-concept of sonic boom alleviation using energy deposition.

The feasibility of TEA CO2 laser-induced plasma for spectrochemical analysis of geological samples in simulated Martian conditions

The present work studies the possibility of using pulsed Transversely Excited Atmospheric (TEA) carbon dioxide laser as an energy source for laser-induced breakdown spectroscopy (LIBS) analysis of rocks under simulated Martian atmospheric conditions. Irradiation of a basaltic rock sample with the laser intensity of 56MWcm−2, in carbon-dioxide gas at a pressure of 9mbar, created target plasma with favorable conditions for excitation of all elements usually found in geological samples. Detection limits of minor constituents (Ba, Cr, Cu, Mn, Ni, Sr, V, and Zr) were in the 3ppm–30ppm range depending on the element. The precision varied between 5% and 25% for concentration levels of 1% to 10ppm, respectively. Generally, the proposed relatively simple TEA CO2 laser-LIBS system provides good sensitivity for geological studies under reduced CO2 pressure.

Time- and space-resolved spectroscopic characterization of laser-induced swine muscle tissue plasma

The spatial-temporal evolution of muscle tissue sample plasma induced by a high-power transversely excited atmospheric (TEA) CO2 pulsed laser at vacuum conditions (0.1–0.01Pa) has been investigated using high-resolution optical emission spectroscopy (OES) and imaging methods. The induced plasma shows mainly electronically excited neutral Na, K, C, Mg, H, Ca, N and O atoms, ionized C+, C2+, C3+, Mg+, Mg2+, N+, N2+, Ca+, O+ and O2+ species and molecular band systems of CN(B2Σ+–X2Σ+), C2(d3Πg–a3Πu), CH(B2Σ−–X2Π; A2Δ–X2Π), NH(A3Π–X3Σ−), OH(A2Σ+–X2 Σ+), and CaOH(B2Σ+–X2Σ+; A2Π–X2Σ+). Time-resolved two-dimensional emission spectroscopy is used to study the expanded distribution of different species ejected during ablation. Spatial and temporal variations of different atoms and ionic excited species are reported. Plasma parameters such as electron density and temperature were measured from the spatio-temporal analysis of different species. Average velocities of some plasma species were estimated.

Efficient Oscillator for 192-μm Optically Pumped Pulsed Laser

An efficient cavity oscillator for a 192-μm pulsed laser radiation is presented when pumped with a transverse excited atmospheric (TEA) CO2 laser. A maximum power of 7.1 kW is achieved from a 100-cm cavity. The oscillation behavior of the 192-μm laser has resulted in an increase in energy of 45 % as compared with a mirror-less process and an energy conversion efficiency of 0.1 %. Oscillation characteristics are discussed including the pulse width and time delay. The laser spot size is measured according to the knife-edge scan technique while the output beam quality M2 factor is about 1.33.

Food powder analysis by using transversely excited atmospheric CO2 laser-induced plasma spectroscopy

A direct and sensitive analysis of food powder sample has successfully been carried out by utilizing the special characteristics of pulsed transversely excited atmospheric (TEA) CO2 laser. In this study, a food powder was placed in a container made of copper plate and covered by a metal mesh. The container was perpendicularly attached on a metal surface. A high-temperature luminous plasma was induced on a metal surface 5 mm above the mesh. Once the plasma was produced, a strong shock wave was induced, blowing-off of the powder from the container to enter into the plasma to be dissociated and excited. By using this method, a semi-quantitative analysis of food powder was made. The detection limits of Cr in the powdered agar and Cd in the powdered rice were 9 mg/kg and 50 mg/kg, respectively.