TEA CO2 Research Articles

Quantification of sodium contaminant on steel surfaces using pulse CO2 laser-induced breakdown spectroscopy

Corrosion is one of the main reasons for in-core accidents in liquid sodium-cooled fast reactors, especially accidents due to fuel cladding pipe damage. It is urgently required to investigate what kind of compound is produced as a corrosion product after the interaction between stainless steel and sodium in fast breeder reactors (FBR). In this work, the identification and quantification of sodium contaminant on steel surfaces has been conducted using laser-induced breakdown spectroscopy utilizing the specific characteristics of a pulse transversely excited atmospheric CO 2 laser. Experimentally, a pulse TEA CO 2 laser (Shibuya, 10.64 μm, 200 ns) was directed and bombarded onto the sodium contaminant deposited on the surface of stainless steel. An excellent emission spectrum of sodium from the contaminant was obtained without any disturbance from analytical lines from the steel itself. A quantification of sodium contaminant on the steel surface has been successfully made by a linear calibration curve obtained from steel containing various concentrations of sodium. The limit of detection of sodium on the metal surface was estimated to be 0.5 mg/kg. Also, a comparative sodium analysis study was qualitatively made by using LIBS utilizing a pulse Nd:YAG laser. The results demonstrate that the present technique of TEA CO 2 LIBS is far superior to the case of Nd:YAG LIBS, as proven by an excellent emission spectrum of sodium with optimum intensity, and low noise and background emission.

Damage effect of TEA CO<sub>2</sub> long wave infrared laser on detector assembly of infrared staring imaging system

Damage effect of TEA CO<sub>2</sub> long wave infrared laser on detector assembly of infrared staring imaging system

Optical emission of graphite plasma generated in ambient air using low-irradiance carbon dioxide laser pulses

Optical emission studies of graphite plasma induced by infrared (IR) Transversely Excited Atmospheric carbon dioxide (TEA CO2) laser pulses in ambient air at atmospheric pressure are reported. The plasma was induced at relatively low-irradiance, up to 40 MW cm−2, and the plasma emission was recorded using time-integrated LIBS measurements. The time profile of the 160 mJ laser pulse is composed of a short, 100 ns long initial spike, and a long 2 μs tail. About 60 mJ is contained in the initial pulse, and the 100-mJ tail contribution is favorable for extended plasma absorption that promotes creation of long-lasting highly-excited plasma. With laser pulse focused behind the target surface, recorded spectra consisted of intensive, sharp atomic and single charged ionic spectral lines of carbon, and trace elements, e.g. Ca, Cu, V, Si, and Ti. Good signal to background ratios obtained indicate potential application in the analysis of impurities in graphite, and also elemental analysis of other materials with high carbon content. The average electron number density was determined from Stark-broadened emission profile of C I 247.9 nm line, and the line intensity ratio of CII 250.9 nm/C I 247.9 nm line pair was used for estimation of ionization temperature. Depending on the applied fluence, electron density was in the range 2.6–4.8 × 1017 cm−3, and ionization temperature between 19,000 and 22,000 K. Beside line spectra, intensive and well-developed band spectra of diatomic molecules C2 (Swan system), and CN (violet system) were obtained. Pulse energy threshold for observation of molecular emission was 50 mJ. From the spectroscopic studies of the emission bands, the rotational and vibrational temperatures were estimated by comparing the experimental and simulated emission spectra. Vibrational and rotational temperatures deduced from Δν = 0 sequences of the Swan system of C2 were 3100 K and 3850 K, respectively. The most intense band of the CN violet system showed strong self-absorption and led to overestimated temperature values, Tvib = Trot = 4900 K.

Analysis of ceramics surface modification induced by pulsed laser treatment

This paper presents the effects of laser light irradiation on the surface of ceramics dating from archaeological site Stubline (Obrenovac, Belgrade), Serbia. Two different pulsed lasers: TEA CO2 (10.6 ?m wavelength, pulse duration tp = 100 ns) and Nd:YAG (wavelengths 1064 nm and 532 nm, tp = 150 ps) have been used for surfaces treatment. Laser irradiation fluence was in the range of 1-20 J/cm2. Ceramics surface modifications induced by pulsed laser treatment were examined by scanning electron microscope, SEM, and the composition with energy dispersive X-ray, EDX, analysis. The tests were performed in order to obtain as much as possible information about the appropriate choice of materials and techniques for the further conservation and restoration of these items. The second objective was to determine the surface modifications induced by pulsed laser treatment above damage threshold (a safe cleaning laser fluence), as an important parameter in the use of lasers for the cleaning of cultural ceramic items.

Stochastic method for determining the coherence length of a TEA CO2 laser

Abstract In this work the results of the measurement of the coherence length of a TEA CO 2 laser developed in DEILAP are presented. A Michelson interferometer of about 5 m of optical path length difference was built for this purpose. A motorized translation optical mount was placed in one arm in order to enable the variation of the optical path length in many wavelengths. The length of the other arm was varied manually in steps of several tens of centimeters. Spatial filtering forced the laser to oscillate in a single transverse mode, TEM 00 . An innovative stochastic technique for data analysis allowed determining the amount of longitudinal modes, the amplitude and the individual average coherence length of each mode as well as the global coherence length of the laser. This technique was later compared with a method based on the analysis of the Fourier transform of the time series obtained at the interferometer input.

Relation Between Discharge Length and Laser Pulse Characteristics in Longitudinally Excited CO2 Laser

A longitudinally excited CO2 laser pumped by a fast discharge emits a short laser pulse, similarly to TEA and Q-switched CO2 lasers. We investigated the relation between the discharge length and the laser pulse characteristics to develop a longitudinally excited CO2 laser producing a high spike laser pulse. We examined discharge lengths of 30, 45, and 60 cm, using the same mirrors and the same excitation circuit with the same input energy. A longer discharge length increased the discharge volume and improved the laser output energy. However, the longer discharge length caused a long discharge formation time (a slow fall time of the discharge voltage) due to the higher discharge impedance, which resulted in a long laser pulse tail. Therefore, the longitudinally excited CO2 laser had optimum conditions for obtaining a high spike laser pulse effectively.

Fast Discharge Circuit for Longitudinally Excited CO2 Laser

In a longitudinally excited CO2 laser with a short laser pulse, similarly to TEA and Q-switched CO2 lasers, a fast discharge is very important. We investigated the use of a fast discharge circuit to obtain a high spike laser pulse in a longitudinally excited CO2 laser. We compared a traditional capacitor-transfer circuit having a buffer capacitance of 700 pF with our direct-drive circuit in which the buffer capacitance is removed. The direct-drive circuit produced a fast discharge and a high spike laser pulse. We also investigated the effect of a resistance connected in parallel with the discharge tube to eliminate low discharge current after the main discharge. A low resistance of 1 kΩ or less acted as a shunt resistance. The shunt resistance was effective in decreasing the energy of the laser pulse tail at high gas pressure.

Optimizing the process of generating the second harmonic of the radiation of a TEA CO_2 laser in a ZnGeP_2 crystal

The creation of a high-intensity source in the 4.6–5.4-µm range is a problem that has attracted the attention of researchers for several decades. This paper describes the optimization of the process of generating the second harmonic of the radiation of a pulse-periodic TEA CO<sub>2</sub> laser by choosing a nonlinear crystal and the temporal shape of the laser-pump pulse. Energy-conversion efficiency of up to 20% has been experimentally obtained in a ZnGeP<sub>2</sub> crystal with mean power of the radiation in the λ=4.8µm region of up to 0.24 W and a pulse repetition rate of 10 Hz.

A study of Roman glass from Mala Barutana/Belgrade Fortress irradiated with pulsed CO2, Nd:YAG and ruby laser — Comparison

Application of non-contact and rapid laser technique, which is minimally invasive, non-contaminant and efficient method, for ancient glass investigation and cleaning is highly desirable for restoration purposes. Irradiation of Roman glass dated from 1st to 4th/5th century AD with TEA CO2 (wavelength 10.6μm; pulse duration tp=100ns), Nd:YAG (wavelength 1064nm and 532nm; tp=150ps) and ruby laser (wavelength 694nm; tp=30ns) in air ambience was studied. For all three lasers, moderate energy densities (15–30J/cm2) induced significant changes of morphology — from superficial exfoliation and occurrence of mosaic structure after few pulses to deep damages and hydrodynamic features after higher number of accumulated shots. Irradiation with moderate energy density, accompanied with plasma appearance in front of the samples, is convenient for numerous potential applications, particularly surface elemental analysis such as laser induced breakdown spectroscopy. On the other hand, lower densities are more suitable for Roman glass cleaning. Calculations of Roman glass surface temperature have shown that pulsed CO2 laser is favorable for surface cleaning and optimal fluence is ~2J/cm2. This was confirmed by additional experiments for fluences 1.5 and 3J/cm2. Morphological changes on the Roman glass surface induced by lasers were studied by optical microscopy (OM) and scanning electron microscopy (SEM). The composition of Roman glass was determined by energy dispersive X-ray analysis (EDX) and inductively coupled plasma (ICP) method. Chemical analysis confirmed that the investigated glass dates from the Roman period.

Amplification of multi-gigawatt 3 ps pulses in an atmospheric CO_2 laser using ac Stark effect

The 3 ps pulses are amplified to ~20 GW peak power in a TEA CO(2) laser using ac Stark broadening. Demonstration of such broadband coherent amplification of 10 μm pulses opens opportunities for a powerful mid-IR source at a high-repetition rate.

Simple Short-Pulse CO2 Laser Excited by Longitudinal Discharge without High-Voltage Switch

We have developed a longitudinally excited CO2 laser without a high-voltage switch. The laser produces a short laser pulse similar to those from TEA and Q-switched CO2 lasers. This system, which is the simplest short-pulse CO2 laser yet constructed, includes a pulsed power supply, a high-speed step-up transformer, a storage capacitor, and a laser tube. At high pressure (4.2 kPa and above), a rapid discharge produces a short laser pulse with a sharp spike pulse. In mixed gas (CO2: N2: He = 1: 1: 2) at a pressure of 9.0 kPa, the laser pulse contains a spike pulse of 218 ns and has a pulse tail length of 16.7 μs.

Performance of a self-switched TEA CO 2 laser with multi/two/single spark channel preioniser

Satisfactory performance of a TEA CO 2 laser of active length 30 cm is reported when self-switched by its own preioniser comprising two mutually coupled parallel spark channels or even one spark channel. A comparison of the performance of the laser with respect to the maximum extractable energy and electro-optic efficiency as a function of number of preionising spark channels is presented. With reduced number of mutually coupled parallel spark channels, the operation approaches the near ballast-free regime, resulting thereby, in an improved performance of the laser.

Sub-wavelength micromachining of silica glass by irradiation of CO2 laser with Fresnel diffraction

We investigated a simple and productive micromachining method of silica glass by ablation using a TEA CO 2 laser (10.6 μm) with a spatial resolution down to sub-wavelength scale. The silica glass was irradiated by the TEA CO 2 laser light through a copper grid mask with square apertures of 20 x 20 μm 2 attached to the silica glass surface. After the irradiation, circular holes with a diameter of several μm were formed on the silica glass surface at the centers of the apertures due to the Fresnel diffraction effect. The minimum diameter of the holes was 3.4 μm. The characteristics of the micromachining are discussed based on the electric field distributions of the CO 2 laser light under the mask using a three-dimensional full-wave electromagnetic field simulation.

CO 2 laser assisted removal of UO 2 and ThO 2 particulates from metal surface

Pulsed laser assisted removal of uranium dioxide and thorium dioxide particulates from stainless steel surface have been studied using a TEA CO 2 laser. Decontamination efficiency is measured as a function of laser fluence and number of pulses. Threshold fluence for the removal of UO 2 particulates has been found to be lower than that required for the removal ThO 2 particulates. Usage of a ZnSe substrate, that is transparent to the laser wavelength used here, enabled us to decouple the cleaning effect arising out of absorption in the particulates from that in the substrate and has contributed towards understanding the mechanism responsible for cleaning. The experimental observations are also corroborated by simple theoretical calculations.

TEA CO2非稳腔激光器远场光束质量的评价

The evaluation methods for far field optical quality of a TEA CO2 laser with a unstable resonator were researched. Based on the real data of the unstable resonator modified by the stable resonator of a high power TEA CO2 laser,three common theoretical evaluation methods were conducted to evaluate the optical quality.Obtained results were compared with that from the far field optical intensity distribution of a designed 2 kW unstable resonator laser.The analysis and comparison show that the unstable resonator can obtain a near diffraction limit and a high optical quality beam and the β factor is 4 times that of the stable resonator.Under the same power level,the far field power density of the unstable resonator is 19 times that of the stable one.Furthermore,the smaller block factor can obtain a higher power in bucket for the unstable resonator.It is concluded that the comprehensive prediction and evaluation of designed unstable resonator need to synthetically use the three theoretical methods to complete.

A sensitive arc detection technique for reliable operation of high repetition rate TEA CO 2 laser

A simple and sensitive technique, which utilizes the sensing of both the discharge current and the visible light emission from the discharge, has been developed to detect the arc formation during the operation of a high repetition rate TEA CO 2 laser. It is shown that the optical detection in the visible spectral region is more sensitive than that it is in the UV region and hence can be used more effectively to monitor the onset of arc formation, while the current signal is useful in the strong arc formation regime. We demonstrate that the trigger signals generated by both the methods can be employed for reliable protection of the laser system from catastrophic damage due to deleterious arc formation.

A 1.35 mJ ammonia Fabry–Perot cavity terahertz pulsed laser with metallic capacitive-mesh input and output couplers

An efficient ammonia Fabry–Perot (F–P) cavity terahertz (THz) laser has been studied experimentally in this article. The input and output couplers also served as sealed windows fabricated by depositing nickel capacitive metallic meshes on ZnSe and high-resistivity silicon substrates have been constructed as a F–P oscillator. Using the THz laser, the properties related to THz pulsed laser such as beam profile, delay, the minimum pump intensity, THz lasing threshold and THz atmospheric transmission have been investigated. Further, the factors such as pump intensity and gas pressure influencing the efficiency of THz laser have also been discussed. Finally, the highest output pulse energies of 1.35 mJ at 90 μ m operating at 1.09 kPa ammonia pressure pumped by a 402 mJ TEA CO 2 laser with 9R (16) line have been generated, and photon conversion efficiencies of 6.5% have been achieved.

Thermodynamic and spectroscopic properties of Nd:YAG–CO 2 Double-Pulse Laser-Induced Iron Plasmas

Double-Pulse Laser-Induced Breakdown Spectroscopy of iron using both Nd:YAG and TEA–CO 2 lasers has been investigated to better understand mechanisms of signal enhancement. The signal dependence on the delay between the two laser pulses shows an enhanced signal when the CO 2 laser pulse interacts with the sample before the Nd:YAG pulse. Signal kinetics and a simple model of sample heating by the CO 2 pulse show that the enhancement during the first 700 ns is due primarily to sample heating. Images of the sample surface after ablation as well as time-integrated pictures of the plasma suggest that particles are ejected from the surface during the first microseconds after the arrival of the CO 2 pulse and provide fuel for the subsequent plasma created by the Nd:YAG laser.

Enhanced efficiency of a mutually coupled parallel spark preioniser

The enhanced efficiency, almost by a factor of 9, of preionisation when the laser is self-switched by a mutually coupled parallel spark preioniser as against its conventional operation with inductively ballasted preioniser, has been demonstrated in the operation of a TEA CO 2 laser. The increased preionisation peak current due to the near ballast free operation of the mutually coupled parallel spark channels is shown to be responsible for the observed behavior.

IR laser-induced CVD of β-Sn/SnSi-nanodisperse alloys from stannane–silane mixture

TEA CO 2 laser-irradiation of equimolar stannane–silane mixture in Ar results in thermal decomposition of both gaseous compounds and chemical vapour deposition of nanostructured films that were analyzed by FTIR and Raman spectroscopy, X-ray diffraction and electron microscopy and shown as composed of crystalline β-Sn nanobodies in amorphous Sn/Si alloy. The co-pyrolytic formation of the Sn/Si alloy involves intermixing/clustering of simultaneously extruded Si and Sn atoms in the gas phase and represents one of few special techniques allowing formation of this rare material.