Emission characteristics and dynamics of the stagnation layer in colliding laser produced plasmas

The expansion dynamics of ion and neutral species in laterally colliding laser produced aluminum plasmas have been investigated using time and space resolved optical emission spectroscopies and spectrally and angularly resolved fast imaging. The emission results highlight a difference in neutral atom and ion distributions in the stagnation layer where, at a time delay of 80 ns, the neutral atoms are localized in the vicinity of the target surface 1 mm from the target surface while singly and doubly charged ions lie predominantly at larger distances, 1.5 and 2 mm, respectively. The imaging results show that the ions were found to form a well defined, but compressed, stagnation layer at the collision front between the two seed plasmas at early times (Dt ~ 80 ns). On the other hand, the excited neutrals were observed to form a V-shaped emission feature at the outer regions of the collision front with enhanced neutral emission in the less dense, cooler regions of the stagnation layer

He+ ion Irradiation on Tungsten Surface in Extreme Conditions

Higher melting point (3695K), lower sputtering yield and most importantly, lower in-bulk, and co-deposit retention at elevated temperature makes tungsten (W) as a potential candidate for plasma-facing component (PFC) in the international thermonuclear experimental reactor (ITER)-divertor. Helium ion (He+) bombardment on W can cause wide variety of microstructural evolution, such as dislocation loops, helium holes/bubbles and fibre-form nanostructures (Fuzz) etc. In this work, 100 eV He+ ion irradiation, at temperature ranges from 500°C to 1000°C, will be performed on mechanically polished mirror like W surfaces. The surface modification and compositional analysis, due to ion irradiation, will be studied using Scanning electron- (SEM) and Atomic force- (AFM) microscopy and X-ray photoelectron spectroscopy (XPS), respectively. The formation of fibre-form nanostructures was observed for temperatures in the range of 650°C to 1000°C. It was also noted that the incident ion energy and the fluence, that the material underwent, were crucial parameters for fibre-form nanostructure formation

Doube-pulse Laser-induced Breakdown Spectroscopy of Multi-element Sample Containing Low- And High-Z Analytes

Laser-induced breakdown spectroscopy (LIBS) is a portable, remote, non-invasive analytical technique which effectively distinguishes neutral and ionic species for a range of low- to high-Z elements in a multi-element target. Subsequently, LIBS holds potential in special nuclear material (SNM) sensing and nuclear forensics requiring minimal sample preparation and detecting isotopic shifts which allows for differentiation in SNM (namely U) enrichment levels. Feasible applications include not only nonproliferation and homeland security but also nuclear fuel prospecting and industrial safeguard endorsement. Elements of higher mass with complex atomic structures, such as U, however, result in crowded emission spectra with LIBS, and characteristic emission lines are challenging to discern. Preliminary research suggests double-pulse LIBS (DPLIBS) improves signal sensitivity for analytes of lower atomic mass over conventional single-pulse LIBS (SPLIBS). This study investigates signal sensitivity for low- and high-Z analytes in a glass matrix containing U (1.3%) comparing DPLIBS to SPLIBS. DPLIBS involves sequential firing of 1064 Nd: YAG (FWHM 9 ns) pre-pulse and 10.6 µm TEA CO2 (FWHM 50-100 ns) heating pulse in near collinear geometry; SPLIBS entails only the Nd:YAG laser. Optimization of experimental parameters including inter-pulse delay and energy follows identification of characteristic lines for bulk analytes Ca, Na, and Si and trace analyte U for both DPLIBS and SPLIBS. Temporally-integrated excitation temperature and electron density as well as neutral-to-ionic species ratio constitute relative figures of merit for both DPLIBS and SPLIBS plasma characterization. Temporally-resolved studies provide insight into high-Z U analyte persistence and signal enhancement with DPLIBS as compared to low-Z bulk analytes. The study predicts and discusses optimal emission conditions of U lines and relative figures of merit in both SPLIBS and DPLIBS

Femtosecond Laser Ablation: Fundamentals and Applications

Abstract Traditionally nanosecond laser pulses have been used for Laser-induced Breakdown Spectroscopy (LIBS) for quantitative and qualitative analysis of the samples. Laser produced plasmas using nanosecond laser pulses have been studied extensively since 1960s. With the advent of short and ultrashort laser pulses, there has been a growing interest in the applications of femtosecond and picosecond lasers for analysis of materials using LIBS and LA-ICP-MS. The fundamentals of laser ablation process using ultrashort laser pulses are not still fully understood. Pulse duration of femtosecond laser pulse is shorter than electron-to-ion energy transfer time and heat conduction time in the sample lattice. This results in different laser ablation and heat dissipation mechanisms as compared to nanosecond laser ablation. In this chapter, the focus will be on understanding the basics of femtosecond laser ablation processes including laser target interaction, ablation efficiency, ablation threshold, laser plasma interactions, and plume hydrodynamics. Analytical figures of merit will be discussed in contrast to nanosecond LIBS. Introduction Laser ablation (LA) and laser-produced plasmas (LPP) have been studied extensively for more than 50 years since the discovery of lasers in the 1960s. The physics involved in laser-plasma generation and subsequent evolution is very complex and contains many processes like heating, melting, vaporization, ejection of particles, and plasma creation and expansion. The laser ablation craters and plasmas produced are dependent on laser beam parameters such as pulse duration, energy, and wavelength, along with the target properties and surroundin

Emission characteristics and dynamics of the stagnation layer in colliding laser produced plasmas

The expansion dynamics of ion and neutral species in laterally colliding laser produced aluminium plasmas have been investigated using time and space resolved optical emission spectroscopy and spectrally and angularly resolved fast imaging. The emission results highlight a difference in neutral atom and ion distributions in the stagnation layer where, at a time delay of 80 ns, the neutral atoms are localised in the vicinity of the target surface (< 1 mm from the target surface) while singly and doubly charged ions lie predominantly at larger distances, < 1.5 mm and < 2 mm respectively. The imaging results show that the ions were found to form a well defined, but compressed, stagnation layer at the collision front between the two seed plasmas at early times (Δt < 80 ns). On the other hand the excited neutrals were observed to form a V shaped emission feature at the outer regions of the collision front with enhanced neutral emission in the less dense, cooler regions of the stagnation layer.Science Foundation IrelandHigher Education AuthorityIrish Research Council for Science, Engineering and Technologyab, li - TS 28.03.1

Emission characteristics and dynamics of the stagnation layer in colliding laser produced plasmas

The expansion dynamics of ion and neutral species in laterally colliding laser produced aluminium plasmas have been investigated using time and space resolved optical emission spectroscopy and spectrally and angularly resolved fast imaging. The emission results highlight a difference in neutral atom and ion distributions in the stagnation layer where, at a time delay of 80 ns, the neutral atoms are localised in the vicinity of the target surface (< 1 mm from the target surface) while singly and doubly charged ions lie predominantly at larger distances, < 1.5 mm and < 2 mm respectively. The imaging results show that the ions were found to form a well defined, but compressed, stagnation layer at the collision front between the two seed plasmas at early times (Δt < 80 ns). On the other hand the excited neutrals were observed to form a V shaped emission feature at the outer regions of the collision front with enhanced neutral emission in the less dense, cooler regions of the stagnation layer.Science Foundation IrelandHigher Education AuthorityIrish Research Council for Science, Engineering and Technologyab, li - TS 28.03.1

Femtosecond laser ablation-based mass spectrometry: An ideal tool for stoichiometric analysis of thin films

An accurate and routinely available method for stoichiometric analysis of thin films is a desideratum of modern materials science where a material’s properties depend sensitively on elemental composition. We thoroughly investigated femtosecond laser ablation-inductively coupled plasma-mass spectrometry (fs-LA-ICP-MS) as an analytical technique for determination of the stoichiometry of thin films down to the nanometer scale. The use of femtosecond laser ablation allows for precise removal of material with high spatial and depth resolution that can be coupled to an ICP-MS to obtain elemental and isotopic information. We used molecular beam epitaxy-grown thin films of LaPd(x)Sb2 and T′-La2CuO4 to demonstrate the capacity of fs-LA-ICP-MS for stoichiometric analysis and the spatial and depth resolution of the technique. Here we demonstrate that the stoichiometric information of thin films with a thickness of ~10 nm or lower can be determined. Furthermore, our results indicate that fs-LA-ICP-MS provides precise information on the thin film-substrate interface and is able to detect the interdiffusion of cations

Standoff 250 m Open-path Detection of Chemical Plumes Using a Broadband Swept-ECQCL

We measure chemical plumes at a 250 m standoff distance by sweeping an external cavity quantum cascade laser over a broad spectral range of 920-1220 cm(-1) at a rate of 200 Hz. (C) 2019 The Author(s)U.S. Department of Energy (DOE) [DE-AC05-76RL01830]This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Standoff chemical plume detection in turbulent atmospheric conditions with a swept-wavelength external cavity quantum cascade laser

Rapid and sensitive standoff measurement techniques are needed for detection of trace chemicals in outdoor plume releases, for example from industrial emissions, unintended chemical leaks or spills, burning of biomass materials, or chemical warfare attacks. Here, we present results from 235 m standoff detection of transient plumes for 5 gas-phase chemicals: Freon 152a (1,1-difluoroethane), Freon 134a (1,1,1,2-tetrafluoroethane), methanol (CH3OH), nitrous oxide (N2O), and ammonia (NH3). A swept-wavelength external cavity quantum cascade laser (ECQCL) measures infrared absorption spectra over the range 955-1195 cm(-1) (8.37- 10.47 mu m), from which chemical concentrations are determined via spectral fits. The fast 400 Hz scan rate of the swept-ECQCL enables measurement above the turbulence time-scales, reducing noise and allowing plume fluctuations to be measured. For high-speed plume detection, noise-equivalent column densities of 1-2 ppm*m are demonstrated with 2.5 ms time resolution, improving to 100-400 ppb*m with 100 ms averaging. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing AgreementOpen access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Standoff detection of chemical plumes from high explosive open detonations using a swept-wavelength external cavity quantum cascade laser

A swept-wavelength external cavity quantum cascade laser (ECQCL) is used to perform standoff detection of combustion gases in a plume generated from an outdoor high-explosive (HE) open detonation. The swept-ECQCL system was located at a standoff distance of 830m from a 41kg charge of LX-14 (polymer-bonded high explosive) and was used to measure the infrared transmission/absorption through the post-detonation plume as it propagated through the beam path. The swept-ECQCL was operated continuously to record broadband absorption spectra at a 200Hz rate over a spectral range from 2050 to 2230cm(-1) (4.48-4.88 mu m). Fitting of measured spectra was used to determine time-resolved column densities of CO, CO2, H2O, and N2O. Analysis of visible video imagery was used to provide timing correlations and to estimate plume dimensions, from which gas mixing ratios were estimated. Measured emission factors and modified combustion efficiency show good agreement with previously reported values.U.S. Department of Energy12 month embargo; first published online 26 October 2020This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]