Spectral evolution of nano-second laser interaction with Ti target in Air

Time-resolved optical emission spectroscopy has been successfully employed to investigate the evolution of plasma produced by the interaction of IR- and visible-pulsed laser beams with a titanium target in ambient air at atmospheric pressure. The characterization of the plasma-assisted pulsed laser ablation of the titanium target is discussed in this study. The emission spectrum produced by the titanium plasma in the wavelength range 200–1,000 nm has been carefully investigated for different experimental conditions. Boltzmann plots have been used in the calculation of the excitation temperature employing Ti II spectral lines at 286.23, 321.71, 325.29, 348.36, and 351.08 nm; this set of lines was tested and proved to be suitable for the measurement of the plasma temperature. The obtained temperature is in good agreement with the one obtained from Ti II spectral lines previously suggested by Hermann et al. [J. Appl. Phys. 77, 2928–2936, 1995, 22]. Moreover, the Stark broadening method has been employed for electron density measurements. In this study, the Stark width of the Ti II spectral line at 350.49 nm was used.     

Laser-induced breakdown spectroscopy: technique,new features,and detection limits of trace elements in Al base alloy

Laser-induced breakdown spectroscopy (LIBS) has proven to be extremely versatile, providing multielement analysis in real time without sample preparation. The principle is based on the ablation of a small amount of target material by interaction of a strong laser beam with a solid target. The laser must have sufficient energy to excite atoms and to ionize them to produce plasma. We aimed to improve the LIBS limit of detection (LOD) and the precision of spectral lines emitted from the produced plasma by optimizing the parameters affecting the LIBS technique. LIBS LOD is affected by many experimental parameters such as interferences, self-absorption, spectral overlap, signal-to-noise ratio, and matrix effects. The plasma in the present study is generated by focusing a 6-ns pulsed Nd–YAG laser at the fundamental wavelength of 1,064 nm onto the Al target in air at atmospheric pressure. The emission spectra are recorded using an SE 200 Echelle spectrometer manufactured by the Catalina Corporation; it is equipped with an ICCD camera type Andor model iStar DH734-18. This spectrometer allows time-resolved spectral acquisition over the whole UV-NIR (200–1,000 nm) spectral range. Calibration curves for Cu, Mg, Mn, Si, Cr, and Fe were obtained with linear regression coefficients around 99 % on the average in aluminum standard alloy samples. The determined LOD has very useful improvements for Cu I at 521.85 nm, Si I at 288.15 nm, Mn I at 482.34 nm, and Cr I at 520.84 nm spectral lines. LOD is improved by 83.8 % for Cu, 49 % for Si, 84.3 % for Mn, and 45 % for Cr lower with respect to the previous works.     

Spectral evolution of nano-second laser interaction with Ti target in nitrogen ambient gas

The present work aimed to study the variation in the plasma parameters (temperature and density) of the Ti plasma generated by 1,064 and 532 nm lasers at different ambient N₂ pressures for different delay times. The characterization of the plasma-assisted pulsed laser ablation of the titanium target is discussed. The emission spectra of the titanium plasma produced in the present study have been carefully investigated over the whole UV–NIR (200–1,000 nm) spectral range. Boltzmann plots of suitable spectral lines have been employed to derive the excitation temperature, and the electron density is derived from the Stark widths of the Ti II spectral line at 350.49 nm.     

Using a DS-DBR laser for widely tunable near-infrared cavity ring-down spectroscopy

Studies into the suitability of a novel, widely tunable telecom L-band (1,563–1,613 nm) digital supermode distributed Bragg reflector (DS-DBR) laser for cavity ring-down spectroscopy (CRDS) are presented. The spectrometer comprised of a 36.6?cm long linear cavity with ring-down times varying between 19–26 μs across the 50 nm DS-DBR wavelength range due to changes in the cavity mirror reflectivities with wavelength. The potential of such a broadband, high-resolution CRD spectrometer was illustrated by investigating several transitions of CO₂ in air, a 5 % calibrated mixture and breath samples. Allan variance measurements at a single wavelength indicated an optimal minimum detectable absorption coefficient (α _min) of 3 × 10^?10 cm^?1 over 20 s.     

Measurement of the Stark Broadening of Atomic Emission Lines in Non–Optically Thin Plasmas by Laser‐Induced Breakdown Spectroscopy

We propose a new method for determining the Stark broadening of atomic emission lines using laser‐induced breakdown spectroscopy. The method allows the determination of the Stark broadening in non–optically thin plasmas, through the introduction of a correction for self‐absorption. Couples of lines of the same species are considered. If one of the Stark broadenings is known, the determination of the other does not require the measurement of the electron density of the plasma. Examples are given for the application of the proposed method to the measurement of the Stark broadening of several aluminum emission lines (Al I at 308.2 nm, Al I at 394.4 nm, and Al I at 396.2 nm).     

Optical Detection of Some Hydrazine Compounds Based on the Surface Plasmon Resonance Band of Silver Nanoparticles

An indirect colorimetric method is presented for spectrophotometric determination of hydrazine, phenylhydrazine, and isoniazid. Reduction of silver ions to silver nanoparticles (AgNPs) by these analytes as active reducing agents in the presence of polyvinylpyrrolidone (PVP) and also cetyltrimethylammonium chloride (CTAC) as a stabilizer is the basis of the proposed method. The changes in plasmon absorbance of the AgNPs at λ = 415 nm in the presence of PVP were proportional to concentration of hydrazine, phenylhydrazine, and isoniazid in the ranges of 4.0–150.0 µM, 1.0–55.0 µM, and 2.0–30.0 µM, respectively, and the detection limit obtained was 0.79 µM. In the presence of CTAC, the linear ranges were 0.5–10.0 and 10.0–300.0 µM for hydrazine, 1.0–40.0 µM for phenylhydrazine, and 0.2–10.0 and 10.0–90.0 µM for isoniazid, and the detection limit was 0.12 µM. The method has been applied for determination of these analytes in different real samples such as boiler feed water and tablet.     

Double-pulse neodymium YAG/Carbon dioxide laser-induced breakdown spectroscopy for excitation of bulk and trace analytes

The mechanisms involved in signal enhancement and persistence of the plasma in double-pulse laser-induced breakdown spectroscopy are investigated, and their implications to improving figures of merit for bulk and trace analytes in sample are discussed. For double-pulse laser-induced breakdown spectroscopy, 1064 nm neodymium YAG laser is used for ablation and 10.6 µm transversely excited atmospheric carbon dioxide laser in near-collinear geometry is used for reheating. Significant improvement in signal detection and sensitivity of both bulk and trace analytes using double-pulse laser-induced breakdown spectroscopy as compared to conventional single-pulse laser-induced breakdown spectroscopy are observed. Using double-pulse laser-induced breakdown spectroscopy in near-collinear geometry, Cu and Fe as bulk and trace analytes, respectively, in brass sample, showed 5 and 6 times improvement in persistence of the spectral emission. Temporal and time-integrated studies show that ionic lines are significantly enhanced compared to neutral lines. Plasma characterization employing spectroscopic methods showed significant enhancement in plasma temperature resulting in higher signal as well as increased plasma persistence of the species studied.     

Photo-physical properties of anisole: temperature, pressure, and bath gas composition dependence of fluorescence spectra and lifetimes

Anisole is a promising candidate for use as fluorescent tracer for gas-phase imaging diagnostics. Its high-fluorescence quantum yield (FQY) and its large Stokes shift lead to improved signal intensity (up to 100 times stronger) compared with the often used toluene. Fluorescence spectra and effective fluorescence lifetimes of gaseous anisole were investigated after picosecond laser excitation at 266 nm as a function of temperature (296–977 K) and bath gas composition (varying amounts of N₂ and O₂) at total pressures in the range of 1–10 bar to provide spectroscopic data and FQY for applications, e.g., in in-cylinder measurements in internal combustion engines. Fluorescence spectra of anisole extend from roughly 270–360 nm with a peak close to 290 nm at 296 K. The spectra show a red-shift with increasing temperature (0.03 nm/K) and O₂ partial pressure (5 nm from N₂ to air). In the investigated temperature range and in pure N₂ at 1 bar total pressure the effective fluorescence lifetime drops with increasing temperature from 13.3 ± 0.5 to 0.05 ± 0.01 ns. Increasing the total pressure of N₂ leads to a small decrease of the lifetime at temperatures above 400 K (e.g., at 525 K from 4.2 ± 0.2 ns at 1 bar to 2.7 ± 0.2 ns at 10 bar). At constant temperature and in the presence of O₂ the lifetimes decrease significantly (e.g., at 296 K from 13.3 ± 0.5 ns in N₂ to 0.40 ± 0.02 ns in air), with this trend diminishing with increasing temperature (e.g., at 675 K from 1.02 ± 0.08 ns in N₂ to 0.25 ± 0.05 ns in air). A phenomenological model that predicts fluorescence lifetimes, i.e., relative quantum yields as a function of temperature, pressure, and O₂ concentration is presented. The photophysics of anisole is discussed in comparison with other aromatics.     

Perturbed angular correlation study of a nanostructured HfO2 film

The hyperfine field at ¹⁸¹Ta lattice sites in a nanostructured HfO₂ thin film was studied by the perturbed angular correlation (PAC) technique. The thin oxide film was deposited by pulsed laser ablation on a silicon substrate kept at 673 K. The thickness was about 25 nm. The radioactive ¹⁸¹Hf ions were produced by neutron activation of the very thin film in the Portuguese research reactor by the reaction ¹⁸⁰Hf(n,γ)¹⁸¹Hf. PAC measurements were carried out at room temperature after annealing at different temperatures up to 1,473 K in air. The PAC technique allows determining the electric field gradient at the ¹⁸¹Ta probe sites. The ¹⁸¹Ta isotopes appear in the sample as disintegration product of ¹⁸¹Hf.     

Influence of plasma chemistry on oxygen triplets

The plasma chemistry of fluorocarbon-oxygen-argon discharges and its influence on prominent oxygen triplets are studied. The oxygen 777 triplet is very important for the measurement of atomic oxygen in low pressure plasmas, since the 777.417 nm spectral line is frequently used for actinometry. In this paper, we identify changes in the individual 777 triplet lines arising from cascade effects from higher energy levels of oxygen, and from resonant energy transfer from energetic carbon atoms in carbon-rich plasmas. The lower energy levels of three oxygen triplets (544 nm, 616 nm, 645 nm) are the upper states of the 777 triplet. Increased emission intensity from the 544, 616, and 645 triplets result in changes to the relative intensity of the individual lines of the 777 triplet, and this can lead to errors in using the 777 triplet, e.g. for actinometry. Also, in operational conditions with strong carbon emission (around 601 nm), the relative intensity of the individual oxygen 777 lines is affected. The upper energy levels of these carbon lines is close to the oxygen 777 upper energy levels, suggesting that resonant energy transfer between the carbon and the oxygen is occurring. The experiments are performed in a commercial semiconductor dielectric etcher operating with dual rf frequencies of 2 MHz and 27 MHz. Pressure (13–19 Pa), rf power (200–1200 W), and gas mixtures (argon with addmixtures of 5–13% oxygen and C₄F₈) are typical in application to dielectric etching.     

针一板介质阻挡放电中电子能量空间分布研究

测量了大气压环境下氩气空心针-板放电等离子体中原子与分子谱线强度的空间分布,分析了等离子体中电子能量的空间分布.实验利用空心针-板放电装置,得到了约3 cm长的放电等离子体弧.在300～800 nm范围内采集发射光谱,发现了强度较高的Ar I谱线、N2第二正带系谱线C 3Ⅱu(v=o)→B 3皿(v=0)以及强度较弱的...     

Plasma property effects on spectral line broadening in double-pulse laser-induced breakdown spectroscopy

Double-pulse Laser-Induced Breakdown Spectroscopy (LIBS) in an orthogonal configuration was used to investigate plasma temperature and electron density effects on Mg II emission spectral line broadening. The experiments were carried out with two Nd:YAG lasers, one operating at 355 nm for ablation and the other one at 1064 nm for plasma reheating in air at atmospheric pressure. Temporally resolved plasma temperature and electron density were measured at various delay times. Data in this study show prolonged emission of Mg II (280.27 nm) as well as enhancement of the signal intensity when using double-pulse excitation compared to the single-pulse case. An enhancement of ～8× was attained with a delay between the laser pulses equal to 1 μs. The enhancement was accompanied by higher plasma temperature and increased electron density. The double-pulse LIBS configuration provides energy to sustain the plasma emission at a period in time when the linewidth is minimum, thereby improving the analytical capabilities of low spectral resolution instrumentation typically used in LIBS system.     

Laser-induced fluorescence temperature determination in fuel–air mixtures without additional fluorescence tracers

A concept for temperature determination of fuel–air mixtures using Laser-Induced Fluorescence (LIF) is presented. For this purpose the fluorescence spectra of gasoline were measured after excitation by frequency quadrupled Nd:YAG laser light at 266 nm in a temperature range between 373 K and 448 K. Experiments were performed with colorless near-standard gasoline conforming to the Euro-super specifications. It is shown that the intensities of two fluorescence bands (290–302 nm and 332–344 nm) can be used to determine the temperature.     

Effect of sintering temperature of Ce<Superscript>3+</Superscript>-doped Lu<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript> phosphors on light emission and properties of crystal structure for white-light-emitting diodes

The effect of the sintering temperature of Ce³⁺-doped Lu₃Al₅O₁₂ (Ce-LuAG) phosphors on the emission and properties of the crystal structure was studied. A cathodoluminescence peak at 317 nm, which was assigned to lattice defects, was exhibited in addition to emission peaks at 508 and 540 nm for the Ce-LuAG phosphors. The intensities of the 317 nm emission peak for the phosphors with mean particle diameters of 5.0 and 10.0 µm formed at a low sintering temperature of 1430 °C were higher than those for the phosphors with mean particle diameters of 18.0 and 20.5 µm formed at a high sintering temperature of 1550 °C. In contrast, the electroluminescence spectra for fabricated white-light-emitting diodes (LEDs) using the phosphors revealed that the intensity of the peak at 540 nm was strong for the mean particle diameters of 18.0 and 20.5 µm. The intensity of the 540 nm peak, which is attributed to the 4f→5d transition of the Ce³⁺ activator, showed a dependence on the sintering temperature. The relationship between the optical properties and the lattice defects is discussed.     

An Innovative Measurement of Extractable Proteins from Concentrated Latex Containing Eggshell Calcium Oxide Compounds by Near-Infrared Spectroscopy

ABSTRACT

Near-infrared reflectance (NIR) spectroscopy, in the spectral range of 1100–2500 nm, was used to measure the amount of the directly extractable proteins (EP) where a small amount can cause a latex allergy to patients. The NIR spectra revealed an amino or a peptide (N-H) of the extractable proteins from the concentrated rubber latex added with sodium dodecyl sulphate (SDS) and calcium chloride, the latter being obtained from the pyrolysis of eggshells at 900°C for 2 hr and dissolving in 2 M HCl. The extractable proteins measured by NIR are equal to 5306.58 ± 1727.00 µg/g (0.53%) close to the value obtained by the modified Lowry method, which is 5566.02 ± 717.39 µg/g (0.56%). A partial least square regression model (PLSR) of the NIR spectra and the extractable protein contents yields a correlation coefficient of .72, a root mean square error of calibration (RMSEC) of 1298 µg/g, and a small bias value of ?0.0002 µg/g. The absorbance peaks at the wavelengths of 1520 nm and 1980 nm are related to the first overtone N-H (υ₁N-H) and the asymmetric combination of N-H, respectively. Furthermore, the absorbance peaks at the wavelengths of 1450 nm and 1920 nm correspond to the first overtone of O-H (υ₁O-H) of the concentrated latex compounds. The results demonstrate the NIR spectroscopy potential as a fast and noninvasive measurement technique.     

Improvement of the Performance of an Acousto-Optical Q-Switched Nd:YAG 946 nm Laser Using a Convex–Plane Cavity

We improve the performance of an acousto-optical Q-switched Nd:YAG 946 nm laser using a convex–plane cavity. We obtain the highest output average power of 2.3 W with a pulse width of 15.3 ns in a 10 kHz 946 nm laser with a convex–plane cavity. The maximum peak power 15.0 kW is about three times higher than that in a plane–plane cavity. Also we investigate the output performances of the pulsed 946 nm laser with the convex–plane cavity at 20 and 50 kHz.     

Temporal follow up of the LTE conditions in aluminum laser induced plasma at different laser energies

In order to analyze the emission spectrum of a laser-induced plasma for obtaining quantitative information on the abundance of the species present in the plasma it is necessary to study the local thermodynamic equilibrium (LTE) conditions in the plasma and determine the best conditions at which they are satisfied. In the present work Nd:YAG laser light pulses (λ=?1064 nm, 6 ns) of different energies (25, 50, 75 and 100 mJ) are focused using a quartz lens (focal length 10 cm) onto certified aluminum alloy samples in air under atmospheric pressure. The emitted spectra are collected and analyzed using an echelle spectrometer coupled with an intensified charge coupled device camera. The temporal history of the plasma is obtained by recording the emission features at predetermined delays and at a fixed gate width (2500 ns). For each spectrum both electron density and excitation temperature are calculated for each delay time and laser pulse energy; we found that the values of the electron density are decreasing from 10¹⁸ to 10¹⁷ cm^-3. The corresponding excitation temperatures were between 30000 and 4000 K depending on the laser pulse energy and the sample used. The LTE conditions were followed up for the different delays and different energies to determine the temporal range in which they are satisfied. It has been found that in the cases of 25- and 50-mJ laser energies, the LTE conditions were satisfied in the chosen delay range (500–5000 ns). On the other hand, for higher laser energies, the LTE conditions were critical at delay times less than 1500 ns and are satisfied for longer delays.     

Determination of Protoporphyrin IX Disodium Salt Based on Fluorescence Quenching of Glutathione-Capped Cadmium/Tellurium Quantum Dots

ABSTRACT

Aqueous glutathione-capped cadmium/tellurium quantum dots with a diameter of about 3 nm were synthesized. The fluorescence was quenched in the presence of protoporphyrin IX disodium salt, with the excitation wavelength at 320 nm. Under the optimal conditions, the quenched fluorescence intensity was linear in the range of 0.096–16 µg · mL^?1 with a concentration of protoporphyrin IX disodium salt, and the detection limit (3σ) was 2.8 × 10^?2 µg · mL^?1. The proposed method has been applied to the determination of protoporphyrin in serum samples with satisfactory results. The interaction mechanism was investigated.     

A 3D-CMOS compatible silicon photo-sensor with a large vertical photosensitive area

This paper introduces design and simulation of a three-dimensional complementary metal–oxide–semiconductor CMOS compatible photo-sensor based on a silicon substrate. In the structure of photo-sensor, a vertical n+/p junction as a photosensitive area is formed on one side of a U-groove, and perpendicular to a lateral n-i-p structure on top-side of the silicon surface. This configuration enables a direct butt-coupling of a fiber-optic to the photosensitive area, which is a privilege for many remote monitoring applications. The device analysis is carried out by a two-dimensional simulation using SILVACO TCAD simulator. The thickness of the photo-sensitive area is investigated by considering the figures of merit for the two different thicknesses of 30 and 50 µm. The simulated results (according to the parameters defined for the Si substrate) show a very low dark current of 70 and 100 (fA/μm) for the 30 and 50 µm thicknesses, respectively. In addition, a high photo-current to dark current ratio of ~3000 is achieved under an intensity of 2 mW/cm² at 633 nm wavelength, according to the wavelength of red He–Ne laser. The sensor demonstrates a responsivity of 0.33 A/W corresponding to 65% external quantum efficiency and a ?3 dB frequency response of 0.2 GHz under a small signal of 2 mW/cm² at 633 nm wavelength for 10 V reverse bias.     

Generation of web-like structures and nanoparticles by femtosecond laser ablation of silicon target in ambient air

Silicon nanoparticles were produced by femtosecond laser ablation in ambient air. Obtained samples were studied using dark-field optical microscopy, scanning electron microscopy and Raman-scattering spectroscopy. Two groups of structures can be found: (1) branched amorphous structures with a minimum element size of about 10 nm and incorporations of nanocrystals (0.6–6.6 nm from Raman scattering analysis); (2) larger crystal particles with smooth surface and a typical size of 50–200 nm that provide directional visible light scattering (at dark-field optical microscopy observations). An influence of environment on resulting phase composition of silicon nanoparticles was investigated by numerical evaluation of nanoparticle’s cooling rate. The calculation shows that cooling in ambient air ensures cooling rate sufficient for crystallization.