Laser-induced Emission Spectra Research Articles

Laser-induced emission spectra of stainless steels and aluminum irradiated with nanopulse lasers without setting delay: potential applications to remote sensing and laser micromachining.

Spectral lines from the impurities held in stainless steel and in aluminum can be clearly identified in the UV and the visible spectra when emission is laser induced. These spectroscopic lines can be initiated in metal irradiated at moderate laser optical densities of about 2.5×108W/cm2. In addition to the lines arising from impurities found in some metals, it was found that some spectroscopic lines from iron oxide formed during irradiation were also detected at the above-mentioned power density. It was found that lines observed from iron oxide are consistent with what is reported in the literature. The investigations reported were produced on samples at optical densities that are sufficient to create an electric field that is about 10 times the air electrical breakdown near the focal point. The results reported were obtained without setting any delay between the laser Q-switch and the data acquisition. The spectroscopic data are comparable to those shown in the literature by laser-induced breakdown spectroscopy in term of signal-to-noise ratio and are promising in detecting impurities such as heavy metals in remote sensing applications, where pulse delay is not always practical due to atmospheric conditions and power requirements. As a marking procedure is used during the investigations, the method demonstrates how spectroscopic monitoring in real time can be applied during a procedure in laser micromachining applications.

IR Laser Induced Emission Spectra of GaN Nanoceramic

Currently, the researchers from around the world pay a lot of attention to search new white light generation sources. Such a device would have huge application potential in the lighting industry. The advantage of a broadband white light source is no necessity to mix few emission lines to obtain a white luminescence, as it is in case of the LED devices. Here, we investigate the broadband laser induced emission spectra of GaN nanoceramic measured under three different infrared excitation lines (1064, 975 and 808 nm). The GaN powder was obtained by thermal decomposition method while the nanoceramic was prepared using low temperature high pressure (LTHP) technique. The sample crystallizes in the hexagonal wurtzite structure and theoretical value of their average grain size calculated using Scherrer equation was 12 nm. The optical characterization of LIE spectra of GaN nanoceramic included the measurements of emission intensity as a function of power density, ambient pressure and luminescence kinetics. The emission spectra were recorded in both VIS (400-900 nm) and NIR (1200-2500 nm) regions (Fig. 1a,1b). It was found that the power dependence exhibit threshold behavior typical for avalanche process for all three excitation lines. The luminescence kinetics measurements show that rise and decay times of LIWE are extremely short in comparison to dielectric materials. It turned out that calculated x and y parameters of recorded emissions lie in the warm region of the CIE chromaticity diagram confirming their low color temperature regardless of the excitation wavelength (Fig. 1c). Finally, a general mechanism of LIE spectra in GaN nanoceramic is discussed.Figure 1. The LIWE intensity of GaN nanoceramic under 975 nm as a function of increasing pumping power density in VIS and NIR regions (a,b). The CIE chromaticity diagram of LIWE generated from GaN nanoceramic upon three various excitation wavelengths (c). The image of LIWE during experiment (d). Figure 1

Laser induced emission spectra of gallium nitride nanoceramics

The paper presents the studies of the intense broadband laser induced emission (LIE) of GaN (gallium nitride) nanoceramics in both the visible and near infrared regions. The GaN nanocrystals crystalized in a hexagonal wurtzite structure with an average grain size of 12 nm calculated using the Scherrer formula. The GaN nanoceramics were compacted by using the low temperature high pressure technique. The optical characterization involved the LIE measurements in the visible and infrared regions relative to excitation power, pressure dependence, and emission kinetic. It was observed that the GaN nanoceramics show extremely short rise and decay times of the laser induced white emission. The photocurrent assisting the laser induced emission of GaN nanoceramics was measured. It was extremely large and increased strongly with the excitation power and the applied electric field.

Exploiting LIBS to analyze selected rocks and to determine their surface hardness based on the diagnostics of laser-induced plasma

The present work introduces a detailed investigation to discriminate between some types of igneous and sedimentary rocks. The used experimental setup was a conventional single-pulse nanosecond system with a neodymium YAG laser at two excitation wavelengths, 1064 nm, and 355 nm. The laser-induced emission spectra of the rock samples were normalized to the irradiance for both utilized laser wavelengths to compensate for the different laser pulse energies used. The surface hardness values of the studied samples were spectroscopically determined via the intensity ratios of the ionic-to-atomic spectral lines of iron in the rock samples. Besides, the laser-induced plasma parameters, namely the plasma temperature and the electron density, were calculated from the obtained spectral data. It is found that the plasma temperature, in the infrared-laser case, was higher than that of the ultraviolet laser while the electron density values were the opposite. Multivariate statistical analysis of the spectroscopic data using the principal component analysis technique revealed the possibility of discrimination between different types of rocks. Furthermore, the laser-induced breakdown spectroscopy results have been validated by comparison to the results of the energy-dispersive X-ray analysis for the same samples.

Scintillation Properties of Ce3+ Doped Silicon-Magnesium-Aluminum-Lithium Glass Scintillators by using Radiation Sources

Glass scintillators can be doped with different elements to improve their luminescence properties. In this study, we present 0.5 wt% Ce3+-doped (58−x)SiO2-4MgO-18Al2O3-20Li2O and (58−x)SiO2- 4MgO-18Al2O3-20LiF glass scintillators. We used a pulsed laser to measure the laser-induced emission spectrum and the decay time with decreasing temperature from 300 K to 10 K. The light intensity of both glass samples increased with decreasing temperature from 300 K to 10 K. Additionally, the two glass samples exhibited a fast decay time of approximately 25 ns. In the photo-induced spectrum, an excitation peak at 312 nm and two emission peaks, at 370 nm and 700 nm, were observed in both the glass samples. The X-ray-induced emission intensity of former is approximately six times higher than that of latter, and only former glass sample exhibits a proton-induced emission spectrum.

Detection of chlorophylls in spores of seven ferns.

Fern spores were traditionally classified into chlorophyllous (green) and nonchlorophyllous (nongreen) types based on the color visible to the naked eye. Recently, a third type, "cryptochlorophyllous spores", is recognized, and these spores are nongreen under white light but contain chlorophylls. Epifluorescence microscopy was previously used to detect chlorophylls in cryptochlorophyllous spores. In addition to epifluorescence microscopy, current study performed some other approaches, including spore-squash epifluorescence, absorption spectra, laser-induced fluorescence emission spectra, thin layer chromatography (TLC), and ultra-high performance liquid chromatography with ultraviolet and mass spectrometric detection (UHPLC-UV-MS) in order to detect chlorophylls of spores of seven ferns (Sphaeropteris lepifera, Ceratopteris thalictroides, Leptochilus wrightii, Leptochilus pothifolius, Lepidomicrosorum buergerianum, Osmunda banksiifolia, and Platycerium grande). Destructive methods, such as TLC and UHPLC-UV-MS, successfully detected chlorophylls inside the spores when their signals of red fluorescence under epifluorescence microscope were masked by spore wall. Although UHPLC-UV-MS analysis was the most sensitive and reliable for determining the chlorophylls of spores, spore-squash epifluorescence is not only reliable but also cost- and time-effective one among our study methods. In addition, we first confirmed that Lepidomicrosorium buergerianum, Leptochilus pothifolius, Leptochilus wrightii, and Platycerium grande, produce cryptochlorophyllous spores.

Luminescence properties of Dy3+ doped lanthanum-calcium-silicaborate glass scintillator

In this research Dy3+-doped lanthanum-calcium-silicaborate glass scintillators, with the formula 25La2O3: 10CaO: 10SiO2: (55-x)B2O3: xDy2O3, were fabricated by using the melt-quenching technique. For the Dy3+ doping concentrations from 0.05 mol% to 0.5 mol% studied the luminescence properties of the Dy3+-doped glass scintillators with various radiation sources, such as X-ray, photo-, laser, and proton. To understand the absorption state, we measured the transmittance spectrum. Furthermore, X-ray, photo- and proton-induced emission spectra were measured to study the transition states of Dy3+-doped glass scintillators. The laser-induced emission spectra were measured at low temperatures in the range from 10 K to 300 K.

Studies on laser induced emission of microdroplets containing Rhodamine 6G solutions in water doped with TiO2 nanoparticles

Studies on the emission spectra of microdroplets containing Rh6G solutions in water doped with TiO2 nanoparticles are reported. The excitation is made by the second harmonic of a pulsed Nd:YAG laser at 532nm, pulse duration at half maximum 6ns and energy varied between 6 and 10mJ. The laser induced emission spectra are analyzed function of TiO2 concentration and pumping laser energy. Comparison between fluorescence dispersed spectra emitted by pendant droplets containing TiO2 nanoparticles with respect to Rh6G water solutions droplets pumped in the same conditions is made. The surface tension measurements of the samples show that with variation of dye and nanoparticles concentrations, surface phenomena take place and influence the behavior of the droplet fluorescence.

Self-absorption effect in nanosecond laser induced plasma emission spectrum

In order to reduce the self-absorption effect of spectral lines in the laser induced plasma emission, which could improve the detection level of laser spectral analysis technology for high-content elements in materials, a plane mirror device was used to constraint plasma in the experiment. The change of the spectral lines with or without the plane mirror device was compared. Without the plane mirror device, the half-maximum line widths of spectral line of the sample element Al, Mg and Mn were 0.16 nm, 0.24 nm and 0.058 nm, respectively. But they were 0.11 nm, 0.13 nm and 0.047 nm with four plane mirrors device constraining plasma. It shows that the self-absorption effect of spectral lines decrease significantly by the use of plane mirror device to restrain plasma on the space, while the spectral line becomes sharper and the intensity is improved significantly. By observing the plasma photos and measuring of plasma temperature and electron density, the reason to reducing the self-absorption effect in laser spectrum is discussed.

Damage Profile of HDPE Polymer using Laser-Induced Plasma

In this paper we studied the laser-induced crater depth, mass, and emission spectra of laser-ablated high-density polyethylene (HDPE) polymer using the laser-induced plasma spectroscopy (LIPS) technique. This study was performed using a Nd:YAG laser with 100 mJ energy and 7 ns pulse width, focused normal to the surface of the sample. The nanoscale change in ablated depth versus number of laser pulses was studied. By using scanning electron microscope (SEM) images, the crater depth and ablated mass were estimated. The LIPS spectral intensities were observed for major and minor elements with depth. The comparison between the LIPS results and SEM images showed that LIPS could be used to estimate the crater depth, which is of interest for some applications such as thin-film lithography measurements and online measurements of thickness in film deposition techniques.

Gas-phase thermometry in a high-pressure cell using BaMgAl10O17:Eu as a thermographic phosphor

We demonstrate the feasibility of laser-induced phosphorescence thermography for gas-phase temperature field measurement in a high-pressure cell. BaMgAl10O17:Eu (BAM) was used as a thermographic phosphor; it shows a blue-shifted laser-induced emission spectrum with increasing temperature. Local temperature was determined from the intensity ratio of two disjunctive emission bands. A new seeding device was developed to suspend the solid thermographic phosphor particles in a gas environment. The particle suspension time was modeled and validated by experiments. The influence of multiple scattering and other aspects of quantitative measurement were examined. The technique is currently capable of measuring up to 650 K, limited by signal intensity. The 2D temperature distributions were measured with a precision better than 60 K at 650 K. Multiple scattering limits the spatial resolution to only about 10 mm along the line of sight.

Gas-Phase Chemistry in Inductively Coupled Plasmas for NO Removal from Mixed Gas Systems

Inductively coupled rf plasmas were used to investigate the removal of NO from a variety of gas mixtures. Laser-induced fluorescence and optical emission spectroscopy were employed to measure the relative gas-phase density of NO as a function of the applied rf power, gas mixture, and catalytic substrate type. In general, the overall density of NO decreases as a function of applied rf power in both NO and N(2)/O(2) plasmas, but the addition of gases such as H(2)O vapor and CH(4), as well as the presence of Au-coated substrates, significantly affects the behavior of NO in these systems. Rotational and vibrational temperatures for NO were measured using laser-induced fluorescence excitation spectra and optical emission spectra. Results show NO vibrational temperatures are about a factor of 5 higher than rotational temperatures and indicate little dependence on applied rf power, feed gas composition, or overall system pressure. Possible mechanisms for the observed changes in [NO] as well as the rotational and vibrational temperature data are addressed.

Clinical trial for detection of dental caries using laser-induced fluorescence ratio reference standard

We present the clinical applicability of fluorescence ratio reference standard (FRRS) to discriminate different stages of dental caries. Toward this, laser-induced autofluorescence emission spectra are recorded in vivo in the 400- to 800-nm spectral range on a miniature fiber optic spectrometer from 65 patients, with a 404-nm diode laser as the excitation source. Autofluorescence spectra of sound teeth consist of a broad emission at 500 nm that is typical of natural enamel, whereas in caries teeth additional peaks are seen at 635 and 680 nm due to emission from porphyrin compounds in oral bacteria. Scatter plots are developed to differentiate sound teeth from enamel caries, sound teeth from dentinal caries, and enamel caries from dentinal caries using the mean fluorescence intensity (FI) and ratios F500F635 and F500F680 measured from 25 sites of sound teeth and 65 sites of carious teeth. The sensitivity and specificity of both the FI and FRRS are determined. It is observed that a diagnostic algorithm based on FRRS scatter plots is able to discriminate enamel caries from sound teeth, dentinal caries from sound teeth, and enamel from dentinal caries with overall sensitivities of 85, 100, and 88% and specificities of 90, 100, and 77%, respectively.

Laser-induced emission spectrum from high-temperature silica-generating flames

High-temperature silica-generating flames were probed with 266 nm plane, linearly polarized light to produce laser-induced emission spectra with prominent peaks at the blue- and red-shifted sides from the probe wavelength. The radiation induced is ascribed to silicon monoxide (SiO) present in the flame, and appears to be caused by a combination of fluorescence and near-resonance-enhanced Raman scattering. The signal contribution due to strongly depolarized radiation near the probe wavelength complicates extraction of size information based on Rayleigh- and Mie-scattering in investigations of silica nanoparticle formation and growth in flames where temperatures are above 2000 K, oxygen partial pressures are moderate and the particulate matter is in its early stages of evolution. However, the observed radiative process may have utility as the basis for temporally and spatially resolved species and temperature diagnostics.

Laser induced emission spectra of polyyne molecules C 2 nH 2 ( n = 5–8)

New optical emission spectra of linear carbon molecules, polyynes C 2 n H 2 ( n = 5–8), were observed upon UV-laser excitation of the 0–0 band of the dipole-allowed transition, 1 Σ u + ← X 1 Σ g + , of size-separated polyyne molecules in hexane. The emission spectra of C 10H 2 showed distinct peaks at 436 and 480 nm with a separation of ∼2100 cm −1 for a stretching vibration of the sp-carbon chain. Weak absorption features were also recorded in near-UV regions in shorter wavelengths to compare with the emission spectra. The spectral features in the emission were assigned to the vibronic bands of the forbidden electronic transition, 1 Δ u → X 1 Σ g + .

Production and shaping of high performance phosphors by using the sol–gel process: Yttrium aluminum garnet (Y3Al5O12)

Luminescent Y3Al5O12:Tb3+ (YAG:Tb3+) phosphor thin films and powders have been successfully prepared by the sol–gel route from alkoxide precursors. Advanced coatings were produced by spray and dip-coating from stabilized sols. X-ray diffraction (XRD), attenuated total reflectance/Fourier transform infrared spectroscopy (ATR/FTIR) and atomic force microscopy (AFM) were used to investigate the structure and morphology of layers. YAG phases of high purity were obtained for both powders and films. AFM study revealed coatings of homogeneous topography, whatever the deposition technique. However, dip-coated samples exhibited a much smoother topography, characterized by a root mean square (rms) roughness much lower than that of spray-coated ones. Laser induced emission spectra and decay times of Tb3+ ions in a spray-coated film were recorded. Measurements exhibit the characteristic green emission of Tb3+. Effectiveness of the Tb3+ doped coatings under UV excitation is also illustrated by pictures.

Structural and optical characterizations of sol–gel based fluorides materials: LiGdF4:Eu3+ and LiYF4:Er3+

Sol–gel synthesis of isostructural LiGdF4:Eu3+ and LiYF4:Er3+ crystallized powders is reported. Furthermore, LiGdF4:Eu3+ coatings were also prepared by dip- and spin-coating methods. In all cases, X-rays diffraction measurements were performed to check materials crystalline purity while infrared spectroscopy analyses showed that the organic groups are removed after annealing treatments at 550 °C in F2 atmosphere. This result was emphasized by long radiative decay time of Er3+ ions in LiYF4 (τ = 10.5 ms) attributed to the absence of both organic residues and hydroxide ions. Laser induced emission spectra of LiGdF4:Eu3+ were recorded upon excitation in both 5D2 and 6P5/2 high lying levels of respectively Eu3+ and Gd3+ ions. Eventually fluorescence decays of rare earth ions were measured and compared in both cases.

The Cs2 ground electronic state by Fourier transform spectroscopy: Dispersion coefficients

This study presents the derivation of an accurate potential energy curve for the ground electronic state of the Cs2 molecule. High resolution laser induced emission spectra data involving vibrational levels of the ground X 1Σg+ state up to v″=135 (16 900 wave numbers) have been determined. The ground state potential energy curve is constructed by combining the inverted perturbation approach for internuclear distances up to 11 Å, with an analytical expression for longer internuclear distances. This potential curve allows an improved derivation of the dissociation energy and of the Coulombic parameters governing the Cs(6s)+Cs(6s) interaction in the electronic ground state, compared with values derived either by calculations or by recent photoassociative spectroscopy measurements. The main constants are C6=6836 (±100) a.u.=32.945 (±0.49)×106 cm−1 Å6, and De=3649.88 (±0.45) cm−1.

Fluorescence and phosphorescence of C 70Ph 10 and C 70Cl 10 in toluene between 5 and 300 K

The present Letter describes the basic emission properties, obtained between 5 and 300 K, for C 70Ph 10 and C 70Cl 10 in toluene. Laser-induced emission spectra with superimposed vibronic features were observed at 5 K in spectra of C 70Ph 10 and C 70Cl 10 in toluene. 0 00 emission lines are tentatively assigned at 593.6 and 611.1 nm, respectively. In a toluene matrix at 5 K, C 70Ph 10 shows two broad emission bands at 615 and 675 nm with millisecond lifetimes assigned to phosphorescence which are not seen at T>180 K . Different spectral features were seen for C 70Ph 10 in heptane and sol–gel matrices.

Electronic states of Bi2

Laser-induced fluorescence and thermal emission spectra of Bi2 have been recorded at high resolution by Fourier transform spectrometry. Extensive analyses, involving the assignment of more than 20 000 lines, have been made of transitions involving the states X 0+ g, a lu(3Σ+ u), A 0+ u(3Σ- u) and E lg. The electronic states of Bi2 are reviewed, and comparison is made with the results of ab initio calculations.