Nitrogen Spectral Lines Research Articles

Laser-induced plasma analysis of ammonia-oxygen and ammonia-oxygen-enriched-air flames at elevated pressures

This study employed Laser-induced breakdown spectroscopy (LIBS) to measure the fuel-oxidizer ratio (FOR) of ammonia combustion with oxygen-enriched air and pure oxygen flames at elevated pressures (100 - 300 kPa). The correlations between the spectral line intensity ratios of nitrogen (N), hydrogen (H), oxygen (O), and equivalence ratio were used to quantify the FOR of flames at various pressures. The effect of pressure on the stability and precision of the calibration profiles for the elemental intensity ratios in flames was investigated. It was observed that the H/O correlation decreases with pressure increase for both ammonia flames. N/O correlations decrease with elevated pressure for the ammonia-oxygen flame. Furthermore, the nitrogen (NII) spectral emission lines at 568 nm and 595 nm were used to estimate the plasma temperature, while the hydrogen (Hα) line at 656 nm was used for electron number density measurements.

Optical emission spectroscopy of vanadium cathodic arc plasma at different nitrogen pressure

Optical emission spectroscopy studies of vanadium plasma in a cathodic-arc discharge in a nitrogen atmosphere have been carried out. Spectral lines of neutral atoms and ions of the cathode material V, V1+, and V2+, and nitrogen N2 and N2+ were observed in the discharge plasma. Analysis and comparison of the intensity of vanadium and nitrogen spectral lines as a function of nitrogen pressure showed that in vacuum excited ions V2+ and V+ are registered, with increasing pressure, the lines V+*, N2*, and N2+* are observed, and at pressures above 0.5 Pa, the neutral vanadium lines are additionally registered. The electron temperature of Te decreases from 5.9 to 3–4 eV with increasing pressure. Studies of cross-sectional scanning electron microscopy images of VN coatings deposited at different nitrogen pressures have shown that a dense, homogeneous, fine-grained microstructure is formed in the coating when the number of neutral V in the plasma is low, while in the presence of a large number of neutrals, the coating structure changes to a dense structure with columnar growth.

Variations in Pulsating Aurora Emission in 337 nm and 391 nm Nitrogen Spectral Lines during Geomagnetic Substorms

Spectroscopic measurements of aurora emissions provide valuable insights into the altitude of electron atmospheric penetration and their maximum energy. To achieve this, the photometers used in the PAIPS (Pulsating Aurora Imaging Photometers System) project are equipped with spectrometers. These spectrometers enable the measurement of auroral emissions in narrow spectral lines with a temporal resolution of milliseconds. In this study, we present two cases of PsA (Pulsating Aurora) measurements in the 337 nm and 391 nm spectral lines. We demonstrate that during quiet geomagnetic conditions the ratio of night sky emissions in these bands is close to one and significantly increases during substorms. We propose and implement a special procedure for estimating this ratio. Our findings reveal that the intensity of emissions in both spectral lines correlates with the AL index of geomagnetic activity. However, the ratio between the emissions fluctuates around constant values over time and does not undergo significant changes throughout the entire PsA event, which can last for more than an hour.

Determination of the reduced electric field in surface dielectric barrier discharge plasmas

In this paper, the experimental determination of the reduced electric field (E/n) in plasma of dielectric coplanar surface barrier discharge (DCSBD) at atmospheric pressure was demonstrated. The plasma characteristics and the experimental setup properties were described, and the optical emission spectrum of the plasma was also measured. The results of optical emission spectroscopy showed the presence of nitrogen molecular bands in the emission spectrum of DCSBD. In particular, the second positive and the first negative systems, as well as low intensity OH and NO lines were identified. The main transport properties of electrons, such as mobility, mean average energy, and diffusion coefficients were calculated using the BOLSIG+ open source software. The dependence of the ratio of intensities of the nitrogen spectral lines on the reduced electric field, the dependence of the E/n on plasma power, and the dependence of the electron energy distribution function (EEDF) on E/n were obtained. An algorithm in the form of a block diagram for determining the reduced electric field by the BOLSIG + program and experimentally measured spectral line intensities are presented. The utilized method is quite simple, accessible and versatile.

A “water window” tomography based on a laser-plasma double-stream gas-puff target soft X-ray source

A desktop laser-plasma double-stream gas-puff target soft X-ray (SXR) source, operating in the so-called “water window” spectral range (λ = 2.3–4.4 nm). was successfully employed to acquire 3D tomographic images in transmission mode, using a Fresnel zone-plate microscope. The microscope, operating at the He-like nitrogen spectral line, 2.88-nm wavelength, allows acquiring 3D SXR volumetric reconstructions with a resolution of a few microns. The development of a compact system offers the possibility to obtain 3D reconstructed images in relatively short time and in a laboratory environment, without the involvement of large “photon facilities”, such as synchrotrons or free electron lasers, however, with the modest volume resolution at this point. The possibility to obtain three-dimensional images in the SXR wavelength range using a compact, laser-plasma based system may be useful for material and life sciences, where it is required to visualize small features of the samples in 3D that are not visible with a single 2D image. Details about the equipment and the setup constructions as well as some imaged samples will be presented and discussed.

Electron density measurement of a lightning stepped leader by oxygen spectral lines

The time-resolved spectrum of a lightning stepped leader in downward process has been obtained by using a slitless spectrograph. Neutral oxygen and nitrogen spectral lines in the near infrared region are observed in the spectra. The electron density of the lightning stepped leader was calculated by using the Stark broadening of the oxygen spectral lines at 777.4 and 844.6 nm. The evolution characteristic of the electron density with time and channel height of the lightning stepped leader was analysed. The results shown that the electron density of the lightning stepped leader was in the order of 1018 cm-3. The electron density decreased when the lightning stepped leader propagates downward to ground.

Electrostatic energy dependence of intensity ratio between nitrogen spectral lines of monovalent ion and neutral atom in electrostatic spark discharge in air

AbstractFor the development of a practical method to estimate the energy of electrostatic air discharge without electrical measurements, the dependence of spectral characteristics of light emission from the spark discharge on electrostatic energy was investigated. It was found that the relative light intensity emitted from a monovalent positive ion of nitrogen (N II) to a nitrogen atom (N I) increased with the electrostatic energy from 0.02 mJ to 20 mJ. In the same electrostatic energy, the intensity ratio, that is the intensity of N II divided by that of N I, increased with the decrease of applied voltage. This implied that the ratio becomes large when increasing the electrostatic energy divided by the breakdown gap length. Separating the measurements into similar voltage groups, the relation between the ratio and the electrostatic energy became clear.

Electrostatic Energy Dependence of Intensity Ratio between Nitrogen Spectral Lines of Monovalent Ion and Neutral Atom in Electrostatic Spark Discharge in Air

Electrostatic Energy Dependence of Intensity Ratio between Nitrogen Spectral Lines of Monovalent Ion and Neutral Atom in Electrostatic Spark Discharge in Air

Development and optimization of a “water window” microscope based on a gas-puff target laser-produced plasma source

A laser-plasma double stream gas-puff target source coupled with Fresnel zone plate (FZP) optics, operating at He-like nitrogen spectral line λ=2.88nm, is capable of acquire complementary information in respect to optical and electron microscopy, allowing to obtain high resolution imaging, compared to the traditional visible light microscopes, with an exposition time of a few seconds. The compact size and versatility of the microscope offers the possibility to perform imaging experiments in the university laboratories, previously restricted to large-scale photon facilities. Source and microscope optimization, and examples of applications will be presented and discussed.

Electron number density measurements using laser-induced breakdown spectroscopy of ionized nitrogen spectral lines

Spectrally broadened, singly ionized nitrogen emission lines are monitored to determine electron number densities in laser-induced plasma from aluminum, nano- and bulk-zinc monoxide, as well as hydrogen-rich plastic and wood targets. The optical emission spectra for N II at the average wavelength of 500.33nm are recorded in standard ambient temperature and pressure environments. For time delays of 25 to 450ns from the onset of the 1064-nm Nd:YAG radiation induced optical breakdown, the electron number densities in the range of 5.1 ±1 ×1019 to 0.22 ±0.04 ×1019cm−3 are inferred from the continuum and the nitrogen spectral line analysis. In addition, the corresponding electron temperatures of 10.1 ±0.6eV to 1 ±0.2eV are determined from the calculated absolute spectral radiance values in the near infrared region. At the early stages of plasma emission, Balmer series hydrogen lines are embedded in free electron radiation yet the broadening of the N II lines yields reliable electron number density values.

Controlled microdroplet transport in an atmospheric pressure microplasma

We report the controlled injection of near-isolated micron-sized liquid droplets into a low temperature He-Ne steady-state rf plasma at atmospheric pressure. The H2O droplet stream is constrained within a 2 mm diameter quartz tube. Imaging at the tube exit indicates a log-normal droplet size distribution with an initial count mean diameter of 15 μm falling to 13 μm with plasma exposure. The radial velocity profile is approximately parabolic indicating near laminar flow conditions with the majority of droplets travelling at >75% of the local gas speed and having a plasma transit time of <100 μs. The maximum gas temperature, determined from nitrogen spectral lines, was below 400 K and the observed droplet size reduction implies additional factors beyond standard evaporation, including charge and surface chemistry effects. The demonstration of controlled microdroplet streams opens up possibilities for gas-phase microreactors and remote delivery of active species for plasma medicine.

Development of a polarization resolved spectroscopic diagnostic for measurements of the vector magnetic field in the Caltech coaxial magnetized plasma jet experiment

In the Caltech coaxial magnetized plasma jet experiment, fundamental studies are carried out relevant to spheromak formation, astrophysical jet formation/propagation, solar coronal physics, and the general behavior of twisted magnetic flux tubes that intercept a boundary. In order to measure the spatial profile of the magnetic field vector for understanding the underlying physics governing the dynamical behavior, a non-perturbing visible emission spectroscopic method is implemented to observe the Zeeman splitting in emission spectra. We have designed and constructed a polarization-resolving optical system that can simultaneously detect the left- and right-circularly polarized emission. The system is applied to singly ionized nitrogen spectral lines. The magnetic field strength is measured with a precision of about ±13 mT. The radial profiles of the azimuthal and axial vector magnetic field components are resolved by using an inversion method.

Rotational CARS N2 thermometry: validation experiments for the influence of nitrogen spectral line broadening by hydrogen

AbstractRotational coherent anti‐Stokes Raman spectroscopy (CARS) in fuel‐rich hydrocarbon flames, with a large content of hydrogen in the product gases (∼20%), has in previous work shown that evaluated temperatures are raised several tens of Kelvin by taking newly derived N2H2 Raman line widths into account. To validate these results, in this work calibrated temperature measurements at around 300, 500 and 700 K were performed in a cell with binary gas mixtures of nitrogen and hydrogen. The temperature evaluation was made with respect to Raman line widths either from self‐broadened nitrogen only, N2N2 [energy‐corrected‐sudden (ECS)], or by also taking nitrogen broadened by hydrogen, N2H2 [Robert–Bonamy (RB)], Raman line widths into account. With increased amount of hydrogen in the cell at constant temperature, the evaluated CARS temperatures were clearly lowered with the use of Raman line widths from self‐broadened nitrogen only, and the case with inclusion of N2H2 Raman line widths was more successful. The difference in evaluated temperatures between the two different sets increases approximately linearly, reaching 20 K (at T ∼ 300 K), 43 K (at T = 500 K) and 61 K (at T = 700 K) at the highest hydrogen concentration (90%). The results from this work further emphasize the importance of using adequate Raman line widths for accurate rotational CARS thermometry. Copyright © 2010 John Wiley & Sons, Ltd.

Improvement of rotational CARS thermometry in fuel‐rich hydrocarbon flames by inclusion of N2‐H2 Raman line widths

AbstractIn rotational coherent anti‐Stokes Raman spectroscopy (CARS) thermometry applied to air‐fed flames, the temperature sensitivity mainly depends on the intensity distribution of the nitrogen spectral lines. Temperatures are estimated by numerical fitting of theoretical spectra to experimental ones, and one uncertainty in the calculation of theoretical CARS spectra for specific flame conditions is the accuracy in utilized line‐broadening coefficients. In a previous article, self‐broadened N2‐N2 line widths were considered in the spectral calculations as well as those of N2‐CO, N2‐CO2, N2‐H2O, and N2‐O2. In the present article, we also include N2‐H2 line widths calculated from a newly developed model, and it is shown that the evaluated temperature from flame spectra increases with increasing mole fractions of hydrogen. For example, in a very rich flame at Φ = 2.5, the use of available line‐width data for all major species gives a temperature raise of 72 K at a temperature of ∼1700 K, in comparison with using self‐broadened N2‐N2 line widths only. Half of this temperature raise is related to the inclusion of N2‐H2 line widths. This article emphasizes the importance of using adequate line‐broadening models for rotational CARS thermometry in flames. Copyright © 2009 John Wiley & Sons, Ltd.

Practical sensor for nitrogen in direct current glow discharges

This paper presents a method for precise measurement of atomic and molecular nitrogen in an oxygen-nitrogen dc plasma. This is achieved by monitoring the intensities of the atomic nitrogen spectral line at 821.6 nm and the molecular nitrogen bandhead at 337.1 nm, relative to the atomic oxygen spectral line at 844.7 nm. Oxygen is one of the most frequently used gases for surface chemical treatment, including deposition and etching, therefore the ability to measure and control the process and chemical composition of the process is essential. To validate this oxygen actimometry method for N2-xO2 (where x varies from 0 to 1) dc plasmas, threshold tests have been performed with Ar actinometry. The optical measurements have been performed using two methods. The first approach uses a USB2000 fiber optic spectrometer, calibrated with a Gigahertz–Optik BN-0102-1 reference standard source, to record the desired spectral lines. The second approach uses narrow bandwidth optical filters (∼0.7–0.07 nm) with central wavelengths of 821.6, 337.1, and 844.69 nm and photodiodes to detect the emission intensity, also calibrated with the same standard source. Optical data are collected for a range of experimental conditions in a flowing glow discharge of N2-xO2 mixture. The maximum dc voltage is 2.2 kV and maximum chamber pressure is 266 Pa. Data from both optical methods are compared and used to interpret the relative atomic and molecular nitrogen concentrations under various operating conditions.

Dual-pulse Laser Induced Breakdown Spectroscopy for analysis of gaseous and aerosol systems: Plasma-analyte interactions

Dual-pulse LIBS has been previously investigated to a large extent on solid and liquid phase analytes, where it has been demonstrated to significantly enhance atomic emission signal intensity, and more importantly, to enhance the analyte peak-to-base and signal-to-noise ratios. This study focuses on the effects of an orthogonal dual-pulse laser configuration on the atomic emission response for both purely gaseous and calcium-based aerosol samples. The gaseous sample consisted of purified (i.e. aerosol free) air, from which nitrogen and oxygen spectral emission lines were analyzed. Measurements for the gaseous system resulted in no notable improvements with the dual-pulse configuration as compared to the single-pulse LIBS. Experiments were also conducted in purified air seeded with calcium-rich particles, which revealed a marked improvement in calcium atomic emission peak-to-base (∼ 2-fold increase) and signal-to-noise ratios (∼ 4-fold increase) with the dual-pulse configuration. In addition to increased analyte response, dual-pulse LIBS yielded an enhanced single-particle sampling rate when compared to conventional LIBS. Transmission measurements with respect to the plasma-creating laser pulse were recorded for both single and dual-pulse methods over a range of temporal delays. In consideration of the spectroscopic and transmission data, the plasma-analyte interactions realized with a dual-pulse methodology are explained in terms of the interaction with the initially expanding plasma shock wave, which differs between gaseous and particulate phase analytes, as reported in a recent study [V. Hohreiter, D.W. Hahn, Calibration effects for laser-induced breakdown spectroscopy of gaseous sample streams: analyte response of gas-phase species versus solid-phase species, Anal. Chem. 77 (2005) 1118–1124].

Semi-Classical Calculations of Stark Broadening Impact Theory of Singly-Ionized Carbon, Nitrogen and Oxygen Spectral Lines

Using the semi-classical perturbation approach by Sahal-Bréchot (1969 Astron. Astrophys. 1, 91, 2 322; 1974 Astron. Astrophys. 35 321; 1991 Astron. Astrophys. 245 322) updated by Dimitrjević and Sahal-Bréchot (1984 J. Quant. Spectrosc. Radiat. Transf. 31 301; 1995 Physica Scripta 52 41) and by Ben Nessib et al. (1996 Physica Scripta 54 608) we have calculated Stark broadening widths of several C II, N II and O II spectral lines and input TOPbase (Opacity Project) sophisticated atomic structure data into the Sahal-Bréchot’s computer code. Then we have compared our results with those of available experiments and with Griem’s (1974) simplified semi-classical data. We show that our theoretical results, the simplified semi-classical calculations and experimental values are in good agreement. We also give new values of Stark broadening widths for several transitions of singly-ionized nitrogen and oxygen.

Temperature dependence of Stark width of the 463.054 nm N II spectral line

Stark width of the 463.054 nm singly ionized nitrogen spectral line, that belong to 3s 3p transi- tion, have been measured in a linear pulsed, low pres- sure, arc discharge. The working gas was helium-nitrogen- oxygen mixture. Electron densities of 0.75 10 23 m 3 to 1.45 10 23 m 3 were determined in the electron temper- ature range between 30 000 K 38 000 K. The measured values have been compared with our calculated data, us- ing the modied semiempirical approximation. On the ba- sis of the agreement among experimental and theoretical Stark width data, the isolated 463.054 nm N II spectral line can be recommended as convenient spectral line for plasma diagnostics.

Measured Stark widths and shifts of several N III spectral lines: Temperature dependence

Stark parameters (width and shift) of four doubly ionized nitrogen spectral lines, that belong to 3s-3p and 3p-3d transitions (lower multiplets), have been measured in a linear pulsed, low pressure, arc discharge in the nitrogen-oxygen and helium-nitrogen-oxygen plasmas in a (30 000 - 54 000) K electron temperature and a (0.75 1023 - 2.8 1023 ) electron density ranges. The measured values have been compared to the existing experimental and calculated data.

Measured Stark widths and shifts of NII, NIII and NIV spectral lines

Stark parameters (widths and shifts) of eight singly, seven doubly and five triply ionized nitrogen spectral lines have been measured in linear pulsed, low pressure, arc discharge in a nitrogen plasma at a 54 000 K electron temperature and a m-3 electron density. The measured values have been compared to the existing experimental and calculated data.