Optical Emission Characterization Research Articles

Optical emission characterization of an atmospheric pressure dielectric barrier discharge in nitrogen: Evolution of CN emissions during PTFE etching

AbstractThe present work investigates the etching of coated polytetrafluoroethylene (PTFE) films using an atmospheric pressure dielectric barrier discharge operating in nitrogen in a filamentary regime. For different treatment durations, the optical emission spectra were recorded over time. Most of the emissions are attributed to the N2 second positive system. The presence of CN is also observed, and its emissions rise with the exposure time of PTFE. This rise is attributed to the density of CN produced. The X‐ray photoelectron spectroscopy surface characterization suggests two etching regimes. This is linked with a change in slope in the intensity evolution of the optical emissions of the CN. At longer times, a fluorinated deposit on the electrode is observed, confirming a different nature of the etched material.

Imaging and characterization of optical emission from ex vivo tissue during conventional and UHDR PBS proton therapy

Objective. Imaging of optical photons emitted from tissue during radiotherapy is a promising technique for real-time visualization of treatment delivery, offering applications in dose verification, treatment monitoring, and retrospective treatment plan comparison. This research aims to explore the feasibility of intensified imaging of tissue luminescence during proton therapy (PT), under both conventional and ultra-high dose rate (UHDR) conditions. Approach. Conventional and UHDR pencil beam scanning (PBS) PT irradiation of fresh ex vivo porcine tissue and tissue-mimicking plastic phantom was imaged using intensified complementary metal-oxide-semiconductor(CMOS) cameras. The optical emission from tissue was characterized during conventional irradiation using both blue and red-sensitive intensifiers to ensure adequate spectral coverage. Spectral characterization was performed using bandpass filters between the lens and sensor. Imaging of conventional proton fields (240 MeV, 10 nA) was performed at 100 Hz frame rate, while UHDR PBS proton delivery (250 MeV, 99 nA) was recorded at 1 kHz frame rate. Dependence of optical emission yield on proton energy was studied using an optical tissue-mimicking plastic phantom and a range shifter. Finally, we demonstrated fast beam tracking capability of fast camera towards in vivo monitoring of FLASH PT. Main results. Under conventional treatment dose rates optical emission was imaged with single spot resolution. Spot profiles were found to agree with the treatment planning system calculation within >90% for all spectral bands and spot intensity was found to vary with spectral filtration. The resultant polychromatic emission presented a maximum intensity at 650 nm and decreasing signal at lower wavelengths, which is consistent with expected attenuation patterns of high fat and muscle tissue. For UHDR beam imaging, optical yield increased with higher proton energy. Imaging at 1 kHz allowed continuous monitoring of delivery during porcine tissue irradiation, with clear identification of individual dwell positions. The number of dwell positions matched the treatment plan in total and per row showing adequate temporal capability of iCMOS imaging. Significance. For the first time, this study characterizes optical emission from tissue during PT and demonstrates our capability of fast optical tracking of pencil proton beam on the tissue anatomy in both conventional and UHDR setting. Similar to the Cherenkov imaging in radiotherapy, this imaging modality could enable a seamless, independent validation of PT treatments.

Optical emission characterization of liquid core fibers filled with colloidal nanoplatelets

Optical emission characterization of liquid core fibers filled with colloidal nanoplatelets

Spectral Studies of Nanosecond Laser Interaction with Aluminum-Based Alloy Containing Traces of Magnesium in Air

Parametric study of optical emission Characterization of the plasma-assisted laser ablation of aluminium-based alloy that contains small traces of magnesium is presented. The emission of lines from the plasma of the target in the wavelength range 200-900nm has been carefully investigated at the same experimental conditions. It was found that all the emission intensities of the ionic and neutral magnesium lines are subjected to self-absorption, whereas the aluminium ionic lines were free from self-absorption. The results assure that, in case of the presence of self- absorption effect, the temperature varies from (1.7952 - 1.1433 eV) as the delay time is varied from 0 to 5 μs. Whereas, in the case of repairing against the effect, it varies from (1.3240 - 0.9447 eV) for the same delay time variation. At the same time, according to the McWhirter criterion, the electron density was high enough to establish plasma in local thermodynamic equilibrium.

Optical emission characterization of laser ablated zirconium plasma

Optical emission characteristics of zirconium (Zr) plasma produced by the fundamental (1064 nm) and second (532 nm) harmonics of an Nd:YAG laser are studied. The temperature measurements have been estimated through the Boltzmann plot method whereas; number density is calculated using Stark broadening profile of 535.07 nm (5p3G → 5s1H) transitions. The variation in the temperature and number density at different laser irradiance has also been investigated using spectroscopic technique. It is observed that temperature and number density increases as laser irradiance is increased. The temperature is also calculated by varying distance from the target surface along the line of propagation of plasma plume.

Optical Emission Characterization of Laser Ablated Zirconium Plasma

Optical Emission Characterization of Laser Ablated Zirconium Plasma

Spectral studies of nanosecond laser interaction with magnesium sulfate target in air

AbstractThe optical emission characterization of the plasma-assisted pulsed laser ablation of the magnesium sulfate target is discussed in this study. The emission spectrum produced by the magnesium sulfate plasma in the wavelength range 200–700 nm has been carefully investigated for different experimental conditions. The spectra analysis was performed by assuming the local thermodynamic equilibrium (LTE) approximation and calculating the plasma temperature with the Boltzmann plot method using neutral Mg spectral lines. The plasma temperature was obtained for different positions along the expansion axis, which allowed obtaining the electron population distribution as a function of the distance from the target. The plasma temperature along the expansion axis allowed evaluating the evolution of the excited states population when the plume expands. Moreover, the Stark broadening method has been employed for electron number density measurements. In this study, the Stark width of the Mg (I) spectral line at 285.21 nm was used. Besides, we have studied the variation of electron temperature (Te) and electron number density (Ne) as a function of laser irradiance.

Halo-shaped flowing atmospheric pressure afterglow: a heavenly design for simplified sample introduction and improved ionization in ambient mass spectrometry.

The flowing atmospheric-pressure afterglow (FAPA) is a promising new source for atmospheric-pressure, ambient desorption/ionization mass spectrometry. However, problems exist with reproducible sample introduction into the FAPA source. To overcome this limitation, a new FAPA geometry has been developed in which concentric tubular electrodes are utilized to form a halo-shaped discharge; this geometry has been termed the halo-FAPA or h-FAPA. With this new geometry, it is still possible to achieve direct desorption and ionization from a surface; however, sample introduction through the inner capillary is also possible and improves interaction between the sample material (solution, vapor, or aerosol) and the plasma to promote desorption and ionization. The h-FAPA operates with a helium gas flow of 0.60 L/min outer, 0.30 L/min inner, and applied current of 30 mA at 200 V for 6 W of power. In addition, separation of the discharge proper and sample material prevents perturbations to the plasma. Optical-emission characterization and gas rotational temperatures reveal that the temperature of the discharge is not significantly affected (<3% change at 450 K) by water vapor during solution-aerosol sample introduction. The primary mass-spectral background species are protonated water clusters, and the primary analyte ions are protonated molecular ions (M + H(+)). Flexibility of the new ambient sampling source is demonstrated by coupling it with a laser ablation unit, a concentric nebulizer, and a droplet-on-demand system for sample introduction. A novel arrangement is also presented in which the central channel of the h-FAPA is used as the inlet to a mass spectrometer.

Generation and characterization of optical emission in highly repetitive pulsed‐glow discharges in air

AbstractTo analyze atmospheric‐pressure transient glow microdischarges powered by a fast high‐voltage pulse train generated by a nonlinear transmission line generator, we conducted a simulation experiment using double rectangular pulsed voltages having variable pulse intervals. The discharges were characterized by optical emission spectro‐scopy. Although the temporal evolution of the spectral line intensities of nitrogen molecules and ions followed the discharge current, the atomic helium line intensity did not follow the current. The development of a discharge at the interface between a helium gas flow column and the surrounding air affects the observed evolution of the spectral lines. The strong effect of metastable helium was confirmed. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 180(2): 17–23, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21223

A VHF driven coaxial atmospheric air plasma: electrical and optical characterization

A coaxially driven VHF plasma source for atmospheric air plasmas has been built and characterized. Electrical and optical characterization of this source present a unique operating regime when compared to state of the art atmospheric systems such as dielectric barrier discharge, pulsed dc, microwave, or ac blown arc discharges. The discharge does not appear to produce streamers or arcs, but instead remains as a steady-state glow located at the end of the inner coaxial power feed. Plasma impedance was determined by comparing the loaded and unloaded impedance of the coaxial source RF input; this termination impedance was combined with a simple high-frequency global model to estimate an electron density of approximately 1011 cm−3 at 400 W delivered power in air. Optical emission characterization of the source shows a monotonic increase in emission with respect with power; the relative intensity of the peaks from excited species, however, remains constant over a power range from 300 to 600 W. This unique source geometry presents a possible pathway for high gas throughput, large area, high power density processes such as surface modification, air purification, media removal and chemical surface treatment.

Generation and Characterization of Optical Emission in Highly Repetitive Pulsed-glow Discharges in Air

To analyze the atmospheric pressure transient glow microdischarge powered by fast high-voltage pulse train generated with a nonlinear transmission line generator, we conducted a simulation experiment with double rectangular pulsed voltages having variable pulse intervals. The discharges were characterized by means of optical emission spectroscopy. Although temporal evolution of spectral line intensities of nitrogen molecule and ion change according to the discharge current, atomic helium line intensity does not follow the current. The discharge development at the interface between a helium gas flow column and the surrounding air affects the observed evolution of the spectral lines. The extensive effect by the metastable helium was confirmed.

Image Analysis: A Tool for Optical-Emission Characterization of Partial-Vacuum Breakdown

Power devices and systems operating in partial vacuum are susceptible to partial discharges, corona, or volume discharges. In this paper, we present an image-analysis technique and its results for optical-emission characterization of a breakdown initiation. The example set for demonstration is breakdown events under a 20-kHz unipolar sinusoidal applied field for a point-to-point electrode geometry at partial vacuum in helium. The voltage and current waveforms along with the light-emission data are collected. The results of the image-analysis technique used to obtain the R/G/B emission characteristics of the breakdown events as a function of time, location, and pressure are presented. The images obtained by a standard 30-ft/s video camera are used for analysis to characterize the progress of the breakdown.

A Long-Wavelength Infrared Photoluminescence Spectrometer for the Characterization of Semiconductor Materials

AbstractA new photoluminescence spectrometer has been developed for the characterization of optical emission in the 2.5 to 14.1 micron wavelength range. This instrument provides high sensitivity for the detection of interband and defect luminescence in a variety of infrared detector materials. The spectrometer utilizes a solid state photomultiplier detector and a circular variable filter, which serves as the resolving element. The entire spectrometer is cooled to 5K in order to decrease thermal radiation emission. Band-edge luminescence at 10.1 microns from HgCdTe samples has been readily detected with argon-ion laser excitation powers less than 70 mW/cm2. Representative spectra from HgCdTe and other infrared detector materials are presented.

Optical emission characterization of a divergent magnetic field electron cyclotron resonance source

High-resolution optical emission experiments have been performed to investigate the application of this technique to the characterization of electron cyclotron resonance (ECR) sources. Preliminary experiments have used Ar and O2 discharges operating between 0.5 and 1.5 mTorr, with 700–2300 W of microwave power, and two distinct magnetic field configurations. Results of these measurements indicate that ECR discharges are optically thick for transitions which terminate on long-lived (metastable) energy levels, producing significant self-absorption. Measurements of emission intensity for Ar and Ar+ lines which are not self-absorbed show that selected transitions can be used to reliably monitor the relative concentrations of these species.