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We present the measurements and analysis of laser-induced breakdown processes in dry air at a wavelength of 193 nm by focusing 180-mJ 10-MW high-power 193-nm UV ArF laser radiation onto a 30-[micro]m-radius spot size. We examine pressures ranging from 40 tort to 5 atm, for laser power densities of 1 TW/[cm.sup.2], well above the threshold power flux for air ionization. The breakdown threshold electric field is measured and compared with classical and quantum theoretical ionization models at this short wavelength. A universal scaling analysis of these results allows one to predict aspects of high-power microwave breakdown based on measured laser breakdown observations. Comparison of 193-nm laser-induced effective field intensities for air breakdown data calculated based on the collisional cascade and multiphoton breakdown theories is used successfully to determine the collisional microwave scaled portion with good agreement regarding both pressure dependence and breakdown threshold electric fields. Using a laser shadowgraphy diagnostic technique, the plasma and shock-wave dynamics are analyzed. Blast shock-wave expansion of the plasma and laser-heated neutral gas is observed with average velocities of 47 km/s, and the temporal shock-wave velocity variation is used to determine electron temperature evolution just behind the shock wave. Index Terms--Air plasma, breakdown scaling, excimer laser, laser-induced plasma, shadowgraphy.

Experiments are performed using 193-nm ultraviolet laser preionization of a seed gas in atmospheric pressure range argon and nitrogen to initiate a discharge that is sustained by 13.56-MHz radiofrequency (RF) power using efficient inductive wave coupling. High-density (4.5 x [10.sup.12]/[cm.sup.3] line average density) large-volume (~500 [cm.sup.3]) 760-torr argon plasma is initiated and maintained for more than 400 ms with 2.2 kW of net RF power coupled to the plasma. Using the same technique, a 50-torr nitrogen plasma with line average electron density of 3.5 x [10.sup.11]/[cm.sup.3] is obtained. The nitrogen plasma volume of 1500 [cm.sup.3] is initiated by the laser and maintained by a net RF power of 3.5 kW for 350 ms. Measurements of the time-varying plasma impedance and optimization of the RF matching for the transition from laser-initiated to RF-sustained plasma are carried out. Both laser-initiated plasmas provide much larger plasma volumes at lower RF power densities than can be obtained by RF alone. Millimeter wave interferometry is used to determine the electron density and the total electron-neutral collision frequency. A new diagnostic technique based on interferometry is developed to evaluate the electron temperature in high-pressure plasmas with inclusion of the neutral heating. Broadband plasma emission spectroscopy is used to illustrate the changes in the ionized species character immediately after the laser pulse and later during the RF pulse. Index Terms--Excimer laser, high pressure, interferometry, plasma, radiofrequency (RF).

This paper presents a study of one possible form of ball lightning. Plasma spheres several centimeters in diameter were produced in atmospheric pressure air. These spheres persisted for up to a half-second after the power supply was turned off. A mathematical theory was derived that predicts the observed lifetime. The theory predicts that the sphere lifetime should scale as the sphere radius squared, which means that large spheres should persist for many seconds. Index Terms--Arc discharges, ball lightning, lightning, plasma confinement, plasma lifetime, plasma scaling law, plasma spheres.

In this work, we have applied optical emission spectroscopy diagnostics to investigate the characteristics of a non-thermal atmospheric pressure helium plasma jet. The discharge characteristics in the active and afterglow region of the plasma jet, that are critical for biomedical applications, have been investigated. The voltage-current characteristics of the plasma discharge were analyzed and the average plasma power was measured to be around 18 W. The effect of addition of small fractions of oxygen at 0.1%-0.5% on the plasma jet characteristics was studied. The addition of oxygen resulted in a decrease in plasma plume length due to the electronegativity property of oxygen. Atomic and molecular lines of selected reactive plasma species that are considered to be useful to induce biochemical reactions such as OH transitions A2Σ+(ν=0,1)→X2Π(Δν=0) at 308 nm and A2Σ+(ν=0,1)→X2Π(Δν=1) at 287 nm, O I transitions 3p5P→3s5S0 at 777.41 nm, and 3p3P→3s3S0 at 844.6 nm, N2(C-B) second positive system with electronic transition C3Πu →B3Πg in the range of 300-450 nm and N2+(B-X) first negative system with electronic transition B2Σu+→X2Σg+(Δν=0) at 391.4 nm have been studied. The atomic emission lines of helium were identified, including the He I transitions 3p3P0→2s3S at 388.8 nm, 3p1P0→ 2s1S at 501.6 nm, 3d3D→2p3P0 at 587.6 nm, 3d1D→2p1P0 at 667.8 nm, 3s3S1→2p3P0 at 706.5 nm, 3s1S0→2p1P0 at 728.1 nm, and Hα transition 2p-3d at 656.3 nm. Using a spectral fitting method, the OH radicals at 306-312 nm, the rotational and vibrational temperatures equivalent to gas temperatures of the discharge was measured and the effective non-equilibrium nature of the plasma jet was demonstrated. Our results show that, in the entire active plasma region, the gas temperature remains at 310 ± 25 K and 340 ± 25 K and it increases to 320 ± 25 K and 360 ± 25 K in the afterglow region of the plasma jet for pure helium and helium/oxygen (0.1%) mixture, respectively. Additionally, the vibrational temperatures range from 2200 ± 100 K and 2500 ± 100 K for pure helium and helium/oxygen (0.1%) mixture, respectively. The plasma jet was tested on heat sensitive polymer films used in biomedical applications such as polyethylene terephthalate and poly-L-lactide samples continuously for several minutes without causing any physical or thermal damage to the films. The plasma jet produces significant reactive species of interest while the gas temperatures remain very low demonstrating its potential for a range of biomedical applications. [ABSTRACT FROM AUTHOR]

We present measurements and analysis of laser induced plasma neutral densities and temperatures in dry air by focusing 200 mJ, 10 MW high power, 193 nm ultraviolet ArF (argon fluoride) laser radiation to a 30 μm radius spot size. We examine these properties that result from multiphoton and collisional cascade processes for pressures ranging from 40 Torr to 5 atm. A laser shadowgraphy diagnostic technique is used to obtain the plasma electron temperature just after the shock front and this is compared with optical emission spectroscopic measurements of nitrogen rotational and vibrational temperatures. Two-color laser interferometry is employed to measure time resolved spatial electron and neutral density decay in initial local thermodynamic equilibrium (LTE) and non-LTE conditions. The radiating species and thermodynamic characteristics of the plasma are analyzed by means of optical emission spectroscopy (OES) supported by SPECAIR, a special OES program for air constituent plasmas. Core plasma rotational and vibrational temperatures are obtained from the emission spectra from the N2C-B(2+) transitions by matching the experimental spectrum results with the SPECAIR simulation results and the results are compared with the electron temperature just behind the shock wave. The plasma density decay measurements are compared with a simplified electron density decay model that illustrates the dominant three-and two-body recombination terms with good correlation. [ABSTRACT FROM AUTHOR]

Steady-state atmospheric pressure nonthermal plasmas can splendidly debilitate bacteria in liquids, gases, and on surfaces, as well as can disintegrate hazardous chemicals. The nonthermal resistive barrier gas discharge at atmospheric pressure is currently investigated for low-temperature sterilization purposes. We have carried out electrical, chemical, optical, and biological studies of the discharge, with the intent of identifying the chemically and biologically active species produced. In this paper, we have demonstrated that effective decontamination can be achieved without causing any damage to the active media.

In this paper, an atmospheric pressure low-temperature plasma pencil generated in helium and helium/oxygen gas mixtures was characterized in detail for its discharge characteristics, plasma power, reactive plasma species produced, plasma density, and plasma temperatures using electrical and optical emission spectroscopy (OES) diagnostics, and its efficacy for biomedical application. A visible plasma plume length of approximately 27 mm was generated using a 60-kHz ac HV power supply. The OES results showed the most intensive plasma emission lines of OH transition A^2\Sigma^+(v=0,1)\toX^2\Pi(\Delta\nu=0) at 308 nm and OH transition A^2\Sigma^+(v=0,1)\toX^2\Pi(\Delta\nu=1) at 287 nm, O I transition 3p^5P\to 3s^5S^0 at 777.41 nm, O I transition 3p^3P\to 3s^3S^0 at 844.6 nm, and N2(C\-B) second positive system with electronic transition C^3\Piu{\to}B^3\Pig in the range 300–450 nm. The effects of controlled oxygen content on the plasma pencil and on various helium plasma emissions and electrical properties are studied. A spatial distribution of reactive plasma species produced by the plasma pencil is presented. The electron density of plasma jet was estimated to be in the order of 2.1\times 10^14~cm^-3 using Stark broadening line profile of the hydrogen alpha emission. The temperatures of afterglow plasma pencil were evaluated using OH rotational temperatures, and the results demonstrate temperatures of 316 and 362 K for pure He and He/ O2 gas mixtures (0.1% O2 ), respectively. Preliminary results on inactivation of Streptococcus pneumoniae on a solid surface and in liquid suspension were carried out using the plasma pencil for biomedical applications. [ABSTRACT FROM PUBLISHER]

ABSTRACT Cold atmospheric plasma (CAP), an ambient temperature ionized gas, is gaining extensive interest as a promising addition to anti-tumor therapy primarily due to the ability to generate and control delivery of electrons, ions, excited molecules, UV photons, and reactive species such as reactive oxygen species (ROS) and reactive nitrogen species (RNS) to a specific site. The heterogeneous composition of CAP offers the opportunity to mediate several signaling pathways that regulate tumor cells. Consequently, the array of CAP generated products has limited the identification of the mechanisms of action on tumor cells. The aim of this work is to assess the cell death response of human myeloid leukemia cells by remote exposure to CAP generated RNS by utilizing a novel resistive barrier discharge system that primarily produces RNS. The effect of variable treatments of CAP generated RNS was tested in THP-1 cell (human monocytic leukemia cell line), a model for hematological malignancy. The number of viable cells was evaluated with erythrosine-B staining, while apoptosis and necrosis was assessed by endonuclease cleavage observed by agarose gel electrophoresis and detection of cells with the exclusionary dye propidium iodide and fluorescently labeled annexin-V by flow cytometry and fluorescent microscopy. Our observations indicate that treatment dosage levels of 45 s of exposure to CAP emitted RNS-induced apoptotic cell death and for higher dosage conditions of ≥50 s of exposure to CAP induced necrosis. Overall the results suggest that CAP emitted RNS play a significant role in the anti-tumor potential of CAP. Biotechnol. Bioeng. 2014;111: 565-574. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

In this work an atmospheric pressure non-thermal resistive barrier (RB) plasma jet was constructed, characterized and was applied for biomedical applications. The RB plasma source can operate in both DC (battery) as well as in standard 60/50 Hz low frequency AC excitation, and it functions effectively in both direct and indirect plasma exposure configurations. The characteristics of the RB plasma jet such as electrical properties, plasma gas temperature and nitric oxides concentration were determined using voltage-current characterization, optical emission spectroscopy and gas analyzer diagnostic techniques. Plasma discharge power of 26.33 W was calculated from voltage-current characterization. An optical emission spectroscopy was applied and the gas temperature which is equivalent to the nitrogen rotational (Trot) temperatures was measured. The concentrations of the reactive oxygen species at different spatial distances from the tip of the plasma jet were measured and the ppm concentration of NO is at the preferred level for a wide range of standard biomedical treatment applications. The ppm values of nitric oxides after the cooling unit are observed to be of the same order of magnitude as compared to plasma jet. The portable RB plasma source was tested to be very effective for decontamination and disinfection of a wide range of foodborne and opportunistic nosocomial pathogens such as Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Bacillus cereus and the preliminary results are presented. The effects of indirect exposure of the portable RBP source on monocytic leukemia cancer cells (THP-1) were also tested and the results demonstrate that a preference for apoptosis in plasma treated THP-1 cells under particular plasma parameters and dosage levels. [ABSTRACT FROM AUTHOR]

This research investigated the modulation of cell death through exposure of non-thermal resistive barrier based indirect air plasma on monocytic leukemia cancer cells (THP-1). Specifically, we explored cell death through apoptosis and necrosis, since generally apoptotic cell death has a limited inflammatory response as compared to necrosis. We have demonstrated a preference for apoptosis in plasma treated THP-1 cells, under specific plasma characteristics and dosage levels, using fluorescent dyes conjugated with annexin V followed by identification of the cells through fluorescent microscopy and flowcytometry diagnostics. At much higher plasma dosages, the necrotic morphologies in the THP-1 cells were observed. The presented outcomes in the death morphologies of plasma treated THP-1 cells signify the need for further investigation on the cellular mechanisms induced by the indirect plasma exposure. The results obtained from this research indicate the significant potential for the use of our portable non-thermal resistive barrier based indirect plasma treatment method as an inexpensive and less invasive method for treating leukemia and other cancerous lesions. [ABSTRACT FROM AUTHOR]

Experiments are performed using 193-nm ultraviolet laser preionization of a seed gas in atmospheric pressure range argon and nitrogen to initiate a discharge that is sustained by 13.56-MHz radiofrequency (RF) power using efficient inductive wave coupling. High-density (4.5 × 1012/cm³ line average density) large-volume (~500 cm³) 760-torr argon plasma is initiated and maintained for more than 400 ms with 2.2 kW of net RF power coupled to the plasma. Using the same technique, a 50-torr nitrogen plasma with line average electron density of 3.5 × 1011/cm³ is obtained. The nitrogen plasma volume of 1500 cm³ is initiated by the laser and maintained by a net RF power of 3.5 kW for 350 ms. Measurements of the time-varying plasma impedance and optimization of the RF matching for the transition from laser-initiated to RF-sustained plasma are carried out. Both laser-initiated plasmas provide much larger plasma volumes at lower RF power densities than can be obtained by RF alone. Millimeter wave interferometry is used to determine the electron density and the total electron-neutral collision frequency. A new diagnostic technique based on interferometry is developed to evaluate the electron temperature in high-pressure plasmas with inclusion of the neutral heating. Broadband plasma emission spectroscopy is used to illustrate the changes in the ionized species character immediately after the laser pulse and later during the RF pulse. [ABSTRACT FROM AUTHOR]